Interaction of laser beams with magnetized substance in a strong magnetic field

NASA Astrophysics Data System (ADS)

Kuzenov, V. V.

2018-03-01

Laser-driven magneto-inertial fusion assumed plasma and magnetic flux compression by quasisymmetric laser-driven implosion of magnetized target. We develop a 2D radiation magnetohydrodynamic code and a formulation for the one-fluid two-temperature equations for simulating compressible non-equilibrium magnetized target plasma. Laser system with pulse radiation with 10 ns duration is considered for numerical experiments. A numerical study of a scheme of magnetized laser-driven implosion in the external magnetic field is carried out.

Polar-Drive--Implosion Physics on OMEGA and the NIF

NASA Astrophysics Data System (ADS)

Radha, P. B.

2012-10-01

Polar drive (PD) permits the execution of direct-drive--ignition experiments on facilities that are configured for x-ray drive such as the National Ignition Facility (NIF) and Laser M'egajoule. Experiments on the OMEGA laser are used to develop and validate models of PD implosions. Results from OMEGA PD shock-timing and warm implosions are presented. Experiments are simulated with the 2-D hydrodynamic code DRACO including full 3-D ray trace to model oblique beams. Excellent agreement is obtained in shock velocity and catch-up in PD geometry in warm, plastic shells. Predicted areal densities are measured in PD implosion experiments. Good agreement between simulation and experiments is obtained in the overall shape of the compressing shell when observed through x-ray backlighting. Simulated images of the hot core, including the effect of magnetic fields, are compared with experiments. Comparisons of simulated and observed scattered light and bang time in PD geometry are presented. Several techniques to increase implosion velocity are presented including beam profile variations and different ablator materials. Results from shimmed-target PD experiments will also be presented. Designs for future PD OMEGA experiments at ignition-relevant intensities will be presented. The implication of these results for NIF-scale plasmas is discussed. Experiments for the NIF in its current configuration, with indirect-drive phase plates, are proposed to study implosion energetics and shell asymmetries. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.

Progress Toward Ignition on the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kauffman, R L

2011-10-17

The principal approach to ignition on the National Ignition Facility (NIF) is indirect drive. A schematic of an ignition target is shown in Figure 1. The laser beams are focused through laser entrance holes at each end of a high-Z cylindrical case, or hohlraum. The lasers irradiate the hohlraum walls producing x-rays that ablate and compress the fuel capsule in the center of the hohlraum. The hohlraum is made of Au, U, or other high-Z material. For ignition targets, the hohlraum is {approx}0.5 cm diameter by {approx}1 cm in length. The hohlraum absorbs the incident laser energy producing x-rays formore » symmetrically imploding the capsule. The fuel capsule is a {approx}2-mm-diameter spherical shell of CH, Be, or C filled with DT fuel. The DT fuel is in the form of a cryogenic layer on the inside of the capsule. X-rays ablate the outside of the capsule, producing a spherical implosion. The imploding shell stagnates in the center, igniting the DT fuel. NIC has overseen installation of all of the hardware for performing ignition experiments, including commissioning of approximately 50 diagnostic systems in NIF. The diagnostics measure scattered optical light, x-rays from the hohlraum over the energy range from 100 eV to 500 keV, and x-rays, neutrons, and charged particles from the implosion. An example of a diagnostic is the Magnetic Recoil Spectrometer (MRS) built by a collaboration of scientists from MIT, UR-LLE, and LLNL shown in Figure 2. MRS measures the neutron spectrum from the implosion, providing information on the neutron yield and areal density that are metrics of the quality of the implosion. Experiments on NIF extend ICF research to unexplored regimes in target physics. NIF can produce more than 50 times the laser energy and more than 20 times the power of any previous ICF facility. Ignition scale hohlraum targets are three to four times larger than targets used at smaller facilities, and the ignition drive pulses are two to five times longer. The larger targets and longer pulse lengths produce unique plasma conditions for laser-plasma instabilities that could reduce hohlraum coupling efficiency. Initial experiments have demonstrated efficient coupling of laser energy to x-rays. X-ray drive greater than 300 eV has been measured in gas-filled ignition hohlraum and shows the expected scaling with laser energy and hohlraum scale size. Experiments are now optimizing capsule implosions for ignition. Ignition conditions require assembling the fuel with sufficient density and temperature for thermonuclear burn. X-rays ablate the outside of the capsule, accelerating and spherically compressing the capsule for assembling the fuel. The implosion stagnates, heating the central core and producing a hot spot that ignites and burns the surrounding fuel. The four main characteristics of the implosion are shell velocity, central hot spot shape, fuel adiabat, and mix. Experiments studying these four characteristics of implosions are used to optimize the implosion. Integrated experiments using cryogenic fuel layer experiments demonstrate the quality of the implosion as the optimization experiments progress. The final compressed fuel conditions are diagnosed by measuring the x-ray emission from the hot core and the neutrons and charged particles produced in the fusion reactions. Metrics of the quality of the implosion are the neutron yield and the shell areal density, as well as the size and shape of the core. The yield depends on the amount of fuel in the hot core and its temperature and is a gauge of the energy coupling to the fuel. The areal density, the density of the fuel times its thickness, diagnoses the fuel assembly, which is measured using the fraction of neutrons that are down scattered passing through the dense shell. The yield and fraction of down scattered neutrons, or shell rho-r, from the cryogenic layered implosions are shown in Figure 3. The different sets of data represent results after a series of implosion optimization experiments. Both yield and areal density show significant increases as a result of the optimization. The experimental Ignition Threshold Factor (ITFX) is a measure of the progress toward ignition. ITFX is analogous to the Lawson Criterion in Magnetic Fusion. Implosions have improved by over a factor of 50 since the first cryogenic layered experiments were done in September 2010. This increase is a measure of the progress made toward the ignition goal in the past year. Optimization experiments are planned in the coming year for continued improvement in implosion performance to achieve the ignition goal. In summary, NIF has made significant progress toward ignition in the 30 months since project completion. Diagnostics and all of the supporting equipment are in place for ignition experiments. The Ignition Campaign is under way as a national collaborative effort of all the National Nuclear Security Administration (NNSA) science laboratories as well as international partners.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Callahan, D. A.; Hurricane, O. A.; Hinkel, D. E.

By increasing the velocity in “high foot” implosions [Dittrich et al., Phys. Rev. Lett. 112, 055002 (2014); Park et al., Phys. Rev. Lett. 112, 055001 (2014); Hurricane et al., Nature 506, 343 (2014); Hurricane et al., Phys. Plasmas 21, 056314 (2014)] on the National Ignition Facility laser, we have nearly doubled the neutron yield and the hotspot pressure as compared to the implosions reported upon last year. The implosion velocity has been increased using a combination of the laser (higher power and energy), the hohlraum (depleted uranium wall material with higher opacity and lower specific heat than gold hohlraums), andmore » the capsule (thinner capsules with less mass). We find that the neutron yield from these experiments scales systematically with a velocity-like parameter of the square root of the laser energy divided by the ablator mass. By connecting this parameter with the inferred implosion velocity (v), we find that for shots with primary yield >1 × 10{sup 15} neutrons, the total yield ∼ v{sup 9.4}. This increase is considerably faster than the expected dependence for implosions without alpha heating (∼v{sup 5.9}) and is additional evidence that these experiments have significant alpha heating.« less

Optimization of a high-yield, low-areal-density fusion product source at the National Ignition Facility with applications in nucleosynthesis experiments

NASA Astrophysics Data System (ADS)

Gatu Johnson, M.; Casey, D. T.; Hohenberger, M.; Zylstra, A. B.; Bacher, A.; Brune, C. R.; Bionta, R. M.; Craxton, R. S.; Ellison, C. L.; Farrell, M.; Frenje, J. A.; Garbett, W.; Garcia, E. M.; Grim, G. P.; Hartouni, E.; Hatarik, R.; Herrmann, H. W.; Hohensee, M.; Holunga, D. M.; Hoppe, M.; Jackson, M.; Kabadi, N.; Khan, S. F.; Kilkenny, J. D.; Kohut, T. R.; Lahmann, B.; Le, H. P.; Li, C. K.; Masse, L.; McKenty, P. W.; McNabb, D. P.; Nikroo, A.; Parham, T. G.; Parker, C. E.; Petrasso, R. D.; Pino, J.; Remington, B.; Rice, N. G.; Rinderknecht, H. G.; Rosenberg, M. J.; Sanchez, J.; Sayre, D. B.; Schoff, M. E.; Shuldberg, C. M.; Séguin, F. H.; Sio, H.; Walters, Z. B.; Whitley, H. D.

2018-05-01

Polar-direct-drive exploding pushers are used as a high-yield, low-areal-density fusion product source at the National Ignition Facility with applications including diagnostic calibration, nuclear security, backlighting, electron-ion equilibration, and nucleosynthesis-relevant experiments. In this paper, two different paths to improving the performance of this platform are explored: (i) optimizing the laser drive, and (ii) optimizing the target. While the present study is specifically geared towards nucleosynthesis experiments, the results are generally applicable. Example data from T2/3He-gas-filled implosions with trace deuterium are used to show that yield and ion temperature (Tion) from 1.6 mm-outer-diameter thin-glass-shell capsule implosions are improved at a set laser energy by switching from a ramped to a square laser pulse shape, and that increased laser energy further improves yield and Tion, although by factors lower than predicted by 1 D simulations. Using data from D2/3He-gas-filled implosions, yield at a set Tion is experimentally verified to increase with capsule size. Uniform D3He-proton spectra from 3 mm-outer-diameter CH shell implosions demonstrate the utility of this platform for studying charged-particle-producing reactions relevant to stellar nucleosynthesis.

Optimization of a high-yield, low-areal-density fusion product source at the National Ignition Facility with applications in nucleosynthesis experiments

DOE PAGES

Gatu Johnson, M.; Casey, D. T.; Hohenberger, M.; ...

2018-05-09

Polar-direct-drive exploding pushers are used as a high-yield, low-areal-density fusion product source at the National Ignition Facility with applications including diagnostic calibration, nuclear security, backlighting, electron-ion equilibration, and nucleosynthesis-relevant experiments. In this paper, two different paths to improving the performance of this platform are explored: (i) optimizing the laser drive, and (ii) optimizing the target. While the present study is specifically geared towards nucleosynthesis experiments, the results are generally applicable. Example data from T 2/ 3He-gas-filled implosions with trace deuterium are used to show that yield and ion temperature (Tion) from 1.6 mm-outer-diameter thin-glass-shell capsule implosions are improved at amore » set laser energy by switching from a ramped to a square laser pulse shape, and that increased laser energy further improves yield and Tion, although by factors lower than predicted by 1 D simulations. Using data from D2-3He-gas-filled implosions, yield at a set Tion is experimentally verified to increase with capsule size. Uniform D-3He-proton spectra from 3 mm-outer-diameter CH shell implosions demonstrate the utility of this platform for studying charged-particle-producing reactions relevant to stellar nucleosynthesis.« less

Optimization of a high-yield, low-areal-density fusion product source at the National Ignition Facility with applications in nucleosynthesis experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gatu Johnson, M.; Casey, D. T.; Hohenberger, M.

Polar-direct-drive exploding pushers are used as a high-yield, low-areal-density fusion product source at the National Ignition Facility with applications including diagnostic calibration, nuclear security, backlighting, electron-ion equilibration, and nucleosynthesis-relevant experiments. In this paper, two different paths to improving the performance of this platform are explored: (i) optimizing the laser drive, and (ii) optimizing the target. While the present study is specifically geared towards nucleosynthesis experiments, the results are generally applicable. Example data from T 2/ 3He-gas-filled implosions with trace deuterium are used to show that yield and ion temperature (Tion) from 1.6 mm-outer-diameter thin-glass-shell capsule implosions are improved at amore » set laser energy by switching from a ramped to a square laser pulse shape, and that increased laser energy further improves yield and Tion, although by factors lower than predicted by 1 D simulations. Using data from D2-3He-gas-filled implosions, yield at a set Tion is experimentally verified to increase with capsule size. Uniform D-3He-proton spectra from 3 mm-outer-diameter CH shell implosions demonstrate the utility of this platform for studying charged-particle-producing reactions relevant to stellar nucleosynthesis.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shvydky, Alex

This volume of LLE Review, covering October–December 2011, features “Crossed-Beam Energy Transfer in Direct-Drive Implosions” by I. V. Igumenshchev, W. Seka, D. H. Edgell, D. T. Michel, D. H. Froula, R. S. Craxton, R. Follett, J. H. Kelly, T. Z. Kosc, J. F. Myatt, T. C. Sangster, A. Shvydky, S. Skupsky, and C. Stoeckl (LLE); V. N. Goncharov and A. V. Maximov (LLE and Department of Mechanical Engineering, U. of Rochester); L. Divol and P. Michel (LLNL); and R. L. McCrory and D. D. Meyerhofer (LLE and Departments of Mechanical Engineering and Physics, U. of Rochester). In this article (p.more » 1), direct-drive–implosion experiments on the OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1995)] have shown discrepancies between simulations of the scattered (non-absorbed) light levels and measured ones that indicates the presence of a mechanism that reduces laser coupling efficiency by 10% to 20%. The authors attribute this degradation in laser coupling to crossed-beam energy transfer (CBET)— which is electromagnetically seeded—low-gain stimulated Brillouin scattering. CBET scatters energy from the central portion of the incoming light beam to outgoing light, reducing the laser absorption and hydrodynamic efficiency of implosions. One-dimensional hydrodynamic simulations including CBET show good agreement with all observables in implosion experiments on OMEGA. Three strategies to mitigate CBET and improve laser coupling are considered: the use of narrow beams, multicolor lasers, and higher-Z ablators. Experiments on OMEGA using narrow beams have demonstrated improvements in implosion performance.« less

Hohlraum-driven mid-Z (SiO2) double-shell implosions on the omega laser facility and their scaling to NIF.

PubMed

Robey, H F; Amendt, P A; Milovich, J L; Park, H-S; Hamza, A V; Bono, M J

2009-10-02

High-convergence, hohlraum-driven implosions of double-shell capsules using mid-Z (SiO2) inner shells have been performed on the OMEGA laser facility [T. R. Boehly, Opt. Commun. 133, 495 (1997)]. These experiments provide an essential extension of the results of previous low-Z (CH) double-shell implosions [P. A. Amendt, Phys. Rev. Lett. 94, 065004 (2005)] to materials of higher density and atomic number. Analytic modeling, supported by highly resolved 2D numerical simulations, is used to account for the yield degradation due to interfacial atomic mixing. This extended experimental database from OMEGA enables a validation of the mix model, and provides a means for quantitatively assessing the prospects for high-Z double-shell implosions on the National Ignition Facility [Paisner, Laser Focus World 30, 75 (1994)].

Demonstration of Ion Kinetic Effects in Inertial Confinement Fusion Implosions and Investigation of Magnetic Reconnection Using Laser-Produced Plasmas

NASA Astrophysics Data System (ADS)

Rosenberg, M. J.

2016-10-01

Shock-driven laser inertial confinement fusion (ICF) implosions have demonstrated the presence of ion kinetic effects in ICF implosions and also have been used as a proton source to probe the strongly driven reconnection of MG magnetic fields in laser-generated plasmas. Ion kinetic effects arise during the shock-convergence phase of ICF implosions when the mean free path for ion-ion collisions (λii) approaches the size of the hot-fuel region (Rfuel) and may impact hot-spot formation and the possibility of ignition. To isolate and study ion kinetic effects, the ratio of N - K =λii /Rfuel was varied in D3He-filled, shock-driven implosions at the Omega Laser Facility and the National Ignition Facility, from hydrodynamic-like conditions (NK 0.01) to strongly kinetic conditions (NK 10). A strong trend of decreasing fusion yields relative to the predictions of hydrodynamic models is observed as NK increases from 0.1 to 10. Hydrodynamics simulations that include basic models of the kinetic effects that are likely to be present in these experiments-namely, ion diffusion and Knudsen-layer reduction of the fusion reactivity-are better able to capture the experimental results. This type of implosion has also been used as a source of monoenergetic 15-MeV protons to image magnetic fields driven to reconnect in laser-produced plasmas at conditions similar to those encountered at the Earth's magnetopause. These experiments demonstrate that for both symmetric and asymmetric magnetic-reconnection configurations, when plasma flows are much stronger than the nominal Alfvén speed, the rate of magnetic-flux annihilation is determined by the flow velocity and is largely insensitive to initial plasma conditions. This work was supported by the Department of Energy Grant Number DENA0001857.

Theory of hydro-equivalent ignition for inertial fusion and its applications to OMEGA and the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nora, R.; Betti, R.; Bose, A.

The theory of ignition for inertial confinement fusion capsules [R. Betti et al., Phys. Plasmas 17, 058102 (2010)] is used to assess the performance requirements for cryogenic implosion experiments on the Omega Laser Facility. The theory of hydrodynamic similarity is developed in both one and two dimensions and tested using multimode hydrodynamic simulations with the hydrocode DRACO [P. B. Radha et al., Phys. Plasmas 12, 032702 (2005)] of hydro-equivalent implosions (implosions with the same implosion velocity, adiabat, and laser intensity). The theory is used to scale the performance of direct-drive OMEGA implosions to the National Ignition Facility (NIF) energy scalesmore » and determine the requirements for demonstrating hydro-equivalent ignition on OMEGA. Hydro-equivalent ignition on OMEGA is represented by a cryogenic implosion that would scale to ignition on the NIF at 1.8 MJ of laser energy symmetrically illuminating the target. It is found that a reasonable combination of neutron yield and areal density for OMEGA hydro-equivalent ignition is 3 to 6 × 10{sup 13} and ∼0.3 g/cm{sup 2}, respectively, depending on the level of laser imprinting. This performance has not yet been achieved on OMEGA.« less

Examining the radiation drive asymmetries present in the high foot series of implosion experiments at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Pak, A.; Divol, L.; Kritcher, A. L.; Ma, T.; Ralph, J. E.; Bachmann, B.; Benedetti, L. R.; Casey, D. T.; Celliers, P. M.; Dewald, E. L.; Döppner, T.; Field, J. E.; Fratanduono, D. E.; Berzak Hopkins, L. F.; Izumi, N.; Khan, S. F.; Landen, O. L.; Kyrala, G. A.; LePape, S.; Millot, M.; Milovich, J. L.; Moore, A. S.; Nagel, S. R.; Park, H.-S.; Rygg, J. R.; Bradley, D. K.; Callahan, D. A.; Hinkel, D. E.; Hsing, W. W.; Hurricane, O. A.; Meezan, N. B.; Moody, J. D.; Patel, P.; Robey, H. F.; Schneider, M. B.; Town, R. P. J.; Edwards, M. J.

2017-05-01

This paper details and examines the origins of radiation drive asymmetries present during the initial High Foot implosion experiments. Such asymmetries are expected to reduce the stagnation pressure and the resulting yield of these experiments by several times. Analysis of reemission and dual axis shock timing experiments indicates that a flux asymmetry, with a P2/P0 amplitude that varies from -10% to -5%, is present during the first shock of the implosion. This first shock asymmetry can be corrected through adjustments to the laser cone fraction. A thin shell model and more detailed radiation hydrodynamic calculations indicate that an additional negative P2/P0 asymmetry during the second or portions of the third shock is required to reach the observed amount of asymmetry in the shape of the ablator at peak implosion velocity. In conjunction with symmetry data from the x-ray self emission produced at stagnation, these models also indicate that after the initially negative P2/P0 flux asymmetry, the capsule experiences a positive P2/P0 flux asymmetry that develops at or before ˜2 ns into the peak of the laser power. Here, direct evidence for this inference, using measurements of the x-ray emission produced by the lasers irradiating the hohlraum, is presented. These data indicate that the reduction in the transmitted inner laser cone energy results from impeded propagation through the plasma associated with the ablation of the capsule target. This paper also correlates measurements of the outer cone laser deposition location with variations in the observed x-ray self emission shape from experiments conducted with nominally the same input conditions.

Examining the radiation drive asymmetries present in the high foot series of implosion experiments at the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pak, A.; Divol, L.; Kritcher, A. L.

This paper details and examines the origins of radiation drive asymmetries present during the initial High Foot implosion experiments. Such asymmetries are expected to reduce the stagnation pressure and the resulting yield of these experiments by several times. Analysis of reemission and dual axis shock timing experiments indicates that a flux asymmetry, with a P2/P0 amplitude that varies from -10 to -5 %, is present during the first shock of the implosion. This first shock asymmetry can be corrected through adjustments to the laser cone fraction. A thin shell model and more detailed radiation hydrodynamic calculations indicate that an additionalmore » negative P2/P0 asymmetry during the second or portions of the third shock is required to reach the observed amount of asymmetry in the shape of the ablator at peak implosion velocity. In conjunction with symmetry data from the x-ray self emission produced at stagnation, these models also indicate that after the initially negative P2/P0 flux asymmetry, the capsule experiences a positive P2/P0 flux asymmetry that develops at or before ~2 ns into the peak of the laser power. Here, direct evidence for this inference, using measurements of the x-ray emission produced by the lasers irradiating the hohlraum, is presented. This data indicates that the reduction in the transmitted inner laser cone energy results from impeded propagation through the plasma associated with the ablation of the capsule target. This paper also correlates measurements of the outer cone laser deposition location with variations in the observed x-ray self emission shape from experiments conducted with nominally the same input conditions.« less

Examining the radiation drive asymmetries present in the high foot series of implosion experiments at the National Ignition Facility

DOE PAGES

Pak, A.; Divol, L.; Kritcher, A. L.; ...

2017-03-24

This paper details and examines the origins of radiation drive asymmetries present during the initial High Foot implosion experiments. Such asymmetries are expected to reduce the stagnation pressure and the resulting yield of these experiments by several times. Analysis of reemission and dual axis shock timing experiments indicates that a flux asymmetry, with a P2/P0 amplitude that varies from -10 to -5 %, is present during the first shock of the implosion. This first shock asymmetry can be corrected through adjustments to the laser cone fraction. A thin shell model and more detailed radiation hydrodynamic calculations indicate that an additionalmore » negative P2/P0 asymmetry during the second or portions of the third shock is required to reach the observed amount of asymmetry in the shape of the ablator at peak implosion velocity. In conjunction with symmetry data from the x-ray self emission produced at stagnation, these models also indicate that after the initially negative P2/P0 flux asymmetry, the capsule experiences a positive P2/P0 flux asymmetry that develops at or before ~2 ns into the peak of the laser power. Here, direct evidence for this inference, using measurements of the x-ray emission produced by the lasers irradiating the hohlraum, is presented. This data indicates that the reduction in the transmitted inner laser cone energy results from impeded propagation through the plasma associated with the ablation of the capsule target. This paper also correlates measurements of the outer cone laser deposition location with variations in the observed x-ray self emission shape from experiments conducted with nominally the same input conditions.« less

Capsule modeling of high foot implosion experiments on the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clark, D. S.; Kritcher, A. L.; Milovich, J. L.

This study summarizes the results of detailed, capsule-only simulations of a set of high foot implosion experiments conducted on the National Ignition Facility (NIF). These experiments span a range of ablator thicknesses, laser powers, and laser energies, and modeling these experiments as a set is important to assess whether the simulation model can reproduce the trends seen experimentally as the implosion parameters were varied. Two-dimensional (2D) simulations have been run including a number of effects—both nominal and off-nominal—such as hohlraum radiation asymmetries, surface roughness, the capsule support tent, and hot electron pre-heat. Selected three-dimensional simulations have also been run tomore » assess the validity of the 2D axisymmetric approximation. As a composite, these simulations represent the current state of understanding of NIF high foot implosion performance using the best and most detailed computational model available. While the most detailed simulations show approximate agreement with the experimental data, it is evident that the model remains incomplete and further refinements are needed. Nevertheless, avenues for improved performance are clearly indicated.« less

Capsule modeling of high foot implosion experiments on the National Ignition Facility

DOE PAGES

Clark, D. S.; Kritcher, A. L.; Milovich, J. L.; ...

2017-03-21

This study summarizes the results of detailed, capsule-only simulations of a set of high foot implosion experiments conducted on the National Ignition Facility (NIF). These experiments span a range of ablator thicknesses, laser powers, and laser energies, and modeling these experiments as a set is important to assess whether the simulation model can reproduce the trends seen experimentally as the implosion parameters were varied. Two-dimensional (2D) simulations have been run including a number of effects—both nominal and off-nominal—such as hohlraum radiation asymmetries, surface roughness, the capsule support tent, and hot electron pre-heat. Selected three-dimensional simulations have also been run tomore » assess the validity of the 2D axisymmetric approximation. As a composite, these simulations represent the current state of understanding of NIF high foot implosion performance using the best and most detailed computational model available. While the most detailed simulations show approximate agreement with the experimental data, it is evident that the model remains incomplete and further refinements are needed. Nevertheless, avenues for improved performance are clearly indicated.« less

Convergent ablation measurements of plastic ablators in gas-filled rugby hohlraums on OMEGA

NASA Astrophysics Data System (ADS)

Casner, A.; Jalinaud, T.; Masse, L.; Galmiche, D.

2015-10-01

Indirect-drive implosions experiments were conducted on the Omega Laser Facility to test the performance of uniformly doped plastic ablators for Inertial Confinement Fusion. The first convergent ablation measurements in gas-filled rugby hohlraums are reported. Ignition relevant limb velocities in the range from 150 to 300 μm .n s-1 have been reached by varying the laser drive energy and the initial capsule aspect ratio. The measured capsule trajectory and implosion velocity are in good agreement with 2D integrated simulations and a zero-dimensional modeling of the implosions. We demonstrate experimentally the scaling law for the maximum implosion velocity predicted by the improved rocket model [Y. Saillard, Nucl. Fusion 46, 1017 (2006)] in the high-ablation regime case.

Fast-Ion Spectrometry of ICF Implosions and Laser-Foil Experiments at the Omega and MTW Laser Facilities

NASA Astrophysics Data System (ADS)

Sinenian, Nareg

Fast ions generated from laser-plasma interactions (LPI) have been used to study inertial confinement fusion (ICF) implosions and laser-foil interactions. LPI, which vary in nature depending on the wavelength and intensity of the driver, generate hot electrons with temperatures ranging from tens to thousands of kilo-electron-volts. These electrons, which accelerate the ions measured in this work, can be either detrimental or essential to implosion performance depending on the ICF scheme employed. In direct-drive hot-spot ignition, hot electrons can preheat the fuel and raise the adiabat, potentially degrading compression in the implosion. The amount of preheat depends on the hot-electron source characteristics and the time duration over which electrons can deposit energy into the fuel. This time duration is prescribed by the evolution of a sheath that surrounds the implosion and traps electrons. Fast-ion measurements have been used to develop a circuit model that describes the time decay of the sheath voltage for typical OMEGA implosions. In the context of electron fast ignition, the produced fast ions are considered a loss channel that has been characterized for the first time. These ions have also been used as a diagnostic tool to infer the temperature of the hot electrons in fast-ignition experiments. It has also been shown that the hot-electron temperature scales with laser intensity as expected, but is enhanced by a factor of 2-3. This enhancement is possibly due to relativistic effects and leads to poor implosion performance. Finally, fast-ion generation by ultra-intense lasers has also been studied using planar targets. The mean and maximum energies of protons and heavy ions has been measured, and it has been shown that a two-temperature hot-electron distribution affects the energies of heavy ions and protons. This work is important for advanced fusion concepts that utilize ion beams and also has applications in medicine. (Copies available exclusively from MIT Libraries, libraries.mit.edu/docs - docs@mit.edu)

Investigation of Electric and Self-Generated Magnetic Fields in Implosion Experiments on OMEGA

NASA Astrophysics Data System (ADS)

Igumenshchev, I. V.; Nilson, P. M.; Goncharov, V. N.; Li, C. K.; Zylstra, A. B.; Petrasso, R. D.

2013-10-01

Electric and self-generated magnetic fields in direct-drive implosion experiments on the OMEGA laser were investigated using proton radiography. The experiments use plastic-shell targets with various surface defects (glue spot, wire, and stalk mount) to seed perturbations and generate localized electromagnetic fields at the ablation surface and in the plasma corona surrounding the targets. Proton radiographs show features from these perturbations and quasi-spherical multiple shell structures around the capsules at earlier times of implosions (up to ~700 ps for a 1-ns laser pulse) indicating the development of the fields. Two-dimensional magnetohydrodynamic simulations of these experiments predict the growth of magnetic fields up to several MG. The simulated distributions of electromagnetic fields were used to produce proton images, which show good agreement with experimental radiographs. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Higher Velocity High-Foot Implosions on the National Ignition Facility Laser

NASA Astrophysics Data System (ADS)

Callahan, Debra

2014-10-01

After the end of the National Ignition Campaign on the National Ignition Facility (NIF) laser, we began a campaign to test capsule performance using a modified laser pulse-shape that delivers higher power early in the pulse (``high foot''). This pulse-shape trades one-dimensional performance (peak compression) for increased hydrodynamic stability. The focus of the experiments this year have been to improve performance by increasing the implosion velocity using higher laser power/energy, depleted uranium hohlraums, and thinner capsules. While the mix of ablator material into the hotspot has been low for all of these implosions, the challenge has been to keep the implosion shape under control. As the peak laser power is increased, the plasma density in the hohlraum is increased - making it more and more challenging for the inner cone beams to reach the midplane of the hohlraum and resulting in an oblate implosion. Depleted uranium hohlraums have higher albedo than Au hohlraums, which leads to additional drive and improved implosion shape. Thinner ablators increase the velocity by reducing the amount of payload; thinner ablators also put less mass into the hohlraum which results in improved inner beam propagation. These techniques have allowed us to push the capsule to higher and higher velocity. In parallel with this effort, we are exploring other hohlraums such as the rugby shaped hohlraum to allow us to push these implosions further. This talk will summarize the progress of the high foot campaign in terms of both capsule and hohlraum performance. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Proton Radiography of Spontaneous Fields, Plasma Flows and Dynamics in X-Ray Driven Inertial-Confinement Fusion Implosions

NASA Astrophysics Data System (ADS)

Li, C. K.; Seguin, F. H.; Frenje, J. A.; Rosenberg, M.; Zylstra, A. B.; Rinderknecht, H. G.; Petrasso, R. D.; Amendt, P. A.; Landen, O. L.; Town, R. P. J.; Betti, R.; Knauer, J. P.; Meyerhofer, D. D.; Back, C. A.; Kilkenny, J. D.; Nikroo, A.

2010-11-01

Backlighting of x-ray-driven implosions in empty hohlraums with mono-energetic protons on the OMEGA laser facility has allowed a number of important phenomena to be observed. Several critical parameters were determined, including plasma flow, three types of spontaneous electric fields and megaGauss magnetic fields. These results provide insight into important issues in indirect-drive ICF. Even though the cavity is effectively a Faraday cage, the strong, local fields inside the hohlraum can affect laser-plasma instabilities, electron distributions and implosion symmetry. They are of fundamental scientific importance for a range of new experiments at the frontiers of high-energy-density physics. Future experiments designed to characterize the field formation and evolution in low-Z gas fill hohlraums will be discussed.

The High-Foot Implosion Campaign on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Hurricane, Omar

2013-10-01

The `High-Foot' platform manipulates the laser pulse-shape coming from the National Ignition Facility (NIF) laser to create an indirect drive 3-shock implosion that is significantly more robust against instability growth involving the ablator and also modestly reduces implosion convergence ratio. This tactic gives up on theoretical high-gain in an inertial confinement fusion implosion in order to obtain better control of the implosion and bring experimental performance in-line with calculated performance, yet keeps the absolute capsule performance relatively high. This approach is generally consistent with the philosophy laid out in a recent international workshop on the topic of ignition science on NIF [``Workshop on the Science of Fusion Ignition on NIF,'' Lawrence Livermore National Laboratory Report, LLNL-TR-570412 (2012). Op cit. V. Gocharov and O.A. Hurricane, ``Panel 3 Report: Implosion Hydrodynamics,'' LLNL-TR-562104 (2012)]. Side benefits our the High-Foot pulse-shape modification appear to be improvements in hohlraum behavior--less wall motion achieved through higher pressure He gas fill and improved inner cone laser beam propagation. Another consequence of the `High-Foot' is a higher fuel adiabat, so there is some relation to direct-drive experiments performed at the Laboratory for Laser Energetics (LLE). In this talk, we will cover the various experimental and theoretical motivations for the High-Foot drive as well as cover the experimental results that have come out of the High-Foot experimental campaign. Most notably, at the time of this writing record DT layer implosion performance with record low levels of inferred mix and excellent agreement with one-dimensional implosion models without the aid of mix models. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Progress of LMJ-relevant implosions experiments on OMEGA

NASA Astrophysics Data System (ADS)

Casner, A.; Philippe, F.; Tassin, V.; Seytor, P.; Monteil, M.-C.; Gauthier, P.; Park, H. S.; Robey, H.; Ross, J.; Amendt, P.; Girard, F.; Villette, B.; Reverdin, C.; Loiseau, P.; Caillaud, T.; Landoas, O.; Li, C. K.; Petrasso, R.; Seguin, F.; Rosenberg, M.; Renaudin, P.

2013-11-01

In preparation of the first ignition attempts on the Laser Mégajoule (LMJ), an experimental program is being pursued on OMEGA to investigate LMJ-relevant hohlraums. First, radiation temperature levels close to 300 eV were recently achieved in reduced-scale hohlraums with modest backscatter losses. Regarding the baseline target design for fusion experiments on LMJ, an extensive experimental database has also been collected for scaled implosions experiments in both empty and gas-filled rugby-shaped hohlraums. We acquired a full picture of hohlraum energetics and implosion dynamics. Not only did the rugby hohlraums show significantly higher x-ray drive energy over the cylindrical hohlraums, but symmetry control by power balance was demonstrated, as well as high-performance D2 implosions enabling the use of a complete suite of neutrons diagnostics. Charged particle diagnostics provide complementary insights into the physics of these x-ray driven implosions. An overview of these results demonstrates our ability to control the key parameters driving the implosion, lending more confidence in extrapolations to ignition-scale targets.

Cryogenic THD and DT layer implosions with high density carbon ablators in near-vacuum hohlraums

DOE PAGES

Meezan, N. B.; Berzak Hopkins, L. F.; Le Pape, S.; ...

2015-06-02

High Density Carbon (HDC or diamond) is a promising ablator material for use in near-vacuum hohlraums, as its high density allows for ignition designs with laser pulse durations of <10 ns. A series of Inertial Confinement Fusion (ICF) experiments in 2013 on the National Ignition Facility [E. I. Moses et al., Phys. Plasmas 16, 041006 (2009)] culminated in a DT layered implosion driven by a 6.8 ns, 2-shock laser pulse. This paper describes these experiments and comparisons with ICF design code simulations. Backlit radiography of a THD layered capsule demonstrated an ablator implosion velocity of 385 km/s with a slightlymore » oblate hot spot shape. Other diagnostics suggested an asymmetric compressed fuel layer. A streak camera-based hot spot self-emission diagnostic (SPIDER) showed a double-peaked history of the capsule self-emission. Simulations suggest that this is a signature of low quality hot spot formation. Changes to the laser pulse and pointing for a subsequent DT implosion resulted in a higher temperature, prolate hot spot and a thermonuclear yield of 1.8 x 10¹⁵ neutrons, 40% of the 1D simulated yield.« less

Systematic Fuel Cavity Asymmetries in Directly Driven Inertial Confinement Fusion Implosions

DOE PAGES

Shah, Rahul C.; Haines, Brian Michael; Wysocki, Frederick Joseph; ...

2017-03-30

Here, we present narrow-band self-emission x-ray images from a titanium tracer layer placed at the fuel-shell interface in 60-laser-beam implosion experiments at the OMEGA facility. The images are acquired during deceleration with inferred convergences of ~9-14. Novel here is that a systematically observed asymmetry of the emission is linked, using full sphere 3D implosion modeling, to performance-limiting low mode asymmetry of the drive.

Recent results of the Defect-Induced Mix Experiments (DIME) on NIF

NASA Astrophysics Data System (ADS)

Schmitt, M. J.; Bradley, P. A.; Cobble, J. A.; Hakel, P.; Hsu, S. C.; Krasheninnikova, N. S.; Kyrala, G. A.; Murphy, T. J.; Obrey, K. A.; Shah, R. C.; Tregillis, I. L.; Craxton, S. C.; McKenty, P. W.; Mancini, R. C.; Johns, H. M.; Joshi, Tirtha; Mayes, Daniel

2012-10-01

Investigations of directly driven implosions have been performed including experiments on Omega, and more recently NIF, to deduce the extent and uniformity of 4π and defect-induced mix near the shell/gas interface of plastic (CH) capsules filled with 5 atm D2 gas. Imaging diagnostics are used to measure the spatial variation of mix caused by the growth of non-uniformities in both capsule and laser drive characteristics. Thin (2μm) layers containing 1-2% (atomic) mid-Z dopants are imaged spectrally at late time in the implosion using multiple monochromatic imaging of H-like and He-like atomic line emission. Areal image backlighting of the capsules provides both r(t) and the symmetry of the implosion. Recent results will be shown including inferred 4π mix width, laser imprint induced mix, and mix from capsule variations.

Enhanced direct-drive implosions with thin high-Z ablation layers.

PubMed

Mostovych, Andrew N; Colombant, Denis G; Karasik, Max; Knauer, James P; Schmitt, Andrew J; Weaver, James L

2008-02-22

New direct-drive spherical implosion experiments with deuterium filled plastic shells have demonstrated significant and absolute (2x) improvements in neutron yield when the shells are coated with a very thin layer ( approximately 200-400 A) of high-Z material such as palladium. This improvement is interpreted as resulting from increased stability of the imploding shell. These results provide for a possible path to control laser imprint and stability in laser-fusion-energy target designs.

Modeling ICF With RAGE, BHR, And The New Laser Package

NASA Astrophysics Data System (ADS)

Cliche, Dylan; Welser-Sherrill, Leslie; Haines, Brian; Mancini, Roberto

2017-10-01

Inertial Confinement Fusion (ICF) is one method used to obtain thermonuclear burn through the either direct or indirect ablation of a millimeter-scale capsule with several lasers. Although progress has been made in theory, experiment, and diagnostics, the community has yet to reach ignition. A way of investigating this is through the use of high performance computer simulations of the implosion. RAGE is an advanced 1D, 2D, and 3D radiation adaptive grid Eulerian code used to simulate hydrodynamics of a system. Due to the unstable nature of two unequal densities accelerating into one another, it is important to include a turbulence model. BHR is a turbulence model which uses Reynolds-averaged Navier-Stokes (RANS) equations to model the mixing that occurs between the shell and fusion fuel material. Until recently, it was still difficult to model direct drive experiments because there was no laser energy deposition model in RAGE. Recently, a new laser energy deposition model has been implemented using the same ray tracing method as the Mazinisin laser package used at the OMEGA laser facility at the Laboratory for Laser Energetics (LLE) in Rochester, New York. Using the new laser package along with BHR for mixing allows us to more accurately simulate ICF implosions and obtain spatially and temporally resolved information (e.g. position, temperature, density, and mix concentrations) to give insight into what is happening inside the implosion.

Three-Dimensional Hydrodynamic Simulations of OMEGA Implosions

NASA Astrophysics Data System (ADS)

Igumenshchev, I. V.

2016-10-01

The effects of large-scale (with Legendre modes less than 30) asymmetries in OMEGA direct-drive implosions caused by laser illumination nonuniformities (beam-power imbalance and beam mispointing and mistiming) and target offset, mount, and layers nonuniformities were investigated using three-dimensional (3-D) hydrodynamic simulations. Simulations indicate that the performance degradation in cryogenic implosions is caused mainly by the target offsets ( 10 to 20 μm), beampower imbalance (σrms 10 %), and initial target asymmetry ( 5% ρRvariation), which distort implosion cores, resulting in a reduced hot-spot confinement and an increased residual kinetic energy of the stagnated target. The ion temperature inferred from the width of simulated neutron spectra are influenced by bulk fuel motion in the distorted hot spot and can result in up to 2-keV apparent temperature increase. Similar temperature variations along different lines of sight are observed. Simulated x-ray images of implosion cores in the 4- to 8-keV energy range show good agreement with experiments. Demonstrating hydrodynamic equivalence to ignition designs on OMEGA requires reducing large-scale target and laser-imposed nonuniformities, minimizing target offset, and employing high-efficient mid-adiabat (α = 4) implosion designs that mitigate cross-beam energy transfer (CBET) and suppress short-wavelength Rayleigh-Taylor growth. These simulations use a new low-noise 3-D Eulerian hydrodynamic code ASTER. Existing 3-D hydrodynamic codes for direct-drive implosions currently miss CBET and noise-free ray-trace laser deposition algorithms. ASTER overcomes these limitations using a simplified 3-D laser-deposition model, which includes CBET and is capable of simulating the effects of beam-power imbalance, beam mispointing, mistiming, and target offset. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Symmetry Tuning with Cone Powers for Defect Induced Mix Experiment Implosions

NASA Astrophysics Data System (ADS)

Krasheninnikova, N.; Schmitt, M.; Murphy, T.; Cobble, J.; Tregillis, I.; Kyrala, G.; Bradley, P.; Hakel, P.; Hsu, S.; Kanzleiter, R.; Obrey, K.; Baumgaertel, J.; Batha, S.; DIME Team

2013-10-01

Recent DIME campaigns have demonstrated the effectiveness of cone power tuning to control the implosion symmetry in PDD configuration. DIME aims to assess the effects of mix on thermonuclear burn during a thin-shell capsule implosion. Plastic shell capsules doped with mid-Z material and filled with 5 atm of DD, are ablatively driven in a PDD laser configuration to a CR of ~7. Time-gated, spectrally and spatially resolved, dopant emission images characterize mix and temperature morphology during the implosion, while neutron diagnostics concurrently give the information about burn. Symmetry should be maintained throughout the implosions to achieve high neutron yield and optimum spectroscopic signal. 2D and 3D computer simulations using code HYDRA were performed to validate and optimize implosion symmetry using cone power tuning. In particular, Omega campaign confirmed P2 tunability with cone powers while experiments on NIF demonstrated that by reducing the energy in polar cones P2 was reduced to <1%. However, during NIF campaigns, self-emission images revealed a complex internal structure around the equator, which was not seen in HYDRA simulations and could be attributed to LPI effects. Subsequent DIME campaigns on NIF were able to eliminate this equatorial feature by reducing the laser drive substantiating the LPI hypothesis. Work performed by LANL under contract DE-AC52-06NA25396 for the National Nuclear Security Administration of the USDoE.

Cryogenic tritium-hydrogen-deuterium and deuterium-tritium layer implosions with high density carbon ablators in near-vacuum hohlraums

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meezan, N. B., E-mail: meezan1@llnl.gov; Hopkins, L. F. Berzak; Pape, S. Le

2015-06-15

High Density Carbon (or diamond) is a promising ablator material for use in near-vacuum hohlraums, as its high density allows for ignition designs with laser pulse durations of <10 ns. A series of Inertial Confinement Fusion (ICF) experiments in 2013 on the National Ignition Facility [Moses et al., Phys. Plasmas 16, 041006 (2009)] culminated in a deuterium-tritium (DT) layered implosion driven by a 6.8 ns, 2-shock laser pulse. This paper describes these experiments and comparisons with ICF design code simulations. Backlit radiography of a tritium-hydrogen-deuterium (THD) layered capsule demonstrated an ablator implosion velocity of 385 km/s with a slightly oblate hot spot shape.more » Other diagnostics suggested an asymmetric compressed fuel layer. A streak camera-based hot spot self-emission diagnostic (SPIDER) showed a double-peaked history of the capsule self-emission. Simulations suggest that this is a signature of low quality hot spot formation. Changes to the laser pulse and pointing for a subsequent DT implosion resulted in a higher temperature, prolate hot spot and a thermonuclear yield of 1.8 × 10{sup 15} neutrons, 40% of the 1D simulated yield.« less

Polar-Direct-Drive Defect Implosions at OMEGA inPreparation for Experiments at NIF

NASA Astrophysics Data System (ADS)

Cobble, J. A.; Schmitt, M. J.; Murphy, T. J.; Tregillis, I. L.; Wysocki, F. J.; Obrey, K. D.; Magelssen, G. R.; Glebov, V.; Bradley, P. A.; Hsu, S. C.; Krasheninnikova, N. V.; Batha, S. H.

2011-10-01

The Defect-Implosion (DIME) campaign involves compressing perturbed spherical capsules with polar direct drive (PDD). For direct-drive implosions at NIF, PDD will be used. We have done simulations and experiments at OMEGA to test our modeling capability for equatorial-plane defects in fusion capsules and for PDD at NIF. Since PDD is anisotropic, we show the results of 0th hydrodynamics of implosions and perturbation-driven features near stagnation. Later presentations discuss defect-induced mix and neutronics, and laser pointing for NIF experiments. Prototype OMEGA shots used 865- μm diameter CH shells filled with 5 atm of D2. Machined channels 30- μm wide and up to 9- μm deep formed the defects. This work has been performed under the auspices of the US DOE, contract number DE-AC52-06NA25396.

A simple method to prevent hard X-ray-induced preheating effects inside the cone tip in indirect-drive fast ignition implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Dongxiao; Shan, Lianqiang; Zhou, Weimin

During fast-ignition implosions, preheating of inside the cone tip caused by hard X-rays can strongly affect the generation and transport of hot electrons in the cone. Although indirect-drive implosions have a higher implosion symmetry, they cause stronger preheating effects than direct-drive implosions. To control the preheating of the cone tip, we propose the use of indirect-drive fast-ignition targets with thicker tips. Experiments carried out at the ShenGuang-III prototype laser facility confirmed that thicker tips are effective for controlling preheating. Moreover, these results were consistent with those of 1D radiation hydrodynamic simulations.

Direct drive: Simulations and results from the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radha, P. B., E-mail: rbah@lle.rochester.edu; Hohenberger, M.; Edgell, D. H.

Direct-drive implosion physics is being investigated at the National Ignition Facility. The primary goal of the experiments is twofold: to validate modeling related to implosion velocity and to estimate the magnitude of hot-electron preheat. Implosion experiments indicate that the energetics is well-modeled when cross-beam energy transfer (CBET) is included in the simulation and an overall multiplier to the CBET gain factor is employed; time-resolved scattered light and scattered-light spectra display the correct trends. Trajectories from backlit images are well modeled, although those from measured self-emission images indicate increased shell thickness and reduced shell density relative to simulations. Sensitivity analyses indicatemore » that the most likely cause for the density reduction is nonuniformity growth seeded by laser imprint and not laser-energy coupling. Hot-electron preheat is at tolerable levels in the ongoing experiments, although it is expected to increase after the mitigation of CBET. Future work will include continued model validation, imprint measurements, and mitigation of CBET and hot-electron preheat.« less

Data driven models of the performance and repeatability of NIF high foot implosions

NASA Astrophysics Data System (ADS)

Gaffney, Jim; Casey, Dan; Callahan, Debbie; Hartouni, Ed; Ma, Tammy; Spears, Brian

2015-11-01

Recent high foot (HF) inertial confinement fusion (ICF) experiments performed at the national ignition facility (NIF) have consisted of enough laser shots that a data-driven analysis of capsule performance is feasible. In this work we use 20-30 individual implosions of similar design, spanning laser drive energies from 1.2 to 1.8 MJ, to quantify our current understanding of the behavior of HF ICF implosions. We develop a probabilistic model for the projected performance of a given implosion and use it to quantify uncertainties in predicted performance including shot-shot variations and observation uncertainties. We investigate the statistical significance of the observed performance differences between different laser pulse shapes, ablator materials, and capsule designs. Finally, using a cross-validation technique, we demonstrate that 5-10 repeated shots of a similar design are required before real trends in the data can be distinguished from shot-shot variations. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-674957.

Improved Understanding of Implosion Symmetry through New Experimental Techniques Connecting Hohlraum Dynamics with Laser Beam Deposition

NASA Astrophysics Data System (ADS)

Ralph, Joseph; Salmonson, Jay; Dewald, Eduard; Bachmann, Benjamin; Edwards, John; Graziani, Frank; Hurricane, Omar; Landen, Otto; Ma, Tammy; Masse, Laurent; MacLaren, Stephen; Meezan, Nathan; Moody, John; Parrilla, Nicholas; Pino, Jesse; Sacks, Ryan; Tipton, Robert

2017-10-01

Understanding what affects implosion symmetry has been a challenge for scientists designing indirect drive inertial confinement fusion experiments on the National Ignition Facility (NIF). New experimental techniques and data analysis have been employed aimed at improving our understanding of the relationship between hohlraum dynamics and implosion symmetry. Thin wall imaging data allows for time-resolved imaging of 10 keV Au l-band x-rays providing for the first time on the NIF, a spatially resolved measurement of laser deposition with time. In the work described here, we combine measurements from the thin wall imaging with time resolved views of the interior of the hohlraum. The measurements presented are compared to hydrodynamic simulations as well as simplified physics models. The goal of this work is to form a physical picture that better explains the relationship of the hohlraum dynamics and capsule ablator on laser beam propagation and implosion symmetry. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

Wavelength Detuning Cross-Beam Energy Transfer Mitigation Scheme for Direct-Drive: Modeling and Evidence from National Ignition Facility Implosions

NASA Astrophysics Data System (ADS)

Marozas, J. A.

2017-10-01

Cross-beam energy transfer (CBET) has been shown to significantly reduce the laser absorption and implosion speed in direct-drive implosion experiments on OMEGA and the National Ignition Facility (NIF). Mitigating CBET assists in achieving ignition-relevant hot-spot pressures in deuterium-tritium cryogenic OMEGA implosions. In addition, reducing CBET permits lower, more hydrodynamically stable, in-flight aspect ratio ignition designs with smaller nonuniformity growth during the acceleration phase. Detuning the wavelengths of the crossing beams is one of several techniques under investigation at the University of Rochester to mitigate CBET. This talk will describe these techniques with an emphasis on wavelength detuning. Recent experiments designed and predicted using multidimensional hydrodynamic simulations including CBET on the NIF have exploited the wavelength arrangement of the NIF beam geometry to demonstrate CBET mitigation through wavelength detuning in polar-direct-drive (PDD) implosions. Shapes and trajectories inferred from time-resolved x-ray radiography of the imploding shell, scattered-light spectra, and hard x-ray spectra generated by suprathermal electrons all indicate a reduction in CBET. These results and their implications for direct-drive ignition will be presented and discussed. In addition, hydrodynamically scaled ignition-relevant designs for OMEGA implosions exploiting wavelength detuning will be presented. Changes required to the OMEGA laser to permit wavelength detuning will be discussed. Future plans for PDD on the NIF including more-uniform implosions with CBET mitigation will be explored. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

High-density carbon capsule experiments on the national ignition facility

DOE PAGES

Ross, J. S.; Ho, D.; Milovich, J.; ...

2015-02-25

Indirect-drive implosions with a high-density carbon (HDC) capsule were conducted on the National Ignition Facility (NIF) to test HDC properties as an ablator material for inertial confinement fusion. In this study, a series of five experiments were completed with 76-μm-thick HDC capsules using a four-shock laser pulse optimized for HDC. The pulse delivered a total energy of 1.3 MJ with a peak power of 360 TW. The experiment demonstrated good laser to target coupling (~90 %) and excellent nuclear performance. Lastly, a deuterium and tritium gas-filled HDC capsule implosion produced a neutron yield of 1.6×10 15 ± 3×10 13, amore » yield over simulated in one dimension of 70%.« less

Hydrodynamic simulations of long-scale-length plasmas for two-plasmon-decay planar-target experiments on the NIF

NASA Astrophysics Data System (ADS)

Solodov, A. A.; Rosenberg, M. J.; Myatt, J. F.; Epstein, R.; Regan, S. P.; Seka, W.; Shaw, J.; Hohenberger, M.; Bates, J. W.; Moody, J. D.; Ralph, J. E.; Turnbull, D. P.; Barrios, M. A.

2016-05-01

The two-plasmon-decay (TPD) instability can be detrimental for direct-drive inertial confinement fusion because it generates high-energy electrons that can preheat the target, thereby reducing target performance. Hydrodynamic simulations to design a new experimental platform to investigate TPD and other laser-plasma instabilities relevant to direct-drive-ignition implosions at the National Ignition Facility are presented. The proposed experiments utilize planar plastic targets with an embedded Mo layer to characterize generation of hot electrons through Mo Kα fluorescence and hard x-ray emission. Different laser-irradiation geometries approximate conditions near both the equator and the pole of a polar-direct-drive implosion.

Neutron temporal diagnostic for high-yield deuterium-tritium cryogenic implosions on OMEGA

DOE PAGES

Stoeckl, C.; Boni, R.; Ehrne, F.; ...

2016-05-10

A next-generation neutron temporal diagnostic (NTD) capable of recording high-quality data for the highest anticipated yield cryogenic DT implosion experiments was recently installed at the Omega Laser Facility. A high-quality measurement of the neutron production width is required to determine the hot-spot pressure achieved in inertial confinement fusion experiments—a key metric in assessing the quality of these implosions. The design of this NTD is based on a fast-rise-time plastic scintillator, which converts the neutron kinetic energy to 350- to 450-nm-wavelength light. The light from the scintillator inside the nose-cone assembly is relayed ~16 m to a streak camera in amore » well-shielded location. An ~200× reduction in neutron background was observed during the first high-yield DT cryogenic implosions compared to the current NTD installation on OMEGA. An impulse response of ~40±10 ps was measured in a dedicated experiment using hard x rays from a planar target irradiated with a 10-ps short pulse from the OMEGA EP laser. Furthermore, the measured instrument response includes contributions from the scintillator rise time, optical relay, and streak camera.« less

Neutron temporal diagnostic for high-yield deuterium–tritium cryogenic implosions on OMEGA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoeckl, C.; Boni, R.; Ehrne, F.

A next-generation neutron temporal diagnostic (NTD) capable of recording high-quality data for the highest anticipated yield cryogenic deuterium–tritium (DT) implosion experiments was recently installed at the Omega Laser Facility. A high-quality measurement of the neutron production width is required to determine the hot-spot pressure achieved in inertial confinement fusion experiments—a key metric in assessing the quality of these implosions. The design of this NTD is based on a fast-rise-time plastic scintillator, which converts the neutron kinetic energy to 350- to 450-nm-wavelength light. The light from the scintillator inside the nose-cone assembly is relayed ∼16 m to a streak camera inmore » a well-shielded location. An ∼200× reduction in neutron background was observed during the first high-yield DT cryogenic implosions compared to the current NTD installation on OMEGA. An impulse response of ∼40 ± 10 ps was measured in a dedicated experiment using hard x-rays from a planar target irradiated with a 10-ps short pulse from the OMEGA EP laser. The measured instrument response includes contributions from the scintillator rise time, optical relay, and streak camera.« less

Neutron temporal diagnostic for high-yield deuterium-tritium cryogenic implosions on OMEGA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoeckl, C.; Boni, R.; Ehrne, F.

A next-generation neutron temporal diagnostic (NTD) capable of recording high-quality data for the highest anticipated yield cryogenic DT implosion experiments was recently installed at the Omega Laser Facility. A high-quality measurement of the neutron production width is required to determine the hot-spot pressure achieved in inertial confinement fusion experiments—a key metric in assessing the quality of these implosions. The design of this NTD is based on a fast-rise-time plastic scintillator, which converts the neutron kinetic energy to 350- to 450-nm-wavelength light. The light from the scintillator inside the nose-cone assembly is relayed ~16 m to a streak camera in amore » well-shielded location. An ~200× reduction in neutron background was observed during the first high-yield DT cryogenic implosions compared to the current NTD installation on OMEGA. An impulse response of ~40±10 ps was measured in a dedicated experiment using hard x rays from a planar target irradiated with a 10-ps short pulse from the OMEGA EP laser. Furthermore, the measured instrument response includes contributions from the scintillator rise time, optical relay, and streak camera.« less

Improving cryogenic deuterium–tritium implosion performance on OMEGA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sangster, T. C.; Goncharov, V. N.; Betti, R.

2013-05-15

A flexible direct-drive target platform is used to implode cryogenic deuterium–tritium (DT) capsules on the OMEGA laser [Boehly et al., Opt. Commun. 133, 495 (1997)]. The goal of these experiments is to demonstrate ignition hydrodynamically equivalent performance where the laser drive intensity, the implosion velocity, the fuel adiabat, and the in-flight aspect ratio (IFAR) are the same as those for a 1.5-MJ target [Goncharov et al., Phys. Rev. Lett. 104, 165001 (2010)] designed to ignite on the National Ignition Facility [Hogan et al., Nucl. Fusion 41, 567 (2001)]. The results from a series of 29 cryogenic DT implosions are presented.more » The implosions were designed to span a broad region of design space to study target performance as a function of shell stability (adiabat) and implosion velocity. Ablation-front perturbation growth appears to limit target performance at high implosion velocities. Target outer-surface defects associated with contaminant gases in the DT fuel are identified as the dominant perturbation source at the ablation surface; performance degradation is confirmed by 2D hydrodynamic simulations that include these defects. A trend in the value of the Lawson criterion [Betti et al., Phys. Plasmas 17, 058102 (2010)] for each of the implosions in adiabat–IFAR space suggests the existence of a stability boundary that leads to ablator mixing into the hot spot for the most ignition-equivalent designs.« less

Improving cryogenic deuterium tritium implosion performance on OMEGA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sangster, T. C.; Goncharov, V. N.; Betti, R.

2013-01-01

A flexible direct-drive target platform is used to implode cryogenic deuterium–tritium (DT) capsules on the OMEGA laser [Boehly et al., Opt. Commun. 133, 495 (1997)]. The goal of these experiments is to demonstrate ignition hydrodynamically equivalent performance where the laser drive intensity, the implosion velocity, the fuel adiabat, and the in-flight aspect ratio (IFAR) are the same as those for a 1.5-MJ target [Goncharov et al., Phys. Rev. Lett. 104, 165001 (2010)] designed to ignite on the National Ignition Facility [Hogan et al., Nucl. Fusion 41, 567 (2001)]. The results from a series of 29 cryogenic DT implosions are presented.more » The implosions were designed to span a broad region of design space to study target performance as a function of shell stability (adiabat) and implosion velocity. Ablation-front perturbation growth appears to limit target performance at high implosion velocities. Target outer-surface defects associated with contaminant gases in the DT fuel are identified as the dominant perturbation source at the ablation surface; performance degradation is confirmed by 2D hydrodynamic simulations that include these defects. A trend in the value of the Lawson criterion [Betti et al., Phys. Plasmas 17, 058102 (2010)] for each of the implosions in adiabat–IFAR space suggests the existence of a stability boundary that leads to ablator mixing into the hot spot for the most ignition-equivalent designs.« less

Fuel gain exceeding unity in an inertially confined fusion implosion.

PubMed

Hurricane, O A; Callahan, D A; Casey, D T; Celliers, P M; Cerjan, C; Dewald, E L; Dittrich, T R; Döppner, T; Hinkel, D E; Berzak Hopkins, L F; Kline, J L; Le Pape, S; Ma, T; MacPhee, A G; Milovich, J L; Pak, A; Park, H-S; Patel, P K; Remington, B A; Salmonson, J D; Springer, P T; Tommasini, R

2014-02-20

Ignition is needed to make fusion energy a viable alternative energy source, but has yet to be achieved. A key step on the way to ignition is to have the energy generated through fusion reactions in an inertially confined fusion plasma exceed the amount of energy deposited into the deuterium-tritium fusion fuel and hotspot during the implosion process, resulting in a fuel gain greater than unity. Here we report the achievement of fusion fuel gains exceeding unity on the US National Ignition Facility using a 'high-foot' implosion method, which is a manipulation of the laser pulse shape in a way that reduces instability in the implosion. These experiments show an order-of-magnitude improvement in yield performance over past deuterium-tritium implosion experiments. We also see a significant contribution to the yield from α-particle self-heating and evidence for the 'bootstrapping' required to accelerate the deuterium-tritium fusion burn to eventually 'run away' and ignite.

Direct drive: Simulations and results from the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radha, P. B.; Hohenberger, M.; Edgell, D. H.

Here, the direct-drive implosion physics is being investigated at the National Ignition Facility. The primary goal of the experiments is twofold: to validate modeling related to implosion velocity and to estimate the magnitude of hot-electron preheat. Implosion experiments indicate that the energetics is well-modeled when cross-beam energy transfer (CBET) is included in the simulation and an overall multiplier to the CBET gain factor is employed; time-resolved scattered light and scattered-light spectra display the correct trends. Trajectories from backlit images are well modeled, although those from measured self-emission images indicate increased shell thickness and reduced shell density relative to simulations. Sensitivitymore » analyses indicate that the most likely cause for the density reduction is nonuniformity growth seeded by laser imprint and not laser-energy coupling. Hot-electron preheat is at tolerable levels in the ongoing experiments, although it is expected to increase after the mitigation of CBET. Future work will include continued model validation, imprint measurements, and mitigation of CBET and hot-electron preheat.« less

Direct drive: Simulations and results from the National Ignition Facility

DOE PAGES

Radha, P. B.; Hohenberger, M.; Edgell, D. H.; ...

2016-04-19

Here, the direct-drive implosion physics is being investigated at the National Ignition Facility. The primary goal of the experiments is twofold: to validate modeling related to implosion velocity and to estimate the magnitude of hot-electron preheat. Implosion experiments indicate that the energetics is well-modeled when cross-beam energy transfer (CBET) is included in the simulation and an overall multiplier to the CBET gain factor is employed; time-resolved scattered light and scattered-light spectra display the correct trends. Trajectories from backlit images are well modeled, although those from measured self-emission images indicate increased shell thickness and reduced shell density relative to simulations. Sensitivitymore » analyses indicate that the most likely cause for the density reduction is nonuniformity growth seeded by laser imprint and not laser-energy coupling. Hot-electron preheat is at tolerable levels in the ongoing experiments, although it is expected to increase after the mitigation of CBET. Future work will include continued model validation, imprint measurements, and mitigation of CBET and hot-electron preheat.« less

LLE Review Quarterly Report (January-March 2002). Volume 90

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donaldson, William R.

2002-03-01

This volume of the LLE Review, covering January-March 2002, features “First Results from Cryogenic Target Implosions on OMEGA” by C. Stoeckl et al. (p. 49). This article describes initial results from direct-drive spherical cryogenic target implosions on the 60-beam OMEGA laser system. These experiments are part of the scientific base leading to direct-drive ignition implosions planned for the National Ignition Facility (NIF). Results shown include neutron yield, secondary-neutron and proton yields, the time of peak neutron emission, and both time-integrated and time-resolved x-ray images of the imploding core. The experimental values are compared with 1-D numerical simulations. The target withmore » an ice-layer nonuniformity of srms = 9 mm showed 30% of the 1-D predicted neutron yield. These initial results are encouraging for future cryogenic implosions on OMEGA and the NIF. Other articles in this issue are titled the following: Equation-of-State Measurements of Porous Materials on OMEGA: Numerical Modeling; Observations of Modulated Shock Waves in Solid Targets Driven by Spatially Modulated Laser Beams; Time-Dependent Electron Thermal Flux Inhibition in direct-Drive Laser Implosions; Precision Spectral Sculpting of Broadband FM Pulses Amplified in a Narrowband Medium; Electric-Field-Induced Motion of Polymer Cholesteric Liquid Crystal Flakes in a Moderately Conductive Fluid; and, Femtosecond Response of a Freestanding LT-GaAs Photoconductive Switch.« less

Technique for fabrication of ultrathin foils in cylindrical geometry for liner-plasma implosion experiments with sub-megaampere currents

DOE PAGES

Yager-Elorriaga, D. A.; Steiner, A. M.; Patel, S. G.; ...

2015-11-19

In this study, we describe a technique for fabricating ultrathin foils in cylindrical geometry for liner-plasma implosion experiments using sub-MA currents. Liners are formed by wrapping a 400 nm, rectangular strip of aluminum foil around a dumbbell-shaped support structure with a non-conducting center rod, so that the liner dimensions are 1 cm in height, 6.55 mm in diameter, and 400 nm in thickness. The liner-plasmas are imploded by discharging ~600 kA with ~200 ns rise time using a 1 MA linear transformer driver, and the resulting implosions are imaged four times per shot using laser-shadowgraphy at 532 nm. As amore » result, this technique enables the study of plasma implosion physics, including the magneto Rayleigh-Taylor, sausage, and kink instabilities on initially solid, imploding metallic liners with university-scale pulsed power machines.« less

Technique for fabrication of ultrathin foils in cylindrical geometry for liner-plasma implosion experiments with sub-megaampere currents

NASA Astrophysics Data System (ADS)

Yager-Elorriaga, D. A.; Steiner, A. M.; Patel, S. G.; Jordan, N. M.; Lau, Y. Y.; Gilgenbach, R. M.

2015-11-01

In this work, we describe a technique for fabricating ultrathin foils in cylindrical geometry for liner-plasma implosion experiments using sub-MA currents. Liners are formed by wrapping a 400 nm, rectangular strip of aluminum foil around a dumbbell-shaped support structure with a non-conducting center rod, so that the liner dimensions are 1 cm in height, 6.55 mm in diameter, and 400 nm in thickness. The liner-plasmas are imploded by discharging ˜600 kA with ˜200 ns rise time using a 1 MA linear transformer driver, and the resulting implosions are imaged four times per shot using laser-shadowgraphy at 532 nm. This technique enables the study of plasma implosion physics, including the magneto Rayleigh-Taylor, sausage, and kink instabilities on initially solid, imploding metallic liners with university-scale pulsed power machines.

Technique for fabrication of ultrathin foils in cylindrical geometry for liner-plasma implosion experiments with sub-megaampere currents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yager-Elorriaga, D. A.; Steiner, A. M.; Patel, S. G.

In this study, we describe a technique for fabricating ultrathin foils in cylindrical geometry for liner-plasma implosion experiments using sub-MA currents. Liners are formed by wrapping a 400 nm, rectangular strip of aluminum foil around a dumbbell-shaped support structure with a non-conducting center rod, so that the liner dimensions are 1 cm in height, 6.55 mm in diameter, and 400 nm in thickness. The liner-plasmas are imploded by discharging ~600 kA with ~200 ns rise time using a 1 MA linear transformer driver, and the resulting implosions are imaged four times per shot using laser-shadowgraphy at 532 nm. As amore » result, this technique enables the study of plasma implosion physics, including the magneto Rayleigh-Taylor, sausage, and kink instabilities on initially solid, imploding metallic liners with university-scale pulsed power machines.« less

Competing effects of collisional ionization and radiative cooling in inertially confined plasmas

NASA Astrophysics Data System (ADS)

Woolsey, N. C.; Hammel, B. A.; Keane, C. J.; Back, C. A.; Moreno, J. C.; Nash, J. K.; Calisti, A.; Mossé, C.; Stamm, R.; Talin, B.; Asfaw, A.; Klein, L. S.; Lee, R. W.

1998-04-01

We describe an experimental investigation, a detailed analysis of the Ar XVII 1s2 1S-1s3p 1P (Heβ) line shape formed in a high-energy-density implosion, and report on one-dimensional radiation-hydrodynamics simulation of the implosion. In this experiment trace quantities of argon are doped into a lower-Z gas-filled core of a plastic microsphere. The dopant level is controlled to ensure that the Heβ transition is optically thin and easily observable. Then the observed line shape is used to derive electron temperatures (Te) and electron densities (ne). The high-energy density plasma, with Te approaching 1 keV and ne=1024 cm-3, is created by placing the microsphere in a gold cylindrical enclosure, the interior of which is directly irradiated by a high-energy laser; the x rays produced by this laser-gold interaction indirectly implode the microsphere. Central to the interpretation of the hydrodynamics of the implosions is the characterization and understanding of the formation of these plasmas. To develop an understanding of the plasma and its temporal evolution, time-resolved Te and ne measurements are extracted using techniques that are independent of the plasma hydrodynamics. Comparing spectroscopic diagnostics with measurements derived from other diagnostic methods, we find the spectroscopic measurements to be reliable and further we find that the experiment-to-experiment comparison shows that these implosions are reproducible.

Evidence for Stratification of Deuterium-Tritium Fuel in Inertial Confinement Fusion Implosions

NASA Astrophysics Data System (ADS)

Casey, D. T.; Frenje, J. A.; Gatu Johnson, M.; Manuel, M. J.-E.; Rinderknecht, H. G.; Sinenian, N.; Séguin, F. H.; Li, C. K.; Petrasso, R. D.; Radha, P. B.; Delettrez, J. A.; Glebov, V. Yu; Meyerhofer, D. D.; Sangster, T. C.; McNabb, D. P.; Amendt, P. A.; Boyd, R. N.; Rygg, J. R.; Herrmann, H. W.; Kim, Y. H.; Bacher, A. D.

2012-02-01

Measurements of the D(d,p)T (dd) and T(t,2n)He4 (tt) reaction yields have been compared with those of the D(t,n)He4 (dt) reaction yield, using deuterium-tritium gas-filled inertial confinement fusion capsule implosions. In these experiments, carried out on the OMEGA laser, absolute spectral measurements of dd protons and tt neutrons were obtained. From these measurements, it was concluded that the dd yield is anomalously low and the tt yield is anomalously high relative to the dt yield, an observation that we conjecture to be caused by a stratification of the fuel in the implosion core. This effect may be present in ignition experiments planned on the National Ignition Facility.

Evidence for stratification of deuterium-tritium fuel in inertial confinement fusion implosions.

PubMed

Casey, D T; Frenje, J A; Johnson, M Gatu; Manuel, M J-E; Rinderknecht, H G; Sinenian, N; Séguin, F H; Li, C K; Petrasso, R D; Radha, P B; Delettrez, J A; Glebov, V Yu; Meyerhofer, D D; Sangster, T C; McNabb, D P; Amendt, P A; Boyd, R N; Rygg, J R; Herrmann, H W; Kim, Y H; Bacher, A D

2012-02-17

Measurements of the D(d,p)T (dd) and T(t,2n)(4)He (tt) reaction yields have been compared with those of the D(t,n)(4)He (dt) reaction yield, using deuterium-tritium gas-filled inertial confinement fusion capsule implosions. In these experiments, carried out on the OMEGA laser, absolute spectral measurements of dd protons and tt neutrons were obtained. From these measurements, it was concluded that the dd yield is anomalously low and the tt yield is anomalously high relative to the dt yield, an observation that we conjecture to be caused by a stratification of the fuel in the implosion core. This effect may be present in ignition experiments planned on the National Ignition Facility.

Understanding Laser-Imprint Effects on Plastic-Target Implosions on OMEGA with New Physics Models

NASA Astrophysics Data System (ADS)

Hu, S. X.; Michel, D. T.; Davis, A. K.; Betti, R.; Radha, P. B.; Campbell, E. M.; Froula, D. H.; Stoeckl, C.

2016-10-01

Using the state-of-the-art physics models (nonlocal thermal transport, cross-beam energy transfer, and first-principles equation of state) recently implemented in our two-dimensional hydrocode DRACO, we have performed a systematic study of laser-imprint effects on plastic-target implosions on OMEGA by both simulations and experiments. Through varying the laser picket intensity, the imploding shells were set at different adiabats ranging from α = 2 to α = 6 . As the shell adiabat α decreases, we observed: (1) the measured shell thickness at the hot spot emission becomes larger than the uniform prediction; (2) the hot-spot core emits and neutron burn starts earlier than the corresponding 1-D prediction; and (3) the measured neutron yields are significantly reduced from their 1-D designs. Most of these experimental observations are well reproduced by our DRACO simulations with laser imprints. These studies clearly identify that laser imprint is the major cause for target performance degradation of OMEGA implosions of α <= 3 . Mitigating laser imprints must be an essential effort to improve low- α target performance in direct-drive inertial confinement fusion ignition attempts. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Gas-filled Rugby hohlraum energetics and implosions experiments on OMEGA

NASA Astrophysics Data System (ADS)

Casner, Alexis; Philippe, F.; Tassin, V.; Seytor, P.; Monteil, M. C.; Villette, B.; Reverdin, C.

2010-11-01

Recent experiments [1,2] have validated the x-ray drive enhancement provided by rugby-shaped hohlraums over cylinders in the indirect drive (ID) approach to inertial confinement fusion (ICF). This class of hohlraum is the baseline design for the Laser Mégajoule program, is also applicable to the National Ignition Facility and could therefore benefit ID Inertial Fusion Energy studies. We have carried out a serie of energetics and implosions experiments with OMEGA ``scale 1'' rugby hohlraums [1,2]. For empty hohlraums these experiments provide complementary measurements of backscattered light along 42 cone, as well as detailed drive history. In the case of gas-filled rugby hohlraums we have also study implosion performance (symmetry, yield, bangtime, hotspot spectra...) using a high contrast shaped pulse leading to a different implosion regime and for a range of capsule convergence ratios. These results will be compared with FCI2 hydrocodes calculations and future experimental campaigns will be suggested. [4pt] [1] F. Philippe et al., Phys. Rev. Lett. 104, 035004 (2010). [0pt] [2] H. Robey et al., Phys. Plasnas 17, 056313 (2010).

Diagnostics for Z-pinch implosion experiments on PTS

NASA Astrophysics Data System (ADS)

Ren, X. D.; Huang, X. B.; Zhou, S. T.; Zhang, S. Q.; Dan, J. K.; Li, J.; Cai, H. C.; Wang, K. L.; Ouyang, K.; Xu, Q.; Duan, S. C.; Chen, G. H.; Wang, M.; Feng, S. P.; Yang, L. B.; Xie, W. P.; Deng, J. J.

2014-12-01

The preliminary experiments of wire array implosion were performed on PTS, a 10 MA z-pinch driver with a 70 ns rise time. A set of diagnostics have been developed and fielded on PTS to study pinch physics and implosion dynamics of wire array. Radiated power measurement for soft x-rays was performed by multichannel filtered x-ray diode array, and flat spectral responses x-ray diode detector. Total x-ray yield was measured by a calibrated, unfiltered nickel bolometer which was also used to obtain pinch power. Multiple time-gated pinhole cameras were used to produce spatial-resolved images of x-ray self-emission from plasmas. Two time-integrated pinhole cameras were used respectively with 20-μm Be filter and with multilayer mirrors to record images produced by >1-keV and 277±5 eV self-emission. An optical streak camera was used to produce radial implosion trajectories, and an x-ray streak camera paired with a horizontal slit was used to record a continuous time-history of emission with one-dimensional spatial resolution. A frequency-doubled Nd:YAG laser (532 nm) was used to produce four frame laser shadowgraph images with 6 ns time interval. We will briefly describe each of these diagnostics and present some typical results from them.

Theoretical quantification of shock-timing sensitivities for direct-drive inertial confinement fusion implosions on OMEGA

DOE PAGES

Cao, D.; Boehly, T. R.; Gregor, M. C.; ...

2018-05-16

Using temporally shaped laser pulses, multiple shocks can be launched in direct-drive inertial confinement fusion implosion experiments to set the shell on a desired isentrope or adiabat. The velocity of the first shock and the times at which subsequent shocks catch up to it are measured through the VISAR diagnostic on OMEGA. Simulations reproduce these velocity and shock-merger time measurements when using laser pulses designed for setting mid-adiabat (α ~ 3) implosions, but agreement degrades for lower-adiabat (α ~ 1) designs. Several possibilities for this difference are studied: errors in placing the target at the center of irradiation (target offset),more » variations in energy between the different incident beams (power imbalance), and errors in modeling the laser energy coupled into the capsule. Simulation results indicate that shock timing is most sensitive to details of the density and temperature profiles in the coronal plasma, which influences the laser energy coupled into the target, and only marginally sensitive to target offset and beam power imbalance. A new technique under development to infer coronal profiles using x-ray self-emission imaging can be applied to the pulse shapes used in shock-timing experiments. In conclusion, this will help identify improved physics models to implement in codes and consequently enhance shock-timing predictive capability for low-adiabat pulses.« less

Analysis of NIF experiments with the minimal energy implosion model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, B., E-mail: bcheng@lanl.gov; Kwan, T. J. T.; Wang, Y. M.

2015-08-15

We apply a recently developed analytical model of implosion and thermonuclear burn to fusion capsule experiments performed at the National Ignition Facility that used low-foot and high-foot laser pulse formats. Our theoretical predictions are consistent with the experimental data. Our studies, together with neutron image analysis, reveal that the adiabats of the cold fuel in both low-foot and high-foot experiments are similar. That is, the cold deuterium-tritium shells in those experiments are all in a high adiabat state at the time of peak implosion velocity. The major difference between low-foot and high-foot capsule experiments is the growth of the shock-inducedmore » instabilities developed at the material interfaces which lead to fuel mixing with ablator material. Furthermore, we have compared the NIF capsules performance with the ignition criteria and analyzed the alpha particle heating in the NIF experiments. Our analysis shows that alpha heating was appreciable only in the high-foot experiments.« less

Hohlraum glint and laser pre-pulse detector for NIF experiments using velocity interferometer system for any reflector.

PubMed

Moody, J D; Clancy, T J; Frieders, G; Celliers, P M; Ralph, J; Turnbull, D P

2014-11-01

Laser pre-pulse and early-time laser reflection from the hohlraum wall onto the capsule (termed "glint") can cause capsule imprint and unwanted early-time shocks on indirect drive implosion experiments. In a minor modification to the existing velocity interferometer system for any reflector diagnostic on NIF a fast-response vacuum photodiode was added to detect this light. The measurements show evidence of laser pre-pulse and possible light reflection off the hohlraum wall and onto the capsule.

Demonstration of High Performance in Layered Deuterium-Tritium Capsule Implosions in Uranium Hohlraums at the National Ignition Facility.

PubMed

Döppner, T; Callahan, D A; Hurricane, O A; Hinkel, D E; Ma, T; Park, H-S; Berzak Hopkins, L F; Casey, D T; Celliers, P; Dewald, E L; Dittrich, T R; Haan, S W; Kritcher, A L; MacPhee, A; Le Pape, S; Pak, A; Patel, P K; Springer, P T; Salmonson, J D; Tommasini, R; Benedetti, L R; Bond, E; Bradley, D K; Caggiano, J; Church, J; Dixit, S; Edgell, D; Edwards, M J; Fittinghoff, D N; Frenje, J; Gatu Johnson, M; Grim, G; Hatarik, R; Havre, M; Herrmann, H; Izumi, N; Khan, S F; Kline, J L; Knauer, J; Kyrala, G A; Landen, O L; Merrill, F E; Moody, J; Moore, A S; Nikroo, A; Ralph, J E; Remington, B A; Robey, H F; Sayre, D; Schneider, M; Streckert, H; Town, R; Turnbull, D; Volegov, P L; Wan, A; Widmann, K; Wilde, C H; Yeamans, C

2015-07-31

We report on the first layered deuterium-tritium (DT) capsule implosions indirectly driven by a "high-foot" laser pulse that were fielded in depleted uranium hohlraums at the National Ignition Facility. Recently, high-foot implosions have demonstrated improved resistance to ablation-front Rayleigh-Taylor instability induced mixing of ablator material into the DT hot spot [Hurricane et al., Nature (London) 506, 343 (2014)]. Uranium hohlraums provide a higher albedo and thus an increased drive equivalent to an additional 25 TW laser power at the peak of the drive compared to standard gold hohlraums leading to higher implosion velocity. Additionally, we observe an improved hot-spot shape closer to round which indicates enhanced drive from the waist. In contrast to findings in the National Ignition Campaign, now all of our highest performing experiments have been done in uranium hohlraums and achieved total yields approaching 10^{16} neutrons where more than 50% of the yield was due to additional heating of alpha particles stopping in the DT fuel.

Demonstration of High Performance in Layered Deuterium-Tritium Capsule Implosions in Uranium Hohlraums at the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Döppner, T.; Callahan, D. A.; Hurricane, O. A.

We report on the first layered deuterium-tritium (DT) capsule implosions indirectly driven by a “highfoot” laser pulse that were fielded in depleted uranium hohlraums at the National Ignition Facility. Recently, high-foot implosions have demonstrated improved resistance to ablation-front Rayleigh-Taylor instability induced mixing of ablator material into the DT hot spot [Hurricane et al., Nature (London) 506, 343 (2014)]. Uranium hohlraums provide a higher albedo and thus an increased drive equivalent to an additional 25 TW laser power at the peak of the drive compared to standard gold hohlraums leading to higher implosion velocity. Additionally, we observe an improved hot-spot shapemore » closer to round which indicates enhanced drive from the waist. In contrast to findings in the National Ignition Campaign, now all of our highest performing experiments have been done in uranium hohlraums and achieved total yields approaching 10 16 neutrons where more than 50% of the yield was due to additional heating of alpha particles stopping in the DT fuel.« less

Demonstration of High Performance in Layered Deuterium-Tritium Capsule Implosions in Uranium Hohlraums at the National Ignition Facility

DOE PAGES

Döppner, T.; Callahan, D. A.; Hurricane, O. A.; ...

2015-07-28

We report on the first layered deuterium-tritium (DT) capsule implosions indirectly driven by a “highfoot” laser pulse that were fielded in depleted uranium hohlraums at the National Ignition Facility. Recently, high-foot implosions have demonstrated improved resistance to ablation-front Rayleigh-Taylor instability induced mixing of ablator material into the DT hot spot [Hurricane et al., Nature (London) 506, 343 (2014)]. Uranium hohlraums provide a higher albedo and thus an increased drive equivalent to an additional 25 TW laser power at the peak of the drive compared to standard gold hohlraums leading to higher implosion velocity. Additionally, we observe an improved hot-spot shapemore » closer to round which indicates enhanced drive from the waist. In contrast to findings in the National Ignition Campaign, now all of our highest performing experiments have been done in uranium hohlraums and achieved total yields approaching 10 16 neutrons where more than 50% of the yield was due to additional heating of alpha particles stopping in the DT fuel.« less

Onset of hydrodynamic mix in high-velocity, highly compressed inertial confinement fusion implosions.

PubMed

Ma, T; Patel, P K; Izumi, N; Springer, P T; Key, M H; Atherton, L J; Benedetti, L R; Bradley, D K; Callahan, D A; Celliers, P M; Cerjan, C J; Clark, D S; Dewald, E L; Dixit, S N; Döppner, T; Edgell, D H; Epstein, R; Glenn, S; Grim, G; Haan, S W; Hammel, B A; Hicks, D; Hsing, W W; Jones, O S; Khan, S F; Kilkenny, J D; Kline, J L; Kyrala, G A; Landen, O L; Le Pape, S; MacGowan, B J; Mackinnon, A J; MacPhee, A G; Meezan, N B; Moody, J D; Pak, A; Parham, T; Park, H-S; Ralph, J E; Regan, S P; Remington, B A; Robey, H F; Ross, J S; Spears, B K; Smalyuk, V; Suter, L J; Tommasini, R; Town, R P; Weber, S V; Lindl, J D; Edwards, M J; Glenzer, S H; Moses, E I

2013-08-23

Deuterium-tritium inertial confinement fusion implosion experiments on the National Ignition Facility have demonstrated yields ranging from 0.8 to 7×10(14), and record fuel areal densities of 0.7 to 1.3 g/cm2. These implosions use hohlraums irradiated with shaped laser pulses of 1.5-1.9 MJ energy. The laser peak power and duration at peak power were varied, as were the capsule ablator dopant concentrations and shell thicknesses. We quantify the level of hydrodynamic instability mix of the ablator into the hot spot from the measured elevated absolute x-ray emission of the hot spot. We observe that DT neutron yield and ion temperature decrease abruptly as the hot spot mix mass increases above several hundred ng. The comparison with radiation-hydrodynamic modeling indicates that low mode asymmetries and increased ablator surface perturbations may be responsible for the current performance.

Controlling dynamics of imploded core plasma for fast ignition

NASA Astrophysics Data System (ADS)

Nagatomo, H.; Johzaki, T.; Sunahara, A.; Shiraga, H.; Sakagami, H.; Cai, H.; Mima, K.

2010-08-01

In the Fast ignition, formation of highly compressed core plasma is one of critical issue. In this work, the effect hydrodynamic instability in cone-guided shell implosion is studied. Two-dimensional radiation hydrodynamic simulations are carried out where realistic seeds of Rayleigh-Taylor instability are imposed. Preliminary results suggest that the instability reduces implosion performance, such as implosion velocity, areal density, and maximum density. In perturbed target implosion, the break-up time of the tip of the cone is earlier than that of ideal unperturbed target implosion case. This is crucial matter for the Fast ignition because the pass for the heating laser is filled with plasma before the shot of heating laser. A sophisticated implosion design of stable and low in-flight aspect ratio is necessary for cone-guided shell implosion.

Theoretical quantification of shock-timing sensitivities for direct-drive inertial confinement fusion implosions on OMEGA

NASA Astrophysics Data System (ADS)

Cao, D.; Boehly, T. R.; Gregor, M. C.; Polsin, D. N.; Davis, A. K.; Radha, P. B.; Regan, S. P.; Goncharov, V. N.

2018-05-01

Using temporally shaped laser pulses, multiple shocks can be launched in direct-drive inertial confinement fusion implosion experiments to set the shell on a desired isentrope or adiabat. The velocity of the first shock and the times at which subsequent shocks catch up to it are measured through the velocity interferometry system for any reflector diagnostic [T. R. Boehly et al., Phys. Plasmas 18, 092706 (2011)] on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Simulations reproduce these velocity and shock-merger time measurements when using laser pulses designed for setting mid-adiabat (α ˜ 3) implosions, but agreement degrades for lower-adiabat (α ˜ 1) designs. Simulation results indicate that the shock timing discrepancy is most sensitive to details of the density and temperature profiles in the coronal plasma, which influences the laser energy coupled into the target, and only marginally sensitive to the target offset and beam power imbalance. To aid in verifying the coronal profile's influence, a new technique under development to infer coronal profiles using x-ray self-emission imaging [A. K. Davis et al., Bull. Am. Phys. Soc. 61, BAPS.2016.DPP.NO8.7 (2016)] can be applied to the pulse shapes used in shock-timing experiments.

Pulsed-power-driven cylindrical liner implosions of laser preheated fuel magnetized with an axial field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Slutz, S. A.; Herrmann, M. C.; Vesey, R. A.

2010-05-15

The radial convergence required to reach fusion conditions is considerably higher for cylindrical than for spherical implosions since the volume is proportional to r{sup 2} versus r{sup 3}, respectively. Fuel magnetization and preheat significantly lowers the required radial convergence enabling cylindrical implosions to become an attractive path toward generating fusion conditions. Numerical simulations are presented indicating that significant fusion yields may be obtained by pulsed-power-driven implosions of cylindrical metal liners onto magnetized (>10 T) and preheated (100-500 eV) deuterium-tritium (DT) fuel. Yields exceeding 100 kJ could be possible on Z at 25 MA, while yields exceeding 50 MJ could bemore » possible with a more advanced pulsed power machine delivering 60 MA. These implosions occur on a much shorter time scale than previously proposed implosions, about 100 ns as compared to about 10 mus for magnetic target fusion (MTF) [I. R. Lindemuth and R. C. Kirkpatrick, Nucl. Fusion 23, 263 (1983)]. Consequently the optimal initial fuel density (1-5 mg/cc) is considerably higher than for MTF (approx1 mug/cc). Thus the final fuel density is high enough to axially trap most of the alpha-particles for cylinders of approximately 1 cm in length with a purely axial magnetic field, i.e., no closed field configuration is required for ignition. According to the simulations, an initial axial magnetic field is partially frozen into the highly conducting preheated fuel and is compressed to more than 100 MG. This final field is strong enough to inhibit both electron thermal conduction and the escape of alpha-particles in the radial direction. Analytical and numerical calculations indicate that the DT can be heated to 200-500 eV with 5-10 kJ of green laser light, which could be provided by the Z-Beamlet laser. The magneto-Rayleigh-Taylor (MRT) instability poses the greatest threat to this approach to fusion. Two-dimensional Lasnex simulations indicate that the liner walls must have a substantial initial thickness (10-20% of the radius) so that they maintain integrity throughout the implosion. The Z and Z-Beamlet experiments are now being planned to test the various components of this concept, e.g., the laser heating of the fuel and the robustness of liner implosions to the MRT instability.« less

Implosion spectroscopy in Rugby hohlraums on OMEGA

NASA Astrophysics Data System (ADS)

Philippe, Franck; Tassin, Veronique; Bitaud, Laurent; Seytor, Patricia; Reverdin, Charles

2014-10-01

The rugby hohlraum concept has been validated in previous experiments on the OMEGA laser facility. This new hohlraum type can now be used as a well-characterized experimental platform to study indirect drive implosion, at higher radiation temperatures than would be feasible at this scale with classical cylindrical hohlraums. Recent experiments have focused on the late stages of implosion and hotspot behavior. The capsules included both a thin buried Titanium tracer layer, 0-3 microns from the inner surface, Argon dopant in the deuterium gas fuel and Germanium doped CH shells, providing a variety of spectral signatures of the plasma conditions in different parts of the target. X-ray spectroscopy and imaging were used to study compression, Rayleigh-Taylor instabilities growth at the inner surface and mix between the shell and gas.

Advances in compact proton spectrometers for inertial-confinement fusion and plasma nuclear science.

PubMed

Seguin, F H; Sinenian, N; Rosenberg, M; Zylstra, A; Manuel, M J-E; Sio, H; Waugh, C; Rinderknecht, H G; Johnson, M Gatu; Frenje, J; Li, C K; Petrasso, R; Sangster, T C; Roberts, S

2012-10-01

Compact wedge-range-filter proton spectrometers cover proton energies ∼3-20 MeV. They have been used at the OMEGA laser facility for more than a decade for measuring spectra of primary D(3)He protons in D(3)He implosions, secondary D(3)He protons in DD implosions, and ablator protons in DT implosions; they are now being used also at the National Ignition Facility. The spectra are used to determine proton yields, shell areal density at shock-bang time and compression-bang time, fuel areal density, and implosion symmetry. There have been changes in fabrication and in analysis algorithms, resulting in a wider energy range, better accuracy and precision, and better robustness for survivability with indirect-drive inertial-confinement-fusion experiments.

A Numerical Model for Two-Plasmon-Decay Hot-Electron Production and Mitigation in Direct-Drive Implosions

NASA Astrophysics Data System (ADS)

Myatt, J. F.; Shaw, J. G.; Solodov, A. A.; Maximov, A. V.; Short, R. W.; Seka, W.; Follett, R. K.; Edgell, D. H.; Froula, D. H.; Goncharov, V. N.

2015-11-01

Hot-electron preheat, caused by laser-plasma instabilities, can impair the performance of inertial confinement fusion implosions. It is therefore imperative to understand processes that can generate hot electrons and to design mitigation strategies should preheat be found to be excessive at the ignition scale (laser-plasma interactions do not follow hydrodynamic scaling). For this purpose, a new 3-D model [laser-plasma simulation environment (LPSE)] has been constructed that computes hot-electron generation in direct-drive plasmas based on the assumption that two-plasmon decay is the dominant, hot-electron-producing instability. It uses an established model of TPD-driven turbulence together with a new GPU based hybrid particle method of hot-electron production. The time-dependent hot-electron power, total energy, and energy spectrum are computed and compared with data from recent OMEGA implosion experiments that have sought to mitigate TPD by the use of multilayered (mid- Z) ablators. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Convergent ablation measurements with gas-filled rugby hohlraum on OMEGA

NASA Astrophysics Data System (ADS)

Casner, A.; Jalinaud, T.; Galmiche, D.

2016-03-01

Convergent ablation experiments with gas-filled rugby hohlraum were performed for the first time on the OMEGA laser facility. A time resolved 1D streaked radiography of capsule implosion is acquired in the direction perpendicular to hohlraum axis, whereas a 2D gated radiography is acquired at the same time along the hohlraum axis on a x-ray framing camera. The implosion trajectory has been measured for various kinds of uniformly doped ablators, including germanium-doped and silicon-doped polymers (CH), at two different doping fraction (2% and 4% at.). Our experiments aimed also at measuring the implosion performance of laminated capsules. A laminated ablator is constituted by thin alternate layers of un-doped and doped CH. It has been previously shown in planar geometry that laminated ablators could mitigate Rayleigh Taylor growth at ablation front. Our results confirm that the implosion of a capsule constituted with a uniform or laminated ablator behaves similarly, in accordance with post-shot simulations performed with the CEA hydrocode FCI2.

Polar-Drive Experiments at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Hohenberger, M.

2014-10-01

To support direct-drive inertial confinement fusion (ICF) experiments at the National Ignition Facility (NIF) in its indirect-drive beam configuration, the polar-drive (PD) concept has been proposed. It requires direct-drive-specific beam smoothing, phase plates, and repointing the NIF beams toward the equator to ensure symmetric target irradiation. First experiments testing the performance of ignition-relevant PD implosions at the NIF have been performed. The goal of these early experiments was to develop a stable, warm implosion platform to investigate laser deposition and laser-plasma instabilities at ignition-relevant plasma conditions, and to develop and validate ignition-relevant models of laser deposition and heat conduction. These experiments utilize the NIF in its current configuration, including beam geometry, phase plates, and beam smoothing. Warm, 2.2-mm-diam plastic shells were imploded with total drive energies ranging from ~ 350 to 750 kJ with peak powers of 60 to 180 TW and peak on-target intensities from 4 ×1014 to 1 . 2 ×1015 W/cm2. Results from these initial experiments are presented, including the level of hot-electron preheat, and implosion symmetry and shell trajectory inferred via self-emission imaging and backlighting. Experiments are simulated with the 2-D hydrodynamics code DRACO including a full 3-D ray trace to model oblique beams, and a model for cross-beam energy transfer (CBET). These simulations indicate that CBET affects the shell symmetry and leads to a loss of energy imparted onto the shell, consistent with the experimental data. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Repetitive output laser system and method using target reflectivity

DOEpatents

Johnson, Roy R.

1978-01-01

An improved laser system and method for implosion of a thermonuclear fuel pellet in which that portion of a laser pulse reflected by the target pellet is utilized in the laser system to initiate a succeeding target implosion, and in which the energy stored in the laser system to amplify the initial laser pulse, but not completely absorbed thereby, is used to amplify succeeding laser pulses initiated by target reflection.

The high velocity, high adiabat, ``Bigfoot'' campaign and tests of indirect-drive implosion scaling

NASA Astrophysics Data System (ADS)

Casey, Daniel

2017-10-01

To achieve hotspot ignition, inertial confinement fusion (ICF) implosions must achieve high hotspot internal energy that is inertially confined by a dense shell of DT fuel. To accomplish this, implosions are designed to achieve high peak implosion velocity, good energy coupling between the hotspot and imploding shell, and high areal-density at stagnation. However, experiments have shown that achieving these simultaneously is extremely challenging, partly because of inherent tradeoffs between these three interrelated requirements. The Bigfoot approach is to intentionally trade off high convergence, and therefore areal-density, in favor of high implosion velocity and good coupling between the hotspot and shell. This is done by intentionally colliding the shocks in the DT ice layer. This results in a short laser pulse which improves hohlraum symmetry and predictability while the reduced compression improves hydrodynamic stability. The results of this campaign will be reviewed and include demonstrated low-mode symmetry control at two different hohlraum geometries (5.75 mm and 5.4 mm diameters) and at two different target scales (5.4 mm and 6.0 mm hohlraum diameters) spanning 300-430 TW in laser power and 0.8-1.7 MJ in laser energy. Results of the 10% scaling between these designs for the hohlraum and capsule will be presented. Hydrodynamic instability growth from engineering features like the capsule fill tube are currently thought to be a significant perturbation to the target performance and a major factor in reducing its performance compared to calculations. Evidence supporting this hypothesis as well as plans going forward will be presented. Ongoing experiments are attempting to measure the impact on target performance from increase in target scale, and the preliminary results will also be discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Reconstruction of Axial Energy Deposition in Magnetic Liner Inertial Fusion Based on PECOS Shadowgraph Unfolds Using the AMR Code FLASH

NASA Astrophysics Data System (ADS)

Adams, Marissa; Jennings, Christopher; Slutz, Stephen; Peterson, Kyle; Gourdain, Pierre; U. Rochester-Sandia Collaboration

2017-10-01

Magnetic Liner Inertial Fusion (MagLIF) experiments incorporate a laser to preheat a deuterium filled capsule before compression via a magnetically imploding liner. In this work, we focus on the blast wave formed in the fuel during the laser preheat component of MagLIF, where approximately 1kJ of energy is deposited in 3ns into the capsule axially before implosion. To model blast waves directly relevant to experiments such as MagLIF, we inferred deposited energy from shadowgraphy of laser-only experiments preformed at the PECOS target chamber using the Z-Beamlet laser. These energy profiles were used to initialize 2-dimensional simulations using by the adaptive mesh refinement code FLASH. Gradients or asymmetries in the energy deposition may seed instabilities that alter the fuel's distribution, or promote mix, as the blast wave interacts with the liner wall. The AMR capabilities of FLASH allow us to study the development and dynamics of these instabilities within the fuel and their effect on the liner before implosion. Sandia Natl Labs is managed by NTES of Sandia, LLC., a subsidiary of Honeywell International, Inc, for the U.S. DOEs NNSA under contract DE-NA0003525.

First High-Convergence Cryogenic Implosion in a Near-Vacuum Hohlraum

NASA Astrophysics Data System (ADS)

Berzak Hopkins, L. F.; Meezan, N. B.; Le Pape, S.; Divol, L.; Mackinnon, A. J.; Ho, D. D.; Hohenberger, M.; Jones, O. S.; Kyrala, G.; Milovich, J. L.; Pak, A.; Ralph, J. E.; Ross, J. S.; Benedetti, L. R.; Biener, J.; Bionta, R.; Bond, E.; Bradley, D.; Caggiano, J.; Callahan, D.; Cerjan, C.; Church, J.; Clark, D.; Döppner, T.; Dylla-Spears, R.; Eckart, M.; Edgell, D.; Field, J.; Fittinghoff, D. N.; Gatu Johnson, M.; Grim, G.; Guler, N.; Haan, S.; Hamza, A.; Hartouni, E. P.; Hatarik, R.; Herrmann, H. W.; Hinkel, D.; Hoover, D.; Huang, H.; Izumi, N.; Khan, S.; Kozioziemski, B.; Kroll, J.; Ma, T.; MacPhee, A.; McNaney, J.; Merrill, F.; Moody, J.; Nikroo, A.; Patel, P.; Robey, H. F.; Rygg, J. R.; Sater, J.; Sayre, D.; Schneider, M.; Sepke, S.; Stadermann, M.; Stoeffl, W.; Thomas, C.; Town, R. P. J.; Volegov, P. L.; Wild, C.; Wilde, C.; Woerner, E.; Yeamans, C.; Yoxall, B.; Kilkenny, J.; Landen, O. L.; Hsing, W.; Edwards, M. J.

2015-05-01

Recent experiments on the National Ignition Facility [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] demonstrate that utilizing a near-vacuum hohlraum (low pressure gas-filled) is a viable option for high convergence cryogenic deuterium-tritium (DT) layered capsule implosions. This is made possible by using a dense ablator (high-density carbon), which shortens the drive duration needed to achieve high convergence: a measured 40% higher hohlraum efficiency than typical gas-filled hohlraums, which requires less laser energy going into the hohlraum, and an observed better symmetry control than anticipated by standard hydrodynamics simulations. The first series of near-vacuum hohlraum experiments culminated in a 6.8 ns, 1.2 MJ laser pulse driving a 2-shock, high adiabat (α ˜3.5 ) cryogenic DT layered high density carbon capsule. This resulted in one of the best performances so far on the NIF relative to laser energy, with a measured primary neutron yield of 1.8 ×1015 neutrons, with 20% calculated alpha heating at convergence ˜27 × .

Core conditions for alpha heating attained in direct-drive inertial confinement fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bose, A.; Woo, K. M.; Betti, R.

It is shown that direct-drive implosions on the OMEGA laser have achieved core conditions that would lead to significant alpha heating at incident energies available on the National Ignition Facility (NIF) scale. The extrapolation of the experimental results from OMEGA to NIF energy assumes only that the implosion hydrodynamic efficiency is unchanged at higher energies. This approach is independent of the uncertainties in the physical mechanism that degrade implosions on OMEGA, and relies solely on a volumetric scaling of the experimentally observed core conditions. It is estimated that the current best-performing OMEGA implosion [Regan et al., Phys. Rev. Lett. 117,more » 025001 (2016)] extrapolated to a 1.9 MJ laser driver with the same illumination configuration and laser-target coupling would produce 125 kJ of fusion energy with similar levels of alpha heating observed in current highest performing indirect-drive NIF implosions.« less

Core conditions for alpha heating attained in direct-drive inertial confinement fusion

DOE PAGES

Bose, A.; Woo, K. M.; Betti, R.; ...

2016-07-07

It is shown that direct-drive implosions on the OMEGA laser have achieved core conditions that would lead to significant alpha heating at incident energies available on the National Ignition Facility (NIF) scale. The extrapolation of the experimental results from OMEGA to NIF energy assumes only that the implosion hydrodynamic efficiency is unchanged at higher energies. This approach is independent of the uncertainties in the physical mechanism that degrade implosions on OMEGA, and relies solely on a volumetric scaling of the experimentally observed core conditions. It is estimated that the current best-performing OMEGA implosion [Regan et al., Phys. Rev. Lett. 117,more » 025001 (2016)] extrapolated to a 1.9 MJ laser driver with the same illumination configuration and laser-target coupling would produce 125 kJ of fusion energy with similar levels of alpha heating observed in current highest performing indirect-drive NIF implosions.« less

Core conditions for alpha heating attained in direct-drive inertial confinement fusion.

PubMed

Bose, A; Woo, K M; Betti, R; Campbell, E M; Mangino, D; Christopherson, A R; McCrory, R L; Nora, R; Regan, S P; Goncharov, V N; Sangster, T C; Forrest, C J; Frenje, J; Gatu Johnson, M; Glebov, V Yu; Knauer, J P; Marshall, F J; Stoeckl, C; Theobald, W

2016-07-01

It is shown that direct-drive implosions on the OMEGA laser have achieved core conditions that would lead to significant alpha heating at incident energies available on the National Ignition Facility (NIF) scale. The extrapolation of the experimental results from OMEGA to NIF energy assumes only that the implosion hydrodynamic efficiency is unchanged at higher energies. This approach is independent of the uncertainties in the physical mechanism that degrade implosions on OMEGA, and relies solely on a volumetric scaling of the experimentally observed core conditions. It is estimated that the current best-performing OMEGA implosion [Regan et al., Phys. Rev. Lett. 117, 025001 (2016)10.1103/PhysRevLett.117.025001] extrapolated to a 1.9 MJ laser driver with the same illumination configuration and laser-target coupling would produce 125 kJ of fusion energy with similar levels of alpha heating observed in current highest performing indirect-drive NIF implosions.

New and improved CH implosions at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Hinkel, D. E.; Doeppner, T.; Kritcher, A. L.; Ralph, J. E.; Jarrott, L. C.; Albert, F.; Benedetti, L. R.; Field, J. E.; Goyon, C. S.; Hohenberger, M.; Izumi, N.; Milovich, J. L.; Bachmann, B.; Casey, D. T.; Yeamans, C. B.; Callahan, D. A.; Hurricane, O. A.

2017-10-01

Improvements to the hohlraum for CH implosions have resulted in near-record hot spot pressures, 225 Gbar. Implosion symmetry and laser energy coupling are improved by using a hohlraum that, compared to the previous high gas-fill hohlraum, is longer, larger, at lower gas fill density, and is fielded at zero wavelength separation to minimize cross-beam energy transfer. With a capsule at 90% of its original size in this hohlraum, implosion symmetry changes from oblate to prolate, at 33% cone fraction. Simulations highlight improved inner beam propagation as the cause of this symmetry change. These implosions have produced the highest yield for CH ablators at modest power and energy, i.e., 360 TW and 1.4 MJ. Upcoming experiments focus on continued improvement in shape as well as an increase in implosion velocity. Further, results and future plans on an increase in capsule size to improve margin will also be presented. Work performed under the auspices of the U.S. D.O.E. by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.

Target Fabrication Technology and New Functional Materials for Laser Fusion and Laser-Plasma Experiment

NASA Astrophysics Data System (ADS)

Nagai, Keiji; Norimatsu, Takayoshi; Izawa, Yasukazu

Target fabrication technique is a key issue of laser fusion. We present a comprehensive, up-to-data compilation of laser fusion target fabrication and relating new materials. To achieve highly efficient laser implosion, organic and inorganic highly spherical millimeter-sized capsules and cryogenic hydrogen layers inside should be uniform in diameter and thickness within sub-micrometer ˜ nanometer error. Porous structured targets and molecular cluster targets are required for laser-plasma experiments and applications. Various technologies and new materials concerning above purposes are summarized including fast-ignition targets, equation-of-state measurement targets, high energy ion generation targets, etc.

Validating Hydrodynamic Growth in National Ignition Facility Implosions

NASA Astrophysics Data System (ADS)

Peterson, J. Luc

2014-10-01

The hydrodynamic growth of capsule imperfections can threaten the success of inertial confinement fusion implosions. Therefore, it is important to design implosions that are robust to hydrodynamic instabilities. However, the numerical simulation of interacting Rayleigh-Taylor and Richtmyer-Meshkov growth in these implosions is sensitive to modeling uncertainties such as radiation drive and material equations of state, the effects of which are especially apparent at high mode number (small perturbation wavelength) and high convergence ratio (small capsule radius). A series of validation experiments were conducted at the National Ignition Facility to test the ability to model hydrodynamic growth in spherically converging ignition-relevant implosions. These experiments on the Hydro-Growth Radiography platform constituted direct measurements of the growth of pre-imposed imperfections up to Legendre mode 160 and a convergence ratio of greater than four using two different laser drives: a ``low-foot'' drive used during the National Ignition Campaign and a larger adiabat ``high-foot'' drive that is modeled to be relatively more robust to ablation front hydrodynamic growth. We will discuss these experiments and how their results compare to numerical simulations and analytic theories of hydrodynamic growth, as well as their implications for the modeling of future designs. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Cryogenic Target-Implosion Experiments on OMEGA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harding, D.R.; Meyerhofer, D.D.; Sangster, T.C.

The University of Rochester’s Laboratory for Laser Energetics has been imploding thick cryogenic targets for six years. Improvements in the Cryogenic Target Handling System and the ability to accurately design laser pulse shapes that properly time shocks and minimize electron preheat, produced high fuel areal densities in deuterium cryogenic targets (202+/-7 mg/cm^2). The areal density was inferred from the energy loss of secondary protons in the fuel (D2) shell. Targets were driven on a low final adiabat (alpha = 2) employing techniques to radially grade the adiabat (the highest adiabat at the ablation surface). The ice layer meets the target-designmore » toughness specification for DT ice of 1-um rms (all modes), while D2 ice layers average 3.0-um-rms roughness. The implosion experiments and the improvements in the quality and understanding of cryogenic targets are presented.« less

Optimizing implosion yields using rugby-shaped hohlraums

NASA Astrophysics Data System (ADS)

Park, Hye-Sook; Robey, H.; Amendt, P.; Philippe, F.; Casner, A.; Caillaud, T.; Bourgade, J.-L.; Landoas, O.; Li, C. K.; Petrasso, R.; Seguin, F.; Rosenberg, M.; Glebov, V. Yu.

2009-11-01

We present the first experimental results on optimizing capsule implosion experiments by using rugby-shaped hohlraums [1] on the Omega laser, University of Rochester. This campaign compared D2-filled capsule performance between standard cylindrical Au hohlraums and rugby-shaped hohlraums for demonstrating the energetics advantages of the rugby geometry. Not only did the rugby-shaped hohlraums show nearly 20% more x-ray drive energy over the cylindrical hohlraums, but also the high-performance design of the capsules provided nearly 20 times more DD neutrons than in any previous Omega hohlraum campaigns, thereby enabling use of neutron temporal diagnostics. Comparison with simulations on neutron burn histories, x-ray core imaging, backscattered laser light and radiation temperature are presented. [1] P. Amendt et al., Phys. Plasmas 15, 012702 (2008)

Progress in indirect and direct-drive planar experiments on hydrodynamic instabilities at the ablation front

DOE PAGES

Casner, A.; Masse, L.; Delorme, B.; ...

2014-12-01

Understanding and mitigating hydrodynamic instabilities and the fuel mix are the key elements for achieving ignition in Inertial Confinement Fusion. Cryogenic indirect-drive implosions on the National Ignition Facility have evidenced that the ablative Rayleigh-Taylor Instability (RTI) is a driver of the hot spot mix. This motivates the switch to a more flexible higher adiabat implosion design [O. A. Hurricane et al., Phys. Plasmas 21, 056313 (2014)]. The shell instability is also the main candidate for performance degradation in low-adiabat direct drive cryogenic implosions [Goncharov et al., Phys. Plasmas 21, 056315 (2014)]. This paper reviews recent results acquired in planar experimentsmore » performed on the OMEGA laser facility and devoted to the modeling and mitigation of hydrodynamic instabilities at the ablation front. In application to the indirect-drive scheme, we describe results obtained with a specific ablator composition such as the laminated ablator or a graded-dopant emulator. In application to the direct drive scheme, we discuss experiments devoted to the study of laser imprinted perturbations with special phase plates. The simulations of the Richtmyer-Meshkov phase reversal during the shock transit phase are challenging, and of crucial interest because this phase sets the seed of the RTI growth. Recent works were dedicated to increasing the accuracy of measurements of the phase inversion. We conclude by presenting a novel imprint mitigation mechanism based on the use of underdense foams. Lastly, the foams induce laser smoothing by parametric instabilities thus reducing the laser imprint on the CH foil.« less

Theoretical quantification of shock-timing sensitivities for direct-drive inertial confinement fusion implosions on OMEGA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, D.; Boehly, T. R.; Gregor, M. C.

Using temporally shaped laser pulses, multiple shocks can be launched in direct-drive inertial confinement fusion implosion experiments to set the shell on a desired isentrope or adiabat. The velocity of the first shock and the times at which subsequent shocks catch up to it are measured through the VISAR diagnostic [T. R. Boehly et al., Phys. Plasmas 18, 092706 (2011)] on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Simulations reproduce these velocity and shock-merger time measurements when using laser pulses designed for setting mid-adiabat (alpha ~ 3) implosions, but agreement degrades for lower-adiabat (alpha ~ 1)more » designs. Several possibilities for this difference are studied: (1) errors in placing the target at the center of irradiation (target offset), (2) variations in energy between the different incident beams (power imbalance), and (3) errors in modeling the laser energy coupled into the capsule. Simulation results indicate that shock timing is most sensitive to details of the density and temperature profiles in the coronal plasma, which influences the laser energy coupled into the target, and only marginally sensitive to target offset and beam power imbalance. A new technique under development to infer coronal profiles using x-ray self-emission imaging [A. K. Davis et al., Bull. Am. Phys. Soc. 61, BAPS.2016.DPP.NO8.7 (2016)] can be applied to the pulse shapes used in shock-timing experiments. This will help identify improved physics models to implement in codes and consequently enhance shock-timing predictive capability for low-adiabat pulses.« less

Use of d-3He proton spectroscopy as a diagnostic of shell rho r in capsule implosion experiments with approximately 0.2 NIF scale high temperature Hohlraums at Omega.

PubMed

Delamater, N D; Wilson, D C; Kyrala, G A; Seifter, A; Hoffman, N M; Dodd, E; Singleton, R; Glebov, V; Stoeckl, C; Li, C K; Petrasso, R; Frenje, J

2008-10-01

We present the calculations and preliminary results from experiments on the Omega laser facility using d-(3)He filled plastic capsule implosions in gold Hohlraums. These experiments aim to develop a technique to measure shell rho r and capsule unablated mass with proton spectroscopy and will be applied to future National Ignition Facility (NIF) experiments with ignition scale capsules. The Omega Hohlraums are 1900 microm length x 1200 microm diameter and have a 70% laser entrance hole. This is approximately a 0.2 NIF scale ignition Hohlraum and reaches temperatures of 265-275 eV similar to those during the peak of the NIF drive. These capsules can be used as a diagnostic of shell rho r, since the d-(3)He gas fill produces 14.7 MeV protons in the implosion, which escape through the shell and produce a proton spectrum that depends on the integrated rho r of the remaining shell mass. The neutron yield, proton yield, and spectra change with capsule shell thickness as the unablated mass or remaining capsule rho r changes. Proton stopping models are used to infer shell unablated mass and shell rho r from the proton spectra measured with different filter thicknesses. The experiment is well modeled with respect to Hohlraum energetics, neutron yields, and x-ray imploded core image size, but there are discrepancies between the observed and simulated proton spectra.

Performance of indirectly driven capsule implosions on the National Ignition Facility using adiabat-shaping

DOE PAGES

Robey, H. F.; Smalyuk, V. A.; Milovich, J. L.; ...

2016-04-01

A series of indirectly driven capsule implosions has been performed on the National Ignition Facility to assess the relative contributions of ablation-front instability growth vs. fuel compression on implosion performance. Laser pulse shapes for both low and high-foot pulses were modified to vary ablation-front growth & fuel adiabat, separately and controllably. Two principal conclusions are drawn from this study: 1) It is shown that an increase in laser picket energy reduces ablation-front instability growth in low-foot implosions resulting in a substantial (3-10X) increase in neutron yield with no loss of fuel compression. 2.) It is shown that a decrease inmore » laser trough power reduces the fuel adiabat in high-foot implosions results in a significant (36%) increase in fuel compression together with no reduction in neutron yield. These results taken collectively bridge the space between the higher compression low-foot results and the higher yield high-foot results.« less

Implosion and heating experiments of fast ignition targets by Gekko-XII and LFEX lasers

NASA Astrophysics Data System (ADS)

Shiraga, H.; Fujioka, S.; Nakai, M.; Watari, T.; Nakamura, H.; Arikawa, Y.; Hosoda, H.; Nagai, T.; Koga, M.; Kikuchi, H.; Ishii, Y.; Sogo, T.; Shigemori, K.; Nishimura, H.; Zhang, Z.; Tanabe, M.; Ohira, S.; Fujii, Y.; Namimoto, T.; Sakawa, Y.; Maegawa, O.; Ozaki, T.; Tanaka, K. A.; Habara, H.; Iwawaki, T.; Shimada, K.; Key, M.; Norreys, P.; Pasley, J.; Nagatomo, H.; Johzaki, T.; Sunahara, A.; Murakami, M.; Sakagami, H.; Taguchi, T.; Norimatsu, T.; Homma, H.; Fujimoto, Y.; Iwamoto, A.; Miyanaga, N.; Kawanaka, J.; Kanabe, T.; Jitsuno, T.; Nakata, Y.; Tsubakimoto, K.; Sueda, K.; Kodama, R.; Kondo, K.; Morio, N.; Matsuo, S.; Kawasaki, T.; Sawai, K.; Tsuji, K.; Murakami, H.; Sarukura, N.; Shimizu, T.; Mima, K.; Azechi, H.

2013-11-01

The FIREX-1 project, the goal of which is to demonstrate fuel heating up to 5 keV by fast ignition scheme, has been carried out since 2003 including construction and tuning of LFEX laser and integrated experiments. Implosion and heating experiment of Fast Ignition targets have been performed since 2009 with Gekko-XII and LFEX lasers. A deuterated polystyrene shell target was imploded with the 0.53- μm Gekko-XII, and the 1.053- μm beam of the LFEX laser was injected through a gold cone attached to the shell to generate hot electrons to heat the imploded fuel plasma. Pulse contrast ratio of the LFEX beam was significantly improved. Also a variety of plasma diagnostic instruments were developed to be compatible with harsh environment of intense hard x-rays (γ rays) and electromagnetic pulses due to the intense LFEX beam on the target. Large background signals around the DD neutron signal in time-of-flight record of neutron detector were found to consist of neutrons via (γ,n) reactions and scattered gamma rays. Enhanced neutron yield was confirmed by carefully eliminating such backgrounds. Neutron enhancement up to 3.5 × 107 was observed. Heating efficiency was estimated to be 10-20% assuming a uniform temperature rise model.

Overview of the National Ignition Campaign (NIC)

NASA Astrophysics Data System (ADS)

Moses, Edward

2010-11-01

The 192-beam National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) is now operational. NIF has conducted 192-beam implosion experiments with energies as high as 1.2 MJ and has also demonstrated the unprecedented energy and pulse shaping control required for ignition experiments. The successful commissioning of the NIF laser is the first step in demonstrating inertial confinement fusion (ICF) ignition in the laboratory. The NIF ignition program is executed via the National Ignition Campaign (NIC)---a partnership between Los Alamos National Laboratory, Lawrence Berkeley Laboratory, LLNL, General Atomics, the University of Rochester Laboratory for Laser Energetics, Sandia National Laboratories, the Massachusetts Institute of Technology, and other national and international partners. The NIC relies on a novel integrated experimental and computational program to tune the target to the conditions required for indirect-drive ignition. This approach breaks the tuning process into four phases. The first two phases involve tuning of the hohlraum and capsule to produce the correct radiation drive, symmetry, and shock timing conditions. The third phase consists of layered cryogenic implosions conducted with a 50%/49%/1% mixture of tritium, hydrogen, and deuterium (THD) respectively. The reduced yield from these THD targets allows the full diagnostic suite to be employed and the presence of the required temperature and fuel areal density to be verified. The final step is DT ignition implosions with expected gains of 10-20. DT ignition experiments will be conducted with Elaser ˜1.2 MJ. Laser energies of 1.8 MJ should be available for subsequent experiments. This talk will review the multi-phase tuning approach to the ignition effort, including the physics issues associated with the various steps, and current and future plans for the NIF ignition program.

Effects of electron-ion temperature equilibration on inertial confinement fusion implosions.

PubMed

Xu, Barry; Hu, S X

2011-07-01

The electron-ion temperature relaxation essentially affects both the laser absorption in coronal plasmas and the hot-spot formation in inertial confinement fusion (ICF). It has recently been reexamined for plasma conditions closely relevant to ICF implosions using either classical molecular-dynamics simulations or analytical methods. To explore the electron-ion temperature equilibration effects on ICF implosion performance, we have examined two Coulomb logarithm models by implementing them into our hydrocodes, and we have carried out hydrosimulations for ICF implosions. Compared to the Lee-More model that is currently used in our standard hydrocodes, the two models predict substantial differences in laser absorption, coronal temperatures, and neutron yields for ICF implosions at the OMEGA Laser Facility [Boehly et al. Opt. Commun. 133, 495 (1997)]. Such effects on the triple-picket direct-drive design at the National Ignition Facility (NIF) have also been explored. Based on the validity of the two models, we have proposed a combined model of the electron-ion temperature-relaxation rate for the overall ICF plasma conditions. The hydrosimulations using the combined model for OMEGA implosions have shown ∼6% more laser absorption, ∼6%-15% higher coronal temperatures, and ∼10% more neutron yield, when compared to the Lee-More model prediction. It is also noticed that the gain for the NIF direct-drive design can be varied by ∼10% among the different electron-ion temperature-relaxation models.

First high-convergence cryogenic implosion in a near-vacuum hohlraum

DOE PAGES

Berzak Hopkins, L.  F.; Meezan, N.  B.; Le Pape, S.; ...

2015-04-29

Recent experiments on the National Ignition Facility [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] demonstrate that utilizing a near-vacuum hohlraum (low pressure gas-filled) is a viable option for high convergence cryogenic deuterium-tritium (DT) layered capsule implosions. This is made possible by using a dense ablator (high-density carbon), which shortens the drive duration needed to achieve high convergence: a measured 40% higher hohlraum efficiency than typical gas-filled hohlraums, which requires less laser energy going into the hohlraum, and an observed better symmetry control than anticipated by standard hydrodynamics simulations. The first series of near-vacuum hohlraum experiments culminated inmore » a 6.8 ns, 1.2 MJ laser pulse driving a 2-shock, high adiabat (α ~ 3.5) cryogenic DT layered high density carbon capsule. This resulted in one of the best performances so far on the NIF relative to laser energy, with a measured primary neutron yield of 1.8 X 10¹⁵ neutrons, with 20% calculated alpha heating at convergence ~27X.« less

Hohlraum-Driven Ignition-Like Double-Shell Implosion Experiments on Omega: Analysis and Interpretation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amendt, P; Robey, H F; Park, H-S

2003-08-22

An experimental campaign to study hohlraum-driven ignition-like double-shell target performance using the Omega laser facility has begun. These targets are intended to incorporate as many ignition-like properties of the proposed National Ignition Facility (NIF) double-shell ignition design [1,2] as possible, given the energy constraints of the Omega laser. In particular, this latest generation of Omega double-shells is nominally predicted to produce over 99% of the (clean) DD neutron yield from the compressional or stagnation phase of the implosion as required in the NIF ignition design. By contrast, previous double-shell experience on Omega [3] was restricted to cases where a significantmore » fraction of the observed neutron yield was produced during the earlier shock convergence phase where the effects of mix are deemed negligibly small. These new targets are specifically designed to have optimized fall-line behavior for mitigating the effects of pusher-fuel mix after deceleration onset and, thereby, providing maximum neutron yield from the stagnation phase. Experimental results from this recent Omega ignition-like double-shell implosion campaign show favorable agreement with two-dimensional integrated hohlraum simulation studies when enhanced (gold) hohlraum M-band (2-5 keV) radiation is included at a level consistent with observations.« less

Performance and Mix Measurements of Indirect Drive Cu-Doped Be Implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casey, D.  T.; Woods, D. T.; Smalyuk, V. A.

2015-05-19

The ablator couples energy between the driver and fusion fuel in inertial confinement fusion (ICF). Because of its low opacity, high solid density, and material properties, beryllium has long been considered an ideal ablator for ICF ignition experiments at the National Ignition Facility. We report here the first indirect drive Be implosions driven with shaped laser pulses and diagnosed with fusion yield at the OMEGA laser. The results show good performance with an average DD neutron yield of ~2 × 10⁹ at a convergence ratio of R₀/R ~ 10 and little impact due to the growth of hydrodynamic instabilities andmore » mix. In addition, the effect of adding an inner liner of W between the Be and DD is demonstrated.« less

Capsule Ablator Inflight Performance Measurements Via Streaked Radiography Of ICF Implosions On The NIF*

NASA Astrophysics Data System (ADS)

Dewald, E. L.; Tommasini, R.; Mackinnon, A.; MacPhee, A.; Meezan, N.; Olson, R.; Hicks, D.; LePape, S.; Izumi, N.; Fournier, K.; Barrios, M. A.; Ross, S.; Pak, A.; Döppner, T.; Kalantar, D.; Opachich, K.; Rygg, R.; Bradley, D.; Bell, P.; Hamza, A.; Dzenitis, B.; Landen, O. L.; MacGowan, B.; LaFortune, K.; Widmayer, C.; Van Wonterghem, B.; Kilkenny, J.; Edwards, M. J.; Atherton, J.; Moses, E. I.

2016-03-01

Streaked 1-dimensional (slit imaging) radiography of 1.1 mm radius capsules in ignition hohlraums was recently introduced on the National Ignition Facility (NIF) and gives an inflight continuous record of capsule ablator implosion velocities, shell thickness and remaining mass in the last 3-5 ns before peak implosion time. The high quality data delivers good accuracy in implosion metrics that meets our requirements for ignition and agrees with recently introduced 2-dimensional pinhole radiography. Calculations match measured trajectory across various capsule designs and laser drives when the peak laser power is reduced by 20%. Furthermore, calculations matching measured trajectories give also good agreement in ablator shell thickness and remaining mass.

Planar hydrodynamic instability computations and experiments with rugby-shaped hohlraums at the Omega laser

NASA Astrophysics Data System (ADS)

Vandenboomgaerde, M.; Liberatore, S.; Galmiche, D.; Casner, A.; Huser, G.; Jadaud, J. P.; Villette, B.

2008-05-01

Implosion of inertial confinement fusion (ICF) capsule is very sensitive to the growth of sphericity perturbations. The control of the feeding of such perturbations and their transport ('feedthrough') through the ablator is a key point to reach ignition. Since 2002 [1, 2], experiments have been designed and performed on the Omega laser facility in order to study these phenomena in planar geometry. A new 'rugby shaped' hohlraum was used [3, 4]. We present experimental results and comparisons with numerical simulations.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hurricane, O. A., E-mail: hurricane1@llnl.gov; Callahan, D. A.; Casey, D. T.

The “High-Foot” platform manipulates the laser pulse-shape coming from the National Ignition Facility laser to create an indirect drive 3-shock implosion that is significantly more robust against instability growth involving the ablator and also modestly reduces implosion convergence ratio. This strategy gives up on theoretical high-gain in an inertial confinement fusion implosion in order to obtain better control of the implosion and bring experimental performance in-line with calculated performance, yet keeps the absolute capsule performance relatively high. In this paper, we will cover the various experimental and theoretical motivations for the high-foot drive as well as cover the experimental resultsmore » that have come out of the high-foot experimental campaign. At the time of this writing, the high-foot implosion has demonstrated record total deuterium-tritium yields (9.3×10{sup 15}) with low levels of inferred mix, excellent agreement with implosion simulations, fuel energy gains exceeding unity, and evidence for the “bootstrapping” associated with alpha-particle self-heating.« less

Kinetic simulation of hydrodynamic equivalent capsule implosions

NASA Astrophysics Data System (ADS)

Kwan, Thomas; Le, Ari; Schmitt, Mark; Herrmann, Hans

2016-10-01

We have carried out simulations of direct-drive hydrodynamic equivalent capsule implosion experiments conducted on Omega laser facility at the Laboratory of Laser Energetics of the University of Rochester. The capsules had a glass shell (SiO2) 4.87 μm with an inner diameter of 1086 μm. One was filled with deuterium (D) and tritium (T) at 6.635 and 2.475 atmospheric pressure respectively. The other capsule with D, T, and He-3 at 2.475, 2.475, and 5.55 atmospheric pressure respectively. The capsules were imploded with 60 laser beams with a square pulse length of 0.6ns of total energy of 15.6 kJ. One-dimensional radiation hydrodynamic calculations with HYDRA and kinetic particle/hybrid simulations with LSP are carried out for the post-shot analysis. HYDRA outputs at 0.6ns are linked to LSP, in which the electrons are treated as a fluid while all the ion dynamics is simulated by the standard particle-in-cell technique. Additionally, simulations with the new photon package in LSP are initiated at the beginning of the implosion to include the implosion phase of the capsule. The simulation results of density, temperature, and velocity profiles of the electrons, D, T, He-3, and SiO2species are compared with HYDRA. Detail comparisons among the kinetic simulations, rad-hydro simulations, and experimental results of neutron yield, yield ratio, fusion burn histories, and shell convergence will be presented to assess plasma kinetic effects. Work performed under the auspices of the US DOE by the Los Alamos National Laboratory under Contract No. W7405-ENG-36.

Prolate-Spheroid (``Rugby-Shaped'') Hohlraum for Inertial Confinement Fusion

NASA Astrophysics Data System (ADS)

Vandenboomgaerde, M.; Bastian, J.; Casner, A.; Galmiche, D.; Jadaud, J.-P.; Laffite, S.; Liberatore, S.; Malinie, G.; Philippe, F.

2007-08-01

A novel rugby-ball shaped hohlraum is designed in the context of the indirect-drive scheme of inertial-confinement fusion (ICF). Experiments were performed on the OMEGA laser and are the first use of rugby hohlraums for ICF studies. Analysis of experimental data shows that the hohlraum energetics is well understood. We show that the rugby-ball shape exhibits advantages over cylinder, in terms of temperature and of symmetry control of the capsule implosion. Simulations indicate that rugby hohlraum driven targets may be candidates for ignition in a context of early Laser MegaJoule experiments with reduced laser energy.

Three-Dimensional Hydrodynamic Simulations of the Effects of Laser Imprint in OMEGA Implosions

NASA Astrophysics Data System (ADS)

Igumenshchev, I. V.; Campbell, E. M.; Goncharov, V. N.; Regan, S. P.; Shvydky, A.; Schmitt, A. J.

2017-10-01

Illumination of direct-drive implosion targets by the OMEGA laser introduces large-amplitude broadband modulations in the absorbed energy from the largest (target size 900- μm) to smallest (speckle size 2- μm) spatial scales. These modulations ``imprint'' perturbations into a target that are amplified because of the secular and Rayleigh-Taylor growths during acceleration and deceleration of the target. The degradation of performance of room-temperature and cryogenic OMEGA implosions caused by these perturbations were simulated in three dimensions using the code ASTER. The highest-resolution simulations resolve perturbation modes as high as l 200 . The high modes l 50to 100 dominate in the perturbation spectrum during the linear growth, while the late-time nonlinear evolution results in domination of modes with l 30to 50 . Smoothing by spectral dispersion reduces the linear-phase mode amplitudes by a factor of 4 and results in substantial improvements in implosion performance that is in good agreement with measurements. The effects of imprint on implosion performance are compared with the effects of other implosion asymmetries, such as those induced because of laser beam imbalance, mistiming and mispointing, and target offset. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Time history prediction of direct-drive implosions on the Omega facility

DOE PAGES

Laffite, S.; Bourgade, J. L.; Caillaud, T.; ...

2016-01-14

We present in this article direct-drive experiments that were carried out on the Omega facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Two different pulse shapes were tested in order to vary the implosion stability of the same target whose parameters, dimensions and composition, remained the same. The direct-drive configuration on the Omega facility allows the accurate time-resolvedmeasurement of the scattered light. We show that, provided the laser coupling is well controlled, the implosion time history, assessed by the “bang-time” and the shell trajectory measurements, can be predicted. This conclusion is independent on the pulse shape. Inmore » contrast, we show that the pulse shape affects the implosion stability, assessed by comparing the target performances between prediction and measurement. For the 1-ns square pulse, the measuredneutron number is about 80% of the prediction. Lastly, for the 2-step 2-ns pulse, we test here that this ratio falls to about 20%.« less

Time history prediction of direct-drive implosions on the Omega facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laffite, S.; Bourgade, J. L.; Caillaud, T.

We present in this article direct-drive experiments that were carried out on the Omega facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Two different pulse shapes were tested in order to vary the implosion stability of the same target whose parameters, dimensions and composition, remained the same. The direct-drive configuration on the Omega facility allows the accurate time-resolvedmeasurement of the scattered light. We show that, provided the laser coupling is well controlled, the implosion time history, assessed by the “bang-time” and the shell trajectory measurements, can be predicted. This conclusion is independent on the pulse shape. Inmore » contrast, we show that the pulse shape affects the implosion stability, assessed by comparing the target performances between prediction and measurement. For the 1-ns square pulse, the measuredneutron number is about 80% of the prediction. Lastly, for the 2-step 2-ns pulse, we test here that this ratio falls to about 20%.« less

Time history prediction of direct-drive implosions on the Omega facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laffite, S.; Bourgade, J. L.; Caillaud, T.

We present in this article direct-drive experiments that were carried out on the Omega facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Two different pulse shapes were tested in order to vary the implosion stability of the same target whose parameters, dimensions and composition, remained the same. The direct-drive configuration on the Omega facility allows the accurate time-resolved measurement of the scattered light. We show that, provided the laser coupling is well controlled, the implosion time history, assessed by the “bang-time” and the shell trajectory measurements, can be predicted. This conclusion is independent on the pulse shape.more » In contrast, we show that the pulse shape affects the implosion stability, assessed by comparing the target performances between prediction and measurement. For the 1-ns square pulse, the measured neutron number is about 80% of the prediction. For the 2-step 2-ns pulse, we test here that this ratio falls to about 20%.« less

Simulation of alternate hohlraum shapes for improved inner beam propagation in indirectly-driven ICF implosions

NASA Astrophysics Data System (ADS)

Robey, H. F.; Berzak Hopkins, L. F.

2017-10-01

Recent indirectly-driven ICF experiments performed on the National Ignition Facility have shown that the propagation of the inner beam cones is impeded late in the laser pulse by the growth of a gold bubble, which is initiated at the location where the outer beams hit the hohlraum wall and which expands radially inward into the hohlraum as the implosion progresses. Late in time, this gold bubble intercepts a significant portion of the inner beams reducing the available energy reaching the waist of the hohlraum and affecting the implosion symmetry. Integrated hohlraum simulations of alternate hohlraum shapes using HYDRA are performed to explore options for reducing the impact of the gold bubble on inner beam propagation. The simulations are based on recent NIF implosions using High-Density Carbon (HDC) ablators, which have shown good performance, but which could benefit from improved inner beam propagation. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.

Numerical studies of the use of thin high-Z layers for reducing laser imprint in direct-drive inertial-fusion targets

NASA Astrophysics Data System (ADS)

Bates, Jason; Schmitt, Andrew; Karasik, Max; Obenschain, Steve

2012-10-01

Using the FAST code, we present numerical studies of the effect of thin metallic layers with high atomic number (high-Z) on the hydrodynamics of directly-driven inertial-confinement-fusion (ICF) targets. Previous experimental work on the NIKE Laser Facility at the U.S. Naval Research Laboratory demonstrated that the use of high-Z layers may be efficacious in reducing laser non-uniformities imprinted on the target during the start-up phase of the implosion. Such a reduction is highly desirable in a direct-drive ICF scenario because laser non-uniformities seed hydrodynamic instabilities that can amplify during the implosion process, prevent uniform compression and spoil high gain. One of the main objectives of the present work is to assess the utility of high-Z layers for achieving greater laser uniformity in polar-drive target designs planned for the National Ignition Facility. To address this problem, new numerical routines have recently been incorporated in the FAST code, including an improved radiation-transfer package and a three-dimensional ray-tracing algorithm. We will discuss these topics, and present initial simulation results for high-Z planar-target experiments planned on the NIKE Laser Facility later this year.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robey, H. F.; MacGowan, B. J.; Landen, O. L.

Indirectly driven capsule implosions on the National Ignition Facility (NIF) [Moses et al., Phys. Plasmas 16, 041006 (2009)] are being performed with the goal of compressing a layer of cryogenic deuterium-tritium (DT) fuel to a sufficiently high areal density (ρR) to sustain the self-propagating burn wave that is required for fusion power gain greater than unity. These implosions are driven with a temporally shaped laser pulse that is carefully tailored to keep the DT fuel on a low adiabat (ratio of fuel pressure to the Fermi degenerate pressure). In this report, the impact of variations in the laser pulse shapemore » (both intentionally and unintentionally imposed) on the in-flight implosion adiabat is examined by comparing the measured shot-to-shot variations in ρR from a large ensemble of DT-layered ignition target implosions on NIF spanning a two-year period. A strong sensitivity to variations in the early-time, low-power foot of the laser pulse is observed. It is shown that very small deviations (∼0.1% of the total pulse energy) in the first 2 ns of the laser pulse can decrease the measured ρR by 50%.« less

Suppression of laser nonuniformity imprinting using a thin high-z coating.

PubMed

Karasik, Max; Weaver, J L; Aglitskiy, Y; Oh, J; Obenschain, S P

2015-02-27

Imprinting of laser nonuniformity is a limiting factor in direct-drive inertial confinement fusion experiments, particularly when available laser smoothing is limited. A thin (∼400  Å) high-Z metal coating is found to substantially suppress laser imprint for planar targets driven by pulse shapes and intensities relevant to implosions on the National Ignition Facility while retaining low adiabat target acceleration. A hybrid of indirect and direct drive, this configuration results in initial ablation by x rays from the heated high-Z layer, creating a large standoff for perturbation smoothing.

Effects of local defect growth in direct-drive cryogenic implosions on OMEGA

NASA Astrophysics Data System (ADS)

Igumenshchev, I. V.; Goncharov, V. N.; Shmayda, W. T.; Harding, D. R.; Sangster, T. C.; Meyerhofer, D. D.

2013-08-01

Spherically symmetric, low-adiabat (adiabat α ≲ 3) cryogenic direct-drive-implosion experiments on the OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1995)] yield less than 10% of the neutrons predicted in one-dimensional hydrodynamic simulations. Two-dimensional hydrodynamic simulations suggest that this performance degradation can be explained assuming perturbations from isolated defects of submicron to tens-of-micron scale on the outer surface or inside the shell of implosion targets. These defects develop during the cryogenic filling process and typically number from several tens up to hundreds for each target covering from about 0.2% to 1% of its surface. The simulations predict that such defects can significantly perturb the implosion and result in the injection of about 1 to 2 μg of the hot ablator (carbon-deuterium) and fuel (deuterium-tritium) materials from the ablation surface into the targets. Both the hot mass injection and perturbations of the shell reduce the final shell convergence ratio and implosion performance. The injected carbon ions radiatively cool the hot spot, reducing the fuel temperature, and further reducing the neutron yield. The negative effect of local defects can be minimized by decreasing the number and size of these defects and/or using more hydrodynamically stable implosion designs with higher shell adiabat.

High-adiabat high-foot inertial confinement fusion implosion experiments on the national ignition facility.

PubMed

Park, H-S; Hurricane, O A; Callahan, D A; Casey, D T; Dewald, E L; Dittrich, T R; Döppner, T; Hinkel, D E; Berzak Hopkins, L F; Le Pape, S; Ma, T; Patel, P K; Remington, B A; Robey, H F; Salmonson, J D; Kline, J L

2014-02-07

This Letter reports on a series of high-adiabat implosions of cryogenic layered deuterium-tritium (DT) capsules indirectly driven by a "high-foot" laser drive pulse at the National Ignition Facility. High-foot implosions have high ablation velocities and large density gradient scale lengths and are more resistant to ablation-front Rayleigh-Taylor instability induced mixing of ablator material into the DT hot spot. Indeed, the observed hot spot mix in these implosions was low and the measured neutron yields were typically 50% (or higher) of the yields predicted by simulation. On one high performing shot (N130812), 1.7 MJ of laser energy at a peak power of 350 TW was used to obtain a peak hohlraum radiation temperature of ∼300  eV. The resulting experimental neutron yield was (2.4±0.05)×10(15) DT, the fuel ρR was (0.86±0.063)  g/cm2, and the measured Tion was (4.2±0.16)  keV, corresponding to 8 kJ of fusion yield, with ∼1/3 of the yield caused by self-heating of the fuel by α particles emitted in the initial reactions. The generalized Lawson criteria, an ignition metric, was 0.43 and the neutron yield was ∼70% of the value predicted by simulations that include α-particle self-heating.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Milovich, J. L., E-mail: milovich1@llnl.gov; Robey, H. F.; Clark, D. S.

Experimental results from indirectly driven ignition implosions during the National Ignition Campaign (NIC) [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] achieved a record compression of the central deuterium-tritium fuel layer with measured areal densities up to 1.2 g/cm{sup 2}, but with significantly lower total neutron yields (between 1.5 × 10{sup 14} and 5.5 × 10{sup 14}) than predicted, approximately 10% of the 2D simulated yield. An order of magnitude improvement in the neutron yield was subsequently obtained in the “high-foot” experiments [O. A. Hurricane et al., Nature 506, 343 (2014)]. However, this yield was obtained at the expensemore » of fuel compression due to deliberately higher fuel adiabat. In this paper, the design of an adiabat-shaped implosion is presented, in which the laser pulse is tailored to achieve similar resistance to ablation-front instability growth, but with a low fuel adiabat to achieve high compression. Comparison with measured performance shows a factor of 3–10× improvement in the neutron yield (>40% of predicted simulated yield) over similar NIC implosions, while maintaining a reasonable fuel compression of >1 g/cm{sup 2}. Extension of these designs to higher laser power and energy is discussed to further explore the trade-off between increased implosion velocity and the deleterious effects of hydrodynamic instabilities.« less

Designing symmetric polar direct drive implosions on the Omega laser facility

NASA Astrophysics Data System (ADS)

Krasheninnikova, Natalia S.; Cobble, James A.; Murphy, Thomas J.; Tregillis, Ian L.; Bradley, Paul A.; Hakel, Peter; Hsu, Scott C.; Kyrala, George A.; Obrey, Kimberly A.; Schmitt, Mark J.; Baumgaertel, Jessica A.; Batha, Steven H.

2014-04-01

Achieving symmetric capsule implosions with Polar Direct Drive [S. Skupsky et al., Phys. Plasmas 11, 2763 (2004); R. S. Craxton et al., Phys. Plasmas 12, 056304 (2005); F. J. Marshall et al., J. Phys. IV France 133, 153-157 (2006)] has been explored during recent Defect Induced Mix Experiment campaign on the Omega facility at the Laboratory for Laser Energetics. To minimize the implosion asymmetry due to laser drive, optimized laser cone powers, as well as improved beam pointings, were designed using 3D radiation-hydrodynamics code HYDRA [M. M. Marinak et al., Phys. Plasmas 3, 2070 (1996)]. Experimental back-lit radiographic and self-emission images revealed improved polar symmetry and increased neutron yield which were in good agreement with 2D HYDRA simulations. In particular, by reducing the energy in Omega's 21.4° polar rings by 16.75%, while increasing the energy in the 58.9° equatorial rings by 8.25% in such a way as to keep the overall energy to the target at 16 kJ, the second Legendre mode (P2) was reduced by a factor of 2, to less than 4% at bang time. At the same time the neutron yield increased by 62%. The polar symmetry was also improved relative to nominal DIME settings by a more radical repointing of OMEGA's 42.0° and 58.9° degree beams, to compensate for oblique incidence and reduced absorption at the equator, resulting in virtually no P2 around bang time and 33% more yield.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casner, A.; Masse, L.; Delorme, B.

Understanding and mitigating hydrodynamic instabilities and the fuel mix are the key elements for achieving ignition in Inertial Confinement Fusion. Cryogenic indirect-drive implosions on the National Ignition Facility have evidenced that the ablative Rayleigh-Taylor Instability (RTI) is a driver of the hot spot mix. This motivates the switch to a more flexible higher adiabat implosion design [O. A. Hurricane et al., Phys. Plasmas 21, 056313 (2014)]. The shell instability is also the main candidate for performance degradation in low-adiabat direct drive cryogenic implosions [Goncharov et al., Phys. Plasmas 21, 056315 (2014)]. This paper reviews recent results acquired in planar experimentsmore » performed on the OMEGA laser facility and devoted to the modeling and mitigation of hydrodynamic instabilities at the ablation front. In application to the indirect-drive scheme, we describe results obtained with a specific ablator composition such as the laminated ablator or a graded-dopant emulator. In application to the direct drive scheme, we discuss experiments devoted to the study of laser imprinted perturbations with special phase plates. The simulations of the Richtmyer-Meshkov phase reversal during the shock transit phase are challenging, and of crucial interest because this phase sets the seed of the RTI growth. Recent works were dedicated to increasing the accuracy of measurements of the phase inversion. We conclude by presenting a novel imprint mitigation mechanism based on the use of underdense foams. Lastly, the foams induce laser smoothing by parametric instabilities thus reducing the laser imprint on the CH foil.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casner, A., E-mail: alexis.casner@cea.fr; Masse, L.; Huser, G.

Understanding and mitigating hydrodynamic instabilities and the fuel mix are the key elements for achieving ignition in Inertial Confinement Fusion. Cryogenic indirect-drive implosions on the National Ignition Facility have evidenced that the ablative Rayleigh-Taylor Instability (RTI) is a driver of the hot spot mix. This motivates the switch to a more flexible higher adiabat implosion design [O. A. Hurricane et al., Phys. Plasmas 21, 056313 (2014)]. The shell instability is also the main candidate for performance degradation in low-adiabat direct drive cryogenic implosions [Goncharov et al., Phys. Plasmas 21, 056315 (2014)]. This paper reviews recent results acquired in planar experimentsmore » performed on the OMEGA laser facility and devoted to the modeling and mitigation of hydrodynamic instabilities at the ablation front. In application to the indirect-drive scheme, we describe results obtained with a specific ablator composition such as the laminated ablator or a graded-dopant emulator. In application to the direct drive scheme, we discuss experiments devoted to the study of laser imprinted perturbations with special phase plates. The simulations of the Richtmyer-Meshkov phase reversal during the shock transit phase are challenging, and of crucial interest because this phase sets the seed of the RTI growth. Recent works were dedicated to increasing the accuracy of measurements of the phase inversion. We conclude by presenting a novel imprint mitigation mechanism based on the use of underdense foams. The foams induce laser smoothing by parametric instabilities thus reducing the laser imprint on the CH foil.« less

Multi-Fluid Interpenetration Mixing in X-ray and Directly Laser driven ICF Capsule Implosions

NASA Astrophysics Data System (ADS)

Wilson, Douglas

2003-10-01

Mix between a surrounding shell and the fuel leads to degradation in ICF capsule performance. Both indirectly (X-ray) and directly laser driven implosions provide a wealth of data to test mix models. One model, the multi-fluid interpenetration mix model of Scannapieco and Cheng (Phys. Lett. A., 299, 49, 2002), was implemented in an ICF code and applied to a wide variety of experiments (e.g. J. D. Kilkenny et al., Proc. Conf Plasm. Phys. Contr. Nuc. Fus. Res. 3, 29(1988), P. Amendt, R. E. Turner, O. L. Landen, Phy. Rev. Lett., 89, 165001 (2002), or Li et al., Phy. Rev. Lett, 89, 165002 (2002)). With its single adjustable parameter fixed, it replicates well the yield degradation with increasing convergence ratio for both directly and indirectly driven capsules. Often, but not always the ion temperatures with mixing are calculated to be higher than in an unmixed implosion, agreeing with observations. Comparison with measured directly driven implosion yield rates ( from the neutron temporal diagnostic or NTD) shows mixing increases rapidly during the burn. The model also reproduces the decrease of the fuel "rho-r" with fill gas pressure, measured by observing escaping deuterons or secondary neutrons. The mix model assumes fully atomically mixed constituents, but when experiments with deuterated plastic layers and 3He fuel are modeled, less that full atomic mix is appropriate. Applying the mix model to the ablator - solid DT interface in indirectly driven ignition capsules for the NIF or LMJ suggests that the capsules will ignite, but that burn after ignition may be somewhat degraded. Situations in which the Scannapieco and Cheng model fails to agree with experiments can guide us to improvements or the development of other models. Some directly driven symmetric implosions suggest that in highly mixed situations, a higher value of the mix parameter may needed. Others show the model underestimating the fuel burn temperature. This work was performed by the Los Alamos National Laboratory under DOE contract number W-7405-Eng-36.

The I-Raum: A new shaped hohlraum for improved inner beam propagation in indirectly-driven ICF implosions on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Robey, H. F.; Berzak Hopkins, L.; Milovich, J. L.; Meezan, N. B.

2018-01-01

Recent work in indirectly-driven inertial confinement fusion implosions on the National Ignition Facility has indicated that late-time propagation of the inner cones of laser beams (23° and 30°) is impeded by the growth of a "bubble" of hohlraum wall material (Au or depleted uranium), which is initiated by and is located at the location where the higher-intensity outer beams (44° and 50°) hit the hohlraum wall. The absorption of the inner cone beams by this "bubble" reduces the laser energy reaching the hohlraum equator at late time driving an oblate or pancaked implosion, which limits implosion performance. In this article, we present the design of a new shaped hohlraum designed specifically to reduce the impact of this bubble by adding a recessed pocket at the location where the outer cones hit the hohlraum wall. This recessed pocket displaces the bubble radially outward, reducing the inward penetration of the bubble at all times throughout the implosion and increasing the time for inner beam propagation by approximately 1 ns. This increased laser propagation time allows one to drive a larger capsule, which absorbs more energy and is predicted to improve implosion performance. The new design is based on a recent National Ignition Facility shot, N170601, which produced a record neutron yield. The expansion rate and absorption of laser energy by the bubble is quantified for both cylindrical and shaped hohlraums, and the predicted performance is compared.

First measurements of deuterium-tritium and deuterium-deuterium fusion reaction yields in ignition-scalable direct-drive implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forrest, C. J.; Radha, P. B.; Knauer, J. P.

In this study, the deuterium-tritium (D-T) and deuterium-deuterium neutron yield ratio in cryogenic inertial confinement fusion (ICF) experiments is used to examine multifluid effects, traditionally not included in ICF modeling. This ratio has been measured for ignition-scalable direct-drive cryogenic DT implosions at the Omega Laser Facility using a high-dynamic-range neutron time-of-flight spectrometer. The experimentally inferred yield ratio is consistent with both the calculated values of the nuclear reaction rates and the measured preshot target-fuel composition. These observations indicate that the physical mechanisms that have been proposed to alter the fuel composition, such as species separation of the hydrogen isotopes, aremore » not significant during the period of peak neutron production in ignition-scalable cryogenic direct-drive DT implosions.« less

First measurements of deuterium-tritium and deuterium-deuterium fusion reaction yields in ignition-scalable direct-drive implosions

DOE PAGES

Forrest, C. J.; Radha, P. B.; Knauer, J. P.; ...

2017-03-03

In this study, the deuterium-tritium (D-T) and deuterium-deuterium neutron yield ratio in cryogenic inertial confinement fusion (ICF) experiments is used to examine multifluid effects, traditionally not included in ICF modeling. This ratio has been measured for ignition-scalable direct-drive cryogenic DT implosions at the Omega Laser Facility using a high-dynamic-range neutron time-of-flight spectrometer. The experimentally inferred yield ratio is consistent with both the calculated values of the nuclear reaction rates and the measured preshot target-fuel composition. These observations indicate that the physical mechanisms that have been proposed to alter the fuel composition, such as species separation of the hydrogen isotopes, aremore » not significant during the period of peak neutron production in ignition-scalable cryogenic direct-drive DT implosions.« less

Evolution of shock through a void in foam

NASA Astrophysics Data System (ADS)

Kim, Y.; Smidt, J. M.; Murphy, T. J.; Douglass, M. R.; Devolder, B. G.; Fincke, J. R.; Schmidt, D. W.; Cardenas, T.; Newman, S. G.; Hamilton, C. E.; Sedillo, T. J.; Los Alamos, NM 87544 Team

2016-10-01

Marble implosion is an experimental campaign intended to study the effects of heterogeneous mix on fusion burn. A spherical capsule is composed of deuterated plastic foam of controlled pore (or void) size with tritium fill in pores. As capsule implosion evolves, the initially separated deuterium and tritium will mix, producing DT yields. Void evolution during implosion is of interest for the Marble campaign. A shock tube, driven by the laser at Omega, was designed to study the evolution of a shock through a foam-filled ``void'' and subsequent void evolution. Targets were comprised of a 100 mg/cc CH foam tube containing a 200-µm diameter, lower density doped foam sphere. High-quality, radiographic images were obtained from both 2% iodine-doped in plastic foam and 15% tin-doped in aerogel foam. These experiments will be used to inform simulations.

The US ICF Ignition Program and the Inertial Fusion Program

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lindl, J D; Hammel, B A; Logan, B G

2003-07-02

There has been rapid progress in inertial fusion in the past few years. This progress spans the construction of ignition facilities, a wide range of target concepts, and the pursuit of integrated programs to develop fusion energy using lasers, ion beams and z-pinches. Two ignition facilities are under construction (NIF in the U.S. and LMJ in France) and both projects are progressing toward an initial experimental capability. The LIL prototype beamline for LMJ and the first 4 beams of NIF will be available for experiments in 2003. The full 192 beam capability of NIF will be available in 2009 andmore » ignition experiments are expected to begin shortly after that time. There is steady progress in the target science and target fabrication in preparation for indirect drive ignition experiments on NIF. Advanced target designs may lead to 5-10 times more yield than initial target designs. There has also been excellent progress on the science of ion beam and z-pinch driven indirect drive targets. Excellent progress on direct-drive targets has been obtained on the Omega laser at the University of Rochester. This includes improved performance of targets with a pulse shape predicted to result in reduced hydrodynamic instability. Rochester has also obtained encouraging results from initial cryogenic implosions. There is widespread interest in the science of fast ignition because of its potential for achieving higher target gain with lower driver energy and relaxed target fabrication requirements. Researchers from Osaka have achieved outstanding implosion and heating results from the Gekko XII Petawatt facility and implosions suitable for fast ignition have been tested on the Omega laser. A broad based program to develop lasers and ions beams for IFE is under way with excellent progress in drivers, chambers, target fabrication and target injection. KrF and Diode Pumped Solid-State lasers (DPSSL) are being developed in conjunction with drywall chambers and direct drive targets. Induction accelerators for heavy ions are being developed in conjunction with thick-liquid protected wall chambers and indirect-drive targets.« less

Demonstration of Ignition Radiation Temperatures in Indirect-Drive Inertial Confinement Fusion Hohlraums

NASA Astrophysics Data System (ADS)

Glenzer, S. H.; MacGowan, B. J.; Meezan, N. B.; Adams, P. A.; Alfonso, J. B.; Alger, E. T.; Alherz, Z.; Alvarez, L. F.; Alvarez, S. S.; Amick, P. V.; Andersson, K. S.; Andrews, S. D.; Antonini, G. J.; Arnold, P. A.; Atkinson, D. P.; Auyang, L.; Azevedo, S. G.; Balaoing, B. N. M.; Baltz, J. A.; Barbosa, F.; Bardsley, G. W.; Barker, D. A.; Barnes, A. I.; Baron, A.; Beeler, R. G.; Beeman, B. V.; Belk, L. R.; Bell, J. C.; Bell, P. M.; Berger, R. L.; Bergonia, M. A.; Bernardez, L. J.; Berzins, L. V.; Bettenhausen, R. C.; Bezerides, L.; Bhandarkar, S. D.; Bishop, C. L.; Bond, E. J.; Bopp, D. R.; Borgman, J. A.; Bower, J. R.; Bowers, G. A.; Bowers, M. W.; Boyle, D. T.; Bradley, D. K.; Bragg, J. L.; Braucht, J.; Brinkerhoff, D. L.; Browning, D. F.; Brunton, G. K.; Burkhart, S. C.; Burns, S. R.; Burns, K. E.; Burr, B.; Burrows, L. M.; Butlin, R. K.; Cahayag, N. J.; Callahan, D. A.; Cardinale, P. S.; Carey, R. W.; Carlson, J. W.; Casey, A. D.; Castro, C.; Celeste, J. R.; Chakicherla, A. Y.; Chambers, F. W.; Chan, C.; Chandrasekaran, H.; Chang, C.; Chapman, R. F.; Charron, K.; Chen, Y.; Christensen, M. J.; Churby, A. J.; Clancy, T. J.; Cline, B. D.; Clowdus, L. C.; Cocherell, D. G.; Coffield, F. E.; Cohen, S. J.; Costa, R. L.; Cox, J. R.; Curnow, G. M.; Dailey, M. J.; Danforth, P. M.; Darbee, R.; Datte, P. S.; Davis, J. A.; Deis, G. A.; Demaret, R. D.; Dewald, E. L.; di Nicola, P.; di Nicola, J. M.; Divol, L.; Dixit, S.; Dobson, D. B.; Doppner, T.; Driscoll, J. D.; Dugorepec, J.; Duncan, J. J.; Dupuy, P. C.; Dzenitis, E. G.; Eckart, M. J.; Edson, S. L.; Edwards, G. J.; Edwards, M. J.; Edwards, O. D.; Edwards, P. W.; Ellefson, J. C.; Ellerbee, C. H.; Erbert, G. V.; Estes, C. M.; Fabyan, W. J.; Fallejo, R. N.; Fedorov, M.; Felker, B.; Fink, J. T.; Finney, M. D.; Finnie, L. F.; Fischer, M. J.; Fisher, J. M.; Fishler, B. T.; Florio, J. W.; Forsman, A.; Foxworthy, C. B.; Franks, R. M.; Frazier, T.; Frieder, G.; Fung, T.; Gawinski, G. N.; Gibson, C. R.; Giraldez, E.; Glenn, S. M.; Golick, B. P.; Gonzales, H.; Gonzales, S. A.; Gonzalez, M. J.; Griffin, K. L.; Grippen, J.; Gross, S. M.; Gschweng, P. H.; Gururangan, G.; Gu, K.; Haan, S. W.; Hahn, S. R.; Haid, B. J.; Hamblen, J. E.; Hammel, B. A.; Hamza, A. V.; Hardy, D. L.; Hart, D. R.; Hartley, R. G.; Haynam, C. A.; Heestand, G. M.; Hermann, M. R.; Hermes, G. L.; Hey, D. S.; Hibbard, R. L.; Hicks, D. G.; Hinkel, D. E.; Hipple, D. L.; Hitchcock, J. D.; Hodtwalker, D. L.; Holder, J. P.; Hollis, J. D.; Holtmeier, G. M.; Huber, S. R.; Huey, A. W.; Hulsey, D. N.; Hunter, S. L.; Huppler, T. R.; Hutton, M. S.; Izumi, N.; Jackson, J. L.; Jackson, M. A.; Jancaitis, K. S.; Jedlovec, D. R.; Johnson, B.; Johnson, M. C.; Johnson, T.; Johnston, M. P.; Jones, O. S.; Kalantar, D. H.; Kamperschroer, J. H.; Kauffman, R. L.; Keating, G. A.; Kegelmeyer, L. M.; Kenitzer, S. L.; Kimbrough, J. R.; King, K.; Kirkwood, R. K.; Klingmann, J. L.; Knittel, K. M.; Kohut, T. R.; Koka, K. G.; Kramer, S. W.; Krammen, J. E.; Krauter, K. G.; Krauter, G. W.; Krieger, E. K.; Kroll, J. J.; La Fortune, K. N.; Lagin, L. J.; Lakamsani, V. K.; Landen, O. L.; Lane, S. W.; Langdon, A. B.; Langer, S. H.; Lao, N.; Larson, D. W.; Latray, D.; Lau, G. T.; Le Pape, S.; Lechleiter, B. L.; Lee, Y.; Lee, T. L.; Li, J.; Liebman, J. A.; Lindl, J. D.; Locke, S. F.; Loey, H. K.; London, R. A.; Lopez, F. J.; Lord, D. M.; Lowe-Webb, R. R.; Lown, J. G.; Ludwigsen, A. P.; Lum, N. W.; Lyons, R. R.; Ma, T.; MacKinnon, A. J.; Magat, M. D.; Maloy, D. T.; Malsbury, T. N.; Markham, G.; Marquez, R. M.; Marsh, A. A.; Marshall, C. D.; Marshall, S. R.; Maslennikov, I. L.; Mathisen, D. G.; Mauger, G. J.; Mauvais, M.-Y.; McBride, J. A.; McCarville, T.; McCloud, J. B.; McGrew, A.; McHale, B.; Macphee, A. G.; Meeker, J. F.; Merill, J. S.; Mertens, E. P.; Michel, P. A.; Miller, M. G.; Mills, T.; Milovich, J. L.; Miramontes, R.; Montesanti, R. C.; Montoya, M. M.; Moody, J.; Moody, J. D.; Moreno, K. A.; Morris, J.; Morriston, K. M.; Nelson, J. R.; Neto, M.; Neumann, J. D.; Ng, E.; Ngo, Q. M.; Olejniczak, B. L.; Olson, R. E.; Orsi, N. L.; Owens, M. W.; Padilla, E. H.; Pannell, T. M.; Parham, T. G.; Patterson, R. W., Jr.; Pavel, G.; Prasad, R. R.; Pendlton, D.; Penko, F. A.; Pepmeier, B. L.; Petersen, D. E.; Phillips, T. W.; Pigg, D.; Piston, K. W.; Pletcher, K. D.; Powell, C. L.; Radousky, H. B.; Raimondi, B. S.; Ralph, J. E.; Rampke, R. L.; Reed, R. K.; Reid, W. A.; Rekow, V. V.; Reynolds, J. L.; Rhodes, J. J.; Richardson, M. J.; Rinnert, R. J.; Riordan, B. P.; Rivenes, A. S.; Rivera, A. T.; Roberts, C. J.; Robinson, J. A.; Robinson, R. B.; Robison, S. R.; Rodriguez, O. R.; Rogers, S. P.; Rosen, M. D.; Ross, G. F.; Runkel, M.; Runtal, A. S.; Sacks, R. A.; Sailors, S. F.; Salmon, J. T.; Salmonson, J. D.; Saunders, R. L.; Schaffer, J. R.; Schindler, T. M.; Schmitt, M. J.; Schneider, M. B.; Segraves, K. S.; Shaw, M. J.; Sheldrick, M. E.; Shelton, R. T.; Shiflett, M. K.; Shiromizu, S. J.; Shor, M.; Silva, L. L.; Silva, S. A.; Skulina, K. M.; Smauley, D. A.; Smith, B. E.; Smith, L. K.; Solomon, A. L.; Sommer, S.; Soto, J. G.; Spafford, N. I.; Speck, D. E.; Springer, P. T.; Stadermann, M.; Stanley, F.; Stone, T. G.; Stout, E. A.; Stratton, P. L.; Strausser, R. J.; Suter, L. J.; Sweet, W.; Swisher, M. F.; Tappero, J. D.; Tassano, J. B.; Taylor, J. S.; Tekle, E. A.; Thai, C.; Thomas, C. A.; Thomas, A.; Throop, A. L.; Tietbohl, G. L.; Tillman, J. M.; Town, R. P. J.; Townsend, S. L.; Tribbey, K. L.; Trummer, D.; Truong, J.; Vaher, J.; Valadez, M.; van Arsdall, P.; van Prooyen, A. J.; Vergel de Dios, E. O.; Vergino, M. D.; Vernon, S. P.; Vickers, J. L.; Villanueva, G. T.; Vitalich, M. A.; Vonhof, S. A.; Wade, F. E.; Wallace, R. J.; Warren, C. T.; Warrick, A. L.; Watkins, J.; Weaver, S.; Wegner, P. J.; Weingart, M. A.; Wen, J.; White, K. S.; Whitman, P. K.; Widmann, K.; Widmayer, C. C.; Wilhelmsen, K.; Williams, E. A.; Williams, W. H.; Willis, L.; Wilson, E. F.; Wilson, B. A.; Witte, M. C.; Work, K.; Yang, P. S.; Young, B. K.; Youngblood, K. P.; Zacharias, R. A.; Zaleski, T.; Zapata, P. G.; Zhang, H.; Zielinski, J. S.; Kline, J. L.; Kyrala, G. A.; Niemann, C.; Kilkenny, J. D.; Nikroo, A.; van Wonterghem, B. M.; Atherton, L. J.; Moses, E. I.

2011-02-01

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of TRAD=300eV and a symmetric implosion to a 100μm diameter hot core.

Electron Shock Ignition of Inertial Fusion Targets

NASA Astrophysics Data System (ADS)

Shang, W. L.; Betti, R.; Hu, S. X.; Woo, K.; Hao, L.; Ren, C.; Christopherson, A. R.; Bose, A.; Theobald, W.

2017-11-01

It is shown that inertial confinement fusion targets designed with low implosion velocities can be shock-ignited using laser-plasma interaction generated hot electrons (hot-e 's) to obtain high energy gains. These designs are robust to multimode asymmetries and are predicted to ignite even for significantly distorted implosions. Electron shock ignition requires tens of kilojoules of hot-e 's which can be produced only at a large laser facility like the National Ignition Facility, with the laser-to-hot-e conversion efficiency greater than 10% at laser intensities ˜1016 W /cm2 .

Electron Shock Ignition of Inertial Fusion Targets.

PubMed

Shang, W L; Betti, R; Hu, S X; Woo, K; Hao, L; Ren, C; Christopherson, A R; Bose, A; Theobald, W

2017-11-10

It is shown that inertial confinement fusion targets designed with low implosion velocities can be shock-ignited using laser-plasma interaction generated hot electrons (hot-e's) to obtain high energy gains. These designs are robust to multimode asymmetries and are predicted to ignite even for significantly distorted implosions. Electron shock ignition requires tens of kilojoules of hot-e's which can be produced only at a large laser facility like the National Ignition Facility, with the laser-to-hot-e conversion efficiency greater than 10% at laser intensities ∼10^{16}  W/cm^{2}.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoeckl, C., E-mail: csto@lle.rochester.edu; Bedzyk, M.; Brent, G.

A high-performance cryogenic DT inertial confinement fusion implosion experiment is an especially challenging backlighting configuration because of the high self-emission of the core at stagnation and the low opacity of the DT shell. High-energy petawatt lasers such as OMEGA EP promise significantly improved backlighting capabilities by generating high x-ray intensities and short emission times. A narrowband x-ray imager with an astigmatism-corrected bent quartz crystal for the Si He{sub α} line at ∼1.86 keV was developed to record backlit images of cryogenic direct-drive implosions. A time-gated recording system minimized the self-emission of the imploding target. A fast target-insertion system capable ofmore » moving the backlighter target ∼7 cm in ∼100 ms was developed to avoid interference with the cryogenic shroud system. With backlighter laser energies of ∼1.25 kJ at a 10-ps pulse duration, the radiographic images show a high signal-to-background ratio of >100:1 and a spatial resolution of the order of 10 μm. The backlit images can be used to assess the symmetry of the implosions close to stagnation and the mix of ablator material into the dense shell.« less

Comparison of high-density carbon implosions in unlined uranium versus gold hohlraums

NASA Astrophysics Data System (ADS)

Dewald, Eduard; Meezan, Nathan; Tommasini, Riccardo; Khan, Shahab; MacKinnon, Andrew; Berzak Hopkins, Laura; Divol, Laurent; Lepape, Sebastien; Moore, Alastair; Schneider, Marilyn; Pak, Arthur; Nikroo, Abbas; Landen, Otto

2016-10-01

In Inertial Confinement Fusion (ICF) implosions, laser energy is converted to x-ray radiation in hohlraums with High-Z walls. At radiation temperatures near 300 eV relevant for ICF experiments, the radiative losses in heating the wall are lower for U than for Au hohlraums. Furthermore, the intensity of the ``M-band'' x-rays with photon energies h ν >1.8 keV is lower for uranium, allowing for reduced capsule dopant concentrations employed to minimize inner ablator preheat and hence keep favorable fuel/ablator interface Atwood numbers. This in turn improves the ablator rocket efficiency and reduces the risk of polluting the hot-spot with emissive dopant material. The first uranium vacuum hohlraum experiments on the National Ignition Facility (NIF) with undoped high-density carbon (HDC, or diamond) capsules have demonstrated 30% lower ``M-band'' intensity relative to Au, resulting in lower inflight ablator thickness due to reduced preheat. In addition, fusion neutron yields are 2x higher in U than in Au hohlraums for D2-gas filled capsule implosions at ICF relevant velocities of 380 +/-20 km/s. These results have led the NIF ICF implosions to routinely employ U hohlraums. Prepared by LLNL under Contract DE-AC52-07NA27344.

On the importance of minimizing "coast-time" in x-ray driven inertially confined fusion implosions

NASA Astrophysics Data System (ADS)

Hurricane, O. A.; Kritcher, A.; Callahan, D. A.; Landen, O.; Patel, P. K.; Springer, P. T.; Casey, D. T.; Dewald, E. L.; Dittrich, T. R.; Döppner, T.; Hinkel, D. E.; Berzak Hopkins, L. F.; Kline, J.; Le Pape, S.; Ma, T.; MacPhee, A. G.; Moore, A.; Pak, A.; Park, H.-S.; Ralph, J.; Salmonson, J. D.; Widmann, K.

2017-09-01

By the time an inertially confined fusion (ICF) implosion has converged a factor of 20, its surface area has shrunk 400 × , making it an inefficient x-ray energy absorber. So, ICF implosions are traditionally designed to have the laser drive shut off at a time, toff, well before bang-time, tBT, for a coast-time of t coast = t B T - t o f f > 1 ns. High-foot implosions on NIF showed a strong dependence of many key ICF performance quantities on reduced coast-time (by extending the duration of laser power after the peak power is first reached), most notably stagnation pressure and fusion yield. Herein we show that the ablation pressure, pabl, which drives high-foot implosions, is essentially triangular in temporal shape, and that reducing tcoast boosts pabl by as much as ˜ 2 × prior to stagnation thus increasing fuel and hot-spot compression and implosion speed. One-dimensional simulations are used to track hydrodynamic characteristics for implosions with various coast-times and various assumed rates of hohlraum cooling after toff to illustrate how the late-time conditions exterior to the implosion can impact the fusion performance. A simple rocket model-like analytic theory demonstrates that reducing coast-time can lead to a ˜ 15 % higher implosion velocity because the reduction in x-ray absorption efficiency at late-time is somewhat compensated by small ( ˜ 5 % - 10 %) ablator mass remaining. Together with the increased ablation pressure, the additional implosion speed for short coast-time implosions can boost the stagnation pressure by ˜ 2 × as compared to a longer coast-time version of the same implosion. Four key dimensionless parameters are identified and we find that reducing coast-time to as little as 500 ps still provides some benefit. Finally, we show how the high-foot implosion data is consistent with the above mentioned picture.

On the importance of minimizing “coast-time” in x-ray driven inertially confined fusion implosions

DOE PAGES

Hurricane, O. A.; Kritcher, A.; Callahan, D. A.; ...

2017-09-01

By the time an inertially confined fusion (ICF) implosion has converged a factor of 20, its surface area has shrunk 400×, making it an inefficient x-ray energy absorber. So, ICF implosions are traditionally designed to have the laser drive shut off at a time, t off, well before bang-time, t BT, for a coast-time of t coast = t BT – t off > 1 ns. High-foot implosions on NIF showed a strong dependence of many key ICF performance quantities on reduced coast-time (by extending the duration of laser power after the peak power is first reached), most notably stagnationmore » pressure and fusion yield. Herein we show that the ablation pressure, p abl, which drives high-foot implosions, is essentially triangular in temporal shape, and that reducing t coast boosts p abl by as much as ~2× prior to stagnation thus increasing fuel and hot-spot compression and implosion speed. One-dimensional simulations are used to track hydrodynamic characteristics for implosions with various coast-times and various assumed rates of hohlraum cooling after t off to illustrate how the late-time conditions exterior to the implosion can impact the fusion performance. A simple rocket model-like analytic theory demonstrates that reducing coast-time can lead to a ~15% higher implosion velocity because the reduction in x-ray absorption efficiency at late-time is somewhat compensated by small (~5%–10%) ablator mass remaining. Together with the increased ablation pressure, the additional implosion speed for short coast-time implosions can boost the stagnation pressure by ~2× as compared to a longer coast-time version of the same implosion. Four key dimensionless parameters are identified and we find that reducing coast-time to as little as 500 ps still provides some benefit. Lastly, we show how the high-foot implosion data is consistent with the above mentioned picture.« less

On the importance of minimizing “coast-time” in x-ray driven inertially confined fusion implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hurricane, O. A.; Kritcher, A.; Callahan, D. A.

By the time an inertially confined fusion (ICF) implosion has converged a factor of 20, its surface area has shrunk 400×, making it an inefficient x-ray energy absorber. So, ICF implosions are traditionally designed to have the laser drive shut off at a time, t off, well before bang-time, t BT, for a coast-time of t coast = t BT – t off > 1 ns. High-foot implosions on NIF showed a strong dependence of many key ICF performance quantities on reduced coast-time (by extending the duration of laser power after the peak power is first reached), most notably stagnationmore » pressure and fusion yield. Herein we show that the ablation pressure, p abl, which drives high-foot implosions, is essentially triangular in temporal shape, and that reducing t coast boosts p abl by as much as ~2× prior to stagnation thus increasing fuel and hot-spot compression and implosion speed. One-dimensional simulations are used to track hydrodynamic characteristics for implosions with various coast-times and various assumed rates of hohlraum cooling after t off to illustrate how the late-time conditions exterior to the implosion can impact the fusion performance. A simple rocket model-like analytic theory demonstrates that reducing coast-time can lead to a ~15% higher implosion velocity because the reduction in x-ray absorption efficiency at late-time is somewhat compensated by small (~5%–10%) ablator mass remaining. Together with the increased ablation pressure, the additional implosion speed for short coast-time implosions can boost the stagnation pressure by ~2× as compared to a longer coast-time version of the same implosion. Four key dimensionless parameters are identified and we find that reducing coast-time to as little as 500 ps still provides some benefit. Lastly, we show how the high-foot implosion data is consistent with the above mentioned picture.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robey, H. F.; Smalyuk, V. A.; Milovich, J. L.

A series of indirectly driven capsule implosions has been performed on the National Ignition Facility to assess the relative contributions of ablation-front instability growth vs. fuel compression on implosion performance. Laser pulse shapes for both low and high-foot pulses were modified to vary ablation-front growth and fuel adiabat, separately and controllably. Three principal conclusions are drawn from this study: (1) It is shown that reducing ablation-front instability growth in low-foot implosions results in a substantial (3-10X) increase in neutron yield with no loss of fuel compression. (2) It is shown that reducing the fuel adiabat in high-foot implosions results inmore » a significant (36%) increase in fuel compression together with a small (10%) increase in neutron yield. (3) Increased electron preheat at higher laser power in high-foot implosions, however, appears to offset the gain in compression achieved by adiabat-shaping at lower power. These results taken collectively bridge the space between the higher compression low-foot results and the higher yield high-foot results.« less

Three-dimensional modeling of direct-drive cryogenic implosions on OMEGA

DOE PAGES

Igumenshchev, I. V.; Goncharov, V. N.; Marshall, F. J.; ...

2016-05-04

The effects of large-scale (with Legendre modes ≲10) laser-imposed nonuniformities in direct-drive cryogenic implosions on the OMEGA laser system are investigated using three-dimension hydrodynamic simulations performed using a newly developed code ASTER. Sources of these nonuniformities include an illumination pattern produced by 60 OMEGA laser beams, capsule offsets (~10 to 20 μm), and imperfect pointing, energy balance, and timing of the beams (with typical σ rms ~10 μm, 10%, and 5 ps, respectively). Two implosion designs using 26-kJ triple-picket laser pulses were studied: a nominal design, in which a 880-μm-diameter capsule is illuminated by the same-diameter beams, and a “R75”more » design using a capsule of 900 μm in diameter and beams of 75% of this diameter. Simulations found that nonuniformities because of capsule offsets and beam imbalance have the largest effect on implosion performance. These nonuniformities lead to significant distortions of implosion cores resulting in an incomplete stagnation. The shape of distorted cores is well represented by neutron images, but loosely in x-rays. Simulated neutron spectra from perturbed implosions show large directional variations and up to ~ 2 keV variation of the hot spot temperature inferred from these spectra. The R75 design is more hydrodynamically efficient because of mitigation of crossed-beam energy transfer, but also suffers more from the nonuniformities. Furthermore, simulations predict a performance advantage of this design over the nominal design when the target offset and beam imbalance σ rms are reduced to less than 5 μm and 5%, respectively.« less

Three-dimensional modeling of direct-drive cryogenic implosions on OMEGA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Igumenshchev, I. V.; Goncharov, V. N.; Marshall, F. J.

The effects of large-scale (with Legendre modes ≲10) laser-imposed nonuniformities in direct-drive cryogenic implosions on the OMEGA laser system are investigated using three-dimension hydrodynamic simulations performed using a newly developed code ASTER. Sources of these nonuniformities include an illumination pattern produced by 60 OMEGA laser beams, capsule offsets (~10 to 20 μm), and imperfect pointing, energy balance, and timing of the beams (with typical σ rms ~10 μm, 10%, and 5 ps, respectively). Two implosion designs using 26-kJ triple-picket laser pulses were studied: a nominal design, in which a 880-μm-diameter capsule is illuminated by the same-diameter beams, and a “R75”more » design using a capsule of 900 μm in diameter and beams of 75% of this diameter. Simulations found that nonuniformities because of capsule offsets and beam imbalance have the largest effect on implosion performance. These nonuniformities lead to significant distortions of implosion cores resulting in an incomplete stagnation. The shape of distorted cores is well represented by neutron images, but loosely in x-rays. Simulated neutron spectra from perturbed implosions show large directional variations and up to ~ 2 keV variation of the hot spot temperature inferred from these spectra. The R75 design is more hydrodynamically efficient because of mitigation of crossed-beam energy transfer, but also suffers more from the nonuniformities. Furthermore, simulations predict a performance advantage of this design over the nominal design when the target offset and beam imbalance σ rms are reduced to less than 5 μm and 5%, respectively.« less

X-ray driven implosions at ignition relevant velocities on the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meezan, N. B.; MacKinnon, A. J.; Hicks, D. G.

2013-05-15

Backlit convergent ablator experiments on the National Ignition Facility [E. I. Moses et al., Phys. Plasmas 16, 041006 (2009)] are indirect drive implosions that study the inflight dynamics of an imploding capsule. Side-on, backlit radiography provides data used by the National Ignition Campaign to measure time-dependent properties of the capsule ablator including its center of mass radius, velocity, and unablated mass. Previously, Callahan [D. A. Callahan et al., Phys. Plasmas 19, 056305 (2012)] and Hicks [D. H. Hicks et al., Phys. Plasmas 19, 122702 (2012)] reported backlit convergent ablator experiments demonstrating velocities approaching those required for ignition. This paper focusesmore » on implosion performance data in the “rocket curve” plane, velocity vs. ablator mass. These rocket curve data, along with supporting numerical simulations, show that the nominal 195 μm-thick ignition capsule would reach the ignition velocity goal V = 370 km/s with low ablator mass remaining–below the goal of M = 0.25 mg. This finding led to experiments with thicker capsule ablators. A recent symmetry capsule experiment with a 20 μm thicker capsule driven by 520 TW, 1.86 MJ laser pulse (along with a companion backlit convergent ablator experiment) appears to have demonstrated V≥350 km/s with ablator mass remaining above the ignition goal.« less

Simultaneous measurement of the HT and DT fusion burn histories in inertial fusion implosions

DOE PAGES

Zylstra, Alex B.; Herrmann, Hans W.; Kim, Yong Ho; ...

2017-05-23

Measuring the thermonuclear burn history is an important way to diagnose inertial fusion implosions. Here, using the gas Cherenkov detectors at the OMEGA laser facility, we measure the HT fusion burn in a H 2+T 2 gas-fueled implosion for the first time. Then, using multiple detectors with varied Cherenkov thresholds, we demonstrate a technique for simultaneously measuring both the HT and DT burn histories from an implosion where the total reaction yields are comparable. This new technique will be used to study material mixing and kinetic phenomena in implosions.

Simultaneous measurement of the HT and DT fusion burn histories in inertial fusion implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zylstra, Alex B.; Herrmann, Hans W.; Kim, Yong Ho

Measuring the thermonuclear burn history is an important way to diagnose inertial fusion implosions. Here, using the gas Cherenkov detectors at the OMEGA laser facility, we measure the HT fusion burn in a H 2+T 2 gas-fueled implosion for the first time. Then, using multiple detectors with varied Cherenkov thresholds, we demonstrate a technique for simultaneously measuring both the HT and DT burn histories from an implosion where the total reaction yields are comparable. This new technique will be used to study material mixing and kinetic phenomena in implosions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shang, W. L.; Betti, R.; Hu, S. X.

Here, it is shown that inertial fusion targets designed with low implosion velocities can be shock ignited using laser–plasma interaction generated hot electrons (hot-e) to obtain high-energy gains. These designs are robust to multimode asymmetries and are predicted to ignite even for significantly distorted implosions. Electron shock ignition requires tens of kilojoules of hot-e, which can only be produced on a large laser facility like the National Ignition Facility, with the laser to hot-e conversion efficiency greater than 10% at laser intensities ~10 16 W/cm 2.

The magnetic recoil spectrometer for measurements of the absolute neutron spectrum at OMEGA and the NIF

DOE PAGES

Casey, D. T.; Frenje, J. A.; Gatu Johnson, M.; ...

2013-04-18

The neutron spectrum produced by deuterium-tritium (DT) inertial confinement fusion implosions contains a wealth of information about implosion performance including the DT yield, iontemperature, and areal-density. The Magnetic Recoil Spectrometer (MRS) has been used at both the OMEGA laser facility and the National Ignition Facility (NIF) to measure the absolute neutron spectrum from 3 to 30 MeV at OMEGA and 3 to 36 MeV at the NIF. These measurements have been used to diagnose the performance of cryogenic target implosions to unprecedented accuracy. Interpretation of MRS data requires a detailed understanding of the MRS response and background. This paper describesmore » ab initio characterization of the system involving Monte Carlo simulations of the MRS response in addition to the commission experiments for in situ calibration of the systems on OMEGA and the NIF.« less

Measurements of Deuterium-Tritium Fuel Fractionation from Kinetic Effects in Ignition-Relevant Direct-Drive Cryogenic Implosions

NASA Astrophysics Data System (ADS)

Forrest, C.; Glebov, V. Yu.; Knauer, J. P.; Radha, P. B.; Regan, S. P.; Sangster, T. C.; Stoeckl, C.

2016-10-01

Measurements of DT and DD reaction yields have been studied using ignition-relevant, cryogenically cooled deuterium-tritium gas-filled cryogenic DT targets in inertial confinement fusion (ICF) implosions. In these experiments, carried out at the Omega Laser Facility, highresolution time-of-flight spectroscopy was used to measure the primary neutron peak distribution required to infer the DT and DD reaction yields. From these measurements, it will be shown that the yield ratio has a χ2/per degree of freedom of 0.67 as compared with the measured fraction of the target fuel composition. This observation indicates that kinetic effects leading to species separation are insignificant in ICF ignition-relevant DT implosions on OMEGA. This material is based upon work supported by the Department Of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

The magnetic recoil spectrometer for measurements of the absolute neutron spectrum at OMEGA and the NIF.

PubMed

Casey, D T; Frenje, J A; Johnson, M Gatu; Séguin, F H; Li, C K; Petrasso, R D; Glebov, V Yu; Katz, J; Magoon, J; Meyerhofer, D D; Sangster, T C; Shoup, M; Ulreich, J; Ashabranner, R C; Bionta, R M; Carpenter, A C; Felker, B; Khater, H Y; LePape, S; MacKinnon, A; McKernan, M A; Moran, M; Rygg, J R; Yeoman, M F; Zacharias, R; Leeper, R J; Fletcher, K; Farrell, M; Jasion, D; Kilkenny, J; Paguio, R

2013-04-01

The neutron spectrum produced by deuterium-tritium (DT) inertial confinement fusion implosions contains a wealth of information about implosion performance including the DT yield, ion-temperature, and areal-density. The Magnetic Recoil Spectrometer (MRS) has been used at both the OMEGA laser facility and the National Ignition Facility (NIF) to measure the absolute neutron spectrum from 3 to 30 MeV at OMEGA and 3 to 36 MeV at the NIF. These measurements have been used to diagnose the performance of cryogenic target implosions to unprecedented accuracy. Interpretation of MRS data requires a detailed understanding of the MRS response and background. This paper describes ab initio characterization of the system involving Monte Carlo simulations of the MRS response in addition to the commission experiments for in situ calibration of the systems on OMEGA and the NIF.

Indications of Bulk-Fluid Motion in Direct-Drive Implosions

NASA Astrophysics Data System (ADS)

Mannion, O. M.; Anderson, K. S.; Forrest, C. J.; Glebov, V. Yu.; Goncharov, V. N.; Knauer, J. P.; Radha, P. B.; Regan, S. P.; Sangster, T. C.; Stoeckl, C.

2017-10-01

The neutron spectrum produced by a burning plasma encodes essential information about the fusion products and serves as an important diagnostic for inertial confinement fusion experiments. At the Omega Laser Facility, neutron time-of-flight measurements are used to interpret the first and second moment of the neutron spectrum. These moments have been shown to be directly related to properties of the plasma, such as bulk fluid motion and apparent ion temperature. New measurement devices allow for unprecedented accuracy in the measurement of these moments and will provide a better understanding of the performance of direct-drive implosions. We present measurements of the first moment of the DT and D2 peaks in DT implosions and show that variations in the first moment indicate bulk fluid motion of the plasma. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Designing symmetric polar direct drive implosions on the Omega laser facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krasheninnikova, Natalia S.; Cobble, James A.; Murphy, Thomas J.

2014-04-15

Achieving symmetric capsule implosions with Polar Direct Drive [S. Skupsky et al., Phys. Plasmas 11, 2763 (2004); R. S. Craxton et al., Phys. Plasmas 12, 056304 (2005); F. J. Marshall et al., J. Phys. IV France 133, 153–157 (2006)] has been explored during recent Defect Induced Mix Experiment campaign on the Omega facility at the Laboratory for Laser Energetics. To minimize the implosion asymmetry due to laser drive, optimized laser cone powers, as well as improved beam pointings, were designed using 3D radiation-hydrodynamics code HYDRA [M. M. Marinak et al., Phys. Plasmas 3, 2070 (1996)]. Experimental back-lit radiographic and self-emissionmore » images revealed improved polar symmetry and increased neutron yield which were in good agreement with 2D HYDRA simulations. In particular, by reducing the energy in Omega's 21.4° polar rings by 16.75%, while increasing the energy in the 58.9° equatorial rings by 8.25% in such a way as to keep the overall energy to the target at 16 kJ, the second Legendre mode (P{sub 2}) was reduced by a factor of 2, to less than 4% at bang time. At the same time the neutron yield increased by 62%. The polar symmetry was also improved relative to nominal DIME settings by a more radical repointing of OMEGA's 42.0° and 58.9° degree beams, to compensate for oblique incidence and reduced absorption at the equator, resulting in virtually no P{sub 2} around bang time and 33% more yield.« less

The control of hot-electron preheat in shock-ignition implosions

NASA Astrophysics Data System (ADS)

Trela, J.; Theobald, W.; Anderson, K. S.; Batani, D.; Betti, R.; Casner, A.; Delettrez, J. A.; Frenje, J. A.; Glebov, V. Yu.; Ribeyre, X.; Solodov, A. A.; Stoeckl, M.; Stoeckl, C.

2018-05-01

In the shock-ignition scheme for inertial confinement fusion, hot electrons resulting from laser-plasma instabilities can play a major role during the late stage of the implosion. This article presents the results of an experiment performed on OMEGA in the so-called "40 + 20 configuration." Using a recent calibration of the time-resolved hard x-ray diagnostic, the hot electrons' temperature and total energy were measured. One-dimensional radiation-hydrodynamic simulations have been performed that include hot electrons and are in agreement with the measured neutron-rate-averaged areal density. For an early spike launch, both experiment and simulations show the detrimental effect of hot electrons on areal density and neutron yield. For a later spike launch, this effect is minimized because of a higher compression of the target.

Impact of flows on ion temperatures inferred from neutron spectra in asymmetrically driven OMEGA DT implosions

NASA Astrophysics Data System (ADS)

Gatu Johnson, M.; Frenje, J.; Lahmann, B.; Seguin, F.; Petrasso, R.; Appelbe, B.; Chittenden, J.; Walsh, C.; Delettrez, J.; Igumenshchev, I.; Knauer, J. P.; Glebov, V. Yu.; Forrest, C.; Grimble, W.; Marshall, F.; Michel, T.; Stoeckl, C.; Haines, B. M.; Zylstra, A. B.

2017-10-01

Ion temperatures (Tion) in Inertial Confinement Fusion (ICF) experiments have traditionally been inferred from the broadening of primary neutron spectra. Directional motion (flow) of the fuel at burn, expected to arise due to asymmetries imposed by e.g. engineering features or drive non-uniformity, also impacts broadening and may lead to artificially inflated ``Tion'' values. Flow due to low-mode asymmetries is expected to give rise to line-of-sight variations in measured Tion, as observed in OMEGA cryogenic DT implosions but not in similar experiments at the NIF. In this presentation, we report on OMEGA experiments with intentional drive asymmetry designed for testing the ability to accurately predict and measure line-of-sight differences in apparent Tion due to low-mode asymmetry-seeded flows. The measurements are contrasted to CHIMERA, RAGE and ASTER simulations, providing insight into implosion dynamics and the relative importance of laser drive non-uniformity, stalk and offset as sources of asymmetry. The results highlight the complexity of hot-spot dynamics, which is a problem that must be mastered to achieve ICF ignition. This work was supported in part by the U.S. DOE, NLUF and LLE.

Direct-drive inertial confinement fusion: A review

NASA Astrophysics Data System (ADS)

Craxton, R. S.; Anderson, K. S.; Boehly, T. R.; Goncharov, V. N.; Harding, D. R.; Knauer, J. P.; McCrory, R. L.; McKenty, P. W.; Meyerhofer, D. D.; Myatt, J. F.; Schmitt, A. J.; Sethian, J. D.; Short, R. W.; Skupsky, S.; Theobald, W.; Kruer, W. L.; Tanaka, K.; Betti, R.; Collins, T. J. B.; Delettrez, J. A.; Hu, S. X.; Marozas, J. A.; Maximov, A. V.; Michel, D. T.; Radha, P. B.; Regan, S. P.; Sangster, T. C.; Seka, W.; Solodov, A. A.; Soures, J. M.; Stoeckl, C.; Zuegel, J. D.

2015-11-01

The direct-drive, laser-based approach to inertial confinement fusion (ICF) is reviewed from its inception following the demonstration of the first laser to its implementation on the present generation of high-power lasers. The review focuses on the evolution of scientific understanding gained from target-physics experiments in many areas, identifying problems that were demonstrated and the solutions implemented. The review starts with the basic understanding of laser-plasma interactions that was obtained before the declassification of laser-induced compression in the early 1970s and continues with the compression experiments using infrared lasers in the late 1970s that produced thermonuclear neutrons. The problem of suprathermal electrons and the target preheat that they caused, associated with the infrared laser wavelength, led to lasers being built after 1980 to operate at shorter wavelengths, especially 0.35 μm—the third harmonic of the Nd:glass laser—and 0.248 μm (the KrF gas laser). The main physics areas relevant to direct drive are reviewed. The primary absorption mechanism at short wavelengths is classical inverse bremsstrahlung. Nonuniformities imprinted on the target by laser irradiation have been addressed by the development of a number of beam-smoothing techniques and imprint-mitigation strategies. The effects of hydrodynamic instabilities are mitigated by a combination of imprint reduction and target designs that minimize the instability growth rates. Several coronal plasma physics processes are reviewed. The two-plasmon-decay instability, stimulated Brillouin scattering (together with cross-beam energy transfer), and (possibly) stimulated Raman scattering are identified as potential concerns, placing constraints on the laser intensities used in target designs, while other processes (self-focusing and filamentation, the parametric decay instability, and magnetic fields), once considered important, are now of lesser concern for mainline direct-drive target concepts. Filamentation is largely suppressed by beam smoothing. Thermal transport modeling, important to the interpretation of experiments and to target design, has been found to be nonlocal in nature. Advances in shock timing and equation-of-state measurements relevant to direct-drive ICF are reported. Room-temperature implosions have provided an increased understanding of the importance of stability and uniformity. The evolution of cryogenic implosion capabilities, leading to an extensive series carried out on the 60-beam OMEGA laser [Boehly et al., Opt. Commun. 133, 495 (1997)], is reviewed together with major advances in cryogenic target formation. A polar-drive concept has been developed that will enable direct-drive-ignition experiments to be performed on the National Ignition Facility [Haynam et al., Appl. Opt. 46(16), 3276 (2007)]. The advantages offered by the alternative approaches of fast ignition and shock ignition and the issues associated with these concepts are described. The lessons learned from target-physics and implosion experiments are taken into account in ignition and high-gain target designs for laser wavelengths of 1/3 μm and 1/4 μm. Substantial advances in direct-drive inertial fusion reactor concepts are reviewed. Overall, the progress in scientific understanding over the past five decades has been enormous, to the point that inertial fusion energy using direct drive shows significant promise as a future environmentally attractive energy source.

LLE Review Quarterly Report January - March 2012. Volume 130

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shvydky, Alex

2012-03-01

This volume of the LLE Review, covering January–March 2012, features “OMEGA Polar-Drive Target Designs,” by P. B. Radha, J. A. Marozas, F. J. Marshall, A. Shvydky, T. J. B. Collins, V. N. Goncharov, R. L. McCrory, P. W. McKenty, D. D. Meyerhofer, T. C. Sangster, and S. Skupsky. This article (p. 57) describes low-adiabat, cryogenic-deuterium–tritium, and warm-plastic-shell polar-drive (PD)–implosion designs for the OMEGA laser. The designs are at two different on-target laser intensities, each at a different in-flight aspect ratio (IFAR). The first design permits one to study implosion energetics and target performance closer to ignition-relevant intensities (7 X 10more » 14 W/cm 2 at the quarter-critical surface), where nonlocal heat conduction and laser–plasma interactions can play an important role, but at lower values of IFAR (~22). The second design permits one to study implosion energetics and target performance at a lower intensity (3 X 10 14 W/cm 2) but at higher IFAR (~32), where the shell instability can play an important role. The higher IFAR designs are accessible on the existing OMEGA Laser System only at lower intensities. Implosions at ignition-relevant intensities can be obtained only by reducing target radius, although only at smaller values of IFAR. Polar-drive geometry requires repointing the laser beams to improve shell symmetry. The higher-intensity designs optimize target performance by repointing beams to a lesser extent and compensate for the reduced equatorial drive by increasing beam energies for the repointed beams and using custom beam profiles that improve equatorial illumination at the expense of irradiation at higher latitudes. These designs will be studied when new phase plates for the OMEGA Laser System, corresponding to the smaller target radii and custom beam profiles, are obtained. Implosion results from the combined set of high-intensity and high-IFAR implosions should yield valuable data to validate models of laser-energy deposition, heat conduction, nonuniformity growth, and fuel assembly in PD geometry.« less

Three-dimensional hydrodynamic simulations of OMEGA implosions

NASA Astrophysics Data System (ADS)

Igumenshchev, I. V.; Michel, D. T.; Shah, R. C.; Campbell, E. M.; Epstein, R.; Forrest, C. J.; Glebov, V. Yu.; Goncharov, V. N.; Knauer, J. P.; Marshall, F. J.; McCrory, R. L.; Regan, S. P.; Sangster, T. C.; Stoeckl, C.; Schmitt, A. J.; Obenschain, S.

2017-05-01

The effects of large-scale (with Legendre modes ≲ 10) asymmetries in OMEGA direct-drive implosions caused by laser illumination nonuniformities (beam-power imbalance and beam mispointing and mistiming), target offset, and variation in target-layer thickness were investigated using the low-noise, three-dimensional Eulerian hydrodynamic code ASTER. Simulations indicate that these asymmetries can significantly degrade the implosion performance. The most important sources of the asymmetries are the target offsets ( ˜10 to 20 μm), beam-power imbalance ( σrms˜10 %), and variations ( ˜5 %) in target-layer thickness. Large-scale asymmetries distort implosion cores, resulting in a reduced hot-spot confinement and an increased residual kinetic energy of implosion targets. The ion temperature inferred from the width of simulated neutron spectra is influenced by bulk fuel motion in the distorted hot spot and can result in up to an ˜1 -keV increase in apparent temperature. Similar temperature variations along different lines of sight are observed. Demonstrating hydrodynamic equivalence to ignition designs on OMEGA requires a reduction in large-scale target and laser-imposed nonuniformities, minimizing target offset, and employing highly efficient mid-adiabat (α = 4) implosion designs, which mitigate cross-beam energy transfer and suppress short-wavelength Rayleigh-Taylor growth.

Near-vacuum hohlraums for driving fusion implosions with high density carbon ablatorsa)

NASA Astrophysics Data System (ADS)

Berzak Hopkins, L. F.; Le Pape, S.; Divol, L.; Meezan, N. B.; Mackinnon, A. J.; Ho, D. D.; Jones, O. S.; Khan, S.; Milovich, J. L.; Ross, J. S.; Amendt, P.; Casey, D.; Celliers, P. M.; Pak, A.; Peterson, J. L.; Ralph, J.; Rygg, J. R.

2015-05-01

Recent experiments at the National Ignition Facility [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] have explored driving high-density carbon ablators with near-vacuum hohlraums, which use a minimal amount of helium gas fill. These hohlraums show improved efficiency relative to conventional gas-filled hohlraums in terms of minimal backscatter, minimal generation of suprathermal electrons, and increased hohlraum-capsule coupling. Given these advantages, near-vacuum hohlraums are a promising choice for pursuing high neutron yield implosions. Long pulse symmetry control, though, remains a challenge, as the hohlraum volume fills with material. Two mitigation methodologies have been explored, dynamic beam phasing and increased case-to-capsule ratio (larger hohlraum size relative to capsule). Unexpectedly, experiments have demonstrated that the inner laser beam propagation is better than predicted by nominal simulations, and an enhanced beam propagation model is required to match measured hot spot symmetry. Ongoing work is focused on developing a physical model which captures this enhanced propagation and on utilizing the enhanced propagation to drive longer laser pulses than originally predicted in order to reach alpha-heating dominated neutron yields.

High performance capsule implosions on the OMEGA Laser facility with rugby hohlraumsa)

NASA Astrophysics Data System (ADS)

Robey, H. F.; Amendt, P.; Park, H.-S.; Town, R. P. J.; Milovich, J. L.; Döppner, T.; Hinkel, D. E.; Wallace, R.; Sorce, C.; Strozzi, D. J.; Philippe, F.; Casner, A.; Caillaud, T.; Landoas, O.; Liberatore, S.; Monteil, M.-C.; Séguin, F.; Rosenberg, M.; Li, C. K.; Petrasso, R.; Glebov, V.; Stoeckl, C.; Nikroo, A.; Giraldez, E.

2010-05-01

Rugby-shaped hohlraums have been proposed as a method for x-ray drive enhancement for indirectly driven capsule implosions. This concept has recently been tested in a series of shots on the OMEGA laser facility [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)]. In this paper, experimental results are presented comparing the performance of D2-filled capsules between standard cylindrical Au hohlraums and rugby-shaped hohlraums. The rugby hohlraums demonstrated 18% more x-ray drive energy as compared with the cylinders, and the high-performance design of these implosions (both cylinder and rugby) also provided ≈20× more deuterium (DD) neutrons than any previous indirectly driven campaign on OMEGA and ≈3× more than ever achieved on NOVA [E. M. Campbell, Laser Part. Beams 9, 209 (1991)] implosions driven with nearly twice the laser energy. This increase in performance enables, for the first time, a measurement of the neutron burn history and imaging of the neutron core shapes in an indirectly driven implosion. Previous DD neutron yields had been too low to register this key measurement of capsule performance and the effects of dynamic mix. A wealth of additional data on the fuel areal density from the suite of charged particle diagnostics was obtained on a subset of the shots that used D H3e rather than D2 fuel. Comparisons of the experimental results with numerical simulations are shown to be in very good agreement. The design techniques employed in this campaign, e.g., smaller laser entrance holes and hohlraum case-to-capsule ratios, provide added confidence in the pursuit of ignition on the National Ignition Facility [J. D. Lindl, P. Amendt, R. L. Berger et al., Phys. Plasmas 11, 339 (2004)].

High Performance Capsule Implosions on the Omega Laser Facility with Rugby Hohlraums

NASA Astrophysics Data System (ADS)

Robey, Harry F.

2009-11-01

Rugby-shaped hohlraums have been proposed as a method for x-ray drive enhancement for indirectly-driven capsule implosions [1]. This concept has recently been tested in a series of shots on the OMEGA laser facility at the Laboratory for Laser Energetics at the University of Rochester. In this talk, experimental results are presented comparing the performance of D2-filled capsules between standard cylindrical Au hohlraums and rugby-shaped hohlraums. Not only did the rugby hohlraums demonstrate 18% more x-ray drive energy as compared with the cylinders, but the high-performance design of these implosions (both cylinder and rugby) also provided 20X more DD neutrons than any previous indirectly-driven campaign on Omega (and 3X more than ever achieved on Nova implosions driven with nearly twice the laser energy). This increase in performance enables, for the first time, a measurement of the neutron burn history of an indirectly-driven implosion. Previous DD neutron yields had been too low to register this key measurement of capsule performance and the effects of dynamic mix. A wealth of additional data on the fuel areal density from the suite of charged particle diagnostics was obtained on a subset of the shots that used D^3He rather than D2 fuel. Comparisons of the experimental results with numerical simulations are shown to be in excellent agreement. The design techniques employed in this campaign, e.g., smaller NIF-like laser entrance holes and hohlraum case-to-capsule ratios, provide added confidence in the pursuit of ignition on the National Ignition Facility. [4pt] [1] P. Amendt, C. Cerjan, D. E. Hinkel, J. L. Milovich, H.-S. Park, and H. F. Robey, ``Rugby-like hohlraum experimental designs for demonstrating x-ray drive enhancement'', Phys. Plasmas 15, 012702 (2008).

Measuring symmetry of implosions in cryogenic Hohlraums at the NIF using gated x-ray detectors (invited).

PubMed

Kyrala, G A; Dixit, S; Glenzer, S; Kalantar, D; Bradley, D; Izumi, N; Meezan, N; Landen, O L; Callahan, D; Weber, S V; Holder, J P; Glenn, S; Edwards, M J; Bell, P; Kimbrough, J; Koch, J; Prasad, R; Suter, L; Kline, J L; Kilkenny, J

2010-10-01

Ignition of imploding inertial confinement capsules requires, among other things, controlling the symmetry with high accuracy and fidelity. We have used gated x-ray imaging, with 10 μm and 70 ps resolution, to detect the x-ray emission from the imploded core of symmetry capsules at the National Ignition Facility. The measurements are used to characterize the time dependent symmetry and the x-ray bang time of the implosion from two orthogonal directions. These measurements were one of the primary diagnostics used to tune the parameters of the laser and Hohlraum to vary the symmetry and x-ray bang time of the implosion of cryogenically cooled ignition scale deuterium/helium filled plastic capsules. Here, we will report on the successful measurements performed with up to 1.2 MJ of laser energy in a fully integrated cryogenics gas-filled ignition-scale Hohlraum and capsule illuminated with 192 smoothed laser beams. We will describe the technique, the accuracy of the technique, and the results of the variation in symmetry with tuning parameters, and explain how that set was used to predictably tune the implosion symmetry as the laser energy, the laser cone wavelength separation, and the Hohlraum size were increased to ignition scales. We will also describe how to apply that technique to cryogenically layered tritium-hydrogen-deuterium capsules.

The effect of shock dynamics on compressibility of ignition-scale National Ignition Facility implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zylstra, A. B.; Frenje, J. A.; Séguin, F. H.

The effects of shock dynamics on compressibility of indirect-drive ignition-scale surrogate implosions, CH shells filled with D 3He gas, have been studied using charged-particle spectroscopy. Spectral measurements of D 3He protons produced at the shock-bang time probe the shock dynamics and in-flight characteristics of an implosion. The proton shock yield is found to vary by over an order of magnitude. A simple model relates the observed yield to incipient hot-spot adiabat, suggesting that implosions with rapid radiation-power increase during the main drive pulse may have a 2x higher hot-spot adiabat, potentially reducing compressibility. A self-consistent 1-D implosion model was usedmore » to infer the areal density (pR) and the shell center-of-mass radius (R cm) from the downshift of the shock-produced D 3He protons. The observed pR at shock-bang time is substantially higher for implosions, where the laser drive is on until near the compression bang time ('short-coast'), while longer-coasting implosions have lower pR. This corresponds to a much larger temporal difference between the shock- and compression-bang time in the long-coast implosions (~800 ps) than in the short-coast (~400 ps); this will be verified with a future direct bang-time diagnostic. This model-inferred differential bang time contradicts radiation-hydrodynamic simulations, which predict constant 700–800 ps differential independent of coasting time. This result is potentially explained by uncertainties in modeling late-time ablation drive on the capsule. In an ignition experiment, an earlier shock-bang time resulting in an earlier onset of shell deceleration, potentially reducing compression and, thus, fuel pR.« less

The effect of shock dynamics on compressibility of ignition-scale National Ignition Facility implosions

DOE PAGES

Zylstra, A. B.; Frenje, J. A.; Séguin, F. H.; ...

2014-11-03

The effects of shock dynamics on compressibility of indirect-drive ignition-scale surrogate implosions, CH shells filled with D 3He gas, have been studied using charged-particle spectroscopy. Spectral measurements of D 3He protons produced at the shock-bang time probe the shock dynamics and in-flight characteristics of an implosion. The proton shock yield is found to vary by over an order of magnitude. A simple model relates the observed yield to incipient hot-spot adiabat, suggesting that implosions with rapid radiation-power increase during the main drive pulse may have a 2x higher hot-spot adiabat, potentially reducing compressibility. A self-consistent 1-D implosion model was usedmore » to infer the areal density (pR) and the shell center-of-mass radius (R cm) from the downshift of the shock-produced D 3He protons. The observed pR at shock-bang time is substantially higher for implosions, where the laser drive is on until near the compression bang time ('short-coast'), while longer-coasting implosions have lower pR. This corresponds to a much larger temporal difference between the shock- and compression-bang time in the long-coast implosions (~800 ps) than in the short-coast (~400 ps); this will be verified with a future direct bang-time diagnostic. This model-inferred differential bang time contradicts radiation-hydrodynamic simulations, which predict constant 700–800 ps differential independent of coasting time. This result is potentially explained by uncertainties in modeling late-time ablation drive on the capsule. In an ignition experiment, an earlier shock-bang time resulting in an earlier onset of shell deceleration, potentially reducing compression and, thus, fuel pR.« less

Cryogenic thermonuclear fuel implosions on the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glenzer, S. H.; Callahan, D. A.; MacKinnon, A. J.

2012-05-15

The first inertial confinement fusion implosion experiments with equimolar deuterium-tritium thermonuclear fuel have been performed on the National Ignition Facility. These experiments use 0.17 mg of fuel with the potential for ignition and significant fusion yield conditions. The thermonuclear fuel has been fielded as a cryogenic layer on the inside of a spherical plastic capsule that is mounted in the center of a cylindrical gold hohlraum. Heating the hohlraum with 192 laser beams for a total laser energy of 1.6 MJ produces a soft x-ray field with 300 eV temperature. The ablation pressure produced by the radiation field compresses themore » initially 2.2-mm diameter capsule by a factor of 30 to a spherical dense fuel shell that surrounds a central hot-spot plasma of 50 {mu}m diameter. While an extensive set of x-ray and neutron diagnostics has been applied to characterize hot spot formation from the x-ray emission and 14.1 MeV deuterium-tritium primary fusion neutrons, thermonuclear fuel assembly is studied by measuring the down-scattered neutrons with energies in the range of 10 to 12 MeV. X-ray and neutron imaging of the compressed core and fuel indicate a fuel thickness of (14 {+-} 3) {mu}m, which combined with magnetic recoil spectrometer measurements of the fuel areal density of (1 {+-} 0.09) g cm{sup -2} result in fuel densities approaching 600 g cm{sup -3}. The fuel surrounds a hot-spot plasma with average ion temperatures of (3.5 {+-} 0.1) keV that is measured with neutron time of flight spectra. The hot-spot plasma produces a total fusion neutron yield of 10{sup 15} that is measured with the magnetic recoil spectrometer and nuclear activation diagnostics that indicate a 14.1 MeV yield of (7.5{+-}0.1) Multiplication-Sign 10{sup 14} which is 70% to 75% of the total fusion yield due to the high areal density. Gamma ray measurements provide the duration of nuclear activity of (170 {+-} 30) ps. These indirect-drive implosions result in the highest areal densities and neutron yields achieved on laser facilities to date. This achievement is the result of the first hohlraum and capsule tuning experiments where the stagnation pressures have been systematically increased by more than a factor of 10 by fielding low-entropy implosions through the control of radiation symmetry, small hot electron production, and proper shock timing. The stagnation pressure is above 100 Gbars resulting in high Lawson-type confinement parameters of P{tau} Asymptotically-Equal-To 10 atm s. Comparisons with radiation-hydrodynamic simulations indicate that the pressure is within a factor of three required for reaching ignition and high yield. This will be the focus of future higher-velocity implosions that will employ additional optimizations of hohlraum, capsule and laser pulse shape conditions.« less

Progress toward a unified kJ-machine CANDY

NASA Astrophysics Data System (ADS)

Kitagawa, Yoneyoshi; Mori, Yoshitaka; Komeda, Osamu; Hanayama, Ryohei; Ishii, Katsuhiro; Okihara, Shinichiro; Fujita, Kazuhisa; Nakayama, Suisei; Sekine, Takashi; Sato, Nakahiro; Kurita, Takashi; Kawashima, Toshiyuki; Watari, Takeshi; Kan, Hirofumi; Nakamura, Naoki; Kondo, Takuya; Fujine, Manabu; Azuma, Hirozumi; Motohiro, Tomoyoshi; Hioki, Tatsumi; Kakeno, Mitsutaka; Nishimura, Yasuhiko; Sunahara, Atsushi; Sentoku, Yasuhiko; Miura, Eisuke; Arikawa, Yasunobu; Nagai, Takahiro; Abe, Yuki; Ozaki, Satoshi; Noda, Akira

2016-03-01

To construct a unified experimental machine CANDY using a kJ DPSSL driver in the fast-ignition scheme, the Laser for Fast Ignition Experiment (LFEX) at Osaka is used, showing that the laser-driven ions heat the preimploded core of a deuterated polystyrene (CD) shell target from 0.8 keV to 2 keV, resulting in 5 x 108 DD neutrons best ever obtained in the scheme. 4-J/10-Hz DPSSL laser HAMA is for the first time applied to the CD shell implosion- core heating experiments in the fast ignition scheme to yield neutrons and also to a continuous target injection, which yields neutrons of 3 x 105 n/4πsr n/shot.

Two-Dimensional Simulations of Electron Shock Ignition at the Megajoule Scale

NASA Astrophysics Data System (ADS)

Shang, W.; Betti, R.

2016-10-01

Shock ignition uses a late strong shock to ignite the hot spot of an inertial confinement fusion capsule. In the standard shock-ignition scheme, an ignitor shock is launched by the ablation pressure from a spike in laser intensity. Recent experiments on OMEGA have shown that focused beams with intensity up to 6 ×1015 W /cm2 can produce copious amounts of hot electrons. The hot electrons are produced by laser-plasma instabilities (LPI's) and can carry up to 15 % of the instantaneous laser power. Megajoule-scale targets will likely produce even more hot electrons because of the large plasma scale length. We show that it is possible to design ignition targets with low implosion velocities that can be shock ignited using LPI-generated hot electrons to obtain high energy gains. These designs are robust to low-mode asymmetries and they ignite even for highly distorted implosions. Electron shock ignition requires tens of kilojoules of hot electrons, which can only be produced on a large laser facility like the National Ignition Facility. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Towards an Integrated Model of the NIC Layered Implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, O S; Callahan, D A; Cerjan, C J

A detailed simulation-based model of the June 2011 National Ignition Campaign (NIC) cryogenic DT experiments is presented. The model is based on integrated hohlraum-capsule simulations that utilize the best available models for the hohlraum wall, ablator, and DT equations of state and opacities. The calculated radiation drive was adjusted by changing the input laser power to match the experimentally measured shock speeds, shock merger times, peak implosion velocity, and bangtime. The crossbeam energy transfer model was tuned to match the measured time-dependent symmetry. Mid-mode mix was included by directly modeling the ablator and ice surface perturbations up to mode 60.more » Simulated experimental values were extracted from the simulation and compared against the experiment. The model adjustments brought much of the simulated data into closer agreement with the experiment, with the notable exception of the measured yields, which were 15-45% of the calculated yields.« less

Simulations of Foils Irradiated by Finite Laser Spots

NASA Astrophysics Data System (ADS)

Phillips, Lee

2006-10-01

Recent proposed designs (Obenchain et al., Phys. Plasmas 13 056320 (2006)) for direct-drive ICF targets for energy applications involve high implosion velocities with lower laser energies combined with higher irradiances. The use of high irradiances increases the likelihood of deleterious laser plasma instabilities (LPI) that may lead, for example, to the generation of fast electrons. The proposed use of a 248 nm KrF laser is expected to minimize LPI, and this is being studied by experiments on NRL's NIKE laser. Here we report on simulations aimed at designing and interpreting these experiments. The 2d simulations employ a modification of the FAST code to ablate plasma from CH and DT foils using laser pulses with arbitrary spatial and temporal profiles. These include the customary hypergaussian NIKE profile, gaussian profiles, and combinations of these. The simulations model the structure of the ablating plasma and the absorption of the laser light, providing parameters for design of the experiment and indicating where the relevant LPI (two-plasmon, Raman) may be observed.

Demonstration of Fuel Hot-Spot Pressure in Excess of 50 Gbar for Direct-Drive, Layered Deuterium-Tritium Implosions on OMEGA

NASA Astrophysics Data System (ADS)

Regan, S. P.; Goncharov, V. N.; Igumenshchev, I. V.; Sangster, T. C.; Betti, R.; Bose, A.; Boehly, T. R.; Bonino, M. J.; Campbell, E. M.; Cao, D.; Collins, T. J. B.; Craxton, R. S.; Davis, A. K.; Delettrez, J. A.; Edgell, D. H.; Epstein, R.; Forrest, C. J.; Frenje, J. A.; Froula, D. H.; Gatu Johnson, M.; Glebov, V. Yu.; Harding, D. R.; Hohenberger, M.; Hu, S. X.; Jacobs-Perkins, D.; Janezic, R.; Karasik, M.; Keck, R. L.; Kelly, J. H.; Kessler, T. J.; Knauer, J. P.; Kosc, T. Z.; Loucks, S. J.; Marozas, J. A.; Marshall, F. J.; McCrory, R. L.; McKenty, P. W.; Meyerhofer, D. D.; Michel, D. T.; Myatt, J. F.; Obenschain, S. P.; Petrasso, R. D.; Radha, P. B.; Rice, B.; Rosenberg, M. J.; Schmitt, A. J.; Schmitt, M. J.; Seka, W.; Shmayda, W. T.; Shoup, M. J.; Shvydky, A.; Skupsky, S.; Solodov, A. A.; Stoeckl, C.; Theobald, W.; Ulreich, J.; Wittman, M. D.; Woo, K. M.; Yaakobi, B.; Zuegel, J. D.

2016-07-01

A record fuel hot-spot pressure Phs=56 ±7 Gbar was inferred from x-ray and nuclear diagnostics for direct-drive inertial confinement fusion cryogenic, layered deuterium-tritium implosions on the 60-beam, 30-kJ, 351-nm OMEGA Laser System. When hydrodynamically scaled to the energy of the National Ignition Facility, these implosions achieved a Lawson parameter ˜60 % of the value required for ignition [A. Bose et al., Phys. Rev. E 93, LM15119ER (2016)], similar to indirect-drive implosions [R. Betti et al., Phys. Rev. Lett. 114, 255003 (2015)], and nearly half of the direct-drive ignition-threshold pressure. Relative to symmetric, one-dimensional simulations, the inferred hot-spot pressure is approximately 40% lower. Three-dimensional simulations suggest that low-mode distortion of the hot spot seeded by laser-drive nonuniformity and target-positioning error reduces target performance.

Demonstration of fuel hot-spot pressure in excess of 50 Gbar for direct-drive, layered deuterium-tritium implosions on OMEGA

DOE PAGES

Regan, S. P.; Goncharov, V. N.; Igumenshchev, I. V.; ...

2016-07-07

A record fuel hot-spot pressure P hs = 56±7 Gbar was inferred from x-ray and nuclear diagnostics for direct-drive inertial confinement fusion cryogenic, layered deuterium–tritium implosions on the 60-beam, 30-kJ, 351-nm OMEGA Laser System. When hydrodynamically scaled to the energy of the National Ignition Facility (NIF), these implosions achieved a Lawson parameter ~60% of the value required for ignition [A. Bose et al., Phys. Rev. E (in press)], similar to indirect-drive implosions [R. Betti et al., Phys. Rev. Lett. 114, 255003 (2015)], and nearly half of the direct-drive ignition-threshold pressure. Relative to symmetric, one-dimensional simulations, the inferred hot-spot pressure ismore » ~40% lower. Furthermore, three-dimensional simulations suggest that low-mode distortion of the hot spot seeded by laser-drive nonuniformity and target-positioning error reduces target performance.« less

Demonstration of fuel hot-spot pressure in excess of 50 Gbar for direct-drive, layered deuterium-tritium implosions on OMEGA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Regan, S. P.; Goncharov, V. N.; Igumenshchev, I. V.

A record fuel hot-spot pressure P hs = 56±7 Gbar was inferred from x-ray and nuclear diagnostics for direct-drive inertial confinement fusion cryogenic, layered deuterium–tritium implosions on the 60-beam, 30-kJ, 351-nm OMEGA Laser System. When hydrodynamically scaled to the energy of the National Ignition Facility (NIF), these implosions achieved a Lawson parameter ~60% of the value required for ignition [A. Bose et al., Phys. Rev. E (in press)], similar to indirect-drive implosions [R. Betti et al., Phys. Rev. Lett. 114, 255003 (2015)], and nearly half of the direct-drive ignition-threshold pressure. Relative to symmetric, one-dimensional simulations, the inferred hot-spot pressure ismore » ~40% lower. Furthermore, three-dimensional simulations suggest that low-mode distortion of the hot spot seeded by laser-drive nonuniformity and target-positioning error reduces target performance.« less

Electron Shock Ignition of Inertial Fusion Targets

DOE PAGES

Shang, W. L.; Betti, R.; Hu, S. X.; ...

2017-11-07

Here, it is shown that inertial fusion targets designed with low implosion velocities can be shock ignited using laser–plasma interaction generated hot electrons (hot-e) to obtain high-energy gains. These designs are robust to multimode asymmetries and are predicted to ignite even for significantly distorted implosions. Electron shock ignition requires tens of kilojoules of hot-e, which can only be produced on a large laser facility like the National Ignition Facility, with the laser to hot-e conversion efficiency greater than 10% at laser intensities ~10 16 W/cm 2.

Implosion dynamics measurements at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Hicks, D. G.; Meezan, N. B.; Dewald, E. L.; Mackinnon, A. J.; Olson, R. E.; Callahan, D. A.; Döppner, T.; Benedetti, L. R.; Bradley, D. K.; Celliers, P. M.; Clark, D. S.; Di Nicola, P.; Dixit, S. N.; Dzenitis, E. G.; Eggert, J. E.; Farley, D. R.; Frenje, J. A.; Glenn, S. M.; Glenzer, S. H.; Hamza, A. V.; Heeter, R. F.; Holder, J. P.; Izumi, N.; Kalantar, D. H.; Khan, S. F.; Kline, J. L.; Kroll, J. J.; Kyrala, G. A.; Ma, T.; MacPhee, A. G.; McNaney, J. M.; Moody, J. D.; Moran, M. J.; Nathan, B. R.; Nikroo, A.; Opachich, Y. P.; Petrasso, R. D.; Prasad, R. R.; Ralph, J. E.; Robey, H. F.; Rinderknecht, H. G.; Rygg, J. R.; Salmonson, J. D.; Schneider, M. B.; Simanovskaia, N.; Spears, B. K.; Tommasini, R.; Widmann, K.; Zylstra, A. B.; Collins, G. W.; Landen, O. L.; Kilkenny, J. D.; Hsing, W. W.; MacGowan, B. J.; Atherton, L. J.; Edwards, M. J.

2012-12-01

Measurements have been made of the in-flight dynamics of imploding capsules indirectly driven by laser energies of 1-1.7 MJ at the National Ignition Facility [Miller et al., Nucl. Fusion 44, 228 (2004)]. These experiments were part of the National Ignition Campaign [Landen et al., Phys. Plasmas 18, 051002 (2011)] to iteratively optimize the inputs required to achieve thermonuclear ignition in the laboratory. Using gated or streaked hard x-ray radiography, a suite of ablator performance parameters, including the time-resolved radius, velocity, mass, and thickness, have been determined throughout the acceleration history of surrogate gas-filled implosions. These measurements have been used to establish a dynamically consistent model of the ablative drive history and shell compressibility throughout the implosion trajectory. First results showed that the peak velocity of the original 1.3-MJ Ge-doped polymer (CH) point design using Au hohlraums reached only 75% of the required ignition velocity. Several capsule, hohlraum, and laser pulse changes were then implemented to improve this and other aspects of implosion performance and a dedicated effort was undertaken to test the sensitivity of the ablative drive to the rise time and length of the main laser pulse. Changing to Si rather than Ge-doped inner ablator layers and increasing the pulse length together raised peak velocity to 93% ± 5% of the ignition goal using a 1.5 MJ, 420 TW pulse. Further lengthening the pulse so that the laser remained on until the capsule reached 30% (rather than 60%-70%) of its initial radius, reduced the shell thickness and improved the final fuel ρR on companion shots with a cryogenic hydrogen fuel layer. Improved drive efficiency was observed using U rather than Au hohlraums, which was expected, and by slowing the rise time of laser pulse, which was not. The effect of changing the Si-dopant concentration and distribution, as well as the effect of using a larger initial shell thickness were also examined, both of which indicated that instabilities seeded at the ablation front are a significant source of hydrodynamic mix into the central hot spot. Additionally, a direct test of the surrogacy of cryogenic fuel layered versus gas-filled targets was performed. Together all these measurements have established the fundamental ablative-rocket relationship describing the dependence of implosion velocity on fractional ablator mass remaining. This curve shows a lower-than-expected ablator mass at a given velocity, making the capsule more susceptible to feedthrough of instabilities from the ablation front into the fuel and hot spot. This combination of low velocity and low ablator mass indicates that reaching ignition on the NIF will require >20 μm (˜10%) thicker targets and laser powers at or beyond facility limits.

Implosion dynamics measurements at the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hicks, D. G.; Meezan, N. B.; Dewald, E. L.

2012-12-15

Measurements have been made of the in-flight dynamics of imploding capsules indirectly driven by laser energies of 1-1.7 MJ at the National Ignition Facility [Miller et al., Nucl. Fusion 44, 228 (2004)]. These experiments were part of the National Ignition Campaign [Landen et al., Phys. Plasmas 18, 051002 (2011)] to iteratively optimize the inputs required to achieve thermonuclear ignition in the laboratory. Using gated or streaked hard x-ray radiography, a suite of ablator performance parameters, including the time-resolved radius, velocity, mass, and thickness, have been determined throughout the acceleration history of surrogate gas-filled implosions. These measurements have been used tomore » establish a dynamically consistent model of the ablative drive history and shell compressibility throughout the implosion trajectory. First results showed that the peak velocity of the original 1.3-MJ Ge-doped polymer (CH) point design using Au hohlraums reached only 75% of the required ignition velocity. Several capsule, hohlraum, and laser pulse changes were then implemented to improve this and other aspects of implosion performance and a dedicated effort was undertaken to test the sensitivity of the ablative drive to the rise time and length of the main laser pulse. Changing to Si rather than Ge-doped inner ablator layers and increasing the pulse length together raised peak velocity to 93% {+-} 5% of the ignition goal using a 1.5 MJ, 420 TW pulse. Further lengthening the pulse so that the laser remained on until the capsule reached 30% (rather than 60%-70%) of its initial radius, reduced the shell thickness and improved the final fuel {rho}R on companion shots with a cryogenic hydrogen fuel layer. Improved drive efficiency was observed using U rather than Au hohlraums, which was expected, and by slowing the rise time of laser pulse, which was not. The effect of changing the Si-dopant concentration and distribution, as well as the effect of using a larger initial shell thickness were also examined, both of which indicated that instabilities seeded at the ablation front are a significant source of hydrodynamic mix into the central hot spot. Additionally, a direct test of the surrogacy of cryogenic fuel layered versus gas-filled targets was performed. Together all these measurements have established the fundamental ablative-rocket relationship describing the dependence of implosion velocity on fractional ablator mass remaining. This curve shows a lower-than-expected ablator mass at a given velocity, making the capsule more susceptible to feedthrough of instabilities from the ablation front into the fuel and hot spot. This combination of low velocity and low ablator mass indicates that reaching ignition on the NIF will require >20 {mu}m ({approx}10%) thicker targets and laser powers at or beyond facility limits.« less

Capsule implosion optimization during the indirect-drive National Ignition Campaign

NASA Astrophysics Data System (ADS)

Landen, O. L.; Edwards, J.; Haan, S. W.; Robey, H. F.; Milovich, J.; Spears, B. K.; Weber, S. V.; Clark, D. S.; Lindl, J. D.; MacGowan, B. J.; Moses, E. I.; Atherton, J.; Amendt, P. A.; Boehly, T. R.; Bradley, D. K.; Braun, D. G.; Callahan, D. A.; Celliers, P. M.; Collins, G. W.; Dewald, E. L.; Divol, L.; Frenje, J. A.; Glenzer, S. H.; Hamza, A.; Hammel, B. A.; Hicks, D. G.; Hoffman, N.; Izumi, N.; Jones, O. S.; Kilkenny, J. D.; Kirkwood, R. K.; Kline, J. L.; Kyrala, G. A.; Marinak, M. M.; Meezan, N.; Meyerhofer, D. D.; Michel, P.; Munro, D. H.; Olson, R. E.; Nikroo, A.; Regan, S. P.; Suter, L. J.; Thomas, C. A.; Wilson, D. C.

2011-05-01

Capsule performance optimization campaigns will be conducted at the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Nucl. Fusion 44, 228 (2004)] to substantially increase the probability of ignition. The campaigns will experimentally correct for residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models using a variety of ignition capsule surrogates before proceeding to cryogenic-layered implosions and ignition experiments. The quantitative goals and technique options and down selections for the tuning campaigns are first explained. The computationally derived sensitivities to key laser and target parameters are compared to simple analytic models to gain further insight into the physics of the tuning techniques. The results of the validation of the tuning techniques at the OMEGA facility [J. M. Soures et al., Phys. Plasmas 3, 2108 (1996)] under scaled hohlraum and capsule conditions relevant to the ignition design are shown to meet the required sensitivity and accuracy. A roll-up of all expected random and systematic uncertainties in setting the key ignition laser and target parameters due to residual measurement, calibration, cross-coupling, surrogacy, and scale-up errors has been derived that meets the required budget. Finally, we show how the tuning precision will be improved after a number of shots and iterations to meet an acceptable level of residual uncertainty.

Hohlraum energetics scaling to 520 TW on the National Ignition Facilitya)

NASA Astrophysics Data System (ADS)

Kline, J. L.; Callahan, D. A.; Glenzer, S. H.; Meezan, N. B.; Moody, J. D.; Hinkel, D. E.; Jones, O. S.; MacKinnon, A. J.; Bennedetti, R.; Berger, R. L.; Bradley, D.; Dewald, E. L.; Bass, I.; Bennett, C.; Bowers, M.; Brunton, G.; Bude, J.; Burkhart, S.; Condor, A.; Di Nicola, J. M.; Di Nicola, P.; Dixit, S. N.; Doeppner, T.; Dzenitis, E. G.; Erbert, G.; Folta, J.; Grim, G.; Glenn, S.; Hamza, A.; Haan, S. W.; Heebner, J.; Henesian, M.; Hermann, M.; Hicks, D. G.; Hsing, W. W.; Izumi, N.; Jancaitis, K.; Jones, O. S.; Kalantar, D.; Khan, S. F.; Kirkwood, R.; Kyrala, G. A.; LaFortune, K.; Landen, O. L.; Lagin, L.; Larson, D.; Pape, S. Le; Ma, T.; MacPhee, A. G.; Michel, P. A.; Miller, P.; Montincelli, M.; Moore, A. S.; Nikroo, A.; Nostrand, M.; Olson, R. E.; Pak, A.; Park, H. S.; Patel, J. P.; Pelz, L.; Ralph, J.; Regan, S. P.; Robey, H. F.; Rosen, M. D.; Ross, J. S.; Schneider, M. B.; Shaw, M.; Smalyuk, V. A.; Strozzi, D. J.; Suratwala, T.; Suter, L. J.; Tommasini, R.; Town, R. P. J.; Van Wonterghem, B.; Wegner, P.; Widmann, K.; Widmayer, C.; Wilkens, H.; Williams, E. A.; Edwards, M. J.; Remington, B. A.; MacGowan, B. J.; Kilkenny, J. D.; Lindl, J. D.; Atherton, L. J.; Batha, S. H.; Moses, E.

2013-05-01

Indirect drive experiments have now been carried out with laser powers and energies up to 520 TW and 1.9 MJ. These experiments show that the energy coupling to the target is nearly constant at 84% ± 3% over a wide range of laser parameters from 350 to 520 TW and 1.2 to 1.9 MJ. Experiments at 520 TW with depleted uranium hohlraums achieve radiation temperatures of ˜330 ± 4 eV, enough to drive capsules 20 μm thicker than the ignition point design to velocities near the ignition goal of 370 km/s. A series of three symcap implosion experiments with nearly identical target, laser, and diagnostics configurations show the symmetry and drive are reproducible at the level of ±8.5% absolute and ±2% relative, respectively.

Mitigation of cross-beam energy transfer: Implication of two-state focal zooming on OMEGA

NASA Astrophysics Data System (ADS)

Froula, D. H.; Kessler, T. J.; Igumenshchev, I. V.; Betti, R.; Goncharov, V. N.; Huang, H.; Hu, S. X.; Hill, E.; Kelly, J. H.; Meyerhofer, D. D.; Shvydky, A.; Zuegel, J. D.

2013-08-01

Cross-beam energy transfer (CBET) during OMEGA low-adiabat cryogenic experiments reduces the hydrodynamic efficiency by ˜35%, which lowers the calculated one-dimensional (1-D) yield by a factor of 7. CBET can be mitigated by reducing the diameter of the laser beams relative to the target diameter. Reducing the diameter of the laser beams by 30%, after a sufficient conduction zone has been generated (two-state zooming), is predicted to maintain low-mode uniformity while recovering 90% of the kinetic energy lost to CBET. A radially varying phase plate is proposed to implement two-state zooming on OMEGA. A beam propagating through the central half-diameter of the phase plate will produce a large spot, while a beam propagating through the outer annular region of the phase plate will produce a narrower spot. To generate the required two-state near-field laser-beam profile, a picket driver with smoothing by spectral dispersion (SSD) would pass through an apodizer, forming a beam of half the standard diameter. A second main-pulse driver would co-propagate without SSD through its own apodizer, forming a full-diameter annular beam. Hydrodynamic simulations, using the designed laser spots produced by the proposed zooming scheme on OMEGA, show that implementing zooming will increase the implosion velocity by 25% resulting in a 4.5× increase in the 1-D neutron yield. Demonstrating zooming on OMEGA would validate a viable direct-drive CBET mitigation scheme and help establish a pathway to hydrodynamically equivalent direct-drive-ignition implosions by increasing the ablation pressure (1.6×), which will allow for more stable implosions at ignition-relevant velocities.

Performance of beryllium targets with full-scale capsules in low-fill 6.72-mm hohlraums on the National Ignition Facility

DOE PAGES

Simakov, A. N.; Wilson, D. C.; Yi, S. A.; ...

2017-05-10

When used with 1.06-mm beryllium (Be) capsules on the National Ignition Facility, gold hohlraums with the inner diameter of 5.75 mm and helium gas fill density of 1.6 mg/cm 3 exhibit significant drive degradation due to laser energy backscatter (of order 14%–17%) and “missing” X-ray drive energy (about 32% during the main pulse). Also, hard to simulate cross-beam energy transfer (CBET) must be used to control the implosion symmetry. Larger, 6.72-mm hohlraums with fill densities ≤0.6 mg/cm 3 generally offer improved drive efficiency, reduced hot-electron preheat, and better control of the implosion symmetry without CBET. Recently, we carried out anmore » exploratory campaign to evaluate performance of 1.06-mm Be capsules in such hohlraums and determine optimal hohlraum parameters. Specifically, we performed in this paper a hohlraum fill-density scan with a three-shock, 9.5-ns laser pulse and found that an appropriate axial laser repointing and azimuthal outer-quad splitting resulted in significantly improved hohlraum energetics at fill densities ≤0.3 mg/cm 3 (with backscattered and “missing” energies being of about 5% and 23% of the total laser energy, respectively). The capsule shape at stagnation was slightly oblate and improved with lowering the fill density. We also performed an implosion with a lower-picket, 12.6-ns pulse at the hohlraum fill density of 0.15 mg/cm 3 to observe comparable hohlraum energetics (about 3% of backscattered and 27% of “missing” energy) but an even more oblate implosion shape. Finally, achieving symmetric implosions of 1.06-mm Be capsules in low-fill, 6.72-mm gold hohlraums with reasonably low-adiabat pulses may not be feasible. However, symmetric implosions have recently been successfully demonstrated in such hohlraums with 0.8-mm Be capsules.« less

Analysis of staged Z-pinch implosion trajectories from experiments on Zebra

NASA Astrophysics Data System (ADS)

Ross, Mike P.; Conti, F.; Darling, T. W.; Ruskov, E.; Valenzuela, J.; Wessel, F. J.; Beg, F.; Narkis, J.; Rahman, H. U.

2017-10-01

The Staged Z-pinch plasma confinement concept relies on compressing an annular liner of high-Z plasma onto a target plasma column of deuterium fuel. The interface between the liner and target is stable against the Magneto-Rayleigh-Taylor Instability, which leads to effective fuel compression and makes the concept interesting as a potential fusion reactor. The liner initiates as a neutral gas puff, while the target plasma is a partially ionized (Zeff < 10 percent column ejected from a coaxial plasma gun. The Zebra pulsed power generator (1 MA peak current, 100 ns rise time) provides the discharge that ionizes the liner and drives the Z-pinch implosion. Diverse diagnostics observe the 100-300 km/s implosions including silicon diodes, photo-conducting detectors (PCDs), laser shadowgraphy, an XUV framing camera, and a visible streak camera. The imaging diagnostics track instabilities smaller than 0.1 mm, and Z-pinch diameters below 2.5 mm are seen at peak compression. This poster correlates the data from these diagnostics to elucidate implosion behavior dependencies on liner gas, liner pressure, target pressure, and applied, axial-magnetic field. Funded by the Advanced Research Projects Agency - Energy, DE-AR0000569.

Influence and measurement of mass ablation in ICF implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spears, B K; Hicks, D; Velsko, C

2007-09-05

Point design ignition capsules designed for the National Ignition Facility (NIF) currently use an x-ray-driven Be(Cu) ablator to compress the DT fuel. Ignition specifications require that the mass of unablated Be(Cu), called residual mass, be known to within 1% of the initial ablator mass when the fuel reaches peak velocity. The specifications also require that the implosion bang time, a surrogate measurement for implosion velocity, be known to +/- 50 ps RMS. These specifications guard against several capsule failure modes associated with low implosion velocity or low residual mass. Experiments designed to measure and to tune experimentally the amount ofmore » residual mass are being developed as part of the National Ignition Campaign (NIC). Tuning adjustments of the residual mass and peak velocity can be achieved using capsule and laser parameters. We currently plan to measure the residual mass using streaked radiographic imaging of surrogate tuning capsules. Alternative techniques to measure residual mass using activated Cu debris collection and proton spectrometry have also been developed. These developing techniques, together with bang time measurements, will allow us to tune ignition capsules to meet NIC specs.« less

Radiation characteristics and implosion dynamics of tungsten wire array Z-pinches on the YANG accelerator

NASA Astrophysics Data System (ADS)

Huang, Xian-Bin; Yang, Li-Bing; Li, Jing; Zhou, Shao-Tong; Ren, Xiao-Dong; Zhang, Si-Qun; Dan, Jia-Kun; Cai, Hong-Chun; Duan, Shu-Chao; Chen, Guang-Hua; Zhang, Zheng-Wei; Ouyang, Kai; Li, Jun; Zhang, Zhao-Hui; Zhou, Rong-Guo; Wang, Gui-Lin

2012-05-01

We investigated the radiation characteristics and implosion dynamics of low-wire-number cylindrical tungsten wire array Z-pinches on the YANG accelerator with a peak current 0.8-1.1 MA and a rising time ~ 90 ns. The arrays are made up of (8-32) × 5 μm wires 6/10 mm in diameter and 15 mm in height. The highest X-ray power obtained in the experiments was about 0.37 TW with the total radiation energy ~ 13 kJ and the energy conversion efficiency ~ 9% (24 × 5 μm wires, 6 mm in diameter). Most of the X-ray emissions from tungsten Z-pinch plasmas were distributed in the spectral band of 100-600 eV, peaked at 250 and 375 eV. The dominant wavelengths of the wire ablation and the magneto-Rayleigh—Taylor instability were found and analyzed through measuring the time-gated self-emission and laser interferometric images. Through analyzing the implosion trajectories obtained by an optical streak camera, the run-in velocities of the Z-pinch plasmas at the end of the implosion phase were determined to be about (1.3-2.1) × 107 cm/s.

Theoretical and simulation research of hydrodynamic instabilities in inertial-confinement fusion implosions

NASA Astrophysics Data System (ADS)

Wang, LiFeng; Ye, WenHua; He, XianTu; Wu, JunFeng; Fan, ZhengFeng; Xue, Chuang; Guo, HongYu; Miao, WenYong; Yuan, YongTeng; Dong, JiaQin; Jia, Guo; Zhang, Jing; Li, YingJun; Liu, Jie; Wang, Min; Ding, YongKun; Zhang, WeiYan

2017-05-01

Inertial fusion energy (IFE) has been considered a promising, nearly inexhaustible source of sustainable carbon-free power for the world's energy future. It has long been recognized that the control of hydrodynamic instabilities is of critical importance for ignition and high-gain in the inertial-confinement fusion (ICF) hot-spot ignition scheme. In this mini-review, we summarize the progress of theoretical and simulation research of hydrodynamic instabilities in the ICF central hot-spot implosion in our group over the past decade. In order to obtain sufficient understanding of the growth of hydrodynamic instabilities in ICF, we first decompose the problem into different stages according to the implosion physics processes. The decomposed essential physics pro- cesses that are associated with ICF implosions, such as Rayleigh-Taylor instability (RTI), Richtmyer-Meshkov instability (RMI), Kelvin-Helmholtz instability (KHI), convergent geometry effects, as well as perturbation feed-through are reviewed. Analyti- cal models in planar, cylindrical, and spherical geometries have been established to study different physical aspects, including density-gradient, interface-coupling, geometry, and convergent effects. The influence of ablation in the presence of preheating on the RTI has been extensively studied by numerical simulations. The KHI considering the ablation effect has been discussed in detail for the first time. A series of single-mode ablative RTI experiments has been performed on the Shenguang-II laser facility. The theoretical and simulation research provides us the physical insights of linear and weakly nonlinear growths, and nonlinear evolutions of the hydrodynamic instabilities in ICF implosions, which has directly supported the research of ICF ignition target design. The ICF hot-spot ignition implosion design that uses several controlling features, based on our current understanding of hydrodynamic instabilities, to address shell implosion stability, has been briefly described, several of which are novel.

First Measurements of Deuterium-Tritium and Deuterium-Deuterium Fusion Reaction Yields in Ignition-Scalable Direct-Drive Implosions

NASA Astrophysics Data System (ADS)

Forrest, C. J.; Radha, P. B.; Knauer, J. P.; Glebov, V. Yu.; Goncharov, V. N.; Regan, S. P.; Rosenberg, M. J.; Sangster, T. C.; Shmayda, W. T.; Stoeckl, C.; Gatu Johnson, M.

2017-03-01

The deuterium-tritium (D-T) and deuterium-deuterium neutron yield ratio in cryogenic inertial confinement fusion (ICF) experiments is used to examine multifluid effects, traditionally not included in ICF modeling. This ratio has been measured for ignition-scalable direct-drive cryogenic DT implosions at the Omega Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997), 10.1016/S0030-4018(96)00325-2] using a high-dynamic-range neutron time-of-flight spectrometer. The experimentally inferred yield ratio is consistent with both the calculated values of the nuclear reaction rates and the measured preshot target-fuel composition. These observations indicate that the physical mechanisms that have been proposed to alter the fuel composition, such as species separation of the hydrogen isotopes [D. T. Casey et al., Phys. Rev. Lett. 108, 075002 (2012), 10.1103/PhysRevLett.108.075002], are not significant during the period of peak neutron production in ignition-scalable cryogenic direct-drive DT implosions.

Evaluating the MMI diagnostic on OMEGA direct-drive shots

NASA Astrophysics Data System (ADS)

Baumgaertel, J. A.; Bradley, P. A.; Cobble, J. A.; Fincke, J.; Hakel, P.; Hsu, S. C.; Kanzleiter, R.; Krasheninnikova, N. S.; Murphy, T. J.; Schmitt, M. J.; Shah, R.; Tregillis, I.; Obrey, K.; Mancini, R. C.; Joshi, T.; Johns, H.; Mayes, D.

2013-10-01

The Defect-Induced Mix Experiment (DIME) project utilized Multiple Monochromatic Imagers (MMI) on symmetric and polar direct-drive shots conducted on the OMEGA laser. The MMI provides spatially and spectrally resolved data of capsule implosions and resultant dopant emissions. The capsules had radii of 430 μm, with CH shells that included an inner layer doped with 1-2 atom % Ti, and a gas fill of 5 atm deuterium. Simulations of the target implosion by codes HYDRA and RAGE are post-processed with self-emission and MMI synthetic diagnostic tools and quantitatively compared to the MMI data to determine the utility of using it for mix model validation. MMI data shows the location of dopants, which are used to diagnose mix. Sensitivities of synthetic MMI images and yield to laser drive and mix levels are explored. Finally, RAGE results, clean and with mix, are compared with time-dependent streak camera data. This work is supported by US DOE/NNSA, performed at LANL, operated by LANS LLC under contract DE-AC52-06NA25396.

Observation of Compressible Plasma Mix in Cylindrically Convergent Implosions

NASA Astrophysics Data System (ADS)

Barnes, Cris W.; Batha, Steven H.; Lanier, Nicholas E.; Magelssen, Glenn R.; Tubbs, David L.; Dunne, A. M.; Rothman, Steven R.; Youngs, David L.

2000-10-01

An understanding of hydrodynamic mix in convergent geometry will be of key importance in the development of a robust ignition/burn capability on NIF, LMJ and future pulsed power machines. We have made use of the OMEGA laser facility at the University of Rochester to investigate directly the mix evolution in a convergent geometry, compressible plasma regime. The experiments comprise a plastic cylindrical shell imploded by direct laser irradiation. The cylindrical shell surrounds a lower density plastic foam which provides sufficient back pressure to allow the implosion to stagnate at a sufficiently high radius to permit quantitative radiographic diagnosis of the interface evolution near turnaround. The susceptibility to mix of the shell-foam interface is varied by choosing different density material for the inner shell surface (thus varying the Atwood number). This allows the study of shock-induced Richtmyer-Meshkov growth during the coasting phase, and Rayleigh-Taylor growth during the stagnation phase. The experimental results will be described along with calculational predictions using various radiation hydrodynamics codes and turbulent mix models.

Finite Atwood Number Effects on Deceleration-Phase Instability in Room-Temperature Direct-Drive Implosions

NASA Astrophysics Data System (ADS)

Miller, S.; Knauer, J. P.; Radha, P. B.; Goncharov, V. N.

2017-10-01

Performance degradation in direct-drive inertial confinement fusion implosions can be caused by several effects, one of which is Rayleigh-Taylor (RT) instability growth during the deceleration phase. In room-temperature plastic target implosions, this deceleration-phase RT growth is enhanced by the density discontinuity and finite Atwood numbers at the fuel-pusher interface. For the first time, an experimental campaign at the Omega Laser Facility systematically varied the ratio of deuterium-to-tritium (D-to-T) within the DT gas fill to change the Atwood number. The goal of the experiment was to understand the effects of Atwood number variation on observables like apparent ion temperature, yield, and variations in areal density and bulk fluid motion, which lead to broadening of neutron spectra along different lines of sight. Simulations by the hydrodynamic codes LILAC and DRACO were used to study growth rates for different D-to-T ratios and identify observable quantities effected by Atwood number variation. Results from simulations and the experiment are presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Direct-drive inertial confinement fusion: A review

DOE Office of Scientific and Technical Information (OSTI.GOV)

Craxton, R. S.; Anderson, K. S.; Boehly, T. R.

The direct-drive, laser-based approach to inertial confinement fusion (ICF) is reviewed from its inception following the demonstration of the first laser to its implementation on the present generation of high-power lasers. The review focuses on the evolution of scientific understanding gained from target-physics experiments in many areas, identifying problems that were demonstrated and the solutions implemented. The review starts with the basic understanding of laser–plasma interactions that was obtained before the declassification of laser-induced compression in the early 1970s and continues with the compression experiments using infrared lasers in the late 1970s that produced thermonuclear neutrons. The problem of suprathermalmore » electrons and the target preheat that they caused, associated with the infrared laser wavelength, led to lasers being built after 1980 to operate at shorter wavelengths, especially 0.35 μm—the third harmonic of the Nd:glass laser—and 0.248 μm (the KrF gas laser). The main physics areas relevant to direct drive are reviewed. The primary absorption mechanism at short wavelengths is classical inverse bremsstrahlung. Nonuniformities imprinted on the target by laser irradiation have been addressed by the development of a number of beam-smoothing techniques and imprint-mitigation strategies. The effects of hydrodynamic instabilities are mitigated by a combination of imprint reduction and target designs that minimize the instability growth rates. Several coronal plasma physics processes are reviewed. The two-plasmon–decay instability, stimulated Brillouin scattering (together with cross-beam energy transfer), and (possibly) stimulated Raman scattering are identified as potential concerns, placing constraints on the laser intensities used in target designs, while other processes (self-focusing and filamentation, the parametric decay instability, and magnetic fields), once considered important, are now of lesser concern for mainline direct-drive target concepts. Filamentation is largely suppressed by beam smoothing. Thermal transport modeling, important to the interpretation of experiments and to target design, has been found to be nonlocal in nature. Advances in shock timing and equation-of-state measurements relevant to direct-drive ICF are reported. Room-temperature implosions have provided an increased understanding of the importance of stability and uniformity. The evolution of cryogenic implosion capabilities, leading to an extensive series carried out on the 60-beam OMEGA laser [Boehly et al., Opt. Commun. 133, 495 (1997)], is reviewed together with major advances in cryogenic target formation. A polar-drive concept has been developed that will enable direct-drive–ignition experiments to be performed on the National Ignition Facility [Haynam et al., Appl. Opt. 46(16), 3276 (2007)]. The advantages offered by the alternative approaches of fast ignition and shock ignition and the issues associated with these concepts are described. The lessons learned from target-physics and implosion experiments are taken into account in ignition and high-gain target designs for laser wavelengths of 1/3 μm and 1/4 μm. Substantial advances in direct-drive inertial fusion reactor concepts are reviewed. Overall, the progress in scientific understanding over the past five decades has been enormous, to the point that inertial fusion energy using direct drive shows significant promise as a future environmentally attractive energy source.« less

Direct-drive inertial confinement fusion: A review

DOE PAGES

Craxton, R. S.; Anderson, K. S.; Boehly, T. R.; ...

2015-11-25

In this study, the direct-drive, laser-based approach to inertial confinement fusion (ICF) is reviewed from its inception following the demonstration of the first laser to its implementation on the present generation of high-power lasers. The review focuses on the evolution of scientific understanding gained from target-physics experiments in many areas, identifying problems that were demonstrated and the solutions implemented. The review starts with the basic understanding of laser–plasma interactions that was obtained before the declassification of laser-induced compression in the early 1970s and continues with the compression experiments using infrared lasers in the late 1970s that produced thermonuclear neutrons. Themore » problem of suprathermal electrons and the target preheat that they caused, associated with the infrared laser wavelength, led to lasers being built after 1980 to operate at shorter wavelengths, especially 0.35 um—the third harmonic of the Nd:glass laser—and 0.248 um (the KrF gas laser). The main physics areas relevant to direct drive are reviewed. The primary absorption mechanism at short wavelengths is classical inverse bremsstrahlung. Nonuniformities imprinted on the target by laser irradiation have been addressed by the development of a number of beam-smoothing techniques and imprint-mitigation strategies. The effects of hydrodynamic instabilities are mitigated by a combination of imprint reduction and target designs that minimize the instability growth rates. Several coronal plasma physics processes are reviewed. The two-plasmon–decay instability, stimulated Brillouin scattering (together with cross-beam energy transfer), and (possibly) stimulated Raman scattering are identified as potential concerns, placing constraints on the laser intensities used in target designs, while other processes (self-focusing and filamentation, the parametric decay instability, and magnetic fields), once considered important, are now of lesser concern for mainline direct-drive target concepts. Filamentation is largely suppressed by beam smoothing. Thermal transport modeling, important to the interpretation of experiments and to target design, has been found to be non-local in nature. Advances in shock timing and equation-of-state measurements relevant to direct-drive ICF are reported. Room-temperature implosions have provided an increased understanding of the importance of stability and uniformity. The evolution of cryogenic implosion capabilities, leading to an extensive series carried out on the 60-beam OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)], is reviewed together with major advances in cryogenic target formation. A polar-drive concept has been developed that will enable direct-drive–ignition experiments to be performed on the National Ignition Facility [C. A. Haynam et al., Appl. Opt. 46 (16), 3276 (2007)]. The advantages offered by the alternative approaches of fast ignition and shock ignition and the issues associated with these concepts are described. The lessons learned from target-physics and implosion experiments are taken into account in ignition and high-gain target designs for laser wavelengths of 1/3 μm and 1/4 μm. Substantial advances in direct-drive inertial fusion reactor concepts are reviewed. Overall, the progress in scientific understanding over the past five decades has been enormous, to the point that inertial fusion energy using direct drive shows significant promise as a future environmentally attractive energy source.« less

Direct-drive inertial confinement fusion: A review

DOE Office of Scientific and Technical Information (OSTI.GOV)

Craxton, R. S.; Anderson, K. S.; Boehly, T. R.

In this study, the direct-drive, laser-based approach to inertial confinement fusion (ICF) is reviewed from its inception following the demonstration of the first laser to its implementation on the present generation of high-power lasers. The review focuses on the evolution of scientific understanding gained from target-physics experiments in many areas, identifying problems that were demonstrated and the solutions implemented. The review starts with the basic understanding of laser–plasma interactions that was obtained before the declassification of laser-induced compression in the early 1970s and continues with the compression experiments using infrared lasers in the late 1970s that produced thermonuclear neutrons. Themore » problem of suprathermal electrons and the target preheat that they caused, associated with the infrared laser wavelength, led to lasers being built after 1980 to operate at shorter wavelengths, especially 0.35 um—the third harmonic of the Nd:glass laser—and 0.248 um (the KrF gas laser). The main physics areas relevant to direct drive are reviewed. The primary absorption mechanism at short wavelengths is classical inverse bremsstrahlung. Nonuniformities imprinted on the target by laser irradiation have been addressed by the development of a number of beam-smoothing techniques and imprint-mitigation strategies. The effects of hydrodynamic instabilities are mitigated by a combination of imprint reduction and target designs that minimize the instability growth rates. Several coronal plasma physics processes are reviewed. The two-plasmon–decay instability, stimulated Brillouin scattering (together with cross-beam energy transfer), and (possibly) stimulated Raman scattering are identified as potential concerns, placing constraints on the laser intensities used in target designs, while other processes (self-focusing and filamentation, the parametric decay instability, and magnetic fields), once considered important, are now of lesser concern for mainline direct-drive target concepts. Filamentation is largely suppressed by beam smoothing. Thermal transport modeling, important to the interpretation of experiments and to target design, has been found to be non-local in nature. Advances in shock timing and equation-of-state measurements relevant to direct-drive ICF are reported. Room-temperature implosions have provided an increased understanding of the importance of stability and uniformity. The evolution of cryogenic implosion capabilities, leading to an extensive series carried out on the 60-beam OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)], is reviewed together with major advances in cryogenic target formation. A polar-drive concept has been developed that will enable direct-drive–ignition experiments to be performed on the National Ignition Facility [C. A. Haynam et al., Appl. Opt. 46 (16), 3276 (2007)]. The advantages offered by the alternative approaches of fast ignition and shock ignition and the issues associated with these concepts are described. The lessons learned from target-physics and implosion experiments are taken into account in ignition and high-gain target designs for laser wavelengths of 1/3 μm and 1/4 μm. Substantial advances in direct-drive inertial fusion reactor concepts are reviewed. Overall, the progress in scientific understanding over the past five decades has been enormous, to the point that inertial fusion energy using direct drive shows significant promise as a future environmentally attractive energy source.« less

Three-dimensional hydrodynamic simulations of OMEGA implosions

DOE PAGES

Igumenshchev, I. V.; Michel, D. T.; Shah, R. C.; ...

2017-03-30

Here, the effects of large-scale (with Legendre modes ≲10) asymmetries in OMEGA direct-drive implosions caused by laser illumination nonuniformities (beam-power imbalance and beam mispointing and mistiming), target offset, and variation in target-layer thickness were investigated using the low-noise, three-dimensional Eulerian hydrodynamic code ASTER. Simulations indicate that these asymmetries can significantly degrade the implosion performance. The most important sources of the asymmetries are the target offsets (~10 to 20 μm), beam-power imbalance (σ rms ~ 10%), and variations (~5%) in target-layer thickness. Large-scale asymmetries distort implosion cores, resulting in a reduced hot-spot confinement and an increased residual kinetic energy of implosionmore » targets. The ion temperature inferred from the width of simulated neutron spectra is influenced by bulk fuel motion in the distorted hot spot and can result in up to an ~1 -keV increase in apparent temperature. Similar temperature variations along different lines of sight are observed. Demonstrating hydrodynamic equivalence to ignition designs on OMEGA requires a reduction in large-scale target and laser-imposed nonuniformities, minimizing target offset, and employing highly efficient mid-adiabat (α = 4) implosion designs, which mitigate cross-beam energy transfer and suppress short-wavelength Rayleigh–Taylor growth.« less

Three-dimensional hydrodynamic simulations of OMEGA implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Igumenshchev, I. V.; Michel, D. T.; Shah, R. C.

Here, the effects of large-scale (with Legendre modes ≲10) asymmetries in OMEGA direct-drive implosions caused by laser illumination nonuniformities (beam-power imbalance and beam mispointing and mistiming), target offset, and variation in target-layer thickness were investigated using the low-noise, three-dimensional Eulerian hydrodynamic code ASTER. Simulations indicate that these asymmetries can significantly degrade the implosion performance. The most important sources of the asymmetries are the target offsets (~10 to 20 μm), beam-power imbalance (σ rms ~ 10%), and variations (~5%) in target-layer thickness. Large-scale asymmetries distort implosion cores, resulting in a reduced hot-spot confinement and an increased residual kinetic energy of implosionmore » targets. The ion temperature inferred from the width of simulated neutron spectra is influenced by bulk fuel motion in the distorted hot spot and can result in up to an ~1 -keV increase in apparent temperature. Similar temperature variations along different lines of sight are observed. Demonstrating hydrodynamic equivalence to ignition designs on OMEGA requires a reduction in large-scale target and laser-imposed nonuniformities, minimizing target offset, and employing highly efficient mid-adiabat (α = 4) implosion designs, which mitigate cross-beam energy transfer and suppress short-wavelength Rayleigh–Taylor growth.« less

Demonstration of Fuel Hot-Spot Pressure in Excess of 50 Gbar for Direct-Drive, Layered Deuterium-Tritium Implosions on OMEGA.

PubMed

Regan, S P; Goncharov, V N; Igumenshchev, I V; Sangster, T C; Betti, R; Bose, A; Boehly, T R; Bonino, M J; Campbell, E M; Cao, D; Collins, T J B; Craxton, R S; Davis, A K; Delettrez, J A; Edgell, D H; Epstein, R; Forrest, C J; Frenje, J A; Froula, D H; Gatu Johnson, M; Glebov, V Yu; Harding, D R; Hohenberger, M; Hu, S X; Jacobs-Perkins, D; Janezic, R; Karasik, M; Keck, R L; Kelly, J H; Kessler, T J; Knauer, J P; Kosc, T Z; Loucks, S J; Marozas, J A; Marshall, F J; McCrory, R L; McKenty, P W; Meyerhofer, D D; Michel, D T; Myatt, J F; Obenschain, S P; Petrasso, R D; Radha, P B; Rice, B; Rosenberg, M J; Schmitt, A J; Schmitt, M J; Seka, W; Shmayda, W T; Shoup, M J; Shvydky, A; Skupsky, S; Solodov, A A; Stoeckl, C; Theobald, W; Ulreich, J; Wittman, M D; Woo, K M; Yaakobi, B; Zuegel, J D

2016-07-08

A record fuel hot-spot pressure P_{hs}=56±7  Gbar was inferred from x-ray and nuclear diagnostics for direct-drive inertial confinement fusion cryogenic, layered deuterium-tritium implosions on the 60-beam, 30-kJ, 351-nm OMEGA Laser System. When hydrodynamically scaled to the energy of the National Ignition Facility, these implosions achieved a Lawson parameter ∼60% of the value required for ignition [A. Bose et al., Phys. Rev. E 93, 011201(R) (2016)], similar to indirect-drive implosions [R. Betti et al., Phys. Rev. Lett. 114, 255003 (2015)], and nearly half of the direct-drive ignition-threshold pressure. Relative to symmetric, one-dimensional simulations, the inferred hot-spot pressure is approximately 40% lower. Three-dimensional simulations suggest that low-mode distortion of the hot spot seeded by laser-drive nonuniformity and target-positioning error reduces target performance.

Mitigation of cross-beam energy transfer in symmetric implosions on OMEGA using wavelength detuning

DOE PAGES

Edgell, D. H.; Follett, R. K.; Igumenshchev, I. V.; ...

2017-06-13

The effects of frequency detuning laser beams in direct-drive symmetric implosions were investigated with a 3-D cross-beam energy transfer (CBET) model. Our model shows that interactions between beams with relative angles between 45° and 90° are most significant for CBET in OMEGA direct-drive implosions. There is no net exchange in power between beams but there is significant redistribution of power from the ingoing central portion of the beam profile to the outgoing edge as it is exiting the plasma, reducing the total absorbed power. Furthermore, redistribution of laser power because of CBET increases the root-mean-square (rms) absorption nonuniformity by anmore » order of magnitude. CBET mitigation by shifting relative wavelengths of three groups of laser beams fed by each of the different beamlines was modeled. At an on-target wavelength shift of Δλ ~ 10 Å, the total laser absorption was maximized, and the rms absorption nonuniformity was near minimum. In order to completely decouple the three groups of beams from each other requires wavelength shifts Δλ > 30 Å.« less

Mitigation of cross-beam energy transfer in symmetric implosions on OMEGA using wavelength detuning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Edgell, D. H.; Follett, R. K.; Igumenshchev, I. V.

The effects of frequency detuning laser beams in direct-drive symmetric implosions were investigated with a 3-D cross-beam energy transfer (CBET) model. Our model shows that interactions between beams with relative angles between 45° and 90° are most significant for CBET in OMEGA direct-drive implosions. There is no net exchange in power between beams but there is significant redistribution of power from the ingoing central portion of the beam profile to the outgoing edge as it is exiting the plasma, reducing the total absorbed power. Furthermore, redistribution of laser power because of CBET increases the root-mean-square (rms) absorption nonuniformity by anmore » order of magnitude. CBET mitigation by shifting relative wavelengths of three groups of laser beams fed by each of the different beamlines was modeled. At an on-target wavelength shift of Δλ ~ 10 Å, the total laser absorption was maximized, and the rms absorption nonuniformity was near minimum. In order to completely decouple the three groups of beams from each other requires wavelength shifts Δλ > 30 Å.« less

Symmetry control using beam phasing in ~0.2 NIF scale high temperature Hohlraum experiment on OMEGA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Delamater, Norman D; Wilson, Goug C; Kyrala, George A

2009-01-01

Results are shown from recent experiments at the Omega laser facility, using 40 Omega beams driving the hohlraum with 3 cones from each side and up to 19.5 kJ of laser energy. Beam phasing is achieved by decreasing the energy separately in each of the three cones, by 3 kJ, for a total drive energy of 16.5kJ. This results in a more asymmetric drive, which will vary the shape of the imploded symmetry capsule core from round to oblate or prolate in a systematic and controlled manner. These results would be the first demonstration of beam phasing for implosions inmore » such 'high temperature' (275 eV) hohlraums at Omega. Dante measurements confirmed the predicted peak drive temperatures of 275 eV. Implosion core time dependent x-ray images were obtained from framing camera data which show the expected change in symmetry due to beam phasing and which also agree well with post processed hydro code calculations. Time resolved hard x-ray data has been obtained and it was found that the hard x-rays are correlated mainly with the low angle 21{sup o} degree cone.« less

Diagnostics for Magnetically Driven Implosions on the 1-MA MAIZE Facility

NASA Astrophysics Data System (ADS)

Campbell, Paul; Yager-Elorriaga, David; Miller, Stephanie; Woolstrum, Jeff; Jones, Michael; Jordan, Nicholas; Lau, Y. Y.; Gilgenbach, Ronald; McBride, Ryan

2017-10-01

The Michigan Accelerator for Inductive Z-pinch Experiments (MAIZE) is a 3-m-diameter Linear Transformer Driver (LTD) at the University of Michigan which supplies a fast electrical pulse (0-1 MA in 100 ns, for matched loads) to various experimental configurations. In order to better investigate these loads, new diagnostics are being developed. First, an EUV/XUV micro-channel plate pinhole camera and a UV laser imaging system are being implemented to better observe the instability structures that form during implosions. Second, an x-pinch radiography diagnostic is being developed to probe deeper into the plasma loads. Third, Rogowski coils are being developed for enhanced load current measurements. Finally, a bolometry system and photo-conducting diamond (PCD) detectors will be implemented to measure x-ray power and energy. These new systems, combined with the existing twelve-frame laser shadowgraphy, and b-dot current monitors, will be powerful tools for the investigation of imploding z-pinch experiments. This research was supported by the DOE through award DE-SC0012328, Sandia National Laboratories contract DE-NA0003525, the National Science Foundation, and a Nuclear Regulatory Commission new-faculty development Grant. D.Y.E. was supported by an NSF fello.

Increased nuclear energy yields from the fast implosion of cold shells driven by nonlinear laser plasma interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hora, H.

1976-02-01

The nonlinear interaction force between intense laser fields and cold plasma shells efficiently transforms radiant energy into mechanical energy of implosion. This transfer of energy has been considered before in numerical experiments and it is treated here analytically in a didactic example starting with an inhomogeneous Rayleigh density profile. Up to 50% of the laser energy can be transformed into the energy of compression if a single ''untailored'' pulse of 2.5 x 10/sup 16/ W/cm/sup 2/ intensity and of only a few picosecond duration is used for spherical illumination of a shell. If the pulse is short enough to reducemore » collisional thermalization, then the collapse and compression of the plasma can remain at the threshold of Fermi degeneracy and still be adiabatic. This results in nuclear reaction gains G, based on the deposited energy, E/sub 0/, and without ..cap alpha..-particle reheating, of G=400 for E/sub 0/=2.25 kJ ((D--T reaction), 900 kJ (D--D), 13 MJ (H--B). About 1000 times less laser energy is necessary than in the case of gas dynamic ablation resulting in the same nuclear reaction yields. (AIP)« less

Interplay of Laser-Plasma Interactions and Inertial Fusion Hydrodynamics.

PubMed

Strozzi, D J; Bailey, D S; Michel, P; Divol, L; Sepke, S M; Kerbel, G D; Thomas, C A; Ralph, J E; Moody, J D; Schneider, M B

2017-01-13

The effects of laser-plasma interactions (LPI) on the dynamics of inertial confinement fusion hohlraums are investigated via a new approach that self-consistently couples reduced LPI models into radiation-hydrodynamics numerical codes. The interplay between hydrodynamics and LPI-specifically stimulated Raman scatter and crossed-beam energy transfer (CBET)-mostly occurs via momentum and energy deposition into Langmuir and ion acoustic waves. This spatially redistributes energy coupling to the target, which affects the background plasma conditions and thus, modifies laser propagation. This model shows reduced CBET and significant laser energy depletion by Langmuir waves, which reduce the discrepancy between modeling and data from hohlraum experiments on wall x-ray emission and capsule implosion shape.

Relationship between symmetry and laser pulse shape in low-fill hohlraums at the National Ignition Facility

NASA Astrophysics Data System (ADS)

MacLaren, Steve; Zylstra, A. B.; Yi, A.; Kline, J. L.; Kyrala, G. A.; Kot, L. B.; Loomis, E. N.; Perry, T. S.; Shah, R. C.; Masse, L. P.; Ralph, J. E.; Khan, S. F.

2017-10-01

Typically in indirect-drive inertial confinement fusion (ICF) hohlraums cryogenic helium gas fill is used to impede the motion of the hohlraum wall plasma as it is driven by the laser pulse. A fill of 1 mg/cc He has been used to significantly suppress wall motion in ICF hohlraums at the National Ignition Facility (NIF); however, this level of fill also causes laser-plasma instabilities (LPI) which result in hot electrons, time-dependent symmetry swings and reduction in drive due to increased backscatter. There are currently no adequate models for these phenomena in codes used to simulate integrated ICF experiments. A better compromise is a fill in the range of 0.3 0.6 mg/cc, which has been shown to provide some reduction in wall motion without incurring significant LPI effects. The wall motion in these low-fill hohlraums and the resulting effect on symmetry due to absorption of the inner cone beams by the outer cone plasma can be simulated with some degree of accuracy with the hydrodynamics and inverse Bremsstrahlung models in ICF codes. We describe a series of beryllium capsule implosions in 0.3 mg/cc He fill hohlraums that illustrate the effect of pulse shape on implosion symmetry in the ``low-fill'' regime. In particular, we find the shape of the beginning or ``foot'' of the pulse has significant leverage over the final symmetry of the stagnated implosion. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.

First downscattered neutron images from Inertial Confinement Fusion experiments at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Guler, Nevzat; Aragonez, Robert J.; Archuleta, Thomas N.; Batha, Steven H.; Clark, David D.; Clark, Deborah J.; Danly, Chris R.; Day, Robert D.; Fatherley, Valerie E.; Finch, Joshua P.; Gallegos, Robert A.; Garcia, Felix P.; Grim, Gary; Hsu, Albert H.; Jaramillo, Steven A.; Loomis, Eric N.; Mares, Danielle; Martinson, Drew D.; Merrill, Frank E.; Morgan, George L.; Munson, Carter; Murphy, Thomas J.; Oertel, John A.; Polk, Paul J.; Schmidt, Derek W.; Tregillis, Ian L.; Valdez, Adelaida C.; Volegov, Petr L.; Wang, Tai-Sen F.; Wilde, Carl H.; Wilke, Mark D.; Wilson, Douglas C.; Atkinson, Dennis P.; Bower, Dan E.; Drury, Owen B.; Dzenitis, John M.; Felker, Brian; Fittinghoff, David N.; Frank, Matthias; Liddick, Sean N.; Moran, Michael J.; Roberson, George P.; Weiss, Paul; Buckles, Robert A.; Cradick, Jerry R.; Kaufman, Morris I.; Lutz, Steve S.; Malone, Robert M.; Traille, Albert

2013-11-01

Inertial Confinement Fusion experiments at the National Ignition Facility (NIF) are designed to understand and test the basic principles of self-sustaining fusion reactions by laser driven compression of deuterium-tritium (DT) filled cryogenic plastic (CH) capsules. The experimental campaign is ongoing to tune the implosions and characterize the burning plasma conditions. Nuclear diagnostics play an important role in measuring the characteristics of these burning plasmas, providing feedback to improve the implosion dynamics. The Neutron Imaging (NI) diagnostic provides information on the distribution of the central fusion reaction region and the surrounding DT fuel by collecting images at two different energy bands for primary (13-15 MeV) and downscattered (10-12 MeV) neutrons. From these distributions, the final shape and size of the compressed capsule can be estimated and the symmetry of the compression can be inferred. The first downscattered neutron images from imploding ICF capsules are shown in this paper.

Monochromatic x-ray radiography for areal-density measurement of inertial fusion energy fuel in fast ignition experiment.

PubMed

Fujioka, Shinsuke; Fujiwara, Takashi; Tanabe, Minoru; Nishimura, Hiroaki; Nagatomo, Hideo; Ohira, Shinji; Inubushi, Yuichi; Shiraga, Hiroyuki; Azechi, Hiroshi

2010-10-01

Ultrafast, two-dimensional x-ray imaging is an important diagnostics for the inertial fusion energy research, especially in investigating implosion dynamics at the final stage of the fuel compression. Although x-ray radiography was applied to observing the implosion dynamics, intense x-rays emitted from the high temperature and dense fuel core itself are often superimposed on the radiograph. This problem can be solved by coupling the x-ray radiography with monochromatic x-ray imaging technique. In the experiment, 2.8 or 5.2 keV backlight x-rays emitted from laser-irradiated polyvinyl chloride or vanadium foils were selectively imaged by spherically bent quartz crystals with discriminating the out-of-band emission from the fuel core. This x-ray radiography system achieved 24 μm and 100 ps of spatial and temporal resolutions, respectively.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hurricane, O. A.; Thomas, C.; Olson, R.

Recent data on implosions using identical hohlraums and very similar laser drives underscores the conundrum of making a clear choice of one ablator over another. Table I shows a comparison of Be and CH in a nominal length, gold, 575 μm-diameter, 1.6 mg/cc He gas-fill hohlraum while Table II shows a comparison of undoped HDC and CH in a +700 length, gold, 575 μm diameter, 1.6 mg/cc He gas fill hohlraum. As can be seen in the tables, the net integrated fusion performance of these ablators is the same to within error bars. In the case of the undoped HDCmore » and CH ablators, the hot spot shapes of the implosions were nearly indistinguishable for the experiments listed in Table II.« less

Thin Shell, High Velocity Inertial Confinement Fusion Implosions on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Ma, T.; Hurricane, O. A.; Callahan, D. A.; Barrios, M. A.; Casey, D. T.; Dewald, E. L.; Dittrich, T. R.; Döppner, T.; Haan, S. W.; Hinkel, D. E.; Berzak Hopkins, L. F.; Le Pape, S.; MacPhee, A. G.; Pak, A.; Park, H.-S.; Patel, P. K.; Remington, B. A.; Robey, H. F.; Salmonson, J. D.; Springer, P. T.; Tommasini, R.; Benedetti, L. R.; Bionta, R.; Bond, E.; Bradley, D. K.; Caggiano, J.; Celliers, P.; Cerjan, C. J.; Church, J. A.; Dixit, S.; Dylla-Spears, R.; Edgell, D.; Edwards, M. J.; Field, J.; Fittinghoff, D. N.; Frenje, J. A.; Gatu Johnson, M.; Grim, G.; Guler, N.; Hatarik, R.; Herrmann, H. W.; Hsing, W. W.; Izumi, N.; Jones, O. S.; Khan, S. F.; Kilkenny, J. D.; Knauer, J.; Kohut, T.; Kozioziemski, B.; Kritcher, A.; Kyrala, G.; Landen, O. L.; MacGowan, B. J.; Mackinnon, A. J.; Meezan, N. B.; Merrill, F. E.; Moody, J. D.; Nagel, S. R.; Nikroo, A.; Parham, T.; Ralph, J. E.; Rosen, M. D.; Rygg, J. R.; Sater, J.; Sayre, D.; Schneider, M. B.; Shaughnessy, D.; Spears, B. K.; Town, R. P. J.; Volegov, P. L.; Wan, A.; Widmann, K.; Wilde, C. H.; Yeamans, C.

2015-04-01

Experiments have recently been conducted at the National Ignition Facility utilizing inertial confinement fusion capsule ablators that are 175 and 165 μ m in thickness, 10% and 15% thinner, respectively, than the nominal thickness capsule used throughout the high foot and most of the National Ignition Campaign. These three-shock, high-adiabat, high-foot implosions have demonstrated good performance, with higher velocity and better symmetry control at lower laser powers and energies than their nominal thickness ablator counterparts. Little to no hydrodynamic mix into the DT hot spot has been observed despite the higher velocities and reduced depth for possible instability feedthrough. Early results have shown good repeatability, with up to 1 /2 the neutron yield coming from α -particle self-heating.

Challenges Surrounding the Injection and Arrival of Targets at LIFE Fusion Chamber Center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miles, R; Spaeth, M; Manes, K

2010-12-01

IFE target designers must consider several engineering requirements in addition to the physics requirements for successful target implosion. These considerations include low target cost, high manufacturing throughput, the ability of the target to survive the injection into the fusion chamber and arrive in a condition and physical position consistent with proper laser-target interaction and ease of post-implosion debris removal. This article briefly describes these considerations for the Laser Inertial Fusion-based Energy (LIFE) targets currently being designed.

Composite x-ray pinholes for time-resolved microphotography of laser compressed targets.

PubMed

Attwood, D T; Weinstein, B W; Wuerker, R F

1977-05-01

Composite x-ray pinholes having dichroic properties are presented. These pinholes permit both x-ray imaging and visible alignment with micron accuracy by presenting different apparent apertures in these widely disparate regions of the spectrum. Their use is mandatory in certain applications in which the x-ray detection consists of a limited number of resolvable elements whose use one wishes to maximize. Mating the pinhole camera with an x-ray streaking camera is described, along with experiments which spatially and temporally resolve the implosion of laser irradiated targets.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Caillaud, T.; Landoas, O.; Briat, M.

Inertial confinement fusion (ICF) requires a high resolution ({approx}10 {mu}m) neutron imaging system to observe deuterium and tritium (DT) core implosion asymmetries. A new large (150 mm entrance diameter: scaled for Laser MegaJoule [P. A. Holstein, F. Chaland, C. Charpin, J. M. Dufour, H. Dumont, J. Giorla, L. Hallo, S. Laffite, G. Malinie, Y. Saillard, G. Schurtz, M. Vandenboomgaerde, and F. Wagon, Laser and Particle Beams 17, 403 (1999)]) neutron imaging detector has been developed for such ICF experiments. The detector has been fully characterized using a linear accelerator and a {sup 60}Co {gamma}-ray source. A penumbral aperture was usedmore » to observe DT-gas-filled target implosions performed on the OMEGA laser facility. [T. R. Boehly, D. L. Brown, R. S. Craxton, R. L. Keck, J. P. Knauer, J. H. Kelly, T. J. Kessler, S. A. Kumpan, S. J. Loucks, S. A. Letzring, F. J. Marshall, R. L. McCrory, S. F. B. Morse, W. Seka, J. M. Soures, and C. P. Verdon, Opt. Commun. 133, 495 (1997)] Neutron core images of 14 MeV with a resolution of 15 {mu}m were obtained and are compared to x-ray images of comparable resolution.« less

Development of an inertial confinement fusion platform to study charged-particle-producing nuclear reactions relevant to nuclear astrophysics

DOE PAGES

Gatu Johnson, M.; Zylstra, A. B.; Bacher, A.; ...

2017-03-28

Here, this paper describes the development of a platform to study astrophysically relevant nuclear reactions using inertial-confinement fusion implosions on the OMEGA and National Ignition Facility laser facilities, with a particular focus on optimizing the implosions to study charged-particle- producing reactions. Primary requirements on the platform are high yield, for high statistics in the fusion product measurements, combined with low areal density, to allow the charged fusion products to escape. This is optimally achieved with direct-drive exploding pusher implosions using thin-glass-shell capsules. Mitigation strategies to eliminate a possible target sheath potential which would accelerate the emitted ions are discussed. Themore » potential impact of kinetic effects on the implosions is also considered. The platform is initially employed to study the complementary T(t,2n)α, T( 3He,np)α and 3He( 3He,2p)α reactions. Proof-of-principle results from the first experiments demonstrating the ability to accurately measure the energy and yields of charged particles are presented. Lessons learned from these experiments will be used in studies of other reactions. Ultimately, the goals are to explore thermonuclear reaction rates and fundamental nuclear physics in stellarlike plasma environments, and to push this new frontier of nuclear astrophysics into unique regimes not reachable through existing platforms, with thermal ion velocity distributions, plasma screening, and low reactant energies.« less

Development of an inertial confinement fusion platform to study charged-particle-producing nuclear reactions relevant to nuclear astrophysics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gatu Johnson, M.; Zylstra, A. B.; Bacher, A.

Here, this paper describes the development of a platform to study astrophysically relevant nuclear reactions using inertial-confinement fusion implosions on the OMEGA and National Ignition Facility laser facilities, with a particular focus on optimizing the implosions to study charged-particle- producing reactions. Primary requirements on the platform are high yield, for high statistics in the fusion product measurements, combined with low areal density, to allow the charged fusion products to escape. This is optimally achieved with direct-drive exploding pusher implosions using thin-glass-shell capsules. Mitigation strategies to eliminate a possible target sheath potential which would accelerate the emitted ions are discussed. Themore » potential impact of kinetic effects on the implosions is also considered. The platform is initially employed to study the complementary T(t,2n)α, T( 3He,np)α and 3He( 3He,2p)α reactions. Proof-of-principle results from the first experiments demonstrating the ability to accurately measure the energy and yields of charged particles are presented. Lessons learned from these experiments will be used in studies of other reactions. Ultimately, the goals are to explore thermonuclear reaction rates and fundamental nuclear physics in stellarlike plasma environments, and to push this new frontier of nuclear astrophysics into unique regimes not reachable through existing platforms, with thermal ion velocity distributions, plasma screening, and low reactant energies.« less

Laser imprint reduction for the critical-density foam buffered target driven by a relatively strong foot pulse at early stage of laser implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, J. W., E-mail: li-jiwei@iapcm.ac.cn; He, X. T.; Institute of Applied Physics and Computational Mathematics, P. O. Box 8009, Beijing 100094

In order to reduce the effect of laser imprint in direct-drive ignition scheme a low-density foam buffered target has been proposed. This target is driven by a laser pulse with a low-intensity foot at the early stage of implosion, which heats the foam and elongates the thermal conduction zone between the laser absorption region and ablation front, increasing the thermal smoothing effect. In this paper, a relatively strong foot pulse is adopted to irradiate the critical-density foam buffered target. The stronger foot, near 1 × 10{sup 14 }W/cm{sup 2}, is able to drive a radiative shock in the low-density foam, which helps smoothmore » the shock and further reduce the effect of laser imprint. The radiative shock also forms a double ablation front structure between the two ablation fronts to further stabilize the hydrodynamics, achieving the similar results to a target with a high-Z dopant in the ablator. 2D analysis shows that for the critical-density foam buffered target irradiated by the strong foot pulse, the laser imprint can be reduced due to the radiative shock in the foam and an increased thermal smoothing effect. It seems viable for the critical-density foam buffered target to be driven by a relatively strong foot pulse with the goal of reducing the laser imprint and achieving better implosion symmetry in the direct-drive laser fusion.« less

Capsule implosion optimization during the indirect-drive National Ignition Campaign

DOE Office of Scientific and Technical Information (OSTI.GOV)

Landen, O. L.; Edwards, J.; Haan, S. W.

2011-05-15

Capsule performance optimization campaigns will be conducted at the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Nucl. Fusion 44, 228 (2004)] to substantially increase the probability of ignition. The campaigns will experimentally correct for residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models using a variety of ignition capsule surrogates before proceeding to cryogenic-layered implosions and ignition experiments. The quantitative goals and technique options and down selections for the tuning campaigns are first explained. The computationally derived sensitivities to key laser and target parameters are compared to simple analyticmore » models to gain further insight into the physics of the tuning techniques. The results of the validation of the tuning techniques at the OMEGA facility [J. M. Soures et al., Phys. Plasmas 3, 2108 (1996)] under scaled hohlraum and capsule conditions relevant to the ignition design are shown to meet the required sensitivity and accuracy. A roll-up of all expected random and systematic uncertainties in setting the key ignition laser and target parameters due to residual measurement, calibration, cross-coupling, surrogacy, and scale-up errors has been derived that meets the required budget. Finally, we show how the tuning precision will be improved after a number of shots and iterations to meet an acceptable level of residual uncertainty.« less

Inertial confinement fusion method producing line source radiation fluence

DOEpatents

Rose, Ronald P.

1984-01-01

An inertial confinement fusion method in which target pellets are imploded in sequence by laser light beams or other energy beams at an implosion site which is variable between pellet implosions along a line. The effect of the variability in position of the implosion site along a line is to distribute the radiation fluence in surrounding reactor components as a line source of radiation would do, thereby permitting the utilization of cylindrical geometry in the design of the reactor and internal components.

Novel characterization of capsule x-ray drive at the National Ignition Facility.

PubMed

MacLaren, S A; Schneider, M B; Widmann, K; Hammer, J H; Yoxall, B E; Moody, J D; Bell, P M; Benedetti, L R; Bradley, D K; Edwards, M J; Guymer, T M; Hinkel, D E; Hsing, W W; Kervin, M L; Meezan, N B; Moore, A S; Ralph, J E

2014-03-14

Indirect drive experiments at the National Ignition Facility are designed to achieve fusion by imploding a fuel capsule with x rays from a laser-driven hohlraum. Previous experiments have been unable to determine whether a deficit in measured ablator implosion velocity relative to simulations is due to inadequate models of the hohlraum or ablator physics. ViewFactor experiments allow for the first time a direct measure of the x-ray drive from the capsule point of view. The experiments show a 15%-25% deficit relative to simulations and thus explain nearly all of the disagreement with the velocity data. In addition, the data from this open geometry provide much greater constraints on a predictive model of laser-driven hohlraum performance than the nominal ignition target.

Laser-plasma interactions and implosion symmetry in rugby hohlraums

NASA Astrophysics Data System (ADS)

Michel, Pierre; Berger, R. L.; Lasinski, B. F.; Ross, J. S.; Divol, L.; Williams, E. A.; Meeker, D.; Langdon, B. A.; Park, H.; Amendt, P.

2011-10-01

Cross-beam energy transfer is studied in the context of ``rugby''-hohlraum experiments at the Omega laser facility in FY11, in preparation for future NIF experiments. The transfer acts in opposite direction between rugby and cylinder hohlraums due to the different beam pointing geometries and flow patterns. Its interaction with backscatter is also different as both happen in similar regions inside rugby hohlraums. We will analyze the effects of non-linearities and temporal beam smoothing on energy transfer using the code pF3d. Calculations will be compared to experiments at Omega; analysis of future rugby hohlraum experiments on NIF will also be presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

The high velocity, high adiabat, "Bigfoot" campaign and tests of indirect-drive implosion scaling

NASA Astrophysics Data System (ADS)

Casey, D. T.; Thomas, C. A.; Baker, K. L.; Spears, B. K.; Hohenberger, M.; Khan, S. F.; Nora, R. C.; Weber, C. R.; Woods, D. T.; Hurricane, O. A.; Callahan, D. A.; Berger, R. L.; Milovich, J. L.; Patel, P. K.; Ma, T.; Pak, A.; Benedetti, L. R.; Millot, M.; Jarrott, C.; Landen, O. L.; Bionta, R. M.; MacGowan, B. J.; Strozzi, D. J.; Stadermann, M.; Biener, J.; Nikroo, A.; Goyon, C. S.; Izumi, N.; Nagel, S. R.; Bachmann, B.; Volegov, P. L.; Fittinghoff, D. N.; Grim, G. P.; Yeamans, C. B.; Gatu Johnson, M.; Frenje, J. A.; Rice, N.; Kong, C.; Crippen, J.; Jaquez, J.; Kangas, K.; Wild, C.

2018-05-01

The Bigfoot approach is to intentionally trade off high convergence, and therefore areal-density, in favor of high implosion velocity and good coupling between the laser, hohlraum, shell, and hotspot. This results in a short laser pulse that improves hohlraum symmetry and predictability, while the reduced compression reduces hydrodynamic instability growth. The results thus far include demonstrated low-mode symmetry control at two different hohlraum geometries (5.75 mm and 5.4 mm diameters) and at two different target scales (5.4 mm and 6.0 mm hohlraum diameters) spanning 300-405 TW in laser power and 0.8-1.6 MJ in laser energy. Additionally, by carefully scaling the 5.4 mm design to 6.0 mm, an increase in target scale of 13%, equivalent to 40% increase in laser energy, has been demonstrated.

Interplay of Laser-Plasma Interactions and Inertial Fusion Hydrodynamics

DOE PAGES

Strozzi, D. J.; Bailey, D. S.; Michel, P.; ...

2017-01-12

The effects of laser-plasma interactions (LPI) on the dynamics of inertial confinement fusion hohlraums are investigated in this work via a new approach that self-consistently couples reduced LPI models into radiation-hydrodynamics numerical codes. The interplay between hydrodynamics and LPI—specifically stimulated Raman scatter and crossed-beam energy transfer (CBET)—mostly occurs via momentum and energy deposition into Langmuir and ion acoustic waves. This spatially redistributes energy coupling to the target, which affects the background plasma conditions and thus, modifies laser propagation. In conclusion, this model shows reduced CBET and significant laser energy depletion by Langmuir waves, which reduce the discrepancy between modeling andmore » data from hohlraum experiments on wall x-ray emission and capsule implosion shape.« less

Fast heating of ultrahigh-density plasma as a step towards laser fusion ignition.

PubMed

Kodama, R; Norreys, P A; Mima, K; Dangor, A E; Evans, R G; Fujita, H; Kitagawa, Y; Krushelnick, K; Miyakoshi, T; Miyanaga, N; Norimatsu, T; Rose, S J; Shozaki, T; Shigemori, K; Sunahara, A; Tampo, M; Tanaka, K A; Toyama, Y; Yamanaka, T; Zepf, M

2001-08-23

Modern high-power lasers can generate extreme states of matter that are relevant to astrophysics, equation-of-state studies and fusion energy research. Laser-driven implosions of spherical polymer shells have, for example, achieved an increase in density of 1,000 times relative to the solid state. These densities are large enough to enable controlled fusion, but to achieve energy gain a small volume of compressed fuel (known as the 'spark') must be heated to temperatures of about 108 K (corresponding to thermal energies in excess of 10 keV). In the conventional approach to controlled fusion, the spark is both produced and heated by accurately timed shock waves, but this process requires both precise implosion symmetry and a very large drive energy. In principle, these requirements can be significantly relaxed by performing the compression and fast heating separately; however, this 'fast ignitor' approach also suffers drawbacks, such as propagation losses and deflection of the ultra-intense laser pulse by the plasma surrounding the compressed fuel. Here we employ a new compression geometry that eliminates these problems; we combine production of compressed matter in a laser-driven implosion with picosecond-fast heating by a laser pulse timed to coincide with the peak compression. Our approach therefore permits efficient compression and heating to be carried out simultaneously, providing a route to efficient fusion energy production.

Integrated simulation of magnetic-field-assist fast ignition laser fusion

NASA Astrophysics Data System (ADS)

Johzaki, T.; Nagatomo, H.; Sunahara, A.; Sentoku, Y.; Sakagami, H.; Hata, M.; Taguchi, T.; Mima, K.; Kai, Y.; Ajimi, D.; Isoda, T.; Endo, T.; Yogo, A.; Arikawa, Y.; Fujioka, S.; Shiraga, H.; Azechi, H.

2017-01-01

To enhance the core heating efficiency in fast ignition laser fusion, the concept of relativistic electron beam guiding by external magnetic fields was evaluated by integrated simulations for FIREX class targets. For the cone-attached shell target case, the core heating performance deteriorates by applying magnetic fields since the core is considerably deformed and most of the fast electrons are reflected due to the magnetic mirror formed through the implosion. On the other hand, in the case of a cone-attached solid ball target, the implosion is more stable under the kilo-tesla-class magnetic field. In addition, feasible magnetic field configuration is formed through the implosion. As a result, the core heating efficiency doubles by magnetic guiding. The dependence of core heating properties on the heating pulse shot timing was also investigated for the solid ball target.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Temporal, Mauro; Canaud, Benoit; Cayzac, Witold

The alpha-particle energy deposition mechanism modifies the ignition conditions of the thermonuclear Deuterium-Tritium fusion reactions, and constitutes a key issue in achieving high gain in Inertial Confinement Fusion implosions. One-dimensional hydrodynamic calculations have been performed with the code Multi-IFE to simulate the implosion of a capsule directly irradiated by a laser beam. The diffusion approximation for the alpha energy deposition has been used to optimize three laser profiles corresponding to different implosion velocities. A Monte-Carlo package has been included in Multi-IFE to calculate the alpha energy transport, and in this case the energy deposition uses both the LP and themore » BPS stopping power models. Homothetic transformations that maintain a constant implosion velocity have been used to map out the transition region between marginally-igniting and high-gain configurations. Furthermore, the results provided by the two models have been compared and it is found that – close to the ignition threshold – in order to produce the same fusion energy, the calculations performed with the BPS model require about 10% more invested energy with respect to the LP model.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weilacher, F.; Radha, P. B., E-mail: rbah@lle.rochester.edu; Collins, T. J. B.

Ongoing polar-direct-drive (PDD) implosions on the National Ignition Facility (NIF) [J. D. Lindl and E. I. Moses, Phys. Plasmas 18, 050901 (2011)] use existing NIF hardware, including indirect-drive phase plates. This limits the performance achievable in these implosions. Spot shapes are identified that significantly improve the uniformity of PDD NIF implosions; outer surface deviation is reduced by a factor of 7 at the end of the laser pulse and hot-spot distortion is reduced by a factor of 2 when the shell has converged by a factor of ∼10. As a result, the neutron yield increases by approximately a factor ofmore » 2. This set of laser spot shapes is a combination of circular and elliptical spots, along with elliptical spot shapes modulated by an additional higher-intensity ellipse offset from the center of the beam. This combination is motivated in this paper. It is also found that this improved implosion uniformity is obtained independent of the heat conduction model. This work indicates that significant improvement in performance can be obtained robustly with the proposed spot shapes.« less

Thin shell, high velocity inertial confinement fusion implosions on the national ignition facility.

PubMed

Ma, T; Hurricane, O A; Callahan, D A; Barrios, M A; Casey, D T; Dewald, E L; Dittrich, T R; Döppner, T; Haan, S W; Hinkel, D E; Berzak Hopkins, L F; Le Pape, S; MacPhee, A G; Pak, A; Park, H-S; Patel, P K; Remington, B A; Robey, H F; Salmonson, J D; Springer, P T; Tommasini, R; Benedetti, L R; Bionta, R; Bond, E; Bradley, D K; Caggiano, J; Celliers, P; Cerjan, C J; Church, J A; Dixit, S; Dylla-Spears, R; Edgell, D; Edwards, M J; Field, J; Fittinghoff, D N; Frenje, J A; Gatu Johnson, M; Grim, G; Guler, N; Hatarik, R; Herrmann, H W; Hsing, W W; Izumi, N; Jones, O S; Khan, S F; Kilkenny, J D; Knauer, J; Kohut, T; Kozioziemski, B; Kritcher, A; Kyrala, G; Landen, O L; MacGowan, B J; Mackinnon, A J; Meezan, N B; Merrill, F E; Moody, J D; Nagel, S R; Nikroo, A; Parham, T; Ralph, J E; Rosen, M D; Rygg, J R; Sater, J; Sayre, D; Schneider, M B; Shaughnessy, D; Spears, B K; Town, R P J; Volegov, P L; Wan, A; Widmann, K; Wilde, C H; Yeamans, C

2015-04-10

Experiments have recently been conducted at the National Ignition Facility utilizing inertial confinement fusion capsule ablators that are 175 and 165  μm in thickness, 10% and 15% thinner, respectively, than the nominal thickness capsule used throughout the high foot and most of the National Ignition Campaign. These three-shock, high-adiabat, high-foot implosions have demonstrated good performance, with higher velocity and better symmetry control at lower laser powers and energies than their nominal thickness ablator counterparts. Little to no hydrodynamic mix into the DT hot spot has been observed despite the higher velocities and reduced depth for possible instability feedthrough. Early results have shown good repeatability, with up to 1/2 the neutron yield coming from α-particle self-heating.

High-Areal-Density Fuel Assembly in Direct-Drive Cryogenic Implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sangster, T.C.; Goncharov, V.N.; Radha, P.B.

The first observation of ignition-relevant areal-density deuterium from implosions of capsules with cryogenic fuel layers at ignition-relevant adiabats is reported. The experiments were performed on the 60-beam, 30-kJUV OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Neutron-averaged areal densities of 202+-7 mg/cm^2 and 182+-7 mg/cm^2 (corresponding to estimated peak fuel densities in excess of 100 g/cm^3) were inferred using an 18-kJ direct-drive pulse designed to put the converging fuel on an adiabat of 2.5. These areal densities are in good agreement with the predictions of hydrodynamic simulations indicating that the fuel adiabat can be accuratelymore » controlled under ignition-relevant conditions.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Betti, R.; Christopherson, A. R.; Spears, B. K.

Estimating the level of alpha heating and determining the onset of the burning plasma regime is essential to finding the path towards thermonuclear ignition. In a burning plasma, the alpha heating exceeds the external input energy to the plasma. Using a simple model of the implosion, it is shown that a general relation can be derived, connecting the burning plasma regime to the yield enhancement due to alpha heating and to experimentally measurable parameters such as the Lawson ignition parameter. A general alpha-heating curve is found, independent of the target and suitable to assess the performance of all laser fusionmore » experiments whether direct or indirect drive. The onset of the burning plasma regime inside the hot spot of current implosions on the National Ignition Facility requires a fusion yield of about 50 kJ.« less

Thin Shell, High Velocity Inertial Confinement Fusion Implosions on the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, T.; Hurricane, O. A.; Callahan, D. A.

Experiments have recently been conducted at the National Ignition Facility utilizing inertial confinement fusion capsule ablators that are 175 and 165 μm in thickness, 10% and 15% thinner, respectively, than the nominal thickness capsule used throughout the high foot and most of the National Ignition Campaign. These three-shock, high-adiabat, high-foot implosions have demonstrated good performance, with higher velocity and better symmetry control at lower laser powers and energies than their nominal thickness ablator counterparts. Little to no hydrodynamic mix into the DT hot spot has been observed despite the higher velocities and reduced depth for possible instability feedthrough. Earlier resultsmore » have shown good repeatability, with up to 1/2 the neutron yield coming from α-particle self-heating.« less

Simulations of fill tube effects on the implosion of high-foot NIF ignition capsules

NASA Astrophysics Data System (ADS)

Dittrich, T. R.; Hurricane, O. A.; Berzak-Hopkins, L. F.; Callahan, D. A.; Casey, D. T.; Clark, D.; Dewald, E. L.; Doeppner, T.; Haan, S. W.; Hammel, B. A.; Harte, J. A.; Hinkel, D. E.; Kozioziemski, B. J.; Kritcher, A. L.; Ma, T.; Nikroo, A.; Pak, A. E.; Parham, T. G.; Park, H.-S.; Patel, P. K.; Remington, B. A.; Salmonson, J. D.; Springer, P. T.; Weber, C. R.; Zimmerman, G. B.; Kline, J. L.

2016-05-01

Encouraging results have been obtained using a strong first shock during the implosion of carbon-based ablator ignition capsules. These “high-foot” implosion results show that capsule performance deviates from 1D expectations as laser power and energy are increased. A possible cause of this deviation is the disruption of the hot spot by jets originating in the capsule fill tube. Nominally, a 10 μm outside diameter glass (SiO2) fill tube is used in these implosions. Simulations indicate that a thin coating of Au on this glass tube may lessen the hotspot disruption. These results and other mitigation strategies will be presented.

Laser-plasma interactions in magnetized environment

NASA Astrophysics Data System (ADS)

Shi, Yuan; Qin, Hong; Fisch, Nathaniel J.

2018-05-01

Propagation and scattering of lasers present new phenomena and applications when the plasma medium becomes strongly magnetized. With mega-Gauss magnetic fields, scattering of optical lasers already becomes manifestly anisotropic. Special angles exist where coherent laser scattering is either enhanced or suppressed, as we demonstrate using a cold-fluid model. Consequently, by aiming laser beams at special angles, one may be able to optimize laser-plasma coupling in magnetized implosion experiments. In addition, magnetized scattering can be exploited to improve the performance of plasma-based laser pulse amplifiers. Using the magnetic field as an extra control variable, it is possible to produce optical pulses of higher intensity, as well as compress UV and soft x-ray pulses beyond the reach of other methods. In even stronger giga-Gauss magnetic fields, laser-plasma interaction enters a relativistic-quantum regime. Using quantum electrodynamics, we compute a modified wave dispersion relation, which enables correct interpretation of Faraday rotation measurements of strong magnetic fields.

Effects of the P2 M-band flux asymmetry of laser-driven gold Hohlraums on the implosion of ICF ignition capsule

NASA Astrophysics Data System (ADS)

Li, Yongsheng; Gu, Jianfa; Wu, Changshu; Song, Peng; Dai, Zhensheng; Li, Shuanggui; Li, Xin; Kang, Dongguo; Gu, Peijun; Zheng, Wudi; Zou, Shiyang; Ding, Yongkun; Lan, Ke; Ye, Wenhua; Zhang, Weiyan

2016-07-01

Low-mode asymmetries in the laser-indirect-drive inertial confinement fusion implosion experiments conducted on the National Ignition Facility [G. H. Miller et al., Nucl. Fusion 44, S228 (2004)] are deemed the main obstacles hindering further improvement of the nuclear performance of deuterium-tritium-layered capsules. The dominant seeds of these asymmetries include the P2 and P4 asymmetries of x-ray drives and P2 asymmetry introduced by the supporting "tent." Here, we explore the effects of another possible seed that can lead to low-mode asymmetric implosions, i.e., the M-band flux asymmetry (MFA) in laser-driven cylindrical gold Hohlraums. It is shown that the M-band flux facilitates the ablation and acceleration of the shell, and that positive P2 MFAs can result in negative P2 asymmetries of hot spots and positive P2 asymmetries of shell's ρR. An oblate or toroidal hot spot, depending on the P2 amplitude of MFA, forms at stagnation. The energy loss of such a hot spot via electron thermal conduction is seriously aggravated not only due to the enlarged hot spot surface but also due to the vortices that develop and help transferring thermal energy from the hotter center to the colder margin of such a hot spot. The cliffs of nuclear performance for the two methodologies of applying MFA (i.e., symmetric flux in the presence of MFA and MFA added for symmetric soft x-ray flux) are obtained locating at 9.5% and 5.0% of P2/P0 amplitudes, respectively.

Effects of the P2 M-band flux asymmetry of laser-driven gold Hohlraums on the implosion of ICF ignition capsule

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yongsheng; Graduate School, China Academy of Engineering Physics, Beijing 100088; Gu, Jianfa

Low-mode asymmetries in the laser-indirect-drive inertial confinement fusion implosion experiments conducted on the National Ignition Facility [G. H. Miller et al., Nucl. Fusion 44, S228 (2004)] are deemed the main obstacles hindering further improvement of the nuclear performance of deuterium-tritium-layered capsules. The dominant seeds of these asymmetries include the P2 and P4 asymmetries of x-ray drives and P2 asymmetry introduced by the supporting “tent.” Here, we explore the effects of another possible seed that can lead to low-mode asymmetric implosions, i.e., the M-band flux asymmetry (MFA) in laser-driven cylindrical gold Hohlraums. It is shown that the M-band flux facilitates themore » ablation and acceleration of the shell, and that positive P2 MFAs can result in negative P2 asymmetries of hot spots and positive P2 asymmetries of shell's ρR. An oblate or toroidal hot spot, depending on the P2 amplitude of MFA, forms at stagnation. The energy loss of such a hot spot via electron thermal conduction is seriously aggravated not only due to the enlarged hot spot surface but also due to the vortices that develop and help transferring thermal energy from the hotter center to the colder margin of such a hot spot. The cliffs of nuclear performance for the two methodologies of applying MFA (i.e., symmetric flux in the presence of MFA and MFA added for symmetric soft x-ray flux) are obtained locating at 9.5% and 5.0% of P2/P0 amplitudes, respectively.« less

In-flight observations of low-mode ρR asymmetries in NIF implosions

DOE PAGES

Zylstra, A. B.; Frenje, J. A.; Seguin, F. H.; ...

2015-05-01

Charged-particle spectroscopy is used to assess implosion symmetry in ignition-scale indirect-drive implosions for the first time. Surrogate D 3He gas-filled implosions at the National Ignition Facility produce energetic protons via D+ 3He fusion that are used to measure the implosion areal density (ρR) at the shock-bang time. By using protons produced several hundred ps before the main compression bang, the implosion is diagnosed in-flight at a convergence ratio of 3-5 just prior to peak velocity. This isolates acceleration-phase asymmetry growth. For many surrogate implosions, proton spectrometers placed at the north pole and equator reveal significant asymmetries with amplitudes routinely ≳10%,more » which are interpreted as l=2 Legendre modes. With significant expected growth by stagnation, it is likely that these asymmetries would degrade the final implosion performance. X-ray self-emission images at stagnation show asymmetries that are positively correlated with the observed in-flight asymmetries and comparable in magnitude, contradicting growth models; this suggests that the hot-spot shape does not reflect the stagnated shell shape or that significant residual kinetic energy exists at stagnation. More prolate implosions are observed when the laser drive is sustained (“no-coast”), implying a significant time-dependent asymmetry in peak drive.« less

In-flight observations of low-mode ρR asymmetries in NIF implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zylstra, A. B., E-mail: zylstra@mit.edu; Frenje, J. A.; Séguin, F. H.

2015-05-15

Charged-particle spectroscopy is used to assess implosion symmetry in ignition-scale indirect-drive implosions for the first time. Surrogate D{sup 3}He gas-filled implosions at the National Ignition Facility produce energetic protons via D+{sup 3}He fusion that are used to measure the implosion areal density (ρR) at the shock-bang time. By using protons produced several hundred ps before the main compression bang, the implosion is diagnosed in-flight at a convergence ratio of 3–5 just prior to peak velocity. This isolates acceleration-phase asymmetry growth. For many surrogate implosions, proton spectrometers placed at the north pole and equator reveal significant asymmetries with amplitudes routinely ≳10%,more » which are interpreted as ℓ=2 Legendre modes. With significant expected growth by stagnation, it is likely that these asymmetries would degrade the final implosion performance. X-ray self-emission images at stagnation show asymmetries that are positively correlated with the observed in-flight asymmetries and comparable in magnitude, contradicting growth models; this suggests that the hot-spot shape does not reflect the stagnated shell shape or that significant residual kinetic energy exists at stagnation. More prolate implosions are observed when the laser drive is sustained (“no-coast”), implying a significant time-dependent asymmetry in peak drive.« less

First Measurements of Deuterium-Tritium and Deuterium-Deuterium Fusion Reaction Yields in Ignition-Scalable Direct-Drive Implosions.

PubMed

Forrest, C J; Radha, P B; Knauer, J P; Glebov, V Yu; Goncharov, V N; Regan, S P; Rosenberg, M J; Sangster, T C; Shmayda, W T; Stoeckl, C; Gatu Johnson, M

2017-03-03

The deuterium-tritium (D-T) and deuterium-deuterium neutron yield ratio in cryogenic inertial confinement fusion (ICF) experiments is used to examine multifluid effects, traditionally not included in ICF modeling. This ratio has been measured for ignition-scalable direct-drive cryogenic DT implosions at the Omega Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)OPCOB80030-401810.1016/S0030-4018(96)00325-2] using a high-dynamic-range neutron time-of-flight spectrometer. The experimentally inferred yield ratio is consistent with both the calculated values of the nuclear reaction rates and the measured preshot target-fuel composition. These observations indicate that the physical mechanisms that have been proposed to alter the fuel composition, such as species separation of the hydrogen isotopes [D. T. Casey et al., Phys. Rev. Lett. 108, 075002 (2012)PRLTAO0031-900710.1103/PhysRevLett.108.075002], are not significant during the period of peak neutron production in ignition-scalable cryogenic direct-drive DT implosions.

Progress in detailed modelling of low foot and high foot implosion experiments on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Clark, D. S.; Weber, C. R.; Eder, D. C.; Haan, S. W.; Hammel, B. A.; Hinkel, D. E.; Jones, O. S.; Kritcher, A. L.; Marinak, M. M.; Milovich, J. L.; Patel, P. K.; Robey, H. F.; Salmonson, J. D.; Sepke, S. M.

2016-05-01

Several dozen high convergence inertial confinement fusion ignition experiments have now been completed on the National Ignition Facility (NIF). These include both “low foot” experiments from the National Ignition Campaign (NIC) and more recent “high foot” experiments. At the time of the NIC, there were large discrepancies between simulated implosion performance and experimental data. In particular, simulations over predicted neutron yields by up to an order of magnitude, and some experiments showed clear evidence of mixing of ablator material deep into the hot spot that could not be explained at the time. While the agreement between data and simulation improved for high foot implosion experiments, discrepancies nevertheless remain. This paper describes the state of detailed modelling of both low foot and high foot implosions using 1-D, 2-D, and 3-D radiation hydrodynamics simulations with HYDRA. The simulations include a range of effects, in particular, the impact of the plastic membrane used to support the capsule in the hohlraum, as well as low-mode radiation asymmetries tuned to match radiography measurements. The same simulation methodology is applied to low foot NIC implosion experiments and high foot implosions, and shows a qualitatively similar level of agreement for both types of implosions. While comparison with the experimental data remains imperfect, a reasonable level of agreement is emerging and shows a growing understanding of the high-convergence implosions being performed on NIF.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strozzi, D. J.; Bailey, D. S.; Michel, P.

The effects of laser-plasma interactions (LPI) on the dynamics of inertial confinement fusion hohlraums are investigated in this work via a new approach that self-consistently couples reduced LPI models into radiation-hydrodynamics numerical codes. The interplay between hydrodynamics and LPI—specifically stimulated Raman scatter and crossed-beam energy transfer (CBET)—mostly occurs via momentum and energy deposition into Langmuir and ion acoustic waves. This spatially redistributes energy coupling to the target, which affects the background plasma conditions and thus, modifies laser propagation. In conclusion, this model shows reduced CBET and significant laser energy depletion by Langmuir waves, which reduce the discrepancy between modeling andmore » data from hohlraum experiments on wall x-ray emission and capsule implosion shape.« less

Inline CBET Model Including SRS Backscatter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bailey, David S.

2015-06-26

Cross-beam energy transfer (CBET) has been used as a tool on the National Ignition Facility (NIF) since the first energetics experiments in 2009 to control the energy deposition in ignition hohlraums and tune the implosion symmetry. As large amounts of power are transferred between laser beams at the entrance holes of NIF hohlraums, the presence of many overlapping beat waves can lead to stochastic ion heating in the regions where laser beams overlap [P. Michel et al., Phys. Rev. Lett. 109, 195004 (2012)]. Using the CBET gains derived in this paper, we show how to implement these equations in amore » ray-based laser source for a rad-hydro code.« less

Experimental demonstration of low laser-plasma instabilities in gas-filled spherical hohlraums at laser injection angle designed for ignition target

NASA Astrophysics Data System (ADS)

Lan, Ke; Li, Zhichao; Xie, Xufei; Chen, Yao-Hua; Zheng, Chunyang; Zhai, Chuanlei; Hao, Liang; Yang, Dong; Huo, Wen Yi; Ren, Guoli; Peng, Xiaoshi; Xu, Tao; Li, Yulong; Li, Sanwei; Yang, Zhiwen; Guo, Liang; Hou, Lifei; Liu, Yonggang; Wei, Huiyue; Liu, Xiangming; Cha, Weiyi; Jiang, Xiaohua; Mei, Yu; Li, Yukun; Deng, Keli; Yuan, Zheng; Zhan, Xiayu; Zhang, Haijun; Jiang, Baibin; Zhang, Wei; Deng, Xuewei; Liu, Jie; Du, Kai; Ding, Yongkun; Wei, Xiaofeng; Zheng, Wanguo; Chen, Xiaodong; Campbell, E. M.; He, Xian-Tu

2017-03-01

Octahedral spherical hohlraums with a single laser ring at an injection angle of 55∘ are attractive concepts for laser indirect drive due to the potential for achieving the x-ray drive symmetry required for high convergence implosions. Laser-plasma instabilities, however, are a concern given the long laser propagation path in such hohlraums. Significant stimulated Raman scattering has been observed in cylindrical hohlraums with similar laser propagation paths during the ignition campaign on the National Ignition Facility (NIF). In this Rapid Communication, experiments demonstrating low levels of laser-driven plasma instability (LPI) in spherical hohlraums with a laser injection angle of 55∘ are reported and compared to that observed with cylindrical hohlraums with injection angles of 28 .5∘ and 55∘, similar to that of the NIF. Significant LPI is observed with the laser injection of 28 .5∘ in the cylindrical hohlraum where the propagation path is similar to the 55∘ injection angle for the spherical hohlraum. The experiments are performed on the SGIII laser facility with a total 0.35 -μ m incident energy of 93 kJ in a 3 nsec pulse. These experiments demonstrate the role of hohlraum geometry in LPI and demonstrate the need for systematic experiments for choosing the optimal configuration for ignition studies with indirect drive inertial confinement fusion.

Experimental demonstration of low laser-plasma instabilities in gas-filled spherical hohlraums at laser injection angle designed for ignition target.

PubMed

Lan, Ke; Li, Zhichao; Xie, Xufei; Chen, Yao-Hua; Zheng, Chunyang; Zhai, Chuanlei; Hao, Liang; Yang, Dong; Huo, Wen Yi; Ren, Guoli; Peng, Xiaoshi; Xu, Tao; Li, Yulong; Li, Sanwei; Yang, Zhiwen; Guo, Liang; Hou, Lifei; Liu, Yonggang; Wei, Huiyue; Liu, Xiangming; Cha, Weiyi; Jiang, Xiaohua; Mei, Yu; Li, Yukun; Deng, Keli; Yuan, Zheng; Zhan, Xiayu; Zhang, Haijun; Jiang, Baibin; Zhang, Wei; Deng, Xuewei; Liu, Jie; Du, Kai; Ding, Yongkun; Wei, Xiaofeng; Zheng, Wanguo; Chen, Xiaodong; Campbell, E M; He, Xian-Tu

2017-03-01

Octahedral spherical hohlraums with a single laser ring at an injection angle of 55^{∘} are attractive concepts for laser indirect drive due to the potential for achieving the x-ray drive symmetry required for high convergence implosions. Laser-plasma instabilities, however, are a concern given the long laser propagation path in such hohlraums. Significant stimulated Raman scattering has been observed in cylindrical hohlraums with similar laser propagation paths during the ignition campaign on the National Ignition Facility (NIF). In this Rapid Communication, experiments demonstrating low levels of laser-driven plasma instability (LPI) in spherical hohlraums with a laser injection angle of 55^{∘} are reported and compared to that observed with cylindrical hohlraums with injection angles of 28.5^{∘} and 55^{∘}, similar to that of the NIF. Significant LPI is observed with the laser injection of 28.5^{∘} in the cylindrical hohlraum where the propagation path is similar to the 55^{∘} injection angle for the spherical hohlraum. The experiments are performed on the SGIII laser facility with a total 0.35-μm incident energy of 93 kJ in a 3 nsec pulse. These experiments demonstrate the role of hohlraum geometry in LPI and demonstrate the need for systematic experiments for choosing the optimal configuration for ignition studies with indirect drive inertial confinement fusion.

Design of an Experiment to Observe Laser-Plasma Interactions on NIKE

NASA Astrophysics Data System (ADS)

Phillips, L.; Weaver, J.; Manheimer, W.; Zalesak, S.; Schmitt, A.; Fyfe, D.; Afeyan, B.; Charbonneau-Lefort, M.

2007-11-01

Recent proposed designs (Obenschain et al., Phys. Plasmas 13 056320 (2006)) for direct-drive ICF targets for energy applications involve high implosion velocities combined with higher laser irradiances. The use of high irradiances increases the likelihood of deleterious laser plasma instabilities (LPI) that may lead, for example, to the generation of fast electrons. The proposed use of a 248 nm KrF laser to drive these targets is expected to minimize LPI; this is being studied by experiments at NRL's NIKE facility. We used a modification of the FAST code that models laser pulses with arbitrary spatial and temporal profiles to assist in designing these experiments. The goal is to design targets and pulseshapes to create plasma conditions that will produce sufficient growth of LPI to be observable on NIKE. Using, for example, a cryogenic DT target that is heated by a brief pulse and allowed to expand freely before interacting with a second, high-intensity pulse, allows the development of long scalelengths at low electron temperatures and leads to a predicted 20-efold growth in two-plasmon amplitude.

A measurable Lawson criterion and hydro-equivalent curves for inertial confinement fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, C. D.; Betti, R.; Departments of Mechanical Engineering and Physics and Astronomy, University of Rochester, Rochester, New York 14623

2008-10-15

It is shown that the ignition condition (Lawson criterion) for inertial confinement fusion (ICF) can be cast in a form dependent on the only two parameters of the compressed fuel assembly that can be measured with existing techniques: the hot spot ion temperature (T{sub i}{sup h}) and the total areal density ({rho}R{sub tot}), which includes the cold shell contribution. A marginal ignition curve is derived in the {rho}R{sub tot}, T{sub i}{sup h} plane and current implosion experiments are compared with the ignition curve. On this plane, hydrodynamic equivalent curves show how a given implosion would perform with respect to themore » ignition condition when scaled up in the laser-driver energy. For 3<{sub n}<6 keV, an approximate form of the ignition condition (typical of laser-driven ICF) is {sub n}{sup 2.6}{center_dot}<{rho}R{sub tot}>{sub n}>50 keV{sup 2.6}{center_dot} g/cm{sup 2}, where <{rho}R{sub tot}>{sub n} and {sub n} are the burn-averaged total areal density and hot spot ion temperature, respectively. Both quantities are calculated without accounting for the alpha-particle energy deposition. Such a criterion can be used to determine how surrogate D{sub 2} and subignited DT target implosions perform with respect to the one-dimensional ignition threshold.« less

Evaluation of Wavelength Detuning to Mitigate Cross-Beam Energy Transfer Using the Nike Laser

NASA Astrophysics Data System (ADS)

McKenty, P. W.; Marozas, J. A.; Weaver, J.; Obenschain, S. P.; Schmitt, A. J.

2015-11-01

Cross-beam energy transfer (CBET) has become a serious threat to the overall success of direct-drive experiments, and especially for polar-direct-drive (PDD) ignition experiments. CBET redirects incident laser light before it can be absorbed into the target, thereby degrading overall target performance. CBET is particularly detrimental over the equator of the target, which is hydrodynamically very sensitive to such losses in the PDD configuration. A promising solution uses laser wavelength detuning between beams to shift the resonance, thereby reducing the interaction cross section between them. Testing this process for direct drive is now underway at the Nike laser at the Naval Research Laboratory. Calculations evaluating the effect CBET has on the scattered-light signals indicate such an experiment will demonstrate the benefits of wavelength detuning for direct-drive implosions. Two-dimensional simulation results will be presented, predicting the effect for both spherical and cylindrical experiments. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Low-adiabat rugby hohlraum experiments on the National Ignition Facility: Comparison with high-flux modeling and the potential for gas-wall interpenetration

NASA Astrophysics Data System (ADS)

Amendt, Peter; Ross, J. Steven; Milovich, Jose L.; Schneider, Marilyn; Storm, Erik; Callahan, Debra A.; Hinkel, Denise; Lasinski, Barbara; Meeker, Don; Michel, Pierre; Moody, John; Strozzi, David

2014-11-01

Rugby-shaped gold hohlraums driven by a nominal low-adiabat laser pulse shape have been tested on the National Ignition Facility. The rugby affords a higher coupling efficiency than a comparably sized cylinder hohlraum or, alternatively, improved drive symmetry and laser beam clearances for a larger hohlraum with similar cylinder wall area and laser energy. A first (large rugby hohlraum) shot at low energy (0.75 MJ) to test laser backscatter resulted in a moderately oblate CH capsule implosion, followed by a high energy shot (1.3 MJ) that gave a highly oblate compressed core according to both time-integrated and -resolved x-ray images. These implosions used low wavelength separation (1.0 Å) between the outer and inner cones to provide an alternative platform free of significant cross-beam energy transfer for simplified hohlraum dynamics. Post-shot 2- and 3-D radiation-hydrodynamic simulations using the high-flux model [M. D. Rosen et al., High Energy Density Phys. 7, 180 (2011)], however, give nearly round implosions for both shots, in striking contrast with observations. An analytic assessment of Rayleigh-Taylor hydrodynamic instability growth on the gold-helium gas-fill interface shows the potential for significant linear growth, saturation and transition to a highly nonlinear state. Candidate seeds for instability growth include laser speckle during the early-time laser picket episode in the presence of only partial temporal beam smoothing (1-D smoothing by spectral dispersion and polarization smoothing) and intensity modulations from quad-to-quad and beam overlap. Radiation-hydrodynamic 2-D simulations adapted to include a dynamic fall-line mix model across the unstable Au-He interface show good agreement with the observed implosion symmetry for both shots using an interface-to-fall-line penetration fraction of 100%. Physically, the potential development of an instability layer in a rugby hohlraum is tantamount to an enhanced wall motion leading to hindered inner-beam propagation, due largely to the confluence of rugby shape and low ray angles relative to the hohlraum symmetry axis. A significant inward pointing shift of 500 μm in the outer cones for the third (full energy) shot of the series was used to improve the inner-beam propagation, resulting in a nearly symmetric x-ray self-emission image of the compressed core and reduced sensitivity to mix. Comparatively low time-dependent symmetry swings were also measured, and a significantly lower hot electron fraction was measured for potentially favorable fuel adiabat control. The outer cone stimulated Brillouin scatter levels jumped significantly, but remedial measures such as the use of a boron dopant in the Au wall are planned. A continuing trend of delayed implosion times is found in rugby hohlraums, suggesting levels of unaccounted hohlraum energy (˜150-200 kJ) similar to what is inferred in cylinder hohlraums. A mix-based physical scenario is described, based on suppressed channel heat flux to the dense gold wall from a temperature-gradient reversal induced by a multispecies plasma lapse rate [P. Amendt, C. Bellei, and S. C. Wilks, Phys. Rev. Lett. 109, 075002 (2012)].

Observation of LPI Thresholds for the Nike Laser

NASA Astrophysics Data System (ADS)

Weaver, J. L.; Oh, J.; Afeyan, B.; Charbonneau-Lefort, M.; Phillips, L.; Seely, J.; Kehne, D.; Brown, C.; Obenschain, S.; Schmitt, A. J.; Feldman, U.; Holland, G.; Lehmberg, R. H.; McLean, E.; Manka, C.

2008-11-01

The Nike laser is being used to study thresholds for laser plasma instabilities (LPI) at intensities (10^15-10^16 W/cm^2) relevant to advanced implosion designs for direct drive inertial confinement fusion. The combination of short wavelength (248 nm), large bandwidth (1-2 THz), and beam smoothing by induced spatial incoherence available with this krypton-fluoride laser make these experiments unique among current facilities. This talk will present an overview of results with an emphasis on the two-plasmon decay instability (2φp). Measurements of x-rays and emission near ^1/2φo and ^3/2 φo harmonics of the laser wavelength have been collected over a wide range of intensities for both solid and foam targets. Data indicate collective multiple-angle driven excitation compatible with previous observations using solid planar targets.

Understanding the effects of laser imprint on plastic-target implosions on OMEGA

DOE PAGES

Hu, S. X.; Michel, D. T.; Davis, A. K.; ...

2016-10-03

Understanding the effects of laser imprint on target performance is critical to the success of direct-drive inertial confinement fusion. Directly measuring the disruption caused by laser imprints to the imploding shell and hot-spot formation, in comparison with multidimensional radiation–hydrodynamic simulations, can provide a clear picture of how laser nonuniformities cause target performance to degrade. With the recently developed x-ray self-emission imaging technique and the state-of-the-art physics models recently implemented in the two-dimensional hydrocode DRACO, a systematic study of laser-imprint effects on warm target implosions on OMEGA has been performed using both experimental results and simulations. By varying the laser-picket intensity,more » the imploding shells were set at different adiabats (from α = 2 to α = 6). As the shell adiabats decreased, it was observed that (1) the measured shell thickness at the time the hot spot lit up became larger than the uniform one-dimensional (1-D) predictions; (2) the hot-spot core emitted earlier than the corresponding 1-D predictions; (3) the measured neutron yield first increased then decreased as the shell adiabat α was reduced; and (4) the hot-spot size reduced as α decreased for cases where SSD (smoothing by spectral dispersion) was on but became larger for low-α shots in cases where SSD was off. Most of these experimental observations are well reproduced by DRACO simulations with laser imprints including modes up to λ max = 200. In addition, these studies identify the importance of laser imprint as the major source of degrading target performance for OMEGA implosions of adiabat α ≤ 3. Mitigating laser imprints is required to improve low-α target performance.« less

Understanding the effects of laser imprint on plastic-target implosions on OMEGA

NASA Astrophysics Data System (ADS)

Hu, S. X.; Michel, D. T.; Davis, A. K.; Betti, R.; Radha, P. B.; Campbell, E. M.; Froula, D. H.; Stoeckl, C.

2016-10-01

Understanding the effects of laser imprint on target performance is critical to the success of direct-drive inertial confinement fusion. Directly measuring the disruption caused by laser imprints to the imploding shell and hot-spot formation, in comparison with multidimensional radiation-hydrodynamic simulations, can provide a clear picture of how laser nonuniformities cause target performance to degrade. With the recently developed x-ray self-emission imaging technique and the state-of-the-art physics models recently implemented in the two-dimensional hydrocode DRACO, a systematic study of laser-imprint effects on warm target implosions on OMEGA has been performed using both experimental results and simulations. By varying the laser-picket intensity, the imploding shells were set at different adiabats (from α = 2 to α = 6). As the shell adiabats decreased, it was observed that (1) the measured shell thickness at the time the hot spot lit up became larger than the uniform one-dimensional (1-D) predictions; (2) the hot-spot core emitted earlier than the corresponding 1-D predictions; (3) the measured neutron yield first increased then decreased as the shell adiabat α was reduced; and (4) the hot-spot size reduced as α decreased for cases where SSD (smoothing by spectral dispersion) was on but became larger for low-α shots in cases where SSD was off. Most of these experimental observations are well reproduced by DRACO simulations with laser imprints including modes up to λmax = 200. These studies identify the importance of laser imprint as the major source of degrading target performance for OMEGA implosions of adiabat α ≤ 3. Mitigating laser imprints is required to improve low-α target performance.

Understanding the effects of laser imprint on plastic-target implosions on OMEGA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, S. X.; Michel, D. T.; Davis, A. K.

Understanding the effects of laser imprint on target performance is critical to the success of direct-drive inertial confinement fusion. Directly measuring the disruption caused by laser imprints to the imploding shell and hot-spot formation, in comparison with multidimensional radiation–hydrodynamic simulations, can provide a clear picture of how laser nonuniformities cause target performance to degrade. With the recently developed x-ray self-emission imaging technique and the state-of-the-art physics models recently implemented in the two-dimensional hydrocode DRACO, a systematic study of laser-imprint effects on warm target implosions on OMEGA has been performed using both experimental results and simulations. By varying the laser-picket intensity,more » the imploding shells were set at different adiabats (from α = 2 to α = 6). As the shell adiabats decreased, it was observed that (1) the measured shell thickness at the time the hot spot lit up became larger than the uniform one-dimensional (1-D) predictions; (2) the hot-spot core emitted earlier than the corresponding 1-D predictions; (3) the measured neutron yield first increased then decreased as the shell adiabat α was reduced; and (4) the hot-spot size reduced as α decreased for cases where SSD (smoothing by spectral dispersion) was on but became larger for low-α shots in cases where SSD was off. Most of these experimental observations are well reproduced by DRACO simulations with laser imprints including modes up to λ max = 200. In addition, these studies identify the importance of laser imprint as the major source of degrading target performance for OMEGA implosions of adiabat α ≤ 3. Mitigating laser imprints is required to improve low-α target performance.« less

Direct-drive inertial confinement fusion research at the Laboratory for Laser Energetics: charting the path to thermonuclear ignition

NASA Astrophysics Data System (ADS)

McCrory, R. L.; Regan, S. P.; Loucks, S. J.; Meyerhofer, D. D.; Skupsky, S.; Betti, R.; Boehly, T. R.; Craxton, R. S.; Collins, T. J. B.; Delettrez, J. A.; Edgell, D.; Epstein, R.; Fletcher, K. A.; Freeman, C.; Frenje, J. A.; Glebov, V. Yu.; Goncharov, V. N.; Harding, D. R.; Igumenshchev, I. V.; Keck, R. L.; Kilkenny, J. D.; Knauer, J. P.; Li, C. K.; Marciante, J.; Marozas, J. A.; Marshall, F. J.; Maximov, A. V.; McKenty, P. W.; Myatt, J.; Padalino, S.; Petrasso, R. D.; Radha, P. B.; Sangster, T. C.; Séguin, F. H.; Seka, W.; Smalyuk, V. A.; Soures, J. M.; Stoeckl, C.; Yaakobi, B.; Zuegel, J. D.

2005-10-01

Significant theoretical and experimental progress continues to be made at the University of Rochester's Laboratory for Laser Energetics (LLE), charting the path to direct-drive inertial confinement fusion (ICF) ignition. Direct drive offers the potential for higher-gain implosions than x-ray drive and is a leading candidate for an inertial fusion energy power plant. LLE's direct-drive ICF ignition target designs for the National Ignition Facility (NIF) are based on hot-spot ignition. A cryogenic target with a spherical DT-ice layer, within or without a foam matrix, enclosed by a thin plastic shell, will be directly irradiated with ~1.5 MJ of laser energy. Cryogenic and plastic/foam (surrogate-cryogenic) targets that are hydrodynamically scaled from these ignition target designs are imploded on the 60-beam, 30 kJ, UV OMEGA laser system to validate the key target physics issues, including energy coupling, hydrodynamic instabilities and implosion symmetry. Prospects for direct-drive ignition on the NIF are extremely favourable, even while it is in its x-ray-drive irradiation configuration, with the development of the polar-direct-drive concept. A high-energy petawatt capability is being constructed at LLE next to the existing 60-beam OMEGA compression facility. This OMEGA EP (extended performance) laser will add two short-pulse, 2.6 kJ beams to the OMEGA laser system to backlight direct-drive ICF implosions and study fast-ignition physics with focused intensities up to 6 × 1020 W cm-2.

A high-resolution integrated model of the National Ignition Campaign cryogenic layered experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, O. S.; Cerjan, C. J.; Marinak, M. M.

A detailed simulation-based model of the June 2011 National Ignition Campaign cryogenic DT experiments is presented. The model is based on integrated hohlraum-capsule simulations that utilize the best available models for the hohlraum wall, ablator, and DT equations of state and opacities. The calculated radiation drive was adjusted by changing the input laser power to match the experimentally measured shock speeds, shock merger times, peak implosion velocity, and bangtime. The crossbeam energy transfer model was tuned to match the measured time-dependent symmetry. Mid-mode mix was included by directly modeling the ablator and ice surface perturbations up to mode 60. Simulatedmore » experimental values were extracted from the simulation and compared against the experiment. Although by design the model is able to reproduce the 1D in-flight implosion parameters and low-mode asymmetries, it is not able to accurately predict the measured and inferred stagnation properties and levels of mix. In particular, the measured yields were 15%-40% of the calculated yields, and the inferred stagnation pressure is about 3 times lower than simulated.« less

Characterizing Hohlraum Plasma Conditions at the National Ignition Facility (NIF) Using X-ray Spectroscopy

NASA Astrophysics Data System (ADS)

Barrios, Maria Alejandra

2015-11-01

Improved hohlraums will have a significant impact on increasing the likelihood of indirect drive ignition at the NIF. In indirect-drive Inertial Confinement Fusion (ICF), a high-Z hohlraum converts laser power into a tailored x-ray flux that drives the implosion of a spherical capsule filled with D-T fuel. The x-radiation drive to capsule coupling sets the velocity, adiabat, and symmetry of the implosion. Previous experiments in gas-filled hohlraums determined that the laser-hohlraum energy coupling is 20-25% less than modeled, therefore identifying energy loss mechanisms that reduce the efficacy of the hohlraum drive is central to improving implosion performance. Characterizing the plasma conditions, particularly the plasma electron temperature (Te) , is critical to understanding mechanism that affect the energy coupling such as the laser plasma interactions (LPI), hohlraum x-ray conversion efficiency, and dynamic drive symmetry. The first Te measurements inside a NIF hohlraum, presented here, were achieved using K-shell X-ray spectroscopy of an Mn-Co tracer dot. The dot is deposited on a thin-walled CH capsule, centered on the hohlraum symmetry axis below the laser entrance hole (LEH) of a bottom-truncated hohlraum. The hohlraum x-ray drive ablates the dot and causes it to flow upward, towards the LEH, entering the hot laser deposition region. An absolutely calibrated streaked spectrometer with a line of sight into the LEH records the temporal history of the Mn and Co X-ray emission. The measured (interstage) Lyα/ Heα line ratios for Co and Mn and the Mn-Heα/Co-Heα isoelectronic line ratio are used to infer the local plasma Te from the atomic physics code SCRAM. Time resovled x-ray images perpendicular to the hohlraum axis record the dot expansion and trajectory into the LEH region. The temporal evolution of the measured Te and dot trajectory are compared with simulations from radiation-hydrodynamic codes. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344.

High-Areal-Density Fuel Assembly in Direct-Drive Cryogenic Implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sangster, T. C.; Goncharov, V. N.; Radha, P. B.

The first observation of ignition-relevant areal-density deuterium from implosions of capsules with cryogenic fuel layers at ignition-relevant adiabats is reported. The experiments were performed on the 60-beam, 30-kJ{sub UV} OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Neutron-averaged areal densities of 202{+-}7 mg/cm{sup 2} and 182{+-}7 mg/cm{sup 2} (corresponding to estimated peak fuel densities in excess of 100 g/cm{sup 3}) were inferred using an 18-kJ direct-drive pulse designed to put the converging fuel on an adiabat of 2.5. These areal densities are in good agreement with the predictions of hydrodynamic simulations indicating that the fuelmore » adiabat can be accurately controlled under ignition-relevant conditions.« less

Alpha Heating and Burning Plasmas in Inertial Confinement Fusion.

PubMed

Betti, R; Christopherson, A R; Spears, B K; Nora, R; Bose, A; Howard, J; Woo, K M; Edwards, M J; Sanz, J

2015-06-26

Estimating the level of alpha heating and determining the onset of the burning plasma regime is essential to finding the path towards thermonuclear ignition. In a burning plasma, the alpha heating exceeds the external input energy to the plasma. Using a simple model of the implosion, it is shown that a general relation can be derived, connecting the burning plasma regime to the yield enhancement due to alpha heating and to experimentally measurable parameters such as the Lawson ignition parameter. A general alpha-heating curve is found, independent of the target and suitable to assess the performance of all laser fusion experiments whether direct or indirect drive. The onset of the burning plasma regime inside the hot spot of current implosions on the National Ignition Facility requires a fusion yield of about 50 kJ.

Measurements of Hard X-Ray Emission Suggest Absorption Along the Path of the Inner Beams in High Foot Implosion Experiments on the NIF

NASA Astrophysics Data System (ADS)

Ralph, Joseph; Pak, Arthur; Otto, Landen; Kritcher, Andrea; Ma, Tammy; Charles, Jarrott; Callahan, Debra; Hinkel, Denise; Berzak Hopkins, Laura; Moody, John; Khan, Shahab; Doeppner, Tilo; Rygg, Ryan; Hurricane, Omar

2016-10-01

The current high foot hohlraum design fielded on the National Ignition Facility is aimed at providing uniform x-ray drive to provide a spherical implosion by lowering the gas fill from 1.6 to 0.6 mg/cc and increasing the hohlraum width from 5.75 to 6.72 mm while maintaining the same 1.8 mm capsule diameter from previous designs. These changes are intended to improve beam propagation without the need for crossed beam energy transfer. Analysis of the measurements of hard x-ray emission from the gated x-ray detector (GXD) and the static x-ray imager (SXI) looking through the laser entrance hole indicate a significant fraction of the inner beam incident energy is absorbed in the high z blow-off region (either uranium or gold) before reaching the inner wall near the equator. Comparison of inner beam absorption in this region and its effect on the implosion symmetry measurements will be presented. Additionally, the sensitivity of this absorption feature and therefore the implosion symmetry to the pulse shape, hohlraum fill pressure and fraction of energy in beams depositing energy at the hohlraum equator will be discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Hybrid strategy for increasing fusion performance and stagnation pressure in x-ray driven inertially confined fusion implosions on the NIF

NASA Astrophysics Data System (ADS)

Hurricane, O. A.; Callahan, D. A.; Edwards, M. J.; Casey, D.; Doeppner, T.; Hohenberger, M.; Hinkel, D.; Berzak Hopkins, L.; Le Pape, S.; MacLaren, S.; Masse, L.; Thomas, C.; Zylstra, A.

2017-10-01

Post NIC (2012), more stable and lower convergence implosions were developed and used as part of a `basecamp' strategy to identify obstacles to further performance. From 2013-2015 by probing away from a conservative working implosion in-steps towards conditions of higher velocity and compression, `Fuel Gain' and alpha-heating were obtained. In the process, performance cliffs unrelated to `mix' were identified the most impactful of which were symmetry control of the implosion and hydro seeded by engineering features. From 2015-2017 we focused on mitigating poor symmetry control and engineering improvements on fill-tubes and capsule mounting techniques. The results were more efficient implosions that can obtain the same performance levels as the earlier implosions, but with less laser energy. Presently, the best of these implosions is poised to step into a burning plasma state. Here, we describe the next step in our strategy that involves using the data we've acquired across parameter space to make a step to the largest symmetric implosions that can be fielded on NIF with the energy available. We describe the key principles that form the foundation of this approach. Performed under the auspices of U.S. Dept. of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

In-flight observations of low-mode ρR asymmetries in NIF implosionsa)

NASA Astrophysics Data System (ADS)

Zylstra, A. B.; Frenje, J. A.; Séguin, F. H.; Rygg, J. R.; Kritcher, A.; Rosenberg, M. J.; Rinderknecht, H. G.; Hicks, D. G.; Friedrich, S.; Bionta, R.; Meezan, N. B.; Olson, R.; Atherton, J.; Barrios, M.; Bell, P.; Benedetti, R.; Berzak Hopkins, L.; Betti, R.; Bradley, D.; Callahan, D.; Casey, D.; Collins, G.; Dewald, E. L.; Dixit, S.; Döppner, T.; Edwards, M. J.; Gatu Johnson, M.; Glenn, S.; Grim, G.; Hatchett, S.; Jones, O.; Khan, S.; Kilkenny, J.; Kline, J.; Knauer, J.; Kyrala, G.; Landen, O.; LePape, S.; Li, C. K.; Lindl, J.; Ma, T.; Mackinnon, A.; Manuel, M. J.-E.; Meyerhofer, D.; Moses, E.; Nagel, S. R.; Nikroo, A.; Parham, T.; Pak, A.; Petrasso, R. D.; Prasad, R.; Ralph, J.; Robey, H. F.; Ross, J. S.; Sangster, T. C.; Sepke, S.; Sinenian, N.; Sio, H. W.; Spears, B.; Tommasini, R.; Town, R.; Weber, S.; Wilson, D.; Yeamans, C.; Zacharias, R.

2015-05-01

Charged-particle spectroscopy is used to assess implosion symmetry in ignition-scale indirect-drive implosions for the first time. Surrogate D3He gas-filled implosions at the National Ignition Facility produce energetic protons via D+3He fusion that are used to measure the implosion areal density (ρR) at the shock-bang time. By using protons produced several hundred ps before the main compression bang, the implosion is diagnosed in-flight at a convergence ratio of 3-5 just prior to peak velocity. This isolates acceleration-phase asymmetry growth. For many surrogate implosions, proton spectrometers placed at the north pole and equator reveal significant asymmetries with amplitudes routinely ≳ 10 % , which are interpreted as ℓ = 2 Legendre modes. With significant expected growth by stagnation, it is likely that these asymmetries would degrade the final implosion performance. X-ray self-emission images at stagnation show asymmetries that are positively correlated with the observed in-flight asymmetries and comparable in magnitude, contradicting growth models; this suggests that the hot-spot shape does not reflect the stagnated shell shape or that significant residual kinetic energy exists at stagnation. More prolate implosions are observed when the laser drive is sustained ("no-coast"), implying a significant time-dependent asymmetry in peak drive.

Progress in hohlraum physics for the National Ignition Facilitya)

NASA Astrophysics Data System (ADS)

Moody, J. D.; Callahan, D. A.; Hinkel, D. E.; Amendt, P. A.; Baker, K. L.; Bradley, D.; Celliers, P. M.; Dewald, E. L.; Divol, L.; Döppner, T.; Eder, D. C.; Edwards, M. J.; Jones, O.; Haan, S. W.; Ho, D.; Hopkins, L. B.; Izumi, N.; Kalantar, D.; Kauffman, R. L.; Kilkenny, J. D.; Landen, O.; Lasinski, B.; LePape, S.; Ma, T.; MacGowan, B. J.; MacLaren, S. A.; Mackinnon, A. J.; Meeker, D.; Meezan, N.; Michel, P.; Milovich, J. L.; Munro, D.; Pak, A. E.; Rosen, M.; Ralph, J.; Robey, H. F.; Ross, J. S.; Schneider, M. B.; Strozzi, D.; Storm, E.; Thomas, C.; Town, R. P. J.; Widmann, K. L.; Kline, J.; Kyrala, G.; Nikroo, A.; Boehly, T.; Moore, A. S.; Glenzer, S. H.

2014-05-01

Advances in hohlraums for inertial confinement fusion at the National Ignition Facility (NIF) were made this past year in hohlraum efficiency, dynamic shape control, and hot electron and x-ray preheat control. Recent experiments are exploring hohlraum behavior over a large landscape of parameters by changing the hohlraum shape, gas-fill, and laser pulse. Radiation hydrodynamic modeling, which uses measured backscatter, shows that gas-filled hohlraums utilize between 60% and 75% of the laser power to match the measured bang-time, whereas near-vacuum hohlraums utilize 98%. Experiments seem to be pointing to deficiencies in the hohlraum (instead of capsule) modeling to explain most of the inefficiency in gas-filled targets. Experiments have begun quantifying the Cross Beam Energy Transfer (CBET) rate at several points in time for hohlraum experiments that utilize CBET for implosion symmetry. These measurements will allow better control of the dynamic implosion symmetry for these targets. New techniques are being developed to measure the hot electron energy and energy spectra generated at both early and late time. Rugby hohlraums offer a target which requires little to no CBET and may be less vulnerable to undesirable dynamic symmetry "swings." A method for detecting the effect of the energetic electrons on the fuel offers a direct measure of the hot electron effects as well as a means to test energetic electron mitigation methods. At higher hohlraum radiation temperatures (including near vacuum hohlraums), the increased hard x-rays (1.8-4 keV) may pose an x-ray preheat problem. Future experiments will explore controlling these x-rays with advanced wall materials.

Z-pinch Plasma Temperature and Implosion Velocity from Laboratory Plasma Jets using Thomson Scattering

NASA Astrophysics Data System (ADS)

Banasek, Jacob; Byvank, Tom; Kusse, Bruce; Hammer, David

2016-10-01

We discuss the use of collective Thomson scattering to determine the implosion velocity and other properties of laboratory plasma jets. The plasma jet is created using a 1 MA pulsed power machine with a 15 μm Al radial foil load. The Thomson scattering laser has a maximum energy of 10 J at 526.5 nm with a pulse duration of 3 ns. Using a time gated ICCD camera and spectrometer system we are able to record the scattered spectrum from 9 or 18 regions along the laser path with sub-mm spatial resolution. Collecting scattered radiation from the same area at two different angles simultaneously enables determination of both the radial and azimuthal velocities. The scattered spectrum for non-magnetized jets indicates a radial implosion velocity of 27 km/s into the jets. A determination of ion and electron temperatures from the scattered spectrum is in progress. Comparing results using a laser energy of 10 J and 1 J shows noticeable effects on plasma jet properties when using 10 J. Therefore the lower laser energy must be used to determine the plasma properties. This research is supported by the NNSA Stewardship Sciences Academic Programs under DOE Cooperative Agreement DE-NA0001836.

Review of high convergence implosion experiments with single and double shell targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Delamater, N. D.; Watt, R. G.; Varnum, W. S.

2002-01-01

Experiments have been been performed in recent years at the Omega laser studying double shell capsules as an a1 teinative, 11011 cryogenic, path towards ignition at NTF. Double shell capsules designed to mitigate the Au M-band radiation asymmetries, were experimentally found to perform well in both spherical and cylindrical hohlraums, achieving near 1-D (-90 %) clean calculated yield at convergence comparable to that required for NIF ignition. Near-term plans include directly driven double shell experiments at Omega, which eliminates Au M-band radiation as a yield degradation m ec h an i s in.

Effects of alpha stopping power modelling on the ignition threshold in a directly-driven inertial confinement fusion capsule

DOE PAGES

Temporal, Mauro; Canaud, Benoit; Cayzac, Witold; ...

2017-05-25

The alpha-particle energy deposition mechanism modifies the ignition conditions of the thermonuclear Deuterium-Tritium fusion reactions, and constitutes a key issue in achieving high gain in Inertial Confinement Fusion implosions. One-dimensional hydrodynamic calculations have been performed with the code Multi-IFE to simulate the implosion of a capsule directly irradiated by a laser beam. The diffusion approximation for the alpha energy deposition has been used to optimize three laser profiles corresponding to different implosion velocities. A Monte-Carlo package has been included in Multi-IFE to calculate the alpha energy transport, and in this case the energy deposition uses both the LP and themore » BPS stopping power models. Homothetic transformations that maintain a constant implosion velocity have been used to map out the transition region between marginally-igniting and high-gain configurations. Furthermore, the results provided by the two models have been compared and it is found that – close to the ignition threshold – in order to produce the same fusion energy, the calculations performed with the BPS model require about 10% more invested energy with respect to the LP model.« less

Investigation of the cylindrical vacuum hohlraum energy in the first implosion experiment at the SGIII laser facility

NASA Astrophysics Data System (ADS)

Zhang, Huasen; Jiang, Wei; Ge, Fengjun; Song, Peng; Zou, Shiyang; Huang, Tianxuan; Li, Sanwei; Yang, Dong; Li, Zhichao; Hou, Lifei; Guo, Liang; Che, Xingsen; Du, Huabing; Xie, Xufei; He, Xiaoan; Li, Chaoguang; Zha, Weiyi; Xu, Tao; Liu, Yonggang; Wei, Huiyue; Liu, Xiangming; Chen, Zhongjing; Zhang, Xing; Yan, Ji; Pu, Yudong; Peng, Xiaoshi; Li, Yulong; Gu, Peijun; Zheng, Wudi; Liu, Jie; Ding, Yongkun; Zhu, Shaoping

2018-02-01

The cylindrical vacuum hohlraum energy at the SGIII laser facility [X. T. He and W. Y. Zhang, Eur. Phys. J. D 44, 227 (2007) and W. Zheng et al., High Power Laser Sci. Eng. 4, e21 (2016)] is investigated for the first time. The hohlraum size and the laser energy are intermediate between the Nova and NIF typical hohlraum experiments. It is found that the SGIII hohlraum exhibits an x-ray conversion efficiency of about 85%, which is more close to that of the NIF hohlraum. The LARED simulations of the SGIII hohlraum underestimate about 15% of the radiation flux measured from the laser entrance hole, while the capsule radiation drive inferred from the x-ray bangtime is roughly consistent with the experiments. The underestimation of the SGIII hohlraum radiation flux is mainly caused by the more enclosed laser entrance hole in the LARED simulation. The comparison between the SGIII and NIF hohlraum simulations by LARED indicates that the LARED generally underestimates the measured radiation flux by 15% for the high x-ray conversion efficiency hohlraums, while it can roughly predict the capsule radiation drive inside the hohlraum.

Energy Flow in Dense Off-Equilibrium Plasma

DTIC Science & Technology

2016-07-15

akT e in our system100 i e T T Teller 1966 Smoking Gun Experiment: Laser Breakdown in COLD gas In going from room to liquid Nitrogen temperature...oflaser breakdown have revealed a new phase of off-equilibrium plasma that has a tensile strength similar to a liquid , and reduced ion-electron...approved for public release. Part 1: Energy Balance in Sonoluminescing Dense Plasma Sonoluminescence occurs from rapid implosion of gas bubbles caused to

Note: Tandem Kirkpatrick-Baez microscope with sixteen channels for high-resolution laser-plasma diagnostics

NASA Astrophysics Data System (ADS)

Yi, Shengzhen; Zhang, Zhe; Huang, Qiushi; Zhang, Zhong; Wang, Zhanshan; Wei, Lai; Liu, Dongxiao; Cao, Leifeng; Gu, Yuqiu

2018-03-01

Multi-channel Kirkpatrick-Baez (KB) microscopes, which have better resolution and collection efficiency than pinhole cameras, have been widely used in laser inertial confinement fusion to diagnose time evolution of the target implosion. In this study, a tandem multi-channel KB microscope was developed to have sixteen imaging channels with the precise control of spatial resolution and image intervals. This precise control was created using a coarse assembly of mirror pairs with high-accuracy optical prisms, followed by precise adjustment in real-time x-ray imaging experiments. The multilayers coated on the KB mirrors were designed to have substantially the same reflectivity to obtain a uniform brightness of different images for laser-plasma temperature analysis. The study provides a practicable method to achieve the optimum performance of the microscope for future high-resolution applications in inertial confinement fusion experiments.

Nuclear science experiments with a bright neutron source from fusion reactions on the OMEGA Laser System

NASA Astrophysics Data System (ADS)

Forrest, C. J.; Knauer, J. P.; Schroeder, W. U.; Glebov, V. Yu.; Radha, P. B.; Regan, S. P.; Sangster, T. C.; Sickles, M.; Stoeckl, C.; Szczepanski, J.

2018-04-01

Subnanosecond impulses of 1013 to 1014 neutrons, produced in direct-drive laser inertial confinement fusion implosions, have been used to irradiate deuterated targets at the OMEGA Laser System (Boehly et al., 1997). The target compounds include heavy water (D2O) and deuterated benzene (C6D6). Yields and energy spectra of neutrons from D(n,2n)p to study the breakup reaction have been measured at a forward angle of θlab = 3 .5∘ ± 3.5° with a sensitive, high-dynamic-range neutron time-of-flight spectrometer to infer the double-differential breakup cross section d2 σ/dE d Ω for 14-MeV D-T fusion neutrons.

Optical smoothing of laser imprinting in planar-target experiments on OMEGA EP using multi-FM 1-D smoothing by spectral dispersion

DOE PAGES

Hohenberger, M.; Shvydky, A.; Marozas, J. A.; ...

2016-09-07

Direct-drive ignition on the National Ignition Facility (NIF) requires single-beam smoothing to minimize imprinting of laser nonuniformities that can negatively affect implosion performance. One-dimensional, multi-FM smoothing by spectral dispersion (SSD) has been proposed to provide the required smoothing [J. A. Marozas, J. D. Zuegel, and T. J. B. Collins, Bull. Am. Phys. Soc. 55, 294 (2010)]. A prototype multi-FM SSD system has been integrated into the NIF-like beamline of the OMEGA EP Laser System. Experiments have been performed to verify the smoothing performance by measuring Rayleigh–Taylor growth rates in planar targets of laser-imprinted and preimposed surface modulations. Multi-FM 1-D SSDmore » has been observed to reduce imprint levels by ~50% compared to the nominal OMEGA EP SSD system. In conclusion, the experimental results are in agreement with 2-D DRACO simulations using realistic, time-dependent far-field spot-intensity calculations that emulate the effect of SSD.« less

Optical smoothing of laser imprinting in planar-target experiments on OMEGA EP using multi-FM 1-D smoothing by spectral dispersion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hohenberger, M., E-mail: mhoh@lle.rochester.edu; Shvydky, A.; Marozas, J. A.

Direct-drive ignition on the National Ignition Facility (NIF) requires single-beam smoothing to minimize imprinting of laser nonuniformities that can negatively affect implosion performance. One-dimensional, multi-FM smoothing by spectral dispersion (SSD) has been proposed to provide the required smoothing [Marozas et al., Bull. Am. Phys. Soc. 55, 294 (2010)]. A prototype multi-FM SSD system has been integrated into the NIF-like beamline of the OMEGA EP Laser System. Experiments have been performed to verify the smoothing performance by measuring Rayleigh–Taylor growth rates in planar targets of laser-imprinted and preimposed surface modulations. Multi-FM 1-D SSD has been observed to reduce imprint levels bymore » ∼50% compared to the nominal OMEGA EP SSD system. The experimental results are in agreement with 2-D DRACO simulations using realistic, time-dependent far-field spot-intensity calculations that emulate the effect of SSD.« less

Optical smoothing of laser imprinting in planar-target experiments on OMEGA EP using multi-FM 1-D smoothing by spectral dispersion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hohenberger, M.; Shvydky, A.; Marozas, J. A.

Direct-drive ignition on the National Ignition Facility (NIF) requires single-beam smoothing to minimize imprinting of laser nonuniformities that can negatively affect implosion performance. One-dimensional, multi-FM smoothing by spectral dispersion (SSD) has been proposed to provide the required smoothing [J. A. Marozas, J. D. Zuegel, and T. J. B. Collins, Bull. Am. Phys. Soc. 55, 294 (2010)]. A prototype multi-FM SSD system has been integrated into the NIF-like beamline of the OMEGA EP Laser System. Experiments have been performed to verify the smoothing performance by measuring Rayleigh–Taylor growth rates in planar targets of laser-imprinted and preimposed surface modulations. Multi-FM 1-D SSDmore » has been observed to reduce imprint levels by ~50% compared to the nominal OMEGA EP SSD system. In conclusion, the experimental results are in agreement with 2-D DRACO simulations using realistic, time-dependent far-field spot-intensity calculations that emulate the effect of SSD.« less

High density laser-driven target

DOEpatents

Lindl, John D.

1981-01-01

A high density target for implosion by laser energy composed of a central quantity of fuel surrounded by a high-Z pusher shell with a low-Z ablator-pusher shell spaced therefrom forming a region filled with low-density material.

Exploring the limits of case-to-capsule ratio, pulse length, and picket energy for symmetric hohlraum drive on the National Ignition Facility Laser

NASA Astrophysics Data System (ADS)

Callahan, D. A.; Hurricane, O. A.; Ralph, J. E.; Thomas, C. A.; Baker, K. L.; Benedetti, L. R.; Berzak Hopkins, L. F.; Casey, D. T.; Chapman, T.; Czajka, C. E.; Dewald, E. L.; Divol, L.; Döppner, T.; Hinkel, D. E.; Hohenberger, M.; Jarrott, L. C.; Khan, S. F.; Kritcher, A. L.; Landen, O. L.; LePape, S.; MacLaren, S. A.; Masse, L. P.; Meezan, N. B.; Pak, A. E.; Salmonson, J. D.; Woods, D. T.; Izumi, N.; Ma, T.; Mariscal, D. A.; Nagel, S. R.; Kline, J. L.; Kyrala, G. A.; Loomis, E. N.; Yi, S. A.; Zylstra, A. B.; Batha, S. H.

2018-05-01

We present a data-based model for low mode asymmetry in low gas-fill hohlraum experiments on the National Ignition Facility {NIF [Moses et al., Fusion Sci. Technol. 69, 1 (2016)]} laser. This model is based on the hypothesis that the asymmetry in these low fill hohlraums is dominated by the hydrodynamics of the expanding, low density, high-Z (gold or uranium) "bubble," which occurs where the intense outer cone laser beams hit the high-Z hohlraum wall. We developed a simple model which states that the implosion symmetry becomes more oblate as the high-Z bubble size becomes large compared to the hohlraum radius or the capsule size becomes large compared to the hohlraum radius. This simple model captures the trends that we see in data that span much of the parameter space of interest for NIF ignition experiments. We are now using this model as a constraint on new designs for experiments on the NIF.

Recent results from the first polar direct drive plastic capsule implosions on NIF

NASA Astrophysics Data System (ADS)

Schmitt, Mark J.

2012-10-01

Polar direct drive (PDD) offers a simplified platform for conducting strongly driven implosions on NIF to investigate mix, hydro-burn and ignition-relevant physics. Its successful use necessitates a firm understanding and predictive capability of its implosion characteristics including hydro performance, symmetry and yield. To assess this capability, the first two PDD implosions of deuterium filled CH capsules were recently conducted at NIF. The P2 Legendre mode symmetry seen in these implosions agreed with pre-shot predictions even though the 700kJ drive energy produced intensities that far exceeded thresholds for both Raman and Brillouin stimulated scattering. These shots were also the first to employ image backlighting driven by two laser quads. Preliminary results indicate that the yield from the uncoated 2.25 mm diameter, 42 μm thick, CH shells was reduced by about a factor of two owing to as-shot laser drive asymmetries. Similarly, a small (sim50 μm) centroid offset between the upper and lower shell hemispheres seen in the first shot appears to be indicative of the laser quad energies. Overall, the implosion trajectories agreed with pre-shot predictions of bangtime. The second shot incorporated an 80 ?m wide,10 ?m deep depression encircling the equator of the capsule. This engineered feature was imposed to test our capability to predict the effect of high-mode features on yield and mix. A predicted yield reduction factor of 3 was not observed.[4pt] In collaboration with P. A. Bradley, J. A. Cobble, P. Hakel, S. C. Hsu, N. S. Krasheninnikova, G. A. Kyrala, G. R. Magelssen, T. J. Murphy, K. A. Obrey, R. C. Shah, I. L. Tregillis and F. J. Wysocki of Los Alamos National Laboratory; M. Marinak, R. Wallace, T. Parham, M. Cowan, S. Glenn, R. Benedetti and the NIF Operations Team of Lawrence Livermore National Laboratory; R. S. Craxton and P. W. McKenty of the Univ. Rochester; P. Fitzsimmons and A. Nikroo of General Atomics; H. Rinderknecht, M. Rosenberg, and M. G. Johnson, MIT; Work supported by US DOE/NNSA, performed at LANL, operated by LANS LLC under contract DE-AC52-06NA25396.

On krypton-doped capsule implosion experiments at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Chen, Hui; Ma, T.; Nora, R.; Barrios, M. A.; Scott, H. A.; Schneider, M. B.; Berzak Hopkins, L.; Casey, D. T.; Hammel, B. A.; Jarrott, L. C.; Landen, O. L.; Patel, P. K.; Rosenberg, M. J.; Spears, B. K.

2017-07-01

This paper presents the spectroscopic aspects of using Krypton as a dopant in NIF capsule implosions through simulation studies and the first set of NIF experiments. Using a combination of 2D hohlraum and 1D capsule simulations with comprehensive spectroscopic modeling, the calculations focused on the effect of dopant concentration on the implosion, and the impact of gradients in the electron density and temperature to the Kr line features and plasma opacity. Experimental data were obtained from three NIF Kr-dopant experiments, performed with varying Kr dopant concentrations between 0.01% and 0.03%. The implosion performance, hotspot images, and detailed Kr spectral analysis are summarized relative to the predictions. Data show that fuel-dopant spectroscopy can serve as a powerful and viable diagnostic for inertial confinement fusion implosions.

Wavelength-detuning cross-beam energy transfer mitigation scheme for direct drive: Modeling and evidence from National Ignition Facility implosions

NASA Astrophysics Data System (ADS)

Marozas, J. A.; Hohenberger, M.; Rosenberg, M. J.; Turnbull, D.; Collins, T. J. B.; Radha, P. B.; McKenty, P. W.; Zuegel, J. D.; Marshall, F. J.; Regan, S. P.; Sangster, T. C.; Seka, W.; Campbell, E. M.; Goncharov, V. N.; Bowers, M. W.; Di Nicola, J.-M. G.; Erbert, G.; MacGowan, B. J.; Pelz, L. J.; Moody, J.; Yang, S. T.

2018-05-01

Cross-beam energy transfer (CBET) results from two-beam energy exchange via seeded stimulated Brillouin scattering, which detrimentally reduces laser-energy absorption for direct-drive inertial confinement fusion. Consequently, ablation pressure and implosion velocity suffer from the decreased absorption, reducing target performance in both symmetric and polar direct drive. Additionally, CBET alters the time-resolved scattered-light spectra and redistributes absorbed and scattered-light-changing shell morphology and low-mode drive symmetry. Mitigating CBET is demonstrated in inertial confinement implosions at the National Ignition Facility by detuning the laser-source wavelengths (±2.3 Å UV) of the interacting beams. In polar direct drive, wavelength detuning was shown to increase the equatorial region velocity experimentally by 16% and to alter the in-flight shell morphology. These experimental observations are consistent with design predictions of radiation-hydrodynamic simulations that indicate a 10% increase in the average ablation pressure. These results indicate that wavelength detuning successfully mitigates CBET. Simulations predict that optimized phase plates and wavelength-detuning CBET mitigation utilizing the three-legged beam layout of the OMEGA Laser System significantly increase absorption and achieve >100-Gbar hot-spot pressures in symmetric direct drive.

Isolating and quantifying cross-beam energy transfer in direct-drive implosions on OMEGA and the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davis, A. K.; Cao, D.; Michel, D. T.

The angularly-resolved mass ablation rates and ablation front trajectories for Si-coated CH targets were measured in direct-drive inertial confinement fusion experiments to quantify crossbeam energy transfer (CBET) while constraining the hydrodynamic coupling. A polar-direct-drive laser configuration was used, where the equatorial laser beams were dropped from a symmetric direct-drive configuration to suppress CBET at the pole, while allowing it to persist at the equator. The combination of low- and high-CBET conditions in the same implosion allowed the effects of CBET on the ablation rate and ablation pressure to be decoupled from the other physics effects that influence laser-coupling. Hydrodynamic simulationsmore » performed without CBET reproduced the measured ablation rate and ablation front trajectory at the pole of the target, verifying that the other laser-coupling physics effects are well-modeled when CBET effects are negligible. The simulated mass ablation rates and ablation front trajectories were in excellent agreement with the measurements at all angles when a CBET model based on Randall’s equations [C. J. Randall et al., Phys. Fluids 24, 1474 (1981)] was included into the simulations with an optimized multiplier on the CBET gain factor. These measurements were performed on both OMEGA and the National Ignition Facility to access a wide range of plasma conditions, laser intensities, and laser beam geometries. Furthermore, the presence of the CBET gain multiplier required to match the data in all of the configurations tested suggests that additional physics effects, such as intensity variations due to diffraction, shortcomings of extending the 1-D Randall model to 3-D, or polarization effects, should be explored to explain the differences in observed and predicted drive.« less

Isolating and quantifying cross-beam energy transfer in direct-drive implosions on OMEGA and the National Ignition Facility

DOE PAGES

Davis, A. K.; Cao, D.; Michel, D. T.; ...

2016-04-20

The angularly-resolved mass ablation rates and ablation front trajectories for Si-coated CH targets were measured in direct-drive inertial confinement fusion experiments to quantify crossbeam energy transfer (CBET) while constraining the hydrodynamic coupling. A polar-direct-drive laser configuration was used, where the equatorial laser beams were dropped from a symmetric direct-drive configuration to suppress CBET at the pole, while allowing it to persist at the equator. The combination of low- and high-CBET conditions in the same implosion allowed the effects of CBET on the ablation rate and ablation pressure to be decoupled from the other physics effects that influence laser-coupling. Hydrodynamic simulationsmore » performed without CBET reproduced the measured ablation rate and ablation front trajectory at the pole of the target, verifying that the other laser-coupling physics effects are well-modeled when CBET effects are negligible. The simulated mass ablation rates and ablation front trajectories were in excellent agreement with the measurements at all angles when a CBET model based on Randall’s equations [C. J. Randall et al., Phys. Fluids 24, 1474 (1981)] was included into the simulations with an optimized multiplier on the CBET gain factor. These measurements were performed on both OMEGA and the National Ignition Facility to access a wide range of plasma conditions, laser intensities, and laser beam geometries. Furthermore, the presence of the CBET gain multiplier required to match the data in all of the configurations tested suggests that additional physics effects, such as intensity variations due to diffraction, shortcomings of extending the 1-D Randall model to 3-D, or polarization effects, should be explored to explain the differences in observed and predicted drive.« less

Multidimensional Analysis of Direct-Drive Plastic-Shell Implosions on OMEGA

NASA Astrophysics Data System (ADS)

Radha, P. B.

2004-11-01

Direct-drive implosions of plastic shells with the OMEGA laser are used as energy-scaled warm surrogates for ignition cryogenic targets designed for use on the National Ignition Facility. Plastic targets involve varying shell thickness (15 to 33 μm), fill pressures (3 to 15 atm), and shell adiabats. The multidimensional hydrodynamics code DRACO is used to evaluate the effects of capsule-surface roughness and illumination nonuniformities on target performance. These simulations indicate that shell stability during the acceleration phase plays a critical role in determining fusion yields. For shells that are thick enough to survive the Rayleigh--Taylor growth, target yields are significantly reduced by growth of the long (ℓ < 10) and intermediate modes (20 < ℓ < 50) occurring from single-beam laser nonuniformities. The neutron production rate for these thick shells truncates relative to one-dimensional (1-D) predictions. The neutron-rate curves for the thinner shells, however, have significantly lower amplitudes and widths closer to 1-D results, indicating shell breakup during the acceleration phase. The simulation results are consistent with experimental observations. Previously, the stability of plastic-shell implosions had been correlated to a static ``mix-width'' at the boundary of the gas and plastic pusher estimated using a variety of experimental observables and an assumption of spherical symmetry. Results of these 2-D simulations provide a comprehensive understanding of warm-target implosion dynamics without assumptions of spherical symmetry and serve to answer the question of the hydrodynamic surrogacy between these plastic-shell implosions and the cryogenic ignition designs.

Two-Plasmon Decay Mitigation in Direct-Drive Inertial-Confinement-Fusion Experiments Using Multilayer Targets.

PubMed

Follett, R K; Delettrez, J A; Edgell, D H; Goncharov, V N; Henchen, R J; Katz, J; Michel, D T; Myatt, J F; Shaw, J; Solodov, A A; Stoeckl, C; Yaakobi, B; Froula, D H

2016-04-15

Multilayer direct-drive inertial-confinement-fusion targets are shown to significantly reduce two-plasmon decay (TPD) driven hot-electron production while maintaining high hydrodynamic efficiency. Implosion experiments on the OMEGA laser used targets with silicon layered between an inner beryllium and outer silicon-doped plastic ablator. A factor-of-5 reduction in hot-electron generation (>50  keV) was observed in the multilayer targets relative to pure CH targets. Three-dimensional simulations of the TPD-driven hot-electron production using a laser-plasma interaction code (lpse) that includes nonlinear and kinetic effects show good agreement with the measurements. The simulations suggest that the reduction in hot-electron production observed in the multilayer targets is primarily caused by increased electron-ion collisional damping.

Effects of Hot-Spot Geometry on Backscattering and Down-Scattering Neutron Spectra

NASA Astrophysics Data System (ADS)

Mohamed, Z. L.; Mannion, O. M.; Forrest, C. J.; Knauer, J. P.; Anderson, K. S.; Radha, P. B.

2017-10-01

The measured neutron spectrum produced by a fusion experiment plays a key role in inferring observable quantities. One important observable is the areal density of an implosion, which is inferred by measuring the scattering of neutrons. This project seeks to use particle-transport simulations to model the effects of hot-spot geometry on backscattering and down-scattering neutron spectra along different lines of sight. Implosions similar to those conducted at the Laboratory of Laser Energetics are modeled by neutron transport through a DT plasma and a DT ice shell using the particle transport codes MCNP and IRIS. Effects of hot-spot geometry are obtained by ``detecting'' scattered neutrons along different lines of sight. This process is repeated for various hot-spot geometries representing known shape distortions between the hot spot and the shell. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

LPI Experiments at the Nike Laser*

NASA Astrophysics Data System (ADS)

Weaver, J.; Oh, J.; Afeyan, B.; Phillips, L.; Seely, J.; Brown, C.; Karasik, M.; Serlin, V.; Obenschain, S.; Chan, L.-Y.; Kehne, D.; Brown, D.; Schmitt, A.; Velikovich, A.; Feldman, U.; Holland, G.; Aglitskiy, Y.

2007-11-01

Advanced implosion designs under development at NRL for direct drive inertial confinement fusion incorporate high intensity pulses from a krypton-fluoride (KrF) laser to achieve significant gain with lower total laser energy (Etot˜500 kJ). These designs will be affected by the thresholds and magnitudes of laser plasma instabilities (LPI). The Nike laser can create short, high intensity pulses (t <0.4 ns; I>10^15 W/cm^2) to explore how LPI will be influenced by the deep UV (248 nm), broad bandwidth (2-3 THz), and induced spatial incoherence beam smoothing of the NRL KrF laser systems. Previous results demonstrated no visible/VUV signatures of two-plasmon decay (2φp) for overlapped intensities ˜2x10^15 W/cm^2. We have increased the laser intensity and expanded the range of targets and diagnostics. Single and double pulse experiments are being planned with solid, foam, and cryogenic targets. In addition to spectrometers to study SRS, 2φp, SBS, and the parametric decay instability, hard x-ray spectrometers (hν>2 keV) and a scintillator/photomultiplier array (hν>10 keV) have been deployed to examine hot electron generation. *Work supported by U. S. DoE.

The One-Dimensional Cryogenic Implosion Campaign on OMEGA: Modeling, Experiments, and a Statistical Approach to Predict and Understand Direct-Drive Implosions

NASA Astrophysics Data System (ADS)

Betti, R.

2017-10-01

The 1-D campaign on OMEGA is aimed at validating a novel approach to design cryogenic implosion experiments and provide valuable data to improve the accuracy of 1-D physics models. This new design methodology is being tested first on low-convergence, high-adiabat (α 6 to 7) implosions and will subsequently be applied to implosions with increasing convergence up to the level required for a hydro-equivalent demonstration of ignition. This design procedure assumes that the hydrodynamic codes used in implosion designs lack the necessary physics and that measurements of implosion properties are imperfect. It also assumes that while the measurements may have significant systematic errors, the shot-to-shot variations are small and that cryogenic implosion data are reproducible as observed on OMEGA. One of the goals of the 1-D campaign is to find a mapping of the data to the code results and use the mapping relations to design future implosions. In the 1-D campaign, this predictive methodology was used to design eight implosions using a simple two-shock pulse design, leading to pre-shot predictions of yields within 5% and ion temperatures within 4% of the experimental values. These implosions have also produced the highest neutron yield of 1014 in OMEGA cryogenic implosion experiments with an areal density of 100 mg/cm2. Furthermore, the results from this campaign have been used to test the validity of the 1-D physics models used in the radiation-hydrodynamics codes. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DENA0001944 and LLNL under Contract DE-AC52-07NA27344. * In collaboration with J.P. Knauer, V. Gopalaswamy, D. Patel, K.M. Woo, K.S. Anderson, A. Bose, A.R. Christopherson, V.Yu. Glebov, F.J. Marshall, S.P. Regan, P.B. Radha, C. Stoeckl, and E.M. Campbell.

Novel Characterization of Capsule X-Ray Drive at the National Ignition Facility [Using ViewFactor Experiments to Measure Hohlraum X-Radiation Drive from the Capsule Point-of-View in Ignition Experiments on the National Ignition Facility

DOE PAGES

MacLaren, S. A.; Schneider, M. B.; Widmann, K.; ...

2014-03-13

Here, indirect drive experiments at the National Ignition Facility are designed to achieve fusion by imploding a fuel capsule with x rays from a laser-driven hohlraum. Previous experiments have been unable to determine whether a deficit in measured ablator implosion velocity relative to simulations is due to inadequate models of the hohlraum or ablator physics. ViewFactor experiments allow for the first time a direct measure of the x-ray drive from the capsule point of view. The experiments show a 15%–25% deficit relative to simulations and thus explain nearly all of the disagreement with the velocity data. In addition, the datamore » from this open geometry provide much greater constraints on a predictive model of laser-driven hohlraum performance than the nominal ignition target.« less

Laser absorption, power transfer, and radiation symmetry during the first shock of inertial confinement fusion gas-filled hohlraum experiments

NASA Astrophysics Data System (ADS)

Pak, A.; Dewald, E. L.; Landen, O. L.; Milovich, J.; Strozzi, D. J.; Berzak Hopkins, L. F.; Bradley, D. K.; Divol, L.; Ho, D. D.; MacKinnon, A. J.; Meezan, N. B.; Michel, P.; Moody, J. D.; Moore, A. S.; Schneider, M. B.; Town, R. P. J.; Hsing, W. W.; Edwards, M. J.

2015-12-01

Temporally resolved measurements of the hohlraum radiation flux asymmetry incident onto a bismuth coated surrogate capsule have been made over the first two nanoseconds of ignition relevant laser pulses. Specifically, we study the P2 asymmetry of the incoming flux as a function of cone fraction, defined as the inner-to-total laser beam power ratio, for a variety of hohlraums with different scales and gas fills. This work was performed to understand the relevance of recent experiments, conducted in new reduced-scale neopentane gas filled hohlraums, to full scale helium filled ignition targets. Experimental measurements, matched by 3D view factor calculations, are used to infer differences in symmetry, relative beam absorption, and cross beam energy transfer (CBET), employing an analytic model. Despite differences in hohlraum dimensions and gas fill, as well as in laser beam pointing and power, we find that laser absorption, CBET, and the cone fraction, at which a symmetric flux is achieved, are similar to within 25% between experiments conducted in the reduced and full scale hohlraums. This work demonstrates a close surrogacy in the dynamics during the first shock between reduced-scale and full scale implosion experiments and is an important step in enabling the increased rate of study for physics associated with inertial confinement fusion.

Early-Time Symmetry Tuning in the Presence of Cross-Beam Energy Transfer in ICF Experiments on the National Ignition Facility

DOE PAGES

Dewald, E. L.; Milovich, J. L.; Michel, P.; ...

2013-12-01

At the National Ignition Facility (NIF) we have successfully tuned the early time (~2 ns) lowest order Legendre mode (P 2) of the incoming radiation drive asymmetry of indirectly driven ignition capsule implosions by varying the inner power cone fraction. The measured P 2/P 0 sensitivity vs come fraction is similar to calculations, but a significant -15 to -20% P 2/P 0 offset was observed. This can be explained by a considerable early time laser energy transfer from the outer to the inner beams during the laser burn-through of the Laser Entrance Hole (LEH) windows and hohlraum fill gas whenmore » the LEH plasma is still dense and relatively cold.« less

First Liquid Layer Inertial Confinement Fusion Implosions at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Olson, R. E.; Leeper, R. J.; Kline, J. L.; Zylstra, A. B.; Yi, S. A.; Biener, J.; Braun, T.; Kozioziemski, B. J.; Sater, J. D.; Bradley, P. A.; Peterson, R. R.; Haines, B. M.; Yin, L.; Berzak Hopkins, L. F.; Meezan, N. B.; Walters, C.; Biener, M. M.; Kong, C.; Crippen, J. W.; Kyrala, G. A.; Shah, R. C.; Herrmann, H. W.; Wilson, D. C.; Hamza, A. V.; Nikroo, A.; Batha, S. H.

2016-12-01

The first cryogenic deuterium and deuterium-tritium liquid layer implosions at the National Ignition Facility (NIF) demonstrate D2 and DT layer inertial confinement fusion (ICF) implosions that can access a low-to-moderate hot-spot convergence ratio (12 30 ) DT ice layer implosions. Although high CR is desirable in an idealized 1D sense, it amplifies the deleterious effects of asymmetries. To date, these asymmetries prevented the achievement of ignition at the NIF and are the major cause of simulation-experiment disagreement. In the initial liquid layer experiments, high neutron yields were achieved with CRs of 12-17, and the hot-spot formation is well understood, demonstrated by a good agreement between the experimental data and the radiation hydrodynamic simulations. These initial experiments open a new NIF experimental capability that provides an opportunity to explore the relationship between hot-spot convergence ratio and the robustness of hot-spot formation during ICF implosions.

First Liquid Layer Inertial Confinement Fusion Implosions at the National Ignition Facility.

PubMed

Olson, R E; Leeper, R J; Kline, J L; Zylstra, A B; Yi, S A; Biener, J; Braun, T; Kozioziemski, B J; Sater, J D; Bradley, P A; Peterson, R R; Haines, B M; Yin, L; Berzak Hopkins, L F; Meezan, N B; Walters, C; Biener, M M; Kong, C; Crippen, J W; Kyrala, G A; Shah, R C; Herrmann, H W; Wilson, D C; Hamza, A V; Nikroo, A; Batha, S H

2016-12-09

The first cryogenic deuterium and deuterium-tritium liquid layer implosions at the National Ignition Facility (NIF) demonstrate D_{2} and DT layer inertial confinement fusion (ICF) implosions that can access a low-to-moderate hot-spot convergence ratio (1230) DT ice layer implosions. Although high CR is desirable in an idealized 1D sense, it amplifies the deleterious effects of asymmetries. To date, these asymmetries prevented the achievement of ignition at the NIF and are the major cause of simulation-experiment disagreement. In the initial liquid layer experiments, high neutron yields were achieved with CRs of 12-17, and the hot-spot formation is well understood, demonstrated by a good agreement between the experimental data and the radiation hydrodynamic simulations. These initial experiments open a new NIF experimental capability that provides an opportunity to explore the relationship between hot-spot convergence ratio and the robustness of hot-spot formation during ICF implosions.

Unique capabilities for ICF and HEDP research with the KrF laser

NASA Astrophysics Data System (ADS)

Obenschain, Stephen; Bates, Jason; Chan, Lop-Yung; Karasik, Max; Kehne, David; Sethian, John; Serlin, Victor; Weaver, James; Oh, Jaechul; Jenkins, Bruce; Lehmberg, Robert; Hegeler, Frank; Terrell, Stephen; Aglitskiy, Yefim; Schmitt, Andrew

2014-10-01

The krypton-fluoride (KrF) laser provides the shortest wavelength, broadest bandwidth and most uniform target illumination of all developed high-energy lasers. For directly driven targets these characteristics result in higher and more uniform ablation pressures as well as higher intensity thresholds for laser-plasma instability. The ISI beam smoothing scheme implemented on the NRL Nike KrF facility allows easy implementation of focal zooming where the laser radial profile is varied during the laser pulse. The capability for near continuous zooming with KrF would be valuable towards minimizing the effects of cross beam energy transport (CBET) in directly driven capsule implosions. The broad bandwidth ISI beam smoothing that is utilized with the Nike KrF facility may further inhibit certain laser plasma instability. In this presentation we will summarize our current understanding of laser target interaction with the KrF laser and the benefits it provides for ICF and certain HEDP experiments. Status and progress in high-energy KrF laser technology will also be discussed. Work supported by the Deparment of Energy, NNSA.

Three-dimensional simulations of low foot and high foot implosion experiments on the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clark, D. S.; Weber, C. R.; Milovich, J. L.

In order to achieve the several hundred Gbar stagnation pressures necessary for inertial confinement fusion ignition, implosion experiments on the National Ignition Facility (NIF) [E. I. Moses et al., Phys. Plasmas 16, 041006 (2009)] require the compression of deuterium-tritium fuel layers by a convergence ratio as high as forty. Such high convergence implosions are subject to degradation by a range of perturbations, including the growth of small-scale defects due to hydrodynamic instabilities, as well as longer scale modulations due to radiation flux asymmetries in the enclosing hohlraum. Due to the broad range of scales involved, and also the genuinely three-dimensionalmore » (3D) character of the flow, accurately modeling NIF implosions remains at the edge of current simulation capabilities. This study describes the current state of progress of 3D capsule-only simulations of NIF implosions aimed at accurately describing the performance of specific NIF experiments. Current simulations include the effects of hohlraum radiation asymmetries, capsule surface defects, the capsule support tent and fill tube, and use a grid resolution shown to be converged in companion two-dimensional simulations. The results of detailed simulations of low foot implosions from the National Ignition Campaign are contrasted against results for more recent high foot implosions. While the simulations suggest that low foot performance was dominated by ablation front instability growth, especially the defect seeded by the capsule support tent, high foot implosions appear to be dominated by hohlraum flux asymmetries, although the support tent still plays a significant role. Finally, for both implosion types, the simulations show reasonable, though not perfect, agreement with the data and suggest that a reliable predictive capability is developing to guide future implosions toward ignition.« less

Three-dimensional simulations of low foot and high foot implosion experiments on the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clark, D. S.; Weber, C. R.; Milovich, J. L.

In order to achieve the several hundred Gbar stagnation pressures necessary for inertial confinement fusion ignition, implosion experiments on the National Ignition Facility (NIF) [E. I. Moses et al., Phys. Plasmas 16, 041006 (2009)] require the compression of deuterium-tritium fuel layers by a convergence ratio as high as forty. Such high convergence implosions are subject to degradation by a range of perturbations, including the growth of small-scale defects due to hydrodynamic instabilities, as well as longer scale modulations due to radiation flux asymmetries in the enclosing hohlraum. Due to the broad range of scales involved, and also the genuinely three-dimensionalmore » (3D) character of the flow, accurately modeling NIF implosions remains at the edge of current simulation capabilities. This paper describes the current state of progress of 3D capsule-only simulations of NIF implosions aimed at accurately describing the performance of specific NIF experiments. Current simulations include the effects of hohlraum radiation asymmetries, capsule surface defects, the capsule support tent and fill tube, and use a grid resolution shown to be converged in companion two-dimensional simulations. The results of detailed simulations of low foot implosions from the National Ignition Campaign are contrasted against results for more recent high foot implosions. While the simulations suggest that low foot performance was dominated by ablation front instability growth, especially the defect seeded by the capsule support tent, high foot implosions appear to be dominated by hohlraum flux asymmetries, although the support tent still plays a significant role. For both implosion types, the simulations show reasonable, though not perfect, agreement with the data and suggest that a reliable predictive capability is developing to guide future implosions toward ignition.« less

Three-dimensional simulations of low foot and high foot implosion experiments on the National Ignition Facility

DOE PAGES

Clark, D. S.; Weber, C. R.; Milovich, J. L.; ...

2016-03-14

In order to achieve the several hundred Gbar stagnation pressures necessary for inertial confinement fusion ignition, implosion experiments on the National Ignition Facility (NIF) [E. I. Moses et al., Phys. Plasmas 16, 041006 (2009)] require the compression of deuterium-tritium fuel layers by a convergence ratio as high as forty. Such high convergence implosions are subject to degradation by a range of perturbations, including the growth of small-scale defects due to hydrodynamic instabilities, as well as longer scale modulations due to radiation flux asymmetries in the enclosing hohlraum. Due to the broad range of scales involved, and also the genuinely three-dimensionalmore » (3D) character of the flow, accurately modeling NIF implosions remains at the edge of current simulation capabilities. This study describes the current state of progress of 3D capsule-only simulations of NIF implosions aimed at accurately describing the performance of specific NIF experiments. Current simulations include the effects of hohlraum radiation asymmetries, capsule surface defects, the capsule support tent and fill tube, and use a grid resolution shown to be converged in companion two-dimensional simulations. The results of detailed simulations of low foot implosions from the National Ignition Campaign are contrasted against results for more recent high foot implosions. While the simulations suggest that low foot performance was dominated by ablation front instability growth, especially the defect seeded by the capsule support tent, high foot implosions appear to be dominated by hohlraum flux asymmetries, although the support tent still plays a significant role. Finally, for both implosion types, the simulations show reasonable, though not perfect, agreement with the data and suggest that a reliable predictive capability is developing to guide future implosions toward ignition.« less

A hybrid-drive nonisobaric-ignition scheme for inertial confinement fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, X. T., E-mail: xthe@iapcm.ac.cn; Center for Applied Physics and Technology, HEDPS, Peking University, Beijing 100871; IFSA Collaborative Innovation Center of MoE, Shanghai Jiao-Tong University, Shanghai 200240

A new hybrid-drive (HD) nonisobaric ignition scheme of inertial confinement fusion (ICF) is proposed, in which a HD pressure to drive implosion dynamics increases via increasing density rather than temperature in the conventional indirect drive (ID) and direct drive (DD) approaches. In this HD (combination of ID and DD) scheme, an assembled target of a spherical hohlraum and a layered deuterium-tritium capsule inside is used. The ID lasers first drive the shock to perform a spherical symmetry implosion and produce a large-scale corona plasma. Then, the DD lasers, whose critical surface in ID corona plasma is far from the radiationmore » ablation front, drive a supersonic electron thermal wave, which slows down to a high-pressure electron compression wave, like a snowplow, piling up the corona plasma into high density and forming a HD pressurized plateau with a large width. The HD pressure is several times the conventional ID and DD ablation pressure and launches an enhanced precursor shock and a continuous compression wave, which give rise to the HD capsule implosion dynamics in a large implosion velocity. The hydrodynamic instabilities at imploding capsule interfaces are suppressed, and the continuous HD compression wave provides main pdV work large enough to hotspot, resulting in the HD nonisobaric ignition. The ignition condition and target design based on this scheme are given theoretically and by numerical simulations. It shows that the novel scheme can significantly suppress implosion asymmetry and hydrodynamic instabilities of current isobaric hotspot ignition design, and a high-gain ICF is promising.« less

Comparison and analysis of the results of direct-driven targets implosion

NASA Astrophysics Data System (ADS)

Demchenko, N. N.; Dolgoleva, G. V.; Gus'kov, S. Yu; Kuchugov, P. A.; Rozanov, V. B.; Stepanov, R. V.; Zmitrenko, N. V.; Yakhin, R. A.

2017-10-01

The article presents calculation results, which were received for the implosion of the typical cryogenic thermonuclear direct-drive targets that are intended for use at the OMEGA facility, NIF and Russian laser facility. The compression and burning characteristics, which were obtained using various numerical codes of different scientific groups, are compared. The data indicate good agreement between the numerical results. Various sources of target irradiation inhomogeneity and their influence on the implosion parameters are considered. The nominal scales of these disturbances for various facilities are close to each other. The main negative effect on the efficiency of compression and burning is due to the accidental offset of the target from the center of the chamber.

Observation of parametric instabilities in the quarter critical density region driven by the Nike KrF laser

NASA Astrophysics Data System (ADS)

Weaver, J. L.; Oh, J.; Phillips, L.; Afeyan, B.; Seely, J.; Kehne, D.; Brown, C. M.; Obenschain, S. P.; Serlin, V.; Schmitt, A. J.; Feldman, U.; Lehmberg, R. H.; Mclean, E.; Manka, C.

2013-02-01

The krypton-fluoride (KrF) laser is an attractive choice for inertial confinement fusion due to its combination of short wavelength (λ =248 nm), large bandwidth (up to 3 THz), and superior beam smoothing by induced spatial incoherence. These qualities improve the overall hydrodynamics of directly driven pellet implosions and should allow use of increased laser intensity due to higher thresholds for laser plasma instabilities when compared to frequency tripled Nd:glass lasers (λ =351 nm). Here, we report the first observations of the two-plasmon decay instability using a KrF laser. The experiments utilized the Nike laser facility to irradiate solid plastic planar targets over a range of pulse lengths (0.35 ns≤τ≤1.25 ns) and intensities (up to 2×1015 W/cm2). Variation of the laser pulse created different combinations of electron temperature and electron density scale length. The observed onset of instability growth was consistent with the expected scaling that KrF lasers have a higher intensity threshold for instabilities in the quarter critical density region.

Wavelength-detuning cross-beam energy transfer mitigation scheme for direct drive: Modeling and evidence from National Ignition Facility implosions

DOE PAGES

Marozas, J. A.; Hohenberger, M.; Rosenberg, M. J.; ...

2018-05-25

Here, cross-beam energy transfer (CBET) results from two-beam energy exchange via seeded stimulated Brillouin scattering, which detrimentally reduces laser-energy absorption for direct-drive inertial confinement fusion. Consequently, ablation pressure and implosion velocity suffer from the decreased absorption, reducing target performance in both symmetric and polar direct drive. Additionally, CBET alters the time-resolved scattered-light spectra and redistributes absorbed and scattered-light–changing shell morphology and low-mode drive symmetry. Mitigating CBET is demonstrated in inertial confinement implosions at the National Ignition Facility by detuning the laser-source wavelengths (±2.3 Å UV) of the interacting beams. In polar direct drive, wavelength detuning was shown to increase themore » equatorial region velocity experimentally by 16% and to alter the in-flight shell morphology. These experimental observations are consistent with design predictions of radiation–hydrodynamic simulations that indicate a 10% increase in the average ablation pressure. These results indicate that wavelength detuning successfully mitigates CBET. Simulations predict that optimized phase plates and wavelength-detuning CBET mitigation utilizing the three-legged beam layout of the OMEGA Laser System significantly increase absorption and achieve >100-Gbar hot-spot pressures in symmetric direct drive.« less

Wavelength-detuning cross-beam energy transfer mitigation scheme for direct drive: Modeling and evidence from National Ignition Facility implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marozas, J. A.; Hohenberger, M.; Rosenberg, M. J.

Here, cross-beam energy transfer (CBET) results from two-beam energy exchange via seeded stimulated Brillouin scattering, which detrimentally reduces laser-energy absorption for direct-drive inertial confinement fusion. Consequently, ablation pressure and implosion velocity suffer from the decreased absorption, reducing target performance in both symmetric and polar direct drive. Additionally, CBET alters the time-resolved scattered-light spectra and redistributes absorbed and scattered-light–changing shell morphology and low-mode drive symmetry. Mitigating CBET is demonstrated in inertial confinement implosions at the National Ignition Facility by detuning the laser-source wavelengths (±2.3 Å UV) of the interacting beams. In polar direct drive, wavelength detuning was shown to increase themore » equatorial region velocity experimentally by 16% and to alter the in-flight shell morphology. These experimental observations are consistent with design predictions of radiation–hydrodynamic simulations that indicate a 10% increase in the average ablation pressure. These results indicate that wavelength detuning successfully mitigates CBET. Simulations predict that optimized phase plates and wavelength-detuning CBET mitigation utilizing the three-legged beam layout of the OMEGA Laser System significantly increase absorption and achieve >100-Gbar hot-spot pressures in symmetric direct drive.« less

Two-plasmon decay mitigation in direct-drive inertial-confinement-fusion experiments using multilayer targets

DOE PAGES

Follett, R. K.; Delettrez, J. A.; Edgell, D. H.; ...

2016-04-15

Multilayer direct-drive inertial-confinement-fusion (ICF) targets are shown to significantly reduce two-plasmon-decay (TPD) driven hot-electron production while maintaining high hydrodynamic efficiency. Implosion experiments on the OMEGA Laser used targets with silicon layered between an inner beryllium and outer silicon-doped plastic ablator. A factor of five reduction in hot-electron generation (> 50 keV) was observed in the multilayer targets relative to pure CH targets. Three-dimensional simulations of the TPD driven hot-electron production using a laser-plasma interaction code (LPSE) that includes nonlinear and kinetic effects show excellent agreement with the measurements. As a result, the simulations suggest that the reduction in hot-electron productionmore » observed in the multilayer targets is primarily due to increased electron-ion collisional damping.« less

National direct-drive program on OMEGA and the National Ignition Facility

NASA Astrophysics Data System (ADS)

Goncharov, V. N.; Regan, S. P.; Campbell, E. M.; Sangster, T. C.; Radha, P. B.; Myatt, J. F.; Froula, D. H.; Betti, R.; Boehly, T. R.; Delettrez, J. A.; Edgell, D. H.; Epstein, R.; Forrest, C. J.; Glebov, V. Yu; Harding, D. R.; Hu, S. X.; Igumenshchev, I. V.; Marshall, F. J.; McCrory, R. L.; Michel, D. T.; Seka, W.; Shvydky, A.; Stoeckl, C.; Theobald, W.; Gatu-Johnson, M.

2017-01-01

A major advantage of the laser direct-drive (DD) approach to ignition is the increased fraction of laser drive energy coupled to the hot spot and relaxed hot-spot requirements for the peak pressure and convergence ratios relative to the indirect-drive approach at equivalent laser energy. With the goal of a successful ignition demonstration using DD, the recently established national strategy has several elements and involves multiple national and international institutions. These elements include the experimental demonstration on OMEGA cryogenic implosions of hot-spot conditions relevant for ignition at MJ-scale energies available at the National Ignition Facility (NIF) and developing an understanding of laser-plasma interactions and laser coupling using DD experiments on the NIF. DD designs require reaching central stagnation pressures in excess of 100 Gbar. The current experiments on OMEGA have achieved inferred peak pressures of 56 Gbar (Regan et al 2016 Phys. Rev. Lett. 117 025001). Extensive analysis of the cryogenic target experiments and two- and three-dimensional simulations suggest that power balance, target offset, and target quality are the main limiting factors in target performance. In addition, cross-beam energy transfer (CBET) has been identified as the main mechanism reducing laser coupling. Reaching the goal of demonstrating hydrodynamic equivalence on OMEGA includes improving laser power balance, target position, and target quality at shot time. CBET must also be significantly reduced and several strategies have been identified to address this issue.

Down-Bore Two-Laser Heterodyne Velocimetry of an Implosion-Driven Hypervelocity Launcher

NASA Astrophysics Data System (ADS)

Hildebrand, Myles; Huneault, Justin; Loiseau, Jason; Higgins, Andrew J.

2015-06-01

The implosion-driven launcher uses explosives to shock-compress helium, driving well-characterized projectiles to velocities exceeding 10 km/s. The masses of projectiles range between 0.1 - 10 g, and the design shows excellent scalability, reaching similar velocities across different projectile sizes. In the past, velocity measurements have been limited to muzzle velocity obtained via a high-speed videography upon the projectile exiting the launch tube. Recently, Photonic Doppler Velocimetry (PDV) has demonstrated the ability to continuously measure in-bore velocity, even in the presence of significant blow-by of high temperature helium propellant past the projectile. While a single-laser PDV is limited to approximately 8 km/s, a two-laser PDV system is developed that uses two lasers operating near 1550 nm to provide velocity measurement capabilities up to 16 km/s. The two laser PDV system is used to obtain a continuous velocity history of the projectile throughout the entire launch cycle. These continuous velocity data are used to validate models of the launcher cycle and compare different advanced concepts aimed at increasing the projectile velocity to well beyond 10 km/s.

New tuning method of the low-mode asymmetry for ignition capsule implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gu, Jianfa, E-mail: gu-jianfa@iapcm.ac.cn; Dai, Zhensheng; Zou, Shiyang

2015-12-15

In the deuterium-tritium inertial confinement fusion implosion experiments on the National Ignition Facility, the hot spot and the surrounding main fuel layer show obvious P2 asymmetries. This may be caused by the large positive P2 radiation flux asymmetry during the peak pulse resulting form the poor propagation of the inner laser beam in the gas-filled hohlraum. The symmetry evolution of ignition capsule implosions is investigated by applying P2 radiation flux asymmetries during different time intervals. A series of two-dimensional simulation results show that a positive P2 flux asymmetry during the peak pulse results in a positive P2 shell ρR asymmetry;more » while an early time positive P2 flux asymmetry causes a negative P2 in the fuel ρR shape. The opposite evolution behavior of shell ρR asymmetry is used to develop a new tuning method to correct the radiation flux asymmetry during the peak pulse by adding a compensating same-phased P2 drive asymmetry during the early time. The significant improvements of the shell ρR symmetry, hot spot shape, hot spot internal energy, and neutron yield indicate that the tuning method is quite effective. The similar tuning method can also be used to control the early time drive asymmetries.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shiraga, H.; Nagatomo, H.; Theobald, W.

Here, integrated fast ignition experiments were performed at ILE, Osaka, and LLE, Rochester, in which a nanosecond driver laser implodes a deuterated plastic shell in front of the tip of a hollow metal cone and an intense ultrashort-pulse laser is injected through the cone to heat the compressed plasma. Based on the initial successful results of fast electron heating of cone-in-shell targets, large-energy short-pulse laser beam lines were constructed and became operational: OMEGA-EP at Rochester and LFEX at Osaka. Neutron enhancement due to heating with a ~kJ short-pulse laser has been demonstrated in the integrated experiments at Osaka and Rochester.more » The neutron yields are being analyzed by comparing the experimental results with simulations. Details of the fast electron beam transport and the electron energy deposition in the imploded fuel plasma are complicated and further studies are imperative. The hydrodynamics of the implosion was studied including the interaction of the imploded core plasma with the cone tip. Theory and simulation studies are presented on the hydrodynamics of a high-gain target for a fast ignition point design.« less

Exploring symmetry in near-vacuum hohlraums

NASA Astrophysics Data System (ADS)

Berzak Hopkins, L.; Le Pape, S.; Divol, L.; Meezan, N.; MacKinnon, A.; Ho, D. D.; Jones, O.; Khan, S.; Ma, T.; Milovich, J.; Pak, A.; Ross, J. S.; Thomas, C.; Turnbull, D.; Amendt, P.; Wilks, S.; Zylstra, A.; Rinderknecht, H.; Sio, H.; Petrasso, R.

2015-11-01

Recent experiments with near-vacuum hohlraums, which utilize a minimal but non-zero helium fill, have demonstrated performance improvements relative to conventional gas-filled (0.96 - 1.6 mg/cc helium) hohlraums: minimal backscatter, reduced capsule drive degradation, and minimal suprathermal electron generation. Because this is a low laser-plasma interaction platform, implosion symmetry is controlled via pulse-shaping adjustments to laser power balance. Extending this platform to high-yield designs with high-density carbon capsules requires achieving adequate symmetry control throughout the pulse. In simulations, laser propagation is degraded suddenly by hohlraum wall expansion interacting with ablated capsule material. Nominal radiation-hydrodynamics simulations have not yet proven predictive on symmetry of the final hotspot, and experiments show more prolate symmetry than preshot calculations. Recent efforts have focused on understanding the discrepancy between simulated and measured symmetry and on alternate designs for symmetry control through varying cone fraction, trade-offs between laser power and energy, and modifications to case-to-capsule ratio. Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

Laser plasma instability experiments with KrF lasersa)

NASA Astrophysics Data System (ADS)

Weaver, J. L.; Oh, J.; Afeyan, B.; Phillips, L.; Seely, J.; Feldman, U.; Brown, C.; Karasik, M.; Serlin, V.; Aglitskiy, Y.; Mostovych, A. N.; Holland, G.; Obenschain, S.; Chan, L.-Y.; Kehne, D.; Lehmberg, R. H.; Schmitt, A. J.; Colombant, D.; Velikovich, A.

2007-05-01

Deleterious effects of laser-plasma instability (LPI) may limit the maximum laser irradiation that can be used for inertial confinement fusion. The short wavelength (248nm), large bandwidth, and very uniform illumination available with krypton-fluoride (KrF) lasers should increase the maximum usable intensity by suppressing LPI. The concomitant increase in ablation pressure would allow implosion of low-aspect-ratio pellets to ignition with substantial gain (>20) at much reduced laser energy. The proposed KrF-laser-based Fusion Test Facility (FTF) would exploit this strategy to achieve significant fusion power (150MW) with a rep-rate system that has a per pulse laser energy well below 1 MJ. Measurements of LPI using the Nike KrF laser are presented at and above intensities needed for the FTF (I˜2×1015W/cm2). The results to date indicate that LPI is indeed suppressed. With overlapped beam intensity above the planar, single beam intensity threshold for the two-plasmon decay instability, no evidence of instability was observed via measurements of 3/2ωo and 1/2ωo harmonic emissions.

Effects of alpha stopping power modelling on the ignition threshold in a directly-driven inertial confinement fusion capsule

NASA Astrophysics Data System (ADS)

Temporal, Mauro; Canaud, Benoit; Cayzac, Witold; Ramis, Rafael; Singleton, Robert L.

2017-05-01

The alpha-particle energy deposition mechanism modifies the ignition conditions of the thermonuclear Deuterium-Tritium fusion reactions, and constitutes a key issue in achieving high gain in Inertial Confinement Fusion implosions. One-dimensional hydrodynamic calculations have been performed with the code Multi-IFE [R. Ramis, J. Meyer-ter-Vehn, Comput. Phys. Commun. 203, 226 (2016)] to simulate the implosion of a capsule directly irradiated by a laser beam. The diffusion approximation for the alpha energy deposition has been used to optimize three laser profiles corresponding to different implosion velocities. A Monte-Carlo package has been included in Multi-IFE to calculate the alpha energy transport, and in this case the energy deposition uses both the LP [C.K. Li, R.D. Petrasso, Phys. Rev. Lett. 70, 3059 (1993)] and the BPS [L.S. Brown, D.L. Preston, R.L. Singleton Jr., Phys. Rep. 410, 237 (2005)] stopping power models. Homothetic transformations that maintain a constant implosion velocity have been used to map out the transition region between marginally-igniting and high-gain configurations. The results provided by the two models have been compared and it is found that - close to the ignition threshold - in order to produce the same fusion energy, the calculations performed with the BPS model require about 10% more invested energy with respect to the LP model.

Measurement of the shell decompression in direct-drive inertial-confinement-fusion implosions

DOE PAGES

Michel, D. T.; Hu, S. X.; Davis, A. K.; ...

2017-05-10

Measurement of the effect of adiabat (α) on the shell thickness were performed in direct-drive implosions. When reducing the adiabat of the shell from α = 6 to α = 4:5, the shell thickness was measured to decrease from 75 μm to 60 μm, but when decreasing the adiabat further (α = 1:8), the shell thickness was measured to increase to 75 μm. The measured shell thickness, shell trajectories, neutron bang time, and neutron yield were reproduced by two dimensional simulations that include laser imprint, nonlocal thermal transport, cross-beam energy transfer, and first-principles equation-of-state models. The minimum core size wasmore » measured to decrease from 40 μm to 30 μm, consistent with the reduction of the adiabat from α = 6 to α = 1:8. Simulations that neglected imprint reproduced the measured core size of the entire adiabat scan, but signi cantly underestimate the shell thickness for adiabat below ~3. These results show that the decompression of the shell measured for low-adiabat implosions was a result of laser imprint.« less

Measurement of the shell decompression in direct-drive inertial-confinement-fusion implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michel, D. T.; Hu, S. X.; Davis, A. K.

Measurement of the effect of adiabat (α) on the shell thickness were performed in direct-drive implosions. When reducing the adiabat of the shell from α = 6 to α = 4:5, the shell thickness was measured to decrease from 75 μm to 60 μm, but when decreasing the adiabat further (α = 1:8), the shell thickness was measured to increase to 75 μm. The measured shell thickness, shell trajectories, neutron bang time, and neutron yield were reproduced by two dimensional simulations that include laser imprint, nonlocal thermal transport, cross-beam energy transfer, and first-principles equation-of-state models. The minimum core size wasmore » measured to decrease from 40 μm to 30 μm, consistent with the reduction of the adiabat from α = 6 to α = 1:8. Simulations that neglected imprint reproduced the measured core size of the entire adiabat scan, but signi cantly underestimate the shell thickness for adiabat below ~3. These results show that the decompression of the shell measured for low-adiabat implosions was a result of laser imprint.« less

Testing low-mode symmetry control with low-adiabat, extended pulse-lengths in BigFoot implosions on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Hohenberger, Matthias; Casey, D. T.; Thomas, C. A.; Baker, K. L.; Spears, B. K.; Khan, S. F.; Hurricane, O. A.; Callahan, D.

2017-10-01

The Bigfoot approach to indirect-drive inertial confinement fusion (ICF) has been developed as a compromise trading high-convergence and areal densities for high implosion velocities, large adiabats and hydrodynamic stability. Shape control and predictability are maintained by using relatively short laser pulses and merging the shocks within the DT-ice layer. These design choices ultimately limit the theoretically achievable performance, and one strategy to increase the 1-D performance is to reduce the shell adiabat by extending the pulse shape. However, this can result in loss of low-mode symmetry control, as the hohlraum ``bubble,'' the high-Z material launched by the outer-cone beams during the early part of the laser pulse, has more time to expand and will eventually intercept inner-cone beams preventing them from reaching the hohlraum waist, thus losing equatorial capsule drive. We report on experimental results exploring shape control and predictability with extended pulse shapes in BigFoot implosions. Prepared by LLNL under Contract DE-AC52-07NA27344.

Laser-induced damage and fracture in fused silica vacuum windows

NASA Astrophysics Data System (ADS)

Campbell, John H.; Hurst, Patricia A.; Heggins, Dwight D.; Steele, William A.; Bumpas, Stanley E.

1997-05-01

Laser induced damage, that initiates catastrophic fracture, has been observed in large, fused silica lenses that also serve as vacuum barriers in high-fluence positions on the Nova and Beamlet lasers. In nearly all cases damage occurs on the vacuum side of the lens. The damage can lead to catastrophic crack growth if the flaw size exceeds the critical flaw size for SiO2. If the elastic stored energy in the lens in high enough, the lens will fracture into many pieces resulting in an implosion. The consequences of such an implosion can be severe, particularly for large vacuum systems. Three parameters control the degree of fracture in the vacuum barrier window: (1) the elastic stored energy, (2) the ratio of the window thickness to flaw depth and (3) secondary crack propagation. Fracture experiments have ben carried our on 15-cm diameter fused silica windows that contain surface flaws caused by laser damage. The results of these experiments, combined with data from window failures on Beamlet and Nova have been sued to develop design criteria for a 'fail-safe' lens. Specifically the window must be made thick enough such that the peak tensile stress is less than 500 psi and the corresponding ratio of the thickness to critical flaw size is less than 6. Under these conditions a properly mounted window, upon failure, will break into only tow pieces and will not implode. One caveat to these design criteria is that the air leak through the window before secondary crack growth occurs. Finite element stress calculations of a window before and immediately following fracture into two pieces show that the elastic stored energy is redistributed if the fragments 'lock' in place and thereby bridge the opening. In such cases, the peak stresses at the flaw site can increase leading to further crack growth.

Nuclear science experiments with a bright neutron source from fusion reactions on the OMEGA Laser System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forrest, C. J.; Knauer, J. P.; Schroeder, W. U.

Subnanosecond impulses of 10 13 to 10 14 neutrons, produced in direct-drive laser inertial confinement fusion implosions, have been used to irradiate deuterated targets at the OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. The target compounds include heavy water (D 2O) and deuterated benzene (C 6D 6). Yields and energy spectra of neutrons from D(n,2n)p to study the breakup reaction have been measured at a forward angle of θlab = 3.5 degrees plus/minus 3.5 degrees with a sensitive, high-dynamic-range neutron time-of-flight spectrometer to infer the double-differential breakup cross section d2sigma/dEdomega for 14-MeV D–T fusionmore » neutrons.« less

Nuclear science experiments with a bright neutron source from fusion reactions on the OMEGA Laser System

DOE PAGES

Forrest, C. J.; Knauer, J. P.; Schroeder, W. U.; ...

2018-01-31

Subnanosecond impulses of 10 13 to 10 14 neutrons, produced in direct-drive laser inertial confinement fusion implosions, have been used to irradiate deuterated targets at the OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. The target compounds include heavy water (D 2O) and deuterated benzene (C 6D 6). Yields and energy spectra of neutrons from D(n,2n)p to study the breakup reaction have been measured at a forward angle of θlab = 3.5 degrees plus/minus 3.5 degrees with a sensitive, high-dynamic-range neutron time-of-flight spectrometer to infer the double-differential breakup cross section d2sigma/dEdomega for 14-MeV D–T fusionmore » neutrons.« less

Description of the NIF Laser

DOE PAGES

Spaeth, M. L.; Manes, K. R.; Kalantar, D. H.; ...

2017-03-23

The possibility of imploding small capsules to produce mini-fusion explosions was explored soon after the first thermonuclear explosions in the early 1950s. Various technologies have been pursued to achieve the focused power and energy required for laboratory-scale fusion. Each technology has its own challenges. For example, electron and ion beams can deliver the large amounts of energy but must contend with Coulomb repulsion forces that make focusing these beams a daunting challenge. The demonstration of the first laser in 1960 provided a new option. Energy from laser beams can be focused and deposited within a small volume; the challenge becamemore » whether a practical laser system can be constructed that delivers the power and energy required while meeting all other demands for achieving a high-density, symmetric implosion. The National Ignition Facility (NIF) is the laser designed and built to meet the challenges for study of high-energy-density physics and inertial confinement fusion (ICF) implosions. This study describes the architecture, systems, and subsystems of NIF. Finally, it describes how they partner with each other to meet these new, complex demands and describes how laser science and technology were woven together to bring NIF into reality.« less

First Liquid Layer Inertial Confinement Fusion Implosions at the National Ignition Facility

DOE PAGES

Olson, R. E.; Leeper, R. J.; Kline, J. L.; ...

2016-12-07

The first cryogenic deuterium and deuterium-tritium liquid layer implosions at the National Ignition Facility (NIF) demonstrate D 2 and DT layer Inertial Confinement Fusion (ICF) implosions that can access low-to-moderate hot spot convergence ratio (1230) DT ice layer implosions. Although high CR is desirable in an idealized 1D sense, it amplifies the deleterious effects of asymmetries. To date, these asymmetries prevented the achievement of ignition at the NIF and are the major cause of simulation-experiment disagreement. In the initial liquid layer experiments, high neutron yields were achieved with CR’s of 12-17, and the hot spot formation is well understood, demonstratedmore » by good agreement between the experimental data and the radiation hydrodynamic simulations. These initial experiments open a new NIF experimental capability that provides an opportunity to explore the relationship between hot-spot convergence ratio and the robustness of hot-spot formation during ICF implosions.« less

Pressure signature and evaluation of hammer pulses during underwater implosion in confining environments.

PubMed

Gupta, Sachin; Matos, Helio; Shukla, Arun; LeBlanc, James M

2016-08-01

The fluid structure interaction phenomenon occurring in confined implosions is investigated using high-speed three-dimensional digital image correlation (DIC) experiments. Aluminum tubular specimens are placed inside a confining cylindrical structure that is partially open to a pressurized environment. These specimens are hydrostatically loaded until they naturally implode. The implosion event is viewed, and recorded, through an acrylic window on the confining structure. The velocities captured through DIC are synchronized with the pressure histories to understand the effects of confining environment on the implosion process. Experiments show that collapse of the implodable volume inside the confining tube leads to strong oscillating water hammer waves. The study also reveals that the increasing collapse pressure leads to faster implosions. Both peak and average structural velocities increase linearly with increasing collapse pressure. The effects of the confining environment are better seen in relatively lower collapse pressure implosion experiments in which a long deceleration phase is observed following the peak velocity until wall contact initiates. Additionally, the behavior of the confining environment can be viewed and understood through classical water hammer theory. A one-degree-of-freedom theoretical model was created to predict the impulse pressure history for the particular problem studied.

X-ray astronomy in the laboratory with a miniature compact object produced by laser-driven implosion

NASA Astrophysics Data System (ADS)

Fujioka, Shinsuke; Takabe, Hideaki; Yamamoto, Norimasa; Salzmann, David; Wang, Feilu; Nishimura, Hiroaki; Li, Yutong; Dong, Quanli; Wang, Shoujun; Zhang, Yi; Rhee, Yong-Joo; Lee, Yong-Woo; Han, Jae-Min; Tanabe, Minoru; Fujiwara, Takashi; Nakabayashi, Yuto; Zhao, Gang; Zhang, Jie; Mima, Kunioki

2009-11-01

X-ray spectroscopy is an important tool for understanding the extreme photoionization processes that drive the behaviour of non-thermal equilibrium plasmas in compact astrophysical objects such as black holes. Even so, the distance of these objects from the Earth and the inability to control or accurately ascertain the conditions that govern their behaviour makes it difficult to interpret the origin of the features in astronomical X-ray measurements. Here, we describe an experiment that uses the implosion driven by a 3TW, 4kJ laser system to produce a 0.5keV blackbody radiator that mimics the conditions that exist in the neighbourhood of a black hole. The X-ray spectra emitted from photoionized silicon plasmas resemble those observed from the binary stars Cygnus X-3 (refs 7, 8) and Vela X-1 (refs 9, 10 11) with the Chandra X-ray satellite. As well as demonstrating the ability to create extreme radiation fields in a laboratory plasma, our theoretical interpretation of these laboratory spectra contrasts starkly with the generally accepted explanation for the origin of similar features in astronomical observations. Our experimental approach offers a powerful means to test and validate the computer codes used in X-ray astronomy.

Laser-Plasma Interactions on NIKE and the Fusion Test Facility

NASA Astrophysics Data System (ADS)

Phillips, Lee; Weaver, James

2008-11-01

Recent proposed designs for a Fusion Test Facility (FTF) (Obenchain et al., Phys. Plasmas 13 056320 (2006)) for direct-drive ICF targets for energy applications involve high implosion velocities combined with higher laser irradiances. The use of high irradiances increases the likelihood of deleterious laser plasma instabilities (LPI) but the proposed use of a 248 nm KrF laser to drive these targets is expected to minimize the LPI risk. We examine, using simulation results from NRL's FAST hydrocode, the proposed operational regimes of the FTF in relation to the thresholds for the SRS, SBS, and 2-plasmon instabilities. Simulations are also used to help design and interpret ongoing experiments being conducted at NRL's NIKE facility for the purpose of generating and studying LPI. Target geometries and laser pulseshapes were devised in order to create plasma conditions with long scalelengths and low electron temperatures that allow the growth of parametric instabilities. These simulations include the effects of finite beam angles through the use of raytracing.

High-resolution, detailed simulations of low foot and high foot implosion experiments on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Clark, Daniel

2015-11-01

In order to achieve the several hundred Gbar stagnation pressures necessary for inertial confinement fusion ignition, implosion experiments on the National Ignition Facility (NIF) require the compression of deuterium-tritium fuel layers by a convergence ratio as high as forty. Such high convergence implosions are subject to degradation by a range of perturbations, including the growth of small-scale defects due to hydrodynamic instabilities, as well as longer scale modulations due to radiation flux asymmetries in the enclosing hohlraum. Due to the broad range of scales involved, and also the genuinely three-dimensional (3-D) character of the flow, accurately modeling NIF implosions remains at the edge of current radiation hydrodynamics simulation capabilities. This talk describes the current state of progress of 3-D, high-resolution, capsule-only simulations of NIF implosions aimed at accurately describing the performance of specific NIF experiments. Current simulations include the effects of hohlraum radiation asymmetries, capsule surface defects, the capsule support tent and fill tube, and use a grid resolution shown to be converged in companion two-dimensional simulations. The results of detailed simulations of low foot implosions from the National Ignition Campaign are contrasted against results for more recent high foot implosions. While the simulations suggest that low foot performance was dominated by ablation front instability growth, especially the defect seeded by the capsule support tent, high foot implosions appear to be dominated by hohlraum flux asymmetries, although the support tent still plays a significant role. Most importantly, it is found that a single, standard simulation methodology appears adequate to model both implosion types and gives confidence that such a model can be used to guide future implosion designs toward ignition. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

The National Ignition Facility: an experimental platform for studying behavior of matter under extreme conditions

NASA Astrophysics Data System (ADS)

Moses, Edward

2011-11-01

The National Ignition Facility (NIF), a 192-beam Nd-glass laser facility capable of producing 1.8 MJ and 500 TW of ultraviolet light, is now operational at Lawrence Livermore National Laboratory (LLNL). As the world's largest and most energetic laser system, NIF serves as the national center for the U.S. Department of Energy (DOE) and National Nuclear Security Administration to achieve thermonuclear burn in the laboratory and to explore the behavior of matter at extreme temperatures and energy densities. By concentrating the energy from all of its 192 extremely energetic laser beams into a mm3-sized target, NIF can reach the conditions required to initiate fusion reactions. NIF can also provide access to extreme scientific environments: temperatures about 100 million K, densities of 1,000 g/cm3, and pressures 100 billion times atmospheric pressure. These conditions have never been created before in a laboratory and exist naturally only in interiors of the planetary and stellar environments as well as in nuclear weapons. Since August 2009, the NIF team has been conducting experiments in support of the National Ignition Campaign (NIC)—a partnership among LLNL, Los Alamos National Laboratory, General Atomics, the University of Rochester, Sandia National Laboratories, as well as a number of universities and international collaborators. The results from these initial experiments show promise for the relatively near-term achievement of ignition. Capsule implosion experiments at energies up to 1.2 MJ have demonstrated laser energetics, radiation temperatures, and symmetry control that scale to ignition conditions. Of particular importance is the demonstration of peak hohlraum temperatures near 300 eV with overall backscatter less than 10%. Cryogenic target capability and additional diagnostics are being installed in preparation for layered target deuterium-tritium implosions to be conducted later in 2010. Important national security and basic science experiments have also been conducted on NIF. This paper describes the unprecedented experimental capabilities of NIF and the results achieved so far on the path toward ignition, for stockpile stewardship, and the beginning of frontier science experiments. The paper will also address our plans to transition NIF to a national user facility, providing access to NIF for researchers from the DOE laboratories, as well as the national and international academic and fusion energy communities.

First Observation of Cross-Beam Energy Transfer Mitigation for Direct-Drive Inertial Confinement Fusion Implosions Using Wavelength Detuning at the National Ignition Facility.

PubMed

Marozas, J A; Hohenberger, M; Rosenberg, M J; Turnbull, D; Collins, T J B; Radha, P B; McKenty, P W; Zuegel, J D; Marshall, F J; Regan, S P; Sangster, T C; Seka, W; Campbell, E M; Goncharov, V N; Bowers, M W; Di Nicola, J-M G; Erbert, G; MacGowan, B J; Pelz, L J; Yang, S T

2018-02-23

Cross-beam energy transfer (CBET) results from two-beam energy exchange via seeded stimulated Brillouin scattering, which detrimentally reduces ablation pressure and implosion velocity in direct-drive inertial confinement fusion. Mitigating CBET is demonstrated for the first time in inertial-confinement implosions at the National Ignition Facility by detuning the laser-source wavelengths (±2.3  Å UV) of the interacting beams. We show that, in polar direct-drive, wavelength detuning increases the equatorial region velocity experimentally by 16% and alters the in-flight shell morphology. These experimental observations are consistent with design predictions of radiation-hydrodynamic simulations that indicate a 10% increase in the average ablation pressure.

First Observation of Cross-Beam Energy Transfer Mitigation for Direct-Drive Inertial Confinement Fusion Implosions Using Wavelength Detuning at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Marozas, J. A.; Hohenberger, M.; Rosenberg, M. J.; Turnbull, D.; Collins, T. J. B.; Radha, P. B.; McKenty, P. W.; Zuegel, J. D.; Marshall, F. J.; Regan, S. P.; Sangster, T. C.; Seka, W.; Campbell, E. M.; Goncharov, V. N.; Bowers, M. W.; Di Nicola, J.-M. G.; Erbert, G.; MacGowan, B. J.; Pelz, L. J.; Yang, S. T.

2018-02-01

Cross-beam energy transfer (CBET) results from two-beam energy exchange via seeded stimulated Brillouin scattering, which detrimentally reduces ablation pressure and implosion velocity in direct-drive inertial confinement fusion. Mitigating CBET is demonstrated for the first time in inertial-confinement implosions at the National Ignition Facility by detuning the laser-source wavelengths (±2.3 Å UV) of the interacting beams. We show that, in polar direct-drive, wavelength detuning increases the equatorial region velocity experimentally by 16% and alters the in-flight shell morphology. These experimental observations are consistent with design predictions of radiation-hydrodynamic simulations that indicate a 10% increase in the average ablation pressure.

Laser absorption, power transfer, and radiation symmetry during the first shock of inertial confinement fusion gas-filled hohlraum experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pak, A.; Dewald, E. L.; Landen, O. L.

2015-12-15

Temporally resolved measurements of the hohlraum radiation flux asymmetry incident onto a bismuth coated surrogate capsule have been made over the first two nanoseconds of ignition relevant laser pulses. Specifically, we study the P2 asymmetry of the incoming flux as a function of cone fraction, defined as the inner-to-total laser beam power ratio, for a variety of hohlraums with different scales and gas fills. This work was performed to understand the relevance of recent experiments, conducted in new reduced-scale neopentane gas filled hohlraums, to full scale helium filled ignition targets. Experimental measurements, matched by 3D view factor calculations, are usedmore » to infer differences in symmetry, relative beam absorption, and cross beam energy transfer (CBET), employing an analytic model. Despite differences in hohlraum dimensions and gas fill, as well as in laser beam pointing and power, we find that laser absorption, CBET, and the cone fraction, at which a symmetric flux is achieved, are similar to within 25% between experiments conducted in the reduced and full scale hohlraums. This work demonstrates a close surrogacy in the dynamics during the first shock between reduced-scale and full scale implosion experiments and is an important step in enabling the increased rate of study for physics associated with inertial confinement fusion.« less

Full-wave and ray-based modeling of cross-beam energy transfer between laser beams with distributed phase plates and polarization smoothing

DOE PAGES

Follett, R. K.; Edgell, D. H.; Froula, D. H.; ...

2017-10-20

Radiation-hydrodynamic simulations of inertial confinement fusion (ICF) experiments rely on ray-based cross-beam energy transfer (CBET) models to calculate laser energy deposition. The ray-based models assume locally plane-wave laser beams and polarization averaged incoherence between laser speckles for beams with polarization smoothing. The impact of beam speckle and polarization smoothing on crossbeam energy transfer (CBET) are studied using the 3-D wave-based laser-plasma-interaction code LPSE. The results indicate that ray-based models under predict CBET when the assumption of spatially averaged longitudinal incoherence across the CBET interaction region is violated. A model for CBET between linearly-polarized speckled beams is presented that uses raymore » tracing to solve for the real speckle pattern of the unperturbed laser beams within the eikonal approximation and gives excellent agreement with the wavebased calculations. Lastly, OMEGA-scale 2-D LPSE calculations using ICF relevant plasma conditions suggest that the impact of beam speckle on laser absorption calculations in ICF implosions is small (< 1%).« less

Full-wave and ray-based modeling of cross-beam energy transfer between laser beams with distributed phase plates and polarization smoothing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Follett, R. K.; Edgell, D. H.; Froula, D. H.

Radiation-hydrodynamic simulations of inertial confinement fusion (ICF) experiments rely on ray-based cross-beam energy transfer (CBET) models to calculate laser energy deposition. The ray-based models assume locally plane-wave laser beams and polarization averaged incoherence between laser speckles for beams with polarization smoothing. The impact of beam speckle and polarization smoothing on crossbeam energy transfer (CBET) are studied using the 3-D wave-based laser-plasma-interaction code LPSE. The results indicate that ray-based models under predict CBET when the assumption of spatially averaged longitudinal incoherence across the CBET interaction region is violated. A model for CBET between linearly-polarized speckled beams is presented that uses raymore » tracing to solve for the real speckle pattern of the unperturbed laser beams within the eikonal approximation and gives excellent agreement with the wavebased calculations. Lastly, OMEGA-scale 2-D LPSE calculations using ICF relevant plasma conditions suggest that the impact of beam speckle on laser absorption calculations in ICF implosions is small (< 1%).« less

Conceptual design of a fast-ignition laser fusion reactor based on a dry wall chamber

NASA Astrophysics Data System (ADS)

Ogawa, Y.; Goto, T.; Okano, K.; Asaoka, Y.; Hiwatari, R.; Someya, Y.

2008-05-01

The fast ignition is quite attractive for a compact laser fusion reactor, because a sufficiently high pellet gain is available with a small input energy. We designed an inertial fusion reactor based on Fast-ignition Advanced Laser fusion reactor CONcept, called FALCON-D, where a dry wall is employed for a chamber wall. A simple point model shows that the pellet gain G~100 is available with laser energies of 350kJ for implosion, 50kJ for heating. This results in the fusion yield of 40 MJ in one shot. By increasing the repetition rate up to 30 Hz, the fusion power of 1.2 GWth becomes available. Plant system analysis shows the net electric power to be about 0.4 GWe In the fast ignition it is available to employ a low aspect ratio pellet, which is favorable for the stability during the implosion phase. Here the pellet aspect ratio is reduced to be 2 ~ 4, and the optimization of the pulse shape for the implosion laser are carried out by using the 1-D hydrodynamic simulation code ILESTA-1D. A ferritic steel with a tungsten armour is employed for the chamber wall. The feasibility of this dry wall concept is studied from various engineering aspects such as surface melting, physical and chemical sputtering, blistering and exfoliation by helium retention, and thermo-mechanical fatigue, and it is found that blistering and exfoliation due to the helium retention and fatigue failure due to cyclic thermal load are major concerns. The cost analysis shows that the construction cost is moderate but the cost of electricity is slightly expensive.

A compact proton spectrometer for measurement of the absolute DD proton spectrum from which yield and ρR are determined in thin-shell inertial-confinement-fusion implosions.

PubMed

Rosenberg, M J; Zylstra, A B; Frenje, J A; Rinderknecht, H G; Johnson, M Gatu; Waugh, C J; Séguin, F H; Sio, H; Sinenian, N; Li, C K; Petrasso, R D; Glebov, V Yu; Hohenberger, M; Stoeckl, C; Sangster, T C; Yeamans, C B; LePape, S; Mackinnon, A J; Bionta, R M; Talison, B; Casey, D T; Landen, O L; Moran, M J; Zacharias, R A; Kilkenny, J D; Nikroo, A

2014-10-01

A compact, step range filter proton spectrometer has been developed for the measurement of the absolute DD proton spectrum, from which yield and areal density (ρR) are inferred for deuterium-filled thin-shell inertial confinement fusion implosions. This spectrometer, which is based on tantalum step-range filters, is sensitive to protons in the energy range 1-9 MeV and can be used to measure proton spectra at mean energies of ∼1-3 MeV. It has been developed and implemented using a linear accelerator and applied to experiments at the OMEGA laser facility and the National Ignition Facility (NIF). Modeling of the proton slowing in the filters is necessary to construct the spectrum, and the yield and energy uncertainties are ±<10% in yield and ±120 keV, respectively. This spectrometer can be used for in situ calibration of DD-neutron yield diagnostics at the NIF.

A compact proton spectrometer for measurement of the absolute DD proton spectrum from which yield and pR are determined in thin-shell inertial-confinement-fusion implosions

DOE PAGES

Rosenberg, M. J.; Zylstra, A. B.; Frenje, J. A.; ...

2014-10-10

A compact, step range filter proton spectrometer has been developed for the measurement of the absolute DD proton spectrum, from which yield and areal density (ρR) are inferred for deuterium-filled thin-shell inertial confinement fusion implosions. This spectrometer, which is based on tantalum step-range filters, is sensitive to protons in the energy range 1-9 MeV and can be used to measure proton spectra at mean energies of ~1-3 MeV. It has been developed and implemented using a linear accelerator and applied to experiments at the OMEGA laser facility and the National Ignition Facility (NIF). Modeling of the proton slowing in themore » filters is necessary to construct the spectrum, and the yield and energy uncertainties are ±<10% in yield and ±120 keV, respectively. This spectrometer can be used for in situ calibration of DD-neutron yield diagnostics at the NIF« less

A compact proton spectrometer for measurement of the absolute DD proton spectrum from which yield and ρR are determined in thin-shell inertial-confinement-fusion implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosenberg, M. J., E-mail: mrosenbe@mit.edu; Zylstra, A. B.; Frenje, J. A.

2014-10-01

A compact, step range filter proton spectrometer has been developed for the measurement of the absolute DD proton spectrum, from which yield and areal density (ρR) are inferred for deuterium-filled thin-shell inertial confinement fusion implosions. This spectrometer, which is based on tantalum step-range filters, is sensitive to protons in the energy range 1-9 MeV and can be used to measure proton spectra at mean energies of ~1-3 MeV. It has been developed and implemented using a linear accelerator and applied to experiments at the OMEGA laser facility and the National Ignition Facility (NIF). Modeling of the proton slowing in themore » filters is necessary to construct the spectrum, and the yield and energy uncertainties are ±<10% in yield and ±120 keV, respectively. This spectrometer can be used for in situ calibration of DD-neutron yield diagnostics at the NIF.« less

Development of new platforms for hydrodynamic instability and asymmetry measurements in deceleration phase of indirectly-driven implosions on NIF

NASA Astrophysics Data System (ADS)

Pickworth, Louisa

2017-10-01

Hydrodynamic instabilities and asymmetries are a major obstacle in the quest to achieve ignition as they cause pre-existing capsule perturbations to grow and ultimately quench the fusion burn in experiments at the National Ignition Facility (NIF). This talk will review recent developments of the experimental platforms and techniques to measure high-mode instabilities and low-mode asymmetries in the deceleration phase of implosions. These new platforms provide a natural link between the acceleration-phase experiments and neutron performance of layered deuterium-tritium implosions. In one innovative technique, self-emission from the hot spot was enhanced with argon dopant to ``self-backlight'' the shell in-flight around peak compression. Experiments with pre-imposed 2-D perturbations measured instability growth factors, while experiments with 3-D, ``native-roughness'' perturbations measured shell integrity in the deceleration phase of implosions. In a complimentary technique, the inner surface of the shell, along with its low-mode asymmetries and high-mode perturbations were visualized in implosions using x-ray emission of a high-Z dopant added to the inner surface of the capsule. These new measurements were instrumental in revealing unexpected surprises and providing improved understanding of the role of instabilities and asymmetries on implosion performance. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Development of Eulerian Code Modeling for ICF Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bradley, Paul A.

2014-02-27

One of the most pressing unexplained phenomena standing in the way of ICF ignition is understanding mix and how it interacts with burn. Experiments were being designed and fielded as part of the Defect-Induced Mix Experiment (DIME) project to obtain data about the extent of material mix and how this mix influenced burn. Experiments on the Omega laser and National Ignition Facility (NIF) provided detailed data for comparison to the Eulerian code RAGE1. The Omega experiments were able to resolve the mix and provide “proof of principle” support for subsequent NIF experiments, which were fielded from July 2012 through Junemore » 2013. The Omega shots were fired at least once per year between 2009 and 2012. RAGE was not originally designed to model inertial confinement fusion (ICF) implosions. It still lacks lasers, so the code has been validated using an energy source. To test RAGE, the simulation output is compared to data and by means of postprocessing tools that were developed. Here, the various postprocessing tools are described with illustrative examples.« less

Detailed implosion modeling of deuterium-tritium layered experiments on the National Ignition Facilitya)

NASA Astrophysics Data System (ADS)

Clark, D. S.; Hinkel, D. E.; Eder, D. C.; Jones, O. S.; Haan, S. W.; Hammel, B. A.; Marinak, M. M.; Milovich, J. L.; Robey, H. F.; Suter, L. J.; Town, R. P. J.

2013-05-01

More than two dozen inertial confinement fusion ignition experiments with cryogenic deuterium-tritium layers have now been performed on the National Ignition Facility (NIF) [G. H. Miller et al., Opt. Eng. 443, 2841 (2004)]. Each of these yields a wealth of data including neutron yield, neutron down-scatter fraction, burn-averaged ion temperature, x-ray image shape and size, primary and down-scattered neutron image shape and size, etc. Compared to 2-D radiation-hydrodynamics simulations modeling both the hohlraum and the capsule implosion, however, the measured capsule yield is usually lower by a factor of 5 to 10, and the ion temperature varies from simulations, while most other observables are well matched between experiment and simulation. In an effort to understand this discrepancy, we perform detailed post-shot simulations of a subset of NIF implosion experiments. Using two-dimensional HYDRA simulations [M. M. Marinak, et al., Phys. Plasmas 8, 2275 (2001).] of the capsule only, these simulations represent as accurately as possible the conditions of a given experiment, including the as-shot capsule metrology, capsule surface roughness, and ice layer defects as seeds for the growth of hydrodynamic instabilities. The radiation drive used in these capsule-only simulations can be tuned to reproduce quite well the measured implosion timing, kinematics, and low-mode asymmetry. In order to simulate the experiments as accurately as possible, a limited number of fully three-dimensional implosion simulations are also being performed. Despite detailed efforts to incorporate all of the effects known and believed to be important in determining implosion performance, substantial yield discrepancies remain between experiment and simulation. Some possible alternate scenarios and effects that could resolve this discrepancy are discussed.

Isolating and quantifying cross-beam energy transfer in direct-drive implosions on OMEGA and the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davis, A. K., E-mail: adavi@lle.rochester.edu; Cao, D.; Michel, D. T.

The angularly resolved mass ablation rates and ablation-front trajectories for Si-coated CH targets were measured in direct-drive inertial confinement fusion experiments to quantify cross-beam energy transfer (CBET) while constraining the hydrodynamic coupling. A polar-direct-drive laser configuration, where the equatorial laser beams were dropped and the polar beams were repointed from a symmetric direct-drive configuration, was used to limit CBET at the pole while allowing it to persist at the equator. The combination of low- and high-CBET conditions observed in the same implosion allowed for the effects of CBET on the ablation rate and ablation pressure to be determined. Hydrodynamic simulationsmore » performed without CBET agreed with the measured ablation rate and ablation-front trajectory at the pole of the target, confirming that the CBET effects on the pole are small. The simulated mass ablation rates and ablation-front trajectories were in excellent agreement with the measurements at all angles when a CBET model based on Randall's equations [C. J. Randall et al., Phys. Fluids 24, 1474 (1981)] was included into the simulations with a multiplier on the CBET gain factor. These measurements were performed on OMEGA and at the National Ignition Facility to access a wide range of plasma conditions, laser intensities, and laser beam geometries. The presence of the CBET gain multiplier required to match the data in all of the configurations tested suggests that additional physics effects, such as intensity variations caused by diffraction, polarization effects, or shortcomings of extending the 1-D Randall model to 3-D, should be explored to explain the differences in observed and predicted drive.« less

Beryllium implosion experiments at high case-to-capsule ratio on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Zylstra, Alex; Yi, Austin; Kline, John; Kyrala, George; Loomis, Eric; Perry, Ted; Shah, Rahul; Batha, Steve; MacLaren, Steve; Ralph, Joe; Salmonson, Jay; Masse, Laurent; Nikroo, Abbas; Stadermann, Michael; Callahan, Debbie; Hurricane, Omar; Rice, Neal; Huang, Haibo; Kong, Casey

2017-10-01

Using beryllium as an ablator material has several potential advantages for inertial fusion because of its low opacity and thus higher ablation rate. This could enable novel designs taking advantage of the reduced ablation-front growth rate, or operating at lower radiation temperature. To investigate the integrated performance of beryllium implosions, we conducted a tuning campaign leading into DT layered implosions using a 900um radius capsule in a 6.72mm diameter hohlraum (case-to-capsule ratio CCR=3.7); the large CCR enables direct study of the 1-D implosion performance. The tuning campaign shots demonstrate excellent control over the shock timing and implosion symmetry at this CCR. Performance data from the DT experiments will also be discussed. This work was performed under the auspices of the U.S. DoE by LANL under contract DE-AC52-06NA52396.

Developing one-dimensional implosions for inertial confinement fusion science

DOE PAGES

Kline, John L.; Yi, Sunghwan A.; Simakov, Andrei Nikolaevich; ...

2016-12-12

Experiments on the National Ignition Facility show that multi-dimensional effects currently dominate the implosion performance. Low mode implosion symmetry and hydrodynamic instabilities seeded by capsule mounting features appear to be two key limiting factors for implosion performance. One reason these factors have a large impact on the performance of inertial confinement fusion implosions is the high convergence required to achieve high fusion gains. To tackle these problems, a predictable implosion platform is needed meaning experiments must trade-off high gain for performance. LANL has adopted three main approaches to develop a one-dimensional (1D) implosion platform where 1D means measured yield overmore » the 1D clean calculation. A high adiabat, low convergence platform is being developed using beryllium capsules enabling larger case-to-capsule ratios to improve symmetry. The second approach is liquid fuel layers using wetted foam targets. With liquid fuel layers, the implosion convergence can be controlled via the initial vapor pressure set by the target fielding temperature. The last method is double shell targets. For double shells, the smaller inner shell houses the DT fuel and the convergence of this cavity is relatively small compared to hot spot ignition. However, double shell targets have a different set of trade-off versus advantages. As a result, details for each of these approaches are described.« less

Symmetry control in subscale near-vacuum hohlraums

NASA Astrophysics Data System (ADS)

Turnbull, D.; Berzak Hopkins, L. F.; Le Pape, S.; Divol, L.; Meezan, N.; Landen, O. L.; Ho, D. D.; Mackinnon, A.; Zylstra, A. B.; Rinderknecht, H. G.; Sio, H.; Petrasso, R. D.; Ross, J. S.; Khan, S.; Pak, A.; Dewald, E. L.; Callahan, D. A.; Hurricane, O.; Hsing, W. W.; Edwards, M. J.

2016-05-01

Controlling the symmetry of indirect-drive inertial confinement fusion implosions remains a key challenge. Increasing the ratio of the hohlraum diameter to the capsule diameter (case-to-capsule ratio, or CCR) facilitates symmetry tuning. By varying the balance of energy between the inner and outer cones as well as the incident laser pulse length, we demonstrate the ability to tune from oblate, through round, to prolate at a CCR of 3.2 in near-vacuum hohlraums at the National Ignition Facility, developing empirical playbooks along the way for cone fraction sensitivity of various laser pulse epochs. Radiation-hydrodynamic simulations with enhanced inner beam propagation reproduce most experimental observables, including hot spot shape, for a majority of implosions. Specular reflections are used to diagnose the limits of inner beam propagation as a function of pulse length.

Update on 2-D OMEGA Capsule Implosions

NASA Astrophysics Data System (ADS)

Bradley, Paul

2017-10-01

We have an upgraded laser energy deposition package in our AMR-Eulerian radiation-hydrodynamic code called RAGE. As part of our validation effort, we ran 2-D simulations for a series of OMEGA direct drive implosion capsules that have shell thickness ranging from 7.2 to 29.3 μm and different gas fills. These simulations include the effect of surface roughness, laser spot non-uniformity, the mounting stalk, and the glue spot. We examined the sensitivity of our simulated results to mesh resolution and mix model. Our simulated results compare well to the experimental yield, ion temperature, burn width, and x-ray size data. Work performed by Los Alamos National Laboratory under contract DE-AC52-06NA25396 for the National Nuclear Security Administration of the U.S. Department of Energy.

High-Performance Cryogenic Designs for OMEGA and the National Ignition Facility

NASA Astrophysics Data System (ADS)

Goncharov, V. N.; Collins, T. J. B.; Marozas, J. A.; Regan, S. P.; Betti, R.; Boehly, T. R.; Campbell, E. M.; Froula, D. H.; Igumenshchev, I. V.; McCrory, R. L.; Myatt, J. F.; Radha, P. B.; Sangster, T. C.; Shvydky, A.

2016-10-01

The main advantage of laser symmetric direct drive (SDD) is a significantly higher coupled drive laser energy to the hot-spot internal energy at stagnation compared to that of laser indirect drive. Because of coupling losses resulting from cross-beam energy transfer (CBET), however, reaching ignition conditions on the NIF with SDD requires designs with excessively large in-flight aspect ratios ( 30). Results of cryogenic implosions performed on OMEGA show that such designs are unstable to short-scale nonuniformity growth during shell implosion. Several CBET reduction strategies have been proposed in the past. This talk will discuss high-performing designs using several CBET-mitigation techniques, including using drive laser beams smaller than the target size and wavelength detuning. Designs that are predicted to reach alpha burning regimes as well as a gain of 10 to 40 at the NIF-scale will be presented. Hydrodynamically scaled OMEGA designs with similar CBET-reduction techniques will also be discussed. This material is based upon work supported by the Department Of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Updated LPI Thresholds for the Nike Laser*

NASA Astrophysics Data System (ADS)

Weaver, J. L.; Oh, J.; Afeyan, B.; Phillips, L.; Seely, J.; Kehne, D.; Brown, C.; Obenschain, S. P.; Serlin, V.; Schmitt, A. J.; Feldman, U.; Holland, G.; Manka, C.; Lehmberg, R. H.; McLean, E.

2009-11-01

Advanced implosion designs for direct drive inertial confinement fusion use high laser intensities (10^15-10^16 W/cm^2) to achieve gain (g>100) with a reduction in total laser energy (E<1 MJ). Krypton-fluoride lasers such as the Nike laser at NRL are an attractive choice due to their combination of short wavelength (248 nm), large bandwidth (1-2 THz), and beam smoothing by induced spatial incoherence but the potential threat from laser-plasma instabilities (LPI) needs to be assessed. The 2008 LPI campaign at Nike yielded threshold intensities above 10^15 W/cm^2 for the two-plasmon instability, a value higher than reported for 351 nm glass lasers. The experiments used a planar geometry, solid polystyrene targets, and a subset of beams (E<200 J) with a reduced focal spot (d<125 μm). The 2009 campaign extended the shot parameters to higher laser energies (E<1 kJ) and larger spot sizes (d<300 μm). Spectrally-resolved and time-resolved measurements of x-rays and emission near ^1/2φo and ^3/2φo harmonics of the laser wavelength show threshold intensities consistent with the 2008 results. *Work supported by DoE/NNSA

Two-Plasmon Decay: Simulations and Experiments on the NIKE Laser System

NASA Astrophysics Data System (ADS)

Phillips, Lee; Weaver, J. L.; Oh, J.; Schmitt, A. J.; Obenschain, S.; Colombant, D.

2009-11-01

NIKE is a Krf laser system at the Naval Research Laboratory used to explore hydrodynamic stability, equation of state, and other issues arising in the research toward inertial fusion energy. The relatively small KrF wavelength, according to widely used theories, raises the threshold of most parametric instabilities. We report on simulations performed using the FAST3d radiation hydrocode to design TPD experiments. By post-processing the results of the simulations we have designed experiments that have explored the use of simple threshold formulas (from developing theories) and help establish the soundness of our simulational approach. Turning to the targets proposed for ICF energy research, we have found that among the designs for the proposed Fusion Test Facility (Obenschain et al., Phys. Plasmas 13 056320 (2006)), are some that are below LPI thresholds. We have also studied high-gain KrF shock ignition designs and found that they are below LPI thresholds for most of the implosion, becoming susceptible to TPD only late in the pulse.

Addressing Common Technical challenges in Inertial Confinement Fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haynes, Donald A.

2016-09-22

The implosion phase for Inertial Confinement Fusion (ICF) occurs from initiation of the drive until just before stagnation. Evolution of the shell and fusion fuel during the implosion phase is affected by the initial conditions of the target, the drive history. Poor performing implosions are a result of the behavior that occurs during the implosion phase such as low mode asymmetries, mixing of the ablator into the fuel, and the hydrodynamic evolution of initial target features and defects such as the shell mounting hardware. The ultimate results of these effects can only be measured at stagnation. However, studying the implosionmore » phase can be effective for understanding and mitigating these effects and for of ultimately improving the performance of ICF implosions. As the ICF program moves towards the 2020 milestone to “determine the efficacy of ignition”, it will be important to understand the physics that occurs during the implosion phase. This will require both focused and integrated experiments. Focused experiments will provide the understanding and the evidence needed to support any determination concerning the efficacy of ignition.« less

Down-bore two-laser heterodyne velocimetry of an implosion-driven hypervelocity launcher

NASA Astrophysics Data System (ADS)

Hildebrand, Myles; Huneault, Justin; Loiseau, Jason; Higgins, Andrew J.

2017-01-01

The implosion-driven launcher uses explosives to shock-compress helium, driving well-characterized projectiles to velocities exceeding 10 km/s. The masses of projectiles range between 0.1 - 15 g, and the design shows excellent scalability, reaching similar velocities across different projectile sizes. In the past, velocity measurements have been limited to muzzle velocity obtained via a high-speed videography upon the projectile exiting the launch tube. Recently, Photon Doppler Velocimetry (PDV) has demonstrated the ability to continuously measure in-bore velocity, even in the presence of significant blow-by of high temperature helium propellant past the projectile. While a single laser system sampled at 40 GS/s with a 13 GHz detector/scope bandwidth is limited to 8 km/s, a two-laser PDV system is developed that uses two lasers operating near 1550 nm to provide velocity measurement capabilities up to 16 km/s with the same bandwidth and sampling rate. The two-laser PDV system is used to obtain a continuous velocity history of the projectile throughout the entire launch cycle. These internal ballistics trajectories are used to compare different advanced concepts aimed at increasing the projectile velocity to well beyond 10 km/s.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spaeth, M. L.; Manes, K. R.; Kalantar, D. H.

The possibility of imploding small capsules to produce mini-fusion explosions was explored soon after the first thermonuclear explosions in the early 1950s. Various technologies have been pursued to achieve the focused power and energy required for laboratory-scale fusion. Each technology has its own challenges. For example, electron and ion beams can deliver the large amounts of energy but must contend with Coulomb repulsion forces that make focusing these beams a daunting challenge. The demonstration of the first laser in 1960 provided a new option. Energy from laser beams can be focused and deposited within a small volume; the challenge becamemore » whether a practical laser system can be constructed that delivers the power and energy required while meeting all other demands for achieving a high-density, symmetric implosion. The National Ignition Facility (NIF) is the laser designed and built to meet the challenges for study of high-energy-density physics and inertial confinement fusion (ICF) implosions. This study describes the architecture, systems, and subsystems of NIF. Finally, it describes how they partner with each other to meet these new, complex demands and describes how laser science and technology were woven together to bring NIF into reality.« less

First Observation of Cross-Beam Energy Transfer Mitigation for Direct-Drive Inertial Confinement Fusion Implosions Using Wavelength Detuning at the National Ignition Facility

DOE PAGES

Marozas, J. A.; Hohenberger, M.; Rosenberg, M. J.; ...

2018-02-22

Cross-beam energy transfer (CBET) results from two-beam energy exchange via seeded stimulated Brillouin scattering, which detrimentally reduces ablation pressure and implosion velocity in direct-drive inertial confinement fusion. Direct-drive implosions at the National Ignition Facility were conducted to reduce CBET by detuning the laser-source wavelengths (±2.3 Å UV) of the interacting beams over the equatorial region of the target. For the first time, wavelength detuning was shown to increase the equatorial region velocity experimentally by 16% and to alter the in-flight shell morphology. These experimental observations are consistent with design predictions of radiation–hydrodynamic simulations that indicate a 10% increase in themore » average ablation pressure.« less

First Observation of Cross-Beam Energy Transfer Mitigation for Direct-Drive Inertial Confinement Fusion Implosions Using Wavelength Detuning at the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marozas, J. A.; Hohenberger, M.; Rosenberg, M. J.

Cross-beam energy transfer (CBET) results from two-beam energy exchange via seeded stimulated Brillouin scattering, which detrimentally reduces ablation pressure and implosion velocity in direct-drive inertial confinement fusion. Direct-drive implosions at the National Ignition Facility were conducted to reduce CBET by detuning the laser-source wavelengths (±2.3 Å UV) of the interacting beams over the equatorial region of the target. For the first time, wavelength detuning was shown to increase the equatorial region velocity experimentally by 16% and to alter the in-flight shell morphology. These experimental observations are consistent with design predictions of radiation–hydrodynamic simulations that indicate a 10% increase in themore » average ablation pressure.« less

Laser irradiance scaling in polar direct drive implosions on the National Ignition Facility

DOE PAGES

Murphy, T. J.; Krasheninnikova, N. S.; Kyrala, G. A.; ...

2015-09-17

Polar-direct-drive experiments conducted at the National Ignition Facility [E. I. Moses, Fusion Sci. Technol. 54, 361 (2008)] performed at laser irradiance between 1 and 2×10 15 W/cm 2 exhibit increased hard x-ray emission, decreased neutron yield, and reduced areal density as the irradiance is increased. Experimental x-ray images at the higher irradiances show x-ray emission at the equator, as well as degraded symmetry, that is not predicted in hydrodynamic simulations using flux-limited energy transport, but that appear when non-local electron transport together with a model to account for cross beam energy transfer (CBET) is utilized. The reduction in laser powermore » for equatorial beams required in the simulations to reproduce the effects of CBET on the observed symmetry also reproduces the yield degradation consistent with experimental data.« less

Investigating the laser heating of underdense plasmas at conditions relevant to MagLIF

NASA Astrophysics Data System (ADS)

Harvey-Thompson, Adam

2015-11-01

The magnetized Liner Inertial Fusion (MagLIF) scheme has achieved thermonuclear fusion yields on Sandia's Z Facility by imploding a cylindrical liner filled with D2 fuel that is preheated with a multi-kJ laser and pre-magnetized with an axial field Bz = 10 T. The challenge of fuel preheating in MagLIF is to deposit several kJ's of energy into an underdense (ne/ncrit<0.1) fusion fuel over ~ 10 mm target length efficiently and without introducing contaminants that could contribute to unacceptable radiative losses during the implosion. Very little experimental work has previously been done to investigate laser heating of gas at densities, scale lengths, modest intensities (Iλ2 ~ 1014 watts- μm2 /cm2) and magnetization parameters (ωceτe ~ 10) necessary for MagLIF. In particular, magnetization of the preheated plasma suppresses electron thermal conduction, which can modify laser energy coupling. Providing an experimental dataset in this regime is essential to not only understand the dynamics of a MagLIF implosion and stagnation, but also to validate magnetized transport models and better understand the physics of laser propagation in magnetized plasmas. In this talk, we present data and analysis of several experiments conducted at OMEGA-EP and at Z to investigate laser propagation and plasma heating in underdense D2 plasmas under a range of conditions, including densities (ne = 0.05-0.1 nc) and magnetization parmaters (ωceτe ~ 0-10). The results show differences in the electron temperature of the heated plasma and the velocity of the laser burn wave with and without an applied magnetic field. We will show comparisons of these experimental results to 2D and 3D HYDRA simulations, which show that the effect of the magnetic field on the electron thermal conduction needs to be taken into account when modeling laser preheat. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.

Present Status and Prospects of FIREX Project

NASA Astrophysics Data System (ADS)

Mima, K.

2008-07-01

The goal of the first phase of Fast Ignition Realization EXperiment (FIREX) project (FIREX-I) is to demonstrate ignition temperature of 5-10 keV, followed by the second phase to demonstrate ignition and burn. Since starting FIREX-I project, plasma physics study in ILE has been devoted to increase the coupling efficiency and to improve compression performance. The heating efficiency can be increased by the following two ways. 1) A previous experiments indicate that the coupling of heating laser to imploded plasmas increases with coating a low-density. foam used in the experiment, low-Z plastic foam is desired for efficient electron transport. (Lei et al. 2006). 2) Electrons generated in the inner surface of the double cone will return by sheathe potential generated between two cones. A 2-D PIC simulation indicates that hot electron confinement is improved by a factor of 1.7 (Nakamura et al. 2007). Further optimization of cone geometry by 2-D simulation will be presented in the workshop. The implosion performance can be improved by three ways. 1) Low-Z plastic layer coating on the outer surface of the cone: The 2D hydro-simulation PINOCO predicts that the target areal density increases by a factor of 2. 2) Br doped plastic layer on a fuel pellet may significantly moderate the Rayleigh-Taylor instability (Fujioka et al. 2004), making implosion more stable. 3) Reducing vapor gas pressure in a pellet is necessary to suppress strength of a jet that will destroy the cone tip. (Stephens et al. 2005). As for the cryogenic target fabrication, R&D of fabricating foam cryogenic cine shell target are under development by the joint group between Osaka Univ. and NIFS. The amplifier system of the heating laser LFEX is completed in March 2008. The amplification test has demonstrated laser energy of 3 kJ/beam at 3nm bandwidth. The equivalent 12 kJ in 4 beams meets the specification of LFEX. The large tiled gratings for pulse compressor are completed and installed. The short pulse laser will be delivered on a target in September, 2008. The fully integrated fast ignition experiments is scheduled on February 2009 until the end of 2010. If subsequent FIREX-II will start as proposed, the ignition and burn will be demonstrated in parallel to that at NIF and LMJ, providing a scientific database of both central and fast ignition.

Early-time radiation flux symmetry optimization and its effect on gas-filled hohlraum ignition targets on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Milovich, J. L.; Dewald, E. L.; Pak, A.; Michel, P.; Town, R. P. J.; Bradley, D. K.; Landen, O.; Edwards, M. J.

2016-03-01

Achieving ignition on the National Ignition Facility (NIF) is tied to our ability to control and minimize deviations from sphericity of the capsule implosion. Low-mode asymmetries of the hot spot result from the combined effect of radiation drive asymmetries throughout the laser pulse and initial roughness on the capsule surface. In this paper, we report on simulations and experiments designed to assess, measure, and correct the drive asymmetries produced by the early-time (≈first 2 ns or "picket") period of the laser pulse. The drive asymmetry during the picket is commonly thought to introduce distortions in the hot-spot shape at ignition time. However, a more subtle effect not previously considered is that it also leads to an asymmetry in shock velocity and timing, thereby increasing the fuel adiabat and reducing the margin for ignition. It is shown via hydrodynamic simulations that minimizing this effect requires that the early-time asymmetry be kept below 7.5% in the second Legendre mode (P2), thus keeping the loss of performance margin below ≈10% for a layered implosion. Asymmetries during the picket of the laser pulse are measured using the instantaneous self-emission of a high-Z re-emission sphere in place of an ignition capsule in a hohlraum with large azimuthal diagnostic windows. Three dimensional simulations using the code HYDRA (to capture the effect of non-azimuthal hohlraum features) coupled to a cross-beam energy transfer model [Michel et al., Phys. Plasmas 17, 056305 (2010)] are used to establish the surrogacy of the re-emit target and to assess the early-time drive symmetry. Calculations using this model exhibit the same sensitivity to variations in the relative input powers between the different cones of NIF beams as measured for the "Rev5" CH target [Haan et al., Phys Plasmas 18, 051001 (2011)] and reported by Dewald et al. [Phys. Rev. Lett. 111, 235001 (2013)]. The same methodology applied to recently improved implosions using different hohlraum geometries and picket powers show good agreement with experimental data.

Early-time radiation flux symmetry optimization and its effect on gas-filled hohlraum ignition targets on the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Milovich, J. L., E-mail: milovich1@llnl.gov; Dewald, E. L.; Pak, A.

2016-03-15

Achieving ignition on the National Ignition Facility (NIF) is tied to our ability to control and minimize deviations from sphericity of the capsule implosion. Low-mode asymmetries of the hot spot result from the combined effect of radiation drive asymmetries throughout the laser pulse and initial roughness on the capsule surface. In this paper, we report on simulations and experiments designed to assess, measure, and correct the drive asymmetries produced by the early-time (≈first 2 ns or “picket”) period of the laser pulse. The drive asymmetry during the picket is commonly thought to introduce distortions in the hot-spot shape at ignition time.more » However, a more subtle effect not previously considered is that it also leads to an asymmetry in shock velocity and timing, thereby increasing the fuel adiabat and reducing the margin for ignition. It is shown via hydrodynamic simulations that minimizing this effect requires that the early-time asymmetry be kept below 7.5% in the second Legendre mode (P{sub 2}), thus keeping the loss of performance margin below ≈10% for a layered implosion. Asymmetries during the picket of the laser pulse are measured using the instantaneous self-emission of a high-Z re-emission sphere in place of an ignition capsule in a hohlraum with large azimuthal diagnostic windows. Three dimensional simulations using the code HYDRA (to capture the effect of non-azimuthal hohlraum features) coupled to a cross-beam energy transfer model [Michel et al., Phys. Plasmas 17, 056305 (2010)] are used to establish the surrogacy of the re-emit target and to assess the early-time drive symmetry. Calculations using this model exhibit the same sensitivity to variations in the relative input powers between the different cones of NIF beams as measured for the “Rev5” CH target [Haan et al., Phys Plasmas 18, 051001 (2011)] and reported by Dewald et al. [Phys. Rev. Lett. 111, 235001 (2013)]. The same methodology applied to recently improved implosions using different hohlraum geometries and picket powers show good agreement with experimental data.« less

Increased shell entropy as an explanation for observed decreased shell areal densities in OMEGA implosions

NASA Astrophysics Data System (ADS)

Hoffman, Nelson; Herrmann, Hans; Kim, Yongho

2014-10-01

A reduced ion-kinetic (RIK) model used in hydrodynamic simulations has had some success in explaining time- and space-averaged observables characterizing the fusion fuel in hot low-density ICF capsule implosions driven by 1-ns 60-beam laser pulses at OMEGA. But observables characterizing the capsule shell, e.g., the areal density of 12C in a plastic shell, have proved harder to explain. Recently we have found that assuming the shell has higher entropy than expected in a 1D laser-driven RIK simulation allows an explanation of the observed values of 12C areal density, and its dependence on initial shell thickness in a set of DT-filled plastic capsules. If, for example, a 15- μm CH shell implodes on an adiabat two to three times higher than predicted in a typical unmodified RIK simulation, the calculated burn-averaged shell areal density decreases from ~80 mg/cm2 in the unmodified simulation to the observed value of ~25 mg/cm2. We discuss possible mechanisms that could lead to increased entropy in such implosions. Research supported by U.S. Department of Energy under Contract DE-AC52-06NA25396.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hall, G. N., E-mail: hall98@llnl.gov; Izumi, N.; Landen, O. L.

Compton radiography provides a means to measure the integrity, ρR and symmetry of the DT fuel in an inertial confinement fusion implosion near peak compression. Upcoming experiments at the National Ignition Facility will use the ARC (Advanced Radiography Capability) laser to drive backlighter sources for Compton radiography experiments and will use the newly commissioned AXIS (ARC X-ray Imaging System) instrument as the detector. AXIS uses a dual-MCP (micro-channel plate) to provide gating and high DQE at the 40–200 keV x-ray range required for Compton radiography, but introduces many effects that contribute to the spatial resolution. Experiments were performed at energiesmore » relevant to Compton radiography to begin characterization of the spatial resolution of the AXIS diagnostic.« less

Development of the Pushered Single Shell Experimental Platform on NIF

NASA Astrophysics Data System (ADS)

Salmonson, Jay; Dewald, Eduard; Graziani, Frank; MacLaren, Stephan; Pino, Jesse; Ralph, Joseph; Sacks, Ryan; Smalyuk, Vladimir; Tipton, Robert

2017-10-01

The goal of the Pushered Single Shell (PSS) experimental campaign is to study mix of partially ionized ablator material into the hotspot. To do this we use a uniformly Si doped plastic capsule, the inner few microns of which can be doped with a few percent Ge. To diagnose mix, we use separated reactants; deuterating the inner Ge-doped layer, CD/Ge, while putting Tritium into the Hydrogen capsule fill gas. Mix is then inferred by measuring the neutron yields from DD, DT, and TT reactions. In order to accentuate the cooling of the hot-spot due to Bremsstrahlung radiation when Ge is present, we required high hot-spot ion temperatures: 3 keV. This, in turn, requires a fast, symmetric implosion. Using the Two-Shock campaign as a starting point, we increased the capsule radius by 25% to 844 μm and the peak laser power by over 10% to 475 TW. We also used a low, 0.3 mg/cc, He fill in the hohlraum to maintain control over implosion symmetry. This paper will describe the sequence of keyhole, 1DConA, 2DConA, and Symcap experiments we performed over the last year to tune the PSS implosions. We were successful in achieving our design goals; the PSS is the fastest CH capsule implosion in the laboratory, with peak velocity 400 μm, a round hot-spot, with hotspot P2 = 0 within errors, and a hot-spot ion temperature 3.5 keV. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.

Validation of a Laser-Ray Package in an Eulerian Code

NASA Astrophysics Data System (ADS)

Bradley, Paul; Hall, Mike; McKenty, Patrick; Collins, Tim; Keller, David

2014-10-01

A laser-ray absorption package was recently installed in the RAGE code by the Laboratory for Laser Energetics (LLE). In this presentation, we describe our use of this package to implode Omega 60 beam symmetric direct drive capsules. The capsules have outer diameters of about 860 microns, CH plastic shell thicknesses between 8 and 32 microns, DD or DT gas fills between 5 and 20 atmospheres, and a 1 ns square pulse of 23 to 27 kJ. These capsule implosions were previously modeled with a calibrated energy source in the outer layer of the capsule, where we matched bang time and burn ion temperature well, but the simulated yields were two to three times higher than the data. We will run simulations with laser ray energy deposition to the experiments and the results to the yield and spectroscopic data. Work performed by Los Alamos National Laboratory under Contract DE-AC52-06NA25396 for the National Nuclear Security Administration of the U.S. Department of Energy.

Saturation of multi-laser beams laser-plasma instabilities from stochastic ion heating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michel, P.; Williams, E. A.; Divol, L.

2013-05-15

Cross-beam energy transfer (CBET) has been used as a tool on the National Ignition Facility (NIF) since the first energetics experiments in 2009 to control the energy deposition in ignition hohlraums and tune the implosion symmetry. As large amounts of power are transferred between laser beams at the entrance holes of NIF hohlraums, the presence of many overlapping beat waves can lead to stochastic ion heating in the regions where laser beams overlap [P. Michel et al., Phys. Rev. Lett. 109, 195004 (2012)]. This increases the ion acoustic velocity and modifies the ion acoustic waves’ dispersion relation, thus reducing themore » plasma response to the beat waves and the efficiency of CBET. This pushes the plasma oscillations driven by CBET in a regime where the phase velocities are much smaller than both the electron and ion thermal velocities. CBET gains are derived for this new regime and generalized to the case of multi ion species plasmas.« less

Analysis of the National Ignition Facility Ignition Hohlraum Energetics Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Town, R J; Rosen, M D; Michel, P A

2010-11-22

A series of forty experiments on the National Ignition Facility (NIF) [E. I. Moses et al., Phys. Plasmas 16, 041006 (2009)] to study energy balance and implosion symmetry in reduced- and full-scale ignition hohlraums was shot at energies up to 1.3 MJ. This paper reports the findings of the analysis of the ensemble of experimental data obtained that has produced an improved model for simulating ignition hohlraums. Last year the first observation in a NIF hohlraum of energy transfer between cones of beams as a function of wavelength shift between those cones was reported [P. Michel, et al, Phys ofmore » Plasmas, 17, 056305, (2010)]. Detailed analysis of hohlraum wall emission as measured through the laser entrance hole (LEH) has allowed the amount of energy transferred versus wavelength shift to be quantified. The change in outer beam brightness is found to be quantitatively consistent with LASNEX [G. B. Zimmerman and W. L. Kruer, Comments Plasma Phys. Control. Fusion 2, 51 (1975)] simulations using the predicted energy transfer when possible saturation of the plasma wave mediating the transfer is included. The effect of the predicted energy transfer on implosion symmetry is also found to be in good agreement with gated x-ray framing camera images. Hohlraum energy balance, as measured by x-ray power escaping the LEH, is quantitatively consistent with revised estimates of backscatter and incident laser energy combined with a more rigorous non-local-thermodynamic-equilibrium atomic physics model with greater emissivity than the simpler average-atom model used in the original design of NIF targets.« less

Hard x-ray (>100 keV) imager to measure hot electron preheat for indirectly driven capsule implosions on the NIF.

PubMed

Döppner, T; Dewald, E L; Divol, L; Thomas, C A; Burns, S; Celliers, P M; Izumi, N; Kline, J L; LaCaille, G; McNaney, J M; Prasad, R R; Robey, H F; Glenzer, S H; Landen, O L

2012-10-01

We have fielded a hard x-ray (>100 keV) imager with high aspect ratio pinholes to measure the spatially resolved bremsstrahlung emission from energetic electrons slowing in a plastic ablator shell during indirectly driven implosions at the National Ignition Facility. These electrons are generated in laser plasma interactions and are a source of preheat to the deuterium-tritium fuel. First measurements show that hot electron preheat does not limit obtaining the fuel areal densities required for ignition and burn.

Comparison of Raman Scattering Measurements and Modeling in NIF Ignition Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strozzi, D J; Hinkel, D E; Williams, E A

2011-11-04

Recent NIF indirect-drive experiments have shown significant Raman scattering from the inner beams. NIF data has motivated improvements to rad-hydro modeling, leading to the 'high flux model' [M. D. Rosen et al., HEDP 7, 180 (2011)]. Cross-beam energy transfer [P. A. Michel et al., Phys. Plasmas 17, 056305 (2010] in the laser entrance hole is an important tool for achieving round implosions, and is uniformly distributed across the laser spot in rad-hydro simulations (but not necessarily in experiments). We find the Raman linear gain spectra computed with these plasma conditions agree well in time-dependent peak wavelength with the measured data,more » especially when overlapping laser-beam intensities are used. More detailed, spatially non-uniform modeling of the cross-beam transfer has been performed. The resulting gains better follow the time history of the measured backscatter. We shall present the impact of spatially non-uniform energy transfer on SRS gain. This metric is valid when amplification is in a linear regime, and so we shall also present an assessment of whether electron trapping in Langmuir waves can play a role in these shots.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goncharov, V. N.; Skupsky, S.; Boehly, T. R.

Irradiation nonuniformities in direct-drive (DD) inertial confinement fusion experiments generate, or ''imprint,'' surface modulations that degrade the symmetry of the implosion and reduce the target performance. To gain physical insight, an analytical model of imprint is developed. The model takes into account the hydrodynamic flow, the dynamics of the conduction zone, and the mass ablation. The important parameters are found to be the time scale for plasma atmosphere formation and the ablation velocity. The model is validated by comparisons to detailed two-dimensional (2D) hydrocode simulations. The results of the model and simulations are in good agreement with a series ofmore » planar-foil imprint experiments performed on the OMEGA laser system [T.R. Boehly, D.L. Brown, R.S. Craxton et al., Opt. Commun. 133, 495 (1997)]. Direct-drive National Ignition Facility's [J.A. Paisner, J.D. Boyes, S.A. Kumpan, W.H. Lowdermilk, and M.S. Sorem, Laser Focus World 30, 75 (1994)] cryogenic targets are shown to have gains larger than 10 when the rms laser-irradiation nonuniformity is reduced by 2D smoothing by spectral dispersion (SSD) used in the current DD target designs. (c)« less

Radiation hardening of gated x-ray imagers for the National Ignition Facility (invited).

PubMed

Bell, P M; Bradley, D K; Kilkenny, J D; Conder, A; Cerjan, C; Hagmann, C; Hey, D; Izumi, N; Moody, J; Teruya, A; Celeste, J; Kimbrough, J; Khater, H; Eckart, M J; Ayers, J

2010-10-01

The National Ignition Facility will soon be producing x-ray flux and neutron yields higher than any produced in laser driven implosion experiments in the past. Even a non-igniting capsule will require x-ray imaging of near burning plasmas at 10(17) neutrons, requiring x-ray recording systems to work in more hostile conditions than we have encountered in past laser facilities. We will present modeling, experimental data and design concepts for x-ray imaging with electronic recording systems for this environment (ARIANE). A novel instrument, active readout in a nuclear environment, is described which uses the time-of-flight difference between the gated x-ray signal and the neutron which induces a background signal to increase the yield at which gated cameras can be used.

Laser-driven magnetic-flux compression in high-energy-density plasmas.

PubMed

Gotchev, O V; Chang, P Y; Knauer, J P; Meyerhofer, D D; Polomarov, O; Frenje, J; Li, C K; Manuel, M J-E; Petrasso, R D; Rygg, J R; Séguin, F H; Betti, R

2009-11-20

The demonstration of magnetic field compression to many tens of megagauss in cylindrical implosions of inertial confinement fusion targets is reported for the first time. The OMEGA laser [T. R. Boehly, Opt. Commun. 133, 495 (1997)10.1016/S0030-4018(96)00325-2] was used to implode cylindrical CH targets filled with deuterium gas and seeded with a strong external field (>50 kG) from a specially developed magnetic pulse generator. This seed field was trapped (frozen) in the shock-heated gas fill and compressed by the imploding shell at a high implosion velocity, minimizing the effect of resistive flux diffusion. The magnetic fields in the compressed core were probed via proton deflectrometry using the fusion products from an imploding D3He target. Line-averaged magnetic fields between 30 and 40 MG were observed.

Symmetry control in subscale near-vacuum hohlraums

DOE PAGES

Turnbull, D.; Berzak Hopkins, L. F.; Le Pape, S.; ...

2016-05-18

Controlling the symmetry of indirect-drive inertial confinement fusion implosions remains a key challenge. Increasing the ratio of the hohlraum diameter to the capsule diameter (case-to-capsule ratio, or CCR) facilitates symmetry tuning. By varying the balance of energy between the inner and outer cones as well as the incident laser pulse length, we demonstrate the ability to tune from oblate, through round, to prolate at a CCR of 3.2 in near-vacuum hohlraums at the National Ignition Facility, developing empirical playbooks along the way for cone fraction sensitivity of various laser pulse epochs. Radiation-hydrodynamic simulations with enhanced inner beam propagation reproduce mostmore » experimental observables, including hot spot shape, for a majority of implosions. In conclusion, specular reflections are used to diagnose the limits of inner beam propagation as a function of pulse length.« less

Proton emission from cone-in-shell fast-ignition experiments at Omega

NASA Astrophysics Data System (ADS)

Sinenian, N.; Theobald, W.; Frenje, J. A.; Stoeckl, C.; Séguin, F. H.; Li, C. K.; Petrasso, R. D.; Stephens, R. B.

2012-11-01

Measurements of energetic protons from cone-in-shell fast-igniton implosions at Omega have been conducted. In these experiments, charged-particle spectrometers were used to measure a significant population (>1013) of energetic protons (7.5 MeV max.), indicating the presence of strong electric fields. These energetic protons, observed in directions both transverse and forward relative to the direction of the short-pulse laser beam, have been used to study aspects of coupling efficiency of the petawatt fast-ignitior beam. Approximately 5% of the laser energy coupled to hot electrons was lost to fast ions. Forward going protons were less energetic and showed no dependence on laser intensity or whether the cone tip was intact when the short-pulse laser was fired. Maximum energies of protons emitted transverse to the cone-in-shell target scale with incident on-target laser intensity (2-6×1018W-cm-2), as described by the ponderomotive scaling (∝I1/2). It is shown that these protons are accelerated from the entire cone, rather than from the cone tip alone. These protons were used to estimate the lower limit on the hot-electron temperature, which was found to be hotter than the ponderomotive scaling by factors of 2-3.

The Defect Induced Mix Experiment (DIME) for NIF

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmitt, Mark J; Bradley, Paul A; Cobble, James A

2012-06-18

LANL will perform two Defect Induced Mix Experiment (DIME) implosion campaigns on NIF in July and September, 2012. This presentation describes the goals for these shots and the experimental configuration and diagnostic set up to collect the appropriate data. The first two-shot campaign will focus on executing polar direct drive (PDD) implosions of plastic CH capsules filled with deuterium gas. Gas filling will be performed through a fill tube at target chamber center. A vanadium backligher foil will provide x-rays to radiograph the last half of the implosion to compare the implosion trajectory with modeling predictions. An equatorial groove inmore » one of the capsules will be present to determine its effect on implosion dynamics. The second DIME campaign will commission and use a spectral imager (MMI) to examine the evolution of thin capsule layers doped with either Ge or Ga at 1.85%. Spectral line emission from these layers will quantify the mix width at the inner shell radius and near an equatorial groove feature.« less

A compact neutron spectrometer for characterizing inertial confinement fusion implosions at OMEGA and the NIF

DOE PAGES

Zylstra, A. B.; Gatu Johnson, M.; Frenje, J. A.; ...

2014-06-04

A compact spectrometer for measurements of the primary deuterium-tritium neutron spectrum has been designed and implemented on the OMEGA laser facility. This instrument uses the recoil spectrometry technique, where neutrons produced in an implosion elastically scatter protons in a plastic foil, which are subsequently detected by a proton spectrometer. This diagnostic is capable of measuring the yield to ~±10% accuracy, and mean neutron energy to ~±50 keV precision. As these compact spectrometers can be readily placed at several locations around an implosion, effects of residual fuel bulk flows during burn can be measured. Future improvements to reduce the neutron energymore » uncertainty to ±15-20 keV are discussed, which will enable measurements of fuel velocities to an accuracy of ~±25-40 km/s.« less

Physics-Based Computational Algorithm for the Multi-Fluid Plasma Model

DTIC Science & Technology

2014-06-30

applying it to study laser - 20 Physics-Based Multi-Fluid Plasma Algorithm Shumlak Figure 6: Blended finite element method applied to the species...separation problem in capsule implosions. Number densities and electric field are shown after the laser drive has compressed the multi-fluid plasma and...6 after the laser drive has started the compression. A separation clearly develops. The solution is found using an explicit advance (CFL=1) for the

Proceedings of Symposium on Physics of Target Implosion and Pulsed Power Techniques Held in Yokohama, Japan on 30 September-1 October 1987

DTIC Science & Technology

1988-02-01

Japan. -- ,, mnm mmmm m m mil II m mlmmmm PREFACE A It is reported that by using the Nd glass laser, experiments of beam-target interaction are carried...Beam 8. 14.00-14.30 T. Ishimoto and T. Kato (Waseda Univ.) Electron Current Effect on Stability of Plasma Channel 9. 14.30-15.00 S. Kawata, M ...Matsumoto and Y. Masubuchi (Tech. Univ. Nagaoka) Numerical Simulation in LIB ICF 10. 15.00-15.30 J. M . Perlado (Univ. Politec. Madrid) Simulation Code for ICF

Shell stability and conditions analyzed using a new method of extracting shell areal density maps from spectrally resolved images of direct-drive inertial confinement fusion implosions

DOE PAGES

Johns, H. M.; Mancini, R. C.; Nagayama, T.; ...

2016-01-25

In warm target direct-drive inertial confinement fusion implosion experiments performed at the OMEGA laser facility, plastic micro-balloons doped with a titanium tracer layer in the shell and filled with deuterium gas were imploded using a low-adiabat shaped laser pulse. Continuum radiation emitted in the core is transmitted through the tracer layer and the resulting spectrum recorded with a gated multi-monochromatic x-ray imager (MMI). Titanium K-shell line absorption spectra observed in the data are due to transitions in L-shell titanium ions driven by the backlighting continuum. The MMI data consist of an array of spectrally resolved images of the implosion. Thesemore » 2-D space-resolved titanium spectral features constrain the plasma conditions and areal density of the titanium doped region of the shell. The MMI data were processed to obtain narrow-band images and space resolved spectra of titanium spectral features. Shell areal density maps, ρL(x,y), extracted using a new method using both narrow-band images and space resolved spectra are confirmed to be consistent within uncertainties. We report plasma conditions in the titanium-doped region of electron temperature (Te) = 400 ± 28 eV, electron number density (N e) = 8.5 × 10 24 ± 2.5 × 10 24 cm –3, and average areal density = 86 ± 7 mg/cm 2. Fourier analysis of areal density maps reveals shell modulations caused by hydrodynamic instability growth near the fuel-shell interface in the deceleration phase. We observe significant structure in modes l = 2–9, dominated by l = 2. We extract a target breakup fraction of 7.1 ± 1.5% from our Fourier analysis. Furthermore, a new method for estimating mix width is evaluated against existing literature and our target breakup fraction. We estimate a mix width of 10.5 ±1 μm.« less

Laser-plasma interactions in direct-drive ignition plasmas

NASA Astrophysics Data System (ADS)

Froula, D. H.; Michel, D. T.; Igumenshchev, I. V.; Hu, S. X.; Yaakobi, B.; Myatt, J. F.; Edgell, D. H.; Follett, R.; Glebov, V. Yu; Goncharov, V. N.; Kessler, T. J.; Maximov, A. V.; Radha, P. B.; Sangster, T. C.; Seka, W.; Short, R. W.; Solodov, A. A.; Sorce, C.; Stoeckl, C.

2012-12-01

Direct-drive ignition is most susceptible to multiple-beam laser-plasma instabilities, as the single-beam intensities are low (Is ˜ 1014 W cm-2) and the electron temperature in the underdense plasma is high (Te ≃ 3.5 keV). Cross-beam energy transfer is driven by multiple laser beams and can significantly reduce the hydrodynamic efficiency in direct-drive experiments on OMEGA (Boehly et al 1997 Opt. Commun. 133 495). Reducing the radii of the laser beams significantly increases the hydrodynamic efficiency at the cost of an increase in the low-mode modulations. Initial 2D hydrodynamic simulations indicate that zooming, transitioning the laser-beam radius prior to the main drive, does not increase low-mode nonuniformities. The combination of zooming and dynamic bandwidth reduction will provide a 30% effective increase in the drive energy on OMEGA direct-drive implosions. It was shown that two-plasmon decay (TPD) can be driven by multiple laser beams and both planar and spherical experiments were performed to study the hot electrons generated by TPD. The fraction of laser energy converted to hot electrons scales with the hot-electron temperature for all geometries and over a wide range of intensities. At ignition-relevant intensities, the fraction of laser energy converted to hot electrons is measured to decrease by an order of magnitude when the ablator material is changed from carbon-hydrogen to aluminum. The TPD results are compared with a multiple-beam linear theory and a nonlinear Zakharov model.

Laser propagation measurements in long-scale-length underdense plasmas relevant to magnetized liner inertial fusion.

PubMed

Harvey-Thompson, A J; Sefkow, A B; Wei, M S; Nagayama, T; Campbell, E M; Blue, B E; Heeter, R F; Koning, J M; Peterson, K J; Schmitt, A

2016-11-01

We report experimental results and simulations showing efficient laser energy coupling into plasmas at conditions relevant to the magnetized liner inertial fusion (MagLIF) concept. In MagLIF, to limit convergence and increase the hydrodynamic stability of the implosion, the fuel must be efficiently preheated. To determine the efficiency and physics of preheating by a laser, an Ar plasma with n_{e}/n_{crit}∼0.04 is irradiated by a multi-ns, multi-kJ, 0.35-μm, phase-plate-smoothed laser at spot-averaged intensities ranging from 1.0×10^{14} to 2.5×10^{14}W/cm^{2} and pulse widths from 2 to 10 ns. Time-resolved x-ray images of the laser-heated plasma are compared to two-dimensional radiation-hydrodynamic simulations that show agreement with the propagating emission front, a comparison that constrains laser energy deposition to the plasma. The experiments show that long-pulse, modest-intensity (I=1.5×10^{14}W/cm^{2}) beams can efficiently couple energy (∼82% of the incident energy) to MagLIF-relevant long-length (9.5 mm) underdense plasmas. The demonstrated heating efficiency is significantly higher than is thought to have been achieved in early integrated MagLIF experiments [A. B. Sefkow et al., Phys. Plasmas 21, 072711 (2014)10.1063/1.4890298].

Laser propagation measurements in long-scale-length underdense plasmas relevant to magnetized liner inertial fusion

NASA Astrophysics Data System (ADS)

Harvey-Thompson, A. J.; Sefkow, A. B.; Wei, M. S.; Nagayama, T.; Campbell, E. M.; Blue, B. E.; Heeter, R. F.; Koning, J. M.; Peterson, K. J.; Schmitt, A.

2016-11-01

We report experimental results and simulations showing efficient laser energy coupling into plasmas at conditions relevant to the magnetized liner inertial fusion (MagLIF) concept. In MagLIF, to limit convergence and increase the hydrodynamic stability of the implosion, the fuel must be efficiently preheated. To determine the efficiency and physics of preheating by a laser, an Ar plasma with ne/nc r i t˜0.04 is irradiated by a multi-ns, multi-kJ, 0.35-μm, phase-plate-smoothed laser at spot-averaged intensities ranging from 1.0 ×1014 to 2.5 ×1014W /c m2 and pulse widths from 2 to 10 ns. Time-resolved x-ray images of the laser-heated plasma are compared to two-dimensional radiation-hydrodynamic simulations that show agreement with the propagating emission front, a comparison that constrains laser energy deposition to the plasma. The experiments show that long-pulse, modest-intensity (I =1.5 ×1014W /c m2 ) beams can efficiently couple energy (˜82 % of the incident energy) to MagLIF-relevant long-length (9.5 mm) underdense plasmas. The demonstrated heating efficiency is significantly higher than is thought to have been achieved in early integrated MagLIF experiments [A. B. Sefkow et al., Phys. Plasmas 21, 072711 (2014), 10.1063/1.4890298].

Laser propagation measurements in long-scale-length underdense plasmas relevant to magnetized liner inertial fusion

DOE PAGES

Harvey-Thompson, A. J.; Sefkow, A. B.; Wei, M. S.; ...

2016-11-02

Here, we report experimental results and simulations showing efficient laser energy coupling into plasmas at conditions relevant to the magnetized liner inertial fusion (MagLIF) concept. In MagLIF, to limit convergence and increase the hydrodynamic stability of the implosion, the fuel must be efficiently preheated. To determine the efficiency and physics of preheating by a laser, an Ar plasma with n e / n c r i t ~ 0.04 is irradiated by a multi-ns, multi-kJ, 0.35-μm, phase-plate-smoothed laser at spot-averaged intensities ranging from 1.0 × 10 14 to 2.5 × 10 14 W / c m 2 andmore » pulse widths from 2 to 10 ns. Time-resolved x-ray images of the laser-heated plasma are compared to two-dimensional radiation-hydrodynamic simulations that show agreement with the propagating emission front, a comparison that constrains laser energy deposition to the plasma. The experiments show that long-pulse, modest-intensity ( I = 1.5 × 10 14 W / c m 2 ) beams can efficiently couple energy ( ~ 82 % of the incident energy) to MagLIF-relevant long-length (9.5 mm) underdense plasmas. The heating efficiency we demonstrate is significantly higher than it was thought to have been achieved in early integrated MagLIF experiments [A. B. Sefkow et al., Phys. Plasmas 21, 072711 (2014)].« less

Laser propagation measurements in long-scale-length underdense plasmas relevant to magnetized liner inertial fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harvey-Thompson, A. J.; Sefkow, A. B.; Wei, M. S.

Here, we report experimental results and simulations showing efficient laser energy coupling into plasmas at conditions relevant to the magnetized liner inertial fusion (MagLIF) concept. In MagLIF, to limit convergence and increase the hydrodynamic stability of the implosion, the fuel must be efficiently preheated. To determine the efficiency and physics of preheating by a laser, an Ar plasma with n e / n c r i t ~ 0.04 is irradiated by a multi-ns, multi-kJ, 0.35-μm, phase-plate-smoothed laser at spot-averaged intensities ranging from 1.0 × 10 14 to 2.5 × 10 14 W / c m 2 andmore » pulse widths from 2 to 10 ns. Time-resolved x-ray images of the laser-heated plasma are compared to two-dimensional radiation-hydrodynamic simulations that show agreement with the propagating emission front, a comparison that constrains laser energy deposition to the plasma. The experiments show that long-pulse, modest-intensity ( I = 1.5 × 10 14 W / c m 2 ) beams can efficiently couple energy ( ~ 82 % of the incident energy) to MagLIF-relevant long-length (9.5 mm) underdense plasmas. The heating efficiency we demonstrate is significantly higher than it was thought to have been achieved in early integrated MagLIF experiments [A. B. Sefkow et al., Phys. Plasmas 21, 072711 (2014)].« less

Rugby-like hohlraum experimental designs for demonstrating x-ray drive enhancement

NASA Astrophysics Data System (ADS)

Amendt, Peter; Cerjan, C.; Hinkel, D. E.; Milovich, J. L.; Park, H.-S.; Robey, H. F.

2008-01-01

A suite of experimental designs for the Omega laser facility [Boehly et al., Opt. Commun. 133, 495 (1997)] using rugby and cylindrical hohlraums is proposed to confirm the energetics benefits of rugby-shaped hohlraums over cylinders under optimal implosion symmetry conditions. Postprocessed Dante x-ray drive measurements predict a 12-17eV (23%-36%) peak hohlraum temperature (x-ray flux) enhancement for a 1ns flattop laser drive history. Simulated core self-emission x-ray histories also show earlier implosion times by 200-400ps, depending on the hohlraum case-to-capsule ratio and laser-entrance-hole size. Capsules filled with 10 or 50atm of deuterium (DD) are predicted to give in excess of 1010 neutrons in two-dimensional hohlraum simulations in the absence of mix, enabling DD burn history measurements for the first time in indirect-drive on Omega. Capsule designs with 50atm of DHe3 are also proposed to make use of proton slowing for independently verifying the drive benefits of rugby hohlraums. Scale-5/4 hohlraum designs are also introduced to provide further margin to potential laser-plasma-induced backscatter and hot-electron production.

Status On Multi-microsecond Prepulse Technique On Sphinx Machine Going From Nested To Single Wire Array For 800 ns Implosion Time Z-pinch

NASA Astrophysics Data System (ADS)

Maury, P.; Calamy, H.; Grunenwald, J.; Lassalle, F.; Zucchini, F.; Loyen, A.; Georges, A.; Morell, A.; Bedoch, J. P.

2009-01-01

The Sphinx machine[1] is a 6 MA, 1 μS driver based on the LTD technology, used for Z-pinch experiments. Important improvements of Sphinx radiation output were recently obtained using a multi-microsecond current prepulse[2]. Total power per unit of length is multiplied by a factor of 6 and FWHM divided by a factor of 2.5. Early breakdown of the wires during the prepulse phase dramatically changes the ablation phase leading to an improvement of axial homogeneity of both the implosion and the final radiating column. As a consequence, the cathode bubble observed on classical shots is definitively removed. The implosion is then centered and zippering effect is reduced, leading to simultaneous x-ray emission of the whole length. A great reproducibility is obtained. Nested arrays were used before to mitigate the Rayleigh-Taylor instabilities during the implosion phase. Further experiments with pre-pulse technique are described here were inner array was removed. The goal of these experiments was to see if long prepulse could give stable enough implosion with single array and at the same time increase the η parameter by reducing the mass of the load. Experimental results of single wire array loads of typical dimension 5 cm in height with implosion time between 700 and 900 ns and diameter varying between 80 and 140 mm are given. Parameters of the loads were varying in term of radius and number of wires. Comparisons with nested wire array loads are done and trends are proposed. Characteristics of both the implosion and the final radiating column are shown. 2D MHD numerical simulations of single wire array become easier as there is no interaction between outer and inner array anymore. A systematic study was done using injection mass model to benchmark simulation with experiments.

Diagnosis of high-temperature implosions using low- and high-opacity Krypton lines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yaakobi, B.; Epstein, R.; Hooper, C.F. Jr.

1996-04-01

High-temperature laser target implosions can be achieved by using relatively thin-shell targets, and they can be. diagnosed by doping the fuel with krypton and measuring K-shell and L-shell lines. Electron temperatures of up to 5 keV at modest compressed densities ({approximately}1-5g/cm{sup 3}) are predicted for such experiments, with ion temperatures peaking above 10 keV at the center. It is found that the profiles of low-opacity (optically thin) lines in the expected density range are dominated by the Doppler broadening and can provide a measurement of the ion temperature if spectrometers of spectral resolution {Delta}{lambda}/{lambda} {ge} 1000 are used. For high-opacitymore » lines, obtained with a higher krypton fill pressure, the measurement of the escape factor can yield the {rho}R of the compressed fuel. At higher densities, Stark broadening of low-opacity lines becomes important and can provide a density measurement, whereas lines of higher opacity can be used to estimate the extent of mixing.« less

X-ray continuum as a measure of pressure and fuel–shell mix in compressed isobaric hydrogen implosion cores

DOE Office of Scientific and Technical Information (OSTI.GOV)

Epstein, R.; Goncharov, V. N.; Marshall, F. J.

Pressure, by definition, characterizes the conditions within an isobaric implosion core at peak compression [Gus'kov et al., Nucl. Fusion 16, 957 (1976); Betti et al., Phys. Plasmas 8, 5257 (2001)] and is a key parameter in quantifying its near-ignition performance [Lawson, Proc. Phys. Soc. London, B 70, 6 (1957); Betti et al., Phys. Plasmas 17, 058102 (2010); Goncharov et al., Phys. Plasmas 21, 056315 (2014); and Glenzer et al., Phys. Plasmas 19, 056318 (2012)]. At high spectral energy, where the x-ray emission from an imploded hydrogen core is optically thin, the emissivity profile can be inferred from the spatially resolvedmore » core emission. This emissivity, which can be modeled accurately under hot-core conditions, is dependent almost entirely on the pressure when measured within a restricted spectral range matched to the temperature range anticipated for the emitting volume. In this way, the hot core pressure at the time of peak emission can be inferred from the measured free-free emissivity profile. The pressure and temperature dependences of the x-ray emissivity and the neutron-production rate explain a simple scaling of the total filtered x-ray emission as a constant power of the total neutron yield for implosions of targets of similar design over a broad range of shell implosion isentropes. This scaling behavior has been seen in implosion simulations and is confirmed by measurements of high-isentrope implosions [Sangster et al., Phys. Plasmas 20, 056317 (2013)] on the OMEGA laser system [Boehly et al., Opt. Commun. 133, 495 (1997)]. Attributing the excess emission from less-stable, low-isentrope implosions, above the level expected from this neutron-yield scaling, to the higher emissivity of shell carbon mixed into the implosion's central hot spot, the hot-spot “fuel–shell” mix mass can be inferred.« less

Machining of Two-Dimensional Sinusoidal Defects on Ignition-Type Capsules to Study Hydrodynamic Instability at the National Ignition Facility

DOE PAGES

Giraldez, E. M.; Hoppe Jr., M. L.; Hoover, D. E.; ...

2016-07-07

Hydrodynamic instability growth and its effects on capsule implosion performance are being studied at the National Ignition Facility (NIF). Experimental results have shown that low-mode instabilities are the primary culprit for yield degradation. Ignition type capsules with machined 2D sinusoidal defects were used to measure low-mode hydrodynamic instability growth in the acceleration phase of the capsule implosion. The capsules were imploded using ignition-relevant laser pulses and the ablation-front modulation growth was measured using x-ray radiography. The experimentally measured growth was in good agreement with simulations.

Capsule performance optimization in the National Ignition Campaigna)

NASA Astrophysics Data System (ADS)

Landen, O. L.; Boehly, T. R.; Bradley, D. K.; Braun, D. G.; Callahan, D. A.; Celliers, P. M.; Collins, G. W.; Dewald, E. L.; Divol, L.; Glenzer, S. H.; Hamza, A.; Hicks, D. G.; Hoffman, N.; Izumi, N.; Jones, O. S.; Kirkwood, R. K.; Kyrala, G. A.; Michel, P.; Milovich, J.; Munro, D. H.; Nikroo, A.; Olson, R. E.; Robey, H. F.; Spears, B. K.; Thomas, C. A.; Weber, S. V.; Wilson, D. C.; Marinak, M. M.; Suter, L. J.; Hammel, B. A.; Meyerhofer, D. D.; Atherton, J.; Edwards, J.; Haan, S. W.; Lindl, J. D.; MacGowan, B. J.; Moses, E. I.

2010-05-01

A capsule performance optimization campaign will be conducted at the National Ignition Facility [G. H. Miller et al., Nucl. Fusion 44, 228 (2004)] to substantially increase the probability of ignition by laser-driven hohlraums [J. D. Lindl et al., Phys. Plasmas 11, 339 (2004)]. The campaign will experimentally correct for residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models before proceeding to cryogenic-layered implosions and ignition attempts. The required tuning techniques using a variety of ignition capsule surrogates have been demonstrated at the OMEGA facility under scaled hohlraum and capsule conditions relevant to the ignition design and shown to meet the required sensitivity and accuracy. In addition, a roll-up of all expected random and systematic uncertainties in setting the key ignition laser and target parameters due to residual measurement, calibration, cross-coupling, surrogacy, and scale-up errors has been derived that meets the required budget.

Capsule performance optimization in the National Ignition Campaign

DOE Office of Scientific and Technical Information (OSTI.GOV)

Landen, O. L.; Bradley, D. K.; Braun, D. G.

2010-05-15

A capsule performance optimization campaign will be conducted at the National Ignition Facility [G. H. Miller et al., Nucl. Fusion 44, 228 (2004)] to substantially increase the probability of ignition by laser-driven hohlraums [J. D. Lindl et al., Phys. Plasmas 11, 339 (2004)]. The campaign will experimentally correct for residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models before proceeding to cryogenic-layered implosions and ignition attempts. The required tuning techniques using a variety of ignition capsule surrogates have been demonstrated at the OMEGA facility under scaled hohlraum and capsule conditions relevant to the ignition designmore » and shown to meet the required sensitivity and accuracy. In addition, a roll-up of all expected random and systematic uncertainties in setting the key ignition laser and target parameters due to residual measurement, calibration, cross-coupling, surrogacy, and scale-up errors has been derived that meets the required budget.« less

A compact neutron spectrometer for characterizing inertial confinement fusion implosions at OMEGA and the NIF.

PubMed

Zylstra, A B; Gatu Johnson, M; Frenje, J A; Séguin, F H; Rinderknecht, H G; Rosenberg, M J; Sio, H W; Li, C K; Petrasso, R D; McCluskey, M; Mastrosimone, D; Glebov, V Yu; Forrest, C; Stoeckl, C; Sangster, T C

2014-06-01

A compact spectrometer for measurements of the primary deuterium-tritium neutron spectrum has been designed and implemented on the OMEGA laser facility [T. Boehly et al., Opt. Commun. 133, 495 (1997)]. This instrument uses the recoil spectrometry technique, where neutrons produced in an implosion elastically scatter protons in a plastic foil, which are subsequently detected by a proton spectrometer. This diagnostic is currently capable of measuring the yield to ~±10% accuracy, and mean neutron energy to ~±50 keV precision. As these compact spectrometers can be readily placed at several locations around an implosion, effects of residual fuel bulk flows during burn can be measured. Future improvements to reduce the neutron energy uncertainty to ±15-20 keV are discussed, which will enable measurements of fuel velocities to an accuracy of ~±25-40 km/s.

A compact neutron spectrometer for characterizing inertial confinement fusion implosions at OMEGA and the NIF

NASA Astrophysics Data System (ADS)

Zylstra, A. B.; Gatu Johnson, M.; Frenje, J. A.; Séguin, F. H.; Rinderknecht, H. G.; Rosenberg, M. J.; Sio, H. W.; Li, C. K.; Petrasso, R. D.; McCluskey, M.; Mastrosimone, D.; Glebov, V. Yu.; Forrest, C.; Stoeckl, C.; Sangster, T. C.

2014-06-01

A compact spectrometer for measurements of the primary deuterium-tritium neutron spectrum has been designed and implemented on the OMEGA laser facility [T. Boehly et al., Opt. Commun. 133, 495 (1997)]. This instrument uses the recoil spectrometry technique, where neutrons produced in an implosion elastically scatter protons in a plastic foil, which are subsequently detected by a proton spectrometer. This diagnostic is currently capable of measuring the yield to ˜±10% accuracy, and mean neutron energy to ˜±50 keV precision. As these compact spectrometers can be readily placed at several locations around an implosion, effects of residual fuel bulk flows during burn can be measured. Future improvements to reduce the neutron energy uncertainty to ±15-20 keV are discussed, which will enable measurements of fuel velocities to an accuracy of ˜±25-40 km/s.

LANL C10.2 Projects in FY13

DOE Office of Scientific and Technical Information (OSTI.GOV)

Batha, Steven H.; Fincke, James R.; Schmitt, Mark J.

2012-06-07

LANL has two projects in C10.2: Defect-Induced Mix Experiment (DIME) (ongoing, several runs at Omega; NIF shots this summer); and Shock/Shear (tested at Omega for two years; NIF shots in second half of FY13). Each project is jointly funded by C10.2, other C10 MTEs, and Science Campaigns. DIME is investigating 4{pi} and feature-induced mix in spherically convergent ICF implosions by using imaging of the mix layer. DIME prepared for NIF by demonstrating its PDD mix platform on Omega including imaging mid-Z doped layers and defects. DIME in FY13 will focus on PDD symmetry-dependent mix and moving burn into the mixmore » region for validation of mix/burn models. Re-Shock and Shear are two laser-driven experiments designed to study the turbulent mixing of materials. In FY-2012 43 shear and re-shock experimental shots were executed on the OMEGA laser and a complete time history obtained for both. The FY-2013 goal is to transition the experiment to NIF where the larger scale will provide a longer time period for mix layer growth.« less

Laser-direct-drive program: Promise, challenge, and path forward

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, E. M.; Goncharov, V. N.; Sangster, T. C.

Along with laser-indirect (x-ray)-drive and magnetic-drive target concepts, laser direct drive is a viable approach to achieving ignition and gain with inertial confinement fusion. In the United States, a national program has been established to demonstrate and understand the physics of laser direct drive. The program utilizes the Omega Laser Facility to conduct implosion and coupling physics at the nominally 30-kJ scale and laser–plasma interaction and coupling physics at the MJ scale at the National Ignition Facility. This paper will discuss the motivation and challenges for laser direct drive and the broad-based program presently underway in the United States.

Laser-direct-drive program: Promise, challenge, and path forward

DOE PAGES

Campbell, E. M.; Goncharov, V. N.; Sangster, T. C.; ...

2017-03-19

Along with laser-indirect (x-ray)-drive and magnetic-drive target concepts, laser direct drive is a viable approach to achieving ignition and gain with inertial confinement fusion. In the United States, a national program has been established to demonstrate and understand the physics of laser direct drive. The program utilizes the Omega Laser Facility to conduct implosion and coupling physics at the nominally 30-kJ scale and laser–plasma interaction and coupling physics at the MJ scale at the National Ignition Facility. This paper will discuss the motivation and challenges for laser direct drive and the broad-based program presently underway in the United States.

Simulation and assessment of ion kinetic effects in a direct-drive capsule implosion experiment

DOE PAGES

Le, Ari Yitzchak; Kwan, Thomas J. T.; Schmitt, Mark J.; ...

2016-10-24

The first simulations employing a kinetic treatment of both fuel and shell ions to model inertial confinement fusion experiments are presented, including results showing the importance of kinetic physics processes in altering fusion burn. A pair of direct drive capsule implosions performed at the OMEGA facility with two different gas fills of deuterium, tritium, and helium-3 are analyzed. During implosion shock convergence, highly non-Maxwellian ion velocity distributions and separations in the density and temperature amongst the ion species are observed. Finally, diffusion of fuel into the capsule shell is identified as a principal process that degrades fusion burn performance.

Symmetry tuning for DIME Campaign

NASA Astrophysics Data System (ADS)

Krasheninnikova, Natalia; Schmitt, Mark; Tregillis, Ian; Bradley, P.; Cobble, J.; Kyrala, G.; Murphy, T.; Obrey, K.; Hsu, S.; Shah, R.; Batha, S.; Craxton, S.; McKenty, P.

2012-10-01

Defect Induced Mix Experiment (DIME) investigates the effects of 4 pi as well as surface feature-driven mix on the directly driven ICF capsule implosion. To minimize the effects of the laser-drive asymmetry, beam pointings, pulse shape, and the energy distribution between the lasers need to be optimized for a particular capsule and shot energy. In support of the DIME experimental campaigns on OMEGA and NIF, symmetry tuning was performed with the rad-hydro code HYDRA. To assess the impact on the symmetry, synthetic radiographs and self-emission images were examined and compared with the experimental results from OMEGA and NIF shots. The dynamics of the capsules imploded under polar direct drive conditions were compared with symmetrically driven ones and the effects of cross-beam transfer and the laser imprinting on the symmetry were also investigated. Work performed by Los Alamos National Laboratory under contract DE-AC52-06NA25396 for the National Nuclear Security Administration of the U.S. Department of Energy.

Progress towards ignition on the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Edwards, M. J.; Patel, P. K.; Lindl, J. D.

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory includes a precision laser system now capable of delivering 1.8 MJ at 500 TW of 0.35-μm light to a target. NIF has been operational since March 2009. A variety of experiments have been completed in support of NIF's mission areas: national security, fundamental science, and inertial fusion energy. NIF capabilities and infrastructure are in place to support its missions with nearly 60 X-ray, optical, and nuclear diagnostic systems. A primary goal of the National Ignition Campaign (NIC) on the NIF was to implode a low-Z capsule filled with ∼0.2 mgmore » of deuterium-tritium (DT) fuel via laser indirect-drive inertial confinement fusion and demonstrate fusion ignition and propagating thermonuclear burn with a net energy gain of ∼5–10 (fusion yield/input laser energy). This requires assembling the DT fuel into a dense shell of ∼1000 g/cm{sup 3} with an areal density (ρR) of ∼1.5 g/cm{sup 2}, surrounding a lower density hot spot with a temperature of ∼10 keV and a ρR ∼0.3 g/cm{sup 2}, or approximately an α-particle range. Achieving these conditions demand precise control of laser and target parameters to allow a low adiabat, high convergence implosion with low ablator fuel mix. We have demonstrated implosion and compressed fuel conditions at ∼80–90% for most point design values independently, but not at the same time. The nuclear yield is a factor of ∼3–10× below the simulated values and a similar factor below the alpha dominated regime. This paper will discuss the experimental trends, the possible causes of the degraded performance (the off-set from the simulations), and the plan to understand and resolve the underlying physics issues.« less

Hard X-ray and Particle Beams Research on 1.7 MA Z-pinch and Laser Plasma Experiments

NASA Astrophysics Data System (ADS)

Shrestha, Ishor; Kantsyrev, Victor; Safronova, Alla; Esaulov, Andrey; Nishio, Mineyuki; Shlyaptseva, Veronica; Keim, Steven; Weller, Michael; Stafford, Austin; Petkov, Emil; Schultz, Kimberly; Cooper, Matthew; PPDL Team

2013-10-01

Studies of hard x-ray (HXR) emission, electron and ion beam generation in z-pinch and laser plasmas are important for Inertial Confinement Fusion (ICF) and development of HXR sources from K-shell and L-shell radiation. The characteristics of HXR and particle beams produced by implosions of planar wire arrays, nested and single cylindrical wire arrays, and X-pinches were analyzed on 100 ns UNR Zebra generator with current up to 1.7 MA. In addition, the comparison of characteristics of HXR and electron beams on Zebra and 350 fs UNR Leopard laser experiments with foils has been performed. The diagnostics include Faraday cups, HXR diodes, different x-ray spectrometers and imaging systems, and ion mass spectrometer using the technique of Thomson parabola. Future work on HXRs and particle beams in HED plasmas is discussed. This work was supported by the DOE/NNSA Cooperative agreement DE-NA0001984 and in part by DE-FC52-06NA27616. This work was also supported by the Defense Threat Reduction Agency, Basic Research Award # HDTRA1-13-1-0033, to University of Nevada, Reno.

A near one-dimensional indirectly driven implosion at convergence ratio 30

NASA Astrophysics Data System (ADS)

MacLaren, S. A.; Masse, L. P.; Czajka, C. E.; Khan, S. F.; Kyrala, G. A.; Ma, T.; Ralph, J. E.; Salmonson, J. D.; Bachmann, B.; Benedetti, L. R.; Bhandarkar, S. D.; Bradley, P. A.; Hatarik, R.; Herrmann, H. W.; Mariscal, D. A.; Millot, M.; Patel, P. K.; Pino, J. E.; Ratledge, M.; Rice, N. G.; Tipton, R. E.; Tommasini, R.; Yeamans, C. B.

2018-05-01

Inertial confinement fusion cryogenic-layered implosions at the National Ignition Facility, while successfully demonstrating self-heating due to alpha-particle deposition, have fallen short of the performance predicted by one-dimensional (1D) multi-physics implosion simulations. The current understanding, from experimental evidence as well as simulations, suggests that engineering features such as the capsule tent and fill tube, as well as time-dependent low-mode asymmetry, are to blame for the lack of agreement. A short series of experiments designed specifically to avoid these degradations to the implosion are described here in order to understand if, once they are removed, a high-convergence cryogenic-layered deuterium-tritium implosion can achieve the 1D simulated performance. The result is a cryogenic layered implosion, round at stagnation, that matches closely the performance predicted by 1D simulations. This agreement can then be exploited to examine the sensitivity of approximations in the model to the constraints imposed by the data.

Testing a new NIF neutron time-of-flight detector with a bibenzyl scintillator on OMEGA.

PubMed

Glebov, V Yu; Forrest, C; Knauer, J P; Pruyne, A; Romanofsky, M; Sangster, T C; Shoup, M J; Stoeckl, C; Caggiano, J A; Carman, M L; Clancy, T J; Hatarik, R; McNaney, J; Zaitseva, N P

2012-10-01

A new neutron time-of-flight (nTOF) detector with a bibenzyl crystal as a scintillator has been designed and manufactured for the National Ignition Facility (NIF). This detector will replace a nTOF20-Spec detector with an oxygenated xylene scintillator currently operational on the NIF to improve the areal-density measurements. In addition to areal density, the bibenzyl detector will measure the D-D and D-T neutron yield and the ion temperature of indirect- and direct-drive-implosion experiments. The design of the bibenzyl detector and results of tests on the OMEGA Laser System are presented.

Spatial resolution measurements of the advanced radiographic capability x-ray imaging system at energies relevant to Compton radiography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hall, G. N.; Izumi, N.; Landen, O. L.

2016-08-03

Compton radiography provides a means to measure the integrity, ρR and symmetry of the DT fuel in an inertial confinement fusion implosion near peak compression. Upcoming experiments at the National Ignition Facility will use the ARC (Advanced Radiography Capability) laser to drive backlighter sources for Compton radiography experiments, and will use the newly commissioned AXIS (ARC X-ray Imaging System) instrument as the detector. AXIS uses a dual-MCP (micro channel plate) to provide gating and high DQE at the 40–200keV x-ray range required for Compton radiography, but introduces many effects that contribute to the spatial resolution. Here, experiments were performed atmore » energies relevant to Compton radiography to begin characterization of the spatial resolution of the AXIS diagnostic.« less

Observation of a reflected shock in an indirectly driven spherical implosion at the national ignition facility.

PubMed

Le Pape, S; Divol, L; Berzak Hopkins, L; Mackinnon, A; Meezan, N B; Casey, D; Frenje, J; Herrmann, H; McNaney, J; Ma, T; Widmann, K; Pak, A; Grimm, G; Knauer, J; Petrasso, R; Zylstra, A; Rinderknecht, H; Rosenberg, M; Gatu-Johnson, M; Kilkenny, J D

2014-06-06

A 200  μm radius hot spot at more than 2 keV temperature, 1  g/cm^{3} density has been achieved on the National Ignition Facility using a near vacuum hohlraum. The implosion exhibits ideal one-dimensional behavior and 99% laser-to-hohlraum coupling. The low opacity of the remaining shell at bang time allows for a measurement of the x-ray emission of the reflected central shock in a deuterium plasma. Comparison with 1D hydrodynamic simulations puts constraints on electron-ion collisions and heat conduction. Results are consistent with classical (Spitzer-Harm) heat flux.

Subpercent-Scale Control of 3D Low Modes of Targets Imploded in Direct-Drive Configuration on OMEGA

NASA Astrophysics Data System (ADS)

Michel, D. T.; Igumenshchev, I. V.; Davis, A. K.; Edgell, D. H.; Froula, D. H.; Jacobs-Perkins, D. W.; Goncharov, V. N.; Regan, S. P.; Shvydky, A.; Campbell, E. M.

2018-03-01

Multiple self-emission x-ray images are used to measure tomographically target modes 1, 2, and 3 up to the end of the target acceleration in direct-drive implosions on OMEGA. Results show that the modes consist of two components: the first varies linearly with the laser beam-energy balance and the second is static and results from physical effects including beam mistiming, mispointing, and uncertainty in beam energies. This is used to reduce the target low modes of low-adiabat implosions from 2.2% to 0.8% by adjusting the beam-energy balance to compensate these static modes.

Formation of carbon allotrope aerosol by colliding plasmas in an inertial fusion reactor

NASA Astrophysics Data System (ADS)

Hirooka, Y.; Sato, H.; Ishihara, K.; Yabuuchi, T.; Tanaka, K. A.

2014-02-01

Along with repeated implosions, the interior of an inertial fusion target chamber is exposed to short pulses of high-energy x-ray, unburned DT-fuel particles, He-ash and pellet debris. As a result, chamber wall materials are subjected to ablation, emitting particles in the plasma state. Ablated particles will either be re-deposited elsewhere or collide with each other, perhaps in the centre-of-symmetry region of the chamber volume. Colliding ablation plasma particles can lead to the formation of clusters to grow into aerosol, possibly floating thereafter, which can deteriorate the subsequent implosion performance via laser scattering, etc. In a laboratory-scale YAG laser setup, the formation of nano-scale aerosol has been demonstrated in vacuum at irradiation power densities of the orders of 108-10 W cm-2 at 10 Hz, each 6 ns long, simulating the high-repetition rate inertial fusion reactor situation. Interestingly, carbon aerosol formation has been observed in the form of fullerene onion, nano- and micro-tubes when laser-ablated plasma plumes of carbon collide with each other. In contrast, colliding plasma plumes of metals tend to generate aerosol in the form of droplets under identical laser irradiation conditions. An atomic and molecular reaction model is proposed to interpret the process of carbon allotrope aerosol formation.

A High-Resolution Integrated Model of the National Ignition Campaign Cryogenic Layered Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, O. S.; Callahan, D. A.; Cerjan, C. J.

A detailed simulation-based model of the June 2011 National Ignition Campaign (NIC) cryogenic DT experiments is presented. The model is based on integrated hohlraum-capsule simulations that utilize the best available models for the hohlraum wall, ablator, and DT equations of state and opacities. The calculated radiation drive was adjusted by changing the input laser power to match the experimentally measured shock speeds, shock merger times, peak implosion velocity, and bangtime. The crossbeam energy transfer model was tuned to match the measured time-dependent symmetry. Mid-mode mix was included by directly modeling the ablator and ice surface perturbations up to mode 60.more » Simulated experimental values were extracted from the simulation and compared against the experiment. The model adjustments brought much of the simulated data into closer agreement with the experiment, with the notable exception of the measured yields, which were 15-40% of the calculated yields.« less

A High-Resolution Integrated Model of the National Ignition Campaign Cryogenic Layered Experiments

DOE PAGES

Jones, O. S.; Callahan, D. A.; Cerjan, C. J.; ...

2012-05-29

A detailed simulation-based model of the June 2011 National Ignition Campaign (NIC) cryogenic DT experiments is presented. The model is based on integrated hohlraum-capsule simulations that utilize the best available models for the hohlraum wall, ablator, and DT equations of state and opacities. The calculated radiation drive was adjusted by changing the input laser power to match the experimentally measured shock speeds, shock merger times, peak implosion velocity, and bangtime. The crossbeam energy transfer model was tuned to match the measured time-dependent symmetry. Mid-mode mix was included by directly modeling the ablator and ice surface perturbations up to mode 60.more » Simulated experimental values were extracted from the simulation and compared against the experiment. The model adjustments brought much of the simulated data into closer agreement with the experiment, with the notable exception of the measured yields, which were 15-40% of the calculated yields.« less

Visualization of irrigant flow and cavitation induced by Er:YAG laser within a root canal model.

PubMed

Matsumoto, Himeka; Yoshimine, Yoshito; Akamine, Akifumi

2011-06-01

Laser-activated irrigation (LAI) has recently been introduced as an innovative method for root canal irrigation. However, there is limited information about the cleaning mechanism of an Er:YAG laser. In this study, we visualized the action of laser-induced bubbles and fluid flow in vitro to better understand the physical mechanisms underlying LAI. An Er:YAG laser was equipped with a novel cone-shaped tip with a lateral emission rate of approximately 80%. Laser light was emitted at a pulse energy of 30, 50, or 70 mJ (output energy: 11, 18, or 26 mJ) and a repetition rate of 1 or 20 pulses per second, without air or water spray. Fluid flow dynamics in a root canal model were observed by using glass-bead tracers under a high-speed camera. Moreover, laser-induced bubble patterns were visualized in both free water and the root canal model. Tracers revealed high-speed motion of the fluid. A full cycle of expansion and implosion of vapor and secondary cavitation bubbles were clearly observed. In free water, the vapor bubble expanded for 220 microseconds, and its shape resembled that of an apple. In the root canal model, the vapor bubble expanded in a vertical direction along the canal wall, and bubble expansion continued for ≥700 microseconds. Furthermore, cavitation bubbles were created much more frequently in the canal model than in free water. These results suggest that the cleaning mechanism of an Er:YAG laser within the root canal might depend on rapid fluid motion caused by expansion and implosion of laser-induced bubbles. Copyright © 2011 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Performance of High-Convergence, Layered DT Implosions on Power-Scaling Experiments at National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smalyuk, V. A.; Atherton, L. J.; Benedetti, L. R.

The radiation-driven, low-adiabat, cryogenic DT layered plastic capsule implosions were carried out on the National Ignition Facility (NIF) to study the sensitivity of performance to peak power and drive duration. An implosion with extended drive and at reduced peak power of 350 TW achieved the highest compression with fuel areal density of ~1.3±0.1 g/cm 2, representing a significant step from previously measured ~1.0 g/cm 2 toward a goal of 1.5 g/cm 2. Moreover, for future experiments will focus on understanding and mitigating hydrodynamic instabilities and mix, and improving symmetry required to reach the threshold for thermonuclear ignition on NIF.

Performance of High-Convergence, Layered DT Implosions on Power-Scaling Experiments at National Ignition Facility

DOE PAGES

Smalyuk, V. A.; Atherton, L. J.; Benedetti, L. R.; ...

2013-10-19

The radiation-driven, low-adiabat, cryogenic DT layered plastic capsule implosions were carried out on the National Ignition Facility (NIF) to study the sensitivity of performance to peak power and drive duration. An implosion with extended drive and at reduced peak power of 350 TW achieved the highest compression with fuel areal density of ~1.3±0.1 g/cm 2, representing a significant step from previously measured ~1.0 g/cm 2 toward a goal of 1.5 g/cm 2. Moreover, for future experiments will focus on understanding and mitigating hydrodynamic instabilities and mix, and improving symmetry required to reach the threshold for thermonuclear ignition on NIF.

2-Shock layered tuning campaign

NASA Astrophysics Data System (ADS)

Masse, Laurent; Dittrich, T.; Khan, S.; Kyrala, G.; Ma, T.; MacLaren, S.; Ralph, J.; Salmonson, J.; Tipton, R.; Los Alamos Natl Lab Team; Lawrence Livermore Natl Lab Team

2016-10-01

The 2-Shock platform has been developed to maintain shell sphericity throughout the compression phase of an indirect-drive target implosion and produce a stagnating hot spot in a quasi 1D-like manner. A sub-scale, 1700 _m outer diameter, and thick, 200 _m, uniformly Silicon doped, gas-filled plastic capsule is driven inside a nominal size 5750 _m diameter ignition hohlraum. The hohlraum fill is near vacuum to reduce back-scatter and improve laser/drive coupling. A two-shock pulse of about 1 MJ of laser energy drives the capsule. The thick capsule prevents ablation front feed-through to the imploded core. This platform has demonstrated its efficiency to tune a predictable and reproducible 1-D implosion with a nearly round shape. It has been shown that the high foot performance was dominated by the local defect growth due to the ablation front instability and by the hohlraum radiation asymmetries. The idea here is to take advantage of this 2-Shock platform to design a 1D-like layered implosion and eliminates the deleterious effects of radiation asymmetries and ablation front instability growth. We present the design work and our first experimental results of this near one-dimensional 2-Shock layered design. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.

Three-dimensional modeling of the neutron spectrum to infer plasma conditions in cryogenic inertial confinement fusion implosions

NASA Astrophysics Data System (ADS)

Weilacher, F.; Radha, P. B.; Forrest, C.

2018-04-01

Neutron-based diagnostics are typically used to infer compressed core conditions such as areal density and ion temperature in deuterium-tritium (D-T) inertial confinement fusion (ICF) implosions. Asymmetries in the observed neutron-related quantities are important to understanding failure modes in these implosions. Neutrons from fusion reactions and their subsequent interactions including elastic scattering and neutron-induced deuteron breakup reactions are tracked to create spectra. It is shown that background subtraction is important for inferring areal density from backscattered neutrons and is less important for the forward-scattered neutrons. A three-dimensional hydrodynamic simulation of a cryogenic implosion on the OMEGA Laser System [Boehly et al., Opt. Commun. 133, 495 (1997)] using the hydrodynamic code HYDRA [Marinak et al., Phys. Plasmas 8, 2275 (2001)] is post-processed using the tracking code IRIS3D. It is shown that different parts of the neutron spectrum from the view can be mapped into different regions of the implosion, enabling an inference of an areal-density map. It is also shown that the average areal-density and an areal-density map of the compressed target can be reconstructed with a finite number of detectors placed around the target chamber. Ion temperatures are inferred from the width of the D-D and D-T fusion neutron spectra. Backgrounds can significantly alter the inferred ion temperatures from the D-D reaction, whereas they insignificantly influence the inferred D-T ion temperatures for the areal densities typical of OMEGA implosions. Asymmetries resulting in fluid flow in the core are shown to influence the absolute inferred ion temperatures from both reactions, although relative inferred values continue to reflect the underlying asymmetry pattern. The work presented here is part of the wide range of the first set of studies performed with IRIS3D. This code will continue to be used for post-processing detailed hydrodynamic simulations and interpreting observed neutron spectra in ICF implosions.

X-ray continuum as a measure of pressure and fuel–shell mix in compressed isobaric hydrogen implosion cores

DOE Office of Scientific and Technical Information (OSTI.GOV)

Epstein, R.; Goncharov, V. N.; Marshall, F. J.

Pressure, by definition, characterizes the conditions within an isobaric implosion core at peak compression [Gus’kov et al., Nucl. Fusion 16, 957 (1976); Betti et al., Phys. Plasmas 8, 5257 (2001)] and is a key parameter in quantifying its near-ignition performance [Lawson, Proc. Phys. Soc. London, B 70, 6 (1957); Betti et al., Phys. Plasmas 17, 058102 (2010); Goncharov et al., Phys. Plasmas 21, 056315 (2014); and Glenzer et al., Phys. Plasmas 19, 056318 (2012)]. At high spectral energy, where the x-ray emission from an imploded hydrogen core is optically thin, the emissivity profile can be inferred from the spatially resolvedmore » core emission. This emissivity, which can be modeled accurately under hot-core conditions, is dependent almost entirely on the pressure when measured within a restricted spectral range matched to the temperature range anticipated for the emitting volume. In this way, the hot core pressure at the time of peak emission can be inferred from the measured free-free emissivity profile. The pressure and temperature dependences of the x-ray emissivity and the neutron-production rate explain a simple scaling of the total filtered x-ray emission as a constant power of the total neutron yield for implosions of targets of similar design over a broad range of shell implosion isentropes. This scaling behavior has been seen in implosion simulations and is confirmed by measurements of high-isentrope implosions [Sangster et al., Phys. Plasmas 20, 056317 (2013)] on the OMEGA laser system [Boehly et al., Opt. Commun. 133, 495 (1997)]. Attributing the excess emission from less-stable, low-isentrope implosions, above the level expected from this neutron-yield scaling, to the higher emissivity of shell carbon mixed into the implosion’s central hot spot, the hot-spot “fuel–shell” mix mass can be inferred.« less

High-density carbon ablator ignition path with low-density gas-filled rugby hohlraum

NASA Astrophysics Data System (ADS)

Amendt, Peter; Ho, Darwin D.; Jones, Ogden S.

2015-04-01

A recent low gas-fill density (0.6 mg/cc 4He) cylindrical hohlraum experiment on the National Ignition Facility has shown high laser-coupling efficiency (>96%), reduced phenomenological laser drive corrections, and improved high-density carbon capsule implosion symmetry [Jones et al., Bull. Am. Phys. Soc. 59(15), 66 (2014)]. In this Letter, an ignition design using a large rugby-shaped hohlraum [Amendt et al., Phys. Plasmas 21, 112703 (2014)] for high energetics efficiency and symmetry control with the same low gas-fill density (0.6 mg/cc 4He) is developed as a potentially robust platform for demonstrating thermonuclear burn. The companion high-density carbon capsule for this hohlraum design is driven by an adiabat-shaped [Betti et al., Phys. Plasmas 9, 2277 (2002)] 4-shock drive profile for robust high gain (>10) 1-D ignition performance and large margin to 2-D perturbation growth.

Capsule Performance Optimization for the National Ignition Facility

NASA Astrophysics Data System (ADS)

Landen, Otto

2009-11-01

The overall goal of the capsule performance optimization campaign is to maximize the probability of ignition by experimentally correcting for likely residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models before proceeding to cryogenic-layered implosions and ignition attempts. This will be accomplished using a variety of targets that will set key laser, hohlraum and capsule parameters to maximize ignition capsule implosion velocity, while minimizing fuel adiabat, core shape asymmetry and ablator-fuel mix. The targets include high Z re-emission spheres setting foot symmetry through foot cone power balance [1], liquid Deuterium-filled ``keyhole'' targets setting shock speed and timing through the laser power profile [2], symmetry capsules setting peak cone power balance and hohlraum length [3], and streaked x-ray backlit imploding capsules setting ablator thickness [4]. We will show how results from successful tuning technique demonstration shots performed at the Omega facility under scaled hohlraum and capsule conditions relevant to the ignition design meet the required sensitivity and accuracy. We will also present estimates of all expected random and systematic uncertainties in setting the key ignition laser and target parameters due to residual measurement, calibration, cross-coupling, surrogacy, and scale-up errors, and show that these get reduced after a number of shots and iterations to meet an acceptable level of residual uncertainty. Finally, we will present results from upcoming tuning technique validation shots performed at NIF at near full-scale. Prepared by LLNL under Contract DE-AC52-07NA27344. [4pt] [1] E. Dewald, et. al. Rev. Sci. Instrum. 79 (2008) 10E903. [0pt] [2] T.R. Boehly, et. al., Phys. Plasmas 16 (2009) 056302. [0pt] [3] G. Kyrala, et. al., BAPS 53 (2008) 247. [0pt] [4] D. Hicks, et. al., BAPS 53 (2008) 2.

Probing off-Hugoniot states in Ta, Cu, and Al to 1000 GPa compression with magnetically driven liner implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lemke, R. W., E-mail: rwlemke@sandia.gov; Dolan, D. H.; Dalton, D. G.

We report on a new technique for obtaining off-Hugoniot pressure vs. density data for solid metals compressed to extreme pressure by a magnetically driven liner implosion on the Z-machine (Z) at Sandia National Laboratories. In our experiments, the liner comprises inner and outer metal tubes. The inner tube is composed of a sample material (e.g., Ta and Cu) whose compressed state is to be inferred. The outer tube is composed of Al and serves as the current carrying cathode. Another aluminum liner at much larger radius serves as the anode. A shaped current pulse quasi-isentropically compresses the sample as itmore » implodes. The iterative method used to infer pressure vs. density requires two velocity measurements. Photonic Doppler velocimetry probes measure the implosion velocity of the free (inner) surface of the sample material and the explosion velocity of the anode free (outer) surface. These two velocities are used in conjunction with magnetohydrodynamic simulation and mathematical optimization to obtain the current driving the liner implosion, and to infer pressure and density in the sample through maximum compression. This new equation of state calibration technique is illustrated using a simulated experiment with a Cu sample. Monte Carlo uncertainty quantification of synthetic data establishes convergence criteria for experiments. Results are presented from experiments with Al/Ta, Al/Cu, and Al liners. Symmetric liner implosion with quasi-isentropic compression to peak pressure ∼1000 GPa is achieved in all cases. These experiments exhibit unexpectedly softer behavior above 200 GPa, which we conjecture is related to differences in the actual and modeled properties of aluminum.« less

Probing off-Hugoniot states in Ta, Cu, and Al to 1000 GPa compression with magnetically driven liner implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lemke, R. W.; Dolan, D. H.; Dalton, D. G.

We report on a new technique for obtaining off-Hugoniot pressure vs. density data for solid metals compressed to extreme pressure by a magnetically driven liner implosion on the Z-machine (Z) at Sandia National Laboratories. In our experiments, the liner comprises inner and outer metal tubes. The inner tube is composed of a sample material (e.g., Ta and Cu) whose compressed state is to be inferred. The outer tube is composed of Al and serves as the current carrying cathode. Another aluminum liner at much larger radius serves as the anode. A shaped current pulse quasi-isentropically compresses the sample as itmore » implodes. The iterative method used to infer pressure vs. density requires two velocity measurements. Photonic Doppler velocimetry probes measure the implosion velocity of the free (inner) surface of the sample material and the explosion velocity of the anode free (outer) surface. These two velocities are used in conjunction with magnetohydrodynamic simulation and mathematical optimization to obtain the current driving the liner implosion, and to infer pressure and density in the sample through maximum compression. This new equation of state calibration technique is illustrated using a simulated experiment with a Cu sample. Monte Carlo uncertainty quantification of synthetic data establishes convergence criteria for experiments. Results are presented from experiments with Al/Ta, Al/Cu, and Al liners. Symmetric liner implosion with quasi-isentropic compression to peak pressure ~1000 GPa is achieved in all cases. Lastly, these experiments exhibit unexpectedly softer behavior above 200 GPa, which we conjecture is related to differences in the actual and modeled properties of aluminum.« less

Probing off-Hugoniot states in Ta, Cu, and Al to 1000 GPa compression with magnetically driven liner implosions

DOE PAGES

Lemke, R. W.; Dolan, D. H.; Dalton, D. G.; ...

2016-01-07

We report on a new technique for obtaining off-Hugoniot pressure vs. density data for solid metals compressed to extreme pressure by a magnetically driven liner implosion on the Z-machine (Z) at Sandia National Laboratories. In our experiments, the liner comprises inner and outer metal tubes. The inner tube is composed of a sample material (e.g., Ta and Cu) whose compressed state is to be inferred. The outer tube is composed of Al and serves as the current carrying cathode. Another aluminum liner at much larger radius serves as the anode. A shaped current pulse quasi-isentropically compresses the sample as itmore » implodes. The iterative method used to infer pressure vs. density requires two velocity measurements. Photonic Doppler velocimetry probes measure the implosion velocity of the free (inner) surface of the sample material and the explosion velocity of the anode free (outer) surface. These two velocities are used in conjunction with magnetohydrodynamic simulation and mathematical optimization to obtain the current driving the liner implosion, and to infer pressure and density in the sample through maximum compression. This new equation of state calibration technique is illustrated using a simulated experiment with a Cu sample. Monte Carlo uncertainty quantification of synthetic data establishes convergence criteria for experiments. Results are presented from experiments with Al/Ta, Al/Cu, and Al liners. Symmetric liner implosion with quasi-isentropic compression to peak pressure ~1000 GPa is achieved in all cases. Lastly, these experiments exhibit unexpectedly softer behavior above 200 GPa, which we conjecture is related to differences in the actual and modeled properties of aluminum.« less

BigFoot, a program to reduce risk for indirect drive laser fusion

NASA Astrophysics Data System (ADS)

Thomas, Cliff

2016-10-01

The conventional approach to inertial confinement fusion (ICF) is to maximize compressibility, or, total areal density. To achieve high convergence (40), the laser pulse is shaped to launch a weak first shock, which is followed in turn by 2-3 stronger shocks. Importantly, this has an outsized effect on integrated target physics, as the time it takes the shocks to transit the shell is related to hohlraum wall motion and filling, and can contribute to difficulties achieving an implosion that is fast, tunable, and/or predictable. At its outset, this approach attempts to predict the tradeoff in capsule and hohlraum physics in a case that is challenging, and assumes the hotspot can still reach the temperature and density necessary to self-heat (4-5 keV and 0.1-0.2 g/cm2, respectively). Here, we consider an alternate route to fusion ignition, for which the benefits of predictability, control, and coupling could exceed the benefits of convergence. In this approach we avoid uncertainty, and instead, seek a target that is predictable. To simplify hohlraum physics and limit wall motion we keep the implosion time short (6-7 ns), and design the target to avoid laser-plasma instabilities. Whereas the previous focus was on density, it is now on making a 1D hotspot at low convergence (20) that is robust with respect to alpha heating (5-6 keV, and 0.2-0.3 g/cm2) . At present, we estimate the tradeoff between convergence and control is relatively flat, and advantages in coupling enable high velocity (450-500 um/ns) and high yield (1E17). Were the approach successful, we believe it could reduce barriers to progress, as further improvements could be made with small, incremental increases in areal density. Details regarding the ``BigFoot'' platform and pulse are reported, as well as initial experiments. Work that could enable additional improvements in laser power, laser control, and capsule stability will also be discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Hydro-instability growth of perturbation seeds from alternate capsule-support strategies in indirect-drive implosions on National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martinez, D. A.; Smalyuk, V. A.; MacPhee, A. G.

Hydrodynamic instability growth of the capsule support membranes (or “tents”) and fill tubes has been studied in spherical, glow discharge polymer plastic capsule implosions at the National Ignition Facility (NIF). In NIF implosions, the capsules are supported by tents because the nominal 10-μm thick fill tubes are not strong enough to support capsules by themselves. After it was recognized that the tents had a significant impact of implosion stability, new support methods were investigated, including thicker, 30-μm diameter fill tubes and cantilevered fill tubes, as described in this article. A new “sub-scale” version of the existing x-ray radiography platform wasmore » developed for measuring growing capsule perturbations in the acceleration phase of implosions. It was calibrated using hydrodynamic growth measurements of pre-imposed capsule modulations with Legendre modes of 60, 90, 110, and 140 at convergence ratios up to ~2.4. Subsequent experiments with 3-D perturbations have studied instability growth of 10-μm and 30-μm thick fill tubes to compare them with 30-nm thick tent perturbations at convergence ratios up to ~3. In other experiments, the perturbations from cantilevered fill tubes were measured and compared to the tent perturbations. The cantilevered fill tubes were supported by 12-μm thick SiC rods, offset by 100 μm, 200 μm, and 300 μm from the capsule surfaces. Based on these experiments, 30-μm thick fill tubes and 300-μm offset cantilevered fill tubes were recommended for further tests using layered deuterium-tritium implosions. In conclusion, the effects of x-ray shadowing during the drive and oxygen-induced perturbations during target assembly produced additional seeds for instabilities and were also measured in these experiments.« less

Hydro-instability growth of perturbation seeds from alternate capsule-support strategies in indirect-drive implosions on National Ignition Facility

DOE PAGES

Martinez, D. A.; Smalyuk, V. A.; MacPhee, A. G.; ...

2017-10-20

Hydrodynamic instability growth of the capsule support membranes (or “tents”) and fill tubes has been studied in spherical, glow discharge polymer plastic capsule implosions at the National Ignition Facility (NIF). In NIF implosions, the capsules are supported by tents because the nominal 10-μm thick fill tubes are not strong enough to support capsules by themselves. After it was recognized that the tents had a significant impact of implosion stability, new support methods were investigated, including thicker, 30-μm diameter fill tubes and cantilevered fill tubes, as described in this article. A new “sub-scale” version of the existing x-ray radiography platform wasmore » developed for measuring growing capsule perturbations in the acceleration phase of implosions. It was calibrated using hydrodynamic growth measurements of pre-imposed capsule modulations with Legendre modes of 60, 90, 110, and 140 at convergence ratios up to ~2.4. Subsequent experiments with 3-D perturbations have studied instability growth of 10-μm and 30-μm thick fill tubes to compare them with 30-nm thick tent perturbations at convergence ratios up to ~3. In other experiments, the perturbations from cantilevered fill tubes were measured and compared to the tent perturbations. The cantilevered fill tubes were supported by 12-μm thick SiC rods, offset by 100 μm, 200 μm, and 300 μm from the capsule surfaces. Based on these experiments, 30-μm thick fill tubes and 300-μm offset cantilevered fill tubes were recommended for further tests using layered deuterium-tritium implosions. In conclusion, the effects of x-ray shadowing during the drive and oxygen-induced perturbations during target assembly produced additional seeds for instabilities and were also measured in these experiments.« less

Hydro-instability growth of perturbation seeds from alternate capsule-support strategies in indirect-drive implosions on National Ignition Facility

NASA Astrophysics Data System (ADS)

Martinez, D. A.; Smalyuk, V. A.; MacPhee, A. G.; Milovich, J.; Casey, D. T.; Weber, C. R.; Robey, H. F.; Chen, K.-C.; Clark, D. S.; Crippen, J.; Farrell, M.; Felker, S.; Field, J. E.; Haan, S. W.; Hammel, B. A.; Hamza, A. V.; Stadermann, M.; Hsing, W. W.; Kroll, J. J.; Landen, O. L.; Nikroo, A.; Pickworth, L.; Rice, N.

2017-10-01

Hydrodynamic instability growth of the capsule support membranes (or "tents") and fill tubes has been studied in spherical, glow discharge polymer plastic capsule implosions at the National Ignition Facility (NIF) [Campbell et al., AIP Conf. Proc. 429, 3 (1998)]. In NIF implosions, the capsules are supported by tents because the nominal 10-μm thick fill tubes are not strong enough to support capsules by themselves. After it was recognized that the tents had a significant impact of implosion stability, new support methods were investigated, including thicker, 30-μm diameter fill tubes and cantilevered fill tubes, as described in this article. A new "sub-scale" version of the existing x-ray radiography platform was developed for measuring growing capsule perturbations in the acceleration phase of implosions. It was calibrated using hydrodynamic growth measurements of pre-imposed capsule modulations with Legendre modes of 60, 90, 110, and 140 at convergence ratios up to ˜2.4. Subsequent experiments with 3-D perturbations have studied instability growth of 10-μm and 30-μm thick fill tubes to compare them with 30-nm thick tent perturbations at convergence ratios up to ˜3. In other experiments, the perturbations from cantilevered fill tubes were measured and compared to the tent perturbations. The cantilevered fill tubes were supported by 12-μm thick SiC rods, offset by 100 μm, 200 μm, and 300 μm from the capsule surfaces. Based on these experiments, 30-μm thick fill tubes and 300-μm offset cantilevered fill tubes were recommended for further tests using layered deuterium-tritium implosions. The effects of x-ray shadowing during the drive and oxygen-induced perturbations during target assembly produced additional seeds for instabilities and were also measured in these experiments.

Capsule physics comparison of National Ignition Facility implosion designs using plastic, high density carbon, and beryllium ablators

NASA Astrophysics Data System (ADS)

Clark, D. S.; Kritcher, A. L.; Yi, S. A.; Zylstra, A. B.; Haan, S. W.; Weber, C. R.

2018-03-01

Indirect drive implosion experiments on the National Ignition Facility (NIF) [E. I. Moses et al., Phys. Plasmas 16, 041006 (2009)] have now tested three different ablator materials: glow discharge polymer plastic, high density carbon, and beryllium. How do these different ablators compare in current and proposed implosion experiments on NIF? What are the relative advantages and disadvantages of each? This paper compares these different ablator options in capsule-only simulations of current NIF experiments and potential future designs. The simulations compare the impact of the capsule fill tube, support tent, and interface surface roughness for each case, as well as all perturbations in combination. According to the simulations, each ablator is impacted by the various perturbation sources differently, and each material poses unique challenges in the pursuit of ignition on NIF.

Observation and modeling of interspecies ion separation in inertial confinement fusion implosions via imaging x-ray spectroscopy

DOE PAGES

Joshi, Tirtha Raj; Hakel, Peter; Hsu, Scott C.; ...

2017-03-22

In this article, we report the first direct experimental evidence of interspecies ion separation in direct-drive inertial confinement fusion experiments performed at the OMEGA laser facility via spectrally, temporally, and spatially resolved imaging x-ray-spectroscopy data [S. C. Hsu et al., Europhys. Lett. 115, 65001 (2016)]. These experiments were designed based on the expectation that interspecies ion thermo-diffusion would be the strongest for species with a large mass and charge difference. The targets were spherical plastic shells filled with D2 and a trace amount of Ar (0.1% or 1% by atom). Ar K-shell spectral features were observed primarily between the timemore » of first-shock convergence and slightly before the neutron bang time, using a time- and space-integrated spectrometer, a streaked crystal spectrometer, and two gated multi-monochromatic x-ray imagers fielded along quasi-orthogonal lines of sight. Detailed spectroscopic analyses of spatially resolved Ar K-shell lines reveal the deviation from the initial 1% Ar gas fill and show both Ar-concentration enhancement and depletion at different times and radial positions of the implosion. The experimental results are interpreted using radiation-hydrodynamic simulations that include recently implemented, first-principles models of interspecies ion diffusion. Lastly, the experimentally inferred Ar-atom fraction profiles agree reasonably with calculated profiles associated with the incoming and rebounding first shock.« less

Generation of cylindrically convergent shockwaves in water on the MACH facility

NASA Astrophysics Data System (ADS)

Bland, Simon; Krasik, Ya. E.; Yanuka, D.; Gardner, R.; MacDonald, J.; Virozub, A.; Efimov, S.; Gleizer, S.; Chaturvedi, N.

2017-06-01

We report on the first experiments utilizing MACH facility at Imperial College London to explode copper wire arrays in water, generating extremely symmetric, cylindrical convergent shockwaves. The experiments were carried out with 10mm diameter arrays consisting of 60 × 130 μm wires, and currents >500 kA were achieved despite the high inductance load. Laser backlit framing images and streak photography of the implosion showed a highly uniform, stable shockwave that travelled towards the axis at velocities up to 7.5 kms-1. For the first time, imaging of the shock front has been carried at radii < 0.5 mm, and there is strong evidence that even at radii < 0.1 mm the shock front remains stable, resulting in a convergence ratio of 50:1. 2D hydrodynamic simulations that match the experimentally obtained implosion trajectory suggest pressures of >1 Mbar are produced within 10 μm of the axis, with water densities 3 gcm-3 and temperatures of many 1000 s of Kelvin. The results represent a significant step in the application of the technique to drive different material samples, and calculations of scaling the technique to larger pulsed power facilities are presented. This work was supported by the Institute of Shock Physics, funded by AWE Aldermaston, and the NNSA under DOE Cooperative Agreement Nos. DE-F03-02NA00057 and DE-SC-0001063.

Matter under extreme conditions experiments at the Linac Coherent Light Source

DOE PAGES

Glenzer, S. H.; Fletcher, L. B.; Galtier, E.; ...

2015-12-10

The Matter in Extreme Conditions end station at the Linac Coherent Light Source (LCLS) is a new tool enabling accurate pump-probe measurements for studying the physical properties of matter in the high-energy density physics regime. This instrument combines the world’s brightest x-ray source, the LCLS x-ray beam, with high-power lasers consisting of two nanosecond Nd:glass laser beams and one short-pulse Ti:sapphire laser. These lasers produce short-lived states of matter with high pressures, high temperatures or high densities with properties that are important for applications in nuclear fusion research, laboratory astrophysics and the development of intense radiation sources. In the firstmore » experiments, we have performed highly accurate x-ray diffraction and x-ray Thomson scattering techniques on shock-compressed matter resolving the transition from compressed solid matter to a co-existence regime and into the warm dense matter state. Furthermore, these complex charged-particle systems are dominated by strong correlations and quantum effects. They exist in planetary interiors and laboratory experiments, e.g., during high-power laser interactions with solids or the compression phase of inertial confinement fusion implosions. Applying record peak brightness X rays resolves the ionic interactions at atomic (Ångstrom) scale lengths and measure the static structure factor, which is a key quantity for determining equation of state data and important transport coefficients. Simultaneously, spectrally resolved measurements of plasmon features provide dynamic structure factor information that yield temperature and density with unprecedented precision at micron-scale resolution in dynamic compression experiments. This set of studies demonstrates our ability to measure fundamental thermodynamic properties that determine the state of matter in the high-energy density physics regime.« less

Studies of bandwidth dependence of laser plasma instabilities driven by the Nike laser

NASA Astrophysics Data System (ADS)

Weaver, J.; Kehne, D.; Obenschain, S.; Serlin, V.; Schmitt, A. J.; Oh, J.; Lehmberg, R. H.; Brown, C. M.; Seely, J.; Feldman, U.

2012-10-01

Experiments at the Nike laser facility of the Naval Research Laboratory are exploring the influence of laser bandwidth on laser plasma instabilities (LPI) driven by a deep ultraviolet pump (248 nm) that incorporates beam smoothing by induced spatial incoherence (ISI). In early ISI studies with longer wavelength Nd:glass lasers (1054 nm and 527 nm),footnotetextObenschain, PRL 62(1989);Mostovych, PRL 62(1987);Peyser, Phys. Fluids B 3(1991). stimulated Raman scattering, stimulated Brillouin scattering, and the two plasmon decay instability were reduced when wide bandwidth ISI (δν/ν˜0.03-0.19%) pulses irradiated targets at moderate to high intensities (10^14-10^15 W/cm^2). The current studies will compare the emission signatures of LPI from planar CH targets during Nike operation at large bandwidth (δν˜1THz) to observations for narrower bandwidth operation (δν˜0.1-0.3THz). These studies will help clarify the relative importance of the short wavelength and wide bandwidth to the increased LPI intensity thresholds observed at Nike. New pulse shapes are being used to generate plasmas with larger electron density scale-lengths that are closer to conditions during pellet implosions for direct drive inertial confinement fusion.

Inertial Fusion Target Physics Advantages with the Krypton Fluoride Laser

NASA Astrophysics Data System (ADS)

Obenschain, Stephen

2010-11-01

The krypton fluoride (KrF) laser's short wavelength, broad bandwidth and capability to provide extremely uniform target illumination are advantages towards obtaining high gain direct drive implosions. The short wavelength helps suppress deleterious laser-plasma instabilities, and allows one to employ higher ablation pressures. In addition, the KrF architecture allows one to zoom down the focal diameter to follow the size of the imploding pellet, thereby improving the coupling efficiency. The NRL researchers have been conducting theoretical and experimental studies to quantify the beneficial effects of utilizing KrF light. Experiments using the Nike facility have confirmed that KrF light significantly increases the threshold for laser-plasma instability. This presentation will discuss the observed target physics with KrF light and its effects towards facilitating the high gains needed for power production with inertial fusion. Simulations indicate that shock ignited designs can achieve gains above 200 with KrF energies as low a 1 megajoule. For fusion energy a laser driver must be capable of high repetition rates (5-10 Hz) along with adequate efficiency and durability. The Electra KrF 30-cm aperture electron-beam-pumped amplifier has demonstrated long duration continuous operation at high-repetition rates. This and other advances show that the KrF laser should be able to meet the requirements.

Kinetic physics in ICF: present understanding and future directions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rinderknecht, Hans G.; Amendt, P. A.; Wilks, S. C.

Kinetic physics has the potential to impact the performance of indirect-drive inertial confinement fusion (ICF) experiments. Systematic anomalies in the National Ignition Facility implosion dataset have been identified in which kinetic physics may play a role, including inferred missing energy in the hohlraum, drive asymmetry in near-vacuum hohlraums, low areal density and high burn-averaged ion temperatures (T i ) compared with mainline simulations, and low ratios of the DD-neutron and DT-neutron yields and inferred T i . Several components of ICF implosions are likely to be influenced or dominated by kinetic physics: laser-plasma interactions in the LEH and hohlraum interior;more » the hohlraum wall blowoff, blowoff/gas and blowoff/ablator interfaces; the ablator and ablator/ice interface; and the DT fuel all present conditions in which kinetic physics can significantly affect the dynamics. This review presents the assembled experimental data and simulation results to date, which indicate that the effects of long mean-free-path plasma phenomena and self-generated electromagnetic fields may have a significant impact in ICF targets. Finally, simulation and experimental efforts are proposed to definitively quantify the importance of these effects at ignition-relevant conditions, including priorities for ongoing study.« less

Kinetic physics in ICF: present understanding and future directions

DOE PAGES

Rinderknecht, Hans G.; Amendt, P. A.; Wilks, S. C.; ...

2018-03-19

Kinetic physics has the potential to impact the performance of indirect-drive inertial confinement fusion (ICF) experiments. Systematic anomalies in the National Ignition Facility implosion dataset have been identified in which kinetic physics may play a role, including inferred missing energy in the hohlraum, drive asymmetry in near-vacuum hohlraums, low areal density and high burn-averaged ion temperatures (T i ) compared with mainline simulations, and low ratios of the DD-neutron and DT-neutron yields and inferred T i . Several components of ICF implosions are likely to be influenced or dominated by kinetic physics: laser-plasma interactions in the LEH and hohlraum interior;more » the hohlraum wall blowoff, blowoff/gas and blowoff/ablator interfaces; the ablator and ablator/ice interface; and the DT fuel all present conditions in which kinetic physics can significantly affect the dynamics. This review presents the assembled experimental data and simulation results to date, which indicate that the effects of long mean-free-path plasma phenomena and self-generated electromagnetic fields may have a significant impact in ICF targets. Finally, simulation and experimental efforts are proposed to definitively quantify the importance of these effects at ignition-relevant conditions, including priorities for ongoing study.« less

Kinetic physics in ICF: present understanding and future directions

NASA Astrophysics Data System (ADS)

Rinderknecht, Hans G.; Amendt, P. A.; Wilks, S. C.; Collins, G.

2018-06-01

Kinetic physics has the potential to impact the performance of indirect-drive inertial confinement fusion (ICF) experiments. Systematic anomalies in the National Ignition Facility implosion dataset have been identified in which kinetic physics may play a role, including inferred missing energy in the hohlraum, drive asymmetry in near-vacuum hohlraums, low areal density and high burn-averaged ion temperatures (〈Ti 〉) compared with mainline simulations, and low ratios of the DD-neutron and DT-neutron yields and inferred 〈Ti 〉. Several components of ICF implosions are likely to be influenced or dominated by kinetic physics: laser-plasma interactions in the LEH and hohlraum interior; the hohlraum wall blowoff, blowoff/gas and blowoff/ablator interfaces; the ablator and ablator/ice interface; and the DT fuel all present conditions in which kinetic physics can significantly affect the dynamics. This review presents the assembled experimental data and simulation results to date, which indicate that the effects of long mean-free-path plasma phenomena and self-generated electromagnetic fields may have a significant impact in ICF targets. Simulation and experimental efforts are proposed to definitively quantify the importance of these effects at ignition-relevant conditions, including priorities for ongoing study.

Spatial filter system as an optical relay line

DOEpatents

Hunt, John T.; Renard, Paul A.

1979-01-01

A system consisting of a set of spatial filters that are used to optically relay a laser beam from one position to a downstream position with minimal nonlinear phase distortion and beam intensity variation. The use of the device will result in a reduction of deleterious beam self-focusing and produce a significant increase in neutron yield from the implosion of targets caused by their irradiation with multi-beam glass laser systems.

Investigation of trailing mass in Z-pinch implosions and comparison to experiment

NASA Astrophysics Data System (ADS)

Yu, Edmund

2007-11-01

Wire-array Z pinches represent efficient, high-power x-ray sources with application to inertial confinement fusion, high energy density plasmas, and laboratory astrophysics. The first stage of a wire-array Z pinch is described by a mass ablation phase, during which stationary wires cook off material, which is then accelerated radially inwards by the JxB force. The mass injection rate varies axially and azimuthally, so that once the ablation phase concludes, the subsequent implosion is highly 3D in nature. In particular, a network of trailing mass and current is left behind the imploding plasma sheath, which can significantly affect pinch performance. In this work we focus on the implosion phase, electing to model the mass ablation via a mass injection scheme. Such a scheme has a number of injection parameters, but this freedom also allows us to gain understanding into the nature of the trailing mass network. For instance, a new result illustrates the role of azimuthal correlation. For an implosion which is 100% azimuthally correlated (corresponding to an azimuthally symmetric 2D r-z problem), current is forced to flow on the imploding plasma sheath, resulting in strong Rayleigh-Taylor (RT) growth. If, however, the implosion is not azimuthally symmetric, the additional azimuthal degree of freedom opens up new conducting paths of lower magnetic energy through the trailing mass network, effectively reducing RT growth. Consequently the 3D implosion experiences lower RT growth than the 2D r-z equivalent, and actually results in a more shell-like implosion. A second major goal of this work is to constrain the injection parameters by comparison to a well-diagnosed experimental data set, in which array mass was varied. In collaboration with R. Lemke, M. Desjarlais, M. Cuneo, C. Jennings, D. Sinars, E. Waisman

The Experimental Study of Characterized Noble Gas Puffs Irradiated by Ultra-Short Laser Pulses Compared with X-Pinches as an X-Ray Source

NASA Astrophysics Data System (ADS)

Schultz, Kimberly Ann

The goal of this dissertation is to study the basic physics and X-ray emission (1-10 keV) of two X-ray sources: X-pinch plasmas and a clustered gas-puff irradiated by an ultrashort laser pulse. X-pinches and other typical X-ray sources using solid targets create hot debris that can damage sensitive equipment. Therefore, to perform sensitive backlighting or X-ray effects testing, debris-free sources of radiation must be investigated. In this work, the author presents a broad study of clustered noble gas puffs including characterization measurements and laser heating experiments using several gas nozzles and multiple gases. Ultimately, the goal is to compare the laser-irradiated gas-puff and X-pinch plasmas as X-ray sources. Characterization of the gas puffs is performed at the Radiation Physics Laboratory at the University of Nevada, Reno (UNR) Physics Department using optical interferometry and Rayleigh scattering to determine density and cluster radius. By changing the gas-puff variables control of both the density and cluster size of the gas jets is obtained. Two laser systems provide the high intensities desired for the laser-irradiated gas puff experiments: the UNR Leopard Laser (1-2x1019 W/cm2) and the Lawrence Livermore National Laboratory's Titan Laser (7x1019 W/cm2). X-ray emission is studied as a function of laser pulse parameters, gas target type, gas puff density, and the gas-delay timing between puff initiation and laser interaction with the puff. The tested gases are Ar, Kr, Xe, and four mixtures of the noble gases. Time-resolved X-ray measurements are captured with Silicon diodes and photoconducting diamond detectors. Electron beam detectors include Faraday cups and a high-energy (> 1 MeV) electron spectrometer. Modeling of spectra from X-ray crystal spectrometers provides plasma density and temperature measurement and a molecular dynamics (MD) code describes cluster interactions with the laser pulse. The conversion of laser energy into X rays is also measured. Laser beam transmission through and absorption by the gas puff reveal the complexity of using laser-irradiated gas puffs as X-ray sources. A strong anisotropy of X-ray and electron emissions were observed at both laser facilities. X-pinch plasmas can provide intense hard X rays and strong electron beams originating from small sources with many applications. Recent research has been conducted into four-wire X-pinches at the UNR Zebra machine, a 1-MA pulsed power generator. Two different wire materials are considered in this study, Ag and Mo. We observe a relatively linear correlation between load mass and implosion time for Mo X-pinches; in fact, this relationship also extends to include Ag. Interestingly, X-ray burst features drastically change in shape when the load mass is varied. Advantages of laser-irradiated gas puffs include a lack of damaging debris, high repetition rate, and ease of control. Its disadvantages include its inefficiency at converting electrical energy to X-rays, which is mostly limited by laser efficiency, and relatively low total energy yield. X-pinches, on the other hand, produced kJ of energy in a broad spectral region. However, they create a large amount of debris, have a low repetition rate, and, at 1-MA, have hard-to-predict implosion times.

ICF Implosions, Space-Charge Electric Fields, and Their Impact on Mix and Compression

NASA Astrophysics Data System (ADS)

Knoll, Dana; Chacon, Luis; Simakov, Andrei

2013-10-01

The single-fluid, quasi-neutral, radiation hydrodynamics codes, used to design the NIF targets, predict thermonuclear ignition for the conditions that have been achieved experimentally. A logical conclusion is that the physics model used in these codes is missing one, or more, key phenomena. Two key model-experiment inconsistencies on NIF are: 1) a lower implosion velocity than predicted by the design codes, and 2) transport of pusher material deep into the hot spot. We hypothesize that both of these model-experiment inconsistencies may be a result of a large, space-charge, electric field residing on the distinct interfaces in a NIF target. Large space-charge fields have been experimentally observed in Omega experiments. Given our hypothesis, this presentation will: 1) Develop a more complete physics picture of initiation, sustainment, and dissipation of a current-driven plasma sheath / double-layer at the Fuel-Pusher interface of an ablating plastic shell implosion on Omega, 2) Characterize the mix that can result from a double-layer field at the Fuel-Pusher interface, prior to the onset of fluid instabilities, and 3) Quantify the impact of the double-layer induced surface tension at the Fuel-Pusher interface on the peak observed implosion velocity in Omega.

BOOK REVIEW: Inertial confinement fusion: The quest for ignition and energy gain using indirect drive

NASA Astrophysics Data System (ADS)

Yamanaka, C.

1999-06-01

Inertial confinement fusion (ICF) is an alternative way to control fusion which is based on scaling down a thermonuclear explosion to a small size, applicable for power production, a kind of thermonuclear internal combustion engine. This book extends many interesting topics concerning the research and development on ICF of the last 25 years. It provides a systematic development of the physics basis and also various experimental data on radiation driven implosion. This is a landmark treatise presented at the right time. It is based on the article ``Development of the indirect-drive approach to inertial confinement fusion and the target physics basis for ignition and gain'' by J.D. Lindl, published in Physics of Plasmas, Vol. 2, November 1995, pp. 3933-4024. As is well known, in the United States of America research on the target physics basis for indirect drive remained largely classified until 1994. The indirect drive approaches were closely related to nuclear weapons research at Lawrence Livermore and Los Alamos National Laboratories. In Japan and other countries, inertial confinement fusion research for civil energy has been successfully performed to achieve DT fuel pellet compression up to 1000 times normal density, and indirect drive concepts, such as the `Cannon Ball' scheme, also prevailed at several international conferences. In these circumstances the international fusion community proposed the Madrid Manifesto in 1988, which urged openness of ICF information to promote international collaboration on civil energy research for the future resources of the human race. This proposal was also supported by some of the US scientists. The United States Department of Energy revised its classification guidelines for ICF six years after the Madrid Manifesto. This first book from the USA treating target physics issues, covering topics from implosion dynamics to hydrodynamic stability, ignition physics, high-gain target design and the scope for energy applications is enthusiastically welcomed. The author joined Lawrence Livermore National Laboratory in 1972 to perform intensive theoretical and computational research on implosion and ignition. He was awarded the Edward Teller Medal in 1993. One therefore expects the topics to be treated with authority, and this expectation is well fulfilled. The general treatment throughout the book is to begin with the basic physics of implosion and show how its development leads to an explanation of many fundamental ideas about implosion, via direct drive or indirect drive, particularly ideas associated with radiation transport. This approach is generally successful, with the reader immediately able to relate the theoretical treatments to physical problems. One danger in this approach, however, is that fundamental concepts in implosion often become stressed within the framework of indirect radiation drive of hohlraum targets oriented towards research in the National Ignition Facility. The references in this book to Livermore or Los Alamos internal documents are not yet publicly available, because many are in the process of review for declassification. The reader will have to become accustomed to this situation, which has lasted for a long time but now seems to be gradually improving. The treatise is composed of 13 chapters, including 271 illustrations. An overview of ICF and the historical development of indirect drive in the ICF programme are described in Chapters 1 and 2. Direct drive and indirect drive have different features. The choice of which to use is a very interesting issue. The former has a higher laser-target coupling efficiency but is less uniform in laser irradiation due to discrete beams of lasers. Beam smoothing techniques have a key role in direct drive. The indirect drive by soft X rays which are generated at the inner surface of a hohlraum can have a higher uniform irradiation to reduce the growth of perturbations due to Rayleigh-Taylor (RT) instabilities. The soft X ray drive has much higher ablation rates and is less sensitive to hot electron preheat. A potential disadvantage of indirect drive is the larger scale length of the plasma travelled by the laser beam from the inlet hole to the hohlraum wall. Parametric instabilities in hohlraums have problems because of energy loss and coupling. One of the most important issues for indirect drive is a radiation drive concept which is essentially independent of the driver, such as laser or particle beam. The historical progress of ICF in the USA mainly depended upon the resolution of the fusion database for weaponry. This was a reason to choose indirect drive as the main scheme. Several structures of hohlraum target are described which for a long time were closed to the public. As the minimum energy for ignition depends strongly on the achievable implosion velocity, a great deal of benefit is derived from operating at the highest possible hohlraum temperature and in-flight aspect ratio (IFAR). The conclusion of Chapters 3, 4 and 5 is that achieving an implosion velocity of 3 × 107cm/s with an IFAR-30 Fermi degenerated shell would require a minimum drive temperature of about 200 eV. The hydrodynamic instability, ignition threshold and capsule gain are discussed in Chapter 6. The RT hydrodynamic instability began at the upper limit of the IFAR and hence at the peak implosion velocity. The growth rate of the instability in the acceleration phase was found to be suppressed by the ablation flow at Osaka. Instability during the deceleration phase was primarily stabilized by electron conduction. The combined effects of acceleration, feed-through and deceleration show that the principal modes contributing to perturbations in the fuel have spherical harmonic mode numbers less than about 30-40. The higher modes are rapidly reduced by rarefaction. The lower modes are killed by so-called `fire polishing'. The target uniformity and irradiation uniformity are very effective at suppressing instabilities. The maximum number of e-foldings sets the upper limit of the implosion velocity. This gives the threshold energy of ignition. The minimum capsule energy for ignition for indirect drive is compared with Nuckoll's projections for direct drive. The estimation depends strongly upon the effects of hydrodynamic instability and symmetry in the compressed fuel volume. If the margin of energy is 2, the necessary capsule absorbed energy is about 90 kJ with a radiation temperature of 300 eV. The coupling between driver and capsule is 10-15%, and the driver energy is 0.6-0.9 MJ. The scaling laws for the capsule absorbed power, radius and pulse length with a certain IFAR are given. It is concluded (Chapter 6) that the optimum strategy for gain is operation at the minimum implosion velocity consistent with the desired capsule size and yield, because at the excess implosion velocity the capsules tend to ignite earlier than the optimal point in the compression process. The most crucial issues for the hohlraum target are the coupling efficiency and hohlraum radiation uniformity. Various kinds of devices for hohlraum structures and double cone irradiation schemes have been investigated. These technological developments are energetically described. The implosion symmetry reproducibility (Chapters 7 and 8) for the Precision Nova advanced system meets the requirement of 1% uniformity for ignition experiment time averaged flux. Combined tests of symmetry and hydrodynamic instability as well as the hohlraum plasma conditions estimating the simulated Brillouin scattering (SBS) and simulated Raman scattering (SRS) effects and their influence on the hot electron preheat are summarized in Chapters 9, 10 and 11. The tolerable fraction of hot electrons for keeping the DT fuel preheat at approximately the Fermi specific energy indicates that direct drive capsules are 3 to 4 times larger than the indirect drive capsules. As a conclusion, Chapters 12 and 13 are proudly devoted to the National Ignition Facility and ignition targets. The NIF has a 192 beam, frequency tripled Nd:glass laser system with routine target energies and powers of 1.8 MJ and 500 TW, appropriately pulse shaped. The 192 beams are clustered in groups of 4, so that there are effectively 8 spots in each of the inner cones, and 16 in the outer cones in the hohlraum. Each cluster of 4 beams combines to form an effective f/8 optic. Various kinds of target design are described, for instance, a baseline design 300 eV hohlraum capsule, which absorbs 1.35 MJ of light, an ignition point hydrocarbon (CH) capsule, which is aimed at determining the requirements for symmetry, stability and ignition, and a lower temperature 250 eV capsule with a beryllium ablator, which provides a trade-off between hydroinstabilities and laser-plasma effects. The NIF baseline capsule designs absorb 150 kJ, of which about 25 kJ ends up in the compressed fuel. The central temperature increases to 10 keV when the capsule produces 400 kJ. The fuel energy gain is about 16 at ignition, or when the alpha particle deposition is about 3 times the initial energy delivered to the compressed fuel. The NIF baseline targets are then expected to yield up to 15 MJ and a fuel gain of about 600. Estimates based on NOVA experiments and modelling indicate that SBS, SRS and other plasma hazard processes can be kept within acceptable limits. If these are not attained, the ultimate recourse is to increase the hohlraum size, reduce the laser intensity and reduce the drive temperature to that of the 250 eV design, which has significantly less plasma. The remaining uncertainties can be mitigated by changes in the target design. The author has confidence ignition will be achieved in NIF, which seems to be strongly supported by the Centurion-Halite underground nuclear experiments demonstrating the excellent performance and the basic feasibility of achieving high gain. He thoughtfully adds a comment that developments in direct drive have reached the point where this approach also looks quite promising. NIF will be able to shift rapidly ( <= 1 d) between indirect drive and direct drive. Finally, the short last chapter (Chapter 13) gives an overview on the greatest potential for future ICF power plants. In a book review, questions are usually asked about the readers the book is primarily intended for, whether the book is written at the appropriate level for those readers and whether there are other books that achieve similar objectives. The last section of the Preface states that this book provides an in-depth analysis of theoretical and experimental work on indirect drive ICF classified up to 1994, as well as work carried out throughout the world. It is intended to serve as a reference guide for researchers in the field. Each topic covered contains enough introductory material that the book can also be used at the graduate level by students or newly interested researchers. Most of the laser technology and diagnostic development are not covered at all. To this reviewer that statement is a succinct summary of what the book achieves. Working fusion physicists, particularly in ICF, will find the book to be both instructive and enjoyable. As a secondary market, the book could well be used as a text for a graduate course in laser plasma physics, although some parts are like review papers. As to which books cover some of the same material, W.L. Kruer published Physics of Laser Plasma Interactions (Addison-Wesley, Redwood City, CA, 1988), which is suitable as a textbook for graduate students and also for the plasma physicist in general and C. Yamanaka published Introduction to Laser Fusion (Harwood Academic, Chur, 1991), which is the only book treating implosion physics, lasers, target design and diagnostics prior to the USDOE's declassification. As for the Handbook of Plasma Physics series (edited by M.N. Rosenbluth and R.Z. Sagdeev), Vol. 3, Physics of Laser Plasma (edited by A.H. Rubenchik and S. Witkowski) (Elsevier Science, Amsterdam, 1991) comes to mind. However, this last book is larger, and covers somewhat diverse topics. The typography of the book presently under review is also much to be preferred. In summary, I would strongly recommend the book by Lindl to my colleagues in plasma physics, particularly to those engaged in ICF.

Simulations of a Molecular Cloud experiment using CRASH

NASA Astrophysics Data System (ADS)

Trantham, Matthew; Keiter, Paul; Vandervort, Robert; Drake, R. Paul; Shvarts, Dov

2017-10-01

Recent laboratory experiments explore molecular cloud radiation hydrodynamics. The experiment irradiates a gold foil with a laser producing x-rays to drive the implosion or explosion of a foam ball. The CRASH code, an Eulerian code with block-adaptive mesh refinement, multigroup diffusive radiation transport, and electron heat conduction developed at the University of Michigan to design and analyze high-energy-density experiments, is used to perform a parameter search in order to identify optically thick, optically thin and transition regimes suitable for these experiments. Specific design issues addressed by the simulations are the x-ray drive temperature, foam density, distance from the x-ray source to the ball, as well as other complicating issues such as the positioning of the stalk holding the foam ball. We present the results of this study and show ways the simulations helped improve the quality of the experiment. This work is funded by the LLNL under subcontract B614207 and NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0002956.

Experimental Demonstration of X-Ray Drive Enhancement with Rugby-Shaped Hohlraums

NASA Astrophysics Data System (ADS)

Philippe, F.; Casner, A.; Caillaud, T.; Landoas, O.; Monteil, M. C.; Liberatore, S.; Park, H. S.; Amendt, P.; Robey, H.; Sorce, C.; Li, C. K.; Seguin, F.; Rosenberg, M.; Petrasso, R.; Glebov, V.; Stoeckl, C.

2010-01-01

Rugby-shaped hohlraums have been suggested as a way to enhance x-ray drive in the indirect drive approach to inertial confinement fusion. This Letter presents an experimental comparison of rugby-shaped and cylinder hohlraums used for D2 and DHe3-filled capsules implosions on the Omega laser facility, demonstrating an increase of x-ray flux by 18% in rugby-shaped hohlraums. The highest yields to date for deuterium gas implosions in indirect drive on Omega (1.5×1010 neutrons) were obtained, allowing for the first time the measurement of a DD burn history. Proton spectra measurements provide additional validation of the higher drive in rugby-shaped hohlraums.

Anomalous DD and TT yields relative to the DT yield in inertial-confinement-fusion implosions

NASA Astrophysics Data System (ADS)

Casey, Daniel T.

2011-10-01

Measurements of the D(d,p)T (DD), T(t,2n)4He (TT) and D(t,n)4He (DT) reactions have been conducted using deuterium-tritium gas-filled inertial confinement fusion (ICF) implosions. In these experiments, which were carried out at the OMEGA laser facility, absolute spectral measurements of the DD protons and TT neutrons were conducted and compared to neutron-time-of-flight measured DT-neutron yields. From these measurements, it is concluded that the DD yield is anomalously low and the TT yield is anomalously high relative to the DT yield, an effect that is enhanced with increasing ion temperature. These results can be explained by an enrichment of tritium in the core of an ICF implosion, which may be present in ignition experiments planned on the National Ignition Facility. In addition, the spectral measurements of the TT-neutron spectrum were conducted for the first time at reactant central-mass energies in the range of 15-30 keV. The results from these measurements indicate that the TT reaction proceeds primarily through the direct three-body reaction channel, producing a continuous TT-neutron spectrum in the range 0 - 9.5 MeV. This work was conducted in collaboration with J. A. Frenje, M. Gatu Johnson, M. J.-E. Manuel, H. G. Rinderknecht, N. Sinenian, F. H. Seguin, C. K. Li, R. D. Petrasso, P. B. Radha, J. A. Delettrez, V. Yu Glebov, D. D. Meyerhofer, T. C. Sangster, D. P. McNabb, P. A. Amendt, R. N. Boyd, J. R. Rygg, H. W. Herrmann, Y. H. Kim, G. P. Grim and A. D. Bacher. This work was supported in part by the U.S. Department of Energy (Grant No. DE-FG03-03SF22691), LLE (subcontract Grant No. 412160-001G), LLNL (subcontract Grant No. B504974).

Laser-fusion targets for reactors

DOEpatents

Nuckolls, John H.; Thiessen, Albert R.

1987-01-01

A laser target comprising a thermonuclear fuel capsule composed of a centrally located quantity of fuel surrounded by at least one or more layers or shells of material for forming an atmosphere around the capsule by a low energy laser prepulse. The fuel may be formed as a solid core or hollow shell, and, under certain applications, a pusher-layer or shell is located intermediate the fuel and the atmosphere forming material. The fuel is ignited by symmetrical implosion via energy produced by a laser, or other energy sources such as an electron beam machine or ion beam machine, whereby thermonuclear burn of the fuel capsule creates energy for applications such as generation of electricity via a laser fusion reactor.

Capsule physics comparison of different ablators for NIF implosion designs

NASA Astrophysics Data System (ADS)

Clark, Daniel; Kritcher, Andrea; Yi, Austin; Zylstra, Alex; Haan, Steven; Ralph, Joseph; Weber, Christopher

2017-10-01

Indirect drive implosion experiments on the Naitonal Ignition Facility (NIF) have now tested three different ablator materials: glow discharge polymer (GDP) plastic, high density carbon (HDC), and beryllium. How do these different ablator choices compare in current and future implosion experiments on NIF? What are the relative advantages and disadvantages of each? This talk compares these different ablator options in capsule-only simulations of current NIF experiments and proposed future designs. The simulations compare the impact of the capsule fill tube, support tent, and interface surface roughness for each case, as well as all perturbations in combination. According to the simulations, each ablator is impacted by the various perturbation sources differently, and each material poses unique challenges in the pursuit of ignition. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

High-resolution spectroscopy for Doppler-broadening ion temperature measurements of implosions at the National Ignition Facility.

PubMed

Koch, J A; Stewart, R E; Beiersdorfer, P; Shepherd, R; Schneider, M B; Miles, A R; Scott, H A; Smalyuk, V A; Hsing, W W

2012-10-01

Future implosion experiments at the national ignition facility (NIF) will endeavor to simultaneously measure electron and ion temperatures with temporal and spatial resolution in order to explore non-equilibrium temperature distributions and their relaxation toward equilibrium. In anticipation of these experiments, and with understanding of the constraints of the NIF facility environment, we have explored the use of Doppler broadening of mid-Z dopant emission lines, such as krypton He-α at 13 keV, as a diagnostic of time- and potentially space-resolved ion temperature. We have investigated a number of options analytically and with numerical raytracing, and we have identified several promising candidate spectrometer designs that meet the expected requirements of spectral and temporal resolution and data signal-to-noise ratio for gas-filled exploding pusher implosions, while providing maximum flexibility for use on a variety of experiments that potentially include burning plasma.

LLE Review 116 (July-September 2008)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marozas, J.A., editor

2010-03-12

This issue has the following articles: (1) Optimizing Electron-Positron Pair Production on kJ-Class High-Intensity Lasers for the Purpose of Pair-Plasma Creation; (2) Neutron Yield Study of Direct-Drive, Low-Adiabat Cryogenic D2 Implosions on OMEGA; (3) Al 1s-2p Absorption Spectroscopy of Shock-Wave Heating and Compression in Laser-Driven Planar Foil; (4) A Measurable Lawson Criterion and Hydro-Equivalent Curves for Inertial Confinement Fusion; (5) Pulsed-THz Characterization of Hg-Based, High-Temperature Superconductors; (6) LLE's Summer High School Research Program; (7) FY08 Laser Facility Report; and (8) National Laser Users Facility and External Users Programs.

Adiabat-shaping in indirect drive inertial confinement fusion

DOE PAGES

Baker, K. L.; Robey, H. F.; Milovich, J. L.; ...

2015-05-05

Adiabat-shaping techniques were investigated in this paper in indirect drive inertial confinement fusion experiments on the National Ignition Facility as a means to improve implosion stability, while still maintaining a low adiabat in the fuel. Adiabat-shaping was accomplished in these indirect drive experiments by altering the ratio of the picket and trough energies in the laser pulse shape, thus driving a decaying first shock in the ablator. This decaying first shock is designed to place the ablation front on a high adiabat while keeping the fuel on a low adiabat. These experiments were conducted using the keyhole experimental platform formore » both three and four shock laser pulses. This platform enabled direct measurement of the shock velocities driven in the glow-discharge polymer capsule and in the liquid deuterium, the surrogate fuel for a DT ignition target. The measured shock velocities and radiation drive histories are compared to previous three and four shock laser pulses. This comparison indicates that in the case of adiabat shaping the ablation front initially drives a high shock velocity, and therefore, a high shock pressure and adiabat. The shock then decays as it travels through the ablator to pressures similar to the original low-adiabat pulses when it reaches the fuel. Finally, this approach takes advantage of initial high ablation velocity, which favors stability, and high-compression, which favors high stagnation pressures.« less

Detailed high-resolution three-dimensional simulations of OMEGA separated reactants inertial confinement fusion experiments

DOE PAGES

Haines, Brian Michael; Grim, Gary P.; Fincke, James R.; ...

2016-07-29

Here, we present results from the comparison of high-resolution three-dimensional (3D) simulations with data from the implosions of inertial confinement fusion capsules with separated reactants performed on the OMEGA laser facility. Each capsule, referred to as a “CD Mixcap,” is filled with tritium and has a polystyrene (CH) shell with a deuterated polystyrene (CD) layer whose burial depth is varied. In these implosions, fusion reactions between deuterium and tritium ions can occur only in the presence of atomic mix between the gas fill and shell material. The simulations feature accurate models for all known experimental asymmetries and do not employmore » any adjustable parameters to improve agreement with experimental data. Simulations are performed with the RAGE radiation-hydrodynamics code using an Implicit Large Eddy Simulation (ILES) strategy for the hydrodynamics. We obtain good agreement with the experimental data, including the DT/TT neutron yield ratios used to diagnose mix, for all burial depths of the deuterated shell layer. Additionally, simulations demonstrate good agreement with converged simulations employing explicit models for plasma diffusion and viscosity, suggesting that the implicit sub-grid model used in ILES is sufficient to model these processes in these experiments. In our simulations, mixing is driven by short-wavelength asymmetries and longer-wavelength features are responsible for developing flows that transport mixed material towards the center of the hot spot. Mix material transported by this process is responsible for most of the mix (DT) yield even for the capsule with a CD layer adjacent to the tritium fuel. Consistent with our previous results, mix does not play a significant role in TT neutron yield degradation; instead, this is dominated by the displacement of fuel from the center of the implosion due to the development of turbulent instabilities seeded by long-wavelength asymmetries. Through these processes, the long-wavelength asymmetries degrade TT yield more than the DT yield and thus bring DT/TT neutron yield ratios into agreement with experiment. Finally, we present a detailed comparison of the flows in 2D and 3D simulations.« less

Detailed high-resolution three-dimensional simulations of OMEGA separated reactants inertial confinement fusion experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haines, Brian M., E-mail: bmhaines@lanl.gov; Fincke, James R.; Shah, Rahul C.

We present results from the comparison of high-resolution three-dimensional (3D) simulations with data from the implosions of inertial confinement fusion capsules with separated reactants performed on the OMEGA laser facility. Each capsule, referred to as a “CD Mixcap,” is filled with tritium and has a polystyrene (CH) shell with a deuterated polystyrene (CD) layer whose burial depth is varied. In these implosions, fusion reactions between deuterium and tritium ions can occur only in the presence of atomic mix between the gas fill and shell material. The simulations feature accurate models for all known experimental asymmetries and do not employ anymore » adjustable parameters to improve agreement with experimental data. Simulations are performed with the RAGE radiation-hydrodynamics code using an Implicit Large Eddy Simulation (ILES) strategy for the hydrodynamics. We obtain good agreement with the experimental data, including the DT/TT neutron yield ratios used to diagnose mix, for all burial depths of the deuterated shell layer. Additionally, simulations demonstrate good agreement with converged simulations employing explicit models for plasma diffusion and viscosity, suggesting that the implicit sub-grid model used in ILES is sufficient to model these processes in these experiments. In our simulations, mixing is driven by short-wavelength asymmetries and longer-wavelength features are responsible for developing flows that transport mixed material towards the center of the hot spot. Mix material transported by this process is responsible for most of the mix (DT) yield even for the capsule with a CD layer adjacent to the tritium fuel. Consistent with our previous results, mix does not play a significant role in TT neutron yield degradation; instead, this is dominated by the displacement of fuel from the center of the implosion due to the development of turbulent instabilities seeded by long-wavelength asymmetries. Through these processes, the long-wavelength asymmetries degrade TT yield more than the DT yield and thus bring DT/TT neutron yield ratios into agreement with experiment. Finally, we present a detailed comparison of the flows in 2D and 3D simulations.« less

Detailed high-resolution three-dimensional simulations of OMEGA separated reactants inertial confinement fusion experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haines, Brian Michael; Grim, Gary P.; Fincke, James R.

Here, we present results from the comparison of high-resolution three-dimensional (3D) simulations with data from the implosions of inertial confinement fusion capsules with separated reactants performed on the OMEGA laser facility. Each capsule, referred to as a “CD Mixcap,” is filled with tritium and has a polystyrene (CH) shell with a deuterated polystyrene (CD) layer whose burial depth is varied. In these implosions, fusion reactions between deuterium and tritium ions can occur only in the presence of atomic mix between the gas fill and shell material. The simulations feature accurate models for all known experimental asymmetries and do not employmore » any adjustable parameters to improve agreement with experimental data. Simulations are performed with the RAGE radiation-hydrodynamics code using an Implicit Large Eddy Simulation (ILES) strategy for the hydrodynamics. We obtain good agreement with the experimental data, including the DT/TT neutron yield ratios used to diagnose mix, for all burial depths of the deuterated shell layer. Additionally, simulations demonstrate good agreement with converged simulations employing explicit models for plasma diffusion and viscosity, suggesting that the implicit sub-grid model used in ILES is sufficient to model these processes in these experiments. In our simulations, mixing is driven by short-wavelength asymmetries and longer-wavelength features are responsible for developing flows that transport mixed material towards the center of the hot spot. Mix material transported by this process is responsible for most of the mix (DT) yield even for the capsule with a CD layer adjacent to the tritium fuel. Consistent with our previous results, mix does not play a significant role in TT neutron yield degradation; instead, this is dominated by the displacement of fuel from the center of the implosion due to the development of turbulent instabilities seeded by long-wavelength asymmetries. Through these processes, the long-wavelength asymmetries degrade TT yield more than the DT yield and thus bring DT/TT neutron yield ratios into agreement with experiment. Finally, we present a detailed comparison of the flows in 2D and 3D simulations.« less

Detailed high-resolution three-dimensional simulations of OMEGA separated reactants inertial confinement fusion experiments

NASA Astrophysics Data System (ADS)

Haines, Brian M.; Grim, Gary P.; Fincke, James R.; Shah, Rahul C.; Forrest, Chad J.; Silverstein, Kevin; Marshall, Frederic J.; Boswell, Melissa; Fowler, Malcolm M.; Gore, Robert A.; Hayes-Sterbenz, Anna C.; Jungman, Gerard; Klein, Andreas; Rundberg, Robert S.; Steinkamp, Michael J.; Wilhelmy, Jerry B.

2016-07-01

We present results from the comparison of high-resolution three-dimensional (3D) simulations with data from the implosions of inertial confinement fusion capsules with separated reactants performed on the OMEGA laser facility. Each capsule, referred to as a "CD Mixcap," is filled with tritium and has a polystyrene (CH) shell with a deuterated polystyrene (CD) layer whose burial depth is varied. In these implosions, fusion reactions between deuterium and tritium ions can occur only in the presence of atomic mix between the gas fill and shell material. The simulations feature accurate models for all known experimental asymmetries and do not employ any adjustable parameters to improve agreement with experimental data. Simulations are performed with the RAGE radiation-hydrodynamics code using an Implicit Large Eddy Simulation (ILES) strategy for the hydrodynamics. We obtain good agreement with the experimental data, including the DT/TT neutron yield ratios used to diagnose mix, for all burial depths of the deuterated shell layer. Additionally, simulations demonstrate good agreement with converged simulations employing explicit models for plasma diffusion and viscosity, suggesting that the implicit sub-grid model used in ILES is sufficient to model these processes in these experiments. In our simulations, mixing is driven by short-wavelength asymmetries and longer-wavelength features are responsible for developing flows that transport mixed material towards the center of the hot spot. Mix material transported by this process is responsible for most of the mix (DT) yield even for the capsule with a CD layer adjacent to the tritium fuel. Consistent with our previous results, mix does not play a significant role in TT neutron yield degradation; instead, this is dominated by the displacement of fuel from the center of the implosion due to the development of turbulent instabilities seeded by long-wavelength asymmetries. Through these processes, the long-wavelength asymmetries degrade TT yield more than the DT yield and thus bring DT/TT neutron yield ratios into agreement with experiment. Finally, we present a detailed comparison of the flows in 2D and 3D simulations.

Anomalous neutron yield in indirect-drive inertial-confinement-fusion due to the formation of collisionless shocks in the corona

NASA Astrophysics Data System (ADS)

Zhang, Wen-Shuai; Cai, Hong-Bo; Shan, Lian-Qiang; Zhang, Hua-Sen; Gu, Yu-Qiu; Zhu, Shao-Ping

2017-06-01

Observations of anomalous neutron yield in the indirect-drive inertial confinement fusion implosion experiments conducted at SG-III prototype and SG-II upgrade laser facilities are interpreted. The anomalous mechanism results in a neutron yield which is 100-times higher than that predicted by 1D radiation-hydrodynamic simulations. 2D radiation-hydrodynamic simulations show that the supersonic, radially directed gold (Au) plasma jets arising from the laser-hohlraum interactions can collide with the carbon-deuterium (CD) corona plasma of the compressed pellet. It is found that in the interaction front of the high-Z jet with the low-Z corona, with low density  ˜{{10}20}~\\text{c}{{\\text{m}}-3} and high temperature  ˜keV, kinetic effects become important. Particle-in-cell simulations indicate that an electrostatic shock wave can be driven when the high-temperature Au jet expands into the low-temperature CD corona. Deuterium ions with an amount of  ˜1015 can be accelerated to  ˜25 keV by the collisionless shock wave, thus causing efficient neutron productions though the beam-target method by stopping these energetic ions in the corona. The evaluated neutron yield is consistent with the experiments conducted at SG laser facilities.

Conceptual design of laser fusion reactor KOYO-fast Concepts of reactor system and laser driver

NASA Astrophysics Data System (ADS)

Kozaki, Y.; Miyanaga, N.; Norimatsu, T.; Soman, Y.; Hayashi, T.; Furukawa, H.; Nakatsuka, M.; Yoshida, K.; Nakano, H.; Kubomura, H.; Kawashima, T.; Nishimae, J.; Suzuki, Y.; Tsuchiya, N.; Kanabe, T.; Jitsuno, T.; Fujita, H.; Kawanaka, J.; Tsubakimoto, K.; Fujimoto, Y.; Lu, J.; Matsuoka, S.; Ikegawa, T.; Owadano, Y.; Ueda, K.; Tomabechi, K.; Reactor Design Committee in Ife Forum, Members Of

2006-06-01

We have carried out the design studies of KOYO-Fast laser fusion power plant, using fast ignition cone targets, DPSSL lasers, and LiPb liquid wall chambers. Using fast ignition targets, we could design a middle sized 300 MWe reactor module, with 200 MJ fusion pulse energy and 4 Hz rep-rates, and 1200MWe modular power plants with 4 reactor modules and a 16 Hz laser driver. The liquid wall chambers with free surface cascade flows are proposed for cooling surface quickly enough to a 4 Hz pulse operation. We examined the potential of Yb-YAG ceramic lasers operated at 150˜ 225 K for both implosion and heating laser systems required for a 16-Hz repetition and 8 % total efficiency.

Hollow wall to stabilize and enhance ignition hohlraums

NASA Astrophysics Data System (ADS)

Vandenboomgaerde, M.; Grisollet, A.; Bonnefille, M.; Clérouin, J.; Arnault, P.; Desbiens, N.; Videau, L.

2018-01-01

In the context of the indirect-drive scheme of the inertial-confinement fusion, performance of the gas-filled hohlraums at the National Ignition Facility appears to be reduced. Experiments ascertain a limited efficacy of the laser beam propagation and x-ray conversion. One identified issue is the growth of the gold plasma plume (or bubble) which is generated near the ends of the hohlraum by the impact of the laser beams. This bubble impedes the laser propagation towards the equator of the hohlraum. Furthermore, for high foot or low foot laser pulses, the gold-gas interface of the bubble can be unstable. If this instability should grow to mixing, the x-ray conversion could be degraded. A novel hollow-walled hohlraum is designed, which drastically reduces the growth of the gold bubble and stabilizes the gold-gas interface. The hollow walls are built from the combination of a thin gold foil and a gold domed-wall. We theoretically explain how the bubble expansion can be delayed and the gold-gas interface stabilized. This advanced design lets the laser beams reach the waist of the hohlraum. As a result, the x-ray drive on the capsule is enhanced, and more spherical implosions are obtained. Furthermore, this design only requires intermediate gas fill density to be efficient.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sutcliffe, G. D.; Milanese, L. M.; Orozco, D.

CR-39 detectors are used routinely in inertial confinement fusion (ICF) experiments as a part of nuclear diagnostics. CR-39 is filtered to stop fast ablator ions which have been accelerated from an ICF implosion due to electric fields caused by laser-plasma interactions. In some experiments, the filtering is insufficient to block these ions and the fusion-product signal tracks are lost in the large background of accelerated ion tracks. A technique for recovering signal in these scenarios has been developed, tested, and implemented successfully. The technique involves removing material from the surface of the CR-39 to a depth beyond the endpoint ofmore » the ablator ion tracks. The technique preserves signal magnitude (yield) as well as structure in radiograph images. The technique is effective when signal particle range is at least 10 μm deeper than the necessary bulk material removal.« less

Mitigating the impact of hohlraum asymmetries in National Ignition Facility implosions using capsule shims

DOE PAGES

Clark, D. S.; Weber, C. R.; Smalyuk, V. A.; ...

2016-07-22

Here, current indirect drive implosion experiments on the National Ignition Facility (NIF) are believed to be strongly impacted by long wavelength perturbations driven by asymmetries in the hohlraum x-ray flux. To address this perturbation source, active efforts are underway to develop modified hohlraum designs with reduced asymmetry imprint. An alternative strategy, however, is to modify the capsule design to be more resilient to a given amount of hohlraum asymmetry. In particular, the capsule may be deliberately misshaped, or “shimmed,” so as to counteract the expected asymmetries from the hohlraum. Here, the efficacy of capsule shimming to correct the asymmetries inmore » two recent NIF implosion experiments is assessed using two-dimensional radiation hydrodynamics simulations. Despite the highly time-dependent character of the asymmetries and the high convergence ratios of these implosions, simulations suggest that shims could be highly effective at counteracting current asymmetries and result in factors of a few enhancements in neutron yields. For higher compression designs, the yield improvement could be even greater.« less

Mitigating the impact of hohlraum asymmetries in National Ignition Facility implosions using capsule shims

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clark, D. S.; Weber, C. R.; Smalyuk, V. A.

2016-07-15

Current indirect drive implosion experiments on the National Ignition Facility (NIF) [Moses et al., Phys. Plasmas 16, 041006 (2009)] are believed to be strongly impacted by long wavelength perturbations driven by asymmetries in the hohlraum x-ray flux. To address this perturbation source, active efforts are underway to develop modified hohlraum designs with reduced asymmetry imprint. An alternative strategy, however, is to modify the capsule design to be more resilient to a given amount of hohlraum asymmetry. In particular, the capsule may be deliberately misshaped, or “shimmed,” so as to counteract the expected asymmetries from the hohlraum. Here, the efficacy ofmore » capsule shimming to correct the asymmetries in two recent NIF implosion experiments is assessed using two-dimensional radiation hydrodynamics simulations. Despite the highly time-dependent character of the asymmetries and the high convergence ratios of these implosions, simulations suggest that shims could be highly effective at counteracting current asymmetries and result in factors of a few enhancements in neutron yields. For higher compression designs, the yield improvement could be even greater.« less

Hydro-scaling of DT implosions on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Patel, Pravesh; Spears, Brian; Clark, Dan

2017-10-01

Recent implosion experiments on the National Ignition Facility (NIF) exceed 50 kJ in fusion yield and exhibit yield amplifications of >2.5-3x due to alpha-particle self-heating of the hot-spot. Two methods to increase the yield are (i) to improve the implosion quality, or stagnation pressure, at fixed target scale (by increasing implosion velocity, reducing 3D effects, etc.), and (ii) to hydrodynamically scale the capsule and absorbed energy. In the latter case the stagnation pressure remains constant, but the yield-in the absence of alpha-heating-increases as Y S 4 . 5 , where the capsule radius is increased by S, and the absorbed energy by S3 . With alpha-heating the increase with scale is considerably stronger. We present projections in the performance of current DT experiments, and the extrapolations to ignition, based on applying hydro-scaling theory and accounting for the effect of alpha-heating. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Simulations of Fuel Assembly and Fast-Electron Transport in Integrated Fast-Ignition Experiments on OMEGA

NASA Astrophysics Data System (ADS)

Solodov, A. A.; Theobald, W.; Anderson, K. S.; Shvydky, A.; Epstein, R.; Betti, R.; Myatt, J. F.; Stoeckl, C.; Jarrott, L. C.; McGuffey, C.; Qiao, B.; Beg, F. N.; Wei, M. S.; Stephens, R. B.

2013-10-01

Integrated fast-ignition experiments on OMEGA benefit from improved performance of the OMEGA EP laser, including higher contrast, higher energy, and a smaller focus. Recent 8-keV, Cu-Kα flash radiography of cone-in-shell implosions and cone-tip breakout measurements showed good agreement with the 2-D radiation-hydrodynamic simulations using the code DRACO. DRACO simulations show that the fuel assembly can be further improved by optimizing the compression laser pulse, evacuating air from the shell, and by adjusting the material of the cone tip. This is found to delay the cone-tip breakout by ~220 ps and increase the core areal density from ~80 mg/cm2 in the current experiments to ~500 mg/cm2 at the time of the OMEGA EP beam arrival before the cone-tip breakout. Simulations using the code LSP of fast-electron transport in the recent integrated OMEGA experiments with Cu-doped shells will be presented. Cu-doping is added to probe the transport of fast electrons via their induced Cu K-shell fluorescent emission. This material is based upon work supported by the Department of Energy National Nuclear Security Administration DE-NA0001944 and the Office of Science under DE-FC02-04ER54789.

Investigation of ion kinetic effects in direct-drive exploding-pusher implosions at the NIF

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosenberg, M. J., E-mail: mrosenbe@mit.edu; Zylstra, A. B.; Séguin, F. H.

Measurements of yield, ion temperature, areal density (ρR), shell convergence, and bang time have been obtained in shock-driven, D{sub 2} and D{sup 3}He gas-filled “exploding-pusher” inertial confinement fusion (ICF) implosions at the National Ignition Facility to assess the impact of ion kinetic effects. These measurements probed the shock convergence phase of ICF implosions, a critical stage in hot-spot ignition experiments. The data complement previous studies of kinetic effects in shock-driven implosions. Ion temperature and fuel ρR inferred from fusion-product spectroscopy are used to estimate the ion-ion mean free path in the gas. A trend of decreasing yields relative to themore » predictions of 2D DRACO hydrodynamics simulations with increasing Knudsen number (the ratio of ion-ion mean free path to minimum shell radius) suggests that ion kinetic effects are increasingly impacting the hot fuel region, in general agreement with previous results. The long mean free path conditions giving rise to ion kinetic effects in the gas are often prevalent during the shock phase of both exploding pushers and ablatively driven implosions, including ignition-relevant implosions.« less

Three-dimensional modeling of the neutron spectrum to infer plasma conditions in cryogenic inertial confinement fusion implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weilacher, F.; Radha, P. B.; Forrest, C.

Neutron-based diagnostics are typically used to infer compressed core conditions such as areal density and ion temperature in deuterium–tritium (D–T) inertial confinement fusion (ICF) implosions. Asymmetries in the observed neutron-related quantities are important to understanding failure modes in these implosions. Neutrons from fusion reactions and their subsequent interactions including elastic scattering and neutron-induced deuteron breakup reactions are tracked to create spectra. Here, it is shown that background subtraction is important for inferring areal density from backscattered neutrons and is less important for the forward-scattered neutrons. A three-dimensional hydrodynamic simulation of a cryogenic implosion on the OMEGA Laser System [T. R.more » Boehly et al., Opt. Commun. 133, 495 (1997)] using the hydrodynamic code HYDRA [M. M. Marinak et al., Phys. Plasmas 8, 2275 (2001)] is post-processed using the tracking code IRIS3D. It is shown that different parts of the neutron spectrum from the view can be mapped into different regions of the implosion, enabling an inference of an areal-density map. It is also shown that the average areal-density and an areal-density map of the compressed target can be reconstructed with a finite number of detectors placed around the target chamber. Ion temperatures are inferred from the width of the D–D and D–T fusion neutron spectra. Backgrounds can significantly alter the inferred ion temperatures from the D–D reaction, whereas they insignificantly influence the inferred D–T ion temperatures for the areal densities typical of OMEGA implosions. Asymmetries resulting in fluid flow in the core are shown to influence the absolute inferred ion temperatures from both reactions, although relative inferred values continue to reflect the underlying asymmetry pattern. The work presented here is part of the wide range of the first set of studies performed with IRIS3D. Finally, this code will continue to be used for post-processing detailed hydrodynamic simulations and interpreting observed neutron spectra in ICF implosions.« less

Three-dimensional modeling of the neutron spectrum to infer plasma conditions in cryogenic inertial confinement fusion implosions

DOE PAGES

Weilacher, F.; Radha, P. B.; Forrest, C.

2018-04-26

Neutron-based diagnostics are typically used to infer compressed core conditions such as areal density and ion temperature in deuterium–tritium (D–T) inertial confinement fusion (ICF) implosions. Asymmetries in the observed neutron-related quantities are important to understanding failure modes in these implosions. Neutrons from fusion reactions and their subsequent interactions including elastic scattering and neutron-induced deuteron breakup reactions are tracked to create spectra. Here, it is shown that background subtraction is important for inferring areal density from backscattered neutrons and is less important for the forward-scattered neutrons. A three-dimensional hydrodynamic simulation of a cryogenic implosion on the OMEGA Laser System [T. R.more » Boehly et al., Opt. Commun. 133, 495 (1997)] using the hydrodynamic code HYDRA [M. M. Marinak et al., Phys. Plasmas 8, 2275 (2001)] is post-processed using the tracking code IRIS3D. It is shown that different parts of the neutron spectrum from the view can be mapped into different regions of the implosion, enabling an inference of an areal-density map. It is also shown that the average areal-density and an areal-density map of the compressed target can be reconstructed with a finite number of detectors placed around the target chamber. Ion temperatures are inferred from the width of the D–D and D–T fusion neutron spectra. Backgrounds can significantly alter the inferred ion temperatures from the D–D reaction, whereas they insignificantly influence the inferred D–T ion temperatures for the areal densities typical of OMEGA implosions. Asymmetries resulting in fluid flow in the core are shown to influence the absolute inferred ion temperatures from both reactions, although relative inferred values continue to reflect the underlying asymmetry pattern. The work presented here is part of the wide range of the first set of studies performed with IRIS3D. Finally, this code will continue to be used for post-processing detailed hydrodynamic simulations and interpreting observed neutron spectra in ICF implosions.« less

LLE review

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bradley, D.K.

1989-01-01

This volume of the LLE Review, covering the period October--December 1989, contains an article discussing saturation effects and power-balance considerations in the design of high-power lasers and an article describing numerical modeling of the effects of power imbalances on target behavior. The advanced technology section reports on the development of a liquid crystal laser-beam apodizer and an experiment to study the high-intensity ionization of noble gases. Finally, the activities of the National Laser Users Facility and the GDL and OMEGA laser facilities are summarized. The highlights of this issue are: The problem of achieving power balance in high-efficiency, multibeam lasersmore » has been studied in terms of gain-saturation effects and the nonlinear nature of harmonic frequency conversion. It is shown that power imbalance can be minimized by balancing the gains and losses in equivalent amplification stages in each beamline. The effects of target implosion behavior of various power-imbalance sources in the OMEGA laser system have been studied using the two-dimensional hydrodynamics code ORCHID. The simulations show good agreement with an experiment in which a deliberate power imbalance was applied to the target drive. Laser-beam apodizers with large clear apertures have been fabricated using cholesteric liquid crystals. A soft-edge profile has been achieved by filling a cell with two separate liquid crystals with different selective-reflection bands, and allowing them to partially mix at the interface. A study of the ionization of noble gases in the tunneling regime using high- intensity, 1-ps pulses from the tabletop terawatt laser (T{sup 3}) has been carried out. The measured ion production is well predicted by a Coulomb barrier suppression ionization theory.« less

Precision shock tuning on the national ignition facility.

PubMed

Robey, H F; Celliers, P M; Kline, J L; Mackinnon, A J; Boehly, T R; Landen, O L; Eggert, J H; Hicks, D; Le Pape, S; Farley, D R; Bowers, M W; Krauter, K G; Munro, D H; Jones, O S; Milovich, J L; Clark, D; Spears, B K; Town, R P J; Haan, S W; Dixit, S; Schneider, M B; Dewald, E L; Widmann, K; Moody, J D; Döppner, T D; Radousky, H B; Nikroo, A; Kroll, J J; Hamza, A V; Horner, J B; Bhandarkar, S D; Dzenitis, E; Alger, E; Giraldez, E; Castro, C; Moreno, K; Haynam, C; LaFortune, K N; Widmayer, C; Shaw, M; Jancaitis, K; Parham, T; Holunga, D M; Walters, C F; Haid, B; Malsbury, T; Trummer, D; Coffee, K R; Burr, B; Berzins, L V; Choate, C; Brereton, S J; Azevedo, S; Chandrasekaran, H; Glenzer, S; Caggiano, J A; Knauer, J P; Frenje, J A; Casey, D T; Johnson, M Gatu; Séguin, F H; Young, B K; Edwards, M J; Van Wonterghem, B M; Kilkenny, J; MacGowan, B J; Atherton, J; Lindl, J D; Meyerhofer, D D; Moses, E

2012-05-25

Ignition implosions on the National Ignition Facility [J. D. Lindl et al., Phys. Plasmas 11, 339 (2004)] are underway with the goal of compressing deuterium-tritium fuel to a sufficiently high areal density (ρR) to sustain a self-propagating burn wave required for fusion power gain greater than unity. These implosions are driven with a very carefully tailored sequence of four shock waves that must be timed to very high precision to keep the fuel entropy and adiabat low and ρR high. The first series of precision tuning experiments on the National Ignition Facility, which use optical diagnostics to directly measure the strength and timing of all four shocks inside a hohlraum-driven, cryogenic liquid-deuterium-filled capsule interior have now been performed. The results of these experiments are presented demonstrating a significant decrease in adiabat over previously untuned implosions. The impact of the improved shock timing is confirmed in related deuterium-tritium layered capsule implosions, which show the highest fuel compression (ρR~1.0 g/cm(2)) measured to date, exceeding the previous record [V. Goncharov et al., Phys. Rev. Lett. 104, 165001 (2010)] by more than a factor of 3. The experiments also clearly reveal an issue with the 4th shock velocity, which is observed to be 20% slower than predictions from numerical simulation.

Analysis of trends in experimental observables: Reconstruction of the implosion dynamics and implications for fusion yield extrapolation for direct-drive cryogenic targets on OMEGA

NASA Astrophysics Data System (ADS)

Bose, A.; Betti, R.; Mangino, D.; Woo, K. M.; Patel, D.; Christopherson, A. R.; Gopalaswamy, V.; Mannion, O. M.; Regan, S. P.; Goncharov, V. N.; Edgell, D. H.; Forrest, C. J.; Frenje, J. A.; Gatu Johnson, M.; Yu Glebov, V.; Igumenshchev, I. V.; Knauer, J. P.; Marshall, F. J.; Radha, P. B.; Shah, R.; Stoeckl, C.; Theobald, W.; Sangster, T. C.; Shvarts, D.; Campbell, E. M.

2018-06-01

This paper describes a technique for identifying trends in performance degradation for inertial confinement fusion implosion experiments. It is based on reconstruction of the implosion core with a combination of low- and mid-mode asymmetries. This technique was applied to an ensemble of hydro-equivalent deuterium-tritium implosions on OMEGA which achieved inferred hot-spot pressures ≈56 ± 7 Gbar [Regan et al., Phys. Rev. Lett. 117, 025001 (2016)]. All the experimental observables pertaining to the core could be reconstructed simultaneously with the same combination of low and mid-modes. This suggests that in addition to low modes, which can cause a degradation of the stagnation pressure, mid-modes are present which reduce the size of the neutron and x-ray producing volume. The systematic analysis shows that asymmetries can cause an overestimation of the total areal density in these implosions. It is also found that an improvement in implosion symmetry resulting from correction of either the systematic mid or low modes would result in an increase in the hot-spot pressure from 56 Gbar to ≈ 80 Gbar and could produce a burning plasma when the implosion core is extrapolated to an equivalent 1.9 MJ symmetric direct illumination [Bose et al., Phys. Rev. E 94, 011201(R) (2016)].

Analysis of trends in experimental observables: Reconstruction of the implosion dynamics and implications for fusion yield extrapolation for direct-drive cryogenic targets on OMEGA

DOE PAGES

Bose, A.; Betti, R.; Mangino, D.; ...

2018-05-29

This paper describes a technique for identifying trends in performance degradation for inertial con finement fusion implosion experiments. It is based on reconstruction of the implosion core with a combination of low- and mid-mode asymmetries. This technique was applied to an ensemble of hydro-equivalent deuterium-tritium implosions on OMEGA that achieved inferred hot-spot pressures ≈56 ± 7 Gbar [S. Regan et al., Phys. Rev. Lett. 117, 025001 (2016)]. All the experimental observables pertaining to the core could be reconstructed simultaneously with the same combination of low and mid modes. This suggests that in addition to low modes, that can cause amore » degradation of the stagnation pressure, mid modes are present that reduce the size of the neutron and x-ray producing volume. The systematic analysis shows that asymmetries can cause an overestimation of the total areal density in these implosions. Finally, it is also found that an improvement in implosion symmetry resulting from correction of either the systematic mid or low modes would result in an increase of the hot-spot pressure from 56 Gbar to ≈ 80 Gbar and could produce a burning plasma when the implosion core is extrapolated to an equivalent 1.9 MJ symmetric direct illumination [A. Bose et al., Phys. Rev. E 94, 011201(R) (2016)].« less

Analysis of trends in experimental observables: Reconstruction of the implosion dynamics and implications for fusion yield extrapolation for direct-drive cryogenic targets on OMEGA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bose, A.; Betti, R.; Mangino, D.

This paper describes a technique for identifying trends in performance degradation for inertial con finement fusion implosion experiments. It is based on reconstruction of the implosion core with a combination of low- and mid-mode asymmetries. This technique was applied to an ensemble of hydro-equivalent deuterium-tritium implosions on OMEGA that achieved inferred hot-spot pressures ≈56 ± 7 Gbar [S. Regan et al., Phys. Rev. Lett. 117, 025001 (2016)]. All the experimental observables pertaining to the core could be reconstructed simultaneously with the same combination of low and mid modes. This suggests that in addition to low modes, that can cause amore » degradation of the stagnation pressure, mid modes are present that reduce the size of the neutron and x-ray producing volume. The systematic analysis shows that asymmetries can cause an overestimation of the total areal density in these implosions. Finally, it is also found that an improvement in implosion symmetry resulting from correction of either the systematic mid or low modes would result in an increase of the hot-spot pressure from 56 Gbar to ≈ 80 Gbar and could produce a burning plasma when the implosion core is extrapolated to an equivalent 1.9 MJ symmetric direct illumination [A. Bose et al., Phys. Rev. E 94, 011201(R) (2016)].« less

High-energy krypton fluoride lasers for inertial fusion.

PubMed

Obenschain, Stephen; Lehmberg, Robert; Kehne, David; Hegeler, Frank; Wolford, Matthew; Sethian, John; Weaver, James; Karasik, Max

2015-11-01

Laser fusion researchers have realized since the 1970s that the deep UV light from excimer lasers would be an advantage as a driver for robust high-performance capsule implosions for inertial confinement fusion (ICF). Most of this research has centered on the krypton-fluoride (KrF) laser. In this article we review the advantages of the KrF laser for direct-drive ICF, the history of high-energy KrF laser development, and the present state of the art and describe a development path to the performance needed for laser fusion and its energy application. We include descriptions of the architecture and performance of the multi-kilojoule Nike KrF laser-target facility and the 700 J Electra high-repetition-rate KrF laser that were developed at the U.S. Naval Research Laboratory. Nike and Electra are the most advanced KrF lasers for inertial fusion research and energy applications.

Assessment of the impact that the capsule fill tube has on implosions conducted with high density carbon ablators

NASA Astrophysics Data System (ADS)

Pak, Arthur; Benedetti, L. R.; Berzak Hopkins, L. F.; Clark, D.; Divol, L.; Dewald, E. L.; Fittinghoff, D.; Izumi, N.; Khan, S. F.; Landen, O.; Lepape, S.; Ma, T.; Marley, E.; Nagel, S.; Volegov, P.; Weber, C.; Bradley, D. K.; Callahan, D.; Grim, G.; Hurricane, O. A.; Patel, P.; Schneider, M. B.; Edwards, M. J.

2017-10-01

In recent inertial confinement implosion experiments conducted at the National Ignition Facility, bright and spatially localized x-ray emission within the hot spot at stagnation has been observed. This emission is associated with higher Z ablator material that is injected into the hot spot by the hydrodynamic perturbation induced by the 5-10 um diameter capsule fill tube. The reactivity of the DT fuel and subsequent yield of the implosion are strongly dependent on the density, temperature, and confinement time achieved throughout the stagnation of the implosion. Radiative losses from higher Z ablator material that mixes into the hot spot as well as non-uniformities in the compression and confinement induced by the fill tube perturbation can degrade the yield of the implosion. This work will examine the impact to conditions at stagnation that results from the fill tube perturbation. This assessment will be based from a pair of experiments conducted with a high density carbon ablator where the only deliberate change was reduction in fill tube diameter from 10 to 5 um. An estimate of the radiative losses and impact on performance from ablator mix injected into the hot spot by the fill tube perturbation will be presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Direct-drive DT implosions with Knudsen number variations

DOE PAGES

Kim, Yong Ho; Herrmann, Hans W.; Hoffman, Nelson M.; ...

2016-05-26

Direct-drive implosions of DT-filled plastic-shells have been conducted at the Omega laser facility, measuring nuclear yields while varying Knudsen numbers (i.e., the ratio of mean free path of fusing ions to the length of fuel region) by adjusting both shell thickness (e.g., 7.5, 15, 20, 30 μm) and fill pressure (e.g., 2, 5, 15 atm). In addition, the fusion reactivity reduction model showed a stronger effect on yield as the Knudsen number increases (or the shell thickness decreases). The Reduced-Ion-Kinetic (RIK) simulation which includes both fusion reactivity reduction and mix model was necessary to provide a better match between themore » observed neutron yields and those simulated.« less

A near one-dimensional 2-shock indirectly driven implosion at convergence ratio 30

NASA Astrophysics Data System (ADS)

MacLaren, Steve

2017-10-01

Inertial confinement fusion implosions at the National Ignition Facility, while successfully demonstrating self-heating due to alpha-particle deposition, have fallen short of the performance predicted by one-dimensional multi-physics implosion simulations. The current understanding, based on simulations as well as experimental evidence, suggests that the principle reason for the disagreement is a breeching of the cold fuel assembly at stagnation which would otherwise completely confine the hot spot. 3-D simulations indicate a combination of low-mode symmetry swings and ablation-front hydrodynamic instability seeded by engineering features such as the capsule tent and fill tube lead to localized thinning and perforation of the stagnated fuel, resulting in a loss of hot spot pressure and energy. We describe a short series of experiments on the NIF designed specifically to avoid these issues in order to understand if, once they are removed, a suspended-fuel-layer deuterium-tritium implosion can achieve 1-D simulated performance. The particular implosion system combines a thick capsule shell with an elevated initial ablation temperature to minimize the ablation front perturbations from the engineering features, and incorporates a large ratio of hohlraum-to-capsule radius as a means to permit a higher degree of control over implosion symmetry. The resulting implosion at a convergence ratio of 30 was not perfectly spherically symmetric as observed by both neutron and time-resolved x-ray imaging diagnostics. However, the stagnation observables match closely the performance predicted by 1D simulations, including, when some hot spot motion is accounted for, the apparent ion temperature. We present this result along with the design for an upcoming 2-shock experiment to test whether this level of agreement with the 1D model can be achieved in the self-heating regime. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.

Hybrid-drive implosion system for ICF targets

DOEpatents

Mark, James W.

1988-08-02

Hybrid-drive implosion systems (20,40) for ICF targets (10,22,42) are described which permit a significant increase in target gain at fixed total driver energy. The ICF target is compressed in two phases, an initial compression phase and a final peak power phase, with each phase driven by a separate, optimized driver. The targets comprise a hollow spherical ablator (12) surroundingly disposed around fusion fuel (14). The ablator is first compressed to higher density by a laser system (24), or by an ion beam system (44), that in each case is optimized for this initial phase of compression of the target. Then, following compression of the ablator, energy is directly delivered into the compressed ablator by an ion beam driver system (30,48) that is optimized for this second phase of operation of the target. The fusion fuel (14) is driven, at high gain, to conditions wherein fusion reactions occur. This phase separation allows hydrodynamic efficiency and energy deposition uniformity to be individually optimized, thereby securing significant advantages in energy gain. In additional embodiments, the same or separate drivers supply energy for ICF target implosion.

Hybrid-drive implosion system for ICF targets

DOEpatents

Mark, James W.

1988-01-01

Hybrid-drive implosion systems (20,40) for ICF targets (10,22,42) are described which permit a significant increase in target gain at fixed total driver energy. The ICF target is compressed in two phases, an initial compression phase and a final peak power phase, with each phase driven by a separate, optimized driver. The targets comprise a hollow spherical ablator (12) surroundingly disposed around fusion fuel (14). The ablator is first compressed to higher density by a laser system (24), or by an ion beam system (44), that in each case is optimized for this initial phase of compression of the target. Then, following compression of the ablator, energy is directly delivered into the compressed ablator by an ion beam driver system (30,48) that is optimized for this second phase of operation of the target. The fusion fuel (14) is driven, at high gain, to conditions wherein fusion reactions occur. This phase separation allows hydrodynamic efficiency and energy deposition uniformity to be individually optimized, thereby securing significant advantages in energy gain. In additional embodiments, the same or separate drivers supply energy for ICF target implosion.

Hybrid-drive implosion system for ICF targets

DOEpatents

Mark, J.W.K.

1987-10-14

Hybrid-drive implosion systems for ICF targets are described which permit a significant increase in target gain at fixed total driver energy. The ICF target is compressed in two phases, an initial compression phase and a final peak power phase, with each phase driven by a separate, optimized driver. The targets comprise a hollow spherical ablator surroundingly disposed around fusion fuel. The ablator is first compressed to higher density by a laser system, or by an ion beam system, that in each case is optimized for this initial phase of compression of the target. Then, following compression of the ablator, energy is directly delivered into the compressed ablator by an ion beam driver system that is optimized for this second phase of operation of the target. The fusion fuel is driven, at high gain, to conditions wherein fusion reactions occur. This phase separation allows hydrodynamic efficiency and energy deposition uniformity to be individually optimized, thereby securing significant advantages in energy gain. In additional embodiments, the same or separate drivers supply energy for ICF target implosion. 3 figs.

Impact of Inner Surface Perturbations on the Stability of Cylindrical Liner Implosion

NASA Astrophysics Data System (ADS)

Weis, Matthew; Peterson, Kyle; Hess, Mark; Lau, Y. Y.; Zhang, Peng; Gilgenbach, Ronald

2015-11-01

This paper studies the effects of initial perturbations on the inner liner surface (ILS) of an imploding cylindrical liner. In MagLIF, nonuniform preheat of the fuel could provide an additional source of spatial nonuniformity on the ILS. A blast wave generated by the laser preheat might trigger the Richtmyer-Meshkov instability (RM) on the ILS which then serves as another seed to the Rayleigh-Taylor instability (RT) during the stagnation (deceleration) phase of the implosion. Another scenario is that the shock initiated from the outer liner surface, during current rise, propagates inward and is reflected at the ILS. This reflected shock would carry the initial ILS perturbations which then serve as an additional seed for the magneto-RT (MRT) during the acceleration phase of the implosion. These potentially dangerous interactions are analyzed using the 2D HYDRA code. The effects of axial magnetic fields, of the initial surface roughness spectrum, and of gas fill or water fill (to examine deceleration phase RT) are studied. M. R. Weis was supported by the Sandia National Laboratories. This work was also supported by DoE Grant DE-SC0012328.

Direct-drive Energetics of laser-Heated Foam Liners for Hohlraums

NASA Astrophysics Data System (ADS)

Moore, Alastair; Thomas, Cliff; Baker, Kevin; Morton, John; Baumann, Ted; Biener, Monika; Bhandarkar, Suhas; Hinkel, Denise; Jones, Oggie; Meezan, Nathan; Moody, John; Nikroo, Abbas; Rosen, Mordy; Hsing, Warren

2016-10-01

Lining the walls of a high-Z hohlraum cavity with a low-density foam is predicted to mitigate the challenge presented by hohlraum wall expansion. Once heated, wall material quickly fills the cavity and can impede laser beam propagation. To avoid this, ignition hohlraums are typically filled with a gas or irradiated with a short (< 10 ns) laser pulse. A gas-fill has the disadvantage that it can cause laser plasma instabilities (LPI), while a short laser pulse limits the design space to reach low-adiabat implosions. Foam-liners offer a potential route to reduce wall motion in a low gas-fill hohlraum with little LPI. Results from quasi 1-D experiments performed at the NIF are presented These characterize the x-ray conversion efficiency, backscattered laser energy and heat propagation in a 250 μm thick Ta2O5 or ZnO foam-liners spanning a range of densities from underdense to overdense, when irradiated at up to 4.9 x 1014 W/cm2 is incident on a planar foam sample, backed by a Au foil and generates a radiation temperature of up to 240eV - conditions equivalent to a single outer cone beam-spot in an ignition hohlraum. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

A framed, 16-image Kirkpatrick–Baez x-ray microscope

DOE PAGES

Marshall, F. J.; Bahr, R. E.; Goncharov, V. N.; ...

2017-09-08

A 16-image Kirkpatrick–Baez (KB)–type x-ray microscope consisting of compact KB mirrors has been assembled for the first time with mirrors aligned to allow it to be coupled to a high-speed framing camera. The high-speed framing camera has four independently gated strips whose emission sampling interval is ~30 ps. Images are arranged four to a strip with ~60-ps temporal spacing between frames on a strip. By spacing the timing of the strips, a frame spacing of ~15 ps is achieved. A framed resolution of ~6-um is achieved with this combination in a 400-um region of laser–plasma x-ray emission in the 2-more » to 8-keV energy range. A principal use of the microscope is to measure the evolution of the implosion stagnation region of cryogenic DT target implosions on the University of Rochester’s OMEGA Laser System. The unprecedented time and spatial resolution achieved with this framed, multi-image KB microscope have made it possible to accurately determine the cryogenic implosion core emission size and shape at the peak of stagnation. In conclusion, these core size measurements, taken in combination with those of ion temperature, neutron-production temporal width, and neutron yield allow for inference of core pressures, currently exceeding 50 GBar in OMEGA cryogenic target implosions.« less

A framed, 16-image Kirkpatrick–Baez x-ray microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marshall, F. J.; Bahr, R. E.; Goncharov, V. N.

A 16-image Kirkpatrick–Baez (KB)–type x-ray microscope consisting of compact KB mirrors has been assembled for the first time with mirrors aligned to allow it to be coupled to a high-speed framing camera. The high-speed framing camera has four independently gated strips whose emission sampling interval is ~30 ps. Images are arranged four to a strip with ~60-ps temporal spacing between frames on a strip. By spacing the timing of the strips, a frame spacing of ~15 ps is achieved. A framed resolution of ~6-um is achieved with this combination in a 400-um region of laser–plasma x-ray emission in the 2-more » to 8-keV energy range. A principal use of the microscope is to measure the evolution of the implosion stagnation region of cryogenic DT target implosions on the University of Rochester’s OMEGA Laser System. The unprecedented time and spatial resolution achieved with this framed, multi-image KB microscope have made it possible to accurately determine the cryogenic implosion core emission size and shape at the peak of stagnation. In conclusion, these core size measurements, taken in combination with those of ion temperature, neutron-production temporal width, and neutron yield allow for inference of core pressures, currently exceeding 50 GBar in OMEGA cryogenic target implosions.« less

Origins of the high flux hohlraum model

NASA Astrophysics Data System (ADS)

Rosen, M. D.; Hinkel, D. E.; Williams, E. A.; Callahan, D. A.; Town, R. P. J.; Scott, H. A.; Kruer, W. L.; Suter, L. J.

2010-11-01

We review how the ``high flux model'' (HFM) helped clarify the performance of the Autumn 09 National Ignition Campaign (NIC) gas filled/capsule imploding hohlraum energetics campaign. This campaign showed good laser-hohlraum coupling, reasonably high drive, and implosion symmetry control via cross beam transfer. Mysteries that remained included the level and spectrum of the Stimulated Raman light, the tendency towards pancaked implosions, and drive that exceeded (standard model) predictions early in the campaign, and lagged those predictions late in the campaign. The HFM uses a detailed configuration accounting (DCA) atomic physics and a generous flux limiter (f=0.2) both of which contribute to predicting a hohlraum plasma that is cooler than the standard, XSN average atom, f=0.05 model. This cooler plasma proved to be key in solving all of those mysteries. Despite past successes of the HFM in correctly modeling Omega Laser Au sphere data and NIC empty hohlraum drive, the model lacked some credibility for this energetics campaign, because it predicted too much hohlraum drive. Its credibility was then boosted by a re-evaluation of the initially reported SRS levels.

Evaluation of laser-driven ion energies for fusion fast-ignition research

NASA Astrophysics Data System (ADS)

Tosaki, S.; Yogo, A.; Koga, K.; Okamoto, K.; Shokita, S.; Morace, A.; Arikawa, Y.; Fujioka, S.; Nakai, M.; Shiraga, H.; Azechi, H.; Nishimura, H.

2017-10-01

We investigate laser-driven ion acceleration using kJ-class picosecond (ps) laser pulses as a fundamental study for ion-assisted fusion fast ignition, using a newly developed Thomson-parabola ion spectrometer (TPIS). The TPIS has a space- and weight-saving design, considering its use in an laser-irradiation chamber in which 12 beams of fuel implosion laser are incident, and, at the same time, demonstrates sufficient performance with its detectable range and resolution of the ion energy required for fast-ignition research. As a fundamental study on laser-ion acceleration using a ps pulse laser, we show proton acceleration up to 40 MeV at 1 × 10^{19} W cm^{-2}. The energy conversion efficiency from the incident laser into protons higher than 6 MeV is 4.6%, which encourages the realization of fusion fast ignition by laser-driven ions.

X-Ray Thomson Scattering and Radiography from Spherical Implosions on the OMEGA Laser

NASA Astrophysics Data System (ADS)

Saunders, A. M.; Laziki-Jenei, A.; Doeppner, T.; Landen, O. L.; MacDonald, M.; Nilsen, J.; Swift, D.; Falcone, R. W.

2017-10-01

X-ray Thomson scattering (XRTS) is an experimental technique that directly probes the physics of warm dense matter by measuring electron density, electron temperature, and ionization state. XRTS in combination with x-ray radiography offers a unique ability to measure an absolute equation of state (EOS) from material under compression. Recent experiments highlight uncertainties in EOS models and the predicted ionization of compressed matter, suggesting more validation of models is needed. We present XRTS and x-ray radiography measurements taken at the OMEGA Laser Facility from directly-driven solid carbon spheres at densities on the order of 1x1024 g cm-3 and temperatures on the order of 30 eV. The results shed light on the equations of state of matter under compression. This work performed under auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and under the Stewardship Science Graduate Fellowship, Grant Number DE- NA0002135.

Detecting fiducials affected by trombone delay in ARC and the main laser alignment at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Awwal, Abdul A. S.; Bliss, Erlan S.; Miller Kamm, Victoria; Leach, Richard R.; Roberts, Randy; Rushford, Michael C.; Lowe-Webb, Roger; Wilhelmsen, Karl

2015-09-01

Four of the 192 beams of the National Ignition Facility (NIF) are currently being diverted into the Advanced Radiographic Capability (ARC) system to generate a sequence of short (1-50 picoseconds) 1053 nm laser pulses. When focused onto high Z wires in vacuum, these pulses create high energy x-ray pulses capable of penetrating the dense, imploding fusion fuel plasma during ignition scale experiments. The transmitted x-rays imaged with x-ray diagnostics can create movie radiographs that are expected to provide unprecedented insight into the implosion dynamics. The resulting images will serve as a diagnostic for tuning the experimental parameters towards successful fusion reactions. Beam delays introduced into the ARC pulses via independent, free-space optical trombones create the desired x-ray image sequence, or movie. However, these beam delays cause optical distortion of various alignment fiducials viewed by alignment sensors in the NIF and ARC beamlines. This work describes how the position of circular alignment fiducials is estimated in the presence of distortion.

Laser Program Annual Report - 1979 Unclassified Excerpts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lindl, J D

The objective of the Lawrence Livermore National Laboratory (LLNL) Inertial Confinement Fusion (ICF) program is to demonstrate the scientific feasibility of ICF for military applications (to develop and utilize the capability to study nuclear weapons physics in support of the weapons program) and for energy-directed uses in the civilian sector. The demonstration of scientific feasibility for both military and civilian objectives will require achieving gains on the order of 10 to 100 in fusion microexplosions. Our major near-term milestones include the attainment of high compression, one-hundred to one-thousand times (100 to 1000X) liquid D-T density in the thermonuclear fuel andmore » ignition of thermonuclear burn. In 1979, our laser fusion experiments and analysis programs focused on two important areas related to achieving this goal: conducting x-ray-driven implosions of a variety of D-T-filled fuel capsule's to unprecedented high densities ({approx}> 50X liquid D-T density) and the determination of the scaling of hot electrons and thermal radiation in hohlraums.« less

A broadband proton backlighting platform to probe shock propagation in low-density systems

DOE PAGES

Sio, H.; Hua, R.; Ping, Y.; ...

2017-01-17

A proton backlighting platform has been developed for the study of strong shock propagation in low-density systems in planar geometry. Electric fields at the converging shock front in inertial confinement fusion implosions have been previously observed, demonstrating the presence of—and the need to understand—strong electric fields not modeled in standard radiation-hydrodynamic simulations. In this planar configuration, long-pulse ultraviolet lasers are used to drive a strong shock into a gas-cell target, while a short-pulse proton backlighter side-on radiographs the shock propagation. Finally, the capabilities of the platform are presented here. Future experiments will vary shock strength and gas fill, to probemore » shock conditions at different Z and T e.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goncharov, V.N.; Knauer, J.P.; McKenty, P.W.

(B204)Hydrodynamic instabilities seeded by laser imprint and surface roughness limit the compression ratio and neutron yield in the direct-drive inertial confinement fusion target designs. New improved-performance designs use adiabat shaping to increase the entropy of only the outer portion of the shell, reducing the instability growth. The inner portion of the shell is kept on a lower entropy to maximize shell compressibility. The adiabat shaping is implemented using a high-intensity picket in front of the main-drive pulse. The picket launches a strong shock that decays as it propagates through the shell. This increases the ablation velocity and reduces the Rayleigh-Taylormore » growth rates. In addition, as shown earlier [T.J.B. Collis and S. Skupsky, Phys. Plasmas 9 275 (2002)], the picket reduces the instability seed due to the laser imprint. To test the results of calculations, a series of the picket pulse implosions of CH capsules were performed on the OMEGA laser system [T.R. Boehly, D .L. Brown, R.S. Craxton, et al., Opt. Commun. 133, 495 (1997)]. The experiments demonstrated a significant improvement in target yields for the pulses with the picket compared to the pulses without the picket. Results of the theory and experiments with adiabat shaping are being extended to future OMEGA and the National Ignition Facility's [J.A. Paisner, J.D. Boyes, S.A. Kumpan, W.H. Lowdermilk, and M.S. Sorem, Laser Focus World 30, 75 (1994)] cryogenic target designs.« less

Mitigating the impact of hohlraum asymmetries in National Ignition Facility implosions using capsule shims

NASA Astrophysics Data System (ADS)

Clark, Daniel; Weber, Christopher; Smalyuk, Vladimir; Robey, Harry; Kritcher, Andrea; Milovich, Jose; Salmonson, Jay

2016-10-01

Current indirect drive implosion experiments on the National Ignition Facility (NIF) are believed to be strongly impacted by long wavelength perturbations driven by asymmetries in the hohlraum x-ray flux. To address this perturbation source, active efforts are underway to develop modified hohlraum designs with reduced asymmetry imprint. An alternative strategy, however, is to modify the capsule design to be more resilient to a given amount of hohlraum asymmetry. In particular, the capsule may be deliberately misshaped, or ``shimmed,'' so as to counteract the expected asymmetries from the hohlraum. Here, the efficacy of capsule shimming to correct the asymmetries in two recent NIF implosion experiments is assessed using two-dimensional radiation hydrodynamics simulations. Despite the highly time-dependent character of the asymmetries and the high convergence ratios of these implosions, simulations suggest that shims could be highly effective at counteracting current asymmetries and result in factors of a few enhancements in neutron yields. For higher compression designs, the yield improvement could be even greater. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Shock timing measurements and analysis in deuterium-tritium-ice layered capsule implosions on NIF

NASA Astrophysics Data System (ADS)

Robey, H. F.; Celliers, P. M.; Moody, J. D.; Sater, J.; Parham, T.; Kozioziemski, B.; Dylla-Spears, R.; Ross, J. S.; LePape, S.; Ralph, J. E.; Hohenberger, M.; Dewald, E. L.; Berzak Hopkins, L.; Kroll, J. J.; Yoxall, B. E.; Hamza, A. V.; Boehly, T. R.; Nikroo, A.; Landen, O. L.; Edwards, M. J.

2014-02-01

Recent advances in shock timing experiments and analysis techniques now enable shock measurements to be performed in cryogenic deuterium-tritium (DT) ice layered capsule implosions on the National Ignition Facility (NIF). Previous measurements of shock timing in inertial confinement fusion implosions [Boehly et al., Phys. Rev. Lett. 106, 195005 (2011); Robey et al., Phys. Rev. Lett. 108, 215004 (2012)] were performed in surrogate targets, where the solid DT ice shell and central DT gas were replaced with a continuous liquid deuterium (D2) fill. These previous experiments pose two surrogacy issues: a material surrogacy due to the difference of species (D2 vs. DT) and densities of the materials used and a geometric surrogacy due to presence of an additional interface (ice/gas) previously absent in the liquid-filled targets. This report presents experimental data and a new analysis method for validating the assumptions underlying this surrogate technique. Comparison of the data with simulation shows good agreement for the timing of the first three shocks, but reveals a considerable discrepancy in the timing of the 4th shock in DT ice layered implosions. Electron preheat is examined as a potential cause of the observed discrepancy in the 4th shock timing.

Multiple Experimental Platform Consistency at NIF

NASA Astrophysics Data System (ADS)

Benedetti, L. R.; Barrios, M. A.; Bradley, D. K.; Eder, D. C.; Khan, S. F.; Izumi, N.; Jones, O. S.; Ma, T.; Nagel, S. R.; Peterson, J. L.; Rygg, J. R.; Spears, B. K.; Town, R. P.

2013-10-01

ICF experiments at NIF utilize several platforms to assess different metrics of implosion quality. In addition to the point design-a target capsule of DT ice inside a thin plastic ablator-notable platforms include: (i) Symmetry Capsules(SymCaps), mass-adjusted CH capsules filled with DT gas for similar hydrodynamic performance without the need for a DT crystal; (ii) D:3He filled SymCaps, designed for low neutron yield implosions to accommodate a variety of x-ray and optical diagnostics; and (iii) Convergent Ablators, SymCaps coupled with x-radiography to assess in-flight velocity and symmetry of the implosion over ~1 ns before stagnation and burn. These platforms are expected to be good surrogates for one another, and their hohlraum and implosion performance variations have been simulated in detail. By comparing results of similar experiments, we isolate platform-specific variations. We focus on the symmetry, convergence, and timing of x-ray emission as observed in each platform as this can be used to infer stagnation pressure and temperature. This work performed under the auspices of the U.S. Dept. of Energy by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-640865.

Improved Performance of High Areal Density Indirect Drive Implosions at the National Ignition Facility using a Four-Shock Adiabat Shaped Drive

DOE PAGES

Casey, D. T.; Milovich, J. L.; Smalyuk, V. A.; ...

2015-09-01

Hydrodynamic instabilities can cause capsule defects and other perturbations to grow and degrade implosion performance in ignition experiments at the National Ignition Facility (NIF). Here, we show the first experimental demonstration that a strong unsupported first shock in indirect drive implosions at the NIF reduces ablation front instability growth leading to a 3 to 10 times higher yield with fuel ρR > 1 g=cm 2. This work shows the importance of ablation front instability growth during the National Ignition Campaign and may provide a path to improved performance at the high compression necessary for ignition.

Method for producing small hollow spheres

DOEpatents

Hendricks, C.D.

1979-01-09

Method is disclosed for producing small hollow spheres of glass, metal or plastic, wherein the sphere material is mixed with or contains as part of the composition a blowing agent which decomposes at high temperature (T [approx gt] 600 C). As the temperature is quickly raised, the blowing agent decomposes and the resulting gas expands from within, thus forming a hollow sphere of controllable thickness. The thus produced hollow spheres (20 to 10[sup 3] [mu]m) have a variety of application, and are particularly useful in the fabrication of targets for laser implosion such as neutron sources, laser fusion physics studies, and laser initiated fusion power plants. 1 fig.

Method and apparatus for producing small hollow spheres

DOEpatents

Hendricks, Charles D.

1979-01-01

Method and apparatus for producing small hollow spheres of glass, metal or plastic, wherein the sphere material is mixed with or contains as part of the composition a blowing agent which decomposes at high temperature (T.gtoreq.600.degree. C.). As the temperature is quickly raised, the blowing agent decomposes and the resulting gas expands from within, thus forming a hollow sphere of controllable thickness. The thus produced hollow spheres (20 to 10.sup.3 .mu.m) have a variety of application, and are particularly useful in the fabrication of targets for laser implosion such as neutron sources, laser fusion physics studies, and laser initiated fusion power plants.

Method for producing small hollow spheres

DOEpatents

Hendricks, Charles D. [Livermore, CA

1979-01-09

Method for producing small hollow spheres of glass, metal or plastic, wherein the sphere material is mixed with or contains as part of the composition a blowing agent which decomposes at high temperature (T .gtorsim. 600.degree. C). As the temperature is quickly raised, the blowing agent decomposes and the resulting gas expands from within, thus forming a hollow sphere of controllable thickness. The thus produced hollow spheres (20 to 10.sup.3 .mu.m) have a variety of application, and are particularly useful in the fabrication of targets for laser implosion such as neutron sources, laser fusion physics studies, and laser initiated fusion power plants.

Observation of interspecies ion separation in inertial-confinement-fusion implosions

DOE PAGES

Hsu, Scott C.; Joshi, Tirtha Raj; Hakel, Peter; ...

2016-10-24

Here we report direct experimental evidence of interspecies ion separation in direct-drive, inertial-confinement-fusion experiments on the OMEGA laser facility. These experiments, which used plastic capsules with D 2/Ar gas fill (1% Ar by atom), were designed specifically to reveal interspecies ion separation by exploiting the predicted, strong ion thermo-diffusion between ion species of large mass and charge difference. Via detailed analyses of imaging x-ray-spectroscopy data, we extract Ar-atom-fraction radial profiles at different times, and observe both enhancement and depletion compared to the initial 1%-Ar gas fill. The experimental results are interpreted with radiation-hydrodynamic simulations that include recently implemented, first-principles modelsmore » of interspecies ion diffusion. Finally, the experimentally inferred Ar-atom-fraction profiles agree reasonably, but not exactly, with calculated profiles associated with the incoming and rebounding first shock.« less

A novel method to recover DD fusion proton CR-39 data corrupted by fast ablator ions at OMEGA and the National Ignition Facility

NASA Astrophysics Data System (ADS)

Sutcliffe, G. D.; Milanese, L. M.; Orozco, D.; Lahmann, B.; Gatu Johnson, M.; Séguin, F. H.; Sio, H.; Frenje, J. A.; Li, C. K.; Petrasso, R. D.; Park, H.-S.; Rygg, J. R.; Casey, D. T.; Bionta, R.; Turnbull, D. P.; Huntington, C. M.; Ross, J. S.; Zylstra, A. B.; Rosenberg, M. J.; Glebov, V. Yu.

2016-11-01

CR-39 detectors are used routinely in inertial confinement fusion (ICF) experiments as a part of nuclear diagnostics. CR-39 is filtered to stop fast ablator ions which have been accelerated from an ICF implosion due to electric fields caused by laser-plasma interactions. In some experiments, the filtering is insufficient to block these ions and the fusion-product signal tracks are lost in the large background of accelerated ion tracks. A technique for recovering signal in these scenarios has been developed, tested, and implemented successfully. The technique involves removing material from the surface of the CR-39 to a depth beyond the endpoint of the ablator ion tracks. The technique preserves signal magnitude (yield) as well as structure in radiograph images. The technique is effective when signal particle range is at least 10 μm deeper than the necessary bulk material removal.

A novel method to recover DD fusion proton CR-39 data corrupted by fast ablator ions at OMEGA and the National Ignition Facility.

PubMed

Sutcliffe, G D; Milanese, L M; Orozco, D; Lahmann, B; Gatu Johnson, M; Séguin, F H; Sio, H; Frenje, J A; Li, C K; Petrasso, R D; Park, H-S; Rygg, J R; Casey, D T; Bionta, R; Turnbull, D P; Huntington, C M; Ross, J S; Zylstra, A B; Rosenberg, M J; Glebov, V Yu

2016-11-01

CR-39 detectors are used routinely in inertial confinement fusion (ICF) experiments as a part of nuclear diagnostics. CR-39 is filtered to stop fast ablator ions which have been accelerated from an ICF implosion due to electric fields caused by laser-plasma interactions. In some experiments, the filtering is insufficient to block these ions and the fusion-product signal tracks are lost in the large background of accelerated ion tracks. A technique for recovering signal in these scenarios has been developed, tested, and implemented successfully. The technique involves removing material from the surface of the CR-39 to a depth beyond the endpoint of the ablator ion tracks. The technique preserves signal magnitude (yield) as well as structure in radiograph images. The technique is effective when signal particle range is at least 10 μm deeper than the necessary bulk material removal.

Shock timing experiments on the National Ignition Facility: Initial results and comparison with simulation

NASA Astrophysics Data System (ADS)

Robey, H. F.; Boehly, T. R.; Celliers, P. M.; Eggert, J. H.; Hicks, D.; Smith, R. F.; Collins, R.; Bowers, M. W.; Krauter, K. G.; Datte, P. S.; Munro, D. H.; Milovich, J. L.; Jones, O. S.; Michel, P. A.; Thomas, C. A.; Olson, R. E.; Pollaine, S.; Town, R. P. J.; Haan, S.; Callahan, D.; Clark, D.; Edwards, J.; Kline, J. L.; Dixit, S.; Schneider, M. B.; Dewald, E. L.; Widmann, K.; Moody, J. D.; Döppner, T.; Radousky, H. B.; Throop, A.; Kalantar, D.; DiNicola, P.; Nikroo, A.; Kroll, J. J.; Hamza, A. V.; Horner, J. B.; Bhandarkar, S. D.; Dzenitis, E.; Alger, E.; Giraldez, E.; Castro, C.; Moreno, K.; Haynam, C.; LaFortune, K. N.; Widmayer, C.; Shaw, M.; Jancaitis, K.; Parham, T.; Holunga, D. M.; Walters, C. F.; Haid, B.; Mapoles, E. R.; Sater, J.; Gibson, C. R.; Malsbury, T.; Fair, J.; Trummer, D.; Coffee, K. R.; Burr, B.; Berzins, L. V.; Choate, C.; Brereton, S. J.; Azevedo, S.; Chandrasekaran, H.; Eder, D. C.; Masters, N. D.; Fisher, A. C.; Sterne, P. A.; Young, B. K.; Landen, O. L.; Van Wonterghem, B. M.; MacGowan, B. J.; Atherton, J.; Lindl, J. D.; Meyerhofer, D. D.; Moses, E.

2012-04-01

Capsule implosions on the National Ignition Facility (NIF) [Lindl et al., Phys. Plasmas 11, 339 (2004)] are underway with the goal of compressing deuterium-tritium (DT) fuel to a sufficiently high areal density (ρR) to sustain a self-propagating burn wave required for fusion power gain greater than unity. These implosions are driven with a carefully tailored sequence of four shock waves that must be timed to very high precision in order to keep the DT fuel on a low adiabat. Initial experiments to measure the strength and relative timing of these shocks have been conducted on NIF in a specially designed surrogate target platform known as the keyhole target. This target geometry and the associated diagnostics are described in detail. The initial data are presented and compared with numerical simulations. As the primary goal of these experiments is to assess and minimize the adiabat in related DT implosions, a methodology is described for quantifying the adiabat from the shock velocity measurements. Results are contrasted between early experiments that exhibited very poor shock timing and subsequent experiments where a modified target geometry demonstrated significant improvement.

Exploration of kinetic and multiple-ion-fluids effects in D3He and T3He gas-filled ICF implosions using multiple nuclear reaction histories

NASA Astrophysics Data System (ADS)

Sio, Hong; Rinderknecht, Hans; Rosenberg, Michael; Zylstra, Alex; Séguin, Fredrick; Gatu Johnson, Maria; Li, Chikang; Petrasso, Richard; Hoffman, Nelson; Kagan, Krigory; Molvig, Kim; Amendt, Peter; Bellei, Claudio; Wilks, Scott; Stoeckl, Christian; Glebov, Vladimir; Betti, Riccardo; Sangster, Thomas; Katz, Joseph

2014-10-01

To explore kinetic and multi-ion-fluid effects in D3He and T3He gas-filled shock-driven implosions, multiple nuclear reaction histories were measured using the upgraded Particle Temporal Diagnostic (PTD) on OMEGA. For D3He gas-filled implosions, the relative timing of the DD and D3He reaction histories were measured with 20 ps precision. For T3He gas-filled implosions (with 1-2% deuterium), the relative timing of the DT and D3He reaction histories were measured with 10 ps precision. The observed differences between the reaction histories on these two OMEGA experiments are contrasted to 1-D single-ion hydro simulations for different gas-fill pressure and gas mixture. This work is supported in part by the U.S. DOE, LLNL, LLE, and NNSA SSGF.

Designing cylindrical implosion experiments on NIF to study deceleration phase of Rayleigh-Taylor

NASA Astrophysics Data System (ADS)

Vazirani, N.; Kline, J. L.; Loomis, E.; Sauppe, J. P.; Palaniyappan, S.; Flippo, K.; Srinivasan, B.; Malka, E.; Bose, A.; Shvarts, D.

2017-10-01

The Rayleigh-Taylor (RT) hydrodynamic instability occurs when a lower density fluid pushes on a higher density fluid. This occurs in inertial confinement fusion (ICF) implosions at each of the capsule interfaces during the initial acceleration and the deceleration as it stagnates. The RT instabilities mix capsule material into the fusion fuel degrading the Deuterium-Tritium reactivity and ultimately play a key role in limiting target performance. While significant effort has focused on understanding RT at the outer capsule surface, little work has gone into understanding the inner surface RT instability growth during the deceleration phase. Direct measurements of the RT instability are difficult to make at high convergence in a spherical implosion. Here we present the design of a cylindrical implosion system for the National Ignition Facility for studying deceleration phase RT. We will discuss the experimental design, the estimated instability growth, and our outstanding concerns.

Impact of High-Z Coatings on the Ablation Pressure of Laser Driven Targets.

NASA Astrophysics Data System (ADS)

Mostovych, Andrew; Oh, Jaechul; Schmitt, Andrew; Weaver, James

2007-11-01

Recent hydrodynamic experiments [1] with planar high-Z coated targets at the Naval Research Laboratory and spherical implosion experiments with high-Z coated shell targets [2] at the Omega facility all show significant improvement in target stability as a result of the high-Z coatings. For better understanding of the hydrodynamic processes it is important to know the changes in ablation pressure as a result of the high-Z layers. Using the Nike Laser, we have conducted new experiments to measure the change in shock speed of planar CH targets that are irradiated with and without the presence of a 200 Ang. gold high-Z coating. The evolution of shock propagation inside the targets is diagnosed with VISAR probing while average shock velocities are also measured by shock breakout detection from the stepped rear surface of the targets. We find that the high-Z layers produce a time dependent ablation pressure which is detected via the observation of non-steady shocks in the targets. Experimental results and comparisons to hydrodynamic simulations will be presented. Work supported by U. S. Department of Energy. [1] S.P. Obenschain et al., Phys. Plasmas 9, 2234 (2002). [2] A.N. Mostovych et al., APS Abstracts DPPFO3002M, (2005).

Wire Array Z-pinches on Sphinx Machine: Experimental Results and Relevant Points of Microsecond Implosion Physics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calamy, H.; Hamann, F.; Lassalle, F.

Centre d'Etudes de Gramat (France) has developed an efficient long implosion time (800 ns) Aluminum plasma radiation source (PRS). Based on the LTD technology, the SPHINX facility is developed as a 1-3MJ, 1{mu}s rise time, 4-10 MA current driver. In this paper, it was used in 1MJ, 4MA configuration to drive Aluminum nested wire arrays Z-pinches with K-shell yield up to 20 kJ and a FWHM of the x-ray pulse of about 50 ns. We present latest SPHINX experiments and some of the main physic issues of the microsecond regime. Experimental setup and results are described with the aim ofmore » giving trends that have been obtained. The main features of microsecond implosion of wire arrays can be analyzed thanks to same methods and theories as used for faster Z-pinches. The effect of load polarity was examined. The stability of the implosion , one of the critical point of microsecond wire arrays due to the load dimensions imposed by the time scale, is tackled. A simple scaling from 100 ns Z-pinch results to 800 ns ones gives good results and the use of nested arrays improves dramatically the implosion quality and the Kshell yield of the load. However, additional effects such as the impact of the return current can geometry on the implosion have to be taken into account on our loads. Axial inhomogeneity of the implosion the origin of which is not yet well understood occurs in some shots and impacts the radiation output. The shape of the radiative pulse is discussed and compared with the homogeneity of the implosion. Numerical 2D R-Z and R-{theta} simulations are used to highlight some experimental results and understand the plasma conditions during these microsecond wire arrays implosions.« less

Wire Array Z-pinches on Sphinx Machine: Experimental Results and Relevant Points of Microsecond Implosion Physics

NASA Astrophysics Data System (ADS)

Calamy, H.; Hamann, F.; Lassalle, F.; Bayol, F.; Mangeant, C.; Morell, A.; Huet, D.; Bedoch, J. P.; Chittenden, J. P.; Lebedev, S. V.; Jennings, C. A.; Bland, S. N.

2006-01-01

Centre d'Etudes de Gramat (France) has developed an efficient long implosion time (800 ns) Aluminum plasma radiation source (PRS). Based on the LTD technology, the SPHINX facility is developed as a 1-3MJ, 1μs rise time, 4-10 MA current driver. In this paper, it was used in 1MJ, 4MA configuration to drive Aluminum nested wire arrays Z-pinches with K-shell yield up to 20 kJ and a FWHM of the x-ray pulse of about 50 ns. We present latest SPHINX experiments and some of the main physic issues of the microsecond regime. Experimental setup and results are described with the aim of giving trends that have been obtained. The main features of microsecond implosion of wire arrays can be analyzed thanks to same methods and theories as used for faster Z-pinches. The effect of load polarity was examined. The stability of the implosion , one of the critical point of microsecond wire arrays due to the load dimensions imposed by the time scale, is tackled. A simple scaling from 100 ns Z-pinch results to 800 ns ones gives good results and the use of nested arrays improves dramatically the implosion quality and the Kshell yield of the load. However, additional effects such as the impact of the return current can geometry on the implosion have to be taken into account on our loads. Axial inhomogeneity of the implosion the origin of which is not yet well understood occurs in some shots and impacts the radiation output. The shape of the radiative pulse is discussed and compared with the homogeneity of the implosion. Numerical 2D R-Z and R-θ simulations are used to highlight some experimental results and understand the plasma conditions during these microsecond wire arrays implosions.

Uniformity of cylindrical imploding underwater shockwaves at very small radii

NASA Astrophysics Data System (ADS)

Yanuka, D.; Rososhek, A.; Bland, S. N.; Krasik, Ya. E.

2017-11-01

We compare the convergent shockwaves generated from underwater, cylindrical arrays of copper wire exploded by multiple kilo-ampere current pulses on nanosecond and microsecond scales. In both cases, the pulsed power devices used for the experiments had the same stored energy (˜500 J) and the wire mass was adjusted to optimize energy transfer to the shockwave. Laser backlit framing images of the shock front were achieved down to the radius of 30 μm. It was found that even in the case of initial azimuthal non-symmetry, the shock wave self-repairs in the final stages of its motion, leading to a highly uniform implosion. In both these and previous experiments, interference fringes have been observed in streak and framing images as the shockwave approached the axis. We have been able to accurately model the origin of the fringes, which is due to the propagation of the laser beam diffracting off the uniform converging shock front. The dynamics of the shockwave and its uniformity at small radii indicate that even with only 500 J stored energies, this technique should produce pressures above 1010 Pa on the axis, with temperatures and densities ideal for warm dense matter research.

Capsule Performance Optimization in the National Ignition Campaign

DOE Office of Scientific and Technical Information (OSTI.GOV)

Landen, O L; MacGowan, B J; Haan, S W

2009-10-13

A capsule performance optimization campaign will be conducted at the National Ignition Facility to substantially increase the probability of ignition. The campaign will experimentally correct for residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models before proceeding to cryogenic-layered implosions and ignition attempts. The required tuning techniques using a variety of ignition capsule surrogates have been demonstrated at the Omega facility under scaled hohlraum and capsule conditions relevant to the ignition design and shown to meet the required sensitivity and accuracy. In addition, a roll-up of all expected random and systematic uncertainties in setting themore » key ignition laser and target parameters due to residual measurement, calibration, cross-coupling, surrogacy, and scale-up errors has been derived that meets the required budget.« less

Capsule performance optimization in the national ignition campaign

NASA Astrophysics Data System (ADS)

Landen, O. L.; MacGowan, B. J.; Haan, S. W.; Edwards, J.

2010-08-01

A capsule performance optimization campaign will be conducted at the National Ignition Facility [1] to substantially increase the probability of ignition. The campaign will experimentally correct for residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models before proceeding to cryogenic-layered implosions and ignition attempts. The required tuning techniques using a variety of ignition capsule surrogates have been demonstrated at the Omega facility under scaled hohlraum and capsule conditions relevant to the ignition design and shown to meet the required sensitivity and accuracy. In addition, a roll-up of all expected random and systematic uncertainties in setting the key ignition laser and target parameters due to residual measurement, calibration, cross-coupling, surrogacy, and scale-up errors has been derived that meets the required budget.

Three-Dimensional Modeling of Low-Mode Asymmetries in OMEGA Cryogenic Implosions

NASA Astrophysics Data System (ADS)

Anderson, K. S.; McKenty, P. W.; Shvydky, A.; Collins, T. J. B.; Forrest, C. J.; Knauer, J. P.; Marozas, J. A.; Marshall, F. J.; Radha, P. B.; Sefkow, A. B.; Marinak, M. M.

2017-10-01

In direct-drive inertial confinement fusion implosions, long-wavelength asymmetries resulting from target offset, laser power imbalance, beam mispointing, etc. can be highly detrimental to target performance. Characterizing the effects of these asymmetry sources requires 3-D simulations performed in full-sphere geometry to accurately capture the evolution of shell perturbations and hot-spot flow. This paper will present 3-D HYDRA simulations characterizing the impact of these perturbation sources on yield and shell modulation. Various simulated observables are generated, and trends are analyzed and compared with experimental data. This material is based on work supported by the Department of Energy National Nuclear Security Administration under Award Numbers DE-NA0001944 and performed under the auspices of the LLNL under Contract No. DE-AC52-07NA27344.

The Hohlraum Drive Campaign on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Moody, John D.

2013-10-01

The Hohlraum drive effort on the National Ignition Facility (NIF) laser has three primary goals: 1) improve hohlraum performance by improving laser beam propagation, reducing backscatter from laser plasma interactions (LPI), controlling x-ray and electron preheat, and modifying the x-ray drive spectrum; 2) improve understanding of crossbeam energy transfer physics to better evaluate this as a symmetry tuning method; and 3) improve modeling in order to find optimum designs. Our experimental strategy for improving performance explores the impact of significant changes to the hohlraum shape, wall material, gasfill composition, and gasfill density on integrated implosion experiments. We are investigating the performance of a rugby-shaped design that has a significantly larger diameter (7 mm) at the waist than our standard 5.75 mm diameter cylindrical-shaped hohlraum but maintains approximately the same wall area. We are also exploring changes to the gasfill composition in cylindrical hohlraums by using neopentane at room temperature to compare with our standard helium gasfill. In addition, we are also investigating higher He gasfill density (1.6 mg/cc vs nominal 0.96 mg/cc) and increased x-ray drive very early in the pulse. Besides these integrated experiments, our strategy includes experiments testing separate aspects of the hohlraum physics. These include time-resolved and time-integrated measurements of cross-beam transfer rates and laser-beam spatial power distribution at early and late times using modified targets. Non-local thermal equilibrium modeling and heat transport relevant to ignition experiments are being studied using sphere targets on the Omega laser system. These simpler targets provide benchmarks for improving our modeling tools. This talk will summarize the results of the Hohlraum Drive campaign and discuss future directions. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA2-344.

Fast ignition realization experiment with high-contrast kilo-joule peta-watt LFEX laser and strong external magnetic field

NASA Astrophysics Data System (ADS)

Fujioka, Shinsuke; Arikawa, Yasunobu; Kojima, Sadaoki; Johzaki, Tomoyuki; Nagatomo, Hideo; Sawada, Hiroshi; Lee, Seung Ho; Shiroto, Takashi; Ohnishi, Naofumi; Morace, Alessio; Vaisseau, Xavier; Sakata, Shohei; Abe, Yuki; Matsuo, Kazuki; Farley Law, King Fai; Tosaki, Shota; Yogo, Akifumi; Shigemori, Keisuke; Hironaka, Yoichiro; Zhang, Zhe; Sunahara, Atsushi; Ozaki, Tetsuo; Sakagami, Hitoshi; Mima, Kunioki; Fujimoto, Yasushi; Yamanoi, Kohei; Norimatsu, Takayoshi; Tokita, Shigeki; Nakata, Yoshiki; Kawanaka, Junji; Jitsuno, Takahisa; Miyanaga, Noriaki; Nakai, Mitsuo; Nishimura, Hiroaki; Shiraga, Hiroyuki; Kondo, Kotaro; Bailly-Grandvaux, Mathieu; Bellei, Claudio; Santos, João Jorge; Azechi, Hiroshi

2016-05-01

A petawatt laser for fast ignition experiments (LFEX) laser system [N. Miyanaga et al., J. Phys. IV France 133, 81 (2006)], which is currently capable of delivering 2 kJ in a 1.5 ps pulse using 4 laser beams, has been constructed beside the GEKKO-XII laser facility for demonstrating efficient fast heating of a dense plasma up to the ignition temperature under the auspices of the Fast Ignition Realization EXperiment (FIREX) project [H. Azechi et al., Nucl. Fusion 49, 104024 (2009)]. In the FIREX experiment, a cone is attached to a spherical target containing a fuel to prevent a corona plasma from entering the path of the intense heating LFEX laser beams. The LFEX laser beams are focused at the tip of the cone to generate a relativistic electron beam (REB), which heats a dense fuel core generated by compression of a spherical deuterized plastic target induced by the GEKKO-XII laser beams. Recent studies indicate that the current heating efficiency is only 0.4%, and three requirements to achieve higher efficiency of the fast ignition (FI) scheme with the current GEKKO and LFEX systems have been identified: (i) reduction of the high energy tail of the REB; (ii) formation of a fuel core with high areal density using a limited number (twelve) of GEKKO-XII laser beams as well as a limited energy (4 kJ of 0.53-μm light in a 1.3 ns pulse); (iii) guiding and focusing of the REB to the fuel core. Laser-plasma interactions in a long-scale plasma generate electrons that are too energetic to efficiently heat the fuel core. Three actions were taken to meet the first requirement. First, the intensity contrast of the foot pulses to the main pulses of the LFEX was improved to >109. Second, a 5.5-mm-long cone was introduced to reduce pre-heating of the inner cone wall caused by illumination of the unconverted 1.053-μm light of implosion beam (GEKKO-XII). Third, the outside of the cone wall was coated with a 40-μm plastic layer to protect it from the pressure caused by imploding plasma. Following the above improvements, conversion of 13% of the LFEX laser energy to a low energy portion of the REB, whose slope temperature is 0.7 MeV, which is close to the ponderomotive scaling value, was achieved. To meet the second requirement, the compression of a solid spherical ball with a diameter of 200-μm to form a dense core with an areal density of ˜0.07 g/cm2 was induced by a laser-driven spherically converging shock wave. Converging shock compression is more hydrodynamically stable compared to shell implosion, while a hot spot cannot be generated with a solid ball target. Solid ball compression is preferable also for compressing an external magnetic field to collimate the REB to the fuel core, due to the relatively small magnetic Reynolds number of the shock compressed region. To meet the third requirement, we have generated a strong kilo-tesla magnetic field using a laser-driven capacitor-coil target. The strength and time history of the magnetic field were characterized with proton deflectometry and a B-dot probe. Guidance of the REB using a 0.6-kT field in a planar geometry has been demonstrated at the LULI 2000 laser facility. In a realistic FI scenario, a magnetic mirror is formed between the REB generation point and the fuel core. The effects of the strong magnetic field on not only REB transport but also plasma compression were studied using numerical simulations. According to the transport calculations, the heating efficiency can be improved from 0.4% to 4% by the GEKKO and LFEX laser system by meeting the three requirements described above. This efficiency is scalable to 10% of the heating efficiency by increasing the areal density of the fuel core.

ARES Modeling of High-foot Implosions (NNSA Milestone #5466)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hurricane, O. A.

ARES “capsule only” simulations demonstrated results of applying an ASC code to a suite of high-foot ICF implosion experiments. While a capability to apply an asymmetric FDS drive to the capsule-only model using add-on Python routines exists, it was not exercised here. The ARES simulation results resemble the results from HYDRA simulations documented in A. Kritcher, et al., Phys. Plasmas, 23, 052709 (2016); namely, 1D simulation and data are in reasonable agreement for the lowest velocity experiments, but diverge from each other at higher velocities.

X-ray source development for EXAFS measurements on the National Ignition Facility.

PubMed

Coppari, F; Thorn, D B; Kemp, G E; Craxton, R S; Garcia, E M; Ping, Y; Eggert, J H; Schneider, M B

2017-08-01

Extended X-ray absorption Fine Structure (EXAFS) measurements require a bright, spectrally smooth, and broad-band x-ray source. In a laser facility, such an x-ray source can be generated by a laser-driven capsule implosion. In order to optimize the x-ray emission, different capsule types and laser irradiations have been tested at the National Ignition Facility (NIF). A crystal spectrometer is used to disperse the x-rays and high efficiency image plate detectors are used to measure the absorption spectra in transmission geometry. EXAFS measurements at the K-edge of iron at ambient conditions have been obtained for the first time on the NIF laser, and the requirements for optimization have been established.

Foam encapsulated targets

DOEpatents

Nuckolls, John H.; Thiessen, Albert R.; Dahlbacka, Glen H.

1983-01-01

Foam encapsulated laser-fusion targets wherein a quantity of thermonuclear fuel is embedded in low density, microcellular foam which serves as an electron conduction channel for symmetrical implosion of the fuel by illumination of the target by one or more laser beams. The fuel, such as DT, is contained within a hollow shell constructed of glass, for example, with the foam having a cell size of preferably no greater than 2 .mu.m, a density of 0.065 to 0.6.times.10.sup.3 kg/m.sup.3, and external diameter of less than 200 .mu.m.

Simulations of High-Gain Shock-Ignited Inertial-Confinement-Fusion Implosions Using Less Than 1 MJ of Direct KrF Laser Energy

DTIC Science & Technology

2009-05-01

transport, and thermonuclear burn. Using FAST, three classes of shock-ignited targets were designed that achieve one-dimensional fusion - energy gains in the...MJ) G a in Figure 1: Results of one-dimensional simulations showing the fusion energy gain as a function of KrF laser energy for three classes of...rises smoothly (according to a double power (a) Spike width: 160 ps (b) Spike power: 1530 TW Figure 4: Examples of fusion - energy gain contours for a shock

Planar Two-Plasmon-Decay Experiments at Polar-Direct-Drive Ignition-Relevant Scale Lengths at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Rosenberg, M. J.; Solodov, A. A.; Seka, W.; Myatt, J. F.; Regan, S. P.; Hohenberger, M.; Epstein, R.; Collins, T. J. B.; Turnbull, D. P.; Ralph, J. E.; Barrios, M. A.; Moody, J. D.

2015-11-01

Results from the first experiments at the National Ignition Facility (NIF) to probe two-plasmon -decay (TPD) hot-electron production at scale lengths relevant to polar-direct-drive (PDD) ignition are reported. The irradiation on one side of a planar CH foil generated a plasma at the quarter-critical surface with a predicted density gradient scale length of Ln ~ 600 μm , a measured electron temperature of Te ~ 3 . 5 to 4.0 keV, an overlapped laser intensity of I ~ 6 ×1014 W/cm2, and a predicted TPD threshold parameter of η ~ 4 . The hard x-ray spectrum and the Kα emission from a buried Mo layer were measured to infer the hot-electron temperature and the fraction of total laser energy converted to TPD hot electrons. Optical emission at ω/2 correlated with the time-dependent hard x-ray signal confirms that TPD is responsible for the hot-electron generation. The effect of laser beam angle of incidence on TPD hot-electron generation was assessed, and the data show that the beam angle of incidence did not have a strong effect. These results will be used to benchmark simulations of TPD hot-electron production at conditions relevant to PDD ignition-scale implosions. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Interaction of doughnut-shaped laser pulses with glasses

DOE PAGES

Zhukov, Vladimir P.; Rubenchik, Alexander M.; Fedoruk, Mikhail P.; ...

2017-01-26

Non-Gaussian laser beams can open new opportunities for microfabrication, including ultrashort laser direct writing. By using a model based on Maxwell’s equations, we investigate the dynamics of doughnut-shaped laser beams focused inside fused silica glass, in comparison with Gaussian pulses of the same energy. The laser propagation dynamics reveals intriguing features of beam splitting and sudden collapse toward the beam axis, overcoming the intensity clamping effect. The resulting structure of light absorption represents a very hot, hollow nanocylinder, which can lead to an implosion process that brings matter to extreme thermodynamic states. Furthermore, by monitoring the simulations of the lasermore » beam scattering we see a considerable difference in both the blueshift and the angular distribution of scattered light for different laser energies, suggesting that investigations of the spectra of scattered radiation can be used as a diagnostic of laser-produced electron plasmas in transparent materials.« less

Observation of Interspecies Ion Separation in Inertial-Confinement-Fusion Implosions via Imaging X-ray spectroscopy

NASA Astrophysics Data System (ADS)

Joshi, Tirtha Raj

2016-10-01

Interspecies ion separation has been proposed as a yield-degradation mechanism in inertial-confinement-fusion (ICF) experiments. We present direct experimental evidence of interspecies ion separation in direct-drive ICF experiments performed at the OMEGA laser facility. These experiments were designed based on the fact that interspecies ion thermo-diffusion would be strongest for species with large mass and charge difference. The targets were spherical plastic shells filled with D2 and Ar (1% by atom). Ar K-shell spectral features were observed primarily between the time of first-shock convergence and slightly before neutron bang time, using a time- and space-integrated spectrometer, streaked crystal spectrometer, and two gated multi-monochromatic X-ray imagers fielded along quasi-orthogonal lines-of-sight. Detailed spectroscopic analyses of spatially resolved Ar K-shell lines reveal deviation from the initial 1%-Ar gas fill and show both Ar-concentration enhancement and depletion at different times and radial positions of the implosion. The experimental results are interpreted with radiation-hydrodynamic simulations that include recently implemented, first-principles models of interspecies ion diffusion. The experimentally inferred Ar-atom-fraction profiles agree gently with calculated profiles associated with the incoming and rebounding first shock. This work was done in collaboration with P. Hakel, S. C. Hsu, E. L. Vold, M. J. Schmitt, N. M. Hoffman, R. M. Rauenzahn, G. Kagan, X.-Z. Tang, Y. Kim, and H. W. Herrmann of LANL, and R. C. Mancini of UNR. LA-UR-16-24804. Supported by the LANL ICF and ASC Programs under US-DoE contract no. DE-AC52-06NA25396.

Fast ignition realization experiment with high-contrast kilo-joule peta-watt LFEX laser and strong external magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fujioka, Shinsuke, E-mail: sfujioka@ile.osaka-u.ac.jp; Arikawa, Yasunobu; Kojima, Sadaoki

A petawatt laser for fast ignition experiments (LFEX) laser system [N. Miyanaga et al., J. Phys. IV France 133, 81 (2006)], which is currently capable of delivering 2 kJ in a 1.5 ps pulse using 4 laser beams, has been constructed beside the GEKKO-XII laser facility for demonstrating efficient fast heating of a dense plasma up to the ignition temperature under the auspices of the Fast Ignition Realization EXperiment (FIREX) project [H. Azechi et al., Nucl. Fusion 49, 104024 (2009)]. In the FIREX experiment, a cone is attached to a spherical target containing a fuel to prevent a corona plasma frommore » entering the path of the intense heating LFEX laser beams. The LFEX laser beams are focused at the tip of the cone to generate a relativistic electron beam (REB), which heats a dense fuel core generated by compression of a spherical deuterized plastic target induced by the GEKKO-XII laser beams. Recent studies indicate that the current heating efficiency is only 0.4%, and three requirements to achieve higher efficiency of the fast ignition (FI) scheme with the current GEKKO and LFEX systems have been identified: (i) reduction of the high energy tail of the REB; (ii) formation of a fuel core with high areal density using a limited number (twelve) of GEKKO-XII laser beams as well as a limited energy (4 kJ of 0.53-μm light in a 1.3 ns pulse); (iii) guiding and focusing of the REB to the fuel core. Laser–plasma interactions in a long-scale plasma generate electrons that are too energetic to efficiently heat the fuel core. Three actions were taken to meet the first requirement. First, the intensity contrast of the foot pulses to the main pulses of the LFEX was improved to >10{sup 9}. Second, a 5.5-mm-long cone was introduced to reduce pre-heating of the inner cone wall caused by illumination of the unconverted 1.053-μm light of implosion beam (GEKKO-XII). Third, the outside of the cone wall was coated with a 40-μm plastic layer to protect it from the pressure caused by imploding plasma. Following the above improvements, conversion of 13% of the LFEX laser energy to a low energy portion of the REB, whose slope temperature is 0.7 MeV, which is close to the ponderomotive scaling value, was achieved. To meet the second requirement, the compression of a solid spherical ball with a diameter of 200-μm to form a dense core with an areal density of ∼0.07 g/cm{sup 2} was induced by a laser-driven spherically converging shock wave. Converging shock compression is more hydrodynamically stable compared to shell implosion, while a hot spot cannot be generated with a solid ball target. Solid ball compression is preferable also for compressing an external magnetic field to collimate the REB to the fuel core, due to the relatively small magnetic Reynolds number of the shock compressed region. To meet the third requirement, we have generated a strong kilo-tesla magnetic field using a laser-driven capacitor-coil target. The strength and time history of the magnetic field were characterized with proton deflectometry and a B-dot probe. Guidance of the REB using a 0.6-kT field in a planar geometry has been demonstrated at the LULI 2000 laser facility. In a realistic FI scenario, a magnetic mirror is formed between the REB generation point and the fuel core. The effects of the strong magnetic field on not only REB transport but also plasma compression were studied using numerical simulations. According to the transport calculations, the heating efficiency can be improved from 0.4% to 4% by the GEKKO and LFEX laser system by meeting the three requirements described above. This efficiency is scalable to 10% of the heating efficiency by increasing the areal density of the fuel core.« less

Experimental room temperature hohlraum performance study on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Ralph, J. E.; Strozzi, D.; Ma, T.; Moody, J. D.; Hinkel, D. E.; Callahan, D. A.; MacGowan, B. J.; Michel, P.; Kline, J. L.; Glenzer, S. H.; Albert, F.; Benedetti, L. R.; Divol, L.; MacKinnon, A. J.; Pak, A.; Rygg, J. R.; Schneider, M. B.; Town, R. P. J.; Widmann, K.; Hsing, W.; Edwards, M. J.

2016-12-01

Room temperature or "warm" (273 K) indirect drive hohlraum experiments have been conducted on the National Ignition Facility with laser energies up to 1.26 MJ and compared to similar cryogenic or "cryo" (˜20 K) experiments. Warm experiments use neopentane (C5H12) as the low pressure hohlraum fill gas instead of helium, and propane (C3H8) to replace the cryogenic DT or DHe3 capsule fill. The increased average Z of the hohlraum fill leads to increased inverse bremsstrahlung absorption and an overall hotter hohlraum plasma in simulations. The cross beam energy transfer (CBET) from outer laser beams (pointed toward the laser entrance hole) to inner beams (pointed at the equator) was inferred indirectly from measurements of Stimulated Raman Scattering (SRS). These experiments show that a similar hot spot self-emission shape can be produced with less CBET in warm hohlraums. The measured inner cone SRS reflectivity (as a fraction of incident power neglecting CBET) is ˜2.5 × less in warm than cryo shots with similar hot spot shapes, due to a less need for CBET. The measured outer-beam stimulated the Brillouin scattering power that was higher in the warm shots, leading to a ceiling on power to avoid the optics damage. These measurements also show that the CBET induced by the flow where the beams cross can be effectively mitigated by a 1.5 Å wavelength shift between the inner and outer beams. A smaller scale direct comparison indicates that warm shots give a more prolate implosion than cryo shots with the same wavelength shift and pulse shape. Finally, the peak radiation temperature was found to be between 5 and 7 eV higher in the warm than the corresponding cryo experiments after accounting for differences in backscatter.

Integrated Fast-Ignition Core-Heating Experiments on OMEGA

NASA Astrophysics Data System (ADS)

Theobald, W.

2010-11-01

Integrated fast-ignition core-heating experiments are carried out at the Omega Laser Facility. Plastic (CD) shell targets with a re-entrant gold cone are compressed with a ˜20-kJ, UV low-adiabat laser pulse. A 1-kJ, 10-ps pulse from OMEGA EP generates fast electrons in the hollow cone that are transported into the compressed core. The experiments demonstrate a significant enhancement of the neutron yield. The neutron-yield enhancement caused by the high-intensity pulse is 1.5 x 10^7, which is more than 150% of the implosion yield. For the first time, measurements of the breakout time of the compression-induced shock wave through the cone were performed for the same targets as used in the integrated experiments. The shock breakout was measured to be ˜100 ps after peak neutron production. The experiments demonstrate that the cone tip is intact at the time when the short-pulse laser interacts with the cone. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement Nos. DE-FC52-08NA28302, DE-FC02-04ER54789, and DE-FG02-05ER54839. [4pt] In collaboration with A. A. Solodov, K. S. Anderson, R. Betti (LLE/FSC); C. Stoeckl, T.R. Boehly, R.S. Craxton, J.A. Delettrez, V.Yu. Glebov, J.P. Knauer, F.J. Marshall, K.L. Marshall, D.D. Meyerhofer,^ P.M. Nilson, T.C. Sangster, W. Seka (LLE); F.N. Beg (UCSD), H. Habara (ILE), P.K. Patel (LLNL), R.B. Stephens (GA); J.A. Frenje, N. Sinenian (PSFC/MIT).