MHD simulation studies of z-pinch shear flow stabilization
NASA Astrophysics Data System (ADS)
Paraschiv, I.; Bauer, B. S.; Sotnikov, V. I.; Makhin, V.; Siemon, R. E.
2003-10-01
The development of the m=0 instability in a z-pinch in the presence of sheared plasma flows is investigated with the aid of a two-dimensional magnetohydrodynamic (MHD) simulation code (MHRDR). The linear growth rates are compared to the results obtained by solving the ideal MHD linearized equations [1] and to the results obtained using a 3D hybrid simulation code [2]. The instability development is followed into the nonlinear regime where its growth and saturation are examined. [1] V.I. Sotnikov, I. Paraschiv, V. Makhin, B.S. Bauer, J.-N. Leboeuf, and J.M. Dawson, "Linear analysis of sheared flow stabilization of global magnetohydrodynamic instabilities based on the Hall fluid mode", Phys. Plasmas 9, 913 (2002). [2] V.I. Sotnikov, V. Makhin, B.S. Bauer, P. Hellinger, P. Travnicek, V. Fiala, J.-N. Leboeuf, "Hybrid Simulations of Current-Carrying Instabilities in Z-pinch Plasmas with Sheared Axial Flow", AIP Conference Proceedings, Volume 651, Dense Z-Pinches: 5th International Conference on Dense Z-Pinches, edited by J. Davis et al., page 396, June 2002.
High energy density Z-pinch plasmas using flow stabilization
Shumlak, U. Golingo, R. P. Nelson, B. A. Bowers, C. A. Doty, S. A. Forbes, E. G. Hughes, M. C. Kim, B. Knecht, S. D. Lambert, K. K. Lowrie, W. Ross, M. P. Weed, J. R.
2014-12-15
The ZaP Flow Z-Pinch research project[1] at the University of Washington investigates the effect of sheared flows on MHD instabilities. Axially flowing Z-pinch plasmas are produced that are 100 cm long with a 1 cm radius. The plasma remains quiescent for many radial Alfvén times and axial flow times. The quiescent periods are characterized by low magnetic mode activity measured at several locations along the plasma column and by stationary visible plasma emission. Plasma evolution is modeled with high-resolution simulation codes – Mach2, WARPX, NIMROD, and HiFi. Plasma flow profiles are experimentally measured with a multi-chord ion Doppler spectrometer. A sheared flow profile is observed to be coincident with the quiescent period, and is consistent with classical plasma viscosity. Equilibrium is determined by diagnostic measurements: interferometry for density; spectroscopy for ion temperature, plasma flow, and density[2]; Thomson scattering for electron temperature; Zeeman splitting for internal magnetic field measurements[3]; and fast framing photography for global structure. Wall stabilization has been investigated computationally and experimentally by removing 70% of the surrounding conducting wall to demonstrate no change in stability behavior.[4] Experimental evidence suggests that the plasma lifetime is only limited by plasma supply and current waveform. The flow Z-pinch concept provides an approach to achieve high energy density plasmas,[5] which are large, easy to diagnose, and persist for extended durations. A new experiment, ZaP-HD, has been built to investigate this approach by separating the flow Z-pinch formation from the radial compression using a triaxial-electrode configuration. This innovation allows more detailed investigations of the sheared flow stabilizing effect, and it allows compression to much higher densities than previously achieved on ZaP by reducing the linear density and increasing the pinch current. Experimental results and
ZaP-HD: High Energy Density Z-Pinch Plasmas using Sheared Flow Stabilization
NASA Astrophysics Data System (ADS)
Golingo, R. P.; Shumlak, U.; Nelson, B. A.; Claveau, E. L.; Doty, S. A.; Forbes, E. G.; Hughes, M. C.; Kim, B.; Ross, M. P.; Weed, J. R.
2015-11-01
The ZaP-HD flow Z-pinch project investigates scaling the flow Z-pinch to High Energy Density Plasma, HEDP, conditions by using sheared flow stabilization. ZaP used a single power supply to produce 100 cm long Z-pinches that were quiescent for many radial Alfven times and axial flow-through times. The flow Z-pinch concept provides an approach to achieve HED plasmas, which are dimensionally large and persist for extended durations. The ZaP-HD device replaces the single power supply from ZaP with two separate power supplies to independently control the plasma flow and current in the Z-pinch. Equilibrium is determined by diagnostic measurements of the density with interferometry and digital holography, the plasma flow and temperature with passive spectroscopy, the magnetic field with surface magnetic probes, and plasma emission with optical imaging. The diagnostics fully characterize the plasma from its initiation in the coaxial accelerator, through the pinch, and exhaust from the assembly region. The plasma evolution is modeled with high resolution codes: Mach2, WARPX, and NIMROD. Experimental results and scaling analyses are presented. This work is supported by grants from the U.S. Department of Energy and the U.S. National Nuclear Security Administration.
NASA Astrophysics Data System (ADS)
Nelson, B. A.; Shumlak, U.; Golingo, R. P.; Claveau, E. L.; McLean, H. S.; Schmidt, A. E.
2015-11-01
The ZaP experiment produces long-lived sheared-flow-stabilized Z-pinch plasmas up to 126 cm in length for several flow-through times, and up to thousands of Alfvén times. Experimental measurements of the magnetic structure along the full length of the plasma column show an axially uniform Z-pinch plasma during the observed quiescent period. Interferometry, fast-framing images, and Rogowskii coils corroborate the existence of a pinched plasma during this quiescent period of time. Detailed two-dimensional non-linear magnetohydrodynamic (MHD) calculations have been performed showing the formation and assembly of long-length, long-lived Z-pinches. Experimentally-observed plasma lifetimes and velocity-shear profiles are shown to be consistent with calculations of viscous-damping timescales based on the measured plasma parameters. A newly-funded ARPA-E ALPHA project, the Fusion Z-pinch Experiment ``FuZE'' is being constructed at the University of Washington, in collaboration with the Lawrence Livermore National Laboratory. FuZE will study scaling and stability of the successful ZaP experiment to higher pinch currents. The FuZE experimental design, goals, and plans, based on ZaP experimental results, will be presented.
NASA Astrophysics Data System (ADS)
Ross, M. P.; Shumlak, U.
2016-10-01
The ZaP-HD flow Z-pinch project provides a platform to explore how shear flow stabilized Z-pinches could scale to high-energy-density plasma (plasma with pressures exceeding 1 Mbar) and fusion reactor conditions. The Z-pinch is a linear plasma confinement geometry in which the plasma carries axial electric current and is confined by its self-induced magnetic field. ZaP-HD generates shear stabilized, axisymmetric Z-pinches with stable lifetimes approaching 60 μs. The goal of the project is to increase the plasma density and temperature compared to the previous ZaP project by compressing the plasma to smaller radii (≈1 mm). Radial and axial plasma electron density structure is measured using digital holographic interferometry (DHI), which provides the necessary fine spatial resolution. ZaP-HD's DHI system uses a 2 ns Nd:YAG laser pulse with a second harmonic generator (λ = 532 nm) to produce holograms recorded by a Nikon D3200 digital camera. The holograms are numerically reconstructed with the Fresnel transform reconstruction method to obtain the phase shift caused by the interaction of the laser beam with the plasma. This provides a two-dimensional map of line-integrated electron density, which can be Abel inverted to determine the local number density. The DHI resolves line-integrated densities down to 3 × 1020 m-2 with spatial resolution near 10 μm. This paper presents the first application of Fresnel transform reconstruction as an analysis technique for a plasma diagnostic, and it analyzes the method's accuracy through study of synthetic data. It then presents an Abel inversion procedure that utilizes data on both sides of a Z-pinch local number density profile to maximize profile symmetry. Error estimation and Abel inversion are applied to the measured data.
Scaling the Shear-flow Stabilized Z-pinch to Reactor Conditions
NASA Astrophysics Data System (ADS)
McLean, H. S.; Schmidt, A.; Shumlak, U.; Nelson, B. A.; Golingo, R. P.; Cleveau, E.
2015-11-01
We present a conceptual design along with scaling calculations for a pulsed fusion reactor based on the shear-flow-stabilized Z-pinch device. Experiments performed on the ZaP device, at the University of Washington, have demonstrated stable operation for durations of 20 usec at ~100kA discharge current for pinches that are ~1 cm in diameter and 100 cm long. The inverse of the pinch diameter and plasma energy density scale strongly with pinch current and calculations show that maintaining stabilization durations of ~7 usec for increased discharge current (~15x) in a shortened pinch (10 cm) results in a pinch diameter of ~200 um and plasma conditions that approach those needed to support significant fusion burn and energy gain (Ti ~ 30keV, density ~ 3e26/m3, ntau ~1.4e20 sec/m3). Compelling features of the concept include operation at modest discharge current (1.5 MA) and voltage (40kV) along with direct adoption of liquid metals for at least one electrode--technological capabilities that have been proven in existing, commercial, pulse power devices such as large ignitrons. LLNL-ABS-674920. This work performed under the auspices of the U.S. Department of Energy ARPAe ALPHA Program by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
The ZaP Flow Z-Pinch Project - Final Technical Report
Shumlak, Uri; Nelson, Brian A.
2013-12-31
The ZaP Flow Z-Pinch Project is a project to extend the performance of the flow Z-pinch experiment at the University of Washington to investigate and isolate the relevant physics of the stabilizing effect of plasma flow. Experimental plasmas have exhibited an enhanced stability under certain operating parameters which generate a flow state (axial flows in Z-pinches and VH mode in tokamaks). Flow has also been suggested as the stabilizing mechanism in astrophysical jets.
Analysis of Conical Wire Array Z-Pinch Stability with a Center Wire
Martinez, D.; Presura, R.; Wright, S.; Plechaty, C.; Neff, S.; Wanex, L.; Ampleford, D. J.
2009-01-21
Adding a center wire on the axis of a conical wire array produces conditions suitable for studying shear flow stabilization of the Z-pinch. The conical wire array produces and axial plasma flow while the center wire introduces a radial variation of the axial velocity. Experiments of this array configuration were preformed on the 1 MA Zebra Z-pinch generator and showed stabilization of the kink instability when a center wire was present. Comparison with equivalent cylindrical wire arrays indicates that the shear flow stabilization plays a role in the stabilization of the kink instability.
Study of the stability of Z-pinch implosions with different initial density profiles
Rousskikh, A. G.; Zhigalin, A. S.; Labetskaya, N. A.; Chaikovsky, S. A.; Yushkov, G. Yu.; Oreshkin, V. I.; Batrakov, A. V.; Baksht, R. B.
2014-05-15
Stability of metal-puff Z pinches was studied experimentally. Experiments were carried out on a facility producing a load current up to 450 kA with a rise time of 450 ns. In a metal-puff Z pinch, the plasma shell is produced due to evaporation of the electrode material during the operation of a vacuum arc. In the experiment to be reported, a single-shell and a shell-on-jet pinch load with magnesium electrodes were used. Two-dimensional, 3 ns gated, visible-light images were taken at different times during the implosion. When the shell was formed from a collimated plasma flow with small radial divergence, Rayleigh–Taylor (RT) instability typical of gas-puff implosions was recorded. The RT instability was completely suppressed in a mode where the initial density distribution of the shell approached a tailored density profile [A. L. Velikovich et al., Phys. Rev. Lett. 77, 853 (1996)].
Polytropic scaling of a flow Z-pinch
NASA Astrophysics Data System (ADS)
Hughes, M. C.; Shumlak, U.; Nelson, B. A.; Golingo, R. P.; Claveau, E. L.; Doty, S. A.; Forbes, E. G.; Kim, B.; Ross, M. P.; Weed, J. R.
2015-11-01
The ZaP Flow Z-Pinch project investigates the use of velocity shear to mitigate MHD instabilities. The ZaP-HD experiment produces 50 cm long pinches of varying radii. The power to the experiment is split between the plasma formation and acceleration process and the pinch assembly and compression process. Once the pinch is formed, low magnetic fluctuations indicate a quiescent, long-lived pinch. The split power supply allows more control of the pinch current than previous machine iterations, with a designed range from 50 to 150 kA. Radial force balance leads to the Bennett relation which indicates that as the pinch compresses due to increasing currents, the plasma pressure and/or linear density must change. Through ion spectroscopy and digital holographic interferometry coupled with magnetic measurements of the pinch current, the components of the Bennett relation can be fully measured. A scaling relation is then assumed to follow a polytrope as the pinch pressure, initially approximately 250 kPa, increases from an initially formed state to much higher values, approaching 100 MPa. A preliminary analysis of pinch scaling is shown corroborating with other diagnostics on the machine along with extrapolations to required currents for an HEDLP machine. This work is supported by grants from the U.S. Department of Energy and the U.S. National Nuclear Security Administration.
NASA Astrophysics Data System (ADS)
Ross, Michael; Shumlak, Uri; Nelson, Brian; Golingo, Raymond; Hughes, Michal; Forbes, Eleanor; Paliwoda, Matt
2014-10-01
The ZaP-HD Flow Z-Pinch experiment investigates how flow shear stabilized Z-pinches scale to higher densities and temperatures. Determining how such plasmas scale up may reveal their utility as test beds for HEDP physics. Scaling towards HEDP conditions requires compressing the plasma to a smaller size with increased plasma current. Measuring the internal structure of a smaller, hotter plasma requires high-resolution diagnostics. To measure electron density profiles, the ZaP-HD team uses holographic interferometry with 30 micron resolution. A new Nd:YAG laser is employed in concert with a consumer digital camera to record holograms, which are numerically reconstructed to obtain the phase shift caused by the interaction of the laser with the plasma. The numerical reconstruction provides a two-dimensional map of chord-integrated electron density, which can be inverted to radial profiles under the assumption of axisymmetry. Measurements of Z-pinch density structure are presented. This work is supported by grants from the U.S. Department of Energy and the U.S. National Nuclear Security Administration.
Quasi-steady accelerator operation on the ZAP flow Z-pinch
NASA Astrophysics Data System (ADS)
Hughes, M. C.; Shumlak, U.; Golingo, R. P.; Nelson, B. A.; Ross, M. P.
2014-12-01
The ZaP Flow Z-Pinch Experiment utilizes sheared flows to stabilize an otherwise unstable equilibrium. The sheared flows are maintained by streaming high velocity plasma parallel to the pinch. Previous operations of the machine show depletion of the accelerator's neutral gas supply late in the pulse leading to pinch instability. The current distribution in the accelerator exhibits characteristic modes during this operation, which is corroborated by interferometric signals. The decrease in density precipitates a loss of plasma quiescence in the pinch, which occurs on a timescale related to the flow velocity from the plasma source. To abate the depletion, the geometry of the accelerator is altered to increase the neutral gas supply. The design creates a standing deflagration front in the accelerator that persists for the pulse duration. The new operating mode is characterized by the same diagnostics as the previous mode. The lessons learned in the accelerator operations have been applied to the design of a new experiment, ZaP-HD. This work was supported by grants from the Department of Energy and the National Nuclear Security Administration.
Quasi-steady accelerator operation on the ZAP flow Z-pinch
Hughes, M. C. Shumlak, U. Golingo, R. P. Nelson, B. A. Ross, M. P.
2014-12-15
The ZaP Flow Z-Pinch Experiment utilizes sheared flows to stabilize an otherwise unstable equilibrium. The sheared flows are maintained by streaming high velocity plasma parallel to the pinch. Previous operations of the machine show depletion of the accelerator’s neutral gas supply late in the pulse leading to pinch instability. The current distribution in the accelerator exhibits characteristic modes during this operation, which is corroborated by interferometric signals. The decrease in density precipitates a loss of plasma quiescence in the pinch, which occurs on a timescale related to the flow velocity from the plasma source. To abate the depletion, the geometry of the accelerator is altered to increase the neutral gas supply. The design creates a standing deflagration front in the accelerator that persists for the pulse duration. The new operating mode is characterized by the same diagnostics as the previous mode. The lessons learned in the accelerator operations have been applied to the design of a new experiment, ZaP-HD. This work was supported by grants from the Department of Energy and the National Nuclear Security Administration.
Investigating plasma viscosity with fast framing photography in the ZaP-HD Flow Z-Pinch experiment
NASA Astrophysics Data System (ADS)
Weed, Jonathan Robert
The ZaP-HD Flow Z-Pinch experiment investigates the stabilizing effect of sheared axial flows while scaling toward a high-energy-density laboratory plasma (HEDLP > 100 GPa). Stabilizing flows may persist until viscous forces dissipate a sheared flow profile. Plasma viscosity is investigated by measuring scale lengths in turbulence intentionally introduced in the plasma flow. A boron nitride turbulence-tripping probe excites small scale length turbulence in the plasma, and fast framing optical cameras are used to study time-evolved turbulent structures and viscous dissipation. A Hadland Imacon 790 fast framing camera is modified for digital image capture, but features insufficient resolution to study turbulent structures. A Shimadzu HPV-X camera captures the evolution of turbulent structures with great spatial and temporal resolution, but is unable to resolve the anticipated Kolmogorov scale in ZaP-HD as predicted by a simplified pinch model.
NASA Astrophysics Data System (ADS)
Kubes, P.; Prykarpatsky, A. K.; Zagrodzinski, J.; Prykarpatsky, Y. A.
In this article we will follow the approach developed in articles N.~N.~Bogoliubov, V.~Hr.~Samoilenko, Ukr. Fiz. Zh., 37, 147 (1992); J.~Gibbon, Physica D, 3, 503 (1981) using modern Lie--algebraic and symplectic geometry methods. It is devoted to the description of Boltzman--Vlasov type kinetic equations and some two--dimensional hydrodynamic Benney type flows associated with them. In our case of the cylindrical symmetry taking place at the interrupted magnetic z--pinch in plasma we used intensively the corresponding two--dimensionality of the plasma flow under consideration which made it possible to build a kinetic model of the plasmoid vortex structure with a conserved number of linkages of vortex lines. The latter can be used to explain the observed earlier stability of the plasmoid structure at the magnetic z--pinch.
Bocchi, M.; Ummels, B.; Chittenden, J. P.; Lebedev, S. V.; Frank, A.; Blackman, E. G.
2013-04-10
The physics of accretion disks is of fundamental importance for understanding of a wide variety of astrophysical sources that includes protostars, X-ray binaries, and active galactic nuclei. The interplay between hydrodynamic flows and magnetic fields and the potential for turbulence-producing instabilities is a topic of active research that would benefit from the support of dedicated experimental studies. Such efforts are in their infancy, but in an effort to push the enterprise forward we propose an experimental configuration which employs a modified cylindrical wire array Z-pinch to produce a rotating plasma flow relevant to accretion disks. We present three-dimensional resistive magnetohydrodynamic simulations which show how this approach can be implemented. In the simulations, a rotating plasma cylinder or ring is formed, with typical rotation velocity {approx}30 km s{sup -1}, Mach number {approx}4, and Reynolds number in excess of 10{sup 7}. The plasma is also differentially rotating. Implementation of different external magnetic field configurations is discussed. It is found that a modest uniform vertical field of 1 T can affect the dynamics of the system and could be used to study magnetic field entrainment and amplification through differential rotation. A dipolar field potentially relevant to the study of accretion columns is also considered.
Qiu, X. M.; Huang, L.; Jian, G. D.
2007-03-15
The Rayleigh-Taylor (RT) instability in Z pinches with sheared axial flow (SAF) is analyzed using finite Larmor radius (FLR) magnetohydrodynamic theory, in whose momentum equation the FLR effect (also referred to as the effect of gyroviscosity) is introduced through an anisotropic ion (FLR) stress tensor. A dispersion relation is derived for the linear RT instability. Both analytical and numerical solutions of the dispersion equation are given. The results indicate that the short-wavelength modes of the RT instability can be stabilized by a sufficient FLR, whereas the long-wavelength modes can be stabilized by a sufficient SAF. In the small-wavenumber region, for normalized wavenumber K<2.4, the hybrid RT/KH (Kelvin-Helmholtz) instability is shown to be the most difficult to stabilize. However the synergistic effect of the SAF and gyroviscosity can mitigate both the RT instability in the large-wavenumber region (K>2.4) and the hybrid RT/KH instability in the small-wavenumber region. In addition, this synergistic effect can compress the RT instability to a narrow wavenumber region. Even the thorough stabilization of the RT instability in the large-wavenumber region is possible with a sufficient SAF and a sufficient gyroviscosity.
Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch
Vogman, G. V.; Shumlak, U.
2011-10-13
Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian function associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. As a result, these measurements are used to gain a better understanding of Z-pinch equilibria.
Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch
Vogman, G. V.; Shumlak, U.
2011-10-13
Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian functionmore » associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. As a result, these measurements are used to gain a better understanding of Z-pinch equilibria.« less
NASA Technical Reports Server (NTRS)
Miernik, Janie
2011-01-01
Fusion-based nuclear propulsion has the potential to enable fast interplanetary transportation. Shorter trips are better for humans in the harmful radiation environment of deep space. Nuclear propulsion and power plants can enable high Ispand payload mass fractions because they require less fuel mass. Fusion energy research has characterized the Z-Pinch dense plasma focus method. (1) Lightning is form of pinched plasma electrical discharge phenomena. (2) Wire array Z-Pinch experiments are commonly studied and nuclear power plant configurations have been proposed. (3) Used in the field of Nuclear Weapons Effects (NWE) testing in the defense industry, nuclear weapon x-rays are simulated through Z-Pinch phenomena.
Coleman, P L; Lamppa, D C; Madden, R E; Wilson-Elliott, K; Jones, B; Ampleford, D J; Bliss, D E; Jennings, C; Bixler, A; Krishnan, M
2012-08-01
For gas puff Z-pinches, the K-shell x-ray yield is maximized with the use of a multi-shell nozzle. Optimization of the yield, verification of hydrodynamic models of the nozzle flows, and plausible MHD code modeling of the implosions require data on the radial and axial (R,Z) distribution of mass in the nozzle's flow field. Interferometry is a well-established technique for acquiring such data. We describe the development and use of a two-dimensional interferometer with emphasis on the required data reduction methods. We also show that the instrument can derive the flow from each individual nozzle in a multi-shell system.
Design of the Fusion Z-Pinch Experiment - FuZE
NASA Astrophysics Data System (ADS)
Shumlak, U.; McLean, H. S.; Nelson, B. A.; Golingo, R. P.; Schmidt, A.; Claveau, E. L.
2015-11-01
Based on the successful results of the sheared flow stabilized (SFS) Z-pinch from ZaP and ZaP-HD, a new experiment FuZE is designed to scale the plasma performance to fusion conditions. The SFS Z-pinch is immune to the instabilities that plague the conventional Z-pinch yet maintains the same favorable radial scaling. The plasma density and temperature increase rapidly with decreasing plasma radius, which naturally leads to a compact configuration at fusion conditions. The SFS Z-pinch is being investigated as a novel approach to a compact fusion device in a new collaborative ARPA-E ALPHA project with the University of Washington and Lawrence Livermore National Laboratory. The project includes an experimental effort coupled with high-fidelity physics modeling using kinetic and fluid simulations. Along with scaling law analysis, computational and experimental results that have informed the design and development of the FuZE apparatus are presented. This work is supported by an award from US ARPA-E.
Rotating plasma disks in dense Z-pinch experiments
Bennett, M. J. E-mail: s.lebedev@imperial.ac.uk; Lebedev, S. V. E-mail: s.lebedev@imperial.ac.uk; Suttle, L.; Burdiak, G.; Suzuki-Vidal, F.; Hare, J.; Swadling, G.; Patankar, S.; Bocchi, M.; Chittenden, J. P.; Smith, R.; Hall, G. N.; Frank, A.; Blackman, E.; Drake, R. P.; Ciardi, A.
2014-12-15
We present data from the first z-pinch experiments aiming to simulate aspects of accretion disk physics in the laboratory. Using off axis ablation flows from a wire array z-pinch we demonstrate the formation of a hollow disk structure that rotates at 60 kms{sup −1} for 150 ns. By analysing the Thomson scattered spectrum we make estimates for the ion and electron temperatures as T{sub i} ∼ 60 eV and ZT{sub e} ∼ 150 to 200 eV.
Z-Pinch Fusion for Energy Applications
SPIELMAN,RICK B.
2000-01-01
Z pinches, the oldest fusion concept, have recently been revisited in light of significant advances in the fields of plasma physics and pulsed power engineering. The possibility exists for z-pinch fusion to play a role in commercial energy applications. We report on work to develop z-pinch fusion concepts, the result of an extensive literature search, and the output for a congressionally-mandated workshop on fusion energy held in Snowmass, Co July 11-23,1999.
Z-pinch equilibrium and instability analysis with digital holographic interferometry
NASA Astrophysics Data System (ADS)
Ross, M. P.; Shumlak, U.; Nelson, B. A.; Golingo, R. P.; Hughes, M. C.; Claveau, E. L.; Weed, J. R.; Forbes, E. G.; Doty, S. A.; Kim, B.
2015-11-01
The ZaP-HD Flow Z-Pinch project generates flow shear stabilized Z-pinches, providing a platform to explore how such plasmas could scale to HEDP and fusion reactor conditions. To scale up the plasma's density and temperature, it must be compressed to a smaller size making measurements more difficult. Digital holographic interferometry (DHI) employing a pulsed Nd:YAG laser and consumer DSLR camera can spatially resolve the plasma's electron density. The Fresnel reconstruction method allows expedient numerical data reconstruction. Obtaining electron density radial profiles relies on applying an Abel inversion to convert measured line-integrated density, and the inversion process provides an independent measure of plasma symmetry. Entire Z-pinch equilibria (n, P, T, and B profiles) can be computed by applying physical models to the density data. Tracking the time evolution of pressure and density can reveal the presence of non-adiabatic heating mechanisms. Imaging the size scales of instabilities enables relative measures of viscosity at different positions and times. Error estimation of measured density profiles is presented along with observed asymmetric instabilities. This work is supported by grants from the U.S. Department of Energy and the U.S. National Nuclear Security Administration.
NASA Astrophysics Data System (ADS)
Wessel, F. J.; Rahman, H. U.; Ney, P.; Valenzuela, J.; Beg, F.; McKee, E.; Darling, T.
2016-03-01
This paper is dedicated to Norman Rostoker, our (FJW and HUR) mentor and long-term collaborator, who will always be remembered for the incredible inspiration that he has provided us. Norman's illustrious career dealt with a broad range of fundamental-physics problems and we were fortunate to have worked with him on many important topics: intense-charged-particle beams, field-reversed configurations, and Z-pinches. Rostoker 's group at the University of CA, Irvine was well known for having implemented many refinements to the Z-pinch, that make it more stable, scalable, and efficient, including the development of: the gas-puff Z-pinch [1], which provides for the use of an expanded range of pinch-load materials; the gas-mixture Z-pinch [2], which enhances the pinch stability and increases its radiation efficiency; e-beam pre-ionization [3], which enhances the uniformity of the initial-breakdown process in a gas pinch; magnetic-flux-compression [4, 5], which allows for the amplification of an axial-magnetic field Bz; the Z-θ pinch [6], which predicts fusion in a pinch-on-fiber configuration; the Staged Z-pinch (SZP) [7], which allows for the amplification of the pinch self-magnetic field, Bθ , in addition to a Bz, and leads to a stable implosion and high-gain fusion [8, 9, 10]. This paper describes the physical basis for a magneto-inertial compression in a liner-on-target SZP [11]. Initially a high-atomic-number liner implodes under the action of the J →×B → , Lorentz Force. As the implosion becomes super Alfvénic, magnetosonic waves form, transporting current and magnetic field through the liner toward the interface of the low-atomic-number target. The target implosion remains subsonic with its surface bounded by a stable-shock front. Shock waves that pass into the target provide a source of target plasma pre-heat. At peak compression the assembly is compressed by liner inertia, with flux compression producing an intense-magnetic field near the target
Thermonuclear fusion in a staged Z-Pinch
NASA Astrophysics Data System (ADS)
van Drie, Alan David
2001-05-01
The Staged Z-Pinch idea was born out of trying to understand the enhanced X-ray yield from shell onto target Z-Pinches I performed in the late 1980s as an undergraduate student at UCI [1]. The idea was further matured through later successes of multi-shell implosions demonstrated at UCI, the Ecole Polytechnique in France, and the Kurchatov Institute in Russia. The Staged Z-Pinch is based upon a hybrid of a Z-Z and Z- Θ Pinch, i.e., an outer Z-Pinch drives Z and Θ currents on a separate coaxial inner target, through compression of axial and azimuthal magnetic fields trapped between the two. These fields provide magnetic shear stabilization. The load configurations tested were: 4 cm dia. Kr hollow gas shell liner with a 1.7 cm dia. D2 hollow gas shell and solid D2 gas jet targets. It is experimentally and computationally observed, that the Kr liner achieves a spectrum of high charge states, which peels off and accelerates ahead of the bulk of the liner. As this Kr implodes onto the deuterium core, it compresses the axial and azimuthal magnetic fields trapped in the liner-target gap, driving the target as a Staged Z-Pinch. In addition, axial current is constantly transferring from the liner to the deuterium target, and eventually dominates over the staged z-pinching of the target and instead drives it as a Z-Pinch. Even without any initial axial Bz field both the peeling and implosion of the target appear RT stable. I call this type of load configuration a Peeled Pinch. For our Staged Z-Pinch experiments, I designed and assembled a mega-ampere, μ s-class pulsed-power driver [2]. This would drive the Kr liner at current levels of 1.2 MA with implosion times of about 150 ns. To study the pinch I developed and installed neutron, optical, and x-ray diagnostics. For neutrons this includes: Ag activation, bubble and TOF detectors. For optical this includes: a N2 laser schlieren and a streak camera diagnostics. For x-rays this includes: a pinhole camera, XRDS and PINs.
NASA Astrophysics Data System (ADS)
Jensen, T. H.; Chu, M. S.
1981-06-01
The 'bumpy Z-pinch' is a magnetic configuration with potential usefulness for fusion reactors. A conceptually simple version of the configuration is axisymmetric. It contains regions of closed and open field lines. In the region of closed field lines, the field line topology is much like that of a tokamak; these regions link the region of open field lines around the axis of symmetry. Assuming that the plasma spontaneously maintains an equilibrium as described by Taylor (1974), it is possible to maintain indefinitely the regions of closed field lines by driving an axial current through the plasma in the region of open field lines. The ratio between the total axial driven current and the total poloidal current in each of the tokamak-like regions can, in principle, be made arbitrarily small, which means that the load impedance can be arbitrarily large. In addition, the configuration has the inherent virtue similar to that of the spheromak that the tokamak-like part of the plasma does not link any material coils.
RYUTOV,D.D.; DERZON,MARK S.; MATZEN,M. KEITH
1999-10-25
The spectacular progress made during the last few years in reaching high energy densities in fast implosions of annular current sheaths (fast Z pinches) opens new possibilities for a broad spectrum of experiments, from x-ray generation to controlled thermonuclear fusion and astrophysics. Presently Z pinches are the most intense laboratory X ray sources (1.8 MJ in 5 ns from a volume 2 mm in diameter and 2 cm tall). Powers in excess of 200 TW have been obtained. This warrants summarizing the present knowledge of physics that governs the behavior of radiating current-carrying plasma in fast Z pinches. This survey covers essentially all aspects of the physics of fast Z pinches: initiation, instabilities of the early stage, magnetic Rayleigh-Taylor instability in the implosion phase, formation of a transient quasi-equilibrium near the stagnation point, and rebound. Considerable attention is paid to the analysis of hydrodynamic instabilities governing the implosion symmetry. Possible ways of mitigating these instabilities are discussed. Non-magnetohydrodynamic effects (anomalous resistivity, generation of particle beams, etc.) are summarized. Various applications of fast Z pinches are briefly described. Scaling laws governing development of more powerful Z pinches are presented. The survey contains 36 figures and more than 300 references.
Ryutov, D.D.; Derzon, M.S.; Matzen, M.K.
1998-07-01
The spectacular progress made during the last few years in reaching high energy densities in fast implosions of annular current sheaths (fast Z pinches) opens new possibilities for a broad spectrum of experiments, from x-ray generation to controlled thermonuclear fusion and astrophysics. Presently Z pinches are the most intense laboratory X ray sources (1.8 MJ in 5 ns from a volume 2 mm in diameter and 2 cm tall). Powers in excess of 200 TW have been obtained. This warrants summarizes the present knowledge of physics that governs the behavior of radiating current-carrying plasma in fast Z-pinches. This survey covers essentially all aspects of the physics of fast Z pinches: initiation, instabilities of the early stage, magnetic Rayleigh-Taylor instability in the implosion phase, formation of a transient quasi-equilibrium near the stagnation point, and rebound. Considerable attention is paid to the analysis of hydrodynamic instabilities governing the implosion symmetry. Possible ways of mitigating these instabilities are discussed. Non-magnetohydrodynamic effects (anomalous resistivity, generation of particle beams, etc.) are summarized. Various applications of fast Z pinches are briefly described. Scaling laws governing development of more powerful Z pinches are presented. The survey contains 52 figures and nearly 300 references.
Sheared Flow as a Stabilizing Mechanism in Astrophysical Jets
NASA Astrophysics Data System (ADS)
Wanex, Lucas F.; Tendeland, Erik
2007-01-01
It has been hypothesized that the sustained narrowness observed in the asymptotic cylindrical region of bipolar outflows from Young Stellar Objects (YSO) indicates that these jets are magnetically collimated. The j z × B ϕ force observed in z-pinch plasmas is a possible explanation for these observations. However, z-pinch plasmas are subject to current driven instabilities (CDI). The interest in using z-pinches for controlled nuclear fusion has lead to an extensive theory of the stability of magnetically confined plasmas. Analytical, numerical, and experimental evidence from this field suggest that sheared flow in magnetized plasmas can reduce the growth rates of the sausage and kink instabilities. Here we propose the hypothesis that sheared helical flow can exert a similar stabilizing influence on CDI in YSO jets.
Optimized Minimal Inductance Transmission Line Configuration for Z-Pinch Experiments
Hurricane, O
2003-10-16
Successful dynamic Z-pinch experiments generally require good current delivery to the target load. Power flow losses through highly inductive transmission line configurations reduce the current available to the load. In this Brief Report, a variational calculus technique is used to determine the transmission line configuration that produces the least possible inductance and therefore the best possible current delivery for Z-pinch experiments.
PBFA Z: A 20-MA z-pinch driver for plasma radiation sources
Spielman, R.B.; Breeze, S.F.; Deeney, C.
1996-07-01
Sandia National Laboratories is completing a major modification to the PBFA-II facility. PBFA Z will be a z-pinch driver capable of delivering up to 20 MA to a z-pinch load. It optimizes the electrical coupling to the implosion energy of z pinches at implosion velocities of {approximately} 40 cm/{mu}s. Design constraints resulted in an accelerator with a 0.12-{Omega} impedance, a 10.25-nH inductance, and a 120-ns pulse width. The design required new water transmission lines, insulator stack, and vacuum power feeds. Current is delivered to the z-pinch load through four, self-magnetically-insulated vacuum transmission lines and a double post-hole convolute. A variety of design codes are used to model the power flow. These predict a peak current of 20 MA to a z-pinch load having a 2-cm length, a 2-cm radius, and a 15--mg mass, coupling 1.5 MJ into kinetic energy. We present 2-D Rad-Hydro calculations showing MJ x-ray outputs from tungsten wire-array z pinches.
Spectroscopic study in Z-pinch discharge
Garamoon, A.A.; Saudy, A.H.; Shark, W.
1995-12-31
The temporal variation of the emitted line intensity has been investigated, and thus an important information about the dynamic ionization stages in the Z-pinch discharge has been studied. Also the electron temperature Te, has been deduced by using a spectroscopic technique.
Fast Z - Pinch Study in Russia and Related Problems
NASA Astrophysics Data System (ADS)
Grabovskii, E. V.
2002-12-01
The fast Z pinches are considered as a perspective source of powerful soft x-ray emission for the ICF pellet ignition. The physical phenomena which take place in process fast of Z-pinch implosion are under investigation in the TRINITI (Troisk), in the RSC Kurchatov Institute (KI, Moscow) and the HCEI (Tomsk). In the KI the possibility of terawatt electrical power transfer in small volume hohlraum during nanosecond time duration is studied. In the TRINITI the physics of multi wire arrays implosion, the rate of plasma production in current-driven wire arrays, the conversion of pulsed power energy into x-ray emission are studied. In the HCEI (Tomsk) the stability of double gas puff implosion and the influence of gas puff regime and current pulse duration on the implosion and emitted x-ray spectrum are under investigation. The HCEI develops the new components of pulse power multi spark switches and the generators of impulse currents (LTD) with duration of an energy supply less than 100 ns. As available way to get the pulsed power generator with multi tens megaampere current the joint team of scientists from the laboratories of the TRINITI, the Efremov Institute, RFNC VNIITF (Snezinsk) have developed the concept of the Baikal facility. The KI designs, creates and tests the plasma erosion switches for the module of the Baikal facility. The inductive storage, the systems of magnetic field compression and the explosive open switches are developed in the TRINITI and the Efremov Institute. The development of new design of the pulse power generators and physics of fast Z-pinch implosion aims to create next advanced generation of powerful driver for ICF.
Z pinches: the past, present, and future
NASA Astrophysics Data System (ADS)
Sweeney, M. A.; Yonas, G.
1998-11-01
Intense electron and light ion beam and z pinch research is based on pulsed power capabilities developed at the Atomic Weapons Establishment in the early 1960s to test the resistance of weapon components to radiation bursts by using short-duration bremsstrahlung sources. Research at Sandia and at the Kurchatov Institute in the 1970s led to an electron beam approach to inertial confinement fusion (ICF). The electron approach ended in 1979 when it was realized that the bremsstrahlung could significantly degrade the fuel compression. ICF research on a more promising approach, light ions, began in the late 1970s with the discovery, at Cornell, Sandia, and the Naval Research Laboratory, of efficient ways to produce intense beams of light ions. At the same time as emergence of the ion approach, z pinches that had produced copious keV x rays since the early 1970s were examined as a way to generate lower-voltage x rays to drive an ICF capsule. In this poster we review the research paths that led to these changes and predict what the future may hold for the z-pinch technology being pursued at Sandia.
A Gas Embedded Z-pinch Driven by SPEED2 Generator
Soto, Leopoldo; Moreno, Jose; Sylvester, Gustavo; Silva, Patricio; Zambra, Marcelo; Pavez, Cristian; Clausse, Alejandro
2006-12-04
A gas embedded Z-pinch has been implemented using the SPEED2 generator (4.1 {mu}F equivalent Marx generator capacity, 300 kV, 4 MA in short circuit, 187 kJ, 400 ns rise time, dI/dt{approx}1013 A/s). Initial conditions to produce a gas embedded z-pinch with enhanced stability by means resistive effects and by finite Larmor radius effects were obtained and electrodes were constructed in order to obtain a double column Z-pinch and a hollow discharge. Experiments were carried out in deuterium at mega amperes currents. Current derivative and voltage signals have been obtained. In addition interferograms have been obatined using a pulse Nd-YAG laser (8ns FWMH at 532nm). Preliminary results on neutron emission were also obtained.
Fusion Propulsion Z-Pinch Engine Concept
NASA Technical Reports Server (NTRS)
Miernik, J.; Statham, G.; Fabisinski, L.; Maples, C. D.; Adams, R.; Polsgrove, T.; Fincher, S.; Cassibry, J.; Cortez, R.; Turner, M.; Percy, T.
2011-01-01
Fusion-based nuclear propulsion has the potential to enable fast interplanetary transportation. Due to the great distances between the planets of our solar system and the harmful radiation environment of interplanetary space, high specific impulse (Isp) propulsion in vehicles with high payload mass fractions must be developed to provide practical and safe vehicles for human spaceflight missions. The Z-Pinch dense plasma focus method is a Magneto-Inertial Fusion (MIF) approach that may potentially lead to a small, low cost fusion reactor/engine assembly1. Recent advancements in experimental and theoretical understanding of this concept suggest favorable scaling of fusion power output yield 2. The magnetic field resulting from the large current compresses the plasma to fusion conditions, and this process can be pulsed over short timescales (10(exp -6 sec). This type of plasma formation is widely used in the field of Nuclear Weapons Effects testing in the defense industry, as well as in fusion energy research. A Decade Module 2 (DM2), approx.500 KJ pulsed-power is coming to the RSA Aerophysics Lab managed by UAHuntsville in January, 2012. A Z-Pinch propulsion concept was designed for a vehicle based on a previous fusion vehicle study called "Human Outer Planet Exploration" (HOPE), which used Magnetized Target Fusion (MTF) 3 propulsion. The reference mission is the transport of crew and cargo to Mars and back, with a reusable vehicle.
Magnetic Rayleigh-Taylor instability mitigation in large-diameter gas puff Z-pinch implosions
Qi, N.; Sze, H.; Failor, B. H.; Banister, J.; Levine, J. S.; Riordan, J. C.; Steen, P.; Sincerny, P.; Lojewski, D.
2008-02-15
Recently, a new approach for efficiently generating K-shell x-rays in large-diameter, long-implosion time, structured argon gas Z-pinches has been demonstrated based on a 'pusher-stabilizer-radiator' model. In this paper, direct observations of the Rayleigh-Taylor instability mitigation of a 12-cm diameter, 200-ns implosion time argon Z-pinch using a laser shearing interferometer (LSI) and a laser wavefront analyzer (LWA) are presented. Using a zero-dimensional snowplow model, the imploding plasma trajectories are calculated with the driver current waveforms and the initial mass distributions measured using the planar laser induced fluorescence method. From the LSI and LWA images, the plasma density and trajectory during the implosion are measured. The measured trajectory agrees with the snowplow calculations. The suppression of hydromagnetic instabilities in the ''pusher-stabilizer-radiator'' structured loads, leading to a high-compression ratio, high-yield Z-pinch, is discussed. For comparison, the LSI and LWA images of an alternative load (without stabilizer) show the evolution of a highly unstable Z-pinch.
Plasma channel and Z-pinch dynamics for heavy ion transport
Ponce-Marquez, David
2002-07-09
A self stabilized, free standing, z-pinch plasma channel has been proposed to deliver the high intensity heavy ion beam from the end of a driver to the fuel target in a heavy ion inertial fusion power plant. The z-pinch relaxes emittance and energy spread requirements requiring a lower cost driver. A z-pinch transport would reduce the number of beam entry port holes to the target chamber from over a hundred to four as compared to neutralized ballistic focusing thus reducing the driver hardware exposure to neutron flux. Experiments where a double pulse discharge technique is used, z-pinch plasma channels with enhanced stability are achieved. Typical parameters are 7 kV pre-pulse discharge and 30 kV main bank discharge with 50 kA of channel current in a 7 torr background gas atmosphere. This work is an experimental study of these plasma channels examining the relevant physics necessary to understand and model such plasmas. Laser diagnostics measured the dynamical properties of neutrals and plasma. Schlieren and phase contrast techniques probe the pre-pulse gas dynamics and infrared interferometry and faraday effect polarimetry are used on the z-pinch to study its electron density and current distribution. Stability and repeatability of the z-pinch depend on the initial conditions set by the pre-pulse. Results show that the z-pinch channel is wall stabilized by an on-axis gas density depression created by the pre-pulse through hydrodynamic expansion where the ratio of the initial gas density to the final gas density is > 10/1. The low on-axis density favors avalanching along the desired path for the main bank discharge. Pinch time is around 2 s from the main bank discharge initiation with a FWHM of {approx} 2 cm. Results also show that typical main bank discharge plasma densities reach 10{sup 17} cm{sup -3} peak on axis for a 30 kV, 7 torr gas nitrogen discharge. Current rise time is limited by the circuit-channel inductance with the highest contribution to the
Instability Control in a Staged Z-pinch
WESSEL, Frank J
2011-04-22
A \\Staged Z-Pinch is a fusion-energy concept in which stored-electric energy is first converted into plasma-liner-kinetic energy, and then transferred to a coaxialtarget plasma [H. U. Rahman, F. J. Wessel, and N. Rostoker, Phys. Rev. Lett. 74, p. 714(1996)]. Proper choice of the liner and target materials, and their initial radii and mass densities, leads to dynamic stabilization, current amplification, and shock heating of the target. Simulations suggest that this configuration has merit as a alternative inertial-confinement-fusion concept, and may provide an energy release exceeding thermonuclear break-even, if tested on one of many newer pulsed power systems, for example those located at Sandia National Laboratories.
Bailey, James E.; Haines, Malcolm G.; Chandler, Gordon Andrew; Bliss, David Emery; Olson, Richard Edward; Sanford, Thomas W. L.; Olson, Craig Lee; Nash, Thomas J.; Ruiz, Carlos L.; Matzen, Maurice Keith; Idzorek, George C.; Stygar, William A.; Apruzese, John P.; Cuneo, Michael Edward; Cooper, Gary Wayne; Chittenden, Jeremy Paul; Chrien, Robert E.; Slutz, Stephen A.; Mock, Raymond Cecil; Leeper, Ramon Joe; Sarkisov, Gennady Sergeevich; Peterson, Darrell L.; Lemke, Raymond William; Mehlhorn, Thomas Alan; Roderick, Norman Frederick; Watt, Robert G.
2004-06-01
Progress in understanding the physics of dynamic-hohlraums is reviewed for a system capable of generating 13 TW of axial radiation for high temperature (>200 eV) radiation-flow experiments and ICF capsule implosions.
Experimental astrophysics with high power lasers and Z pinches
Remington, B A; Drake, R P; Ryutov, D D
2004-12-10
With the advent of high energy density (HED) experimental facilities, such as high-energy lasers and fast Z-pinch, pulsed-power facilities, mm-scale quantities of matter can be placed in extreme states of density, temperature, and/or velocity. This has enabled the emergence of a new class of experimental science, HED laboratory astrophysics, wherein the properties of matter and the processes that occur under extreme astrophysical conditions can be examined in the laboratory. Areas particularly suitable to this class of experimental astrophysics include the study of opacities relevant to stellar interiors; equations of state relevant to planetary interiors; strong shock driven nonlinear hydrodynamics and radiative dynamics, relevant to supernova explosions and subsequent evolution; protostellar jets and high Mach-number flows; radiatively driven molecular clouds and nonlinear photoevaporation front dynamics; and photoionized plasmas relevant to accretion disks around compact objects, such as black holes and neutron stars.
Sheared Flow as a Stabilizing Mechanism in Astrophysical Jets
NASA Astrophysics Data System (ADS)
Wanex, Lucas F.
2007-05-01
It has been hypothesized that the sustained narrowness observed in the asymptotic cylindrical region of bipolar outflows from Young Stellar Objects (YSO) suggests that an intrinsic collimating mechanism is present in these jets. The jz × Bθ force observed in z-pinch plasmas is a possible explanation for these observations. However, z-pinch plasmas are subject to current driven instabilities (CDI). The interest in using z-pinches for controlled nuclear fusion has lead to an extensive theory on the stability of magnetically confined plasmas. Analytical, numerical, and experimental evidence from this field suggest that sheared flow in magnetized plasmas can reduce the growth rates of the sausage and kink instabilities. Here we propose the hypothesis that sheared helical flow can exert a similar stabilizing influence on CDI in YSO jets. Experimental, analytical, and numerical analysis of sheared flow in magnetohydrodynamic plasmas with and without helical magnetic fields is presented. The results support the hypothesis that sheared flow and sheared magnetic fields may impart a stabilizing influence in astrophysical jets. Future laboratory experiments are proposed that will provide enhanced support for this conclusion. Work supported by DOE/NNSA under UNR grant DE-FC52-01NV14050.
Progress in Z-pinch inertial fusion energy.
Weed, John Woodruff
2010-03-01
The goal of z-pinch inertial fusion energy (IFE) is to extend the single-shot z-pinch inertial confinement fusion (ICF) results on Z to a repetitive-shot z-pinch power plant concept for the economical production of electricity. Z produces up to 1.8 MJ of x-rays at powers as high as 230 TW. Recent target experiments on Z have demonstrated capsule implosion convergence ratios of 14-21 with a double-pinch driven target, and DD neutron yields up to 8x10exp10 with a dynamic hohlraum target. For z-pinch IFE, a power plant concept is discussed that uses high-yield IFE targets (3 GJ) with a low rep-rate per chamber (0.1 Hz). The concept includes a repetitive driver at 0.1 Hz, a Recyclable Transmission Line (RTL) to connect the driver to the target, high-yield targets, and a thick-liquid wall chamber. Recent funding by a U.S. Congressional initiative for $4M for FY04 is supporting research on RTLs, repetitive pulsed power drivers, shock mitigation, full RTL cycle planned experiments, high-yield IFE targets, and z-pinch power plant technologies. Recent results of research in all of these areas are discussed, and a Road Map for Z-Pinch IFE is presented.
Z-Pinch Pulsed Plasma Propulsion Technology Development
NASA Technical Reports Server (NTRS)
Polsgrove, Tara; Adams, Robert B.; Fabisinski, Leo; Fincher, Sharon; Maples, C. Dauphne; Miernik, Janie; Percy, Tom; Statham, Geoff; Turner, Matt; Cassibry, Jason; Cortez, Ross; Santarius, John
2010-01-01
Fusion-based propulsion can enable fast interplanetary transportation. Magneto-inertial fusion (MIF) is an approach which has been shown to potentially lead to a low cost, small reactor for fusion break even. The Z-Pinch/dense plasma focus method is an MIF concept in which a column of gas is compressed to thermonuclear conditions by an axial current (I approximates 100 MA). Recent advancements in experiments and the theoretical understanding of this concept suggest favorable scaling of fusion power output yield as I(sup 4). This document presents a conceptual design of a Z-Pinch fusion propulsion system and a vehicle for human exploration. The purpose of this study is to apply Z-Pinch fusion principles to the design of a propulsion system for an interplanetary spacecraft. This study took four steps in service of that objective; these steps are identified below. 1. Z-Pinch Modeling and Analysis: There is a wealth of literature characterizing Z-Pinch physics and existing Z-Pinch physics models. In order to be useful in engineering analysis, simplified Z-Pinch fusion thermodynamic models are required to give propulsion engineers the quantity of plasma, plasma temperature, rate of expansion, etc. The study team developed these models in this study. 2. Propulsion Modeling and Analysis: While the Z-Pinch models characterize the fusion process itself, propulsion models calculate the parameters that characterize the propulsion system (thrust, specific impulse, etc.) The study team developed a Z-Pinch propulsion model and used it to determine the best values for pulse rate, amount of propellant per pulse, and mixture ratio of the D-T and liner materials as well as the resulting thrust and specific impulse of the system. 3. Mission Analysis: Several potential missions were studied. Trajectory analysis using data from the propulsion model was used to determine the duration of the propulsion burns, the amount of propellant expended to complete each mission considered. 4
On the possibility of neutron generation in an imploding TiD{sub 2} puff Z pinch
Baksht, Rina B.; Oreshkin, Vladimir I.; Rousskikh, Alexander G.
2013-08-15
Simulation of implosion of a TiD{sub 2} puff Z pinch is reported. The Z pinch is supposed to be produced by the plasma flow generated by a vacuum arc, as described by Rousskikh et al.[Phys. Plasmas 18, 092707 (2011)]. To simulate the implosion, a one-dimensional two-temperature radiative magnetohydrodynamics code was used. The simulation has shown that neutrons are generated during the implosion of a TiD{sub 2} puff Z pinch due to thermalization of the pinch plasma stagnated on axis. It has been shown that the necessary condition for neutron generation is that the ion temperature must be substantially higher than the electron temperature. For a pinch current of 1 MA, the predicted yield of 'thermal' neutrons is 2.5 × 10{sup 9} neutrons/shot.
Study of gas-puff Z-pinches on COBRA
Qi, N.; Rosenberg, E. W.; Gourdain, P. A.; Grouchy, P. W. L. de; Kusse, B. R.; Hammer, D. A.; Bell, K. S.; Shelkovenko, T. A.; Potter, W. M.; Atoyan, L.; Cahill, A. D.; Evans, M.; Greenly, J. B.; Hoyt, C. L.; Pikuz, S. A.; Schrafel, P. C.; Kroupp, E.; Fisher, A.; Maron, Y.
2014-11-15
Gas-puff Z-pinch experiments were conducted on the 1 MA, 200 ns pulse duration Cornell Beam Research Accelerator (COBRA) pulsed power generator in order to achieve an understanding of the dynamics and instability development in the imploding and stagnating plasma. The triple-nozzle gas-puff valve, pre-ionizer, and load hardware are described. Specific diagnostics for the gas-puff experiments, including a Planar Laser Induced Fluorescence system for measuring the radial neutral density profiles along with a Laser Shearing Interferometer and Laser Wavefront Analyzer for electron density measurements, are also described. The results of a series of experiments using two annular argon (Ar) and/or neon (Ne) gas shells (puff-on-puff) with or without an on- (or near-) axis wire are presented. For all of these experiments, plenum pressures were adjusted to hold the radial mass density profile as similar as possible. Initial implosion stability studies were performed using various combinations of the heavier (Ar) and lighter (Ne) gasses. Implosions with Ne in the outer shell and Ar in the inner were more stable than the opposite arrangement. Current waveforms can be adjusted on COBRA and it was found that the particular shape of the 200 ns current pulse affected on the duration and diameter of the stagnated pinched column and the x-ray yield.
Radiation-Hydromagnetic Models of a Z-Pinch Implosion with an Axial Magnetic Field
NASA Astrophysics Data System (ADS)
Clark, R. W.; Giuliani, J. L.; Terry, R.; Davis, J.; Velikovich, A. L.
1997-11-01
Experimental results on a 1MA pulser suggest that axial magnetic fields can stabilize z-pinch implosions and enhance the compression ratio(S. Sorokin and S. Chaikovsky, Dense Z-Pinches, AIP Conf. Proc. 299, p.83 (1993).). The present theoretical work calculates the effects of an axial magnetic field on the plasma and field profiles in an imploding z-pinch. The initial mass configuration is an annular shell of krypton. The 1-D simulation model includes: resistive diffusion (skin effect) for both the azimuthal and axial fields, ionization dynamics, and non-LTE radiation transport. Unlike the constant pulser current of self-similar models for the screw-pinch, a transmission line is used to model the circuit of a realistic ~10MA pulser. The implosion dynamics resulting from an axial field generated by a twisted return current cage will be compared with results due to an initial field from external Helmholtz coils. The dependence of the radiative performance on compression ratio, which in turn is a function of inital field strength or cage twist, will be discussed.
Study of magnetic fields and current in the Z pinch at stagnation
Ivanov, V. V.; Anderson, A. A.; Astanovitskiy, A. L.; Nalajala, V.; Dmitriev, O.; Papp, D.
2015-09-15
The structure of magnetic fields in wire-array Z pinches at stagnation was studied using a Faraday rotation diagnostic at the wavelength of 266 nm. The electron plasma density and the Faraday rotation angle in plasma were calculated from images of the three-channel polarimeter. The magnetic field was reconstructed with Abel transform, and the current was estimated using a simple model. Several shots with wire-array Z pinches at 0.5–1.5 MA were analyzed. The strength of the magnetic field measured in plasma of the stagnated pinch was in the range of 1–2 MG. The magnetic field and current profile in plasma near the neck on the pinch were reconstructed, and the size of the current-carrying plasma was estimated. It was found that current flowed in the large-size trailing plasma near the dense neck. Measurements of the magnetic field near the bulge on the pinch also showed current in trailing plasma. A distribution of current in the large-size trailing plasma can prevent the formation of multi-MG fields in the Z pinch.
Study of magnetic fields and current in the Z pinch at stagnation
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; Anderson, A. A.; Papp, D.; Astanovitskiy, A. L.; Nalajala, V.; Dmitriev, O.
2015-09-01
The structure of magnetic fields in wire-array Z pinches at stagnation was studied using a Faraday rotation diagnostic at the wavelength of 266 nm. The electron plasma density and the Faraday rotation angle in plasma were calculated from images of the three-channel polarimeter. The magnetic field was reconstructed with Abel transform, and the current was estimated using a simple model. Several shots with wire-array Z pinches at 0.5-1.5 MA were analyzed. The strength of the magnetic field measured in plasma of the stagnated pinch was in the range of 1-2 MG. The magnetic field and current profile in plasma near the neck on the pinch were reconstructed, and the size of the current-carrying plasma was estimated. It was found that current flowed in the large-size trailing plasma near the dense neck. Measurements of the magnetic field near the bulge on the pinch also showed current in trailing plasma. A distribution of current in the large-size trailing plasma can prevent the formation of multi-MG fields in the Z pinch.
Z-Pinch Discharge in Laser Produced Plasma
Sterling, E.; Lunney, J. G.
2010-10-08
A fast coaxial electrical discharge, with relatively low current, was used to produce a Z-pinch effect in a laser produced aluminum plasma. The ion flux in the laser plasma was monitored with a Langmuir ion probe. The line density in the plasma column was controlled by using an aperture to select the portion of the laser plasma which enters the discharge cell. The Z-pinch dynamics were recorded using time-resolved imaging of the visible self-emission; the plasma was pinched to about one-third of the initial radius. Both the laser and Z-pinch plasmas were diagnosed using time-and space-resolved spectroscopy; substantial heating was observed. The measured behaviour of the pinch was compared with predictions of the slug model.
A Z-Pinch Driven Fusion Reactor Concept
NASA Astrophysics Data System (ADS)
Derzon, Mark; Rochau, Gregory; Spielman, Rick; Slutz, Stephen; Rochau, G. E.; Peterson, R. R.; Peterson, P. F.
1999-11-01
Recent z-pinch target physics progress has encouraged us to consider how a power reactor could be configured based on a fast z-pinch driver. Initial cost estimates show that recyclable transmission lines (RTLs) are economically viable. Providing 'standoff' between the primary power supply and the target, which is what disposable RTLs provide, has historically been the main obstacle to the consideration of pinches as fusion drivers. We will be introducing basic reactor scaling in terms of shot rate, yield, tritium breeding and neutron flux, etc. This concept has advantages in that z-pinches provide a robust mechanical environment, as well as a chamber which does not require low-pressure pumping between shots and the wall lifetime is expected to be limited factors other than neutron damage. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
Polycrystalline diamond based detector for Z-pinch plasma diagnosis
Liu Linyue; Zhao Jizhen; Chen Liang; Ouyang Xiaoping; Wang Lan
2010-08-15
A detector setup based on polycrystalline chemical-vapor-deposition diamond film is developed with great characteristics: low dark current (lower than 60 pA within 3 V/{mu}m), fast pulsed response time (rise time: 2-3 ns), flat spectral response (3-5 keV), easy acquisition, low cost, and relative large sensitive area. The characterizing data on Qiangguang-I accelerator show that this detector can satisfy the practical requirements in Z-pinch plasma diagnosis very well, which offers a promising prototype for the x-ray detection in Z-pinch diagnosis.
{alpha} Heating in a Stagnated Z-pinch
Appelbe, Brian; Chittenden, Jeremy
2009-01-21
A computational investigation of a scheme for magneto-inertial confinement fusion in a Z-pinch is carried out. In the scheme implosion of a deuterium-tritium fuel mass is preceded by formation of a hotspot containing warm, dense plasma on axis. The presence of the hotspot increases energy yield. Compression of the hotspot by the main fuel mass initiates thermonuclear burn. There is significant heating of the plasma by thermonuclear {alpha} particles which are confined by the strong magnetic field of the Z-pinch.
Physics issues relevant during stagnation phase of the Z pinch
NASA Astrophysics Data System (ADS)
Yu, Edmund
2006-10-01
Wire-array Z pinches are the most powerful laboratory x-ray sources. However, the physics driving the stagnation phase, during which the pinch collapses on axis and subsequently radiates, remains somewhat mysterious. In particular the stagnated pinch resists undergoing radiative collapse, and the radiated energy is several times the kinetic energy of the imploding plasma. In recent years, a number of theories, as well as direct 3D numerical simulation, have been developed to address these phenomena. This work will highlight some of the physics issues relevant during this complicated phase of the Z pinch. Possibilities for future work will be discussed, and, with a little luck, performed.
9th International Conference on Dense Z-Pinches
Bott-Suzuki, Simon
2015-08-31
DOE OFES supported the 9th International Conference on Z-Pinches (DZP 2014) held in Napa, CA in August 2014. Funds were used to support travel for several US students, and to disseminate information through the publication of a proceedings volume.
Z-pinch experiments on Saturn at 30 TW
NASA Astrophysics Data System (ADS)
Spielman, R. B.; Dukart, R. J.; Hanson, D. L.; Hammel, B. A.; Hsing, W. W.; Matzen, M. K.; Porter, J. L.
We have recently completed the first gas-puff z-pinch on Saturn (32 TW, 1.4 MJ, 1.9 MV, 40-ns FWHM, and 0.11 ohm). These experiments used the most powerful driver to date for fast z-pinch experiments. Saturn, a 36 module accelerator, uses a double post-hole vacuum convolute to deliver the total machine current to the load. The 10-nH Saturn z-pinch diode is capable of delivering a peak current of 10.5 MA. We diagnosed the current using segmented Rogowski coils at the insulator, resistive shunts in the vacuum transmission lines, and B-dot loops and piezoelectric pressure gauges near the load. On most shots electrical losses in the vacuum convolute were minimal with nearly complete current delivery to the z-pinch load. We have conducted experiments with deuterium, neon, argon, krypton, and xenon gas puffs. A maximum total radiation yield of 505 + or - 25 kJ was obtained with xenon. The peak keV X-ray yields were 100 + or - 5 kJ for neon K-shell radiation, 30 + or - 4 kJ for krypton L-shell radiation, and 39 + or - 4 kJ for argon K-shell radiation.
Z-pinch experiments on Saturn at 30 TW
NASA Astrophysics Data System (ADS)
Spielman, R. B.; Dukart, R. J.; Hanson, D. L.; Hammel, B. A.; Hsing, W. W.; Matzen, M. K.; Porter, J. L.
1989-12-01
We have recently completed the first gas-puff Z-pinch experiments on Saturn (32 TW, 1.4 MJ, 1.9 MV, 40-ns FWHM, and 0.11 Ω). These experiments used the most powerful driver to date for fast Z-pinch experiments. Saturn, a 36 module accelerator, uses a double post-hole vacuum convolute to deliver the total machine current to the load. The 10-nH Saturn Z-pinch diode is capable of delivering a peak current of 10.5 MA. We diagnosed the current using segmented Rogowski coils at the insulator, resistive shunts in the vacuum transmission lines, and B-dot loops and piezoelectric pressure gauges near the load. On most shots electrical losses in the vacuum convolute were minimal with nearly complete current delivery to the Z-pinch load. We have conducted experiments with deuterium, neon, argon, krypton, and xenon gas puffs. A maximum total radiation yield of 505+/-25 kJ was obtained with xenon. The peak keV x-ray yields were 100+/-5 kJ for neon L-shell radiation, 30+/-4 kJ for krypton l-shell radiation, and 39+/-4 kJ for argon K-shell radiation.
Magnetic Field Measurements in Wire-Array Z-Pinches
NASA Astrophysics Data System (ADS)
Syed, Wasif; Hammer, David; Lipson, Michal
2006-10-01
Understanding the evolution of the magnetic field topology and magnitude in the high energy density plasmas produced by wire-array Z-pinches is of critical importance for their ultimate application to stockpile stewardship and inertial confinement fusion^1. A method to determine the magnetic field profile in megampere level wire-array Z-pinches with high spatial and temporal resolution is under development. An ideal method would be passive and non-perturbing, such as Faraday rotation of laser light. We are developing a method involving temporally-resolved Faraday rotation through a sensing waveguide placed in the vicinity of, and eventually in, a wire-array Z-pinch^2. We present measurements of the magnetic field outside of a wire-array, and progress on measurements within the array. Our ideal device is a ``thin film waveguide'' coupled to an optical fiber system. While these sensing devices may not survive for long in a dense Z-pinch, they may provide useful information for a significant fraction of the current pulse. We present preliminary theoretical and experimental results. 1. M. Keith Matzen, M. A. Sweeney, R. G. Adams et al., Phys. Plasmas 12, 055503 (2005). 2. W. Syed, D. A. Hammer, M. Lipson, R. B. van Dover, AIP Proceedings of the 6th International Conference on Dense Z-Pinches, University of Oxford, UK, July 25-28, 2005. *This research was sponsored by the National Nuclear Security Administration under the Stockpile Stewardship Academic Alliances program through DOE Cooperative Agreement DE-F03-02NA00057.
Fusion burn dynamics in dense Z-pinch (DZP)
Krakowski, R.A.
1990-04-01
The fusion burn dynamics and energy yield of the dense Z-pinch (DZP) are examined using a profile-averaged, zero-dimensional, time dependent model. A range of conditions (fuel, line density, voltage, fusion-product heating, enthalpy endloss, density and temperature profiles, current rise rate, electrode impurities) are examined. Magneto-hydrodynamic stability is assumed, and initial conditions are based on those ideally existing after the melting and ionization of a solid fiber of fusion fuel. Plasma conditions required of neutron sources for materials testing ({dot S}{sub n} {ge} 10{sup 19} n/s) and for possible commercial power production (ratio of fusion energy yield to energy input, Q{sub p} {approx equal} 15, lower values if reversible recovery of a fraction of the magnetic energy is possible) are described. If f{sub B} {approx gt} 0.8 fractional fuel burnup is possible in a nominal 800-ns DT discharge (200-ns current-rise phase at 20 MV/m followed by a 500-ns constant-current crowbarred phase), reactor-relevant values of Q{sub p} may be possible. For the simpler (and shorter) constant-voltage discharge (e.g., no voltage crowbar) the value of Q{sub p} is in the range 5--10 for discharges below 200-ns duration. Smaller levels of fuel burnup, shorter discharges, or generally lower levels of Q{sub p} will require a reversible energy transfer system to meet reactor energy-balance requirements. Imposition of a plasma current rise-time constraint that may be needed for stable plasma operation (e.g., I > 10{sup 12} A/s) will burnup, Q{sub p} and discharge time to an extent where reversible energy/transfer system will be required to meet reactor energy- balance requirements. 25 refs.
Resolving microstructures in Z pinches with intensity interferometry
Apruzese, J. P.; Kroupp, E.; Maron, Y.; Giuliani, J. L.; Thornhill, J. W.
2014-03-15
Nearly 60 years ago, Hanbury Brown and Twiss [R. Hanbury Brown and R. Q. Twiss, Nature 178, 1046 (1956)] succeeded in measuring the 30 nrad angular diameter of Sirius using a new type of interferometry that exploited the interference of photons independently emitted from different regions of the stellar disk. Its basis was the measurement of intensity correlations as a function of detector spacing, with no beam splitting or preservation of phase information needed. Applied to Z pinches, X pinches, or laser-produced plasmas, this method could potentially provide spatial resolution under one micron. A quantitative analysis based on the work of Purcell [E. M. Purcell, Nature 178, 1449 (1956)] reveals that obtaining adequate statistics from x-ray interferometry of a Z-pinch microstructure would require using the highest-current generators available. However, using visible light interferometry would reduce the needed photon count and could enable its use on sub-MA machines.
Seeded perturbations in wire array z-pinches.
Robinson, Allen Conrad; Kantsyrev, Victor Leonidovich; Wunsch, Scott Edward; Oliver, Bryan Velten; Lebedev, Sergey V.; Safronova, Alla S.; Maxwell, J.; McKenney, John Lee; Ampleford, David J.; Rapley, J.; Bott, S. C.; Palmer, J. B. A.; Bland, Simon Nicholas; Jones, Brent Manley; Chittenden, Jeremy Paul; Garasi, Christopher Joseph; Hall, Gareth Neville; Mehlhorn, Thomas Alan; Deeney, Christopher
2004-11-01
The impact of 3D structure on wire array z-pinch dynamics is a topic of current interest, and has been studied by the controlled seeding of wire perturbations. First, Al wires were etched at Sandia, creating 20% radial perturbations with variable axial wavelength. Observations of magnetic bubble formation in the etched regions during experiments on the MAGPIE accelerator are discussed and compared to 3D MHD modeling. Second, thin NaF coatings of 1 mm axial extent were deposited on Al wires and fielded on the Zebra accelerator. Little or no axial transport of the NaF spectroscopic dopant was observed in spatially resolved K-shell spectra, which places constraints on particle diffusivity in dense z-pinch plasmas. Finally, technology development for seeding perturbations is discussed.
X-ray results from a modified nozzle and double gas puff z pinch
Chang, T.; Fisher, A.; Van Drie, A. )
1991-03-15
The nozzle and the anode of the UCI (University of California, Irvine) {ital z}-pinch facility were modified to study the influence of the anode-cathode geometrical structure on the stability of the pinch and the x-ray yield of the pinch. The anode was modified from a honey-comb to a hollow cylinder with a 4-cm diameter and a {similar to}3.5-mm wall thickness, placed 2 cm below the cathode. The cavity in the center of the cathode was enlarged from 6-mm diameter to 36 mm. The design of the cathode and the anode showed a marked improvement of the pinch stability over the previous design. Both zirconium and carbon-carbon nozzle were used for the Kr and Ne {ital z} pinches. After a few tens of shots the Zr nozzle was melted at the edge and the pinch degraded, while the carbon-carbon nozzle did not sustain any damage for more than 300 shots. Some shots showed the {ital di}/{ital dt} at the implosion is {similar to}5 times higher than the {ital di}/{ital dt} at the beginning of the discharge, this has never been obtained at UCI before. This ratio of the initial {ital di}/{ital dt} to pinch {ital di}/{ital dt} is a measure of the pinch quality. By serendipity it was found that double gas puff {ital z} pinch increased the hard x-ray ({gt}1 keV) output by about an order of magnitude. The nozzle was then modified to allow double puff operation. A 3.4-mm-diam hole was opened at the center of the nozzle and a plunger was inserted from the top to control the mass of the gas entering the hole. The diagnostics include {ital di}/{ital dt} coil, soft, and hard x-ray diodes. Soft and hard x-ray emission are both enhanced by the double gas puff {ital z} pinch.
Radiating Shock Properties in the Z-pinch Dynamic Hohlraum
Rochau, Gregory A.; Bailey, J. E.; Chandler, G.; Lemke, R.; Peterson, K.; Slutz, S.; Maron, Y.; Fisher, V.; Stambulchik, E.; MacFarlane, J.
2009-09-10
The Z-pinch dynamic hohlraum is a high-power x-ray source used for a variety of high energy-density physics applications including high temperature opacity measurements and inertial confinement fusion (ICF). The system consists of a tungsten wire-array Z pinch that implodes onto a low-density CH{sub 2} foam launching a radiating shock that heats the hohlraum to radiation temperatures >200 eV. The temperature and density evolution of this shock have been inferred through the measurement of time- and space-resolved line emission from Si atoms locally doped in the CH{sub 2} foam. The observed emission spectra are analyzed through comparison to collisional-radiative calculations that include a detailed treatment of line-shapes and the effect of non-local radiation on the atomic level populations. As a complement to the detailed spectral data, the radial and azimuthal distribution of the axially directed shock emission is recorded with time-gated x-ray pinhole images that provide information on the spatial profile of the shock conditions. Together with broadband x-ray power measurements, these data provide a comprehensive suite of information to determine the shock dynamics and associated energetics of the Z-pinch dynamic hohlraum.
Characterization of Z-Pinch Driven Hohlraum Radiation Sources*
NASA Astrophysics Data System (ADS)
Porter, J. L.; Chandler, G. A.; Deeney, C.; Fehl, D. L.; Noack, D. D.; Olson, R. E.; Ruggles, L. E.; Seaman, J. F.; Spielman, R. B.; Torres, J. A.; Vargas, M. F.; Bartlett, R. J.; Benage, J. F., Jr.; Idzorek, G. C.
1996-11-01
We have developed a z-pinch-driven soft x-ray radiation source that is near-Planckian in spectral shape and very uniform over spatial dimensions of several millimeters. We create this radiation source by surrounding a z-pinch implosion with a high-Z radiation case (a hohlraum). This experimental arrangement is referred to as the =B3vacuum hohlraum=B2 configuration. We have measured hohlraum temperatures of greater than 75 eV which last for 10=B9s of nanoseconds using the 7-MA Saturn accelerator. We will begin z-pinch experiments this fall using the 16-MA PBFA-Z accelerator. The PBFA-Z driver will be able to produce hohlraums with radiation temperatures well in excess of 100 eV. In this presentation we will describe measurements of the time history of the x-ray power, spectrum, and spatial uniformity of hohlraums produced using the Saturn accelerator. We will also present preliminary measurements of the radiation temperature of hohlraums created using the recently commissioned PBFA-Z accelerator. *This work supported by the U.S. Department of Energy under contract DE-AC04-94AL85000.
Argon z-pinch implosions on Phoenix
Fisher, A.; Peterson, G.; Nolting, E.
1995-12-31
Upgrades to the Phoenix front end have resulted in a three-fold increase in Argon K-shell x-ray yields. Lack of a transit time isolator between the center conductor and ground necessitated powering the gas-puff hardware with batteries and supplying control via fiber optic cables. A simple gas flow model was developed to optimize the valve/nozzle design. The gas-puff valve and nozzle were modified to produce a 250-{micro}s density rise time. This short rise-time allowed firing on the gas plateau which improved reproducibility. Front end power flow was improved by opening the MITL from 8 to 10-mm and by increasing the dog-leg at the nozzle to obstruct UV light. The highest yield shots were achieved with a 4-cm long load using a 3.5-cm mean diameter nozzle with a mean inward tilt of 13.75 degrees. X-ray pulse widths ranged between 7--15 ns and x-ray pinhole photos suggest uniform assembly on axis. Results and documentation of the Phoenix upgrades are presented.
History of HERMES III diode to z-pinch breakthrough and beyond :
Sanford, Thomas Williamlou.
2013-04-01
HERMES III and Z are two flagship accelerators of Sandias pulsed-power program developed to generate intense -ray fields for the study of nuclear radiation effects, and to explore high energy-density physics (including the production of intense x-ray fields for Inertia Confinement Fusion [ICF]), respectively. A diode at the exit of HERMES III converts its 20-MeV electron beam into -rays. In contrast, at the center of Z, a z-pinch is used to convert its 20-MA current into an intense burst of x-rays. Here the history of how the HERMES III diode emerged from theoretical considerations to actual hardware is discussed. Next, the reverse process of how the experimental discovery of wire-array stabilization in a z-pinch, led to a better theory of wirearray implosions and its application to one of the ICF concepts on Z--the DH (Dynamic Hohlraum) is reviewed. Lastly, the report concludes with how the unexpected axial radiation asymmetry measured in the DH is understood. The first discussion illustrates the evolution of physics from theory-to-observationto- refinement. The second two illustrate the reverse process of observationto- theory-to refinement. The histories are discussed through the vehicle of my research at Sandia, illustrating the unique environment Sandia provides for personal growth and development into a scientific leader.
Ion Beam Driven Shock Device Using Accelerated High Density Plasmoid by Phased Z-Pinch
NASA Astrophysics Data System (ADS)
Horioka, Kazuhiko; Aizawa, Tatsuhiko; Tsuchida, Minoru
1997-07-01
Different from three methods to generate high shock pressure by acceleration of high density plasma or particles (intense ion beams, plasma gun and rail gun) having their intrinsic deficiencies, new frontier is proposed to propel the shock physics and chemistry by using the high density plasma. In the present paper, new scheduled Z-pinch method is developed as a new device to generate high shock pressure. In the present method, plasma density can be compressed to the order of 10^18 to 10^19 cm-3, and high density plasma can be accelerated by zippering together with axial shock pressure, resulting in high-velocity launching of flyer. In the present paper, systematic experimental works are performed to demonstrate that high energy plasma flow can be electro-magnetically driven by the scheduled capillary Z-pinch, and to characterize the ion velocity and its current density. The estimated value of ion speed from the plasma-measurement reaches to 7 x 10^7 cm/s corresponding to 70 to 100 KeV for Ar. Copper flyer can be shot with the velocity range from 1km/s to 3km/s in the standard condition.
Z-Pinch fusion-based nuclear propulsion
NASA Astrophysics Data System (ADS)
Miernik, J.; Statham, G.; Fabisinski, L.; Maples, C. D.; Adams, R.; Polsgrove, T.; Fincher, S.; Cassibry, J.; Cortez, R.; Turner, M.; Percy, T.
2013-02-01
Fusion-based nuclear propulsion has the potential to enable fast interplanetary transportation. Due to the great distances between the planets of our solar system and the harmful radiation environment of interplanetary space, high specific impulse (Isp) propulsion in vehicles with high payload mass fractions must be developed to provide practical and safe vehicles for human space flight missions. The Z-Pinch dense plasma focus method is a Magneto-Inertial Fusion (MIF) approach that may potentially lead to a small, low cost fusion reactor/engine assembly [1]. Recent advancements in experimental and theoretical understanding of this concept suggest favorable scaling of fusion power output yield [2]. The magnetic field resulting from the large current compresses the plasma to fusion conditions, and this process can be pulsed over short timescales (10-6 s). This type of plasma formation is widely used in the field of Nuclear Weapons Effects testing in the defense industry, as well as in fusion energy research. A Z-Pinch propulsion concept was designed for a vehicle based on a previous fusion vehicle study called "Human Outer Planet Exploration" (HOPE), which used Magnetized Target Fusion (MTF) [3] propulsion. The reference mission is the transport of crew and cargo to Mars and back, with a reusable vehicle. The analysis of the Z-Pinch MIF propulsion system concludes that a 40-fold increase of Isp over chemical propulsion is predicted. An Isp of 19,436 s and thrust of 3812 N s/pulse, along with nearly doubling the predicted payload mass fraction, warrants further development of enabling technologies.
Radiating Shock Measurements in the Z-Pinch Dynamic Hohlraum
Rochau, G. A.; Bailey, J. E.; Chandler, G. A.; Lemke, R. W.; Peterson, K. J.; Slutz, S. A.; Maron, Y.; Fisher, D. V.; Fisher, V. I.; Stambulchik, E.; Dunham, G. S.; MacFarlane, J. J.; Schroen, D. G.
2008-03-28
The Z-pinch dynamic hohlraum is an x-ray source for high energy-density physics studies that is heated by a radiating shock to radiation temperatures >200 eV. The time-dependent 300-400 eV electron temperature and 15-35 mg/cc density of this shock have been measured for the first time using space-resolved Si tracer spectroscopy. The shock x-ray emission is inferred from these measurements to exceed 50 TW, delivering >180 kJ to the hohlraum.
Nonlinear Rayleigh-Taylor instabilities in fast Z pinches
Miles, Aaron R.
2009-03-15
A simplified analytic model is presented to describe the implosion of a plasma column by an azimuthal magnetic field of sufficient magnitude to drive a strong shock wave into the plasma. This model is employed together with buoyancy-drag-based models of nonlinear single-mode and turbulent multimode Rayleigh-Taylor growth to investigate the mixing process in such fast Z pinches. These models give predictions that characterize limitations the instability can impose on the implosion in terms of maximum convergence ratios attainable for an axially coherent pinch. Both the implosion and instability models are validated with results from high-resolution numerical simulations.
NASA Astrophysics Data System (ADS)
Subhash, P. V.; Madhavan, S.; Sakthivel, N.; Mishra, V.; Majalee, Aaditya V.; Pahari, P.; Chaturvedi, S.
2011-08-01
This paper reports a computational optimization study for an inverse z-pinch magnetized target fusion system (MTF). This has been carried out by varying various parameters such as the magnetizing current, the initial liner radius and thickness, liner length, etc. One-dimensional (1D) magneto-hydrodynamic (MHD) calculations are used for this purpose. Capacitor bank parameters are held constant, as is also the inner conductor radius. The Kadomtsev stability parameter Q0 is kept constant at 0.9 and the maximum plasma β at 0.4. The optimization study has yielded several parametric sets with an energy gain of more than unity, i.e. fusion energy output that exceeds the initial energy in the capacitor bank. A physical explanation for the local optimal points is provided through an energy flow analysis. For one case with energy gain exceeding unity, a simple liner stability analysis has been performed. This involves analytical calculations of the time points at which different liner modes become unstable. For these analytical studies, time-dependent parameters, such as liner acceleration, effective thickness of the liner region that still remains solid, and effective material strength, are obtained from 1D MHD simulations.
Axial Instability Growth in Tungsten Wire Array Z-Pinches
NASA Astrophysics Data System (ADS)
Cahill, Adam; Knapp, Patrick; Greenly, John; Pikuz, Sergei; Shelkovenko, Tania; Hammer, David
2010-11-01
The individual exploding wires in wire array z-pinches have been shown to suffer from axially non-uniformity beginning from the moment of plasma formation. This non-uniformity grows in amplitude and wavelength until it reaches what appears to be a material dependent wavelength at the time array implosion begins. Previous work by Knapp et al. [1] studied the temporal evolution of this instability in aluminum wire arrays. We have extended that work to include the evolution of tungsten wire array instabilities. Time gated laser shadowgraphy is used to track wavelength and amplitude over a series of shots to develop a record of the instability's growth. We attempt to identify array parameters which significantly contribute to the growth of this instability. [4pt] [1] Knapp, P. F., J. B. Greenly, P. A. Gourdain, C. L. Hoyt, M. R. Martin, S. A. Pikuz, C. E. Seyler, T. A. Shelkovenko, and D. A. Hammer. ``Growth and Saturation of the Axial Instability in Low Wire Number Wire Array Z Pinches.'' Physics of Plasmas 17 (2010). Web.
Simulation of Wire-Array Z Pinches with ALEGRA
NASA Astrophysics Data System (ADS)
Chantrenne, Sophie; Bliss, David; Cochrane, Kyle; Coverdale, Christine; Deeney, Chris; Hall, Clint; Haill, Thomas; Jones, Brent; Lepell, Paul; Oliver, Bryan; Sinars, Daniel
2006-10-01
Wire-array z pinches provide the x-ray radiation drive for Inertial Confinement Fusion Experiments at Sandia National Laboratories. A physical understanding of the physics of wire-array z pinches is important in providing a future radiation source capable of driving high-yield fusion capsules. Modeling of wire-array implosions on the Z machine were performed using the 2-D radiation MHD code Alegra. These new calculations use more accurate initial conditions that are more representative of the experimental data, allowing us to model the implosion through stagnation, to avoid radiation collapse, and to generate a radiation pulse that compares well with data. Code predictions will be compared with tungsten & aluminum wire-array data from Z. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U.S. Department of Energy under Contract No. DE-AC04- 94AL85000. a Ktech Corporation, 1300 Eubank Blvd. S.E., Albuquerque, NM 87123-3336
D-D fusion experiments using fast z pinches
Spielman, R.B.; Baldwin, G.T.; Cooper, G.
1994-04-01
The development of high current (I > 10 MA) drivers provides us with a new tool for the study of neutron-producing plasmas in the thermal regime. The imploded deuterium mass (or collisionality) increases as I{sup 2} and the ability of the driver to heat the plasma to relevant fusion temperatures improves as the power of the driver increases. Additionally, fast (< 100 ns) implosions are more stable to the usual MHD instabilities that plagued the traditional slower implosions. We describe experiments in which deuterium gas puffs or CD{sub 2} fiber arrays were imploded in a fast z-pinch configuration on Sandia`s Saturn facility generating up to 3 {times} 10{sup 12} D-D neutrons. These experiments were designed to explore the physics of neutron-generating plasmas in a z-pinch geometry. Specifically, we intended to produce neutrons from a nearly thermal plasma where the electrons and ions have a nearly Maxwellian distribution. This is to be clearly differentiated from the more usual D-D beam-target neutrons generated in many dense plasma focus (DPF) devices.
D-D fusion experiments using fast Z pinches
Spielman, R.B.; Baldwin, G.T.; Cooper, G.
1998-03-01
The development of high current (I > 10 MA) drivers provides the authors with a new tool for the study of neutron-producing plasmas in the thermal regime. The imploded deuterium mass (or collisionality) increases as I{sup 2} and the ability of the driver to heat the plasma to relevant fusion temperatures improves as the power of the driver increases. Additionally, fast (<100 ns) implosions are more stable to the usual MHD instabilities that plagued the traditional slower implosions. The authors describe experiments in which deuterium gas puffs or CD{sub 2} fiber arrays were imploded in a fast z-pinch configuration on Sandia`s Saturn facility generating up to 3 {times} 10{sup 12} D-D neutrons. These experiments were designed to explore the physics of neutron-generating plasmas in a z-pinch geometry. Specifically, the authors intended to produce neutrons from a nearly thermal plasma where the electrons and ions have a nearly Maxwellian distribution. This is to be clearly differentiated from the more usual D-D beam-target neutrons generated in many dense plasma focus (DPF) devices.
NASA Astrophysics Data System (ADS)
Klir, Daniel
2007-03-01
This thesis presents the results of fibre Z-pinch experiments carried out on the Z-150 device at the CTU in Prague. The generator that was used to drive the experiments consisted of one capacitor of 3e-6 F capacitance. In the case of 20 kV charging voltage, the current was peaking at 80 kA with a 850 ns quarter period. The Z-pinch was formed from carbon fibres of 15 micrometer diameter and 1 cm length. The discharge was observed by a large number of diagnostic tools. This comprehensive set of diagnostics enabled us to describe the gross dynamics of the Z-pinch. It was found out that after the breakdown a low density coronal plasma was formed while the fibre diameter remained almost unchanged. This low density corona was carrying almost all the current of the order of 10 kA. When the current had built up, the implosion of the corona onto the central fibre occurred. The implosion velocity approached the value of 2e5 m/s. When the imploded corona had reached the fibre, the dip in dI/dt, voltage peak up to 10 kV, and XUV pulse of a 10-30 ns width were observed. XUV radiation was emitted from several bright spots which corresponded to the interaction of m=0 instability necks with the dense core. The electron temperature and density were approximately 80 eV and 10e25 per cubic meter, respectively. Although the presence of a fibre did not significantly suppress MHD instabilities, they were not disruptive. After the fibre ablation, i.e. after 500 ns, material evaporated from electrodes started to play a dominant role. The observed plasma column seemed to be MHD unstable and when m=0 instabilities had developed, X-ray pulses were emitted from several hot spots, particularly near the anode. At that time the voltage peak of up to 30 kV was detected.
A kind of fast shutter for Z pinch diagnosis device
NASA Astrophysics Data System (ADS)
Wang, Liangping; Zhang, Xinjun; Sun, Tieping; Mao, Wentin
2016-09-01
A kind of fast shutter for protecting the diagnosis devices in Z pinch experiments is introduced in this paper. The shutter is composed of a pulling rod, a magnetic core, and a solenoid. Different from the traditional coils which were used at the voltage of 220 V, the solenoid we used must endure the high voltage of 5-10 kV and the deformation which maybe caused by the 5-10 T intense magnetic field. A creative configuration for the solenoid is developed including the winding guide, insulating sleeve, and stainless-steel sleeve. The experimental results show that the configuration of the solenoid is effective. The velocity of the valve is nearly 19 m/s and the time jitter of the shutdown is within 75 μs.
Spectroscopic study of z-pinch stagnation on Z.
Maron, Yitzhak; Weingarten, L.; Starobinets, A.; Fisher, V.; Jennings, Christopher A.; Ampleford, David J.; Bailey, James E.; Yu, Edmund P.; Bernshtam, V.; Cuneo, Michael Edward; Rochau, Gregory Alan; Coverdale, Christine Anne; Jones, Brent Manley; Hansen, Stephanie B.
2010-11-01
Fast z-pinches provide intense 1-10 keV photon energy radiation sources. Here, we analyze time-, space-, and spectrally-resolved {approx}2 keV K-shell emissions from Al (5% Mg) wire array implosions on Sandia's Z machine pulsed power driver. The stagnating plasma is modeled as three separate radial zones, and collisional-radiative modeling with radiation transport calculations are used to constrain the temperatures and densities in these regions, accounting for K-shell line opacity and Doppler effects. We discuss plasma conditions and dynamics at the onset of stagnation, and compare inferences from the atomic modeling to three-dimensional magneto-hydrodynamic simulations.
Tungsten Z-Pinch Long Implosions on the Saturn Generator
DOUGLAS,MELISSA R.; DEENEY,CHRISTOPHER; SPIELMAN,RICK B.; COVERDALE,CHRISTINE A.; RODERICK,N.F.; HAINES,M.G.
1999-11-05
Recent success on the Saturn and Z accelerators at Sandia National Laboratories have demonstrated the ability to scale z-pinch parameters to increasingly larger current pulsed power facilities. Next generation machines will require even larger currents (>20 MA), placing further demands on pulsed power technology. To this end, experiments have been carried out on Saturn operating in a long pulse mode, investigating the potential of lower voltages and longer implosion times while still maintaining pinch fidelity. High wire number, 25 mm diameter tungsten arrays were imploded with implosion times ranging from 130 to 240 ns. The results were comparable to those observed in the Saturn short pulse mode, with risetimes on the order of 4.5 to 6.5 ns. Experimental data will be presented, along with two dimensional radiation magnetohydrodynamic simulations used to explain and reproduce the experiment.
Light detonation wave in a cylindrical Z-pinch
NASA Astrophysics Data System (ADS)
Yusupaliev, U.; Sysoev, N. N.; Shuteev, S. A.; Elenskii, V. G.
2015-09-01
A secondary compression wave previously observed by other researchers in a cylindrical Z-pinch has been identified in this work as a light detonation wave. It appears on the inner surface of a discharge chamber under the action of the intense ultraviolet radiation from a plasma pinch at the stage of its maximum compression. The condition of the light detonation wave has been determined experimentally. The dependence of its Mach number on a generalized dimensionless variable has been determined taking into account the conservation laws for the light detonation wave including the pressure of the gas, expenses on the formation of the surface plasma, and the energy of ionization of the gas involved in the wave. An analogy with the laser-supported detonation wave created by intense laser radiation has been revealed. The indicated dependence is within the error of measurement in agreement with the experimental data for light detonation waves created by both methods.
Conceptual Design of a Z-Pinch Fusion Propulsion System
NASA Technical Reports Server (NTRS)
Adams, Robert; Polsgrove, Tara; Fincher, Sharon; Fabinski, Leo; Maples, Charlotte; Miernik, Janie; Stratham, Geoffrey; Cassibry, Jason; Cortez, Ross; Turner, Matthew; Santarius, John; Percy, Thomas
2010-01-01
This slide presentation reviews a project that aims to develop a conceptual design for a Z-pinch thruster, that could be applied to develop advanced thruster designs which promise high thrust/high specific impulse propulsion. Overviews shows the concept of the design, which use annular nozzles with deuterium-tritium (D-T) fuel and a Lithium mixture as a cathode, Charts show the engine performance as a function of linear mass, nozzle performance (i.e., plasma segment trajectories), and mission analysis for possible Mars and Jupiter missions using this concept for propulsion. Slides show views of the concepts for the vehicle configuration, thrust coil configuration, the power management system, the structural analysis of the magnetic nozzle, the thermal management system, and the avionics suite,
Gas Puff Preionization For Improved X-ray Yield from Z-Pinch Plasma Radiating Sources
NASA Astrophysics Data System (ADS)
Moosman, B.; Commisso, R. J.; Fisher, A.; Stephanakis, S. J.; Weber, B. V.
1998-11-01
Azimuthally symmetric preionization via peripheral UV illumination is suggested as a method for improving x-ray yield in gas puff z-pinches. UV gas preionization was characterized via high-sensitivity interferometry and deployed on the DECADE MODULE 2 (DM2). The UV preionization is provided by a high-current, 40-kA, surface discharge on the inner diameter of a ring located near the gas puff and produces 1-10 % gas ionization. Early experiments on DM2 indicated that UV preionization may eliminate sporadic low x-ray yield shots from a series of similar initial condition shots. E-beam preionization using a single carbon brush, pointed perpendicular to the gas flow, was also characterized. The use of multiple high impedance e-beam guns for gas preionization presents a possible alternative to high current UV preionization.
Circuit model for the inverse Z-pinch wire array switch.
Waisman, Eduardo Mario; Cuneo, Michael Edward; Harvey-Thompson, A.; Lebedev, Sergey V.
2010-06-01
A 0D circuit code is introduced to study the wire array switch concept introduced in. It has been implemented and researched at Imperial College. An exploding wire array, the switch, is in parallel with the load, an imploding wire array. Most of the current flows in the exploding array until it expands and becomes highly resistive. The 0D code contains simple models of Joule energy deposition and plasma expansion for W and Al wires. The purpose of the device is to produce fast Z-pinch implosion, below 100ns on MAGPIE and the Sandia Z machine. Self and mutual inductances are taken into consideration as well as the rocket model for wire ablation. The switch characteristics of the exploding array are prescribed and tuned up to agree with MAGPIE shots. The dependence of the device on the configuration of the arrays is studied and scaling to ZR conditions is explored.
Magnetohydrodynamic simulation of solid-deuterium-initiated Z-pinch experiments
Sheehey, P.T.
1994-02-01
Solid-deuterium-initiated Z-pinch experiments are numerically simulated using a two-dimensional resistive magnetohydrodynamic model, which includes many important experimental details, such as ``cold-start`` initial conditions, thermal conduction, radiative energy loss, actual discharge current vs. time, and grids of sufficient size and resolution to allow realistic development of the plasma. The alternating-direction-implicit numerical technique used meets the substantial demands presented by such a computational task. Simulations of fiber-initiated experiments show that when the fiber becomes fully ionized rapidly developing m=0 instabilities, which originated in the coronal plasma generated from the ablating fiber, drive intense non-uniform heating and rapid expansion of the plasma column. The possibility that inclusion of additional physical effects would improve stability is explored. Finite-Larmor-radius-ordered Hall and diamagnetic pressure terms in the magnetic field evolution equation, corresponding energy equation terms, and separate ion and electron energy equations are included; these do not change the basic results. Model diagnostics, such as shadowgrams and interferograms, generated from simulation results, are in good agreement with experiment. Two alternative experimental approaches are explored: high-current magnetic implosion of hollow cylindrical deuterium shells, and ``plasma-on-wire`` (POW) implosion of low-density plasma onto a central deuterium fiber. By minimizing instability problems, these techniques may allow attainment of higher temperatures and densities than possible with bare fiber-initiated Z-pinches. Conditions for significant D-D or D-T fusion neutron production may be realizable with these implosion-based approaches.
Current redistribution and generation of kinetic energy in the stagnated Z pinch.
Ivanov, V V; Anderson, A A; Papp, D; Astanovitskiy, A L; Talbot, B R; Chittenden, J P; Niasse, N
2013-07-01
The structure of magnetic fields was investigated in stagnated wire-array Z pinches using a Faraday rotation diagnostic at the wavelength of 266 nm. The distribution of current in the pinch and trailing material was reconstructed. A significant part of current can switch from the main pinch to the trailing plasma preheated by x-ray radiation of the pinch. Secondary implosions of trailing plasma generate kinetic energy and provide enhanced heating and radiation of plasma at stagnation. Hot spots in wire-array Z pinches also provide enhanced radiation of the Z pinch. A collapse of a single hot spot radiates 1%-3% of x-ray energy of the Z pinch with a total contribution of hot spots of 10%-30%.
Electromagnetic Wave Propagation Through the ZR Z-Pinch Accelerator
Rose, D. V.; Welch, D. R.; Madrid, E. A.; Miller, C. L.; Clark, R. E.; Stygar, W. A.; Struve, K.; Corcoran, P. A.; Whitney, B.
2009-01-21
A fully three-dimensional electromagnetic model of the major pulsed power components of the 26-MA ZR accelerator is presented. This large-scale simulation model tracks the evolution of electromagnetic waves through the intermediate storage capacitors, laser-triggered gas switches, pulse-forming lines, water switches, tri-plate transmission lines, and water convolute to the vacuum insulator stack. The plates at the insulator stack are coupled to a transmission line circuit model of the four-level magnetically-insulated transmission line section and post-hole convolutes. The vacuum section circuit model is terminated by either a short-circuit load or dynamic models of imploding z-pinch loads. The simulations results are compared with electrical measurements made throughout the ZR accelerator and good agreement is found, especially for times before and up to peak load power. This modeling effort represents new opportunities for modeling existing and future large-scale pulsed power systems used in a variety of high energy density physics and radiographic applications.
Viscous Heating At Stagnation In Z-Pinches
Haines, M. G.
2009-01-21
The viscous heating associated with m = 0 MHD instabilities in the stagnated Z-pinch is developed further. It would appear that the larger numerical (Neumann) viscosity plus De Bar corrections in simulation codes to yield energy conservation might be another way of representing viscous heating, but in this case the viscosity is inserted to smooth shock discontinuities. However the viscous heating per unit volume appears to be independent of the coefficient of viscosity itself because the fastest growing MHD mode is itself determined by the viscous damping. Therefore it could be argued that, though the correct physics is not in the codes, the resulting heating is not sensitive to the fact that numerical viscosity instead is employed. In addition, by chance, the model of magnetic bubbles first introduced by Lovberg et al. and Riley et al., and later by Rudakov et al. to explain phenomenologically extra heating of the ions leads to the same heating rate as in Haines et al. For the stainless steel array in which T{sub i} was predicted and measured to be >200 KeV while T{sub e} = 3 KeV the ion viscous heating is dominant. However, for the low current experiment by Kroupp et al. in which the ion kinematic viscosity is much smaller than the resistive diffusivity there is resistive damping of MHD modes, and no ions viscous heating should be expected.
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.
Diagnostics for Z-pinch implosion experiments on PTS
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.
2014-12-15
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.
Analytic model for the dynamic Z-pinch
Piriz, A. R. Sun, Y. B.; Tahir, N. A.
2015-06-15
A model is presented for describing the cylindrical implosion of a shock wave driven by an accelerated piston. It is based in the identification of the acceleration of the shocked mass with the acceleration of the piston. The model yields the separate paths of the piston and the shock. In addition, by considering that the shocked region evolves isentropically, the approximate profiles of all the magnitudes in the shocked region are obtained. The application to the dynamic Z-pinch is presented and the results are compared with the well known snowplow and slug models which are also derived as limiting cases of the present model. The snowplow model is seen to yield a trajectory in between those of the shock and the piston. Instead, the neglect of the inertial effects in the slug model is seen to produce a too fast implosion, and the pressure uniformity is shown to lead to an unphysical instantaneous piston stopping when the shock arrives to the axis.
Implicit XMHD Modeling of Fast Z-Pinches
NASA Astrophysics Data System (ADS)
Martin, Matthew
2013-10-01
The numerical modeling of fast Z-Pinches as applied to magnetically driven inertial confinement fusion concepts is typically performed under the resistive- magnetohydrodynamic (MHD) model. We derive the limitations of this model as currently applied to modeling such targets and present numerical test problems that demonstrate the physical error introduced through the approximations inherent in resistive-MHD. We then compare the resistive-MHD model to simulations utilizing new implicit algorithms for the efficient solution of the extended-magnetohydrodynamic (XMHD) system of equations. Herein we define XMHD as a quasi-neutral electro-magnetic two-fluid model. We present specific examples where the XMHD system of equations is required for modeling magnetically driven ICF targets if large physical errors are to be avoided in the numerical solution of the system. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
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.
2006-01-05
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 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-{theta} simulations are used to highlight some experimental results and understand the plasma conditions during these microsecond wire arrays implosions.
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.
Comparison of 1D stagnation solutions to 3D wire-array Z pinch simulations in absence of radiation
NASA Astrophysics Data System (ADS)
Yu, Edmund; Velikovich, Alexander; Maron, Yitzhak
2013-10-01
In the idealized picture of a Z pinch, a cylindrically symmetric plasma shell implodes towards axis. In this 1D (radial) picture, the resulting stagnation is very efficient: all the kinetic energy of the shell converts to internal energy, as for instance in the Noh shock solution or the homogeneous stagnation flow. If we generalize the problem to 2D by deforming the shell from perfectly circular to oblate, the resulting stagnation will not be as efficient. As in the Hiemenz flow, in which a jet of fluid strikes a rigid flat boundary and squirts out to the sides, the more complicated flows allowed in 2D allow flow kinetic energy to redirect rather than stagnate. With this picture in mind, we might expect the stagnation of a wire-array Z pinch, which in actuality forms a highly distorted 3D imploding plasma, to dissipate its kinetic energy inefficiently due to the lack of symmetry, and be indescribable by means of the idealized 1D stagnation solutions. On the other hand, one might expect that if the imploding plasma is sufficiently messy, the non-uniformities might ``wash out,'' allowing a quasi-1D description of the averaged quantities of plasma. In this work we explore this idea, comparing predictions of 1D stagnation solutions with 3D simulation. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC0 4-94AL85000.
Development of laser-based diagnostics for 1-MA z-pinch plasmas
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; Hakel, P.; Mancini, R. C.; Wiewior, P.; Presura, R.; Kindel, J. M.; Shevelko, A. P.; Chalyy, O.; Astanovitskiy, A.; Haboub, A.; Altemara, S. D.; Papp, D.; Durmaz, T.
2009-11-01
The 50 TW Leopard laser coupled with the 1-MA Zebra generator was used for development of new diagnostics of z-pinch plasmas. Two plasma diagnostics are presented: an x-ray broadband backlighting for z-pinch absorption spectroscopy and parametric two-plasmon decay of the laser beam in dense z-pinch plasma. Implementation of new diagnostics on the Zebra generator and the first results are discussed. The absorption spectroscopy is based on backlighting of z-pinch plasma with a broadband x-ray radiation from a Sm laser plasma. Detailed analysis of the absorption spectra yields the electron temperature and density of z-pinch plasma at the non-radiative stage. The parametric two-plasmon decay of intensive laser radiation generates 3/2φ and 1/2φ harmonics. These harmonics can be used to derive a temperature of z-pinch plasma with the electron density near the quarter of critical plasma density.
Theoretical z -pinch scaling relations for thermonuclear-fusion experiments.
Stygar, W A; Cuneo, M E; Vesey, R A; Ives, H C; Mazarakis, M G; Chandler, G A; Fehl, D L; Leeper, R J; Matzen, M K; McDaniel, D H; McGurn, J S; McKenney, J L; Muron, D J; Olson, C L; Porter, J L; Ramirez, J J; Seamen, J F; Speas, C S; Spielman, R B; Struve, K W; Torres, J A; Waisman, E M; Wagoner, T C; Gilliland, T L
2005-08-01
We have developed wire-array z -pinch scaling relations for plasma-physics and inertial-confinement-fusion (ICF) experiments. The relations can be applied to the design of z -pinch accelerators for high-fusion-yield (approximately 0.4 GJ/shot) and inertial-fusion-energy (approximately 3 GJ/shot) research. We find that (delta(a)/delta(RT)) proportional (m/l)1/4 (Rgamma)(-1/2), where delta(a) is the imploding-sheath thickness of a wire-ablation-dominated pinch, delta(RT) is the sheath thickness of a Rayleigh-Taylor-dominated pinch, m is the total wire-array mass, l is the axial length of the array, R is the initial array radius, and gamma is a dimensionless functional of the shape of the current pulse that drives the pinch implosion. When the product Rgamma is held constant the sheath thickness is, at sufficiently large values of m/l, determined primarily by wire ablation. For an ablation-dominated pinch, we estimate that the peak radiated x-ray power P(r) proportional (I/tau(i))(3/2)Rlphigamma, where I is the peak pinch current, tau(i) is the pinch implosion time, and phi is a dimensionless functional of the current-pulse shape. This scaling relation is consistent with experiment when 13 MA < or = I < or = 20 MA, 93 ns < or = tau(i) < or = 169 ns, 10 mm < or = R < or = 20 mm, 10 mm < or = l < or = 20 mm, and 2.0 mg/cm < or = m/l < or = 7.3 mg/cm. Assuming an ablation-dominated pinch and that Rlphigamma is held constant, we find that the x-ray-power efficiency eta(x) congruent to P(r)/P(a) of a coupled pinch-accelerator system is proportional to (tau(i)P(r)(7/9 ))(-1), where P(a) is the peak accelerator power. The pinch current and accelerator power required to achieve a given value of P(r) are proportional to tau(i), and the requisite accelerator energy E(a) is proportional to tau2(i). These results suggest that the performance of an ablation-dominated pinch, and the efficiency of a coupled pinch-accelerator system, can be improved substantially by decreasing the
Stand-off energy sources for Z-pinch implosions
Ryutov, D; Toor, A
1999-07-12
An issue of stand-off energy sources is in an early stage of development. Several concepts have been identified as potential solution of the problem. Those based on the total disconnection between the target assembly and the primary energy source have an obvious advantage in that they allow one to relatively easily protect the permanent part. Indeed, a fast projectile travelling at the velocity of 10 km/s covers the distance of 10 m in 1 ms, the time that is sufficient to mechanically shield the line of site. Auxiliary power supply in the form of an electron beam can be protected by using a magnetic wiggling in the transport channel in the permanent part of the facility. Of some help is also the fact that this auxiliary source operates 10 or so microseconds before the fusion energy release occurs. Another advantage of this approach is related to its compatibility with high rep-rate mode, up to tens pulses per second (because there is no need to insert heavy large-volume parts into the reaction chamber). An obvious disadvantage is that the assembly should contain a more or less complex on-board circuitry. Those concepts that are based on the direct mechanical connection between the external pulse-forming line and the disposable inner part of the transmission line (connected in turn to the Z-pinch diode) have an obvious advantage in eliminating any intermediate steps in delivering the energy to the pinch. They work essentially as the presently used Z-pinch devices and should provide the same high efficiency. A difficulty of this approach is related to the presence of the insulating slot in the walls of the reaction chamber that directly links the disposable inner part of the energy transmission system and permanent external energy source. The slot is vulnerable to mechanical perturbations and neutron irradiation that may propagate into the permanent part of the source and cause a damage to it. Mechanical damage could be reduced by the technique of hydrodynamic
Inward radial transport in differentially rotated plasma discs formed in z-pinch experiments
NASA Astrophysics Data System (ADS)
Lebedev, Sergey; Bennett, M.; Swadling, G. F.; Suttle, L.; Blackman, E.; Burdiak, G.; Chittenden, J. P.; Ciardi, A.; Drake, R. P.; Frank, A.; Hall, G. N.; Hare, J.; Patankar, S.; Smith, R. A.; Suzuki-Vidal, F.
2014-10-01
We will present experimental results showing the development of instabilities and an inward transport of matter in a differentially rotating supersonic plasma disc with dimensionless parameters relevant to modeling physics of astrophysical discs. The converging off-axis plasma flow forming the disc is produced by ablation of wires in a cylindrical wire array z-pinch (1.4 MA, 250 ns) combined with a cusp magnetic field, and the rotating disc is supported in equilibrium by the ram pressure of the flow. The radial profile of rotation velocity in the disc is measured using Doppler shifts of the ion feature of Thomson scattering spectra, while the broadening of the spectra yields the plasma temperature. The evolution of the disc structure is observed with multi-frame XUV and optical cameras, and the plasma density is measured using end-on laser interferometry. The Reynolds number in the disc is sufficiently large (>105) to allow development of turbulence on the time-scale of the experiment, and the observed inward transport of matter with the growth of small scale structures suggests that turbulence is responsible for the transport.
Application of Proton Deflectometry to Z-Pinch Plasma Systems at the Mega-Ampere Scale
NASA Astrophysics Data System (ADS)
Mariscal, Derek; McGuffey, Chris; Valenzuela, Julio; Wei, Mingsheng; Beg, Farhat; Presura, Radu; Haque, Showera; Arias, Angel; Covington, Aaron; Sawada, Hiroshi; Chittenden, Jeremy
2013-10-01
Measuring magnetic fields in z-pinch plasmas is challenging. Typical laser-probing diagnostics are limited by the critical density and large density gradients, while electrical diagnostics have limited spatial resolution. We report the first demonstration of proton deflectometry of z-pinch plasma systems at the mega-ampere scale. The proton beam was produced using the 10J 0.3ps Leopard laser and coupled to z-pinch plasma produced by Zebra, a 1MA pulsed-power driver at the Nevada Terawatt Facility. The magnetic field distorted the proton beam profile, which was recorded on radiochromic film. The experimental data was compared against integrated modeling using the resistive MHD code, Gorgon, for Z-pinch plasmas, in combination with the hybrid PIC code, LSP, for proton-beam trajectory tracking. This comparison provided the field and current configuration for various plasma loads, including wire and foil z-pinches. Funded by the NSF/DoE Partnership in Basic Plasma Scienceand En- gineering under contracts DE-SC-0001992 / PHY-0903876. Use of the Nevada Terawatt Facility was supported by the US DOE, NNSA, under Contract No. DE-FC52-06NA27616.
Development of the 50 TW laser for joint experiments with 1 MA z-pinches
NASA Astrophysics Data System (ADS)
Wiewior, P. P.; Ivanov, V. V.; Chalyy, O.
2010-08-01
A 50 TW high-intensity laser (aka "Leopard" laser) was developed for experiments with the 1 MA z-pinch generator at the University of Nevada, Reno. The laser produces short pulses of 0.35 ps; energy is 15 J. Long pulses are 1 ns; energy is 30 J. The output beam diameter is 80 mm. The Leopard laser applies chirped pulse amplification technology. The laser is based on the 130 fs Ti:Sapphire oscillator, Öffner-type stretcher, Ti:Sapphire regenerative amplifier, mixed Nd:glass rod and disk amplifiers, and vacuum grating compressor. An adaptive optics system ameliorates focusing ability and augments the repetition rate. Two beam terminals are available for experiments: in the vacuum chamber of the z-pinch generator (aka "Zebra"), and a laser-only vacuum chamber (aka "Phoenix" chamber). The Leopard laser coupled to the Zebra z-pinch generator is a powerful diagnostic tool for dense z-pinch plasma. We outline the status, design, architecture and parameters of the Leopard laser, and its coupling to Zebra. We present the methods of laser-based z-pinch plasma diagnostics, which are under development at the University of Nevada, Reno.
Measurements of high energy photons in Z-pinch experiments on primary test stand
Si, Fenni Zhang, Chuanfei; Xu, Rongkun; Yuan, Xi; Huang, Zhanchang; Xu, Zeping; Ye, Fan; Yang, Jianlun; Ning, Jiamin; Hu, Qingyuan; Zhu, Xuebin
2015-08-15
High energy photons are measured for the first time in wire-array Z-pinch experiments on the Primary Test Stand (PTS) which delivers a current up to 8 MA with a rise time of 70 ns. A special designed detecting system composed of three types of detectors is used to measure the average energy, intensity, and pulse waveform of high energy photons. Results from Pb-TLD (thermoluminescence dosimeter) detector indicate that the average energy is 480 keV (±15%). Pulse shape of high energy photons is measured by the photodiode detector consisted of scintillator coupled with a photodiode, and it is correlated with soft x-ray power by the same timing signal. Intensity is measured by both TLD and the photodiode detector, showing good accordance with each other, and it is 10{sup 10} cm{sup −2} (±20%) at 2 m in the horizontal direction. Measurement results show that high energy photons are mainly produced in pinch regions due to accelerated electrons. PTS itself also produces high energy photons due to power flow electrons, which is one order smaller in amplitude than those from pinch region.
Effect of driver impedance on dense plasma focus Z-pinch neutron yield
Sears, Jason E-mail: schmidt36@llnl.gov; Link, Anthony E-mail: schmidt36@llnl.gov; Schmidt, Andrea E-mail: schmidt36@llnl.gov; Welch, Dale
2014-12-15
The Z-pinch phase of a dense plasma focus (DPF) heats the plasma by rapid compression and accelerates ions across its intense electric fields, producing neutrons through both thermonuclear and beam-target fusion. Driver characteristics have empirically been shown to affect performance, as measured by neutron yield per unit of stored energy. We are exploring the effect of driver characteristics on DPF performance using particle-in-cell (PIC) simulations of a kJ scale DPF. In this work, our PIC simulations are fluid for the run-down phase and transition to fully kinetic for the pinch phase, capturing kinetic instabilities, anomalous resistivity, and beam formation during the pinch. The anode-cathode boundary is driven by a circuit model of the capacitive driver, including system inductance, the load of the railgap switches, the guard resistors, and the coaxial transmission line parameters. It is known that the driver impedance plays an important role in the neutron yield: first, it sets the peak current achieved at pinch time; and second, it affects how much current continues to flow through the pinch when the pinch inductance and resistance suddenly increase. Here we show from fully kinetic simulations how total neutron yield depends on the impedance of the driver and the distributed parameters of the transmission circuit. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability for neutron source applications.
Effect of driver impedance on dense plasma focus Z-pinch neutron yield
NASA Astrophysics Data System (ADS)
Sears, Jason; Link, Anthony; Schmidt, Andrea; Welch, Dale
2014-12-01
The Z-pinch phase of a dense plasma focus (DPF) heats the plasma by rapid compression and accelerates ions across its intense electric fields, producing neutrons through both thermonuclear and beam-target fusion. Driver characteristics have empirically been shown to affect performance, as measured by neutron yield per unit of stored energy. We are exploring the effect of driver characteristics on DPF performance using particle-in-cell (PIC) simulations of a kJ scale DPF. In this work, our PIC simulations are fluid for the run-down phase and transition to fully kinetic for the pinch phase, capturing kinetic instabilities, anomalous resistivity, and beam formation during the pinch. The anode-cathode boundary is driven by a circuit model of the capacitive driver, including system inductance, the load of the railgap switches, the guard resistors, and the coaxial transmission line parameters. It is known that the driver impedance plays an important role in the neutron yield: first, it sets the peak current achieved at pinch time; and second, it affects how much current continues to flow through the pinch when the pinch inductance and resistance suddenly increase. Here we show from fully kinetic simulations how total neutron yield depends on the impedance of the driver and the distributed parameters of the transmission circuit. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability for neutron source applications.
Preradiation studies for non-thermal Z-pinch wire load experiments on Saturn
Sanford, T.W.L.; Humphreys, D.R.; Poukey, J.W.; Marder, B.M.; Halbleib, J.A.; Crow, J.T.; Spielman, R.B.; Mock, R.C.
1994-06-01
The implosion dynamics of compact wire arrays on Saturn are explored as a function of wire mass m, wire length {ell}, wire radii R, and radial power-flow feed geometry using the ZORK code. Electron losses and the likelihood of arcing in the radial feed adjacent the wire load are analyzed using the TWOQUICK and CYLTRAN codes. The physical characteristics of the implosion and subsequent thermal radiation production are estimated using the LASNEX code in one dimension. These analyses show that compact tungsten wire arrays with parameters suggested by D. Mosher and with a 21-nH vacuum feed geometry satisfy the empirical scaling criterion I/(M/{ell}) {approximately} 2 MA/(mg/cm) of Mosher for optimizing non-thermal radiation from z pinches, generate low electron losses in the radial feeds, and generate electric fields at the insulator stack below the Charlie Martin flashover limit thereby permitting full power to be delivered to the load. Under such conditions, peak currents of {approximately}5 MA can be delivered to wire loads {approximately}20 ns before the driving voltage reverses at the insulator stack, potentially allowing the m = 0 instability to develop with the subsequent emission of non-thermal radiation as predicted by the Mosher model.
Characterisation of the current switch mechanism in two-stage wire array Z-pinches
Burdiak, G. C.; Lebedev, S. V.; Harvey-Thompson, A. J.; Hall, G. N.; Swadling, G. F.; Suzuki-Vidal, F.; Khoory, E.; Bland, S. N.; Pickworth, L.; Grouchy, P. de; Skidmore, J.; Suttle, L.; Waisman, E. M.
2015-11-15
In this paper, we describe the operation of a two-stage wire array z-pinch driven by the 1.4 MA, 240 ns rise-time Magpie pulsed-power device at Imperial College London. In this setup, an inverse wire array acts as a fast current switch, delivering a current pre-pulse into a cylindrical load wire array, before rapidly switching the majority of the generator current into the load after a 100–150 ns dwell time. A detailed analysis of the evolution of the load array during the pre-pulse is presented. Measurements of the load resistivity and energy deposition suggest significant bulk heating of the array mass occurs. The ∼5 kA pre-pulse delivers ∼0.8 J of energy to the load, leaving it in a mixed, predominantly liquid-vapour state. The main current switch occurs as the inverse array begins to explode and plasma expands into the load region. Electrical and imaging diagnostics indicate that the main current switch may evolve in part as a plasma flow switch, driven by the expansion of a magnetic cavity and plasma bubble along the length of the load array. Analysis of implosion trajectories suggests that approximately 1 MA switches into the load in 100 ns, corresponding to a doubling of the generator dI/dt. Potential scaling of the device to higher current machines is discussed.
The Physics of Long-Pulse Wire Array Z-Pinch Implosions
DOUGLAS,MELISSA R.; DEENEY,CHRISTOPHER; SPIELMAN,RICK B.; COVERDALE,CHRISTINE A.; RODERICK,N.F.; PETERSON,D.L.
1999-12-14
Recent improvements in z-pinch wire array load design at Sandia National Laboratories have led to a substantial increase in pinch performance as measured by radiated powers of up to 280 TW in 4 ns and 1.8 MJ of total radiated energy. Next generation, higher current machines will allow for larger mass arrays and comparable or higher velocity implosions to be reached, possibly extending these result.dis the current is pushed above 20 MA, conventional machine design based on a 100 ns implosion time results in higher voltages, hence higher cost and power flow risk. Another approach, which shifts the risk to the load configuration, is to increase the implosion time to minimize the voltage. This approach is being investigated in a series of experimental campaigns on the Saturn and Z machines. In this paper, both experimental and two dimensional computational modeling of the fist long implosion Z experiments will be presented. The experimental data shows broader pulses, lower powers, and larger pinch diameters compared to the corresponding short pulse data. By employing a nested array configuration, the pinch diameter was reduced by 50% with a corresponding increase in power of > 30%. Numerical simulations suggest load velocity is the dominating mechanism behind these results.
Soft X-Ray Measurements of Z-Pinch-Driven Vacuum Hohlraums
Baker, K.L.; Porter, J.L.; Ruggles, L.E.; Chandler, G.A.; Deeney, Chris; Varas, M.; Moats, Ann; Struve, Ken; Torres, J.; McGurn, J.; Simpson, W.W.; Fehl, D.L.; Chrien, R.E.; Matuska, W.; Idzorek, G.C.
1999-07-21
This article reports the experimental characterization of a z-pinch driven-vacuum hohlraum. The authors have measured soft x-ray fluxes of 5 x 10{sup 12} W/cm{sup 2} radiating from the walls of hohlraums which are 2.4--2.5 cm in diameter by 1 cm tall. The x-ray source used to drive these hohlraums was a z-pinch consisting of a 300 wire tungsten array driven by a 2 MA, 100 ns current pulse. In this hohlraum geometry, the z-pinch x-ray source can produce energies in excess of 800 kJ and powers in excess of 100 TW to drive these hohlraums. The x-rays released in these hohlraums represent greater than a factor of 25 in energy and more than a factor of three in x-ray power over previous laboratory-driven hohlraums.
Jones, B.; Deeney, C.; McKenney, J. L.; Ampleford, D. J.; Coverdale, C. A.; LePell, P. D.; Shelton, K. P.; Safronova, A. S.; Kantsyrev, V. L.; Osborne, G.; Sotnikov, V. I.; Ivanov, V. V.; Fedin, D.; Nalajala, V.; Yilmaz, F.; Shrestha, I.
2008-03-14
Axially localized NaF dopants are coated onto Al cylindrical wire arrays in order to act as spectroscopic tracers in the stagnated z-pinch plasma. Non-local-thermodynamic-equilibrium kinetic models fit to Na K-shell lines provide an independent measurement of the density and temperature that is consistent with spectroscopic analysis of K-shell emissions from Al and an alloyed Mg dopant. Axial transport of the Na dopant is observed, enabling quantitative study of instabilities in dense z-pinch plasmas.
NASA Astrophysics Data System (ADS)
Peterson, Kyle
2004-12-01
Electromagnetic boundary conditions can be troublesome in multi-dimensional magnetohydrodynamic simulations of systems containing complex geometries with multiple circuit paths. Accurate modeling of electromagnetic boundary conditions requires the feedback impedance of conducting plasmas in the computational domain to be modeled self consistently with external circuit boundaries. A new method is presented to dynamically calculate inductive and resistive impedance in multiple circuit paths and determine the electromagnetic boundary conditions in a self consistent manner. The new method was implemented into a two dimensional resistive magnetohydrodynamics code in order to simulate azimuthally opposed magnetic flux compression in a z-pinch configuration. Results of the flux compression simulations demonstrate excellent conservation of energy and circuit stability.
Efficient neutron production from a novel configuration of deuterium gas-puff z-pinch.
Klir, D; Kubes, P; Rezac, K; Cikhardt, J; Kravarik, J; Sila, O; Shishlov, A V; Kovalchuk, B M; Ratakhin, N A; Kokshenev, V A; Labetsky, A Yu; Cherdizov, R K; Fursov, F I; Kurmaev, N E; Dudkin, G N; Nechaev, B A; Padalko, V N; Orcikova, H; Turek, K
2014-03-01
A novel configuration of a deuterium z pinch has been used to generate fusion neutrons. Injecting an outer hollow cylindrical plasma shell around an inner deuterium gas puff, neutron yields from DD reactions reached Y(n)=(2.9 ± 0.3) × 10(12) at 700 ns implosion time and 2.7 MA current. Such a neutron yield means a tenfold increase in comparison with previous deuterium gas puff experiments at the same current generator. The increase of beam-target yields was obtained by a larger amount of current assembled on the z-pinch axis, and subsequently by higher induced voltage and higher energies of deuterons. A stack of CR-39 track detectors on the z-pinch axis showed hydrogen ions up to 38 MeV. Maximum neutron energies of 15 and 22 MeV were observed by radial and axial time-of-flight detectors, respectively. The number of DD neutrons per one joule of stored plasma energy approached 5 × 10(7). This implies that deuterium gas puff z pinches belong to the most efficient plasma-based sources of DD neutrons.
Deuteron Acceleration and Fusion Neutron Production in Z-pinch plasmas
Klir, D.; Kravarik, J.; Kubes, P.; Rezac, K.; Ananeev, S. S.; Bakshaev, Yu. L.; Blinov, P. I.; Chernenko, A. S.; Kazakov, E. D.; Korolev, V. D.; Ustroev, G. I.
2009-01-21
Fusion neutron measurements were carried out on the S-300 generator (Kurchatov Institute, Moscow). We tried deuterated fibers, various types of wire arrays imploding onto a deuterated fiber, and deuterium gas puffs as Z-pinch loads. On the current level of 2 MA, the peak neutron yield of 10{sup 10} was achieved with a deuterium gas-puff. The neutron and deuteron energy spectra were quite similar in various types of Z-pinch configurations. The broad width of radial neutron spectra implied a high radial component of deuteron velocity. On the basis of neutron measurements, we concluded that neutron production mechanism is connected with the study of plasma voltage. It means that the acceleration of fast deuterons is not a secondary process but it reflects the global dynamics of Z-pinch plasmas. For this reason it is useful to add deuterium as a 'tracer' in Z-pinch loads more often. For instance, it seems attractive to prepare wire-arrays from deuterated metal wires such as Pd.
UV Laser Diagnostics of the 1-MA Z-pinch Plasmas
Altemara, S. D.; Ivanov, V. V.; Astanovitskiy, A. L.; Haboub, A.
2009-01-21
The 532 nm laser diagnostic set at the Zebra generator shows the details of the ablation and stagnation phases in cylindrical, planar, and star-like wire arrays but it cannot show the structure of the stagnated z-pinch and the implosion in small diameter loads, 1-3 mm in diameter. The absorption increment and the refraction angle of the 532 nm laser, when passing through the plasma, are too great to obtain quality images. An ultraviolet probing beam at the wavelength of 266 nm was developed to study small-diameter loads and to investigate the structure of the 1-MA z-pinch. The UV radiation has a much smaller absorption increment and refraction angles in plasmas than the 532 nm light and allows for better imaging of the z-pinch plasmas. Estimates showed that UV probing would be able to probe the high-density z-pinch plasma in experiments on the Zebra generator, and the early results of UV probing on the Zebra generator have shown promise.
Lindemuth, Irvin R.
2009-01-21
For approximately four decades, Z-pinches and related geometries have been computationally modeled using unique Alternating Direction Implicit (ADI) numerical methods. Computational results have provided illuminating and often provocative interpretations of experimental results. A number of past and continuing applications are reviewed and discussed.
O-d energetics scaling models for Z-pinch-driven hohlraums
CUNEO,MICHAEL E.; VESEY,ROGER A.; HAMMER,J.H.; PORTER,JOHN L.
2000-06-08
Wire array Z-pinches on the Z accelerator provide the most intense laboratory source of soft x-rays in the world. The unique combination of a highly-Planckian radiation source with high x-ray production efficiency (15% wall plug), large x-ray powers and energies ( >150 TW, {ge}1 MJ in 7 ns), large characteristic hohlraum volumes (0.5 to >10 cm{sup 3}), and long pulse-lengths (5 to 20 ns) may make Z-pinches a good match to the requirements for driving high-yield scale ICF capsules with adequate radiation symmetry and margin. The Z-pinch driven hohlraum approach of Hammer and Porter [Phys.Plasmas, 6, 2129(1999)] may provide a conservative and robust solution to the requirements for high yield, and is currently being studied on the Z accelerator. This paper describes a multiple region, 0-d hohlraum energetic model for Z-pinch driven hohlraums in four configurations. The authors observe consistency between the models and the measured x-ray powers and hohlraum wall temperatures to within {+-}20% in flux, for the four configurations.
A Multiple Z-Pinch Configuration for the Generation of High-Density, Magnetized Plasmas
NASA Astrophysics Data System (ADS)
Tarditi, Alfonso G.
2015-11-01
The z-pinch is arguably the most straightforward and economical approach for the generation and confinement of hot plasmas, with a long history of theoretical investigations and experimental developments. While most of the past studies were focused on countering the natural tendency of z-pinches to develop instabilities, this study attempts to take advantage of those unstable regimes to form a quasi-stable plasma, with higher density and temperature, possibly of interest for a fusion reactor concept. For this purpose, a configuration with four z-pinch discharges, with axis parallel to each other and symmetrically positioned, is considered. Electrodes for the generation of the discharges and magnetic coils are arranged to favor the formation of concave discharge patterns. The mutual attraction from the co-streaming discharge currents enhances this pattern, leading to bent plasma streams, all nearing towards the axis. This configuration is intended to excite and sustain a ``kink'' unstable mode for each z-pinch, eventually producing either plasmoid structures, detached from each discharge, or sustained kink patterns: both these cases appear to lead to plasmas merging in the central region. The feasibility of this approach in creating a higher density, hotter, meta-stable plasma regime is investigated computationally, addressing both the kink excitation phase and the dynamics of the converging plasma columns.
Efficient Neutron Production from a Novel Configuration of Deuterium Gas-Puff Z-Pinch
NASA Astrophysics Data System (ADS)
Klir, D.; Kubes, P.; Rezac, K.; Cikhardt, J.; Kravarik, J.; Sila, O.; Shishlov, A. V.; Kovalchuk, B. M.; Ratakhin, N. A.; Kokshenev, V. A.; Labetsky, A. Yu.; Cherdizov, R. K.; Fursov, F. I.; Kurmaev, N. E.; Dudkin, G. N.; Nechaev, B. A.; Padalko, V. N.; Orcikova, H.; Turek, K.
2014-03-01
A novel configuration of a deuterium z pinch has been used to generate fusion neutrons. Injecting an outer hollow cylindrical plasma shell around an inner deuterium gas puff, neutron yields from DD reactions reached Yn=(2.9±0.3)×1012 at 700 ns implosion time and 2.7 MA current. Such a neutron yield means a tenfold increase in comparison with previous deuterium gas puff experiments at the same current generator. The increase of beam-target yields was obtained by a larger amount of current assembled on the z-pinch axis, and subsequently by higher induced voltage and higher energies of deuterons. A stack of CR-39 track detectors on the z-pinch axis showed hydrogen ions up to 38 MeV. Maximum neutron energies of 15 and 22 MeV were observed by radial and axial time-of-flight detectors, respectively. The number of DD neutrons per one joule of stored plasma energy approached 5×107. This implies that deuterium gas puff z pinches belong to the most efficient plasma-based sources of DD neutrons.
Los Alamos compact toroid, fast-liner, and high-density Z-pinch programs
Linford, R.K.; Sherwood, A.R.; Hammel, J.E.
1981-03-01
The Compact Toroid (CT) and High Density Z-Pinch (HDZP) are two of the plasma configurations presently being studied at Los Alamos. The purpose of these two programs, plus the recently terminated (May 1979) Fast Liner (FL) program, is summarized in this section along with a brief description of the experimental facilities. The remaining sections summarize the recent results and the experimental status.
Recent advances in theoretical and numerical studies of wire array Z-pinch in the IAPCM
Ding, Ning Zhang, Yang Xiao, Delong Wu, Jiming Huang, Jun Yin, Li Sun, Shunkai Xue, Chuang Dai, Zihuan Ning, Cheng Shu, Xiaojian Wang, Jianguo Li, Hua
2014-12-15
Fast Z-pinch has produced the most powerful X-ray radiation source in laboratory and also shows the possibility to drive inertial confinement fusion (ICF). Recent advances in wire-array Z-pinch researches at the Institute of Applied Physics and Computational Mathematics are presented in this paper. A typical wire array Z-pinch process has three phases: wire plasma formation and ablation, implosion and the MRT instability development, stagnation and radiation. A mass injection model with azimuthal modulation coefficient is used to describe the wire initiation, and the dynamics of ablated plasmas of wire-array Z-pinches in (r, θ) geometry is numerically studied. In the implosion phase, a two-dimensional(r, z) three temperature radiation MHD code MARED has been developed to investigate the development of the Magneto-Rayleigh-Taylor(MRT) instability. We also analyze the implosion modes of nested wire-array and find that the inner wire-array is hardly affected before the impaction of the outer wire-array. While the plasma accelerated to high speed in the implosion stage stagnates on the axis, abundant x-ray radiation is produced. The energy spectrum of the radiation and the production mechanism are investigated. The computational x-ray pulse shows a reasonable agreement with the experimental result. We also suggest that using alloyed wire-arrays can increase multi-keV K-shell yield by decreasing the opacity of K-shell lines. In addition, we use a detailed circuit model to study the energy coupling between the generator and the Z-pinch implosion. Recently, we are concentrating on the problems of Z-pinch driven ICF, such as dynamic hohlraum and capsule implosions. Our numerical investigations on the interaction of wire-array Z-pinches on foam convertors show qualitative agreements with experimental results on the “Qiangguang I” facility. An integrated two-dimensional simulation of dynamic hohlraum driven capsule implosion provides us the physical insights of wire
Recent advances in theoretical and numerical studies of wire array Z-pinch in the IAPCM
NASA Astrophysics Data System (ADS)
Ding, Ning; Zhang, Yang; Xiao, Delong; Wu, Jiming; Huang, Jun; Yin, Li; Sun, Shunkai; Xue, Chuang; Dai, Zihuan; Ning, Cheng; Shu, Xiaojian; Wang, Jianguo; Li, Hua
2014-12-01
Fast Z-pinch has produced the most powerful X-ray radiation source in laboratory and also shows the possibility to drive inertial confinement fusion (ICF). Recent advances in wire-array Z-pinch researches at the Institute of Applied Physics and Computational Mathematics are presented in this paper. A typical wire array Z-pinch process has three phases: wire plasma formation and ablation, implosion and the MRT instability development, stagnation and radiation. A mass injection model with azimuthal modulation coefficient is used to describe the wire initiation, and the dynamics of ablated plasmas of wire-array Z-pinches in (r, θ) geometry is numerically studied. In the implosion phase, a two-dimensional(r, z) three temperature radiation MHD code MARED has been developed to investigate the development of the Magneto-Rayleigh-Taylor(MRT) instability. We also analyze the implosion modes of nested wire-array and find that the inner wire-array is hardly affected before the impaction of the outer wire-array. While the plasma accelerated to high speed in the implosion stage stagnates on the axis, abundant x-ray radiation is produced. The energy spectrum of the radiation and the production mechanism are investigated. The computational x-ray pulse shows a reasonable agreement with the experimental result. We also suggest that using alloyed wire-arrays can increase multi-keV K-shell yield by decreasing the opacity of K-shell lines. In addition, we use a detailed circuit model to study the energy coupling between the generator and the Z-pinch implosion. Recently, we are concentrating on the problems of Z-pinch driven ICF, such as dynamic hohlraum and capsule implosions. Our numerical investigations on the interaction of wire-array Z-pinches on foam convertors show qualitative agreements with experimental results on the "Qiangguang I" facility. An integrated two-dimensional simulation of dynamic hohlraum driven capsule implosion provides us the physical insights of wire
Numerical simulation of fiber and wire array Z-pinches with Trac-II
Reisman, D
1998-09-01
Trac-II is a two dimensional axisymmetric resistive MHD code. It simulates all three spatial components (r, z, φ) of the magnetic field and fluid velocity vectors, and the plasma is treated as a single fluid with two temperatures (T_{e},T_{i}). In addition, it can optionally include a self-consistent external circuit. Recent modifications to the code include the addition of the 3-T radiation model, a 4-phase (solid-liquid-vapor-plasma) equation of state model (QEOS), a 4-phase electrical/thermal conductivity model, and an implicit solution of poloidal B_{z},B_{r}) magnetic field diffusion. These changes permit a detailed study of fiber and wire array Z-pinches. Specifically, Trac-II is used to study the wire array Z-pinch at the PBFA-Z pulse power generator at Sandia National Laboratory. First, in 1-D we examine the behavior of a single wire in the Z-pinch. Then, using these results as initial radial conditions in 2-D, we investigate the dynamics of wire array configurations in the r-z and r-θ plane. In the r-z plane we examine the growth of the m=0 or "sausage" instability in single wires within the array. In the r-θ plane we examine the merging behavior between neighboring wires. Special emphasis is placed on trying to explain how instability growth affects the performance of the Z-pinch. Lastly, we introduce Trac-III, a 3-D MHD code, and illustrate the m=1 or "kink" instability. We also discuss how Trac-III can be modified to simulate the wire array Z-pinch.
Characteristics of Al:Mg alloy wire-array z-pinches on the Z generator
Sanford, T.W.L.; Chandler, G.A.; Deeney, C.
1998-12-31
The characteristics of 95% Al:5% Mg alloy wire-array z-pinches formed by the Z generator and their associated x-emission are discussed. The arrays consisted of 180 to 266 wires, with each wire being 20-mm long and mounted at radii of 15, 20, or 25 mm. The implosion time of the loads explored was maintained at {approximately}106 ns by keeping M*R*R constant. M is the array mass that decreased from 7.1 to 4.2 to 2.6 mg as the radius R was increased. Current at the load was measured by B-dot monitors, and piezo-electric pressure gauges. These monitors showed that peak currents of {approximately}19 MA were generated in agreement with Screamer power-flow simulations. The temporally-resolved radiation field was measured by spatially-integrating resistive bolometers, filtered XRDs, and PCDs in 12 discrete channels that spanned the energy range 5 eV to 7 keV. Preliminary analysis indicates that the total radiated energy generated is of the order of 1 MJ and produces a total x-ray power on the order of 65 TW. The K-shell energy yield shows a strong dependence on mass increasing from {approximately}90 to {approximately}200 kJ as the mass decreases from 7.1 to 2.6 mg. Opacity effects are manifested by the share of Mg radiation greatly exceeding its 5% number ratio. Over this range, the associated FWHM of the K-shell emission decreases from 20 to 13 ns and the peak K-shell power increases from 4 to 12 TW, respectively, The x-ray images suggest the presence of a Rayleigh-Taylor instability. Two-dimensional radiation-magnetohydrodynamic simulations in the R-Z plane give insight into the mass distribution arising from this instability.
Chemically etched modulation in wire radius for wire array Z-pinch perturbation studies
Jones, B.; Deeney, C.; McKenney, J.L.; Garrity, J.E.; Lobley, D.K.; Martin, K.L.; Griego, A.E.; Ramacciotti, J.P.; Bland, S.N.; Lebedev, S.V.; Bott, S.C.; Ampleford, D.J.; Palmer, J.B.A.; Rapley, J.; Hall, G.
2004-11-01
A technique for manufacturing wires with imposed modulation in radius with axial wavelengths as short as 1 mm is presented. Extruded aluminum 5056 with 15 {mu}m diameter was masked and chemically etched to reduce the radius by {approx}20% in selected regions. Characterized by scanning electron microscopy, the modulation in radius is a step function with a {approx}10 {mu}m wide conical transition between thick and thin segments, with some pitting in etched regions. Techniques for mounting and aligning these wires in arrays for fast z-pinch experiments will be discussed. Axially mass-modulated wire arrays of this type will allow the study of seeded Rayleigh-Taylor instabilities in z pinches, corona formation, wire initiation with varying current density in the wire core, and correlation of perturbations between adjacent wires. This tool will support magnetohydrodynamics code validation in complex three-dimensional geometries, and perhaps x-ray pulse shaping.
Measurement of emission diameter as a function of time on foam z- pinch plasmas
Lazier, S.E.; Barber, T.L.; Derzon, M.S.; Kellogg, J.W.
1996-05-14
We have developed a streaked imaging capability to make time-resolved measurements of the emission size for low density foam z-pinches. By lens coupling visible emission from the z-pinch target to an array of fiber optics we obtained the emission profile in the visible as a function of time with radial resolution of 300 {mu}m. To measure the emission at temperatures greater than {approx}40 eV the source was slit-imaged or pin-hole imaged onto an x-ray filtered scintillator. Non-uniformities in both visible and x-ray emission were observed. We describe the diagnostics, the image unfold process, and results from the instrument for both visible and x-ray measurements.
Exploring Ways to Improve Predictive Capability of Z-Pinch Calculations
Matuska, W.; Aubrey, J.; Bowers, R.; Lee, H.; Peterson, D.; Deeney, C.; Derzon, M.; Nash, T.
1998-10-19
For some time 2-dimensional RMHD (radiation magneto-hydrodynamic) calculations of radiating z-pinches have been made to agree with integral data (current wave form, yield and power). For these calculations, the agreement with detailed data, such as time-resolved x-ray images, is generally not as good. Correctly modeling the physics of z-pinches, including detailed data, is needed to have true predictive capability. To address this problem, the authors first determine which integral data are most sensitive to the details in the models. With this information, they investigate aspects of the pinch, to which the data is sensitive, using non-standard techniques. For example, the pinch is calculated in (x,y)-geometry to investigate how a non-symmetric implosion affects the simulated data.
Investigation of asymmetry of wire-array Z pinches at stagnation using a 4-channel laser diagnostic
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; Anderson, A. A.
2016-09-01
Asymmetry of wire-array Z-pinches at stagnation was investigated using four synchronized laser beams at the wavelength of 266 nm. These beams were spaced at 45° with respect to each other, allowing a full view of the pinch from four directions. The laser pulse duration was 0.2 ns, with a <0.1 ns temporal accuracy between the four channels. Strong asymmetry was found in Z pinches produced by implosion of asymmetrical wire array loads. Anisotropy of the wire-array Z pinch arises due to the asymmetric implosion and development of plasma instabilities. Understanding the three-dimensional structure of Z-pinches is important for interpretation of data from x-ray and laser diagnostics.
Control of x-ray spectrum emitted from a gas-puff Z-pinch
Takasugi, Keiichi; Miyamoto, Tetsu; Tatsumi, Katsuhiro; Igusa, Takehito
1997-05-05
The axial magnetic field is applied to an annular gas-puff z-pinch for the control of radial dynamics and x-ray emission from the pinched plasma. K-shell and L-shell radiations of Ar ions are detected separately, and only the K-shell radiation is suppressed significantly by the axial field. The radial motion of the plasma is analyzed assuming a simple circuit model. The characteristic radius of the plasma increased with increasing the axial field.
Kantsyrev, V. L.; Esaulov, A. A.; Safronova, A. S.; Osborne, G. C.; Shrestha, I.; Weller, M. E.; Stafford, A.; Shlyaptseva, V. V.; Velikovich, A. L.; Rudakov, L. I.; Williamson, K. M.
2011-10-15
The influence of an induced axial magnetic field on plasma dynamics and radiative characteristics of Z pinches is investigated. An axial magnetic field was induced in a novel Z-pinch load: a double planar wire array with skewed wires (DPWAsk), which represents a planar wire array in an open magnetic configuration. The induced axial magnetic field suppressed magneto-Rayleigh-Taylor (MRT) instabilities (with m = 0 and m = 1 instability modes) in the Z-pinch plasma. The influence of the initial axial magnetic field on the structure of the plasma column at stagnation was manifested through the formation of a more uniform plasma column compared to a standard double planar wire array (DPWA) load [V. L. Kantsyrev et al., Phys. Plasmas 15, 030704 (2008)]. The DPWAsk load is characterized by suppression of MRT instabilities and by the formation of the sub-keV radiation pulse that occurs before the main x-ray peak. Gradients in plasma parameters along the cathode-anode gap were observed and analyzed for DPWAsk loads made from low atomic number Z (Al) and mid-Z (brass) wires.
Application of 2-D simulations to hollow z-pinch implosions
Peterson, D.L.; Bowers, R.L.; Brownell, J.H.
1997-12-01
The application of simulations of z-pinch implosions should have at least two goals: first, to properly model the most important physical processes occurring in the pinch allowing for a better understanding of the experiments and second, provide a design capability for future experiments. Beginning with experiments fielded at Los Alamos on the Pegasus 1 and Pegasus 2 capacitor banks, the authors have developed a methodology for simulating hollow z-pinches in two dimensions which has reproduced important features of the measured experimental current drive, spectrum, radiation pulse shape, peak power and total radiated energy. This methodology employs essentially one free parameter, the initial level of the random density perturbations imposed at the beginning of the 2-D simulation, but in general no adjustments to other parameters are required. Currently the authors are applying this capability to the analysis of recent Saturn and PBFA-Z experiments. The code results provide insight into the nature of the pinch plasma prior to arrival on-axis, during thermalization and development after peak pinch time. Among other things, the simulation results provide an explanation for the production of larger amounts of radiated energy than would be expected from a simple slug-model kinetic energy analysis and the appearance of multiple peaks in the radiation power. The 2-D modeling has also been applied to the analysis of Saturn dynamic hohlraum experiments and is being used in the design of this and other Z-Pinch applications on PBFA-Z.
Preliminary experimental results of tungsten wire-array Z-pinches on primary test stand
Huang, Xian-Bin; Zhou, Shao-Tong; Dan, Jia-Kun; Ren, Xiao-Dong Wang, Kun-Lun; Zhang, Si-Qun; Li, Jing; Xu, Qiang; Cai, Hong-Chun; Duan, Shu-Chao; Ouyang, Kai; Chen, Guang-Hua; Ji, Ce; Wei, Bing; Feng, Shu-Ping; Wang, Meng; Xie, Wei-Ping; Deng, Jian-Jun; Zhou, Xiu-Wen; Yang, Yi
2015-07-15
The Primary Test Stand (PTS) developed at the China Academy of Engineering Physics is a 20 TW pulsed power driver, which can deliver a ∼10 MA, 70 ns rise-time (10%–90%) current to a short-circuit load and has important applications in Z-pinch driven inertial confinement fusion and high energy density physics. Preliminary results of tungsten wire-array Z-pinch experiments on PTS are presented. The load geometries investigated include 15-mm-tall cylindrical single and nested arrays with diameter ranging from 13 mm to 30 mm, consisting of 132–300 tungsten wires with 5–10 μm in diameter. Multiple diagnostics were fielded to characterize the x-ray radiation from wire-array Z pinches. The x-ray peak power (∼50 TW) and total radiated energy (∼500 kJ) were obtained from a single 20-mm-diam array with 80-ns stagnation time. The highest x-ray peak power up to 80 TW with 2.4 ns FWHM was achieved by using a nested array with 20-mm outer diameter, and the total x-ray energy from the nested array is comparable to that of single array. Implosion velocity estimated from the time-resolved image measurement exceeds 30 cm/μs. The detailed experimental results and other findings are presented and discussed.
Study of micro-pinches in wire-array Z pinches
Ivanov, V. V.; Papp, D.; Anderson, A. A.; Talbot, B. R.; Astanovitskiy, A. L.; Nalajala, V.; Dmitriev, O.; Chittenden, J. P.; Niasse, N.; Pikuz, S. A.; Shelkovenko, T. A.
2013-11-15
Bright and hot areas with a high plasma density and temperature are observed in all kinds of Z pinches. We studied bright radiating spots produced by micro-pinches in cylindrical and planar wire-arrays at the 1 MA Zebra pulsed power generator using an x-ray streak camera synchronized with laser diagnostics, x-ray time-gated pinhole camera, and spectroscopy. Hot spots with extremely dense and relatively hot plasma arise during the collapse of the micro-pinches. These hot spots radiate a continuum spectrum with energy >2.5 keV. Typical micro-pinches in Al wire arrays generate x-ray bursts with durations of 0.4–1 ns in the soft x-ray range and 0.1–0.4 ns in the keV range. UV two-frame shadowgraphy shows spatial correlation of hot spots with the collapse and explosion of micro-pinches. Micro-pinches typically occur at the necks of the Z pinch, but can demonstrate a variety of parameters and different dynamics. An analysis of x-ray streak images shows that micro-pinches can generate >20% of the x-ray energy in some types of wire-array Z pinches.
The microscopic Z-pinch process of current-carrying rarefied deuterium plasma shell
Ning, Cheng; Xue, Chuang; Li, Baiwen; Feng, Zhixing
2015-02-15
For insight into the microscopic mechanism of Z-pinch dynamic processes, a code of two-dimensional particle-in-cell (PIC) simulation has been developed in cylindrical coordinates. In principle, the Z-pinch of current-carrying rarefied deuterium plasma shell has been simulated by means of this code. Many results related to the microscopic processes of the Z-pinch are obtained. They include the spatio-temporal distributions of electromagnetic field, current density, forces experienced by the ions and electrons, positions and energy distributions of particles, and trailing mass and current. In radial direction, the electric and magnetic forces exerted on the electrons are comparable in magnitude, while the forces exerted on the ions are mainly the electric forces. So in the Z-pinch process, the electrons are first accelerated in Z direction and get higher velocities; then, they are driven inwards to the axis at the same time by the radial magnetic forces (i.e., Lorentz forces) of them. That causes the separations between the electrons and ions because the ion mass is much larger than the electron's, and in turn a strong electrostatic field is produced. The produced electrostatic field attracts the ions to move towards the electrons. When the electrons are driven along the radial direction to arrive at the axis, they shortly move inversely due to the static repellency among them and their tiny mass, while the ions continue to move inertially inwards, and later get into stagnation, and finally scatter outwards. Near the stagnation, the energies of the deuterium ions mostly range from 0.3 to 6 keV, while the electron energies are mostly from 5 to 35 keV. The radial components, which can contribute to the pinched plasma temperature, of the most probable energies of electron and ion at the stagnation are comparable to the Bennett equilibrium temperature (about 1 keV), and also to the highest temperatures of electron and ion obtained in one dimensional radiation
Two-dimensional effects in hollow core z-pinches
NASA Astrophysics Data System (ADS)
Roderick, N. F.; Hussey, T. W.
Analytic modeling and magnetohydrodynamic simulations have been conducted to investigate two-dimensional effects in imploding plasma shells. These effects include short wavelength disturbances caused by instabilities at the plasma magnetic field interface, long wavelength instabilities associated with plasma annulus formation, and perturbations resulting from the power flow to the plasma annulus. The numerical calculations were carried out using the two-dimensional single-fluid magnetohydrodynamic (MHD) code MACH2 for different plasma density profiles and electrode geometries. Results for short wavelength perturbations show that these phenomena behave in a manner consistent with analytic linear and heuristic nonlinear models. At stagnation they have a negligible effect on the uniformity during the initial coupling to the target, even for large initial perturbations. The disturbances manifest themselves primarily in a rippling of the back of the plasma shell with significant effects, even in this region, not occurring until late in the stagnation process. Long wavelength perturbations produced by a straight axial gas injection for gas puff implosions can lead to pronounced axial nonuniformity, zippering, at stagnation. Variations of the injection conditions and electrode geometry can produce more uniform stagnation. Changes in the mass profile, gas injection angle, and electrode shape can all be used to achieve significantly greater stagnation uniformity. Consistent calculations for an entire implosion process from a gas injection to stagnation including vacuum power flow indicate the degree of coupling of short wavelength, long wavelength and power flow perturbations. Comparison with experimental data show agreement between analytic, numerical and experimental results.
Ablation dynamics in coiled wire-array Z-pinches
Hall, G. N.; Lebedev, S. V.; Suzuki-Vidal, F.; Swadling, G.; Chittenden, J. P.; Bland, S. N.; Harvey-Thompson, A.; Knapp, P. F.; Blesener, I. C.; McBride, R. D.; Chalenski, D. A.; Blesener, K. S.; Greenly, J. B.; Pikuz, S. A.; Shelkovenko, T. A.; Hammer, D. A.; Kusse, B. R.
2013-02-15
Experiments to study the ablation dynamics of coiled wire arrays were performed on the MAGPIE generator (1 MA, 240 ns) at Imperial College, and on the COBRA generator at Cornell University's Laboratory of Plasma Studies (1 MA, 100 ns). The MAGPIE generator was used to drive coiled wires in an inverse array configuration to study the distribution of ablated plasma. Using interferometry to study the plasma distribution during the ablation phase, absolute quantitative measurements of electron line density demonstrated very high density contrasts between coiled ablation streams and inter-stream regions many millimetres from the wire. The measured density contrasts for a coiled array were many times greater than that observed for a conventional array with straight wires, indicating that a much greater axial modulation of the ablated plasma may be responsible for the unique implosion dynamics of coiled arrays. Experiments on the COBRA generator were used to study the complex redirection of plasma around a coiled wire that gives rise to the ablation structure exhibited by coiled arrays. Observations of this complex 3D plasma structure were used to validate the current model of coiled array ablation dynamics [Hall et al., Phys. Rev. Lett. 100, 065003 (2008)], demonstrating irrefutably that plasma flow from the wires behaves as predicted. Coiled wires were observed to ablate and implode in the same manner on both machines, indicating that current rise time should not be an issue for the scaling of coiled arrays to larger machines with fast current rise times.
NASA Astrophysics Data System (ADS)
Velikovich, A. L.; Giuliani, J. L.; Clark, R. W.; Mikitchuk, D.; Kroupp, E.; Maron, Y.; Fisher, A.; Schmit, P. F.
2014-10-01
Recent progress in developing the MagLIF approach to pulsed-power driven inertial confinement fusion has stimulated the interest in observation and mitigation of the magnetic Rayleigh-Taylor instability (MRTI) of liners and Z-pinches imploded in an axial magnetic field. Theoretical analysis of these issues is particularly important because direct numerical simulation of the MRTI development is challenging due to intrinsically 3D helical structure of the fastest-growing modes. We review the analytical small-amplitude theory of the MRTI perturbation development and the weakly nonlinear theory of MRTI mode interaction, emphasizing basic physics, opportunity for 3D code verification against exact analytical solutions, and stabilization criteria. The theory is compared to the experimental results obtained at Weizmann Institute with gas-puff Z pinches and on the Z facility at Sandia with solid liners imploded in an axial magnetic field. Work supported by the US DOE/NNSA, and by the US-Israel Binational Science Foundation. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
Dense Plasma Focus Z-Pinch Fully Kinetic Modeling and Ion Probe-Beam Experiments
NASA Astrophysics Data System (ADS)
Schmidt, Andrea
2013-10-01
The Z-pinch phase of a dense plasma focus (DPF) emits multiple-MeV ions on a cm-scale length, even for kJ-scale devices. The mechanisms through which these physically simple devices generate such high energy beams in a relatively short distance are not fully understood. We are exploring the mechanisms behind these large gradients using the first fully kinetic simulations of a DPF Z-pinch as well as an ion probe beam experiment in which a 4 MeV deuteron beam is injected along the z-axis of a DPF Z-pinch plasma and accelerated. Our table-top DPF has demonstrated >50 MV/m acceleration gradients during 800 J operation using a fast capacitive driver. We have now directly measured the DPF gradients and demonstrated acceleration of an injected ion beam for the first time. Our particle-in-cell simulations have successfully predicted observed DPF ion beams and neutron yield, which past fluid simulations have not reproduced. We have now experimentally measured and observed in the simulations for the first time, electric field oscillations near the lower hybrid frequency. This is suggestive that the lower hybrid drift instability, long speculated to be the cause of the anomalous plasma resistivity that produces large DPF gradients, is playing an important role. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability for accelerator and neutron source applications. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and supported by the Laboratory Directed Research and Development Program (11-ERD-063) at LLNL.
The importance of EBIT data for Z-pinch plasma diagnostics
Safronova, A S; Kantsyrev, V L; Neill, P; Safronova, U I; Fedin, D A; Ouart, N D; Yilmaz, M F; Osborne, G; Shrestha, I; Williamson, K; Hoppe, T; Harris, C; Beiersdorfer, P; Hansen, S
2007-04-04
The results from the last six years of x-ray spectroscopy and spectropolarimetry of high energy density Z-pinch plasmas complemented by experiments with the electron beam ion trap (EBIT) at the Lawrence Livermore National Laboratory (LLNL) are presented. The two topics discussed are the development of M-shell x-ray W spectroscopic diagnostics and K-shell Ti spectropolarimetry of Z-pinch plasmas. The main focus is on radiation from a specific load configuration called an 'X-pinch'. X-pinches are excellent sources for testing new spectral diagnostics and for atomic modelling because of the high density and temperature of the pinch plasmas, which scale from a few {micro}m to several mm in size. They offer a variety of load configurations, which differ in wire connections, number of wires, and wire materials. In this work the study of X-pinches with tungsten wires combined with wires from other, lower-Z materials is reported. Utilizing data produced with the LLNL EBIT at different energies of the electron beam the theoretical prediction of line positions and intensity of M-shell W spectra were tested and calibrated. Polarization-sensitive X-pinch experiments at the University of Nevada, Reno (UNR) provide experimental evidence for the existence of strong electron beams in Ti and Mo X-pinch plasmas and motivate the development of x-ray spectropolarimetry of Z-pinch plasmas. This diagnostic is based on the measurement of spectra recorded simultaneously by two spectrometers with different sensitivity to the linear polarization of the observed lines and compared with theoretical models of polarization-dependent spectra. Polarization-dependent K-shell spectra from Ti X-pinches are presented and compared with model calculations and with spectra generated by a quasi-Maxwellian electron beam at the LLNL EBIT-II electron beam ion trap.
Investigation of Metal Puff Z pinch Based on Multichannel Vacuum Arcs
NASA Astrophysics Data System (ADS)
Rousskikh, A. G.; Oreshkin, V. I.; Zhigalin, A. S.; Chaikovsky, S. A.; Baksht, R. B.; Mitrofanov, K. N.
2015-11-01
The performance of a metal double puff Z-pinch system has been studied experimentally. In this type of system, the outer and inner cylindrical shells were produced by ten plasma guns. Each gun initiates a vacuum arc operating between aluminum electrodes. The net current of the guns was 80 kA. The arc-produced plasma shells were compressed by using a 450-kA, 450-ns driver, and as a result, a plasma column 0.2 cm in diameter was formed. The power of the Al K-line radiation emitted by the plasma for 7 ns was 800 MW/cm.
ALEGRA modeling of gas puff Z-pinch experiments at the ZR facility.
Coleman, P. L.; Flicker, Dawn G.; Coverdale, Christine Anne; Kueny, Christopher Shane; Krishnan, Mahadevan
2010-11-01
Gas puff z-pinch experiments have been proposed for the refurbished Z (ZR) facility for CY2011. Previous gas puff experiments [Coverdale et. al., Phys. Plasmas 14, 056309, 2007] on pre-refurbishment Z established a world record for laboratory fusion neutron yield. New experiments would establish ZR gas puff capability for x-ray and neutron production and could surpass previous yields. We present validation of ALEGRA simulations against previous Z experiments including X-ray and neutron yield, modeling of gas puff implosion dynamics for new gas puff nozzle designs, and predictions of X-ray and neutron yields for the proposed gas puff experiments.
The inverse skin effect in the Z-pinch and plasma focus
NASA Astrophysics Data System (ADS)
Usenko, P. L.; Gaganov, V. V.
2016-08-01
The inverse skin effect and its influence on the dynamics of high-current Z-pinch and plasma focus discharges in deuterium are analyzed. It is shown that the second compression responsible for the major fraction of the neutron yield can be interpreted as a result of the inverse skin effect resulting in the axial concentration of the longitudinal current density and the appearance of a reversed current in the outer layers of plasma pinches. Possible conditions leading to the enhancement of the inverse skin effect and accessible for experimental verification by modern diagnostics are formulated.
Use of spherically bent crystals to diagnose wire array z pinches
Shelkovenko, T.A.; Pikuz, S.A.; Hammer, D.A.; Ampleford, D.J.; Bland, S.N.; Bott, S.C.; Chittenden, J.P.; Lebedev, S.V.
2004-10-01
Spherically bent mica and quartz crystals have provided time-integrated spectra and monochromatic images in self-radiation of wire array z-pinch implosions on the MAGPIE generator (1 MA, 240 ns) at Imperial College. Diagnostics based on spherically bent crystals offer higher efficiencies than those based on flat or convex dispersion elements, allowing positioning far from the pinch with good debris shielding. A mica crystal spectrometer produced an image of the pinch in each emission line with about 100 {mu}m axial resolution. Combining the results of monochromatic imaging and spectra confirmed the presence of bright spots, probably generated by energetic electrons inside the pinch.
NASA Astrophysics Data System (ADS)
Valenzuela, J. C.; Krasheninnikov, I.; Beg, F. N.; Wessel, F.; Rahman, H.; Ney, P.; Presura, R.; McKee, E.; Darling, T.; Covington, A.
2015-11-01
Previous experimental work on staged Z-pinches demonstrated that gas liners can efficiently couple energy and implode uniformly a target-plasma. A 1.5 MA, 1 μs current driver was used to implode a magnetized, Kr liner onto a D + target, producing 1010 neutrons per shot and providing clear evidence of enhanced pinch stability. Time-of-flight data suggest that primary and secondary neutrons were produced. MHD simulations show that in Zebra, a 1.5MA and 100ns rise-time current driver, high fusion gain can be attained when the optimum liner and plasma target conditions are used. In this work we present the design and optimization of a liner-on-target nozzle to be fielded in Zebra and demonstrate high fusion gain at 1 MA current level. The nozzle is composed of an annular high atomic number gas-puff and an on-axis plasma gun that will deliver the ionized deuterium target. The nozzle optimization was carried out using the computational fluid dynamics (CFD) code fluent and the MHD code Mach2. The CFD simulation produces density and temperature profiles, as a function of the nozzle shapes and gas conditions, which are then used in Mach2 to find the optimum plasma liner implosion-pinch conditions. Funded by the US Department of Energy, ARPA-E, Control Number 1184-1527.
Measurements of the parameters of a condensed deuterated Z-pinch on the angara-5-1 facility
NASA Astrophysics Data System (ADS)
Aleksandrov, V. V.; Bryzgunov, V. A.; Grabovski, E. V.; Gritsuk, A. N.; Volobuev, I. V.; Kazakov, E. D.; Kalinin, Yu. G.; Korolev, V. D.; Laukhin, Ya. I.; Medovshchikov, S. F.; Mitrofanov, K. N.; Oleinik, G. M.; Pimenov, V. G.; Smirnova, E. A.; Ustroev, G. I.; Frolov, I. N.
2016-04-01
Results are presented from measurements of the parameters of high-temperature plasma in the Z-pinch neck formed when a current of up to 3.5 MA flows through a low-density polymer load. To enhance the effect of energy concentration, a deuterated microporous polyethylene neck with a mass density of 100 mg/cm3 and diameter of 1-1.3 mm was placed in the central part of the load. During the discharge current pulse, short-lived local hot plasma spots with typical dimensions of about 200-300 μm formed in the neck region. Their formation was accompanied by the generation of soft X-ray pulses with photon energies of E > 0.8 keV and durations of 3-4 ns. The plasma electron temperature in the vicinity of the hot spot was measured from the vacuum UV emission spectra of the iron diagnostic admixture and was found to be about 200-400 eV. The appearance of hot plasma spots was also accompanied by neutron emission with the maximum yield of 3 × 1010 neutrons/shot. The neutron energy spectra were studied by means of the time-of-flight method and were found to be anisotropic with respect to the direction of the discharge current.
Wire-number effects on high-power annular z-pinches and some characteristics at high wire number
SANFORD,THOMAS W. L.
2000-05-23
Characteristics of annular wire-array z-pinches as a function of wire number and at high wire number are reviewed. The data, taken primarily using aluminum wires on Saturn are comprehensive. The experiments have provided important insights into the features of wire-array dynamics critical for high x-ray power generation, and have initiated a renaissance in z-pinches when high numbers of wires are used. In this regime, for example, radiation environments characteristic of those encountered during the early pulses required for indirect-drive ICF ignition on the NIF have been produced in hohlraums driven by x-rays from a z-pinch, and are commented on here.
A high impedance mega-ampere generator for fiber z-pinch experiments
NASA Astrophysics Data System (ADS)
Mitchell, I. H.; Bayley, J. M.; Chittenden, J. P.; Worley, J. F.; Dangor, A. E.; Haines, M. G.; Choi, P.
1996-04-01
At Imperial College a mega-ampere generator for plasma implosion experiments has been designed, built, and commissioned. With a final line impedance of 1.25 Ω this terawatt class generator has been designed primarily to drive a maximum current of 1.8 MA with a rise time of 150 ns into high inductance z-pinch loads of interest to radiative collapse studies. This article describes the design and tests of the generator which has a novel configuration of lines and a new design of a magnetically insulated transmission line (MITL). In summary, the generator consists of four Marx generators each of the Hermes III type (2.4 MV, 84 kJ), each connected to 5 Ω pulse forming lines and trigatron gas switches. The power is fed into the matched 1.25 Ω vertical transfer line which feeds a diode stack and a short conical MITL in vacuum which concentrates the power into the z-pinch load. At 80% charge a current rising to 1.4 MA in 150 ns has been measured in a 15 nH inductive short. Similar results are obtained when using a plasma load.
A short-pulse mode for the SPHINX LTD Z-pinch driver
NASA Astrophysics Data System (ADS)
D'Almeida, Thierry; Lassalle, Francis; Zucchini, Frederic; Loyen, Arnaud; Morell, Alain; Chuvatin, Alexander
2015-11-01
The SPHINX machine is a 6MA, 1 μs, LTD Z-pinch driver at CEA Gramat (France) and primarily used for studying radiation effects. Different power amplification concepts were examined in order to reduce the current rise time without modifying the generator discharge scheme, including the Dynamic Load Current Multiplier (DLCM) proposed by Chuvatin. A DLCM device, capable of shaping the current pulse without reducing the rise time, was developed at CEA. This device proved valuable for isentropic compression experiments in cylindrical geometry. Recently, we achieved a short pulse operation mode by inserting a vacuum closing switch between the DLCM and the load. The current rise time was reduced to ~300 ns. We explored the use of a reduced-height wire array for the Dynamic Flux Extruder in order to improve the wire array compression rate and increase the efficiency of the current transfer to the load. These developments are presented. Potential benefits of these developments for future Z pinch experiments are discussed.
Investigation of Magnetic Field Geometry in Exploding Wire Z-Pinches via Proton Deflectometry
NASA Astrophysics Data System (ADS)
Mariscal, Derek; Beg, Farhat; Wei, Mingsheng; Chittenden, Jeremy; Presura, Radu
2012-10-01
It is often difficult to determine the configuration of B-fields within z-pinch plasma systems. Typical laser probing diagnostics are limited by the critical density, and electrical diagnostics are prone to failure as well as perturbation of the system. The use of proton beams launched by high intensity lasers, and the subsequent tracking of their deflected trajectories, will enable access to field measurements in previously inaccessible plasma densities.The experimental testing of this method is performed at the Nevada Test Facility (NTF) using the 10J 0.3ps Leopard laser coupled to the 1.6MA ZEBRA pulsed power generator. MHD simulations of the z-pinch plasmas are performed with the 3D resistive MHD code, GORGON. Protons are then injected and tracked through the plasma using the 3D PIC Large Scale Plasma code in order to produce possible proton image plane data. The first computational demonstration of protons propagating through single wire and x-pinch plasmas, along with comparison to recent experimental data will be presented.
Ion probe beam experiments and kinetic modeling in a dense plasma focus Z-pinch
Schmidt, A. Ellsworth, J. Falabella, S. Link, A. McLean, H. Rusnak, B. Sears, J. Tang, V.; Welch, D.
2014-12-15
The Z-pinch phase of a dense plasma focus (DPF) emits multiple-MeV ions in a ∼cm length. The mechanisms through which these physically simple devices generate such high energy beams in a relatively short distance are not fully understood. We are exploring the origins of these large gradients using measurements of an ion probe beam injected into a DPF during the pinch phase and the first kinetic simulations of a DPF Z-pinch. To probe the accelerating fields in our table top experiment, we inject a 4 MeV deuteron beam along the z-axis and then sample the beam energy distribution after it passes through the pinch region. Using this technique, we have directly measured for the first time the acceleration of an injected ion beam. Our particle-in-cell simulations have been benchmarked on both a kJ-scale DPF and a MJ-scale DPF. They have reproduced experimentally measured neutron yields as well as ion beams and EM oscillations which fluid simulations do not exhibit. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability for accelerator and neutron source applications.
Predictive Fully Kinetic Modeling of kJ and MJ Dense Plasma Focus Z-Pinches
NASA Astrophysics Data System (ADS)
Link, A.; Ellsworth, J.; Falabella, S.; McLean, H.; Rusnak, B.; Schmidt, A.; Sears, J.; Tang, V.; Welch, D.
2013-10-01
Dense plasma focus (DPF) Z-pinches are compact devices capable of producing MeV ion beams, x-rays, and (for D or DT gas fill) neutrons but the details of the mechanisms which give rise to these strong accelerating gradients are not well understood. We report on progress in developing predictive, fully kinetic simulations of DPF Z-Pinches using the particle-in-cell code LSP. These simulations include full-scale electrodes; both run-in and pinch phases; and post-pinch behavior. Here we present a comparison between simulations and experiments conducted on the LLNL 4 kJ tabletop DPF. Diagnostics allow us to measure neutron yield, plasma oscillations arising from instabilities, DPF ion beam energies, and the acceleration of an externally injected ion probe beam in the pinch region, which can be compared with simulations. We will further report on the initial work to extend these simulations from kJ to MJ-class devices. LLNL-ABS-640759. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and supported by the Laboratory Directed Research and Development Program (11-ERD-063) at LLNL.
Cylindrical liner Z-pinch experiments for fusion research and high-energy-density physics
NASA Astrophysics Data System (ADS)
Burdiak, G. C.; Lebedev, S. V.; Suzuki-Vidal, F.; Swadling, G. F.; Bland, S. N.; Niasse, N.; Suttle, L.; Bennet, M.; Hare, J.; Weinwurm, M.; Rodriguez, R.; Gil, J.; Espinosa, G.
2015-06-01
A gas-filled cylindrical liner z-pinch configuration has been used to drive convergent radiative shock waves into different gases at velocities of 20-50 km s-1. On application of the 1.4 MA, 240 ns rise-time current pulse produced by the Magpie generator at Imperial College London, a series of cylindrically convergent shock waves are sequentially launched into the gas-fill from the inner wall of the liner. This occurs without any bulk motion of the liner wall itself. The timing and trajectories of the shocks are used as a diagnostic tool for understanding the response of the liner z-pinch wall to a large pulsed current. This analysis provides useful data on the liner resistivity, and a means to test equation of state (EOS) and material strength models within MHD simulation codes. In addition to providing information on liner response, the convergent shocks are interesting to study in their own right. The shocks are strong enough for radiation transport to influence the shock wave structure. In particular, we see evidence for both radiative preheating of material ahead of the shockwaves and radiative cooling instabilities in the shocked gas. Some preliminary results from initial gas-filled liner experiments with an applied axial magnetic field are also discussed.
Analytic model to estimate thermonuclear neutron yield in z-pinches using the magnetic Noh problem
NASA Astrophysics Data System (ADS)
Allen, Robert C.
The objective was to build a model which could be used to estimate neutron yield in pulsed z-pinch experiments, benchmark future z-pinch simulation tools and to assist scaling for breakeven systems. To accomplish this, a recent solution to the magnetic Noh problem was utilized which incorporates a self-similar solution with cylindrical symmetry and azimuthal magnetic field (Velikovich, 2012). The self-similar solution provides the conditions needed to calculate the time dependent implosion dynamics from which batch burn is assumed and used to calculate neutron yield. The solution to the model is presented. The ion densities and time scales fix the initial mass and implosion velocity, providing estimates of the experimental results given specific initial conditions. Agreement is shown with experimental data (Coverdale, 2007). A parameter sweep was done to find the neutron yield, implosion velocity and gain for a range of densities and time scales for DD reactions and a curve fit was done to predict the scaling as a function of preshock conditions.
Magnetic Field Measurements in Wire-Array Z-Pinches using Magneto-Optically Active Waveguides
Syed, Wasif; Blesener, Isaac; Hammer, David A.; Lipson, Michal
2009-01-21
Understanding the magnetic field topology in wire-array Z-pinches as a function of time is of great significance to understanding these high-energy density plasmas especially for their ultimate application to stockpile stewardship and inertial confinement fusion. We are developing techniques to measure magnetic fields as a function of space and time using Faraday rotation of a single longitudinal mode (SLM) laser through a magneto-optically active bulk waveguide (multicomponent terbium borate glass) placed adjacent to, or within, the wire array in 1 MA experiments. We have measured fields >10 T with 100 ns rise times outside of a wire-array for the entire duration of the current pulse and as much as {approx}2 T inside a wire-array for {approx}40 ns from the start of current. This is the first time that such rapidly varying and large fields have been measured using these materials. In a dense Z-pinch, these sensing devices may not survive for long but may provide the magnetic field at the position of the sensor that can be used to corroborate magnetic probes, with which we compare our results.
Optical Spectroscopy Measurements of Shock Waves Driven by Intense Z-Pinch Radiation
Asay, J. Bernard, M.; Bailey, J.E.; Carlson, A.L.; Chandler, G.A.; Hall, C.A.; Hanson, D.; Johnston, R.; Lake, P.; Lawrence, J.
1999-04-09
Z-pinches created using the Z accelerator generate {approximately}220 TW, 1.7 MJ radiation pulses that heat large ({approximately}10 cm{sup 3}) hohlraums to 100-150 eV temperatures for times of order 10 nsec. We are performing experiments exploiting this intense radiation to drive shock waves for equation of state studies. The shock pressures are typically 1-10 Mbar with 10 nsec duration in 6-mm-diameter samples. In this paper we demonstrate the ability to perform optical spectroscopy measurements on shocked samples located in close proximity to the z-pinch. These experiments are particularly well suited to optical spectroscopy measurements because of the relatively large sample size and long duration. The optical emission is collected using fiber optics and recorded with a streaked spectrograph. Other diagnostics include VISAR and active shock breakout measurements of the shocked sample and a suite of diagnostics that characterize the radiation drive. Our near term goal is to use the spectral emission to obtain the temperature of the shocked material. Longer term objectives include the examination of deviations of the spectrum from blackbody, line emission from lower density regions, determination of kinetic processes in molecular systems, evaluation of phase transitions such as the onset of metalization in transparent materials, and characterization of the plasma formed when the shock exits the rear surface. An initial set of data illustrating both the potential and the challenge of these measurements is described.
Ion probe beam experiments and kinetic modeling in a dense plasma focus Z-pinch
NASA Astrophysics Data System (ADS)
Schmidt, A.; Ellsworth, J.; Falabella, S.; Link, A.; McLean, H.; Rusnak, B.; Sears, J.; Tang, V.; Welch, D.
2014-12-01
The Z-pinch phase of a dense plasma focus (DPF) emits multiple-MeV ions in a ˜cm length. The mechanisms through which these physically simple devices generate such high energy beams in a relatively short distance are not fully understood. We are exploring the origins of these large gradients using measurements of an ion probe beam injected into a DPF during the pinch phase and the first kinetic simulations of a DPF Z-pinch. To probe the accelerating fields in our table top experiment, we inject a 4 MeV deuteron beam along the z-axis and then sample the beam energy distribution after it passes through the pinch region. Using this technique, we have directly measured for the first time the acceleration of an injected ion beam. Our particle-in-cell simulations have been benchmarked on both a kJ-scale DPF and a MJ-scale DPF. They have reproduced experimentally measured neutron yields as well as ion beams and EM oscillations which fluid simulations do not exhibit. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability for accelerator and neutron source applications.
Magnetic Field Measurements in Wire-Array Z-Pinches using Magneto-Optically Active Waveguides
NASA Astrophysics Data System (ADS)
Syed, Wasif; Hammer, David; Lipson, Michal
2007-11-01
Understanding the magnetic field topology in wire-array Z-pinches as a function of time is of great significance to understanding these high-energy density plasmas. We are developing techniques to measure magnetic fields as a function of space and time using Faraday rotation of a single longitudinal mode (SLM) laser through a magneto-optically active bulk waveguide (terbium borate glass) placed adjacent to, or within, the wire array in experiments on the COBRA pulsed power generator [1]. We have measured fields >10 T with 100 ns rise times outside of a wire-array for the entire duration of the current pulse and as much as ˜2 T inside a wire-array for ˜40 ns from the start of current. This is the first time that such rapidly varying and large fields have been measured using these materials. We will also present our progress on field measurements using an optical fiber sensor and a very small ``thin film waveguide'' coupled to a fiber optic system. In a dense Z-pinch, these sensing devices may not survive for long but may provide the magnetic field at the position of the sensor for a greater fraction of the current pulse than magnetic probes, with which we compare our results. This research was sponsored by NNSA under SSAA program via DOE Coop Agreement DE-F03-02NA00057. [1] W. Syed, D. A. Hammer, & M. Lipson, 34^th ICOPS & 16^th PPPS, Albuquerque, NM, June 2007.
PBFA II-Z: A 20-MA driver for z-pinch experiments
1995-12-01
Sandia is modifying the PBFA II accelerator into a dual use facility. While maintaining the present ion-beam capability, we are developing a long-pulse, high-current operating mode for magnetically-driven implosions. This option, called PBFA II-Z, will require new water transmission lines, a new insulator stack, and new magnetically-insulated transmission lines (MITLs). Each of the existing 36, coaxial water pulse-forming sections will couple to a 4.5-{Omega}, bi-plate water-transmission line. The water transmission lines then feed a four-level insulator stack. The insulators are expected to operate at a maximum, spatially-averaged electric field of {approximately}l00 kV/cm. The MITL design is based on the successful biconic Saturn design. The four ``disk`` feeds will each have a vacuum impedance of {approximately}2.0 {Omega}. The disk feeds are added in parallel using a double post-hole convolute at a diameter of 15 cm. We predict that the accelerator will deliver 20 MA to a 15-mg z-pinch load in 100 ns, making PBFA II-Z the most powerful z-pinch driver in the world providing a pulsed power and load physics scaling testbed for future 40-80-MA drivers.
Magnetic Field Measurements in Wire-Array Z-Pinches using Magneto-Optically Active Waveguides
NASA Astrophysics Data System (ADS)
Syed, Wasif; Blesener, Isaac; Hammer, David A.; Lipson, Michal
2009-01-01
Understanding the magnetic field topology in wire-array Z-pinches as a function of time is of great significance to understanding these high-energy density plasmas especially for their ultimate application to stockpile stewardship and inertial confinement fusion. We are developing techniques to measure magnetic fields as a function of space and time using Faraday rotation of a single longitudinal mode (SLM) laser through a magneto-optically active bulk waveguide (multicomponent terbium borate glass) placed adjacent to, or within, the wire array in 1 MA experiments. We have measured fields >10 T with 100 ns rise times outside of a wire-array for the entire duration of the current pulse and as much as ˜2 T inside a wire-array for ˜40 ns from the start of current. This is the first time that such rapidly varying and large fields have been measured using these materials. In a dense Z-pinch, these sensing devices may not survive for long but may provide the magnetic field at the position of the sensor that can be used to corroborate magnetic probes, with which we compare our results.
Primary experimental results of wire-array Z-pinches on PTS
Huang, X. B. Zhou, S. T. Ren, X. D. Dan, J. K. Wang, K. L. Zhang, S. Q. Li, J. Xu, Q. Cai, H. C. Duan, S. C. Ouyang, K. Chen, G. H. Ji, C. Wang, M. Feng, S. P. Yang, L. B. Xie, W. P. Deng, J. J.
2014-12-15
The Primary Test Stand (PTS) developed at the China Academy of Engineering Physics is a multiterawatt pulsed power driver, which can deliver a ∼10 MA, 70 ns rise-time (10%-90%) current to a short circuit load and has important applications in Z-pinch driven inertial confinement fusion and high energy density physics. In this paper, primary results of tungsten wire-array Z-pinch experiments on PTS are presented. The load geometries investigated include 15-mm-tall cylindrical single and nested arrays with diameter ranging from 14.4-26.4 mm, and consisting of 132∼276 tungsten wires with 5∼10 μm in diameter. Multiple diagnostics were fielded to determine the characteristics of x-ray radiations and to obtain self-emitting images of imploding plasmas. X-ray power up to 80 TW with ∼3 ns FWMH is achieved by using nested wire arrays. The total x-ray energy exceeds 500 kJ and the peak radiation temperature is about 150 eV. Typical velocity of imploding plasmas goes around 3∼5×10{sup 7} cm/s and the radial convergence ratio is between 10 and 20.
Design of the PST: A Diagnostic for 1-D Imaging of Fast Z-Pinch Power Emissions
ROCHAU,GREGORY A.; DERZON,MARK S.; CHANDLER,GORDON A.; LAZIER,STEVEN EARL
2000-08-03
Fast Z-pinch technology developed on the Z machine at Sandia National Laboratories can produce up to 230 TW of thermal x-ray power for applications in inertial confinement fusion (ICF) and weapons physics experiments. During implosion, these Z-pinches develop Rayleigh-Taylor (R-T) instabilities which are very difficult to diagnose and which functionally diminish the overall pinch quality. The Power-Space-Time (PST) instrument is a newly configured diagnostic for measuring the pinch power as a function of both space and time in a Z-pinch. Placing the diagnostic at 90 degrees from the Z-pinch axis, the PST provides a new capability in collecting experimental data on R-T characteristics for making meaningful comparisons to magneto-hydrodynamic computer models. This paper is a summary of the PST diagnostic design. By slit-imaging the Z-pinch x-ray emissions onto a linear scintillator/fiber-optic array coupled to a streak camera system, the PST can achieve {approximately}100 {micro}m spatial resolution and {approximately}1.3 ns time resolution. Calculations indicate that a 20 {micro}m thick scintillating detection element filtered by 1,000 {angstrom} of Al is theoretically linear in response to Plankian x-ray distributions corresponding to plasma temperatures from 40 eV to 150 eV, By calibrating this detection element to x-ray energies up to 5,000 eV, the PST can provide pinch power as a function of height and time in a Z-pinch for temperatures ranging from {approximately}40 eV to {approximately}400 eV. With these system pm-meters, the PST can provide data for an experimental determination of the R-T mode number, amplitude, and growth rate during the late-time pinch implosion.
Z-Pinch Magneto-Inertial Fusion Propulsion Engine Design Concept
NASA Technical Reports Server (NTRS)
Miernik, Janie H.; Statham, Geoffrey; Adams, Robert B.; Polsgrove, Tara; Fincher, Sharon; Fabisinski, Leo; Maples, C. Dauphne; Percy, Thomas K.; Cortez, Ross J.; Cassibry, Jason
2011-01-01
Fusion-based nuclear propulsion has the potential to enable fast interplanetary transportation. Due to the great distances between the planets of our solar system and the harmful radiation environment of interplanetary space, high specific impulse (Isp) propulsion in vehicles with high payload mass fractions must be developed to provide practical and safe vehicles for human spaceflight missions. Magneto-Inertial Fusion (MIF) is an approach which has been shown to potentially lead to a low cost, small fusion reactor/engine assembly (1). The Z-Pinch dense plasma focus method is an MIF concept in which a column of gas is compressed to thermonuclear conditions by an estimated axial current of approximately 100 MA. Recent advancements in experiments and the theoretical understanding of this concept suggest favorable scaling of fusion power output yield as I(sup 4) (2). The magnetic field resulting from the large current compresses the plasma to fusion conditions, and this is repeated over short timescales (10(exp -6) sec). This plasma formation is widely used in the field of Nuclear Weapons Effects (NWE) testing in the defense industry, as well as in fusion energy research. There is a wealth of literature characterizing Z-Pinch physics and existing models (3-5). In order to be useful in engineering analysis, a simplified Z-Pinch fusion thermodynamic model was developed to determine the quantity of plasma, plasma temperature, rate of expansion, energy production, etc. to calculate the parameters that characterize a propulsion system. The amount of nuclear fuel per pulse, mixture ratio of the D-T and nozzle liner propellant, and assumptions about the efficiency of the engine, enabled the sizing of the propulsion system and resulted in an estimate of the thrust and Isp of a Z-Pinch fusion propulsion system for the concept vehicle. MIF requires a magnetic nozzle to contain and direct the nuclear pulses, as well as a robust structure and radiation shielding. The structure
DERZON,MARK S.
2000-03-01
The process of combining nuclei (the protons and neutrons inside an atomic nucleus) together with a release of kinetic energy is called fusion. This process powers the Sun, it contributes to the world stockpile of weapons of mass destruction and may one day generate safe, clean electrical power. Understanding the intricacies of fusion power, promised for 50 years, is sometimes difficult because there are a number of ways of doing it. There is hot fusion, cold fusion and con-fusion. Hot fusion is what powers suns through the conversion of mass energy to kinetic energy. Cold fusion generates con-fusion and nobody really knows what it is. Even so, no one is generating electrical power for you and me with either method. In this article the author points out some basic features of the mainstream approaches taken to hot fusion power, as well as describe why z pinches are worth pursuing as a driver for a power reactor and how it may one day generate electrical power for mankind.
Four-color laser diagnostics for Z-pinch and laser-produced plasma.
Ivanov, V V; Anderson, A A; Begishev, I A
2016-01-20
Four-color laser diagnostics were developed for Z-pinch and laser plasma at the 1 MA pulsed power generator. Four harmonics of the Nd:YAG laser at wavelengths of 1064, 532, 266, and 213 nm were produced during the cascade conversion in three nonlinear crystals and propagated together in one beampath. Deep UV probing allows better penetration of the dense plasma. Laser probing at four wavelengths allows observation of plasma in a wide range of densities in one shot of the diagnostic laser. Examples of four-color laser shadowgraphy and interferometry of the wire-array load and laser plasma interaction are presented and discussed. PMID:26835923
Development of absorption spectroscopy for wire-array Z-pinches
NASA Astrophysics Data System (ADS)
Anderson, A.; Ivanov, V. V.; Hakel, P.; Mancini, R. C.; Wiewior, P.; Durmaz, T.; Astanovitskiy, A. L.; Chalyy, O.; Altemara, S. D.; Papp, D.; McKee, E.; Chittenden, J. P.; Niasse, N.; Shevelko, A. P.
2010-11-01
The 50 TW Leopard laser was coupled with the 1 MA Zebra generator for the x-ray backlighting of wire arrays. The Leopard laser is based on the chirped pulse amplification and can operate in subpicosecond or subnanosecond regimes. Several materials were tested in both regimes and samarium was selected for subnanosecond backlighting in the range of 7-9 å. One ray of Al wire-arrays was investigated at the ablation and implosion stages. Two focusing conical spectrometers with mica crystals recorded reference and main spectra on x-ray film. Collimators protected spectrometers against the x-ray burst from the main Z-pinch. Comparison of spectra of backlighting radiation with reference spectra indicates absorption lines in the range of 8.2-8.4 å. The electron temperature of wire-array plasma was estimated from simulations with atomic kinetics models.
Dense Plasma Focus Z-pinches for High Gradient Particle Acceleration
Tang, V; Adams, M L; Rusnak, B
2009-07-24
The final Z-pinch stage of a Dense Plasma Focus (DPF) could be used as a simple, compact, and potentially rugged plasma-based high-gradient accelerator with fields at the 100 MV/m level. In this paper we review previously published experimental beam data that indicate the feasibility of such an DPF-based accelerator, qualitatively discuss the physical acceleration processes in terms of the induced voltages, and as a starting point examine the DPF acceleration potential by numerically applying a self-consistent DPF system model that includes the induced voltage from both macroscopic and instability driven plasma dynamics. Applications to the remote detection of high explosives and a multi-staged acceleration concept are briefly discussed.
Extreme Ultraviolet Light Emission from Z-Pinch Discharge Plasma Source
NASA Astrophysics Data System (ADS)
Watanabe, Masato; Song, Inho; Sakamoto, Toshiro; Kobayashi, Yasunori; Okino, Akitoshi; Mohanty, Smruti R.; Horioka, Kazuhiko; Hotta, Eiki
2006-01-01
A capillary Z-pinch discharge light source for EUV lithography has been developed. Our device is equipped with a water-cooled ceramic capillary and electrodes, and a solid state pulsed power generator. A stacked static induction thyristors are used as switching elements, which enable high repetition rate operation of pulsed power supply. A magnetic switch is connected in series, which not only assists the semiconductor switch but also provides a preionization current. In the present study, EUV radiation emitted from pinching plasma in a xenon-filled capillary was quantitatively measured using an in-band calorimeter. Time-integrated in-band source image was also observed using a pinhole camera system. Furthermore, new electrode system using plasma jet has been developed.
Magneto-Hydrodynamic Modeling in the Design and Interpretation of Wire Array Z-pinches
Chittenden, J. P.; Niasse, N. P.; Jennings, C. A.
2009-01-21
Magneto-hydrodynamic simulations provide a powerful tool for improving our understanding of the complex physical processes underlying the behavior of wire array Z-pinches. We show how, by using large scale parallel 3D simulations of the array as a whole, it is possible to encompass all of the important features of the wire ablation, implosion and stagnation phases and to observe how these phenomena control the X-ray pulse that is achieved. Comparison of code results with experimental data from the 'Z' and MAGPIE pulsed power generators is shown to provide a detailed benchmark test for the models. The simulation results are also used to highlight key areas for future research.
Development of the Axial Instability in Low Wire Number Wire Array Z-Pinches
Knapp, P. F.; Bell, K. S.; Blesener, I. C.; Chalenski, D. A.; Douglass, J. D.; Greenly, J. B.; Martin, M. R.; McBride, R. D.; Pikuz, S. A.; Shelkovenko, T. A.; Hammer, D. A.; Kusse, B. R.; Hall, G. N.
2009-01-21
We are investigating the development of the axial instability, a modulation of the size of the coronal plasma that develops around each wire in wire-array Z-pinches. The modulation is a result of nonuniform ablation of material from the relatively cold wire core. It has long been known that the wavelength of this modulation is constant late in time and, since it is unique to different materials, it has come to be known as the fundamental mode. In these experiments we imaged individual wires with laser shadowgraphy early in time primarily in low wire number, large wire diameter aluminum arrays for ease of viewing. We Observe the development of this modulation from the time of initiation of coronal plasma, obtaining its dominant wavelength and amplitude growth as a function of time. We also studied the instability on coiled wires, which modify the wire ablation mechanism and completely suppress the fundamental mode[Hall2008]. time is discussed.
The effects of insulating coatings and current prepulse on tungsten planar wire array Z-pinches
Li, M. Li, Y.; Sheng, L.; Wang, L. P.; Zhao, C.; Yuan, Y.; Zhang, X. J.; Zhang, M.; Peng, B. D.; Zhang, J. H.; Zhang, S. G.; Qiu, M. T.; Li, X. W.
2015-12-15
This paper presents experimental results on the effects of insulating coatings and current prepulse on tungsten planar wire array Z-pinches on ∼100 ns main current facility. Optical framing images indicated that without a current prepulse the wire ablation process was asymmetrical and the implosion was zippered. The x-ray peak power was ∼320 GW. By using insulating coatings on the wire surface the asymmetry remained, and the processes of ablation and implosion were delayed by ∼30 ns. The x-ray burst was narrow and decreased to ∼200 GW. When current prepulses were used on both standard and insulated wire arrays, implosion symmetry was improved and the x-ray burst was improved (to ∼520 GW peak power). In addition, there was a strong emitting precursor column for insulated loads with the current prepulse.
Equilibrium and Steady State of Dense Z-Pinches Superposing a Small Amount of Axial Flux
NASA Astrophysics Data System (ADS)
Hashimoto, Mitsuhiro; Miyamoto, Tetsu
2016-07-01
The pressure equilibrium and steady state of z-pinches trapping a small amount of axial magnetic flux are studied. The Bennett relation and the Pease-Braginskii-current are modified, taking into account the superposed axial field. The line energy density decreases in the modified Bennett relation, but the decrease is only of the order ɛ2, where ɛ = (the axial field strength at the axis)/(the azimuthal field strength at the plasma periphery) ≪ 1. On the other hand, the current in the steady state can increase without being limited by the Pease-Braginskii-current. Hence, the radiation collapse is prevented. The decrease of line energy density in the modified Bennett relation is almost canceled in the steady state.
MAIZE: a 1 MA LTD-Driven Z-Pinch at The University of Michigan
Gilgenbach, R. M.; Gomez, M. R.; Zier, J. C.; Tang, W. W.; French, D. M.; Lau, Y. Y.; Mazarakis, M. G.; Cuneo, M. E.; Johnston, M. D.; Oliver, B. V.; Mehlhorn, T. A.; Kim, A. A.; Sinebryukhov, V. A.
2009-01-21
Researchers at The University of Michigan have constructed and tested a 1-MA Linear Transformer Driver (LTD), the first of its type to reach the USA. The Michigan Accelerator for Inductive Z-pinch Experiments, (MAIZE), is based on the LTD developed at the Institute of High Current Electronics in collaboration with Sandia National Labs and UM. This LTD utilizes 80 capacitors and 40 spark gap switches, arranged in 40 'bricks,' to deliver a 1 MA, 100 kV pulse with 100 ns risetime into a matched resistive load. Preliminary resistive-load test results are presented for the LTD facility.Planned experimental research programs at UM include: a) Studies of Magneto-Raleigh-Taylor instability of planar foils, and b) Vacuum convolute studies including cathode and anode plasma.
3D MHD Simulations of Radial Wire Array Z-pinches
NASA Astrophysics Data System (ADS)
Niasse, N.; Chittenden, J. P.; Bland, S. N.; Suzuki-Vidal, F. A.; Hall, G. N.; Lebedev, S. V.; Calamy, H.; Zucchini, F.; Lassalle, F.; Bedoch, J. P.
2009-01-01
Recent experiments carried out on the MAGPIE (1 MA, 250 ns), OEDIPE (730 kA, 1.5 μs) and SPHINX (4 MA, 700 ns)[1] facilities have shown the relatively high level of scalability of the Radial Wire Array Z-pinches. These configurations where the wires stretch radially outwards from a central cathode offer numerous advantages over standard cylindrical arrays. In particular, imploding in a very stable and compact way, they seem suitable for coupling to small scale hohlraums. Making use of the 3D resistive magneto-hydrodynamic code GORGON[2] developed at Imperial College, the dynamic of the radial wire arrays is investigated. Influence of the cathode hotspots and wires angle on the x-ray emissions is also discussed. Comparison with experiments is offered to validate the numerical studies.
Behavior of a plasma in a high-density gas-embedded Z-pinch configuration
Shlachter, J.S.
1982-05-01
The theoretical analysis of a high density Z-pinch (HDZP) begins with an examination of the steady state energy balance between ohmic heating and bremsstrahlung radiation losses for a plasma column in pressure equilibrium. The model is then expanded to include the time-varying internal energy and results in a quasi-equilibrium prescription for the load current through a constant radius plasma channel. This set of current waveforms is useful in the design of experimental systems. The behavior of a plasma for physically realizable conditions is first examined by allowing adiabatic changes in the column radius. A more complete model is then developed by incorporating inertial effects into the momentum equation, and the resultant global MHD computational model is compared with more sophisticated, and costly, one- and two-dimensional computer simulations. These comparisons demonstrate the advantages of the global MHD description over previously developed zero-dimensional models.
Current initiation in low-density foam z-pinch plasmas
Derzon, M.; Nash, T.; Allshouse, G.
1996-07-01
Low density agar and aerogel foams were tested as z-pinch loads on the SATURN accelerator. In these first experiments, we studied the initial plasma conditions by measuring the visible emission at early times with a framing camera and 1-D imaging. At later time, near the stagnation when the plasma is hotter, x-ray imaging and spectral diagnostics were used to characterize the plasma. Filamentation and arcing at the current contacts was observed. None of the implosions were uniform along the z-axis. The prime causes of these problems are believed to be the electrode contacts and the current return configuration and these are solvable. Periodic phenomena consistent with the formation of instabilities were observed on one shot, not on others, implying that there may be a way of controlling instabilities in the pinch. Many of the issues involving current initiation may be solvable. Solutions are discussed.
250 kA compact linear transformer driver for wire array z-pinch loads
NASA Astrophysics Data System (ADS)
Bott, S. C.; Haas, D. M.; Madden, R. E.; Ueda, U.; Eshaq, Y.; Collins, G., IV; Gunasekera, K.; Mariscal, D.; Peebles, J.; Beg, F. N.; Mazarakis, M.; Struve, K.; Sharpe, R.
2011-05-01
We present the application of a short rise (˜150ns) 250 kA linear transformer driver (LTD) to wire array z-pinch loads for the first time. The generator is a modification of a previous driver in which a new conical power feed provides a low inductance coupling to wire loads. Performance of the new design using both short circuit and plasma loads is presented and discussed. The final design delivers ˜200kA to a wire array load which is in good agreement with SCREAMER calculations using a simplified representative circuit. Example results demonstrate successful experiments using cylindrical, conical, and inverse wire arrays as well as previously published work on x-pinch loads.
Non-thermal x-ray emission from wire array z-pinches
Ampleford, David; Hansen, Stephanie B.; Jennings, Christopher Ashley; Webb, Timothy Jay; Harper-Slaboszewicz, V.; Loisel, Guillaume Pascal; Flanagan, Timothy McGuire; Bell, Kate Suzanne; Jones, Brent M.; McPherson, Leroy A.; Rochau, Gregory A.; Chittenden, Jeremy P.; Sherlock, Mark; Appelbe, Brian; Giuliani, John; Ouart, Nicholas; Seely, John
2015-12-01
We report on experiments demonstrating the transition from thermally-dominated K-shell line emission to non-thermal, hot-electron-driven inner-shell emission for z pinch plasmas on the Z machine. While x-ray yields from thermal K-shell emission decrease rapidly with increasing atomic number Z, we find that non-thermal emission persists with favorable Z scaling, dominating over thermal emission for Z=42 and higher (hn ≥ 17keV). Initial experiments with Mo (Z=42) and Ag (Z=47) have produced kJ-level emission in the 17-keV and 22-keV Kα lines respectively. We will discuss the electron beam properties that could excite these non - thermal lines. We also report on experiments that have attempted to control non - thermal K - shell line emission by modifying the wire array or load hardware setup.
Ion Viscous Heating in a Magnetohydrodynamically Unstable Z Pinch at Over 2×109 Kelvin
NASA Astrophysics Data System (ADS)
Haines, M. G.; Lepell, P. D.; Coverdale, C. A.; Jones, B.; Deeney, C.; Apruzese, J. P.
2006-02-01
Pulsed power driven metallic wire-array Z pinches are the most powerful and efficient laboratory x-ray sources. Furthermore, under certain conditions the soft x-ray energy radiated in a 5 ns pulse at stagnation can exceed the estimated kinetic energy of the radial implosion phase by a factor of 3 to 4. A theoretical model is developed here to explain this, allowing the rapid conversion of magnetic energy to a very high ion temperature plasma through the generation of fine scale, fast-growing m=0 interchange MHD instabilities at stagnation. These saturate nonlinearly and provide associated ion viscous heating. Next the ion energy is transferred by equipartition to the electrons and thus to soft x-ray radiation. Recent time-resolved iron spectra at Sandia confirm an ion temperature Ti of over 200 keV (2×109 degrees), as predicted by theory. These are believed to be record temperatures for a magnetically confined plasma.
2D radiation-magnetohydrodynamic simulations of SATURN imploding Z-pinches
Hammer, J.H.; Eddleman, J.L.; Springer, P.T.
1995-11-06
Z-pinch implosions driven by the SATURN device at Sandia National Laboratory are modeled with a 2D radiation magnetohydrodynamic (MHD) code, showing strong growth of magneto-Rayleigh Taylor (MRT) instability. Modeling of the linear and nonlinear development of MRT modes predicts growth of bubble-spike structures that increase the time span of stagnation and the resulting x-ray pulse width. Radiation is important in the pinch dynamics keeping the sheath relatively cool during the run-in and releasing most of the stagnation energy. The calculations give x-ray pulse widths and magnitudes in reasonable agreement with experiments, but predict a radiating region that is too dense and radially localized at stagnation. We also consider peaked initial density profiles with constant imploding sheath velocity that should reduce MRT instability and improve performance. 2D krypton simulations show an output x-ray power > 80 TW for the peaked profile.
Rep-rated Z-Pinch Power Plant Concept - Direct Energy Conversion and Shrapnel Generation*
NASA Astrophysics Data System (ADS)
de Groot, John S.; Gronbech-Jensen, Niels; Miller, Greg; Olsen, Craig L.; Rochau, Gary E.; Derzon, Mark S.; Slutz, Steven A.; Spielman, Rick B.; Peterson, Per F.; Rochau, Gregory A.; Pederson, Robert R.
2000-10-01
We are developing direct energy conversion schemes and shrapnel generation models to be used to optimize a high yield z-pinch IFE power plant concept. The concept uses high yield ( 10 GJ) at low rep-rate ( 0.1 Hz), with a Recyclable Transmission Line (RTL) to provide the necessary standoff between the fusion target and the power plant chamber. The RTL would be cast out of a conventional power plant coolant material (such as Li or Flibe) that can be used to absorb the fusion energy, breed tritium, and mitigate the shock to the first wall. Current results of initial work on this concept will be discussed. *Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy Under Contract DE-AC04-94AL85000.
Magneto-Hydrodynamic Modeling in the Design and Interpretation of Wire Array Z-pinches
NASA Astrophysics Data System (ADS)
Chittenden, J. P.; Niasse, N. P.; Jennings, C. A.
2009-01-01
Magneto-hydrodynamic simulations provide a powerful tool for improving our understanding of the complex physical processes underlying the behavior of wire array Z-pinches. We show how, by using large scale parallel 3D simulations of the array as a whole, it is possible to encompass all of the important features of the wire ablation, implosion and stagnation phases and to observe how these phenomena control the X-ray pulse that is achieved. Comparison of code results with experimental data from the 'Z' and MAGPIE pulsed power generators is shown to provide a detailed benchmark test for the models. The simulation results are also used to highlight key areas for future research.
Wire array z-pinch insights for high x-ray power generation
Sanford, T.W.L.; Mock, R.C.; Nash, T.J.
1998-08-01
The discovery that the use of very large numbers of wires enables high x-ray power to be generated from wire-array z-pinches represents a breakthrough in load design for large pulsed power generators, and has permitted high temperatures to be generated in radiation cavities on Saturn. In this paper, changes in x-ray emission characteristics as a function of wire number, array mass, and load radius, for 20-mm-long aluminum arrays on Saturn that led to these breakthrough hohlraum results, are discussed and compared with a few related emission characteristics of high-wire-number aluminum and tungsten arrays on Z. X=ray measurement comparisons with analytic models and 2-D radiation-magnetohydrodynamic (RMHC) code simulations in the x-y and r-z planes provide confidence in the ability of the models and codes to predict future x-ray performance with very-large-number wire arrays.
3D MHD Simulations of Radial Wire Array Z-pinches
Niasse, N.; Chittenden, J. P.; Bland, S. N.; Suzuki-Vidal, F. A.; Hall, G. N.; Lebedev, S. V.; Calamy, H.; Zucchini, F.; Lassalle, F.; Bedoch, J. P.
2009-01-21
Recent experiments carried out on the MAGPIE (1 MA, 250 ns), OEDIPE (730 kA, 1.5 {mu}s) and SPHINX (4 MA, 700 ns)[1] facilities have shown the relatively high level of scalability of the Radial Wire Array Z-pinches. These configurations where the wires stretch radially outwards from a central cathode offer numerous advantages over standard cylindrical arrays. In particular, imploding in a very stable and compact way, they seem suitable for coupling to small scale hohlraums. Making use of the 3D resistive magneto-hydrodynamic code GORGON[2] developed at Imperial College, the dynamic of the radial wire arrays is investigated. Influence of the cathode hotspots and wires angle on the x-ray emissions is also discussed. Comparison with experiments is offered to validate the numerical studies.
Use of vacuum arc plasma guns for a metal puff Z-pinch system
Rousskikh, A. G.; Zhigalin, A. S.; Oreshkin, V. I.; Chaikovsky, S. A.; Labetskaya, N. A.; Baksht, R. B.
2011-09-15
The performance of a metal puff Z-pinch system has been studied experimentally. In this type of system, the initial cylindrical shell 4 cm in diameter was produced by ten plasma guns. Each gun initiates a vacuum arc operating between magnesium electrodes. The net current of the guns was 80 kA. The arc-produced plasma shell was compressed by using a 450-kA, 450-ns driver, and as a result, a plasma column 0.3 cm in diameter was formed. The electron temperature of the plasma reached 400 eV at an average ion concentration of 1.85 {center_dot} 10{sup 18} cm{sup -3}. The power of the Mg K-line radiation emitted by the plasma for 15-30 ns was 300 MW/cm.
Particle drift model for Z-pinch-driven magneto-Rayleigh-Taylor instability
NASA Astrophysics Data System (ADS)
Dan, Jia Kun; Xu, Qiang; Wang, Kun Lun; Ren, Xiao Dong; Huang, Xian Bin
2016-09-01
A theoretical model of Z-pinch driven magneto-Rayleigh-Taylor instability is proposed based on the particle drift point of view, which can explain the helical instability structure observed in premagnetized imploding liner experiments. It is demonstrated that all possible drift motions, including polarization drift, gradient drift, and curvature drift, which can lead to charge separations, each will attribute to an effective gravity acceleration. Theoretical predictions given by this model are dramatically different from those given by previous theories which have been readily recovered in the theory presented here as a limiting case. The theory shows qualitative agreement with available experimental data of the pitch angle and provides certain predictions to be verified.
Design of Z-Pinch and Dense Plasma Focus Powered Vehicles
NASA Technical Reports Server (NTRS)
Polsgrove, Tara; Fincher, Sharon; Adams, Robert B.; Cassibry, Jason; Cortez, Ross; Turner, Matthew; Maples, C. Daphne; Miermik, Janie N.; Statham, Geoffrey N.; Fabisinski, Leo; Santarius, John; Percy, Tom
2011-01-01
Z-pinch and Dense Plasma Focus (DPF) are two promising techniques for bringing fusion power to the field of in-space propulsion. A design team comprising of engineers and scientists from UAHuntsville, NASA's George C. Marshall Space Flight Center and the University of Wisconsin developed concept vehicles for a crewed round trip mission to Mars and an interstellar precursor mission. Outlined in this paper are vehicle concepts, complete with conceptual analysis of the mission profile, operations, structural and thermal analysis and power/avionics design. Additionally engineering design of the thruster itself is included. The design efforts adds greatly to the fidelity of estimates for power density (alpha) and overall performance for these thruster concepts
The role of Z-pinch fusion transmutation of waste in the nuclear fuel cycle.
Smith, James Dean; Drennen, Thomas E.; Rochau, Gary Eugene; Martin, William Joseph; Kamery, William; Phruksarojanakun, Phiphat; Grady, Ryan; Cipiti, Benjamin B.; Wilson, Paul Philip Hood; Mehlhorn, Thomas Alan; Guild-Bingham, Avery; Tsvetkov, Pavel Valeryevich
2007-10-01
The resurgence of interest in reprocessing in the United States with the Global Nuclear Energy Partnership has led to a renewed look at technologies for transmuting nuclear waste. Sandia National Laboratories has been investigating the use of a Z-Pinch fusion driver to burn actinide waste in a sub-critical reactor. The baseline design has been modified to solve some of the engineering issues that were identified in the first year of work, including neutron damage and fuel heating. An on-line control feature was added to the reactor to maintain a constant neutron multiplication with time. The transmutation modeling effort has been optimized to produce more accurate results. In addition, more attention was focused on the integration of this burner option within the fuel cycle including an investigation of overall costs. This report presents the updated reactor design, which is able to burn 1320 kg of actinides per year while producing 3,000 MWth.
Giuliani, J. L.; Thornhill, J. W.; Dasgupta, A.; Velikovich, A. L.; Chong, Y. K.; Mehlhorn, T. A.; Kroupp, E.; Osin, D.; Maron, Y.; Starobinets, A.; Fisher, V.; Zarnitsky, Yu.; Bernshtam, V.; Apruzese, J. P.; Fisher, A.; Deeney, C.
2014-03-15
The difference between the ion thermal and effective temperatures is investigated through simulations of the Ne gas puff z-pinch reported by Kroupp et al. [Phys. Rev. Lett. 107, 105001 (2011)]. Calculations are performed using a 2D, radiation-magnetohydrodynamic code with Tabular Collisional-Radiative Equilibrium, namely Mach2-TCRE [Thornhill et al., Phys. Plasmas 8, 3480 (2001)]. The extensive data set of imaging and K-shell spectroscopy from the experiments provides a challenging validation test for z-pinch simulations. Synthetic visible images of the implosion phase match the observed large scale structure if the breakdown occurs at the density corresponding to the Paschen minimum. At the beginning of stagnation (−4 ns), computed plasma conditions change rapidly showing a rising electron density and a peak in the ion thermal temperature of ∼1.8 keV. This is larger than the ion thermal temperature (<400 eV) inferred from the experiment. By the time of peak K-shell power (0 ns), the calculated electron density is similar to the data and the electron and ion thermal temperatures are equilibrated, as is observed. Effective ion temperatures are obtained from calculated emission line widths accounting for thermal broadening and Doppler velocity shifts. The observed, large effective ion temperatures (∼4 keV) early in the stagnation of this Ne pinch can be explained solely as a combination of compressional ion heating and steep radial velocity gradients near the axis. Approximations in the modeling are discussed in regard to the higher ion thermal temperature and lower electron density early in the stagnation compared to the experimental results.
A compact soft X-ray microscope using an electrode-less Z-pinch source
NASA Astrophysics Data System (ADS)
Horne, S. F.; Silterra, J.; Holber, W.
2009-09-01
Soft X-rays (< 1Kev) are of medical interest both for imaging and microdosimetry applications. X-ray sources at this low energy present a technological challenge. Synchrotrons, while very powerful and flexible, are enormously expensive national research facilities. Conventional X-ray sources based on electron bombardment can be compact and inexpensive, but low x-ray production efficiencies at low electron energies restrict this approach to very low power applications. Laser-based sources tend to be expensive and unreliable. Energetiq Technology, Inc. (Woburn, MA, USA) markets a 92 eV, 10W(2pi sr) electrode-less Z-pinch source developed for advanced semiconductor lithography. A modified version of this commercial product has produced 400 mW at 430 eV (2pi sr), appropriate for water window soft X-ray microscopy. The US NIH has funded Energetiq to design and construct a demonstration microscope using this source, coupled to a condenser optic, as the illumination system. The design of the condenser optic matches the unique characteristics of the source to the illumination requirements of the microscope, which is otherwise a conventional design. A separate program is underway to develop a microbeam system, in conjunction with the RARAF facility at Columbia University, NY, USA. The objective is to develop a focused, sub-micron beam capable of delivering > 1 Gy/second to the nucleus of a living cell. While most facilities of this type are coupled to a large and expensive particle accelerator, the Z-pinch X-ray source enables a compact, stand-alone design suitable to a small laboratory. The major technical issues in this system involve development of suitable focusing X-ray optics. Current status of these programs will be reported. (Supported by NIH grants 5R44RR022488-03 and 5R44RR023753-03)
Implosion dynamics and x-ray generation in small-diameter wire-array Z pinches.
Ivanov, V V; Sotnikov, V I; Kindel, J M; Hakel, P; Mancini, R C; Astanovitskiy, A L; Haboub, A; Altemara, S D; Shevelko, A P; Kazakov, E D; Sasorov, P V
2009-05-01
It is known from experiments that the radiated x-ray energy appears to exceed the calculated implosion kinetic energy and Spitzer resistive heating [C. Deeney, Phys. Rev. A 44, 6762 (1991)] but possible mechanisms of the enhanced x-ray production are still being discussed. Enhanced plasma heating in small-diameter wire arrays with decreased calculated kinetic energy was investigated, and a review of experiments with cylindrical arrays of 1-16 mm in diameter on the 1 MA Zebra generator is presented in this paper. The implosion and x-ray generation in cylindrical wire arrays with different diameters were compared to find a transition from a regime where thermalization of the kinetic energy is the prevailing heating mechanism to regimes with other dominant mechanisms of plasma heating. Loads of 3-8 mm in diameter generate the highest x-ray power at the Zebra generator. The x-ray power falls in 1-2 mm loads which can be linked to the lower efficiency of plasma heating with the lack of kinetic energy. The electron temperature and density of the pinches also depend on the array diameter. In small-diameter arrays, 1-3 mm in diameter, ablating plasma accumulates in the inner volume much faster than in loads of 12-16 mm in diameter. Correlated bubblelike implosions were observed with multiframe shadowgraphy. Investigation of energy balance provides evidence for mechanisms of nonkinetic plasma heating in Z pinches. Formation and evolution of bright spots in Z pinches were studied with a time-gated pinhole camera. A comparison of x-ray images with shadowgrams shows that implosion bubbles can initiate bright spots in the pinch. Features of the implosions in small-diameter wire arrays are discussed to identify mechanisms of energy dissipation.
Soldered Contact and Current Risetime Effects on Negative Polarity Wire Array Z-pinches
Chalenski, D. A.; Kusse, B. R.; Greenly, J. B.; Blesener, I. C.; McBride, R. D.; Hammer, D. A.; Knapp, P. F.
2009-01-21
The Cornell University COBRA pulser is a nominal 1 MA machine, capable of driving up to 32 wire cylindrical Z-pinch arrays. COBRA can operate with variable current risetimes ranging from 100 ns to 200 ns (short and long pulse, respectively). Wires are typically strung with a 'press' contact to the electrode hardware, where the wire is loosely pulled against the hardware and held there to establish electrical contact. The machine is normally negative, but a bolt-on convolute can be used to modify the current path and effectively produce positive polarity operation at the load.Previous research with single wires on a 1-5 kA pulser has shown that soldering the wire, thereby improving the wire/electrode contact, and operating in positive polarity can improve the energy deposition into the wire and enhance wire core expansion. Negative polarity showed no difference. Previous experiments on the negative polarity, 20 MA, 100 ns Z accelerator have shown that improving the contact improved the x-ray yield.Cornell data were collected on 16-wire Aluminum Z-pinch arrays in negative polarity. Experiments were conducted with both short and long current pulses with soldered and no-soldered wire/electrode contacts. The initiation, ablation, implosion and stagnation phases were compared for these four conditions. Time dependent x-ray signals were measured using diodes and diamond detectors. An inductive voltage monitor was used to infer minimum current radius achieved, as defined by a uniform shell of current moving radially inward, producing a time dependent inductance. Total energy data were collected with a metal-strip bolometer. Self-emission data were collected by an XUV 4-frame camera and an optical streak camera.In negative polarity and with short pulses, soldering appeared to produce a smaller radius pinch and decrease variations in the x-ray pulse shape. The bolometer, laser backlighter, 4-frame and streak cameras showed negligible differences in the initiation ablation
Properties of the Best Ar K-Shell Radiators: Two Decades of Data Analysis from Seven Z-Pinch Drivers
Apruzese, J. P.; Commisso, R. J.; Weber, B. V.; Thornhill, J. W.; Giuliani, J. L.; Mosher, D.; Young, F. C.; Coverdale, C. A.; Deeney, C.
2009-01-21
Z Pinches formed from Ar gas puffs have been investigated for more than two decades. Experiments have been performed on many generators; a frequent objective has been maximization of the yield in the K-shell lines. The increase in available current during that time, from 2 to 15 MA, has resulted in a remarkable enhancement in yield from a few kJ on PITHON to {approx}300 kJ on Sandia's Z generator. We have analyzed spectroscopic and other radiation data from seven Z-pinch drivers, some dating back to 1991, in an effort to determine what properties of the pinches correlate with high K-shell yield. The strongest correlation is with the amount of mass that is heated to K-shell emitting temperatures. Those temperatures, effective at emitting Ar K-shell x rays, exhibit a range of {approx}1 to 2.4 keV.
Transition from Beam-Target to Thermonuclear Fusion in High-Current Deuterium Z-Pinch Simulations.
Offermann, Dustin T; Welch, Dale R; Rose, Dave V; Thoma, Carsten; Clark, Robert E; Mostrom, Chris B; Schmidt, Andrea E W; Link, Anthony J
2016-05-13
Fusion yields from dense, Z-pinch plasmas are known to scale with the drive current, which is favorable for many potential applications. Decades of experimental studies, however, show an unexplained drop in yield for currents above a few mega-ampere (MA). In this work, simulations of DD Z-Pinch plasmas have been performed in 1D and 2D for a constant pinch time and initial radius using the code Lsp, and observations of a shift in scaling are presented. The results show that yields below 3 MA are enhanced relative to pure thermonuclear scaling by beamlike particles accelerated in the Rayleigh-Taylor induced electric fields, while yields above 3 MA are reduced because of energy lost by the instability and the inability of the beamlike ions to enter the pinch region.
Analyses in Support of Z-Pinch IFE and Actinide Transmutation - LLNL Progress Report for FY-06
Meier, W R; Moir, R W; Abbott, R
2006-09-19
This report documents results of LLNL's work in support of two studies being conducted by Sandia National Laboratories (SNL): the development of the Z-pinch driven inertial fusion energy (Z-IFE), and the use of Z-pinch driven inertial fusion as a neutron source to destroy actinides from fission reactor spent fuel. LLNL's efforts in FY06 included: (1) Development of a systems code for Z-IFE and use of the code to examine the operating parameter space in terms of design variables such as the Z-pinch driver energy, the chamber pulse repetition rate, the number of chambers making up the power plant, and the total net electric power of the plant. This is covered in Section 3 with full documentation of the model in Appendix A. (2) Continued development of innovative concepts for the design and operation of the recyclable transmission line (RTL) and chamber for Z-IFE. The work, which builds on our FY04 and FY05 contributions, emphasizes design features that are likely to lead to a more attractive power plant including: liquid jets to protect all structures from direct exposure to neutrons, rapid insertion of the RTL to maximize the potential chamber rep-rate, and use of cast flibe for the RTL to reduce recycling and remanufacturing costs and power needs. See Section 4 and Appendix B. (3) Description of potential figures of merit (FOMs) for actinide transmutation technologies and a discussion of how these FOMs apply and can be used in the ongoing evaluation of the Z-pinch actinide burner, referred to as the In-Zinerator. See Section 5. (4) A critique of, and suggested improvements to, the In-Zinerator chamber design in response to the SNL design team's request for feedback on its preliminary design. This is covered in Section 6.
Comments on the critical issues for a high-density gas-embedded Z-pinch CTR reactor concept
NASA Astrophysics Data System (ADS)
Ekdahl, C. A.
1981-02-01
The issues considered critical for the realization of a CTR reactor are discussed for the high density gas embedded z pinch concept. A simple model of the pinch reactor is presented that gives estimates for Q in substantial agreement with elaborate computer studies. An attempt is made to identify such critical points that are amenable to exploratory experiments. There appears to be no fatal flaw in the issues covered that would preclude a viable reactor based on this concept.
Computational investigation of the limits to Pease-Braginskii collapse of a Z-pinch
Nielsen, P.D.
1981-06-01
This dissertation investigates the one-dimensional limits to such a radiation enhanced collapse through the use of a Lagrangian simulation code, LASNEX. The code includes the effects of a wide range of phenomena - opacity, ionization, experimentally determined equations of state, magnetic effects on transport coefficients, and external electrical circuits. Special attention was given to the magnetic field subroutines. They were revised to include ion acoustic and lower hybrid drift induced resistivity and to increase accuracy and efficiency. The magnetic pressure term was differenced in a manner that eliminates any influence of zone size, allowing large, low density zones outside the plasma column. In these large zones, magnetic flux and energy were determined by direct integration instead of summation to increase overall conservation. With these changes, the computational timesteps were determined by phenomena in the plasma instead of the Alfven velocity in the low density region. These modifications improved the accuracy of the code on Z-pinch problems by a factor of 10-100 depending on the minimum pinch radius reached.
Preliminary Results of a 10 kJ Z-Pinch
Cortazar, O. D.; Piriz, A. R.; Prieto, G. Rodriguez; Hoffmann, D. H. H.; Tahir, N. A.
2008-04-07
Preliminary results obtained on 10 kJ Z-pinch device developed at the Plasma and Electrical Discharge Laboratory in the University of Castilla-La Mancha are presented. The device called ENERGU-1 is composed by 8 capacitors (0.5 {mu}F, 75 kV, 20 nH) connected in parallel to a discharge chamber by means of one high power plane transmission line by mean of 8 spark-gaps switches triggered by a 100 kV, 13 ns trigger pulse. The discharge chamber is a cylindrical Pyrex glass tube externally surrounded by a SF{sub 6} isolation atmosphere with the electrodes at the ends. Two different chambers have been studied by discharging the capacitor bank energy in deuterium for optimizing the D-D nuclear fusion reactions: one of 100 mm long by 100 mm inner diameter and the other of the same length and 70 mm inner diameter. Several sequences of ultrahigh speed converter camera photography (5 ns) are presented showing the implosion of plasma columns for different deuterium pressure and currents. Preliminary measurements of integrated 2.45 MeV neutron emissions by a silver activated neutron counter are analyzed as a function of electrical and constructive parameters. A yield of 10{sup 7}-10{sup 8} D-D fusion reactions by shot is reported when the optimum conditions are reached conducting currents of 400-600 kA with a plasma column lifetime above 100 ns.
New compact hohlraum configuration research at the 1.7 MA Z-pinch generator
Kantsyrev, V. L. Shrestha, I. K.; Esaulov, A. A.; Safronova, A. S.; Shlyaptseva, V. V.; Osborne, G. C.; Astanovitsky, A. L.; Weller, M. E.; Stafford, A.; Schultz, K. A.; Cooper, M. C.; Chuvatin, A. S.; Rudakov, L. I.; Velikovich, A. L.; Cuneo, M. E.; Jones, B.; Vesey, R. A.
2014-12-15
A new compact Z-pinch x-ray hohlraum design with parallel-driven x-ray sources was experimentally demonstrated in a full configuration with a central target and tailored shine shields (to provide a symmetric temperature distribution on the target) at the 1.7 MA Zebra generator. This presentation reports on the joint success of two independent lines of research. One of these was the development of new sources – planar wire arrays (PWAs). PWAs turned out to be a prolific radiator. Another success was the drastic improvement in energy efficiency of pulsed-power systems, such as the Load Current Multiplier (LCM). The Zebra/LCM generator almost doubled the plasma load current to 1.7 MA. The two above-mentioned innovative approaches were used in combination to produce a new compact hohlraum design for ICF, as jointly proposed by SNL and UNR. Good agreement between simulated and measured radiation temperature of the central target is shown. Experimental comparison of PWAs with planar foil liners (PFL) - another viable alternative to wire array loads at multi-MA generators show promising data. Results of research at the University of Nevada Reno allowed for the study of hohlraum coupling physics at University-scale generators. The advantages of new hohlraum design applications for multi-MA facilities with W or Au double PWAs or PFL x-ray sources are discussed.
Neutron spectra from beam-target reactions in dense Z-pinches
Appelbe, B. Chittenden, J.
2015-10-15
The energy spectrum of neutrons emitted by a range of deuterium and deuterium-tritium Z-pinch devices is investigated computationally using a hybrid kinetic-MHD model. 3D MHD simulations are used to model the implosion, stagnation, and break-up of dense plasma focus devices at currents of 70 kA, 500 kA, and 2 MA and also a 15 MA gas puff. Instabilities in the MHD simulations generate large electric and magnetic fields, which accelerate ions during the stagnation and break-up phases. A kinetic model is used to calculate the trajectories of these ions and the neutron spectra produced due to the interaction of these ions with the background plasma. It is found that these beam-target neutron spectra are sensitive to the electric and magnetic fields at stagnation resulting in significant differences in the spectra emitted by each device. Most notably, magnetization of the accelerated ions causes the beam-target spectra to be isotropic for the gas puff simulations. It is also shown that beam-target spectra can have a peak intensity located at a lower energy than the peak intensity of a thermonuclear spectrum. A number of other differences in the shapes of beam-target and thermonuclear spectra are also observed for each device. Finally, significant differences between the shapes of beam-target DD and DT neutron spectra, due to differences in the reaction cross-sections, are illustrated.
Use of microsecond current prepulse for dramatic improvements of wire array Z-pinch implosion
NASA Astrophysics Data System (ADS)
Calamy, H.; Lassalle, F.; Loyen, A.; Zucchini, F.; Chittenden, J. P.; Hamann, F.; Maury, P.; Georges, A.; Bedoch, J. P.; Morell, A.
2008-01-01
The Sphinx machine [F. Lassalle et al., "Status on the SPHINX machine based on the 1microsecond LTD technology"] based on microsecond linear transformer driver (LTD) technology is used to implode an aluminium wire array with an outer diameter up to 140mm and maximum current from 3.5to5MA. 700to800ns implosion Z-pinch experiments are performed on this driver essentially with aluminium. Best results obtained before the improvement described in this paper were 1-3TW radial total power, 100-300kJ total yield, and 20-30kJ energy above 1keV. An auxiliary generator was added to the Sphinx machine in order to allow a multi microsecond current to be injected through the wire array load before the start of the main current. Amplitude and duration of this current prepulse are adjustable, with maxima ˜10kA and 50μs. This prepulse dramatically changes the ablation phase leading to an improvement of the axial homogeneity of both the implosion and the final radiating column. Total power was multiplied by a factor of 6, total yield by a factor of 2.5 with a reproducible behavior. This paper presents experimental results, magnetohydrodynamic simulations, and analysis of the effect of such a long current prepulse.
Wire Array Z-pinch Insights for Intense X-ray Power Production
NASA Astrophysics Data System (ADS)
Sanford, T. W. L.
1998-11-01
The discovery [1] that the use of very large numbers of wires enables high x- ray power to be generated from wire-array z-pinches represents a breakthrough in load design for large pulsed power generators, and has permitted high temperatures to be generated in radiation cavities [2] on Saturn [3] and Z [4]. In this paper, changes in x-ray emission characteristics as a function of wire number, array mass, and load radius, for 20-mm-long aluminum arrays on Saturn that led to these breakthrough hohlraum results, are discussed and compared with a few related emission characteristics of high-wire-number aluminum and tungsten arrays on Z. In this discussion, the detailed measurements made with bolometers, filtered XRDs and PCDs, time resolved filtered x-ray pinhole cameras and crystal spectrometers are given meaning by comparison with one, two, and three dimensional radiation-magnetohydrodynamic code simulations. [1] T. W. L. Sanford, et al., Phys. Rev. Lett. 77, 5063 (1996). [2] M. K. Matzen, Phys. Plasmas 4, 1519 (1997). [3] D. D. Bloomquist, et al., Proc. 6th Int. IEEE Pulsed Power Conf., (1987), p. 310. [4] R. B. Spielman, et al., Phys. Plasmas 5, 2105 (1998).
Ion viscous heating in a magnetohydrodynamically unstable Z-pinch at over two billion Kelvin.
Jones, Brent Manley; Coverdale, Christine Anne; LePell, Paul David; Haines, Malcolm G.; Deeney, Christopher
2005-02-01
Pulsed power driven metallic wire-array Z pinches are the most powerful and efficient laboratory x-ray sources. Furthermore, under certain conditions the soft x-ray energy radiated in a 5 ns pulse at stagnation can exceed the estimated kinetic energy of the radial implosion phase by a factor of 3 to 4. A theoretical model is developed here to explain this, allowing the rapid conversion of magnetic energy to a very high ion temperature plasma through the generation of fine scale, fast-growing m=0 interchange MHD instabilities at stagnation. These saturate nonlinearly and provide associated ion viscous heating. Next the ion energy is transferred by equipartition to the electrons and thus to soft x-ray radiation. Recent time-resolved iron spectra at Sandia confirm an ion temperature T{sub i} of over 200 keV (2 x 10{sup 9} degrees), as predicted by theory. These are believed to be record temperatures for a magnetically confined plasma.
Z-pinch diagnostics, plasma and liner instabilities and new x-ray techniques
Oona, H.; Anderson, B.; Benage, J.
1996-09-01
Pulse power experiments of the last several decades have contributed greatly to the understanding of high temperature and high density plasmas and, more recently, to the study of hydrodynamic effects in thick imploding cylinders. Common to all these experiments is the application of a large current pulse to a cylindrically symmetric load, with the resulting Lorenz force compressing the load to produce hydrodynamic motion and/or high temperature, high density plasma. In Los Alamos, Pulsed power experiments are carried out at two facilities. Experiments at low current (from several million to ten million Amperes) are conducted on the Pegasus II capacitor bank. Experiments with higher currents (10`s to 100`s MA range) are performed in Ancho Canyon with the explosively driven Procyon and MAGO magnetic flux compression generator systems. In this paper, the authors present a survey of diagnostic capabilities and results from several sets of experiments. First, they discuss the initiation and growth of instabilities in plasmas generated from the implosion of hollow z-pinches in the pegasus and Procyon experiments. Next they discuss spectroscopic data from the plasmas produced by the MAGO system. They also show time resolved imaging data from thick ({approximately} .4 mm) liner implosions. Finally, the authors discuss improvements to x-ray and visible light imaging and spectrographic diagnostic techniques. The emphasis of this paper is not so much a detailed discussion of the experiments, but a presentation of imaging and spectroscopic results and the implications of these observations to the experiments.
The role of Z-pinches and related configurations in magnetized target fusion
Lindemuth, I.R.
1997-07-10
The use of a magnetic field within a fusion target is now known as Magnetized Target Fusion in the US and as MAGO (Magnitnoye Obzhatiye, or magnetic compression) in Russia. In contrast to direct, hydrodynamic compression of initially ambient-temperature fuel (e.g., ICF), MTF involves two steps: (a) formation of a warm, magnetized, wall-confined plasma of intermediate density within a fusion target prior to implosion; (b) subsequent quasi-adiabatic compression and heating of the plasma by imploding the confining wall, or pusher. In many ways, MTF can be considered a marriage between the more mature MFE and ICF approaches, and this marriage potentially eliminates some of the hurdles encountered in the other approaches. When compared to ICF, MTF requires lower implosion velocity, lower initial density, significantly lower radial convergence, and larger targets, all of which lead to substantially reduced driver intensity, power, and symmetry requirements. When compared to MFE, MTF does not require a vacuum separating the plasma from the wall, and, in fact, complete magnetic confinement, even if possible, may not be desirable. The higher density of MTF and much shorter confinement times should make magnetized plasma formation a much less difficult step than in MFE. The substantially lower driver requirements and implosion velocity of MTF make z-pinch magnetically driven liners, magnetically imploded by existing modern pulsed power electrical current sources, a leading candidate for the target pusher of an MTF system.
Development of the Axial Instability in Low Wire Number Wire Array Z-Pinches
NASA Astrophysics Data System (ADS)
Knapp, P. F.; Bell, K. S.; Blesener, I. C.; Chalenski, D. A.; Greenly, J. B.; Martin, M. R.; McBride, R. D.; Pikuz, S. A.; Shelkovenko, T. A.; Hammer, D. A.; Kusse, B. R.
2008-11-01
We are investigating the development of the axial instability that occurs on wires in wire-array Z-pinches, which manifests itself as a modulation of the size of the coronal plasma. The modulation is evidently a result of non-uniform ablation of material from the wire core. It is known that the wavelength of this modulation reaches a constant as the pinch develops that is a strong function of the material and little else, thus it is known as the fundamental mode. In these experiments we have been imaging individual wires with laser shadowgraphy primarily in low wire number, large wire diameter arrays made with Al, Cu, Ag and other wires. We document the development of this modulation from the beginning of plasma formation and show the wavelength and amplitude growth as a function of time. The magnetic field is also measured using B-dot probes inside the array. The change from a closed to an open field topology and its relation to the instability growth will be discussed.This research was supported by the Stewardship Sciences Academic Alliances program of the National Nuclear Security Administration under DOE Cooperative agreement DE-FC03-02NA00057 and by Sandia National Laboratories contract AO258.
Temperature Evolution of a 1 MA Triple-Nozzle Gas-Puff Z-Pinch
NASA Astrophysics Data System (ADS)
de Grouchy, Philip; Banasek, Jacob; Engelbrecht, Joey; Qi, Niansheng; Atoyan, Levon; Byvank, Tom; Cahill, Adam; Moore, Hannah; Potter, William; Ransohoff, Lauren; Hammer, David; Kusse, Bruce; Laboratory of Plasma Studies Team
2015-11-01
Mitigation of the Rayleigh-Taylor instability (RTI) plays a critical role in optimizing x-ray output at high-energy ~ 13 keV using the triple-nozzle Krypton gas-puff at Sandia National Laboratory. RTI mitigation by gas-puff density profiling using a triple-nozzle gas-puff valve has recently been recently demonstrated on the COBRA 1MA z-pinch at Cornell University. In support of this work we investigate the role of shell cooling in the growth of RTI during gas-puff implosions. Temperature measurements within the imploding plasma shell are recorded using a 527 nm, 10 GW Thomson scattering diagnostic for Neon, Argon and Krypton puffs. The mass-density profile is held constant at 22 microgram per centimeter for all three puffs and the temperature evolution of the imploding material is recorded. In the case of Argon puffs we find that the shell ion and electron effective temperatures remain in equilibrium at around 1keV for the majority of the implosion phase. In contrast scattered spectra from Krypton are dominated by of order 10 keV effective ion temperatures. Supported by the NNSA Stewardship Sciences Academic Programs.
Use of microsecond current prepulse for dramatic improvements of wire array Z-pinch implosion
Calamy, H.; Lassalle, F.; Loyen, A.; Zucchini, F.; Chittenden, J. P.; Hamann, F.; Maury, P.; Georges, A.; Bedoch, J. P.; Morell, A.
2008-01-15
The Sphinx machine [F. Lassalle et al., 'Status on the SPHINX machine based on the 1microsecond LTD technology'] based on microsecond linear transformer driver (LTD) technology is used to implode an aluminium wire array with an outer diameter up to 140 mm and maximum current from 3.5 to 5 MA. 700 to 800 ns implosion Z-pinch experiments are performed on this driver essentially with aluminium. Best results obtained before the improvement described in this paper were 1-3 TW radial total power, 100-300 kJ total yield, and 20-30 kJ energy above 1 keV. An auxiliary generator was added to the Sphinx machine in order to allow a multi microsecond current to be injected through the wire array load before the start of the main current. Amplitude and duration of this current prepulse are adjustable, with maxima {approx}10 kA and 50 {mu}s. This prepulse dramatically changes the ablation phase leading to an improvement of the axial homogeneity of both the implosion and the final radiating column. Total power was multiplied by a factor of 6, total yield by a factor of 2.5 with a reproducible behavior. This paper presents experimental results, magnetohydrodynamic simulations, and analysis of the effect of such a long current prepulse.
Gas Puff Z-Pinches at 1-MA and 200-ns on COBRA
NASA Astrophysics Data System (ADS)
Hammer, David; Qi, Niansheng; Rosenberg, Elliott; Atoyan, Levon; Potter, William; Blesener, Kate; Cahill, Adam; Gourdain, Pierre-Alexandre; Greenly, John; Hoyt, Cad; Kusse, Bruce; Pikuz, Sergei; Schrafel, Peter; Shelkovenko, Tatiana
2013-10-01
We report 6-cm diameter, double-shell gas puff Z-pinch experiments at 1 MA on the COBRA pulsed power generator, in which the implosion dynamics in puff-on-puff load configurations with and without a wire on the pinch axis were studied. Diagnostics used included: Planar Laser Induced Fluorescence Analyzer for measuring initial density profiles of the gas puff; a Laser Shearing Interferometer and a Laser Wavefront Analyzer for density profiles in the implosion and pinch phases; fiber-coupled, gated visible-light spectrometers for radially resolved imploding plasma spectra; gated XUV cameras for implosion dynamics; filtered pinhole x-ray cameras for imaging x-ray emission; and a double-crystal x-ray spectrometer for axially resolved pinch plasma densities and temperatures. From these, we derived the implosion velocity, ion charge states and then the imploding plasma temperatures, obtained the time evolution of the imploding plasma sheath structure and Magnetic Rayleigh-Taylor instability, and observed the most stable implosion with light-ions (Ne) imploding on heavy-ions (Ar), unstable implosions with heavy-ions (Ar) imploding on light-ions (Ne), and tighter, denser and less hot pinch plasma with a wire on axis. Details of the results will be presented. Supported by NNSA under DOE Coop. Agreement DE- NA0001836.
Implosion characteristics and applications of combined tungsten-aluminum Z-pinch planar arrays
NASA Astrophysics Data System (ADS)
Osborne, G. C.; Kantsyrev, V. L.; Esaulov, A. A.; Safronova, A. S.; Weller, M. E.; Shrestha, I.; Williamson, K. M.; Shlyaptseva, V. V.
2013-12-01
An exploration of the implosion properties and X-ray radiation pulses from tungsten-based planar wire array Z-pinch experiments is presented, with an emphasis on loads mixed with aluminum. These experiments were carried out on Zebra, the 1.0 MA pulse power generator at the Nevada Terawatt Facility. A suite of diagnostics was used to study these plasmas, including X-ray and EUV Si diodes, optical imaging, laser shadowgraphy, and time-gated and time-integrated X-ray pinhole imagers and spectrometers. Specifically, loads with relatively large inter-wire gaps where tungsten is placed in the center of a planar configuration composed primarily of aluminum showed unusual characteristics. These loads are shown to generate a "bubbling" effect in which plasma from the ablation of outer aluminum wires is temporarily hindered from converging at the center of the array where the tungsten wire is located. Reproduction of these experiments with variations to load geometry, materials, and mass distribution are also presented and discussed in an attempt to better understand the phenomenon. In addition, a theoretical model has also been applied to better understand the dynamics of the implosions of these loads. Applications of this effect to radiation pulse shaping, particularly with multi-planar arrays, are also discussed.
Ablation dynamics in wire array Z-pinches under modifications on global magnetic field topology
Veloso, Felipe Muñoz-Cordovez, Gonzalo; Donoso-Tapia, Luis; Valenzuela-Villaseca, Vicente; Favre, Mario; Wyndham, Edmund; Suzuki-Vidal, Francisco; Swadling, George; Chittenden, Jeremy
2015-07-15
The dynamics of ablation streams and precursor plasma in cylindrical wire array Z-pinches under temporal variations of the global magnetic field topology is investigated through experiments and numerical simulations. The wire arrays in these experiments are modified by replacing a pair of consecutive wires with wires of a larger diameter. This modification leads to two separate effects, both of which impact the dynamics of the precursor plasma; firstly, current is unevenly distributed between the wires and secondly, the thicker wires take longer to fully ablate. The uneven distribution of current is evidenced in the experiments by the drift of the precursor off axis due to a variation in the global magnetic field topology which modifies the direction of the ablation streams tracking the precursor position. The variation of the global magnetic field due to the presence of thick wires is studied with three-dimensional magnetohydrodynamic (MHD) simulations, showing that the global field changes from the expected toroidal field to a temporally variable topology after breakages appear in the thin wires. This leads to an observed acceleration of the precursor column towards the region closer to the thick wires and later, when thick wires also present breakages, it continues moving away from the original array position as a complicated and disperse object subject to MHD instabilities.
Analyzing Spatially Resolved Z-pinch Spectra to Determine the Nature of ``Bright Spots''*
NASA Astrophysics Data System (ADS)
Apruzese, J. P.; Giuliani, J. L.; Thornhill, J. W.; Ampleford, D. J.; Jones, B.; Coverdale, C. A.
2011-10-01
Wire array Z-pinch implosions which access the K-shell stages of their load elements are usually characterized by spatially nonuniform emission. But, is the existence of the ``bright spots'' due to density enhancement, higher temperature, or some combination of the two? Does the answer vary with atomic number of the load? To investigate this issue we have analyzed spatially resolved spectra from Cu and Al pinches driven by the Z generator. Correlation studies and regression analyses from the derived conditions are employed in order to infer the cause(s) of the local enhancements of K-shell powers. Work supported by U. S. Department of Energy, National Nuclear Security Administration. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE's NNSA under contract DE-AC04-94AL85000. JPA is a consultant to NRL through L3 Communications, Chantilly, VA 20151.
Spectroscopic Studies of the Soft X-Ray Radiation from Gas-Puff Z-Pinches on Cobra
NASA Astrophysics Data System (ADS)
Shelkovenko, T. A.; Pikuz, S. A.; de Grouchy, P. W. L.; Qi, N.; Atoyan, L.; Kusse, B. R.; Hammer, D. A.
2015-11-01
Gas-puff Z-pinch experiments have been conducted on the 0.8-1.2 MA, 100-240 ns pulse duration COBRA pulsed power generator. Triple nozzle gas-puff loads consisting of Ne, Ar and Kr gases in different combination and pressures with pre-ionization were used in the most recent experiments. Photo-conducting diodes (PCDs) and pinhole cameras with different filters were used to study the X-ray timing, intensity and spatial distribution in different energy bands. Spectrographs with spatial and temporal resolution were used to study the soft x-ray radiation from the gas-puff Z-pinches. One spectrograph with two spherically bent mica crystals was used to study radiation with 200 micron spatial resolution and high spectral resolution. An x-ray streak camera with one spherically bent quartz crystal was used to study the x-ray radiation with up to 10 ps temporal resolution. The x-ray spectra were used to estimate spatial and temporal distributions of plasma parameters and determine the intensity of the line and continuum radiation from the Z-pinches plasma. Work supported by the National Nuclear Security Administration Stewardship Sciences Academic Programs under Department of Energy Cooperative Agreement No. DE-NA0001836.
NASA Astrophysics Data System (ADS)
Nobile, Arthur; Balkey, Matthew; Bartos, Jacob; Batha, Steven; Brooks, Paul; Cameron, Bernard; Cobble, James; Cooley, Jason; Day, Robert; Edwards, John; Elliott, Joyce; Elliott, Norman; Fincke, James; Gomez, Veronica; Hatch, Douglas; Keiter, Paul; Kyrala, George; Lanier, Nicholas; Manzanares, Ruben; Papin, Pallas; Perea, Ron; Pierce, Timothy; Randolph, Blaine; Sandoval, David; Sebring, Robert; Rivera, Gerald; Schmidt, Derek; Snow, Ron; Steckle, Warren; Tierney, Thomas; Valdez, Adelaida; Watt, Robert
2004-11-01
Several new targets have recently been developed and fielded to investigate physical phenomena occurring in the high energy density regime. Phenomena studied included interacting hydrodynamic jets, hydrodynamic instabilities in convergent geometry, radiation flow, shock propagation in ignition-relevant materials, and issues associated with double shell targets for achieving ignition on NIF. Targets to study interacting hydrodynamic jets have been fabricated for a NIF campaign. Challenges associated with these targets included producing thin (150 μm) Al disks with 100 and 160 μm precisely placed high quality holes, and fabrication of a thin wall (40 μm) 800 μm diameter cylindrical shock tube filled with low density (90 mg/cm3) carbonized resorcinol formaldehyde foam. Cylindrical targets to investigate hydrodynamic instabilities in convergent geometry as a function of initial surface perturbations have been fabricated. Many experimental campaigns with these targets have been conducted at OMEGA. These targets have been fabricated with a wide range of surface perturbations on an imploding Al marker layer using precision machining methods. The key challenge with these targets was fabrication of a high quality Al marker layer, and placement of specified surface features on the marker layer. Targets to investigate radiation flow and shock propagation in silicon aerogel were developed and fielded at the Sandia Z Pinch facility. The challenging feature associated with these targets was a high quality silicon aerogel disk that is attached to a gold washer containing a hole. Experiments on OMEGA have recently been conducted for the purpose of developing data on radiation absorption and shock propagation through ignition relevant materials. Specifically, we have fabricated targets for these experiments to investigate radiation absorption and shock propagation in Be-Cu alloys. The challenges associated with these targets were fabrication and characterization of very thin Be
Study of soft X-ray emission from Z-pinches with a complex atomic composition
Volkov, G. S.; Zaitsev, V. I.; Grabovski, E. V.; Fedulov, M. V.; Aleksandrov, V. V.; Lakhtyushko, N. I.
2010-03-15
Results are presented from experimental studies of Z-pinches produced by implosion of aluminum and tungsten cylindrical wire arrays in the Angara-5-1 facility. The electron temperature T{sub e} and density n{sub e} of the high-temperature pinch plasma have been determined by analyzing line emission from multicharged ions. For the same mass and radius of the array and the same number of wires in it, the intensity of line emission of H- and He-like Al ions from an imploded Al + W wire array containing even a small amount of tungsten (7 wt %) is one order of magnitude lower than that from an Al array. As the W content increases, the total soft X-ray (SXR) yield increases, while the duration of the SXR pulse decreases. For the 30% W content in the array, the power and duration of the SXR pulse are nearly the same as those recorded during the implosion of a W array with the same linear mass and radius and the same number of wires. Results are also presented from experiments with nested wire arrays in which the outer and inner shells were made of Al and W wires, respectively. It is found that, in this case, the effect of tungsten on the line emission of aluminum is much weaker than that in experiments with arrays in which tungsten and aluminum wires were placed in the same shell, even if the mass of the inner (tungsten) shell was larger than that of the outer (aluminum) one. At the same time, the inner W shell plays a significant role in the implosion dynamics of a nested wire array, reducing the duration of the SXR pulse and increasing the SXR power.
K-α emission spectroscopic analysis from a Cu Z-pinch
Dasgupta, A.; Clark, R. W.; Giuliani, J. L.; Ouart, N. D.; Jones, B.; Ampleford, D. J.; Hansen, S. B.
2013-06-01
Advances in diagnostic techniques at the Sandia Z-facility have facilitated the production of very detailed spectral data. In particular, data from the copper nested wire-array shot Z1975 provides a wealth of information about the implosion dynamics and ionization history of the pinch. Besides the dominant valence K- and L-shell lines in Z1975 spectra, K-α lines from various ionization stages were also observed. K-shell vacancies can be created from inner-shell excitation and ionization by hot electrons and from photo-ionization by high-energy photons; these vacancies are subsequently filled by Auger decay or resonance fluorescence. The latter process produces the K-α emission. For plasmas in collisional equilibrium, K-α emission usually occurs from highly charged ions due to the high electron temperatures required for appreciable excitation of the K-α transitions. Our simulation of Z1975 was carried out with the NRL 1-D DZAPP non-LTE radiation-hydrodynamics model, and the resulting K- and L-shell synthetic spectra are compared with measured radiation data. Our investigation will focus on K-α generation by both impacting electrons and photons. Synthetic K-α spectra will be generated either by self-consistently calculating the K-shell vacancy production in a full Z-pinch simulation, or by post-processing data from a simulation. The analysis of these K-α lines as well as K- and L-shell emission from valence electrons should provide quantitative information about the dynamics of the pinch plasma.
The quest for a z-pinch based fusion energy source—a historical perspective
NASA Astrophysics Data System (ADS)
Sethian, John
1997-05-01
Ever since 1958, when Oscar Anderson observed copious neutrons emanating from a "magnetically self-constricted column of deuterium plasma," scientists have attempted to develop the simple linear pinch into a fusion power source. After all, simple calculations show that if one can pass a current of slightly less than 2 million amperes through a stable D-T plasma, then one could achieve not just thermonuclear break-even, but thermonuclear gain. Moreover, several reactor studies have shown that a simple linear pinch could be the basis for a very attractive fusion system. The problem is, of course, that the seemingly simple act of passing 2 MA through a stable pinch has proven to be quite difficult to accomplish. The pinch tends to disrupt due to instabilities, either by the m=0 (sausage) or m=1 (kink) modes. Curtailing the growth of these instabilities has been the primary thrust of z-pinch fusion research, and over the years a wide variety of formation techniques have been tried. The early pinches were driven by relatively slow capacitive discharges and were formed by imploding a plasma column. The advent of fast pulsed power technology brought on a whole new repertoire of formation techniques, including: fast implosions, laser or field-enhanced breakdown in a uniform volume of gas, a discharge inside a small capillary, a frozen deuterium fiber isolated by vacuum, and staged concepts in which one pinch implodes upon another. And although none of these have yet to be successful, some have come tantalizingly close. This paper will review the history of this four-decade long quest for fusion power.
Wire Array Z-Pinch Insights for Enhanced X-Ray Production
Apruzese, J.P.; Chittenden, J.P.; Greenly, J.B.; Haines, M.G.; Mock, R.C.; Mosher, D.; Peterson, D.L.; Reisman, D.B.; Sanford, T.W.L.; Sinars, D.B.; Spielman, R.B.; Whitnery, K.G.
1999-01-04
Comparisons of measured total radiated x-ray power from annular wire-array z-pinches with a variety of models as a function of wire number, array mass, and load radius are reviewed. The data, which are comprehensive, have provided important insights into the features of wire-array dynamics that are critical for high x-ray power generation. Collectively, the comparisons of the data with the model calculations suggest that a number of underlying dynamical mechanisms involving cylindrical asymmetries and plasma instabilities contribute to the measured characteristics. For example, under the general assumption that the measured risetime of the total-radiated-power pulse is related to the thickness of the plasma shell formed on axis, the Heuristic Model [IEEE Trans. Plasma Sci., 26, 1275 (1998)] agrees with the measured risetime under a number of specific assumptions about the way the breakdown of the wires, the wire-plasma expansion, and the Rayleigh-Taylor instability in the r-z plane, interact. Likewise, in the high wire-number regime (where the wires are calculated to form a plasma shell prior to significant radial motion of the shell) the comparisons show that the variation in the power of the radiation generated as a function of load mass and array radius can be simulated by the 2-D Eulerian-radiation-magnetohydrodynamics code (E-RMHC) [Phys. Plasmas 3, 368 (1996)], using a single random-density perturbation that seeds the Rayleigh-Taylor instability in the r-z plane. For a given pulse-power generator, the comparisons suggest that (1) the smallest interwire gaps compatible with practical load construction and (2) the minimum implosion time consistent with the optimum required energy coupling of the generator to the load should produce the highest total-radiated-power levels.
Improved Stability of Gas-Embedded Z-Pinches Using a Micro-Channel Preionisation
NASA Astrophysics Data System (ADS)
Benage, John; Skowronek, Maurice; Roméas, Paul
1994-03-01
A micro-channel using corona effect at atmospheric pressure, either in hydrogen or in air, is created prior to the triggering of the main discharge. The channel diameter has been measured to have about 10 μm diameter, with a cw intensity of the order of 0.1 mA. The main discharge is powered by a Marx generator delivering a current pulse of 240 kA during 200 ns at the end of a water line having 1 Ω impedance. Four pictures of the pinch are taken at each shot delayed in time, each from the other, from 10 ns to 260 ns. The discharge is seen to remain stable against usual instabilities during more than 500 ns. When a m = 1 instability appears sometime, its relative amplitude seem to remain constant as a function of time, at a very low level. The expansion of the channel takes place at very high velocities. In air, the expansion is slowered at a time corresponding to the maximum intensity. The influence of the micro-channel characteristics has been clearly checked: when it is not well-established, the discharge becomes unstable very early, even with the use of the pointed electrodes.
Design of a 5-MA 100-ns linear-transformer-driver accelerator for wire array Z-pinch experiments
NASA Astrophysics Data System (ADS)
Zhou, Lin; Li, Zhenghong; Wang, Zhen; Liang, Chuan; Li, Mingjia; Qi, Jianmin; Chu, Yanyun
2016-03-01
The linear-transformer-driver (LTD) is a recently developed pulsed-power technology that shows great promise for a number of applications. These include a Z -pinch-driven fission-fusion-hybrid reactor that is being developed by the Chinese Academy of Engineering Physics. In support of the reactor development effort, we are planning to build an LTD-based accelerator that is optimized for driving wire-array Z -pinch loads. The accelerator comprises six modules in parallel, each of which has eight series 0.8-MA LTD cavities in a voltage-adder configuration. Vacuum transmission lines are used from the interior of the adder to the central vacuum chamber where the load is placed. Thus the traditional stack-flashover problem is eliminated. The machine is 3.2 m tall and 12 m in outer diameter including supports. A prototype cavity was built and tested for more than 6000 shots intermittently at a repetition rate of 0.1 Hz. A novel trigger, in which only one input trigger pulse is needed by utilizing an internal trigger brick, was developed and successfully verified in these shots. A full circuit modeling was conducted for the accelerator. The simulation result shows that a current pulse rising to 5.2 MA in 91 ns (10%-90%) can be delivered to the wire-array load, which is 1.5 cm in height, 1.2 cm in initial radius, and 1 mg in mass. The maximum implosion velocity of the load is 32 cm /μ s when compressed to 0.1 of the initial radius. The maximum kinetic energy is 78 kJ, which is 11.7% of the electric energy stored in the capacitors. This accelerator is supposed to enable a radiation energy efficiency of 20%-30%, providing a high efficient facility for research on the fast Z pinch and technologies for repetition-rate-operated accelerators.
Hagenson, R.L.; Tai, A.S.; Krakowski, R.A.; Moses, R.W.
1980-01-01
A conceptual DT fusion reactor concept is described that is based upon the dense Z-pinch (DZP). This study emphasizes plasma modeling and the parametric assessment of the reactor energy balance. To this end simple analytic and numerical models have been developed and evaluated. The resulting optimal reactor operating point promises a high-Q, low-yield system of a scale that may allow the use of conventional high-voltage Marx/water-line technology to drive a potentially very small reactor system.
Investigating radial wire array Z pinches as a compact x-ray source on the Saturn generator
Ampleford, David J.; Bland, S. N.; Jennings, Christopher A.; Lebedev, S. V.; Chittenden, J. P.; Cuneo, Michael E.; McBride, Ryan D.; Jones, Brent Manley; Hall, G. N.; Suzuki-Vidal, F.; et al
2015-08-27
Radial wire array z pinches, where wires are positioned radially outward from a central cathode to a concentric anode, can act as a compact bright x-ray source that could potentially be used to drive a hohlraum. Experiments were performed on the 7-MA Saturn generator using radial wire arrays. These experiments studied a number of potential risks in scaling radial wire arrays up from the 1-MA level, where they have been shown to be a promising compact X-ray source. Data indicates that at 7 MA, radial wire arrays can radiate ~9 TW with 10-ns full-width at half-maximum from a compact pinch.
NASA Astrophysics Data System (ADS)
Syed, Wasif
Understanding the magnetic field topology in wire-array Z-pinches is of great significance for their ultimate application to stockpile stewardship and inertial confinement fusion. We have developed and tested several novel techniques involving material-based sensors to measure magnetic fields as a function of space and time in high energy density plasmas on pulsed power machines. We first briefly introduce a technique that was used to measure a lower limit of the maximum magnetic field of a sub-microsecond duration pulse using magnetic reversal in CoPt thin films. The time-varying magnetic field was generated by an exploding wire array plasma called an X pinch produced on the 0.5 MA, 100 ns pulse duration, XP pulsed power generator. We then introduce a technique based on Faraday rotation that was used to measure magnetic fields in wire-array Z-pinches produced on the 1 MA, 100 ns rise time, COBRA pulsed power generator as well as on the XP generator. This technique measures magnetic fields as a function of space and time using Faraday rotation of a single longitudinal mode (SLM) laser through a magneto-optically active bulk waveguide, multicomponent terbium borate glass, placed adjacent to, or within, the wire array. We have measured fields > 10 T with 100 ns rise times outside of a wire-array Z-pinch for the entire duration (˜250 ns) of the current pulse and as much as ˜2 T inside a wire-array for ˜40 ns from the start of current. This is the first time that such rapidly varying and large fields have been measured using the terbium borate glass. The third method, also based on Faraday rotation of SLM laser light utilized an integrated optical fiber sensor (a fiber-sensor-fiber assembly) on the XP pulsed power generator that also yielded a measurement of the magnetic field of a wire-array Z-pinch for part of the current pulse. Finally, we repeated the third method by fabricating a "thin film waveguide" of terbium borate glass to increase the spatial resolution
Measurement and analysis of x-ray absorption in Al and MgF2 plasmas heated by Z-pinch radiation.
MacFarlane, Joseph John; Rochau, Gregory Alan; Bailey, James E.
2005-06-01
High-power Z pinches on Sandia National Laboratories Z facility can be used in a variety of experiments to radiatively heat samples placed some distance away from the Z-pinch plasma. In such experiments, the heating radiation spectrum is influenced by both the Z-pinch emission and the re-emission of radiation from the high-Z surfaces that make up the Z-pinch diode. To test the understanding of the amplitude and spectral distribution of the heating radiation, thin foils containing both Al and MgF{sub 2} were heated by a 100-130 TW Z pinch. The heating of these samples was studied through the ionization distribution in each material as measured by x-ray absorption spectra. The resulting plasma conditions are inferred from a least-squares comparison between the measured spectra and calculations of the Al and Mg 1s {yields} 2p absorption over a large range of temperatures and densities. These plasma conditions are then compared to radiation-hydrodynamics simulations of the sample dynamics and are found to agree within 1{sigma} to the best-fit conditions. This agreement indicates that both the driving radiation spectrum and the heating of the Al and MgF{sub 2} samples is understood within the accuracy of the spectroscopic method.
Conversion of electromagnetic energy in Z-pinch process of single planar wire arrays at 1.5 MA
Liangping, Wang; Mo, Li; Juanjuan, Han; Ning, Guo; Jian, Wu; Aici, Qiu
2014-06-15
The electromagnetic energy conversion in the Z-pinch process of single planar wire arrays was studied on Qiangguang generator (1.5 MA, 100 ns). Electrical diagnostics were established to monitor the voltage of the cathode-anode gap and the load current for calculating the electromagnetic energy. Lumped-element circuit model of wire arrays was employed to analyze the electromagnetic energy conversion. Inductance as well as resistance of a wire array during the Z-pinch process was also investigated. Experimental data indicate that the electromagnetic energy is mainly converted to magnetic energy and kinetic energy and ohmic heating energy can be neglected before the final stagnation. The kinetic energy can be responsible for the x-ray radiation before the peak power. After the stagnation, the electromagnetic energy coupled by the load continues increasing and the resistance of the load achieves its maximum of 0.6–1.0 Ω in about 10–20 ns.
X-ray absorption spectroscopy for wire-array Z-pinches at the non-radiative stage
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; Hakel, P.; Mancini, R. C.; Chittenden, J. P.; Anderson, A.; Shevelko, A. P.; Wiewior, P.; Durmaz, T.; Altemara, S. D.; Papp, D.; Astanovitskiy, A. L.; Nalajala, V.; Chalyy, O.; Dmitriev, O.
2011-12-01
Absorption spectroscopy was applied to wire-array Z-pinches on the 1 MA pulsed-power Zebra generator at the Nevada Terawatt Facility (NTF). The 50 TW Leopard laser was coupled with the Zebra generator for X-ray backlighting of wire arrays at the ablation stage. Broadband X-ray emission from a laser-produced Sm plasma was used to backlight Al star wire arrays in the range of 7-9 Å. Two time-integrated X-ray conical spectrometers recorded reference and absorption spectra. The spectrometers were shielded from the bright Z-pinch X-ray burst by collimators. The comparison of plasma-transmitted spectra with reference spectra indicates absorption lines in the range of 8.1-8.4 Å. Analysis of Al K-shell absorption spectra with detailed atomic kinetics models shows a distribution of electron temperature in the range of 10-30 eV that was fitted with an effective two-temperature model. Temperature and density distributions in wire-array plasma were simulated with a three-dimension magneto-hydrodynamic code. Post-processing of this code's output yields synthetic transmission spectrum which is in general agreement with the data.
Long implosion time (240 ns) Z-pinch experiments with a large diameter (12 cm) double-shell nozzle
NASA Astrophysics Data System (ADS)
Levine, J. S.; Banister, J. W.; Failor, B. H.; Qi, N.; Song, Y.; Sze, H. M.; Fisher, A.
2004-05-01
Recently, an 8 cm diameter double-shell nozzle has produced argon Z pinches with high K-shell yields with implosion time of 210 ns. To produce even longer implosion time Z pinches for facilities such as Decade Quad [D. Price, et al., "Electrical and Mechanical Design of the Decade Quad in PRS Mode," in Proceedings of the 12th IEEE Pulsed Power Conference, Monterey, CA, edited by C. Stallings and H. Kirbie (IEEE, New York, 1999), p. 489] (9 MA short circuit current at 300 ns), a larger nozzle (12 cm outer diameter) was designed and fabricated. During initial testing on Double-EAGLE [P. Sincerny et al., Proceedings of the 5th IEEE Pulsed Power Conference, Arlington, VA, edited by M. F. Rose and P. J. Turchi (IEEE, New York, 1985), p. 151], 9 kJ of argon K-shell radiation in a 6 ns full width at half maximum pulse was produced with a 240 ns implosion. The initial gas distributions produced by various nozzle configurations have been measured and their impact on the final radiative characteristics of the pinch are presented. The addition of a central jet to increase the initial gas density near the axis is observed to enhance the pinch quality, increasing K-shell yield by 17% and power by 40% in the best configuration tested.
A non-LTE kinetic model for quick analysis of K-shell spectra from Z-pinch plasmas
Li, J. Huang, X. B. Cai, H. C. Yang, L. B. Xie, W. P. Duan, S. C.
2014-12-15
Analyzing and modeling K-shell spectra emitted by low-to moderate-atomic number plasma is a useful and effective way to retrieve temperature density of z-pinch plasmas. In this paper, a non-LTE population kinetic model for quick analysis of K-shell spectra was proposed. The model contains ionization stages from bare nucleus to neutral atoms and includes all the important atomic processes. In the present form of the model, the plasma is assumed to be both optically thin and homogeneous with constant temperature and density, and only steady-state situation is considered. According to the detailed calculations for aluminum plasmas, contours of ratios of certain K-shell lines in electron temperature and density plane as well as typical synthesized spectra were presented and discussed. The usefulness of the model is demonstrated by analyzing the spectrum from a neon gas-puff Z-pinch experiment performed on a 1 MA pulsed-power accelerator.
NASA Astrophysics Data System (ADS)
Ikuta, Kazunari
1987-11-01
The magneto-inertial confinement approach to fusion in a dynamic z-pinch regime is reconsidered using a new method of generating a hot plasma using a frozen deuterium tube as an initial condition. It will be seen that the technology of fabricating deuterium ice tube is possible if available pulse power technology could induce a current on the order of 10 MA along the tube. The dense z-pinch plasma formed from the electromagnetic implosion of this tubular deuterium-tritium ice with a radius of approximately 1 mm can satisfy the Lawson criterion, provided that its length is 1 cm.
NASA Astrophysics Data System (ADS)
Ikuta, Kazunari
1988-02-01
This paper reconsiders the magneto-inertia confinement approach to fusion in dynamic z-pinch with a new method of generating a hot plasma using a frozen deuterium-tritium (D-T) tube as an initial condition. If modern pulsed power technology can induce the high current of the order of 10 MA along the tube, the dense z-pinch plasma formed from the electro-magnetical implosion of thin tubular D-T ice with a radius of about 1 mm can satisfy the Lawson criterion for its 1 cm length.
Sharpe, Robin Arthur; Kingsep, Alexander S. (Kurchatov Institute, Moscow, Russia); Smith, David Lewis; Olson, Craig Lee; Ottinger, Paul F. (Naval Research Laboratory, Washington, DC); Schumer, Joseph Wade (Naval Research Laboratory, Washington, DC); Welch, Dale Robert (Voss Scientific, Albuquerque, NM); Kim, Alexander (High Currents Institute, Tomsk, Russia); Kulcinski, Gerald L. (University of Wisconsin, Madison, WI); Kammer, Daniel C. (University of Wisconsin, Madison, WI); Rose, David Vincent (Voss Scientific, Albuquerque, NM); Nedoseev, Sergei L. (Kurchatov Institute, Moscow, Russia); Pointon, Timothy David; Smirnov, Valentin P.; Turgeon, Matthew C.; Kalinin, Yuri G. (Kurchatov Institute, Moscow, Russia); Bruner, Nichelle "Nicki" (Voss Scientific, Albuquerque, NM); Barkey, Mark E. (University of Alabama, Tuscaloosa, AL); Guthrie, Michael (University of Wisconsin, Madison, WI); Thoma, Carsten (Voss Scientific, Albuquerque, NM); Genoni, Tom C. (Voss Scientific, Albuquerque, NM); Langston, William L.; Fowler, William E.; Mazarakis, Michael Gerrassimos
2007-01-01
Z-Pinch Inertial Fusion Energy (Z-IFE) complements and extends the single-shot z-pinch fusion program on Z to a repetitive, high-yield, power plant scenario that can be used for the production of electricity, transmutation of nuclear waste, and hydrogen production, all with no CO{sub 2} production and no long-lived radioactive nuclear waste. The Z-IFE concept uses a Linear Transformer Driver (LTD) accelerator, and a Recyclable Transmission Line (RTL) to connect the LTD driver to a high-yield fusion target inside a thick-liquid-wall power plant chamber. Results of RTL and LTD research are reported here, that include: (1) The key physics issues for RTLs involve the power flow at the high linear current densities that occur near the target (up to 5 MA/cm). These issues include surface heating, melting, ablation, plasma formation, electron flow, magnetic insulation, conductivity changes, magnetic field diffusion changes, possible ion flow, and RTL mass motion. These issues are studied theoretically, computationally (with the ALEGRA and LSP codes), and will work at 5 MA/cm or higher, with anode-cathode gaps as small as 2 mm. (2) An RTL misalignment sensitivity study has been performed using a 3D circuit model. Results show very small load current variations for significant RTL misalignments. (3) The key structural issues for RTLs involve optimizing the RTL strength (varying shape, ribs, etc.) while minimizing the RTL mass. Optimization studies show RTL mass reductions by factors of three or more. (4) Fabrication and pressure testing of Z-PoP (Proof-of-Principle) size RTLs are successfully reported here. (5) Modeling of the effect of initial RTL imperfections on the buckling pressure has been performed. Results show that the curved RTL offers a much greater buckling pressure as well as less sensitivity to imperfections than three other RTL designs. (6) Repetitive operation of a 0.5 MA, 100 kV, 100 ns, LTD cavity with gas purging between shots and automated operation is
A dual-channel, focusing x-ray spectrograph with uniform dispersion for Z pinch plasmas measurement
Yang Qingguo; Li Zeren; Chen Guanhua; Ye Yan; Huang Xianbin; Cai Hongchun; Li Jing; Xiao Shali
2012-01-15
A dual-channel, focusing x-ray spectrograph with uniform dispersion (i.e., the linear dispersion of this spectrograph is a constant) is described for measuring the x-ray spectra emission from the hot, dense Al Z pinch plasmas. The spectrograph uses double uniform-dispersed crystals (e.g., a Quartz 1010 crystal and a Mica 002 crystal) as dispersion elements and a double-film box as detector to achieve the simultaneous recording of the time integrated spectrum covering a wide spectral range of {approx}5-9 A. Since this spectrograph disperse the x-rays on the detector plane with uniform spacing for every wavelength, it needs not the calibration of the wavelength with spatial coordinate, thereby own the advantages of easiness and veracity for spectra identification. The design of this spectrograph and the example of experiment on the ''Yang'' accelerator are presented.
Direct Measurement of the Acceleration of a Probe Beam by a Dense Plasma Focus Z-Pinch
NASA Astrophysics Data System (ADS)
Ellsworth, J. L.; Falabella, S.; Rusnak, B.; Schmidt, A. E. W.; Tang, V.
2013-10-01
Dense plasma focus (DPF) Z-pinch plasmas produce multiple-MeV ions on a cm-scale length, implying electric field gradients exceeding 100 MV/m in the plasma. We report on the first experiments using a 4 MeV deuteron probe beam to directly measure the electric field gradients produced by the kJ-level DPF experiment at LLNL. This information can be used in conjunction with fully kinetic simulations of DPF plasmas to further our understanding of the mechanisms that produce these beams. An understanding of gradient formation in DPFs is necessary to optimize the gradients in these devices for compact accelerator applications. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and supported by the Laboratory Directed Research and Development Program (11-ERD-063) at LLNL.
Kantsyrev, V. L.; Safronova, A. S.; Esaulov, A. A.; Williamson, K. M.; Shrestha, I.; Ouart, N. D.; Yilmaz, M. F.; Wilcox, P. G.; Osborne, G. C.; Weller, M. E.; Shlyaptseva, V. V.; Chuvatin, A. S.; Rudakov, L. I.; Greenly, J. B.; McBride, R. D.; Knapp, P. F.; Blessener, I. C.; Bell, K. S.; Chalenski, D. A.; Hammer, D. A.
2009-01-21
The presented research focuses on investigation of Z-pinch plasma formation, implosion, and radiation characteristics as a function of the load configuration. The single planar and multi-planar wire arrays as well as compact cylindrical wire arrays were studied on the 1.3 MA UNR Zebra and 1 MA Cornell COBRA generators. The largest yields and powers were found for W and Mo double planar and compact wire arrays. A possibility of radiation pulse shaping was demonstrated. Two types of bright spots were observed in plasmas. A comparison of Mo double planar and compact wire array data indicates the possibility that the same heating mechanism operates during the final implosion and stagnation stages.
Osborne, G C; Kantsyrev, V L; Safronova, A S; Esaulov, A A; Weller, M E; Shrestha, I; Shlyaptseva, V V; Ouart, N D
2012-10-01
Absorption features from K-shell aluminum z-pinch plasmas have recently been studied on Zebra, the 1.7 MA pulse power generator at the Nevada Terawatt Facility. In particular, tungsten plasma has been used as a semi-backlighter source in the generation of aluminum K-shell absorption spectra by placing a single Al wire at or near the end of a single planar W array. All spectroscopic experimental results were recorded using a time-integrated, spatially resolved convex potassium hydrogen phthalate (KAP) crystal spectrometer. Other diagnostics used to study these plasmas included x-ray detectors, optical imaging, laser shadowgraphy, and time-gated and time-integrated x-ray pinhole imagers. Through comparisons with previous publications, Al K-shell absorption lines are shown to be from much lower electron temperature (∼10-40 eV) plasmas than emission spectra (∼350-500 eV).
Table-top water-window soft X-ray microscope using a Z-pinching capillary discharge source
NASA Astrophysics Data System (ADS)
Nawaz, M. F.; Nevrkla, M.; Jancarek, A.; Torrisi, A.; Parkman, T.; Turnova, J.; Stolcova, L.; Vrbova, M.; Limpouch, J.; Pina, L.; Wachulak, P.
2016-07-01
The development and demonstration of a table-top transmission soft X-ray (SXR) microscope, using a laboratory incoherent capillary discharge source has been carried out. This Z-pinching capillary discharge water-window SXR source, is a first of its kind to be used for high spatial resolution microscopy at λ = 2.88 nm (430 eV) . A grazing incidence ellipsoidal condenser mirror is used for focusing of the SXR radiation at the sample plane. The Fresnel zone plate objective lens is used for imaging of the sample onto a back-illuminated (BI) CCD camera. The achieved half-pitch spatial resolution of the microscope approaches 100 nm, as demonstrated by the knife-edge test. Details about the source, and the construction of the microscope are presented and discussed. Additionally, the SXR images of various samples, proving applicability of such microscope for observation of objects in the nanoscale, are shown.
NASA Astrophysics Data System (ADS)
Klir, D.; Shishlov, A. V.; Kokshenev, V. A.; Kubes, P.; Labetsky, A. Yu; Rezac, K.; Cherdizov, R. K.; Cikhardt, J.; Cikhardtova, B.; Dudkin, G. N.; Fursov, F. I.; Garapatsky, A. A.; Kovalchuk, B. M.; Kravarik, J.; Kurmaev, N. E.; Orcikova, H.; Padalko, V. N.; Ratakhin, N. A.; Sila, O.; Turek, K.; Varlachev, V. A.
2015-04-01
Z-pinch experiments with deuterium gas puffs have been carried out on the GIT-12 generator at 3 MA currents. Recently, a novel configuration of a deuterium gas-puff z-pinch was used to accelerate deuterons and to generate fast neutrons. In order to form a homogeneous, uniformly conducting layer at a large initial radius, an inner deuterium gas puff was surrounded by an outer hollow cylindrical plasma shell. The plasma shell consisting of hydrogen and carbon ions was formed at the diameter of 350 mm by 48 plasma guns. A linear mass of the plasma shell was about 5 µg cm-1 whereas a total linear mass of deuterium gas in single or double shell gas puffs was about 100 µg cm-1. The implosion lasted 700 ns and seemed to be stable up to a 5 mm radius. During stagnation, m = 0 instabilities became more pronounced. When a disruption of necks occurred, the plasma impedance reached 0.4 Ω and high energy (>2 MeV) bremsstrahlung radiation together with high energy deuterons were produced. Maximum neutron energies of 33 MeV were observed by axial time-of-flight detectors. The observed neutron spectra could be explained by a suprathermal distribution of deuterons with a high energy tail f≤ft({{E}\\text{d}}\\right)\\propto E\\text{d}-(1.8+/- 0.2) . Neutron yields reached 3.6 × 1012 at a 2.7 MA current. A high neutron production efficiency of 6 × 107 neutrons per one joule of plasma energy resulted from the generation of high energy deuterons and from their magnetization inside plasmas.
Experimental study of star-like and small-diameter wire-array z-pinches on the 1-MA Zebra generator
Ivanov, V. V.; Sotnikov, V. I.; Kindel, J. M.; Hakel, P.; Mancini, R. C.; Astanovitskiy, A. L.; Haboub, A.; Altemara, S. D.; Le Galloudec, B.; Nalajala, V.; Shevelko, A. P.; Kazakov, E. D.
2009-01-21
Star-like wire arrays and small-diameter (1-3 mm in diameter) cylindrical loads were tested in the 1-MA Zebra generator. Mitigation of plasma inhomogeneity was observed in the implosions of star-like loads, which consisted of multiple nested, cylindrical arrays aligned azimuthally such that the wires appear as linear array 'rays' extending from the axis of symmetry. The implosion in these loads is directed along the 'rays' of the star and cascades from wire to wire to the center to form moving plasma columns with smooth leading edges. Despite the low azimuthal symmetry, a star-like wire array produces a stable x-ray pulse with a high peak power and a short duration of 8-12-ns. This can be linked to the stabilization of instabilities due to the multiple nesting. X-ray generation and implosion dynamics in wire arrays 1-16 mm in diameter were investigated to find a transition between the regime with prevailing kinetic energy and 'non-kinetic' plasma heating. Loads 3-8 mm in diameter generate the highest x-ray power at the Zebra generator. The fall of x-ray power in 1-2-mm loads can be linked to the lack of kinetic energy. Laser probing diagnostics show the formation of 'necks' on the pinch during the bubble-like implosion. The energy balance provides the evidence of the enhanced plasma heating in z-pinches. Features of the implosions in small-diameter wire-arrays can help to identify the mechanisms of energy dissipation.
One- and two-dimensional modeling of argon K-shell emission from gas-puff Z-pinch plasmas
NASA Astrophysics Data System (ADS)
Thornhill, J. W.; Chong, Y. K.; Apruzese, J. P.; Davis, J.; Clark, R. W.; Giuliani, J. L.; Terry, R. E.; Velikovich, A. L.; Commisso, R. J.; Whitney, K. G.; Frese, M. H.; Frese, S. D.; Levine, J. S.; Qi, N.; Sze, H.; Failor, B. H.; Banister, J. W.; Coleman, P. L.; Coverdale, C. A.; Jones, B.; Deeney, C.
2007-06-01
In this paper, a theoretical model is described and demonstrated that serves as a useful tool for understanding K-shell radiating Z-pinch plasma behavior. Such understanding requires a self-consistent solution to the complete nonlocal thermodynamic equilibrium kinetics and radiation transport in order to realistically model opacity effects and the high-temperature state of the plasma. For this purpose, we have incorporated into the MACH2 two-dimensional magnetohydrodynamic (MHD) code [R. E. Peterkin et al., J. Comput. Phys. 140, 148 (1998)] an equation of state, called the tabular collisional radiative equilibrium (TCRE) model [J. W. Thornhill et al., Phys. Plasmas 8, 3480 (2001)], that provides reasonable approximations to the plasma's opacity state. MACH2 with TCRE is applied toward analyzing the multidimensional implosion behavior that occurred in Decade Quad (DQ) [D. Price et al., Proceedings of the 12th IEEE Pulsed Power Conference, Monterey, CA, edited by C. Stallings and H. Kirbie (IEEE, New York, 1999), p. 489] argon gas puff experiments that employed a 12cm diameter nozzle with and without a central gas jet on axis. Typical peak drive currents and implosion times in these experiments were ˜6MA and ˜230ns. By using Planar Laser Induced Fluorescence measured initial density profiles as input to the calculations, the effect these profiles have on the ability of the pinch to efficiently produce K-shell emission can be analyzed with this combined radiation-MHD model. The calculated results are in agreement with the experimental result that the DQ central-jet configuration is superior to the no-central-jet experiment in terms of producing more K-shell emission. These theoretical results support the contention that the improved operation of the central-jet nozzle is due to the better suppression of instabilities and the higher-density K-shell radiating conditions that the central-jet configuration promotes. When we applied the model toward projecting argon K
Using 1D theory to understand 3D stagnation of a wire-array Z pinch in the absence of radiation
NASA Astrophysics Data System (ADS)
Yu, Edmund
2015-11-01
Many high-energy-density systems implode towards the axis of symmetry, where it collides on itself, forming a hot plasma. However, experiments show these imploding plasmas develop three-dimensional (3D) structures. As a result, the plasma cannot completely dissipate its kinetic energy at stagnation, instead retaining significant 3D flow. A useful tool for understanding the effects of this residual flow is 3D simulation, but the amount and complexity of information can be daunting. To address this problem, we explore the connection between 3D simulation and one-dimensional (1D) theory. Such a connection, if it exists, is mutually beneficial: 1D theory can provide a clear picture of the underlying dynamics of 3D stagnation. On the other hand, deviations between theory and simulation suggest how 1D theory must be modified to account for 3D effects. In this work, we focus on a 3D, magnetohydrodynamic simulation of a compact wire-array Z pinch. To provide a simpler background against which to test our ideas, we artificially turn off radiation during the stagnation phase. Examination of the initial accumulation of mass on axis reveals oblique collision between jets, shock accretion, and vortex formation. Despite evidence for shock-dominated stagnation, a 1D shockless stagnation solution is more appropriate for describing the global dynamics, in that it reproduces the increase of on-axis density with time. However, the 1D solution must be modified to account for 3D effects: the flows suggest enhanced thermal transport as well as centrifugal force. Upon reaching peak compression, the stagnation transitions to a second phase, in which the high-pressure core on axis expands outward into the remaining imploding plasma. During this phase, a 1D shock solution describes the growth of the shock accretion region, as well as the decrease of on-axis density with time. However, the effect of 3D flows is still present: the on-axis temperature does not cool during expansion, which
Tangri, V.; Harvey-Thompson, Adam James; Giuliani, J. L.; Thornhill, J. W.; Velikovich, A. L.; Apruzese, J. P.; Quart, N. D.; DasGupta, A.; Jones, Brent M.; Jennings, Christopher Ashley
2016-10-19
Radiation-magnetohydrodynamic simulations using the non-LTE Mach2-TCRE code in (r,z) geometry are performed for two pairs of recent Ar gas-puff Z-pinch experiments on the refurbished Z generator with an 8 cm diameter nozzle. One pair of shots had an outer-to-inner shell mass ratio of 1:1.6 and a second pair had a ratio of 1:1.
Neutron production in deuterium gas-puff z-pinch with outer plasma shell at current of 3 MA
NASA Astrophysics Data System (ADS)
Cikhardt, J.; Klir, D.; Rezac, K.; Cikhardtova, B.; Kravarik, J.; Kubes, P.; Sila, O.; Shishlov, A. V.; Cherdizov, R. K.; Frusov, F. I.; Kokshenev, V. A.; Kurmaev, N. E.; Labetsky, A. Yu.; Ratakhin, N. A.; Dudkin, G. N.; Garapatsky, A. A.; Padalko, V. N.; Varlachev, V. A.; Turek, K.; Krasa, J.
2015-11-01
Z-pinch experiments at the current of about 3 MA were carried out on the GIT-12 generator. The outer plasma shell of deuterium gas-puff was generated by the system of 48 plasma guns. This configuration exhibits a high efficiency of the production of DD fusion neutrons with the yield of above 1012 neutrons produced in a single shot with the duration of about 20 ns. The maximum energy of the neutrons produced in this pulse exceeded 30 MeV. The neutron radiation was measured using scintillation TOF detectors, CR-39 nuclear track detectors, bubble detectors BD-PND and BDS-10000 and by several types of nuclear activation detectors. These diagnostic tools were used to measure the anisotropy of neutron fluence and neutron energy spectra. It allows us to estimate the total number of DD neutrons, the contribution of other nuclear reactions, the amount of scattered neutrons, and other parameters of neutron production. This work was supported by the MSMT grants LH13283, LD14089.
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.
Dynamics of a Z Pinch X Ray Source for Heating ICF Relevant Hohlraums to 120-160eV
SANFORD,THOMAS W. L.; OLSON,RICHARD E.; MOCK,RAYMOND CECIL; CHANDLER,GORDON A.; LEEPER,RAMON J.; NASH,THOMAS J.; RUGGLES,LAURENCE E.; SIMPSON,WALTER W.; STRUVE,KENNETH W.; PETERSON,D.L.; BOWERS,R.L.; MATUSKA,W.
2000-07-10
A z-pinch radiation source has been developed that generates 60 {+-} 20 KJ of x-rays with a peak power of 13 {+-} 4 TW through a 4-mm diameter axial aperture on the Z facility. The source has heated NIF (National Ignition Facility)-scale (6-mm diameter by 7-mm high) hohlraums to 122 {+-} 6 eV and reduced-scale (4-mm diameter by 4-mm high) hohlraums to 155 {+-} 8 eV -- providing environments suitable for indirect-drive ICF (Inertial Confinement Fusion) studies. Eulerian-RMHC (radiation-hydrodynamics code) simulations that take into account the development of the Rayleigh-Taylor instability in the r-z plane provide integrated calculations of the implosion, x-ray generation, and hohlraum heating, as well as estimates of wall motion and plasma fill within the hohlraums. Lagrangian-RMHC simulations suggest that the addition of a 6 mg/cm{sup 3} CH{sub 2} fill in the reduced-scale hohlraum decreases hohlraum inner-wall velocity by {approximately}40% with only a 3--5% decrease in peak temperature, in agreement with measurements.
Deuterium Gas-Puff Z-pinch as a Source of Fast Ions Producing Intensive Pulse of Neutrons
NASA Astrophysics Data System (ADS)
Rezac, K.; Cikhardt, J.; Cikhardtova, B.; Klir, D.; Kravarik, J.; Kubes, P.; Sila, O.; Shishlov, A.; Cherdizov, R.; Fursov, F.; Kokshenev, V.; Kovalchuk, B.; Kurmaev, N.; Labetsky, A.; Ratakhin, N.; Turek, K.
2015-11-01
A deuterium gas-puff with outer plasma shell has been examined on GIT-12 generator (on the current level of 3 MA) since 2013. Such a configuration caused more stable implosion at final stage of z-pinch. The consequence of this was a production of intensive pulses of fast ions. During last 4 campaigns in 2013-2015, fast ions were examined by several in-chamber diagnostics such as: stack detector (ion energy), pinhole camera (location of ion source), multi-pinhole camera (asymmetry and anisotropy of ion emission), and ion beam detector (dynamics of ion pulses). A CR-39 track detectors and also GAFCHROMIC HD-V2 films from these diagnostics will be presented. On the basis of obtained results, the solid sample for increasing of neutron yield up to 1e13 could be placed below the cathode mesh. Except of neutron yield, other properties such as: neutron energies (up to 33 MeV), neutron emission time (about 20 ns), and emission anisotropy of neutrons were measured. Such a short and intensive neutron pulse provides various applications. This work was supported by the MSMT project LH13283.
NASA Astrophysics Data System (ADS)
Rousculp, C. L.; Reass, W. A.; Oro, D. M.; Griego, J. R.; Turchi, P. J.; Reinovsky, R. E.; Saunders, A.; Mariam, F. G.; Morris, C.
2014-10-01
The first pulse-power driven, dynamic, liner-on-target experiment was successfully conducted at the Los Alamos proton radiography (pRad) facility. 100% data return was achieved on this experiment including a 21-image pRad movie. The experiment was driven with the PHELIX pulsed-power machine that utilizes a high-efficiency (k ~ 0.93) transformer to couple a small capacitor bank (U ~ 300 kJ) to a low inductance condensed-matter experimental load in a Z-pinch configuration. The current pulse (Ipeak = 3.7 MA, δt ~10 μs) was measured via a fiber optic Faraday rotation diagnostic. The experimental load consisted of a cylindrical Al liner (6 cm diam, 3 cm tall, 0.8 mm thick) and a cylindrical Al target (3 cm diam, 3 cm tall, 0.1 mm thick) that was coated with a thin (0.1 mm) uniform layer of tungsten powder (1 micron diam). It is observed that the shock-launched powder layer fully detaches from the target into a spatially correlated, radially converging (vr ~ 800 m/s) ring. The powder distribution is highly modulated in azimuth indicating particle interactions are significant. Results are compared to MHD simulations. Work supported by United States-DOE under Contract DE-AC52-06NA25396.
Design of a 100 J Dense Plasma Focus Z-pinch Device as a Portable Neutron Source
NASA Astrophysics Data System (ADS)
Jiang, Sheng; Higginson, Drew; Link, Anthony; Liu, Jason; Schmidt, Andrea
2015-11-01
The dense plasma focus (DPF) Z-pinch devices are capable of accelerating ions to high energies through MV/mm-scale electric fields. When deuterium is used as the filling gas, neutrons are generated through beam-target fusion when fast D beams collide with the bulk plasma. The neutron yield on a DPF scales favorably with current, and could be used as portable sources for active interrogation. Past DPF experiments have been optimized empirically. Here we use the particle-in-cell (PIC) code LSP to optimize a portable DPF for high neutron yield prior to building it. In this work, we are designing a DPF device with about 100 J of energy which can generate 106 - 107 neutrons. The simulations are run in the fluid mode for the rundown phase and are switched to kinetic to capture the anomalous resistivity and beam acceleration process during the pinch. A scan of driver parameters, anode geometries and gas pressures are studied to maximize the neutron yield. The optimized design is currently under construction. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and supported by the Laboratory Directed Research and Development Program (15-ERD-034) at LLNL.
NASA Astrophysics Data System (ADS)
Jones, B.; Coverdale, C. A.; Nielsen, D. S.; Jones, M. C.; Deeney, C.; Serrano, J. D.; Nielsen-Weber, L. B.; Meyer, C. J.; Apruzese, J. P.; Clark, R. W.; Coleman, P. L.
2008-10-01
A multicolor, time-gated, soft x-ray pinhole imaging instrument is fielded as part of the core diagnostic set on the 25 MA Z machine [M. E. Savage et al., in Proceedings of the Pulsed Power Plasma Sciences Conference (IEEE, New York, 2007), p. 979] for studying intense wire array and gas puff Z-pinch soft x-ray sources. Pinhole images are reflected from a planar multilayer mirror, passing 277 eV photons with <10 eV bandwidth. An adjacent pinhole camera uses filtration alone to view 1-10 keV photons simultaneously. Overlaying these data provides composite images that contain both spectral as well as spatial information, allowing for the study of radiation production in dense Z-pinch plasmas. Cu wire arrays at 20 MA on Z show the implosion of a colder cloud of material onto a hot dense core where K-shell photons are excited. A 528 eV imaging configuration has been developed on the 8 MA Saturn generator [R. B. Spielman et al., and A. I. P. Conf, Proc. 195, 3 (1989)] for imaging a bright Li-like Ar L-shell line. Ar gas puff Z pinches show an intense K-shell emission from a zippering stagnation front with L-shell emission dominating as the plasma cools.
Jones, B.; Coverdale, C. A.; Nielsen, D. S.; Jones, M. C.; Deeney, C.; Serrano, J. D.; Nielsen-Weber, L. B.; Meyer, C. J.; Apruzese, J. P.; Clark, R. W.; Coleman, P. L.
2008-10-15
A multicolor, time-gated, soft x-ray pinhole imaging instrument is fielded as part of the core diagnostic set on the 25 MA Z machine [M. E. Savage et al., in Proceedings of the Pulsed Power Plasma Sciences Conference (IEEE, New York, 2007), p. 979] for studying intense wire array and gas puff Z-pinch soft x-ray sources. Pinhole images are reflected from a planar multilayer mirror, passing 277 eV photons with <10 eV bandwidth. An adjacent pinhole camera uses filtration alone to view 1-10 keV photons simultaneously. Overlaying these data provides composite images that contain both spectral as well as spatial information, allowing for the study of radiation production in dense Z-pinch plasmas. Cu wire arrays at 20 MA on Z show the implosion of a colder cloud of material onto a hot dense core where K-shell photons are excited. A 528 eV imaging configuration has been developed on the 8 MA Saturn generator [R. B. Spielman et al., and A. I. P. Conf, Proc. 195, 3 (1989)] for imaging a bright Li-like Ar L-shell line. Ar gas puff Z pinches show an intense K-shell emission from a zippering stagnation front with L-shell emission dominating as the plasma cools.
Jones, B; Coverdale, C A; Nielsen, D S; Jones, M C; Deeney, C; Serrano, J D; Nielsen-Weber, L B; Meyer, C J; Apruzese, J P; Clark, R W; Coleman, P L
2008-10-01
A multicolor, time-gated, soft x-ray pinhole imaging instrument is fielded as part of the core diagnostic set on the 25 MA Z machine [M. E. Savage et al., in Proceedings of the Pulsed Power Plasma Sciences Conference (IEEE, New York, 2007), p. 979] for studying intense wire array and gas puff Z-pinch soft x-ray sources. Pinhole images are reflected from a planar multilayer mirror, passing 277 eV photons with <10 eV bandwidth. An adjacent pinhole camera uses filtration alone to view 1-10 keV photons simultaneously. Overlaying these data provides composite images that contain both spectral as well as spatial information, allowing for the study of radiation production in dense Z-pinch plasmas. Cu wire arrays at 20 MA on Z show the implosion of a colder cloud of material onto a hot dense core where K-shell photons are excited. A 528 eV imaging configuration has been developed on the 8 MA Saturn generator [R. B. Spielman et al., and A. I. P. Conf, Proc. 195, 3 (1989)] for imaging a bright Li-like Ar L-shell line. Ar gas puff Z pinches show an intense K-shell emission from a zippering stagnation front with L-shell emission dominating as the plasma cools.
Energy and matter flows in a plasma focus discharge
NASA Astrophysics Data System (ADS)
Vikhrev, V. V.; Suslin, S. V.
2016-01-01
The Plasma Focus is a type of z-pinch that is widely used for both basic research and applied tasks, e.g., as materials modification or research on intense plasma flows. Although the basic mechanisms of z-pinch compression are well-known, many of the processes that occur in the plasma focus have received less attention. This article is devoted to the study of plasma jets and some of its consequences in plasma focus discharges.
Larger sized wire arrays on 1.5 MA Z-pinch generator
Safronova, A. S. Kantsyrev, V. L. Weller, M. E. Shlyaptseva, V. V. Shrestha, I. K. Esaulov, A. A. Stafford, A.; Chuvatin, A. S.; Coverdale, C. A.; Jones, B.
2014-12-15
Experiments on the UNR Zebra generator with Load Current Multiplier (LCM) allow for implosions of larger sized wire array loads than at standard current of 1 MA. Advantages of larger sized planar wire array implosions include enhanced energy coupling to plasmas, better diagnostic access to observable plasma regions, and more complex geometries of the wire loads. The experiments with larger sized wire arrays were performed on 1.5 MA Zebra with LCM (the anode-cathode gap was 1 cm, which is half the gap used in the standard mode). In particular, larger sized multi-planar wire arrays had two outer wire planes from mid-atomic-number wires to create a global magnetic field (gmf) and plasma flow between them. A modified central plane with a few Al wires at the edges was put in the middle between outer planes to influence gmf and to create Al plasma flow in the perpendicular direction (to the outer arrays plasma flow). Such modified plane has different number of empty slots: it was increased from 6 up to 10, hence increasing the gap inside the middle plane from 4.9 to 7.7 mm, respectively. Such load configuration allows for more independent study of the flows of L-shell mid-atomic-number plasma (between the outer planes) and K-shell Al plasma (which first fills the gap between the edge wires along the middle plane) and their radiation in space and time. We demonstrate that such configuration produces higher linear radiation yield and electron temperatures as well as advantages of better diagnostics access to observable plasma regions and how the load geometry (size of the gap in the middle plane) influences K-shell Al radiation. In particular, K-shell Al radiation was delayed compared to L-shell mid-atomic-number radiation when the gap in the middle plane was large enough (when the number of empty slots was increased up to ten)
Osborne, Glenn C.; Esaulov, Andrey A.; Apruzese, John P.; Shrestha, I.; Kantsyrev, Victor Leonidovich; Shlyaptseva, V.; Coverdale, Christine Anne; Rudakov, Leonid I.; Williamson, K. M.; Deeney, Christopher; Ouart, Nicholas D.; Weller, M. E.; Safronova, Alla S.
2010-07-01
The planar wire array research on Zebra at UNR that started in 2005 continues experiments with new types of planar loads with results for consideration and comprehensive analysis [see, for example, Kantsyrev et al, HEDP 5, 115 (2009)]. The detailed studies of radiative properties of such loads are important and spectroscopy and imaging constitute a very valuable and informative diagnostic tool. The set of theoretical codes is implemented which provides non-LTE kinetics, wire ablation dynamic, and MHD modeling. This talk is based on the results of new recent experiments with planar wire arrays on Zebra at UNR. We start with results on radiative properties of a uniform single planar wire array (SPWA) from alloyed Al wires and move to combined triple planar wire arrays (TPWA) made from two materials, Cu and Al. Such combined TPWA includes three planar wire rows that are parallel to each other and made of either Cu or Al alloyed wires. Three different configurations (Al/Cu/Al, Cu/Al/Cu, and Cu/Cu/Al) are considered and compared with each other, and with the results from SPWA of the same materials. X-ray time-gated and time integrated pinhole images and spectra are analyzed together with bolometer, PCD, and XRD measurements, and optical images. Emphasis is made on the radiative properties and temporal and spatial evolution of plasma parameters of such two-component plasmas. The opacity effects are considered and the important question of what causes K-shell Al lines to be optically thin in combined TPWAs is addressed. In conclusion, the new findings from studying multi-planar wire array implosions are summarized and their input to Z-pinch radiation physics is discussed.
Xiao, Delong; Ding, Ning; Sun, Shunkai; Ye, Fan; Ning, Jiamin; Hu, Qingyuan; Chen, Faxin; Qin, Yi; Xu, Rongkun; Li, Zhenghong
2014-04-15
The interaction of a light tungsten wire-array Z-pinch with an embedded heavy foam converter, whose mass ratio is typically less than 0.16, is numerically analyzed and experimentally investigated on the 1.3 MA “QiangGuang I” facility. Computational results show that this implosion process can be divided into three stages: acceleration of the tungsten wire-array plasma, collision, and stagnation. The tungsten plasma is accelerated to a high speed by the J × B force and interacts weakly with the foam plasma in the first stage. Strong energy conversions take place in the second collision stage. When the high speed tungsten plasma impacts on the foam converter, the plasma is thermalized and a radial radiation peak is produced. Meanwhile, a shock wave is generated due to the collision. After the shock rebounds from the axis and meets the W/Foam boundary, the plasma stagnates and the second radial radiation peak appears. The collision and stagnation processes were observed and the two-peak radial radiation pulse was produced in experiments. Increasing the wire-array radius from 4 mm to 6 mm, the kinetic energy of the tungsten plasma is increased, causing a stronger thermalization and generating a higher first radiation peak. Experimental results also showed a higher ratio of the first peak to the second peak in the case of larger wire-array radius. If we add a thin CH film cover onto the surface of the embedded foam converter, the first radiation peak will be hardly changed, because the acceleration of the tungsten plasma is not evidently affected by the film cover. However, the second radiation peak decreases remarkably due to the large load mass and the corresponding weak compression.
McBride, R. D.; Shelkovenko, T. A.; Pikuz, S. A.; Hammer, D. A.; Greenly, J. B.; Kusse, B. R.; Douglass, J. D.; Knapp, P. F.; Bell, K. S.; Blesener, I. C.; Chalenski, D. A.
2009-01-15
Experimental results are presented that characterize the implosion dynamics and radiation output of wire-array Z pinches on the 1-MA, 100-ns rise-time Cornell Beam Research Accelerator (COBRA) [J. B. Greenly et al., Rev. Sci. Instrum. 79, 073501 (2008)]. The load geometries investigated include 20-mm-tall cylindrical arrays ranging from 4 to 16 mm in diameter, and consisting of 8, 16, or 32 wires of either tungsten, aluminum, or Invar (64% iron, 36% nickel). Diagnostics fielded include an optical streak camera, a time-gated extreme-ultraviolet framing camera, a laser shadowgraph system, time-integrated pinhole cameras, an x-ray wide-band focusing spectrograph with spatial resolution, an x-ray streak camera, a load voltage monitor, a Faraday cup, a bolometer, silicon diodes, and diamond photoconducting detectors. The data produced by the entire suite of diagnostics are analyzed and presented to provide a detailed picture of the overall implosion process and resulting radiation output on COBRA. The highest x-ray peak powers (300-500 GW) and total energy yields (6-10 kJ) were obtained using 4-mm-diameter arrays that stagnated before peak current. Additional findings include a decrease in soft x-ray radiation prior to stagnation as the initial wire spacing was changed from 1.6 mm to 785 {mu}m, and a timing correlation between the onset of energetic electrons, hard x-ray generation, and the arrival of trailing current on axis - a correlation that is likely due to the formation of micropinches. The details of these and other findings are presented and discussed.
Observed Multi-Decade DD and DT Z-Pinch Fusion Rate Scaling in 5 Dense Plasma Focus Fusion Machines
Hagen, E. C.; Lowe, D. R.; O'Brien, R.; Meehan, B. T.
2013-06-18
Dense Plasma Focus (DPF) machines are in use worldwide or a wide variety of applications; one of these is to produce intense, short bursts of fusion via r-Z pinch heating and compression of a working gas. We have designed and constructed a series of these, ranging from portable to a maximum energy storage capacity of 2 MJ. Fusion rates from 5 DPF pulsed fusion generators have been measured in a single laboratory using calibrated activation detectors. Measured rates range from ~ 1015 to more than 1019 fusions per second have been measured. Fusion rates from the intense short (20 – 50 ns) periods of production were inferred from measurement of neutron production using both calibrated activation detectors and scintillator-PMT neutron time of flight (NTOF) detectors. The NTOF detectors are arranged to measure neutrons versus time over flight paths of 30 Meters. Fusion rate scaling versus energy and current will be discussed. Data showing observed fusion cutoff at D-D fusion yield levels of approximately 1*1012, and corresponding tube currents of ~ 3 MA will be shown. Energy asymmetry of product neutrons will also be discussed. Data from the NTOF lines of sight have been used to measure energy asymmetries of the fusion neutrons. From this, center of mass energies for the D(d,n)3He reaction are inferred. A novel re-entrant chamber that allows extremely high single pulse neutron doses (> 109 neutrons/cm2 in 50 ns) to be supplied to samples will be described. Machine characteristics and detector types will be discussed.
NASA Astrophysics Data System (ADS)
McBride, R. D.; Shelkovenko, T. A.; Pikuz, S. A.; Hammer, D. A.; Greenly, J. B.; Kusse, B. R.; Douglass, J. D.; Knapp, P. F.; Bell, K. S.; Blesener, I. C.; Chalenski, D. A.
2009-01-01
Experimental results are presented that characterize the implosion dynamics and radiation output of wire-array Z pinches on the 1-MA, 100-ns rise-time Cornell Beam Research Accelerator (COBRA) [J. B. Greenly et al., Rev. Sci. Instrum. 79, 073501 (2008)]. The load geometries investigated include 20-mm-tall cylindrical arrays ranging from 4to16mm in diameter, and consisting of 8, 16, or 32 wires of either tungsten, aluminum, or Invar (64% iron, 36% nickel). Diagnostics fielded include an optical streak camera, a time-gated extreme-ultraviolet framing camera, a laser shadowgraph system, time-integrated pinhole cameras, an x-ray wide-band focusing spectrograph with spatial resolution, an x-ray streak camera, a load voltage monitor, a Faraday cup, a bolometer, silicon diodes, and diamond photoconducting detectors. The data produced by the entire suite of diagnostics are analyzed and presented to provide a detailed picture of the overall implosion process and resulting radiation output on COBRA. The highest x-ray peak powers (300-500GW) and total energy yields (6-10kJ) were obtained using 4-mm-diameter arrays that stagnated before peak current. Additional findings include a decrease in soft x-ray radiation prior to stagnation as the initial wire spacing was changed from 1.6mmto785μm, and a timing correlation between the onset of energetic electrons, hard x-ray generation, and the arrival of trailing current on axis—a correlation that is likely due to the formation of micropinches. The details of these and other findings are presented and discussed.
Characteristics of implosion and radiation for aluminum planar wire array z-pinch at 1.5 MA
Wang Liangping; Wu Jian; Li Mo; Han Juanjuan; Guo Ning; Wu Gang; Qiu Aici
2012-12-15
Planar wire arrays Z pinches were carried out on Qiangguang generator (1.5 MA, 100 ns). Loads with varied row widths (6-24 mm) and wire numbers (10-34) were employed in the experiments. The implosion dynamics of planar wire arrays has been studied. Meanwhile, the changes of the implosion time, radiation yield and power with array mass, inter-wire gap, and array width were investigated. The images of a soft X-ray camera exhibit that the trailing mass, precursor column, and R-T instability exist during the implosion phase, and when m = 0 maybe accompanied with m = 1, instability will rapidly develop after stagnation. The implosion trajectories show that loads will implode by the snowplow mode and about 50% of total initial array mass will participate in the final implosion. The maximum total X-ray energy is 22 kJ with a power of 630 GW, while the maximum K-shell yield is 3.9 kJ with a power of 158 GW. Experiments with different planar wire arrays show that the value of m{sub P}D{sub 0}{sup 2} (the product of line mass and squared width) is the critical factor which affects the implosion time and the X-ray products of the wire arrays. The optimum value of m{sub P}D{sub 0}{sup 2} should be in the range of 200-400 {mu}gcm and the inter-wire gap should be less than 1 mm.
Neutron Production in Deuterium Gas-Puff Z-Pinch Implosions on Refurbished Z
NASA Astrophysics Data System (ADS)
Clark, R. W.; Velikovich, A. L.; Davis, J.; Giuliani, J. L.; Coverdale, C. A.; Flicker, D.
2009-11-01
Earlier experiments with deuterium gas puff implosions on Z [Coverdale et al., Phys. Plasmas 14, 022706 and 056309 (2007)] demonstrated reproducible production of high neutron yields, up to ˜3x10^13, a large part of which might be of thermonuclear origin. We report a scoping study for such experiments on refurbished Z which can implode deuterium gas-puff loads at high-current, longer pulse (˜250 ns) regime. Significantly higher thermal DD neutron yields are predicted for ZR. We discuss the relative roles of kinetic-to-thermal energy conversion and adiabatic compression in heating the central deuterium column to the fusion temperature. We quantify the effect on the thermal neutron yield produced by loading the outer shells of the multi-shell gas-puff with a heavier gas to improve matching of the implosion to the current pulse, by additional heating of the central jet area with a Z-Beamlet laser and by applying an axial magnetic field in order to stabilize the implosion from a large initial radius.
Modifying Wire Array Z-pinch Ablation Structure and Implosion Dynamics Using Coiled Arrays
Hall, Gareth N.; Bland, Simon N.; Lebedev, Sergey V.; Chittenden, Jeremy P.; Palmer, James B. A.; Suzuki-Vidal, Francisco A.; Swadling, George F.; Niasse, Nicolas; Knapp, P. F.; Blesener, I. C.; McBride, R. D.; Chalenski, D. A.; Bell, K. S.; Greenly, J. B.; Blanchard, T.; Wilhelm, H.; Hammer, D. A.; Kusse, B. R.; Bott, Simon C.
2009-01-21
Coiled arrays, a cylindrical array in which each wire is formed into a helix, suppress the modulation of ablation at the fundamental wavelength. Outside the vicinity of the wire cores, ablation flow from coiled arrays is modulated at the coil wavelength and has a 2-stream structure in the r,{theta} plane. Within the vicinity of the helical wires, ablation is concentrated at positions with the greatest azimuthal displacement and plasma is axially transported from these positions such that the streams become aligned with sections of the coil furthest from the array axis. The GORGON MHD code accurately reproduces this observed ablation structure, which can be understood in terms of JxB forces that result from the interaction of the global magnetic field with a helical current path as well as additional current paths suggested by the simulations. With this ability to control where ablation streamers occur, large wavelength coils were constructed such that the breaks that form in the wires had sufficient axial separation to prevent perturbations in the implosion sheath from merging. This produces a new mode of implosion in which the global instability can be controlled and perturbations correlated between all wires in an array. For large wavelength 8-wire coiled arrays, this produced a dramatic increase in x-ray power, equalling that of a 32-wire straight array. These experiments were carried out on the MAGPIE generator (1 MA, 240 ns) at Imperial College, and the COBRA generator (1 MA, 100 ns) at Cornell University.
Computational modeling of long implosion time z pinches on the Saturn generator
NASA Astrophysics Data System (ADS)
Douglas, Melissa; Coverdale, Christine; Deeney, Christopher; Roderick, Norman
2000-10-01
Long implosion time wire array experiments have been carried out on the 7-MA Saturn accelerator at Sandia National Laboratories. Such experiments are motivated by the incentive that longer implosion times translate to reduced cost and power flow risk to existing and future, high current generators. However, this mode of driver is desirable only if similar implosion velocities and subsequent powers can be achieved that are comparable to a short pulse mode, i.e., 50 ns implosion time. To investigate pinch performance in the long pulse mode, wire number scans were performed with Al at 32 mm and 40 mm array diameters. Wire numbers ranged from 32 to 440 wires and the mass at each diameter was kept essentially constant. This experimental series also included a number of nested array shots with a 20 mm diam. inner array and a 40 mm diam. outer array, where wire number was varied in both arrays while maintaining a constant implosion time. Experimental results will be briefly summarized and a suite of radiation magnetohydrodynamic simulations that provide insight into the experimental trends will be presented. *Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US Department of Energy under Contract DE-AC04-94AL85000.
Low impedance z-pinch drivers without post-hole convolute current adders.
Savage, Mark Edward; Seidel, David Bruce; Mendel, Clifford Will, Jr.
2009-09-01
Present-day pulsed-power systems operating in the terawatt regime typically use post-hole convolute current adders to operate at sufficiently low impedance. These adders necessarily involve magnetic nulls that connect the positive and negative electrodes. The resultant loss of magnetic insulation results in electron losses in the vicinity of the nulls that can severely limit the efficiency of the delivery of the system's energy to a load. In this report, we describe an alternate transformer-based approach to obtaining low impedance. The transformer consists of coils whose windings are in parallel rather than in series, and does not suffer from the presence of magnetic nulls. By varying the pitch of the coils windings, the current multiplication ratio can be varied, leading to a more versatile driver. The coupling efficiency of the transformer, its behavior in the presence of electron flow, and its mechanical strength are issues that need to be addressed to evaluate the potential of transformer-based current multiplication as a viable alternative to conventional current adder technology.
Theory of formation of helical structures in a perfectly conducting, premagnetized Z-pinch liner
NASA Astrophysics Data System (ADS)
Yu, Edmund; Velikovich, Alexander; Peterson, Kyle
2014-10-01
The magnetized liner inertial fusion (MagLIF) concept uses an azimuthal magnetic field to collapse a thick metallic liner containing preheated fusion fuel. A critical component of the concept is an axial magnetic field, permeating both the fuel and surrounding liner, which reduces the compression necessary to achieve fusion conditions. Recent experiments demonstrate that a liner premagnetized with a 10 T axial field develops helical structures with a pitch significantly larger than an estimate of Bz /Bθ would suggest. The cause of the helical perturbations is still not understood. In this work, we present an analytic, linear theory in which we model the liner as a perfectly conducting metal, and study how bumps and divots on its surface redirect current flow, resulting in perturbations to B as well as j × B . We show that in the presence of axial and azimuthal magnetic field, the theory predicts divots will grow and deform at an angle determined by the magnetic field. We compare theoretical results with three dimensional, resistive MHD simulations. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the National Nuclear Security Administration under DE-AC04-94AL85000.
Time-resolved EUV spectra from nitrogen Z-pinching capillary discharge
NASA Astrophysics Data System (ADS)
Nevrkla, Michal; Jančárek, Alexandr; Nawaz, Fahad; Parkman, Tomáś; Vrbová, Miroslava
2015-05-01
Time-integrated spectra and time-resolved spectra (20 ns resolution) of nitrogen discharge plasma radiation were recorded and analyzed. Plasma was created by a 70 kA, 29 ns rise-time current pulse flowing through a 5 mm inner diameter, 224 mm long capillary filled with nitrogen to initial pressure ˜0.1 ÷ 1 kPa. Spectra were captured in the wavelength range 8.3 ÷ 14 nm. This spectral region contains nitrogen Balmer series lines including potentially lasing NVII 2 - 3 transition1. Spectral lines were identified using the NIST database and the FLY kinetic code. Together with spectra the capillary current was measured. Due to the low inductance design of the driver, the pinch is observable directly from the measured current. 13.38 nm NVII 2 - 3 line was observed in gated, and also in time-integrated spectra for currents <60 kA. For higher gas-filling pressure also other Balmer series lines were observed.
Wang, Kun-lun; Ren, Xiao-dong; Huang, Xian-bin; Zhang, Si-qun; Zhou, Shao-tong; Dan, Jia-kun; Li, Jing; Xu, Qiang; Ouyang, Kai; Cai, Hong-chun; Wei, Bing; Ji, Ce; Feng, Shu-ping; Wang, Meng; Xie, Wei-ping; Deng, Jian-jun
2015-11-01
Fast z-pinch is a very efficient way of converting electromagnetic energy to radiation. With an 8-10 MA current on primary test stand facility, about 1 MJ electromagnetic energy is delivered to vacuum chamber, which heats z-pinch plasma to radiate soft x-ray. To develop a pulsed high power x-ray source, we studied the applicability of diagnosing x-ray power from tungsten wire array z-pinch with a flat spectral response x-ray diode (FSR-XRD). The detector was originally developed to diagnose radiation of a hohlraum in SG-III prototype laser facility. It utilized a gold cathode XRD and a specially configured compound gold filter to yield a nearly flat spectral response in photon energy range of 0.1-4 keV. In practice, it was critical to avoid surface contamination of gold cathode. It is illustrated that an exposure of an XRD to multiple shots caused a significant change of response. Thus, in diagnosing x-ray power and energy, we used each XRD in only one shot after calibration. In a shot serial, output of FSR-XRD was compared with output of a nickel bolometer. In these shots, the outputs agreed with each other within their uncertainties which were about 12% for FSR-XRD and about 15% for bolometer. Moreover, the ratios between the FSR-XRD and the bolometer among different shots were explored. In 8 shots, the standard deviation of the ratio was 6%. It is comparable to XRD response change of 7%. PMID:26628136
Wang, Kun-lun; Ren, Xiao-dong; Huang, Xian-bin Zhang, Si-qun; Zhou, Shao-tong; Dan, Jia-kun; Li, Jing; Xu, Qiang; Ouyang, Kai; Cai, Hong-chun; Wei, Bing; Ji, Ce; Feng, Shu-ping; Wang, Meng; Xie, Wei-ping; Deng, Jian-jun
2015-11-15
Fast z-pinch is a very efficient way of converting electromagnetic energy to radiation. With an 8-10 MA current on primary test stand facility, about 1 MJ electromagnetic energy is delivered to vacuum chamber, which heats z-pinch plasma to radiate soft x-ray. To develop a pulsed high power x-ray source, we studied the applicability of diagnosing x-ray power from tungsten wire array z-pinch with a flat spectral response x-ray diode (FSR-XRD). The detector was originally developed to diagnose radiation of a hohlraum in SG-III prototype laser facility. It utilized a gold cathode XRD and a specially configured compound gold filter to yield a nearly flat spectral response in photon energy range of 0.1-4 keV. In practice, it was critical to avoid surface contamination of gold cathode. It is illustrated that an exposure of an XRD to multiple shots caused a significant change of response. Thus, in diagnosing x-ray power and energy, we used each XRD in only one shot after calibration. In a shot serial, output of FSR-XRD was compared with output of a nickel bolometer. In these shots, the outputs agreed with each other within their uncertainties which were about 12% for FSR-XRD and about 15% for bolometer. Moreover, the ratios between the FSR-XRD and the bolometer among different shots were explored. In 8 shots, the standard deviation of the ratio was 6%. It is comparable to XRD response change of 7%.
Sandord, T.W.L.; Olson, R.E.; Chandler, G.A.; Hebron, D.E.; Mock, R.C.; Leeper, R.J.; Nash, T.J.; Ruggles, L.E.; Simpson, W.W.; Struve, K.W.; Vesey, R.A.; Bowers, R.L.; Matuska, W.; Peterson, D.L.; Peterson, R.R.
1999-08-25
Hohlraums of full ignition scale (6-mm diameter by 7-mm length) have been heated by x-rays from a z-pinch target on Z to a variety of temperatures and pulse shapes which can be used to simulate the early phases of the National Ignition Facility (NIF) temperature drive. The pulse shape is varied by changing the on-axis target of the z pinch in a static-wall-hohlraum geometry. A 2-{micro}m-thick walled Cu cylindrical target of 8-mm diameter filled with 10 mg/cm{sup 3} CH, for example, produces foot-pulse conditions of {minus}85 eV for a duration of {approximately} 10 ns, while a solid cylindrical target of 5-mm diameter and 14-mg/cm{sup 3} CH generates first-step-pulse conditions of {approximately} 122 eV for a duration of a few ns. Alternatively, reducing the hohlraum size (to 4-mm diameter by 4-mm length) with the latter target has increased the peak temperature to {approximately} 150 eV, which is characteristic of a second-step-pulse temperature. In general, the temperature T of these x-ray driven hohlraums is in agreement with the Planckian relation (T-(P/A){sup 1/4}). P is the measured x-ray input power and A is the surface area of the hohlraum. Fully-integrated 2-D radiation-hydrodynamic simulations of the z pinch and subsequent hohlraum heating show plasma densities within the useful volume of the hohlraums to be on the order of air or less.
Jones, B.; Ampleford, D. J.; Vesey, R. A.; Cuneo, M. E.; Coverdale, C. A.; Waisman, E. M.; Jones, M. C.; Fowler, W. E.; Stygar, W. A.; Serrano, J. D.; Vigil, M. P.; Esaulov, A. A.; Kantsyrev, V. L.; Safronova, A. S.; Williamson, K. M.; Chuvatin, A. S.; Rudakov, L. I.
2010-03-26
An indirect drive configuration is proposed wherein multiple compact Z-pinch x-ray sources surround a secondary hohlraum. Planar compact wire arrays allow reduced primary hohlraum surface area compared to cylindrical loads. Implosions of planar arrays are studied at up to 15 TW x-ray power on Saturn with radiated yields exceeding the calculated kinetic energy, suggesting other heating paths. X-ray power and yield scaling studied from 1-6 MA motivates viewfactor modeling of four 6-MA planar arrays producing 90 eV radiation temperature in a secondary hohlraum.
NASA Astrophysics Data System (ADS)
Aleksandrov, V. V.; Volkov, G. S.; Grabovski, E. V.; Gritsuk, A. N.; Lakhtyushko, N. I.; Medovshchikov, S. F.; Oleinik, G. M.; Svetlov, E. V.
2014-02-01
Results are presented from measurements of the anisotropy of energy losses in high-current Z-pinches produced by the implosion of wire arrays at the ANGARA-5-1 facility at load currents of up to 4MA. The energy losses were measured in the radial direction and along the pinch axis from the anode side. The main diagnostics were time-integrated thermocouple calorimeters, nanosecond X-ray diodes (XRDs) with different filters, and a foil radiation calorimeter with a time resolution of 2 μs. The azimuthal anisotropy of energy losses was measured for different wire array configurations and different shapes of the high-voltage electrode. The presence of strong initial azimuthal inhomogeneity of the wire mass distribution (sectioned arrays), as well as the use of conical electrodes instead of plane ones, does not increase the azimuthal inhomogeneity of the total energy losses. For cylindrical wire arrays, energy losses in the radial direction are compared with those along the pinch axis. According to XRD and calorimetric measurements, the radiation yield per unit solid angle along the pinch axis is two to three times lower than that in the radial direction. In the axial direction, the energy flux density of the expanding plasma is two to three times lower than the radiation intensity. The measured radiation yield across the pinch is 2.5-5 kJ/sr, while that along the pinch axis is 1-2 kJ/sr. The results obtained by means of XRDs agree to within measurement errors with those obtained using the radiation calorimeter. It is found that the energy per unit solid angle carried by the expanding plasma in the radial direction does not exceed 10% of the soft X-ray yield. Analysis of the structure of time-integrated pinhole images and signals from the radial and axial XRDs shows that radiation emitted in the radial direction from the hot central region of the pinch is partially screened by the less dense surrounding plasma halo, whereas radiation emitted in the axial direction is a
NASA Astrophysics Data System (ADS)
Anderson, Austin; Ivanov, Vladimir; Papp, Daniel; Talbot, Bjorn; Astanovitskiy, Alexey
2013-10-01
The ablation and implosion stages of wire array z-pinches were studied using laser-based x-ray imaging at the 1-MA Zebra pulse power generator at the University of Nevada, Reno. X-ray backlighting at the wavelength of 6.65 Å was provided by hitting a Si target with the 50 TW Leopard laser. Laser-based radiography allows flexibility in both the timing and the position of the x-ray source. The issue of the method is the small energy of the laser pulse compared to radiation of the Z pinch. A spherically bent quartz crystal can give spatial resolution <10 microns and spectral linewidth of the x-ray on the order of 10-4. X-ray imaging allows viewing of the dense core of plasma column during the ablation stage. Wires with diameters 7.6-15 were resolved in test shots. Images of the wire-array at the ablation stage are discussed. Work was supported by the DOE grant DE-SC0008824 and DOE/NNSA UNR grant DE-FC52-06NA27616.
Gomez, M. R.; Zier, J. C.; Gilgenbach, R. M.; French, D. M.; Tang, W.; Lau, Y. Y.
2008-09-15
Soft metal gaskets (indium and silver) were used to reduce contact resistance between the wire and the electrode in an aluminum wire Z pinch by more than an order of magnitude over the best weighted contact case. Clamping a gasket over a Z-pinch wire compresses the wire to the electrode with a greater normal force than possible with wire weights. Average contact resistance was reduced from the range of 100-3000 {omega} (depending on wire weight mass) to 1-10 {omega} with soft metal gaskets. Single wire experiments (13 {mu}m Al 5056) on a 16 kA, 100 kV Marx bank showed an increase in light emission (97%) and emission volume (100%) of the plasma for the reduced contact resistance cases. The measured increases in plasma volume and light emission indicate greater energy deposition in the ablated wire. Additionally, dual-wire experiments showed plasma edge effects were significantly decreased in the soft metal gasket contact case. The average height of the edge effects was reduced by 51% and the width of the edge effects was increased by 40%, thus the gasket contact case provided greater axial uniformity in the plasma expansion profile of an individual wire.
Gomez, M R; Zier, J C; Gilgenbach, R M; French, D M; Tang, W; Lau, Y Y
2008-09-01
Soft metal gaskets (indium and silver) were used to reduce contact resistance between the wire and the electrode in an aluminum wire Z pinch by more than an order of magnitude over the best weighted contact case. Clamping a gasket over a Z-pinch wire compresses the wire to the electrode with a greater normal force than possible with wire weights. Average contact resistance was reduced from the range of 100-3000 Omega (depending on wire weight mass) to 1-10 Omega with soft metal gaskets. Single wire experiments (13 microm Al 5056) on a 16 kA, 100 kV Marx bank showed an increase in light emission (97%) and emission volume (100%) of the plasma for the reduced contact resistance cases. The measured increases in plasma volume and light emission indicate greater energy deposition in the ablated wire. Additionally, dual-wire experiments showed plasma edge effects were significantly decreased in the soft metal gasket contact case. The average height of the edge effects was reduced by 51% and the width of the edge effects was increased by 40%, thus the gasket contact case provided greater axial uniformity in the plasma expansion profile of an individual wire.
Huang, B.; Tomizuka, T.; Xie, B.; Sakai, Y.; Zhu, Q.; Song, I.; Okino, A.; Xiao, F.; Watanabe, M.; Hotta, E.
2013-11-15
The development and use of a single-fluid two-temperature approximated 2-D Magneto-Hydrodynamics code is reported. Z-pinch dynamics and the evolution of Magneto-Rayleigh-Taylor (MRT) instabilities in a gas jet type Extreme Ultraviolet (EUV) source are investigated with this code. The implosion and stagnation processes of the Z-pinch dynamics and the influence of initial perturbations (single mode, multi- mode, and random seeds) on MRT instability are discussed in detail. In the case of single mode seeds, the simulation shows that the growth rates for mm-scale wavelengths up to 4 mm are between 0.05 and 0.065 ns{sup −1}. For multi-mode seeds, the mode coupling effect leads to a series of other harmonics, and complicates MRT instability evolution. For perturbation by random seeds, the modes evolve to longer wavelengths and finally converge to a mm-scale wavelength approximately 1 mm. MRT instabilities can also alter the pinch stagnation state and lead to temperature and density fluctuations along the Z axis, which eventually affects the homogeneity of the EUV radiation output. Finally, the simulation results are related to experimental results to discuss the mitigations of MRT instability.
Increasing the K-shell yield of line radiation in Z-pinch implosions using alloyed Al/Mg wire-arrays
Xiao Delong; Ding Ning; Xue Chuang; Huang Jun; Zhang Yang; Ning Cheng; Sun Shunkai
2013-01-15
The variation of the K-shell yield of pure aluminum wire-array Z-pinch implosions with load parameters is discussed. The mechanism and the efficiency of increasing the K-shell yield using alloyed Al/Mg wire-arrays are numerically investigated. It has been shown that the maximum K-shell yield from a pure aluminum wire-array Z-pinch implosion can be obtained at an optimal load mass for a given generator and at a fixed initial wire-array radius. This optimal load mass is determined by the load energy coupling with the generator, the capability of Z-pinch plasmas to emit the K-shell radiation, and the self absorption of K-shell lines. For different generators, the optimal load mass increases as the drive current increases, and the line absorption limits the further increase of K-shell radiation. The coupled energy per ion is likely decreasing with increased mass, so the plasma might not be able to ionize into the K-shell. Also, the ability of the plasma to radiatively cool can increase with mass, thus, making it difficult for the plasma to ionize into and remain in the K-shell during the stagnation phase of the implosion. Alloyed Al/Mg wire-arrays were thus suggested to be used to decrease the opacity of K-shell lines and to increase the overall K-shell yield. In this paper, we show that using alloyed Al/Mg wire-arrays will decrease the opacity and increase the K-shell yield remarkably if the plasma is optically thick. We will also show that the efficiency of increasing the K-shell yield with alloyed Al/Mg wire-arrays cannot increase indefinitely. The ratio of K-shell yield from an alloyed Al/Mg wire-array to that from a pure aluminum wire-array reaches a limit. For example, we show that when the mass share of magnesium is 10% then this limit is 1.2, and for a 50% mass share, the limit is 1.3.
Sherar, A.G.
1996-10-01
An algebraic method to compute the macroscopic radial-averaged quantities (thickness, density, radial velocity) of the plasma sheet in the first compression of simple z-pinches is presented. Following the snowplow model, a set of MHD equations is written in a reference system in which the internal boundary of the plasma sheet is at rest. The magnetic pressure and the energy losses are both modeled as functions of the radius of the sheet, and a time-independent algebraic equation is obtained. Finding the roots of this expression, the thickness of the plasma sheet as a function of its radius can be computed. The temporal evolution of all the quantities of the plasma sheet can also be obtained making an appropriate change to the reference system. Computed values of the temperature of the sheet are in agreement with experimental values. The ranges of validity for the numerical values of the modeling parameters are analyzed.
Advanced stability analysis for laminar flow control
NASA Technical Reports Server (NTRS)
Orszag, S. A.
1981-01-01
Five classes of problems are addressed: (1) the extension of the SALLY stability analysis code to the full eighth order compressible stability equations for three dimensional boundary layer; (2) a comparison of methods for prediction of transition using SALLY for incompressible flows; (3) a study of instability and transition in rotating disk flows in which the effects of Coriolis forces and streamline curvature are included; (4) a new linear three dimensional instability mechanism that predicts Reynolds numbers for transition to turbulence in planar shear flows in good agreement with experiment; and (5) a study of the stability of finite amplitude disturbances in axisymmetric pipe flow showing the stability of this flow to all nonlinear axisymmetric disturbances.
Sherar, A.G.
1996-12-31
A simple method that allows to estimate the macroscopic variables (width, temperature, density, radial velocity, etc.) of the plasma sheet in the first compression of a z-pinch, is presented. Following the snow-plow model, the radial compression is assumed as a process in which the mass is swept by a sheet of finite width. Very high pressures can be reached inside the sheet due to magnetic compression, higher than the filling gas pressure. A quasi-equilibrium hypothesis for the pressure of the layer is defined. From this assumption the thickness of the dense plasma sheet can be estimated. A set of MHD equations that include a term to compute total energy losses is used. The system of equations is written in the interface reference system in which the internal boundary of the sheet is at rest. In this early stage of the compression, the plasma temperature is mainly due to heavy particles. The results obtained using this model can explain ionic temperatures measured in cold plasmas which cannot be explained from electron-ion collisions. From an analytical study of the formation solution, a well-defined range of validity for each parameter of the model has been found. Based on physical conditions, these ranges of validity give a criterion to understanding the necessary conditions to build and maintain a moving plasma sheet. Using this model, other geometries besides the cylindrical one can be analyzed in the future.
NASA Astrophysics Data System (ADS)
Boldarev, A. S.; Bolkhovitinov, E. A.; Vichev, I. Yu.; Volkov, G. S.; Gasilov, V. A.; Grabovskii, E. V.; Gritsuk, A. N.; Dan'ko, S. A.; Zaitsev, V. I.; Novikov, V. G.; Oleinik, G. M.; Ol'khovskaya, O. G.; Rupasov, A. A.; Fedulov, M. V.; Shikanov, A. S.
2015-02-01
Methods and results of studies of the radiation spectra of high-current Z-pinches with different elemental compositions are presented. To examine a wide spectral range ( E hν = 30-3000 eV), two diagnostics tools were used—a transmission grating and a reflecting mica crystal. The radiation characteristics of the pinch are determined by its elemental composition. For currents of 2-3 MA and low- Z elements (aluminum), the hard end of the radiation spectrum is represented by spectral lines with clearly pronounced K lines, while for high- Z elements (tungsten), the spectrum lies in the softer photon energy range and is quasi-continuous. Two methods of spectrum processing were used to determine the plasma parameters. The parameters of aluminum plasma were traditionally determined from the intensity ratios of the K lines taking into account the plasma transparency for these lines. The spectra of tungsten plasma were compared with the results of computer simulations of pinch compression with allowance for both magnetohydrodynamic and plasma radiation processes. The applicability of these methods of spectral analysis is discussed.
Soft x-ray (0.2
NASA Astrophysics Data System (ADS)
Failor, B. H.; Qi, N.; Levine, J. S.; Sze, H.; Gullickson, E. M.
2004-10-01
Z-pinches can produce intense fluxes of argon K-shell (3 keV) radiation, but typically only a fraction of the load mass near the axis of the pinch radiates in this spectral range. The majority of the mass does not get hot or dense enough to radiate efficiently in the K-shell. We have designed, built, and tested an instrument to image pinch emission, specifically the radial emission profile, at energies below the K-shell in order to track the location of the cooler mass. A gold mirror provides a high-energy cut-off at 2 keV while a transmission grating disperses the incoming radiation and provides a low-energy cutoff at 0.1 keV. A vertical slit images the pinch radiation in the radial direction and the emission profile is recorded with either an extreme ultraviolet-sensitive charge-coupled device camera (time-integrated) or a linear photodiode array (˜1 ns time resolution). We present results for the mirror, grating, and system characterization obtained at the Advanced Light Source synchrotron located at Lawrence Berkeley National Laboratory (Berkeley, CA).
Smith, David Lewis; Heames, Terence John; Parma, Edward J., Jr.; Peters, Curtis D.; Suo-Anttila, Ahti Jorma
2007-09-01
This report documents the key safety and operational aspects of a Z-pinch Externally Driven Nuclear Assembly (ZEDNA) reactor concept which is envisioned to be built and operated at the Z-machine facility in Technical Area IV. Operating parameters and reactor neutronic conditions are established that would meet the design requirements of the system. Accident and off-normal conditions are analyzed using a point-kinetics, one-dimensional thermo-mechanical code developed specifically for ZEDNA applications. Downwind dose calculations are presented to determine the potential dose to the collocated worker and public in the event of a hypothetical catastrophic accident. Current and magnetic impulse modeling and the debris shield design are examined for the interface between the Z machine and the ZEDNA. This work was performed as part of the Advanced Fusion Grand Challenge Laboratory Directed Research and Development Program. The conclusion of this work is that the ZEDNA concept is feasible and could be operated at the Z-machine facility without undue risk to collocated workers and the public.
Boldarev, A. S.; Bolkhovitinov, E. A.; Vichev, I. Yu.; Volkov, G. S.; Gasilov, V. A.; Grabovskii, E. V.; Gritsuk, A. N.; Dan’ko, S. A.; Zaitsev, V. I.; Novikov, V. G.; Oleinik, G. M.; Ol’khovskaya, O. G.; Rupasov, A. A.; Fedulov, M. V.; Shikanov, A. S.
2015-02-15
Methods and results of studies of the radiation spectra of high-current Z-pinches with different elemental compositions are presented. To examine a wide spectral range (E{sub hν} = 30–3000 eV), two diagnostics tools were used—a transmission grating and a reflecting mica crystal. The radiation characteristics of the pinch are determined by its elemental composition. For currents of 2–3 MA and low-Z elements (aluminum), the hard end of the radiation spectrum is represented by spectral lines with clearly pronounced K lines, while for high-Z elements (tungsten), the spectrum lies in the softer photon energy range and is quasi-continuous. Two methods of spectrum processing were used to determine the plasma parameters. The parameters of aluminum plasma were traditionally determined from the intensity ratios of the K lines taking into account the plasma transparency for these lines. The spectra of tungsten plasma were compared with the results of computer simulations of pinch compression with allowance for both magnetohydrodynamic and plasma radiation processes. The applicability of these methods of spectral analysis is discussed.
Flow stabilization by subsurface phonons
Hussein, M. I.; Biringen, S.; Bilal, O. R.; Kucala, A.
2015-01-01
The interaction between a fluid and a solid surface in relative motion represents a dynamical process that is central to the problem of laminar-to-turbulent transition (and consequent drag increase) for air, sea and land vehicles, as well as long-range pipelines. This problem may in principle be alleviated via a control stimulus designed to impede the generation and growth of instabilities inherent in the flow. Here, we show that phonon motion underneath a surface may be tuned to passively generate a spatio-temporal elastic deformation profile at the surface that counters these instabilities. We theoretically demonstrate this phenomenon and the underlying mechanism of frequency-dependent destructive interference of the unstable flow waves. The converse process of flow destabilization is illustrated as well. This approach provides a condensed-matter physics treatment to fluid–structure interaction and a new paradigm for flow control. PMID:27547095
Stability of oscillatory two phase Couette flow
NASA Technical Reports Server (NTRS)
Coward, Adrian V.; Papageorgiou, Demetrios T.
1993-01-01
We investigate the stability of two phase Couette flow of different liquids bounded between plane parallel plates. One of the plates has a time dependent velocity in its own plane, which is composed of a constant steady part and a time harmonic component. In the absence of time harmonic modulations, the flow can be unstable to an interfacial instability if the viscosities are different and the more viscous fluid occupies the thinner of the two layers. Using Floquet theory, we show analytically in the limit of long waves, that time periodic modulations in the basic flow can have a significant influence on flow stability. In particular, flows which are otherwise unstable for extensive ranges of viscosity ratios, can be stabilized completely by the inclusion of background modulations, a finding that can have useful consequences in many practical applications.
Stability of compressible Taylor-Couette flow
NASA Technical Reports Server (NTRS)
Kao, Kai-Hsiung; Chow, Chuen-Yen
1991-01-01
Compressible stability equations are solved using the spectral collocation method in an attempt to study the effects of temperature difference and compressibility on the stability of Taylor-Couette flow. It is found that the Chebyshev collocation spectral method yields highly accurate results using fewer grid points for solving stability problems. Comparisons are made between the result obtained by assuming small Mach number with a uniform temperature distribution and that based on fully incompressible analysis.
Mitrofanov, K. N. Grabovski, E. V.; Gritsuk, A. N.; Laukhin, Ya. N.; Aleksandrov, V. V.; Oleinik, G. M.; Medovshchikov, S. F.; Shevel'ko, A. P.
2013-01-15
Results are presented from experimental studies of the structure of the compressed plasma of a Z-pinch produced during the implosion of a foam-wire load at the current of up to 3 MA. The foam-wire load consisted of two nested cylindrical cascades, one of which was a solid or hollow cylinder made of low-density agar-agar foam, while the other was a wire array. The wall thickness of a hollow foam cylinder was 100-200 {mu}m. The images of the pinch and its spectrum obtained with the help of multiframe X-ray cameras and a grazing incidence spectrograph with a spatial resolution were analyzed. Data on the spatial structure of the emitting regions and the soft X-ray (SXR) spectrum of the Z-pinch in the final stage of compression of a foam-wire load were obtained. The implosion modes characterized by the formation of hot regions during implosion of such loads were revealed. The characteristic scale lengths of the hot regions were determined. It is shown that the energy distribution of SXR photons in the energy range from 80 eV to 1 keV forms the spatial structure of Z-pinch images recorded during the implosion of foam-wire loads. It is revealed that the spectral density of SXR emission in the photon energy range of 300-600 eV from hot Z-pinch regions exceeds the spectral density of radiation from the neighboring Z-pinch regions by more than one order of magnitude. Groups of lines related to the absorption and emission of radiation by atoms and multicharged ions of carbon and oxygen in the outer foam cascade of a foam-wire load were recorded for the first time by analyzing the spatial distribution of the SXR spectra of multicharged ions of the Z-pinch. The groups of absorption lines of ions (C III, O III, O IV, and O VI) corresponding to absorption of SXR photons in the Z-pinch of a tungsten wire array, which served as the inner cascade of a foam-wire load, were identified. The plasma electron temperature measured from the charge composition of carbon and oxygen ions in
NASA Astrophysics Data System (ADS)
Voronchev, V. T.; Kukulin, V. I.
2010-01-01
A new concept of inertial-magnetic confinement fusion is proposed. This concept is based on a high-current Z pinch combined with a femtosecond laser. The fusion target is composed of a D3He fuel contained under a high pressure inside a sealed cylindrical capsule made from metallic 9Be. An electric discharge along the capsule preheats the target and transforms it into a state of compressed liner. A subsequent TW femtosecond-laser pulse focused on a target end face causes ultrafast cold ignition of a small portion of the D3He fuel. This laser impact generates energetic electrons and ions, which trigger a nuclear-physics mechanism of a catalytic heating of the fuel and also creates a detonation shock wave capable of propagating along the plasma filament. It is shown that the self-sustaining fusion burn wave can appear in the D3He-9Be plasma, in which case the bulk of the energy release is carried by nonradioactive ions, with the energy gain being in excess of 50. The possibility of probing the fusion process by means of gamma-ray spectroscopy is also discussed. The radiative-capture reactions 3He( d, γ), D( d, γ), and 3He(3He, γ) naturally accompanying the burning of the D3He fuel are shown to serve as a convenient diagnostic tool. A nuclear “marker” of D3He fusion on the basis of the detection of monochromatic gamma rays produced in the reaction 9Be( α, γn), which is induced in the liner beryllium shell by energetic fusion alpha particles, is also examined.
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.
NASA Astrophysics Data System (ADS)
Haines, Malcolm; Coverdale, Christine; Deeney, Chris; Lepell, P. David; Jones, Brent; Apruzese, J. P.
2006-10-01
Pulsed power driven Z-pinches yield large X-ray powers at stagnation, the energy of which can exceed by up to factors of 3 or 4, the estimated kinetic energy of the implosion. Furthermore, when electron temperatures are measured at stagnation similar in temperatures would not lead to pressure balance. These problems can be resolved by a theoretical model in which short wavelength (ka >> 1, and viscous Lundquist number ˜ 1), fast growing, m=O MHD instabilities reach a saturated amplitude, and the associated viscous dissipation of the vortices leads to ion heating. Equating this heating rate to the equipartition of energy to electrons leads to an estimate of the ion temperature and pinch radius at pressure balance. Extremely high ion temperatures in the range of 200-300 KeV are predicted from this model for stainless steel wire array experiments on Z at Sandia. These have been confirmed from time-resolved Doppler broadening spectroscopic measurements of the optically thin Fe He-δ line. This conversion of magnetic energy into ion thermal energy occurs on the nanosecond timescale, and can prevent radiative collapse. Any accompanying loss of magnetic flux in this highly conducting plasma can be explained by the occurrence of a large number of hot spots along the axis, with electron density and temperature variating not exactly in phase. This leads to a significant value of the integral of E.dl. Dl along the axis due to the grad Pe term in Ohm's law, analogous to the magnetic field generating term found in laser-plasma interactions. Ref 1. M.G. Haines, et al; Phys. Rev. Lett. 96, 075003 (2006) Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-ACO4-94AL85000.
Maury, P.; Calamy, H.; Grunenwald, J.; Lassalle, F.; Zucchini, F.; Loyen, A.; Georges, A.; Morell, A.; Bedoch, J. P.
2009-01-21
The Sphinx machine{sup [1]} is a 6 MA, 1 {mu}S 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{sup [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 {eta} 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.
Phononic subsurface: Flow stabilization by crystals
NASA Astrophysics Data System (ADS)
Hussein, Mahmoud I.; Biringen, Sedat; Bilal, Osama R.; Kucala, Alec
2015-11-01
Flow control is a century-old problem where the goal is to alter a flow's natural state to achieve improved performance, such as delay of laminar-to-turbulent transition or reduction of drag in a fully developed turbulent flow. Meeting this goal promises to significantly reduce the dependence on fossil fuels for global transport. In this work, we show that phonon motion underneath a surface interacting with a flow may be tuned to cause the flow to stabilize, or destabilize, as desired. This concept is demonstrated by simulating a fully developed plane Poiseuille (channel) flow whereby a small portion of an otherwise rigid wall is replaced with a one-dimensional phononic crystal. A Tollmien-Schlichting (TS) wave is introduced to the flow as an evolving disturbance. Upon tuning the frequency-dependent phase and amplitude relations of the surface of the phononic crystal that interfaces with the flow, the TS wave is shown to stabilize, or destabilize, as needed. A theory of subsurface phonons is presented that provides an accurate prediction of this behavior without the need for a flow simulation. This represents an unprecedented capability to passively synchronize wave propagation across a fluid-structure interface and achieve favorable, and predictable, alterations to the flow properties. National Science Foundation, Grant No. 1131802.
General Stability Criterion for Inviscid Parallel Flow
ERIC Educational Resources Information Center
Sun, Liang
2007-01-01
Arnol'd's second stability theorem is approached from an elementary point of view. First, a sufficient criterion for stability is found analytically as either -[mu][subscript 1] less than U[double prime]/U-U[subscript s] less than 0 or 0 less than U[double prime]/U-U[subscript s] in the flow, where U[subscript s] is the velocity at the inflection…
Flame stabilizer for stagnation flow reactor
Hahn, David W.; Edwards, Christopher F.
1999-01-01
A method of stabilizing a strained flame in a stagnation flow reactor. By causing a highly strained flame to be divided into a large number of equal size segments it is possible to stablize a highly strained flame that is on the verge of extinction, thereby providing for higher film growth rates. The flame stabilizer is an annular ring mounted coaxially and coplanar with the substrate upon which the film is growing and having a number of vertical pillars mounted on the top surface, thereby increasing the number of azimuthal nodes into which the flame is divided and preserving an axisymmetric structure necessary for stability.
NASA Astrophysics Data System (ADS)
Whitney, K. G.; Pulsifer, P. E.; Apruzese, J. P.; Thornhill, J. W.; Davis, J.; Chong, Y. K.; Sanford, T. W. L.; Mock, R. C.; Nash, T. J.
2001-08-01
An analysis of x-ray data from two series of Z-pinch shots taken on the short current-risetime Saturn accelerator at Sandia National Laboratories [Proceedings of 6th International IEEE Pulsed Power Conference, Arlington, VA, edited by P. J. Turchi and B. H. Bernstein (IEEE, New York, 1987), p. 310] is presented. In one series, the array radius was held constant and the array mass was varied; in the other series, the array mass was held constant and its radius varied. In both sets of experiments, large wire-number loads (N>=93) of aluminum were used in contrast to earlier small wire-number aluminum array experiments on Saturn where N<=42. Average electron temperatures and ion densities were inferred from the data. In addition, from the measured size of the emission region of K-shell x rays and from the inferred ion density, a fraction of the total array mass that participated in the K-shell emission was inferred and found to be directly correlated to the K-shell yields that were measured. This paper also demonstrates that the yields varied as a function of array mass and radius in much closer agreement with predictions [J. Appl. Phys. 67, 1725 (1990)] than had been observed in the earlier small wire-number experiments. Thus, a serious misperception that the reason for the early disagreement was in the calculations and not in the experiments is corrected. These predictions were made using one-dimensional (1D) magnetohydrodynamics calculations. The density and temperature trends inferred from the data analysis are well-behaved and consistent with the 1D calculations. This data analysis confirms the importance of achieving uniform plasma initial conditions and implosion symmetry when comparing computer code calculations with experiment. When the wire number of an array load is increased, a more uniform shell of plasma is calculated initially as the wires explode and, as the plasma stagnates on axis, the x-ray powers and yields are found experimentally to approach the
MHD stability control in alternate confinement concept experiments
NASA Astrophysics Data System (ADS)
Hooper, E. B.
2006-10-01
High-quality plasma operation and good energy confinement in the alternate confinement experiments require control of ideal and resistive MHD instabilities. New experiments in the revitalized ICC program, supported by modern MHD computational capabilities, are demonstrating progress in this control which significantly extends previous work. Results from the classical tokamak are thereby extended into new parameter regimes, generating insight into the physics. We consider both toroidal and open concepts and, where appropriate, highlight comparisons with the tokamak, ST, and stellarator. The driving forces for ideal MHD modes are characterized using the Frieman-Rotenberg condition, which generalizes the stability analysis by including plasma flow. Stabilizing mechanisms include conducting walls (RFP, spheromak, FRC); plasma shaping as characterized by the magnetic dipole moment (spheromak, FRC); current-profile control (RFP, spheromak); sheared, super-Alfvénic flows (Z-pinch, centrifugal mirror); quadrupole magnetic wells (FRC, mirror); and high kinetic-energy density flow in good curvature regions (gas-dynamic trap). Resistive tearing is stabilized or limited by current profile control, primarily in the RFP and spheromak. Non-MHD mechanisms such as FLR can also be stabilizing and will be most effective if the MHD growth rate is minimized. Most of the experimental work to date has focused on global or large-scale modes; the possible consequences of short-wavelength or local modes will be explored. E. Frieman and M. Rotenberg, Rev. Mod. Phys. 32, 898 (1960).
Stability of Thin Liquid Sheet Flows
NASA Technical Reports Server (NTRS)
McConley, Marc W.; Chubb, Donald L.; McMaster, Matthew S.; Afjeh, Abdollah A.
1997-01-01
A two-dimensional, linear stability analysis of a thin nonplanar liquid sheet flow in vacuum is carried out. A sheet flow created by a narrow slit of W and tau attains a nonplanar cross section as a consequence of cylinders forming on the sheet edge under the influence of surface tension forces. The region where these edge cylinders join the sheet is one of high curvature, and this is found to be the location where instability is most likely to occur. The sheet flow is found to be unstable, but with low growth rates for symmetric wave disturbances and high growth rates for antisymmetric disturbances. By combining the symmetric and antisymmetric disturbance modes, a wide range of stability characteristics is obtained. The product of unstable growth rate and flow time is proportional to the width-to-thickness ratio of the sift generating the sheet Three-dimensional effects can alter these results, particularly when the sheet length-to-width ratio is not much greater than unity.
Stability Analysis of Flow Past a Wingtip
NASA Astrophysics Data System (ADS)
Edstrand, Adam; Schmid, Peter; Taira, Kunihiko; Cattafesta, Louis
2015-11-01
Trailing vortices are commonly associated with diminished aircraft performance by increasing induced drag and producing a wake hazard on following aircraft. Previously, stability analyses have been performed on the Batchelor vortex (Heaton et al., 2009), which models a far field axisymmetric vortex, and airfoil wakes (Woodley & Peake, 1997). Both analyses have shown various instabilities present in these far field vortex-wake flows. This complicates the design of control devices by excluding consideration of near field interactions between the wake and vortex shed from the wing. In this study, we perform temporal and spatial bi-global stability analyses on the near field wake of the flow field behind a NACA0012 wing computed from direct numerical simulation at a chord Reynolds number of 1000. The results identify multiple instabilities including a vortex instability, wake instability, and mixed instability that includes interaction between the wake and vortex. As these modes exhibit wave packets, we perform a wave packet analysis (Obrist & Schmid, 2010), which enables the prediction of spatial mode structures at low computational cost. Furthermore, a bi-global parabolized stability analysis is performed, highlighting disparities between the parallel and parabolized analysis. ONR Grant N00014010824 and NSF PIRE Grant OISE-0968313.
On stability and turbulence of fluid flows
NASA Technical Reports Server (NTRS)
Heisenberg, Werner
1951-01-01
This investigation is divided into two parts, the treatment of the stability problem of fluid flows on the one hand, and that of the turbulent motion on the other. The first part summarizes all previous investigations under a unified point of view, that is, sets up as generally as possible the conditions under which a profile possesses unstable or stable characteristics, and indicates the methods for solution of the stability equation for any arbitrary velocity profile and for calculation of the critical Reynolds number for unstable profiles. In the second part, under certain greatly idealizing assumptions, differential equations for the turbulent motions are derived and from them qualitative information about several properties of the turbulent velocity distribution is obtained.
Hydrodynamic stability of three-dimensional homogeneous flow topologies.
Mishra, Aashwin A; Girimaji, Sharath S
2015-11-01
This article examines the hydrodynamic stability of various homogeneous three-dimensional flow topologies. The influence of inertial and pressure effects on the stability of flows undergoing strain, rotation, convergence, divergence, and swirl are isolated. In marked contrast to two-dimensional topologies, for three-dimensional flows the inertial effects are always destabilizing, whereas pressure effects are always stabilizing. In streamline topologies with a negative velocity-gradient third invariant, inertial effects prevail leading to instability. Vortex-stretching is identified as the underlying instability mechanism. In flows with positive velocity-gradient third derivative, pressure overcomes inertial effects to stabilize the flow. PMID:26651773
Advanced stability theory analyses for laminar flow control
NASA Technical Reports Server (NTRS)
Orszag, S. A.
1980-01-01
Recent developments of the SALLY computer code for stability analysis of laminar flow control wings are summarized. Extensions of SALLY to study three dimensional compressible flows, nonparallel and nonlinear effects are discussed.
Lyapunov stability of flowing magnetohydrodynamic plasmas surrounded by resistive walls
NASA Astrophysics Data System (ADS)
Tasso, H.; Throumoulopoulos, G. N.
2011-07-01
A general stability condition for plasma-vacuum systems with resistive walls is derived by using the Frieman Rotenberg Lagrangian stability formulation [Rev. Mod. Phys. 32, 898 (1960)]. It is shown that the Lyapunov stability limit for external modes does not depend upon the gyroscopic term but upon the sign of the perturbed potential energy only. In the absence of dissipation in the plasma such as viscosity, it is expected that the flow cannot stabilize the system.
Elementary stratified flows with stability at low Richardson number
Barros, Ricardo; Choi, Wooyoung
2014-12-15
We revisit the stability analysis for three classical configurations of multiple fluid layers proposed by Goldstein [“On the stability of superposed streams of fluids of different densities,” Proc. R. Soc. A. 132, 524 (1931)], Taylor [“Effect of variation in density on the stability of superposed streams of fluid,” Proc. R. Soc. A 132, 499 (1931)], and Holmboe [“On the behaviour of symmetric waves in stratified shear layers,” Geophys. Publ. 24, 67 (1962)] as simple prototypes to understand stability characteristics of stratified shear flows with sharp density transitions. When such flows are confined in a finite domain, it is shown that a large shear across the layers that is often considered a source of instability plays a stabilizing role. Presented are simple analytical criteria for stability of these low Richardson number flows.
Studies on dispersive stabilization of porous media flows
NASA Astrophysics Data System (ADS)
Daripa, Prabir; Gin, Craig
2016-08-01
Motivated by a need to improve the performance of chemical enhanced oil recovery (EOR) processes, we investigate dispersive effects on the linear stability of three-layer porous media flow models of EOR for two different types of interfaces: permeable and impermeable interfaces. Results presented are relevant for the design of smarter interfaces in the available parameter space of capillary number, Peclet number, longitudinal and transverse dispersion, and the viscous profile of the middle layer. The stabilization capacity of each of these two interfaces is explored numerically and conditions for complete dispersive stabilization are identified for each of these two types of interfaces. Key results obtained are (i) three-layer porous media flows with permeable interfaces can be almost completely stabilized by diffusion if the optimal viscous profile is chosen, (ii) flows with impermeable interfaces can also be almost completely stabilized for short time, but become more unstable at later times because diffusion flattens out the basic viscous profile, (iii) diffusion stabilizes short waves more than long waves which leads to a "turning point" Peclet number at which short and long waves have the same growth rate, and (iv) mechanical dispersion further stabilizes flows with permeable interfaces but in some cases has a destabilizing effect for flows with impermeable interfaces, which is a surprising result. These results are then used to give a comparison of the two types of interfaces. It is found that for most values of the flow parameters, permeable interfaces suppress flow instability more than impermeable interfaces.
Stability of flows in fluidized beds
Rajagopal, C.
1992-01-01
In this paper we carry out a systematic linearized stability analysis of the state of uniform fluidization for a fluid infused with granular particles. We carry out an interesting optimization procedure which leads to bounds for certain parameters, within which the state of uniform fluidization is stable. We find that this stability depends critically on the structure of the pressure-like term. (VC)
Emergent stability in a large, free-flowing watershed.
Moore, Jonathan W; Beakes, Michael P; Nesbitt, Holly K; Yeakel, Justin D; Patterson, David A; Thompson, Lisa A; Phillis, Corey C; Braun, Douglas C; Favaro, Corinna; Scott, David; Carr-Harris, Charmaine; Atlas, William I
2015-02-01
While it is widely recognized that financial stock portfolios can be stabilized through diverse investments, it is also possible that certain habitats can function as natural portfolios that stabilize ecosystem processes. Here we propose and examine the hypothesis that free-flowing river networks act as such portfolios and confer stability through their integration of upstream geological, hydrological, and biological diversity. We compiled a spatially (142 sites) and temporally (1980-present) extensive data set on fisheries, water flows, and temperatures, from sites within one of the largest watersheds in the world that remains without dams on its mainstem, the Fraser River, British Columbia, Canada. We found that larger catchments had more stable fisheries catches, water flows, and water temperatures than smaller catchments. These data provide evidence that free-flowing river networks function as hierarchically nested portfolios with stability as an emergent property. Thus, free-flowing river networks can represent a natural system for buffering variation and extreme events.
Stability of compressible Taylor-Couette flow
NASA Technical Reports Server (NTRS)
Kao, K.; Chow, C.
1992-01-01
The objectives of this paper are to: (1) develop both analytical and numerical tools that can be used to predict the onset of instability and subsequently to simulate the transition process by which the originally laminar flow evolves into a turbulent flow; and (2) conduct the preliminary investigations with the purpose of understanding the mechanisms of the vortical structures of the compressible flow between tow concentric cylinders.
Linear stability of compressible Taylor-Couette flow
NASA Technical Reports Server (NTRS)
Kao, Kai-Hsiung; Chow, Chuen-Yen
1992-01-01
A temporal stability analysis of compressible Taylor-Couette flow is presented. The viscous flow studied in this paper is contained between two concentric cylinders of infinite length, which are rotating with different angular velocities and are kept at different surface temperatures. The effects of differential rotation and temperature difference on the stability of Taylor-Couette flow are contrasted for a range of Mach numbers ranging from incompressible to Mach 3.0. The relative motion of the cylinders dramatically affects the characteristics of the Couette flow at the onset of instability. The flow is stabilized or destabilized depending upon the temperature ratio and speeds of the two cylinders. Independent of Mach number and temperature ratio, increasing Reynolds number generally promotes a destabilizing effect, indicating the inviscid nature of the Taylor-Couette flow.
Magnetohydrodynamic stability of stochastically driven accretion flows.
Nath, Sujit Kumar; Mukhopadhyay, Banibrata; Chattopadhyay, Amit K
2013-07-01
We investigate the evolution of magnetohydrodynamic (or hydromagnetic as coined by Chandrasekhar) perturbations in the presence of stochastic noise in rotating shear flows. The particular emphasis is the flows whose angular velocity decreases but specific angular momentum increases with increasing radial coordinate. Such flows, however, are Rayleigh stable but must be turbulent in order to explain astrophysical observed data and, hence, reveal a mismatch between the linear theory and observations and experiments. The mismatch seems to have been resolved, at least in certain regimes, in the presence of a weak magnetic field, revealing magnetorotational instability. The present work explores the effects of stochastic noise on such magnetohydrodynamic flows, in order to resolve the above mismatch generically for the hot flows. We essentially concentrate on a small section of such a flow which is nothing but a plane shear flow supplemented by the Coriolis effect, mimicking a small section of an astrophysical accretion disk around a compact object. It is found that such stochastically driven flows exhibit large temporal and spatial autocorrelations and cross-correlations of perturbation and, hence, large energy dissipations of perturbation, which generate instability. Interestingly, autocorrelations and cross-correlations appear independent of background angular velocity profiles, which are Rayleigh stable, indicating their universality. This work initiates our attempt to understand the evolution of three-dimensional hydromagnetic perturbations in rotating shear flows in the presence of stochastic noise.
Stability of stagnation via an expanding accretion shock wave
NASA Astrophysics Data System (ADS)
Velikovich, A. L.; Murakami, M.; Taylor, B. D.; Giuliani, J. L.; Zalesak, S. T.; Iwamoto, Y.
2016-05-01
Stagnation of a cold plasma streaming to the center or axis of symmetry via an expanding accretion shock wave is ubiquitous in inertial confinement fusion (ICF) and high-energy-density plasma physics, the examples ranging from plasma flows in x-ray-generating Z pinches [Maron et al., Phys. Rev. Lett. 111, 035001 (2013)] to the experiments in support of the recently suggested concept of impact ignition in ICF [Azechi et al., Phys. Rev. Lett. 102, 235002 (2009); Murakami et al., Nucl. Fusion 54, 054007 (2014)]. Some experimental evidence indicates that stagnation via an expanding shock wave is stable, but its stability has never been studied theoretically. We present such analysis for the stagnation that does not involve a rarefaction wave behind the expanding shock front and is described by the classic ideal-gas Noh solution in spherical and cylindrical geometry. In either case, the stagnated flow has been demonstrated to be stable, initial perturbations exhibiting a power-law, oscillatory or monotonic, decay with time for all the eigenmodes. This conclusion has been supported by our simulations done both on a Cartesian grid and on a curvilinear grid in spherical coordinates. Dispersion equation determining the eigenvalues of the problem and explicit formulas for the eigenfunction profiles corresponding to these eigenvalues are presented, making it possible to use the theory for hydrocode verification in two and three dimensions.
Linear Stability Analysis of Couette Flow with a Porous Wall
NASA Astrophysics Data System (ADS)
Tilton, Nils; Cortelezzi, Luca
2006-11-01
It is well known that plane Couette flow in a channel with perfectly smooth, impermeable walls is linearly stable for all Reynolds numbers. Little attention has been given in literature to the stability of plane Couette flow when at least one of the walls is porous. In this study, we consider a channel delimited by an impermeable moving wall, which drives the flow, and a stationary, rigid, homogeneous, isotropic, porous block. We perform a three-dimensional linear stability analysis of the fully developed laminar flow in both the channel and the porous block. We restrict the study to sufficiently small permeabilities in order to neglect inertial effects in the porous flow. We solve the coupled linear stability problem, arising from the adjacent channel and porous flows, using a spectral collocation technique. The linear stability analysis takes account of the coupling between the two disturbance fields through boundary conditions recently derived by Ochoa-Tapia and Whitaker (Int. J. Heat Mass Transfer, 38, 1995). We find that Couette flow over a permeable wall is no longer absolutely stable. While the critical Reynolds number tends to infinity as the permeability tends to zero, it decreases drastically for higher permeabilities. We also find a new channel mode and new class of modes in the porous region. We compare and discuss these results in terms of the recently published results of a three-dimensional linear stability analysis of a channel flow with porous walls (Tilton and Cortelezzi, Phys. Fluids 18, 051702, 2006).
Stability of axisymmetric swirl flows of viscous incompressible fluid
NASA Astrophysics Data System (ADS)
Aktershev, S. P.; Kuibin, P. A.
2013-09-01
A new method of solution to the problem of stability of the swirl flow of viscous incompressible fluid is developed. The method based on expansion of the required function into power series of radial coordinate allows an avoidance of difficulties related to numerical integration of the system of differential equations with a singular point. Stability of the Poiseuille flow in a rotating pipe is considered as an example.
A CANDU figure-of-eight flow stability model
Gulshani, P.; Spinks, N.J.
1984-11-01
A stability model of flow oscillations observed in two-phase flow tests in a CANDU-like experimental rig is developed. The model is derived by linearizing and solving one-dimensional, homogeneous two-phase flow conservation equations. The flow oscillations are explained in terms of the response of the pressure in the two-phase region to a change in the single-phase flow. A simple instability criterion valid for high-pressure thermosyphoning is given. The observed and predicted periods and damping ratios are generally found to be in good agreement. Combined with a simple, analytic, steady-state model to give approximate loop operating conditions, the stability model is used to generate stability maps for thermosyphoning conditions.
Stabilization of the Circulation Flow of the Cryogenic Distillation Column
NASA Astrophysics Data System (ADS)
Juromskiy, V. M.
Two-circuit system of automatic stabilization of the hydrodynamics of the cryogenic distillation column is considered. Control system eliminates flooding/depletion of column in long-term mode of operation when the accuracy of stabilization of the circulation flow is better than 1%.
Stability limits of unsteady open capillary channel flow
NASA Astrophysics Data System (ADS)
Grah, Aleksander; Haake, Dennis; Rosendahl, Uwe; Klatte, J.?Rg; Dreyer, Michael E.
This paper is concerned with steady and unsteady flow rate limitations in open capillary channels under low-gravity conditions. Capillary channels are widely used in Space technology for liquid transportation and positioning, e.g. in fuel tanks and life support systems. The channel observed in this work consists of two parallel plates bounded by free liquid surfaces along the open sides. The capillary forces of the free surfaces prevent leaking of the liquid and gas ingestion into the flow.In the case of steady stable flow the capillary pressure balances the differential pressure between the liquid and the surrounding constant-pressure gas phase. Increasing the flow rate in small steps causes a decrease of the liquid pressure. A maximum steady flow rate is achieved when the flow rate exceeds a certain limit leading to a collapse of the free surfaces due to the choking effect. In the case of unsteady flow additional dynamic effects take place due to flow rate transition and liquid acceleration. The maximum flow rate is smaller than in the case of steady flow. On the other hand, the choking effect does not necessarily cause surface collapse and stable temporarily choked flow is possible under certain circumstances.To determine the limiting volumetric flow rate and stable flow dynamic properties, a new stability theory for both steady and unsteady flow is introduced. Subcritical and supercritical (choked) flow regimes are defined. Stability criteria are formulated for each flow type. The steady (subcritical) criterion corresponds to the speed index defined by the limiting longitudinal small-amplitude wave speed, similar to the Mach number. The unsteady (supercritical) criterion for choked flow is defined by a new characteristic number, the dynamic index. It is based on pressure balances and reaches unity at the stability limit.The unsteady model based on the Bernoulli equation and the mass balance equation is solved numerically for perfectly wetting incompressible
Nonlinear dynamics near the stability margin in rotating pipe flow
NASA Technical Reports Server (NTRS)
Yang, Z.; Leibovich, S.
1991-01-01
The nonlinear evolution of marginally unstable wave packets in rotating pipe flow is studied. These flows depend on two control parameters, which may be taken to be the axial Reynolds number R and a Rossby number, q. Marginal stability is realized on a curve in the (R, q)-plane, and the entire marginal stability boundary is explored. As the flow passes through any point on the marginal stability curve, it undergoes a supercritical Hopf bifurcation and the steady base flow is replaced by a traveling wave. The envelope of the wave system is governed by a complex Ginzburg-Landau equation. The Ginzburg-Landau equation admits Stokes waves, which correspond to standing modulations of the linear traveling wavetrain, as well as traveling wave modulations of the linear wavetrain. Bands of wavenumbers are identified in which the nonlinear modulated waves are subject to a sideband instability.
On the linear stability of compressible plane Couette flow
NASA Technical Reports Server (NTRS)
Duck, Peter W.; Erlebacher, Gordon; Hussaini, M. Yousuff
1991-01-01
The linear stability of compressible plane Couette flow is investigated. The correct and proper basic velocity and temperature distributions are perturbed by a small amplitude normal mode disturbance. The full small amplitude disturbance equations are solved numerically at finite Reynolds numbers, and the inviscid limit of these equations is then investigated in some detail. It is found that instability can occur, although the stability characteristics of the flow are quite different from unbounded flows. The effects of viscosity are also calculated, asymptotically, and shown to have a stabilizing role in all the cases investigated. Exceptional regimes to the problem occur when the wavespeed of the disturbances approaches the velocity of either of the walls, and these regimes are also analyzed in some detail. Finally, the effect of imposing radiation-type boundary conditions on the upper (moving) wall (in place of impermeability) is investigated, and shown to yield results common to both bounded and unbounded flows.
On the stability of compressible flow past axisymmetric bodies
NASA Technical Reports Server (NTRS)
Malik, M. R.; Spall, R. E.
1991-01-01
Compressible linear stability theory for axisymmetric flows is presented. The theory is applied to flow past a cylinder and a sharp cone at a Mach number of 5 with adiabatic wall conditions. The effect of transverse curvature and body divergence is studied. It is found that transverse curvature has a stabilizing influence on axisymmetric (first and second mode) disturbances while it has a destabilizing influence on the asymmetric (oblique first mode) disturbances. The body divergence effects are stabilizing for both symmetric and asymmetric disturbances. Comparisons made with the results of planar stability theory show that, for a cylinder, curvature effects become more pronounced with increasing distance along the cylinder. For a sharp cone, these effects become less significant further away from the cone tip since the body radius increases faster than the growth of the boundary layer. The effect of cone angle on stability is also studied.
Linear stability analysis of swirling turbulent flows with turbulence models
NASA Astrophysics Data System (ADS)
Gupta, Vikrant; Juniper, Matthew
2013-11-01
In this paper, we consider the growth of large scale coherent structures in turbulent flows by performing linear stability analysis around a mean flow. Turbulent flows are characterized by fine-scale stochastic perturbations. The momentum transfer caused by these perturbations affects the development of larger structures. Therefore, in a linear stability analysis, it is important to include the perturbations' influence. One way to do this is to include a turbulence model in the stability analysis. This is done in the literature by using eddy viscosity models (EVMs), which are first order turbulence models. We extend this approach by using second order turbulence models, in this case explicit algebraic Reynolds stress models (EARSMs). EARSMs are more versatile than EVMs, in that they can be applied to a wider range of flows, and could also be more accurate. We verify our EARSM-based analysis by applying it to a channel flow and then comparing the results with those from an EVM-based analysis. We then apply the EARSM-based stability analysis to swirling pipe flows and Taylor-Couette flows, which demonstrates the main benefit of EARSM-based analysis. This project is supported by EPSRC and Rolls-Royce through a Dorothy Hodgkin Research Fellowship.
Stability of stratified two-phase flows in inclined channels
NASA Astrophysics Data System (ADS)
Barmak, I.; Gelfgat, A. Yu.; Ullmann, A.; Brauner, N.
2016-08-01
Linear stability of the stratified gas-liquid and liquid-liquid plane-parallel flows in the inclined channels is studied with respect to all wavenumber perturbations. The main objective is to predict the parameter regions in which the stable stratified configuration in inclined channels exists. Up to three distinct base states with different holdups exist in the inclined flows, so that the stability analysis has to be carried out for each branch separately. Special attention is paid to the multiple solution regions to reveal the feasibility of the non-unique stable stratified configurations in inclined channels. The stability boundaries of each branch of the steady state solutions are presented on the flow pattern map and are accompanied by the critical wavenumbers and the spatial profiles of the most unstable perturbations. Instabilities of different nature are visualized by the streamlines of the neutrally stable perturbed flows, consisting of the critical perturbation superimposed on the base flow. The present analysis confirms the existence of two stable stratified flow configurations in a region of low flow rates in the countercurrent liquid-liquid flows. These configurations become unstable with respect to the shear mode of instability. It was revealed that in slightly upward inclined flows the lower and middle solutions for the holdup are stable in the part of the triple solution region, while the upper solution is always unstable. In the case of downward flows, in the triple solution region, none of the solutions are stable with respect to the short-wave perturbations. These flows are stable only in the single solution region at low flow rates of the heavy phase, and the long-wave perturbations are the most unstable ones.
Nonparallel stability of the flow in an axially rotating pipe
NASA Astrophysics Data System (ADS)
del Pino, C.; Ortega-Casanova, J.; Fernandez-Feria, R.
2003-08-01
The linear stability of the developing flow in an axially rotating pipe is analyzed using parabolized stability equations (PSE). The results are compared with those obtained from a near-parallel stability approximation that only takes into account the axial variation of the basic flow. Though the PSE results obviously coincide with the near-parallel ones far downstream, when the flow has reached a Hagen-Poiseuille axial velocity profile with superimposed solid-body rotation, they differ significantly in the developing region. Therefore, the onset of instability strongly depends on the axial evolution of the perturbations. The PSE results are also compared with experimental data from Imao et al. [Exp. Fluids 12 (1992) 277], showing a good agreement in the frequencies and wavelengths of the unstable disturbances, that take the form of spiral waves. Finally, a simple method for detecting one of the conditions to characterize the onset of absolute instability using PSE is given.
Nonparallel stability of the flow in an axially rotating pipe
NASA Astrophysics Data System (ADS)
del Pino, Carlos; Ortega-Casanova, Joaquin; Fernandez-Feria, Ramon
2002-11-01
The linear stability of the developing flow in an axially rotating pipe is analyzed using parabolized stability equations (PSE). The results are compared with those obtained from a near-parallel stability approximation that only takes into account the axial variation of the basic flow. Though the PSE results obviously coincide with the near-parallel ones far downstream, when the flow has reached a Hagen-Poiseuille axial velocity profile with superimposed solid body rotation, they differ significantly in the developing region. Therefore, the onset of instability strongly depends on the axial evolution of the perturbations. The PSE results are also compared with experimental data from Imao et al. [Exp. Fluids 12, 277-285 (1992)], showing a good agreement in the frequencies and wavelengths of the unstable disturbances, that take the form of spiral waves. Finally, a simple method to characterize the onset of absolute instability using PSE is given.
Application of linear stability theory in laminar flow design
NASA Technical Reports Server (NTRS)
Iyer, Venkit; Spall, Robert
1991-01-01
The linear stability of fully three-dimensional supersonic boundary layers formed over swept-wing configurations is investigated using a modified version of the linear stability code COSAL. Configurations studied include a highly swept leading-edge model to be utilized for transition studies in the LARC Low-disturbance Mach 3.5 Pilot Tunnel. The model is a representation of the leading edge of a laminar flow control wing for the F-16XL aircraft. In addition, the region over a laminar flow control glove fitted on the midportion of an F-16XL wing was studied. For each configuration, estimates of the location of the onset of transition were computed using linear stability theory and the e exp N method. The effectiveness of suction in stabilizing the boundary layer over the F-16XL wing glove was also investigated.
Optic flow stabilizes flight in ruby-throated hummingbirds.
Ros, Ivo G; Biewener, Andrew A
2016-08-15
Flying birds rely on visual cues for retinal image stabilization by negating rotation-induced optic flow, the motion of the visual panorama across the retina, through corrective eye and head movements. In combination with vestibular and proprioceptive feedback, birds may also use visual cues to stabilize their body during flight. Here, we test whether artificially induced wide-field motion generated through projected visual patterns elicits maneuvers in body orientation and flight position, in addition to stabilizing vision. To test this hypothesis, we present hummingbirds flying freely within a 1.2 m cylindrical visual arena with a virtual surround rotated at different speeds about its vertical axis. The birds responded robustly to these visual perturbations by rotating their heads and bodies with the moving visual surround, and by adjusting their flight trajectories, following the surround. Thus, similar to insects, hummingbirds appear to use optic flow cues to control flight maneuvers as well as to stabilize their visual inputs.
The inviscid stability of supersonic flow past axisymmetric bodies
NASA Technical Reports Server (NTRS)
Duck, Peter W.
1990-01-01
The supersonic flow past a sharp cone is studied. The associated boundary layer flow (i.e., the velocity and temperature field) is computed. The inviscid linear temporal stability of axisymmetric boundary layers in general is considered, and in particular, a so-called 'triply generalized' inflection condition for 'subsonic' nonaxisymmetric neutral modes is presented. Preliminary numerical results for the stability of the cone boundary layer are presented for a freestream Mach number of 3.8. In particular, a new inviscid mode of instability is seen to occur in certain regimes, and this is shown to be related to a viscous mode found by Duck and Hall (1988).
Stability investigations of airfoil flow by global analysis
NASA Technical Reports Server (NTRS)
Morzynski, Marek; Thiele, Frank
1992-01-01
As the result of global, non-parallel flow stability analysis the single value of the disturbance growth-rate and respective frequency is obtained. This complex value characterizes the stability of the whole flow configuration and is not referred to any particular flow pattern. The global analysis assures that all the flow elements (wake, boundary and shear layer) are taken into account. The physical phenomena connected with the wake instability are properly reproduced by the global analysis. This enhances the investigations of instability of any 2-D flows, including ones in which the boundary layer instability effects are known to be of dominating importance. Assuming fully 2-D disturbance form, the global linear stability problem is formulated. The system of partial differential equations is solved for the eigenvalues and eigenvectors. The equations, written in the pure stream function formulation, are discretized via FDM using a curvilinear coordinate system. The complex eigenvalues and corresponding eigenvectors are evaluated by an iterative method. The investigations performed for various Reynolds numbers emphasize that the wake instability develops into the Karman vortex street. This phenomenon is shown to be connected with the first mode obtained from the non-parallel flow stability analysis. The higher modes are reflecting different physical phenomena as for example Tollmien-Schlichting waves, originating in the boundary layer and having the tendency to emerge as instabilities for the growing Reynolds number. The investigations are carried out for a circular cylinder, oblong ellipsis and airfoil. It is shown that the onset of the wake instability, the waves in the boundary layer, the shear layer instability are different solutions of the same eigenvalue problem, formulated using the non-parallel theory. The analysis offers large potential possibilities as the generalization of methods used till now for the stability analysis.
Numerical studies of transverse curvature effects on transonic flow stability
NASA Technical Reports Server (NTRS)
Macaraeg, M. G.; Daudpota, Q. I.
1992-01-01
A numerical study of transverse curvature effects on compressible flow temporal stability for transonic to low supersonic Mach numbers is presented for axisymmetric modes. The mean flows studied include a similar boundary-layer profile and a nonsimilar axisymmetric boundary-layer solution. The effect of neglecting curvature in the mean flow produces only small quantitative changes in the disturbance growth rate. For transonic Mach numbers (1-1.4) and aerodynamically relevant Reynolds numbers (5000-10,000 based on displacement thickness), the maximum growth rate is found to increase with curvature - the maximum occurring at a nondimensional radius (based on displacement thickness) between 30 and 100.
Remarks on the stability analysis of reactive flows
NASA Technical Reports Server (NTRS)
Scheurer, B.
1987-01-01
A simple model of compressible reacting flow is studied. First, a dispersion relation is derived for the linearized problem making a distinction between frozen and equilibrium sound speed. Second, the stability of the Von Neumann-Richtmyer scheme applied to this model is studied. A natural generalization of the C.F.L. condition is found.
Stability sensitivity to gravity and base flow density modifications
NASA Astrophysics Data System (ADS)
Chen, Kevin; Spedding, Geoffrey
2015-11-01
We present the novel theory of Boussinesq stability sensitivity to the gravitational force and to base flow density modifications. Given a steady-state flow with small density variations, the sensitivity of the stability eigenvalues is computed from the direct and adjoint modes of the linearized Boussinesq equations. Various combinations of the density and velocity components of these modes reveal multiple production and transport mechanisms that contribute to the eigenvalue sensitivity. This sensitivity theory is largely inspired by the study of stable density stratification, which can have seemingly contradictory effects on flow stability. On one hand, stable stratification increases the coherence and persistence of turbulent wakes; on the other hand, it can destabilize vortex structures, such as vortex pairs and rings. We present an application of the sensitivity theory to a stably density-stratified flow around a flat plate at a 90 degree angle of attack. The global mode analysis reveals lightly damped lee wave undulations, and the sensitivity theory shows that regions both immediately upstream and immediately downstream of the plate contribute most significantly to the stability sensitivity. This research was supported by the Viterbi Postdoctoral Fellowship, provided by the Viterbi School of Engineering at the University of Southern California.
Global stability of the focusing effect of fluid jet flows.
Montanero, J M; Rebollo-Muñoz, N; Herrada, M A; Gañán-Calvo, A M
2011-03-01
The global stability of the steady jetting mode of liquid jets focused by coaxial gas streams is analyzed both theoretically and experimentally. Numerical simulations allow one to identify the physical mechanisms responsible for instability in the low viscosity and very viscous regimes of the focused liquid. The characteristic flow rates for which global instability takes place are estimated by a simple scaling analysis. These flow rates do not depend on the pressure drop (energy) applied to the system to produce the microjet. Their dependencies on the liquid viscosity are opposite for the two extremes studied: the characteristic flow rate increases (decreases) with viscosity for very low (high) viscosity liquids. Experiments confirmed the validity of these conclusions. The minimum flow rates below which the liquid meniscus becomes unstable are practically independent of the applied pressure drop for sufficiently large values of this quantity. For all the liquids analyzed, there exists an optimum value of the capillary-to-orifice distance for which the minimum flow rate attains a limiting value. That limiting value represents the lowest flow rate attainable with a given experimental configuration in the steady jetting regime. A two-dimensional stability map with a high degree of validity is plotted on the plane defined by the Reynolds and capillary numbers based on the limiting flow rate.
Equilibrium and stability in vortex and wave flows
NASA Astrophysics Data System (ADS)
Luzzatto-Fegiz, Paolo
This dissertation focuses on the development of theoretical and numerical methodologies to study equilibrium and stability in conservative fluid flows. These techniques include: a bifurcation-diagram approach to obtain the stability properties of families of steady flows; a theory of Hamiltonian resonance for vortex arrays; an efficient numerical method for computing vortices with arbitrary symmetry; and a variational principle for compressible, barotropic or baroclinic flows. We employ these theoretical and numerical approaches to obtain new results regarding the structure and stability of several fundamental vortex and wave flows. The applications that we examine involve simple representations of fundamental fluid problems, which may be regarded as prototypical of flows associated with transport and mixing in the ocean and in the atmosphere, with aquatic animal propulsion, and with the dynamics of vortices in quantum condensates. We address two issues affecting the use of a variational argument to determine stability of families of steady flows. By building on ideas from bifurcation theory, we link turning points in a velocity-impulse diagram to gains or losses of stability. We introduce concepts from imperfection theory into these problems, enabling us to reveal hidden solution branches. The resulting methodology detects exchanges of stability through an "imperfect velocity-impulse" (IVI) diagram. We apply the IVI diagram approach to wide variety of vortex and wave flows. These examples include elliptical vortices, translating and rotating vortex pairs, single and double vortex rows, distributed vortices, as well as steep gravity waves. For a few of the flows considered, our work yields the first available stability boundaries. In addition, the IVI diagram methodology leads us to the discovery of several new families of steady flows, which exhibit lower symmetry. We next examine conditions for the development of an oscillatory instability in two
Stability of flow over axisymmetric bodies with porous suction strips
NASA Technical Reports Server (NTRS)
Nayfeh, A. H.; Reed, H. L.
1982-01-01
Linear triple deck, closed form solutions for mean-flow quantities are developed for axisymmetric incompressible flow past a body with porous strips. The solutions account for upstream influence and are linear superpositions of the flow past the body without suction plus the perturbations due to the suction strips. Flow past the suctionless body is calculated using the Transition Analysis Program System, and a simple linear optimization scheme to determine number, spacing, and mass flow rate through the strips on an axisymmetric body is developed using the linear, triple-deck, closed-form solutions. The theory is demonstrated by predicting optimal strip distributions, and the effect of various adverse pressure-gradient situations on stability is studied.
Variational necessary and sufficient stability conditions for inviscid shear flow
Hirota, M.; Morrison, P. J.; Hattori, Y.
2014-01-01
A necessary and sufficient condition for linear stability of inviscid parallel shear flow is formulated by developing a novel variational principle, where the velocity profile is assumed to be monotonic and analytic. It is shown that unstable eigenvalues of Rayleigh's equation (which is a non-self-adjoint eigenvalue problem) can be associated with positive eigenvalues of a certain self-adjoint operator. The stability is therefore determined by maximizing a quadratic form, which is theoretically and numerically more tractable than directly solving Rayleigh's equation. This variational stability criterion is based on the understanding of Kreĭn signature for continuous spectra and is applicable to other stability problems of infinite-dimensional Hamiltonian systems. PMID:25484600
Microfabricated wire arrays for Z-pinch.
Spahn, Olga Blum; Rowen, Adam M.; Cich, Michael Joseph; Peake, Gregory Merwin; Arrington, Christian L.; Nash, Thomas J.; Klem, John Frederick; Romero, Dustin Heinz
2008-10-01
Microfabrication methods have been applied to the fabrication of wire arrays suitable for use in Z. Self-curling GaAs/AlGaAs supports were fabricated as an initial route to make small wire arrays (4mm diameter). A strain relief structure that could be integrated with the wire was designed to allow displacements of the anode/cathode connections in Z. Electroplated gold wire arrays with integrated anode/cathode bus connections were found to be sufficiently robust to allow direct handling. Platinum and copper plating processes were also investigated. A process to fabricate wire arrays on any substrate with wire thickness up to 35 microns was developed. Methods to handle and mount these arrays were developed. Fabrication of wire arrays of 20mm diameter was demonstrated, and the path to 40mm array fabrication is clear. With some final investment to show array mounting into Z hardware, the entire process to produce a microfabricated wire array will have been demonstrated.
Stability of a rivulet in a co-flowing microchannel
NASA Astrophysics Data System (ADS)
Herrada, Miguel A.; Mohamed, Ahmed S.; Montanero, Jose M.; Ganan-Calvo, Alfonso
2014-11-01
We here analyze the stability of a gas (liquid) rivulet on a hydrophobic (hydrophilic) strip along one of the inner sides of a quadrangular microfluidic channel where a liquid (gas) co-flows. The results essentially differ from those of co-flowing cylindrical capillary jets because the contact-line-anchorage conditions affect the rivulet's instability nature. The temporal stability analysis shows that the rivulet becomes unstable not only for (unperturbed) contact angles larger than 90° (as can be expected) but also for values smaller than that angle. The maximum growth factor exhibits a non-monotonic dependence with respect to the Reynolds number (i.e., the viscosities). In fact, there are intervals of that parameter where the fluid system becomes unstable, while all the perturbations are damped outside that interval. The gaseous rivulet does not stabilize as the Reynolds number decreases, which means that it can be unstable even in the Stokes limit and for contact angles less than 90°. In addition, the stability of a flowing liquid rivulet is not determined by its contact angle exclusively (as occurs in the static case), but by the Reynolds number as well. Liquid rivulets with contact angles less than 90? can be unstable for sufficiently high Reynolds numbers. Partial support from the Ministry of Science and Education, Junta de Extremadura, and Junta de Andalucía (Spain) through Grants Nos. DPI2010-21103, GR10047, and P08-TEP-04128, respectively, is gratefully acknowledged.
Precessing rotating flows with additional shear: Stability analysis
NASA Astrophysics Data System (ADS)
Salhi, A.; Cambon, C.
2009-03-01
We consider unbounded precessing rotating flows in which vertical or horizontal shear is induced by the interaction between the solid-body rotation (with angular velocity Ω0 ) and the additional “precessing” Coriolis force (with angular velocity -ɛΩ0 ), normal to it. A “weak” shear flow, with rate 2ɛ of the same order of the Poincaré “small” ratio ɛ , is needed for balancing the gyroscopic torque, so that the whole flow satisfies Euler’s equations in the precessing frame (the so-called admissibility conditions). The base flow case with vertical shear (its cross-gradient direction is aligned with the main angular velocity) corresponds to Mahalov’s [Phys. Fluids A 5, 891 (1993)] precessing infinite cylinder base flow (ignoring boundary conditions), while the base flow case with horizontal shear (its cross-gradient direction is normal to both main and precessing angular velocities) corresponds to the unbounded precessing rotating shear flow considered by Kerswell [Geophys. Astrophys. Fluid Dyn. 72, 107 (1993)]. We show that both these base flows satisfy the admissibility conditions and can support disturbances in terms of advected Fourier modes. Because the admissibility conditions cannot select one case with respect to the other, a more physical derivation is sought: Both flows are deduced from Poincaré’s [Bull. Astron. 27, 321 (1910)] basic state of a precessing spheroidal container, in the limit of small ɛ . A Rapid distortion theory (RDT) type of stability analysis is then performed for the previously mentioned disturbances, for both base flows. The stability analysis of the Kerswell base flow, using Floquet’s theory, is recovered, and its counterpart for the Mahalov base flow is presented. Typical growth rates are found to be the same for both flows at very small ɛ , but significant differences are obtained regarding growth rates and widths of instability bands, if larger ɛ values, up to 0.2, are considered. Finally, both flow cases
Linear stability of cylindrical Couette flow in the convection regime
NASA Astrophysics Data System (ADS)
Ali, Mohamed E.; McFadden, G. B.
2005-05-01
The instability of steady circular Couette flow with radial heating across a vertically oriented annulus with a rotating inner cylinder and a stationary outer cylinder is investigated using a linear stability analysis. The convection regime base flow is developed for an infinite aspect ratio geometry and constant fluid properties with buoyancy included through the Boussinesq approximation. The base flow is characterized by a dimensionless stratification parameter γ that is proportional to the vertical temperature gradient. Critical stability boundaries are calculated for this assumed base flow with respect to both toroidal and helical disturbances. The numerical investigation is primarily restricted to a radius ratio of 0.6 at a Prandtl number of 100. Critical stability boundaries in Taylor-Grashof number space are presented for two values of the stratification parameter γ (4 and 13). The results follow the development of critical stability from Taylor cells at small Grashof numbers up to a maximum Grashof number used in this calculation of 20 000 and 80 000 for γ =4 and 13, respectively. Results show that increasing the stratification parameter stabilizes the isothermal Taylor vortices, followed by a destabilization at higher azimuthal mode numbers (n>0). The results also show that for γ =4 (close to the conduction regime), two modes are obtained: one is axisymmetric and the other is nonaxisymmetric. However, for the convection regime (large γ) six asymmetric modes are obtained. Finally, the disturbance wavelength, phase speed, and spiral inclination angle are presented as a function of the critical Grashof number for the stratification parameters considered in this work.
Linear Stability Analysis of a Channel Flow with Porous Walls
NASA Astrophysics Data System (ADS)
Tilton, Nils
2005-11-01
This study is motivated by the extensive use of wall-transpiration in numerical studies related to inhibition and control of wall-turbulence. In general, wall-transpiration has been implemented by providing the wall-normal velocity and imposing a no-slip condition on the wall-tangential velocity. Physically, however, the pores cannot be infinitesimally small and, consequently, it is important to address how the presence of the pores affects the slip velocity at the wall and the stability of the boundary layer. Moreover, our work is motivated by the existence of only few studies on the linear stability of channels with porous walls. Our study considers a parallel-plate channel with porous walls such that a longitudinal pressure gradient induces a laminar flow in both the open channel region and the porous walls. Simplified counterparts to the Orr-Sommerfeld and Squire equations are derived for the porous regions that are valid for small permeablities. The linear stability analysis takes account of the coupling between the three disturbance fields through boundary conditions recently derived by Ochoa-Tapia and Whitaker (Int. J. Heat Mass Transfer, Vol. 38, 1995, pp 2635-2646). The resulting Orr-Sommerfeld spectrum and eigenfunctions reduce to those for Poiseuille flow as the permeability of the walls tends to zero, but are altered for greater values. We discuss symmetrical flows where parameters at both porous walls are identical as well as skewed flows where parameters at the two walls differ.
Stability of boundary layers within high-speed viscous flows
NASA Astrophysics Data System (ADS)
Lyttle, Ian John
2003-10-01
A numerical study was undertaken to predict the stability of a variety of high-speed boundary-layer flows. Using a finite-volume code, the Navier-Stokes equations were solved for a series of flows around spherically blunted cones. These solutions were used to perform linear-stability analyses for second-mode disturbances. Two investigations were undertaken using an ideal-gas model: the Stetson experiment and a recent experiment conducted at the Institute of Theoretical and Applied Mechanics in Russia. Comparisons were made with both basic-state and disturbance state quantities. For both cases, linear-growth regions have been identified. For the Stetson case, using an experimentally determined wall-temperature distribution for the basic-state appeared to give better agreement with the experimentally measured growth than does the classical adiabatic-wall boundary condition. For the Russian experiment, initial comparisons were made in order to continue a careful collaboration. A third investigation was made which used a chemical non-equilibrium model, considering a Mach 13.5 flow in upper-atmospheric conditions. The goal of this investigation was to evaluate the sensitivity of second-mode growth predictions to changes (within accepted uncertainties) in thermodynamic, reaction-rate; and transport models. The magnitude of change in the stability results correlated strongly with changes in the basic-state thermal boundary-layer profile, consistent with second-mode theory. The largest change in the stability behavior was observed for the case where the transport model was changed. For high-speed flows, the development of computational techniques is in some ways ahead of the experimental community's ability to verify the results. As these techniques are applied to flows in thermochemical non-equilibrium, the fidelity of the constitutive relationships should be considered.
Stability formalism of a flowing two-fluid plasma
NASA Astrophysics Data System (ADS)
Yamada, Hideaki; Katano, Takayuki; Ishida, Akio; Steinhauer, Loren C.
2003-04-01
An improved formalism for a stability analysis of flowing two-fluid equilibria with constant density is developed. The two-fluid formalism, in which the generalized vorticity of each species is introduced as characteristic quantity, extends the usual single-fluid formalism. A new relation between the perturbed generalized vorticity and the displacement is found for each species. The spectral formalism is developed for stability of axisymmetric equilibrium. The missing elements in the single-fluid analysis of Frieman and Rotenberg [Rev. Mod. Phys. 32, 898 (1960)] are identified.
Stability Analysis of Flow Induced by the Traveling Magnetic Field
NASA Technical Reports Server (NTRS)
Mazuruk, Konstantin
2003-01-01
Re-circulating flow in molten metal columns can be conveniently induced by the axisymmetric traveling magnetic field. A number of applications can benefit from this technique, such as mixing under microgravity environment, or.crysta1 growth from metallic melts. For small magnetic field excitations, the flow is laminar and stationary. As the imposed field increases, a more complex flow will set up in the cylindrical column. Conditions for stable laminar flow are of importance for practical applications. In this work, a linear stability analysis is performed in order to determine the onset of the bifurcation in the system. Here the analysis is restricted to the axisymmetric modes and the low-frequency regime.
Stability Analysis of Flow Induced by the Traveling Magnetic Field
NASA Technical Reports Server (NTRS)
Mazuruk, Konstantin
2003-01-01
Re-circulating flow in molten metal columns can be conveniently induced by the axisymmetric traveling magnetic field. A number of applications can benefit from this technique, such as mixing under microgravity environment, or crysta1 growth from metallic melts. For small magnetic field excitations, the flow is laminar and stationary. As the imposed field increases, a more complex flow will set up in the cylindrical column. Conditions for stable laminar flow are of importance for practical applications. In this work, a linear stability analysis is performed in order to determine the onset of the bifurcation in the system. Here the analysis is restricted to the axisymmetric modes and the low-frequency regime.
Stability of Brillouin flow in planar, conventional, and inverted magnetrons
Simon, D. H.; Lau, Y. Y.; Greening, G.; Wong, P.; Gilgenbach, R. M.; Hoff, B. W.
2015-08-15
The Brillouin flow is the prevalent flow in crossed-field devices. We systematically study its stability in the conventional, planar, and inverted magnetron geometry. To investigate the intrinsic negative mass effect in Brillouin flow, we consider electrostatic modes in a nonrelativistic, smooth bore magnetron. We found that the Brillouin flow in the inverted magnetron is more unstable than that in a planar magnetron, which in turn is more unstable than that in the conventional magnetron. Thus, oscillations in the inverted magnetron may startup faster than the conventional magnetron. This result is consistent with simulations, and with the negative mass property in the inverted magnetron configuration. Inclusion of relativistic effects and electromagnetic effects does not qualitatively change these conclusions.
Stability of stratified two-phase flows in horizontal channels
NASA Astrophysics Data System (ADS)
Barmak, I.; Gelfgat, A.; Vitoshkin, H.; Ullmann, A.; Brauner, N.
2016-04-01
Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems, the stratified flow with a smooth interface is stable only in confined zone of relatively low flow rates, which is in agreement with experiments, but is not predicted by long-wave analysis. Depending on the flow conditions, the critical perturbations can originate mainly at the interface (so-called "interfacial modes of instability") or in the bulk of one of the phases (i.e., "shear modes"). The present analysis revealed that there is no definite correlation between the type of instability and the perturbation wavelength.
Studies of jet thermal stability in a flowing system
NASA Astrophysics Data System (ADS)
Heneghan, S. P.; Martel, C. R.; Williams, T. F.; Ballal, D. R.
1992-06-01
A 'Phoenix rig' single-pass flowing heat-exchanger facility has been devised to test the carbon deposition tendencies of jet fuels in their circulation systems. Three samples each of baseline JP fuels and JP fuels blended with additives have been thus tested, and the results obtained vindicate the usefulness of the Phoenix rig. The blended fuel tests indicated significant improvement in fuel thermal stability; block temperature and test duration increased the total carbon deposits in a nonlinear manner.
Stabilized finite elements for 3D reactive flows
NASA Astrophysics Data System (ADS)
Braack, M.; Richter, Th.
2006-07-01
Objective of this work is the numerical solution of chemically reacting flows in three dimensions described by detailed reaction mechanism. The contemplated problems include, e.g. burners with 3D geometry. Contrary to the usual operator splitting method the equations are treated fully coupled with a Newton solver. This leads to the necessity of the solution of large linear non-symmetric, indefinite systems. Due to the complexity of the regarded problems we combine a variety of numerical methods, as there are goal-oriented adaptive mesh refinement, a parallel multigrid solver for the linear systems and economical stabilization techniques for the stiff problems.By blocking the solution components for every ansatz function and applying special matrix structures for each block of degrees of freedom, we can significantly reduce the required memory effort without worsening the convergence. Considering the Galerkin formulation of the regarded problems this is established by using lumping of the mass matrix and the chemical source terms. However, this technique is not longer feasible for standard stabilized finite elements as for instance Galerkin least squares techniques or streamline diffusion. Those stabilized schemes are well established for Navier-Stokes flows but for reactive flows, they introduce many further couplings into the system compared to Galerkin formulations. In this work, we discuss this issue in connection with combustion in more detail and propose the local projection stabilization technique for reactive flows. Beside the robustness of the arising linear systems we are able to maintain the problem-adapted matrix structures presented above. Finally, we will present numerical results for the proposed methods. In particular, we simulate a methane burner with a detailed reaction system involving 15 chemical species and 84 elementary reactions.
Stability of Flow in a Steam-Water Geothermal Wall
NASA Astrophysics Data System (ADS)
Shulyupin, A. N.
2016-05-01
It has been shown that the existing notion about flow stability in a steam-water well cannot explain all experimentally observed features of the interrelationship between the wellhead pressure and the flow rate. We propose a new interpretation of the stability condition based on the analysis of the reaction of the well and the feed reservoir to bottom hole pressure fluctuations at given conditions at the well inlet and outlet. It has been established that the stable regime corresponds to a negative value of the criterion defined as a ratio between the derivative characteristics of the well and the reservoir, and to obtain a characteristic, it is necessary to take into account the pressure loss in the equipment placed between the wellhead and the medium with a constant pressure. Such an approach and the new interpretation explain the practically observed features of the interrelationship between the wellhead pressure and the flow rate. It has been shown that the additional drag on the wellhead can stabilize the operating conditions of the well.
Optic flow stabilizes flight in ruby-throated hummingbirds.
Ros, Ivo G; Biewener, Andrew A
2016-08-15
Flying birds rely on visual cues for retinal image stabilization by negating rotation-induced optic flow, the motion of the visual panorama across the retina, through corrective eye and head movements. In combination with vestibular and proprioceptive feedback, birds may also use visual cues to stabilize their body during flight. Here, we test whether artificially induced wide-field motion generated through projected visual patterns elicits maneuvers in body orientation and flight position, in addition to stabilizing vision. To test this hypothesis, we present hummingbirds flying freely within a 1.2 m cylindrical visual arena with a virtual surround rotated at different speeds about its vertical axis. The birds responded robustly to these visual perturbations by rotating their heads and bodies with the moving visual surround, and by adjusting their flight trajectories, following the surround. Thus, similar to insects, hummingbirds appear to use optic flow cues to control flight maneuvers as well as to stabilize their visual inputs. PMID:27284072
Lagrangian, Eulerian, and Dynamically Accessible Stability of MHD flows
NASA Astrophysics Data System (ADS)
Andreussi, Tommaso; Morrison, Philip; Pegoraro, Francesco
2012-10-01
Stability conditions of magnetized plasma flows are obtained by exploiting the Hamiltonian structure of the magnetohydrodynamics (MHD) equations and, in particular, by using three kinds of energy principles. First, the Lagrangian energy principle of Ref. [1] is introduced and sufficient stability conditions are presented. Next, plasma flows are described in terms of Eulerian variables and the noncanonical Hamiltonian formulation of MHD [2] is exploited. For symmetric equilibria, the energy-Casimir principle of Ref. [3] is expanded to second order and sufficient conditions for stability to symmetric perturbation are obtained. Then, dynamically accessible variations, i.e. variations that explicitly preserve the invariants of the system, are introduced and the respective energy principle is considered. As in Ref. [4], general criteria for stability are obtained. A comparison between the three different approaches is finally presented. [4pt] [1] E.A. Frieman and M. Rotenberg, Rev. Mod. Phys., 32 898 (1960).[0pt] [2] P.J. Morrison, J.M. Greene, Phys. Rev. Lett., 45 790 (1980).[0pt] [3] T. Andreussi, P.J. Morrison, F. Pegoraro, Phys. Plasmas, 19 052102 (2012).[0pt] [4] E. Hameiri, Phys. Plasmas, 10 2643 (2003).
Stability of layered channel flow of magnetic fluids
NASA Astrophysics Data System (ADS)
Yecko, Philip
2009-03-01
The stability of a sheared interface separating a viscous magnetic fluid (ferrofluid) and an ordinary viscous fluid is examined for arbitrary wavelength disturbances using three dimensional linear perturbation theory. The unperturbed state corresponds to a two-layer Poiseuille profile in which a uniform magnetic field of arbitrary orientation is imposed. Coupling between the field and fluid occurs via the magnetic Maxwell stress tensor, formulated here for nonlinear magnetic material, expanding the scope of previous studies of linear media. Neutral curves and stability characteristics at low Reynolds number are presented and analyzed, and are found to depend sensitively on the linear and nonlinear magnetic properties of the material. The stability properties of the flow are shaped by a small set of the least stable modes of the spectrum, a result that evades single mode or potential flow analyses. The gravest modes can be of different character, resembling either interfacial or shear modes, modified by magnetic effects. The commonly cited ferrofluid interface properties of "stabilization by a tangential field" and "destabilization by a normal field" are shown to be invalid here, although the origins of these features can be identified within this problem.
Influence of flow on interface shape stability in low gravity
NASA Technical Reports Server (NTRS)
Steen, Paul H.
1994-01-01
The objectives are to: (1) Understand the influence in low gravity of flow on interface shape. For example, document and control the influence of axial flow on the Plateau-Rayleigh instability of a liquid bridge; and (2) Extend the ground-based density-matching technique of low gravity simulation to situations with flow; that is, develop Plateau chamber experiments for which flow can be controlled. Containerless containment of liquid by surface tension has broad importance in low gravity. For space vehicles, the behavior of liquid/gas interfaces is crucial to successful liquid management systems. In microgravity science, free interfaces are exploited in various applications. Examples include float-zone crystal growth, phase separation near the critical point of liquid mixtures (spinoidal decomposition) and quenching of miscibility gap molten metal alloys. In some cases, it is desired to stabilize the capillary instability while in others it is desired to induce capillary breakup. In all cases, understanding the stability of interface shape in the presence of liquid motion is central.
The inviscid stability of supersonic flow past a sharp cone
NASA Technical Reports Server (NTRS)
Duck, Peter W.; Shaw, Stephen J.
1990-01-01
The laminar boundary layer which forms on a sharp cone in a supersonic freestream, where lateral curvature plays a key role in the physics of the problem is considered. This flow is then analyzed from the point of view of linear, temporal, inviscid stability. The basic, non-axisymmetric disturbance equations are derived for general flows of this class, and a so called triply generalized inflexion condition is found for the existence of subsonic neutral modes of instability. This condition is analogous to the well-known generalized inflexion condition found in planar flows, although in the present case the condition depends on both axial and aximuthal wavenumbers. Extensive numerical results are presented for the stability problem at a freestream Mach number of 3.8, for a range of streamwise locations. These results reveal that a new mode of instability may occur, peculiar to flows of this type involving curvature. Additionally, asymptotic analyses valid close to the tip of the cone, far downstream of the cone are presented, and these give a partial (asymptotic) description of this additional mode of instability.
Focusing phenomenon and stability of spiral-flow jet
NASA Astrophysics Data System (ADS)
Horii, Kiyoshi; Matsumae, Yuji; Cheng, Xiao M.; Takei, Masahiro; Yasukawa, Eiji
1991-02-01
A new nozzle assembly has been developed for an improved focusing of spiral air jet streams. To obtain a focused and highly stable spiral-flow jet, a nozzle is designed with an annular slit connected to a conical cylinder. Pressurized fluid is forced through the sides of the device into the buffer area and then through the annular slit into the pipe entrance. The fluid, passing through the conical cylinder, develops a spiral structure with a steeper axial velocity distribution, caused by Coanda effect and the instability of flow. The jet stream velocity as well as its focusing phenomenon was experimentally determined using a laser sheet method. The results clearly indicate the focusing characteristic and the high stability of spiral flow jet.
On the stability of MHD equilibria with flow
NASA Astrophysics Data System (ADS)
Andreussi, Tommaso; Morrison, Philip J.; Pegoraro, Francesco
2012-03-01
Three kinds of energy principles arising from the Hamiltonian structure of the (MHD) equations are used to determine sufficient stability conditions. The Lagrangian energy principle of Ref.[1] is presented and the stability conditions for symmetric and non-symmetric perturbations are introduced. Exploiting the noncanonical Hamiltonian formulation of MHD [2] plasma flows are analyzed in terms of Eulerian variables. An energy principle in Eulerian form is deduced for equilibria with a geometric symmetry and sufficient conditions for stability are obtained by expanding a functional F composed of the sum of the Eulerian energy plus Casimir invariants to second order. Next, an energy principle based on dynamically accessible variations [3] that preserve the invariants of the system explicitly is considered. Dynamically accessible variations do not rely on any symmetry and thus give general criteria for stability. Finally, the conditions obtained from the three different approaches are compared and implications about nonlinear stability are discussed.[4pt] [1] E.A. Frieman and M. Rotenberg, Rev. Mod. Phys., 32 898 (1960).[0pt] [2] P.J. Morrison and J.M. Greene, Phys. Rev. Lett., 45 790 (1980).[0pt] [3] P.J. Morrison, Rev. Mod. Phys., 70 467 (1998).
A general method to determine the stability of compressible flows
NASA Technical Reports Server (NTRS)
Guenther, R. A.; Chang, I. D.
1982-01-01
Several problems were studied using two completely different approaches. The initial method was to use the standard linearized perturbation theory by finding the value of the individual small disturbance quantities based on the equations of motion. These were serially eliminated from the equations of motion to derive a single equation that governs the stability of fluid dynamic system. These equations could not be reduced unless the steady state variable depends only on one coordinate. The stability equation based on one dependent variable was found and was examined to determine the stability of a compressible swirling jet. The second method applied a Lagrangian approach to the problem. Since the equations developed were based on different assumptions, the condition of stability was compared only for the Rayleigh problem of a swirling flow, both examples reduce to the Rayleigh criterion. This technique allows including the viscous shear terms which is not possible in the first method. The same problem was then examined to see what effect shear has on stability.
Direct Numerical Simulation of Stable Channel Flow at Large Stability
NASA Astrophysics Data System (ADS)
Nieuwstadt, F. T. M.
2005-08-01
We consider a model for the stable atmospheric boundary at large stability, i.e. near the limit where turbulence is no longer able to survive. The model is a plane horizontally homogeneous channel flow, which is driven by a constant pressure gradient and which has a no-slip wall at the bottom and a free-slip wall at the top. At the lower wall a constant negative temperature flux is imposed. First, we consider a direct numerical simulation of the same channel flow. The simulation is computed with the neutral channel flow as initial condition and computed as a function of time for various values of the stability parameter h/L, where h is the channel height and L is related to the Obukhov length. We find that a turbulent solution is only possible for h/L < 1.25 and for larger values turbulence decays. Next, we consider a theoretical model for this channel flow based on a simple gradient transfer closure. The resulting equations allow an exact solution for the case of a stationary flow. The velocity profile for this solution is almost linear as a function of height in most of the channel. In the limit of infinite Reynolds number, the temperature profile has a logarithmic singularity at the upper wall of the channel. For the cases where a turbulent flow is maintained in the numerical simulation, we find that the velocity and temperature profiles are in good agreement with the results of the theoretical model when the effects of the surface layer on the exchange coefficients are taken into account.
The stability of pipe entrance flows subjected to axisymmetric disturbances
Silva, D.F. da; Moss, E.A. . School of Mechanical Engineering)
1994-03-01
This paper reexamines an important unresolved problem in fluid mechanics--the discrepancy between measurements and predictions of stability in pipe entrance flows. Whereas measured critical Reynolds numbers are relatively insensitive to velocity profile shape in the streamwise direction, the theoretical results indicate a rapid increase, both as the equilibrium profile is approached, and toward the inlet. The current work uses the displacement thickness based Reynolds number as a rational basis on which to compare new stability predictions obtained by means of the Q-Z algorithm, with existing theoretical results. Although the present data are shown to be the only data that are consistent with the classical parallel boundary layer limit towards the inlet, they still deviate increasingly with axial distance from the only available experimental results. By examining pipe inlet stability data in relation to boundary layer measurements and predictions, the work effectively questions the commonly held belief that streamwise variations of flow alone are responsible for these deviations, suggesting that the finite amplitude nature of the applied disturbances is the most likely cause.
Effects of particles on stability of flow-induced precursors.
Zhu, Peng-Wei; Phillips, Andrew W; Edward, Graham
2012-02-01
The effect of two colorant particles with different surface geometries on the stability of shear-induced precursors in isotactic polypropylene was studied after the cessation of shear flow at 140 °C. In the absence of particles, the shear-induced precursors survived for at least 100 s after the shear flow ended. The presence of particles was found to stabilize lower molecular weight chains assisting in the formation of additional shear-induced precursors. The precursors thus formed in the samples containing particles contained two oriented clusters with different molecular weights. Incorporation of lower molecular weight chains in the precursors led to increased dissolution rates of the shear-induced precursors. Particle surface geometry was found to influence precursor dissolution, with planar particles stabilizing the shear-induced precursors to a much greater extent than curved particles. The particles investigated thus act like structural probes to follow quantitatively the dissolution process of precursors after shear and importantly to infer the formation of precursors during shear.
Oxygen Mass Flow Rate Generated for Monitoring Hydrogen Peroxide Stability
NASA Technical Reports Server (NTRS)
Ross, H. Richard
2002-01-01
Recent interest in propellants with non-toxic reaction products has led to a resurgence of interest in hydrogen peroxide for various propellant applications. Because peroxide is sensitive to contaminants, material interactions, stability and storage issues, monitoring decomposition rates is important. Stennis Space Center (SSC) uses thermocouples to monitor bulk fluid temperature (heat evolution) to determine reaction rates. Unfortunately, large temperature rises are required to offset the heat lost into the surrounding fluid. Also, tank penetration to accomodate a thermocouple can entail modification of a tank or line and act as a source of contamination. The paper evaluates a method for monitoring oxygen evolution as a means to determine peroxide stability. Oxygen generation is not only directly related to peroxide decomposition, but occurs immediately. Measuring peroxide temperature to monitor peroxide stability has significant limitations. The bulk decomposition of 1% / week in a large volume tank can produce in excess of 30 cc / min. This oxygen flow rate corresponds to an equivalent temperature rise of approximately 14 millidegrees C, which is difficult to measure reliably. Thus, if heat transfer were included, there would be no temperature rise. Temperature changes from the surrounding environment and heat lost to the peroxide will also mask potential problems. The use of oxygen flow measurements provides an ultra sensitive technique for monitoring reaction events and will provide an earlier indication of an abnormal decomposition when compared to measuring temperature rise.
Electromagnetically Sustained Liquid Metal Flow for Feedback Stabilization Studies
NASA Astrophysics Data System (ADS)
Mirhoseini, Seyyed Mohammad; Volpe, Francesco
2015-11-01
Liquid metal walls in fusion reactors, whether nearly static or rapidly flowing, will be subject to instabilities that will make them locally bulge, thus entering in contact with the plasma, or deplete, hence exposing the underlying solid substrate. To prevent this, research has begun at Columbia University to create liquid metal flows and demonstrate their stabilization by electromagnetic forces, adjusted in feedback with thickness measurements. Here we present initial results regarding the sustainment of a flow of Galinstan (a gallium, indium, tin alloy) by a special pump consisting of a ferromagnetic rotor, with permanent magnets mounted on it. The magnetic field is partly ``frozen'' in the liquid metal surrounding the rotor. Therefore, as the field rotates, the liquid metal rotates as well, although with a slip factor. This solution was preferred to conventional pumps, which would enter in electrical contact with the metal flow. The pump, 3D-printed at Columbia, allows to adjust the flow-velocity from few mm/s to several cm/s.
Stability and transitions of the second grade Poiseuille flow
NASA Astrophysics Data System (ADS)
Özer, Saadet; Şengül, Taylan
2016-09-01
In this study we consider the stability and transitions for the Poiseuille flow of a second grade fluid which is a model for non-Newtonian fluids. We restrict our attention to perturbation flows in an infinite pipe with circular cross section that are independent of the axial coordinate. We show that unlike the Newtonian (ɛ = 0) case, in the second grade model (ɛ > 0 case), the time independent base flow exhibits transitions as the Reynolds number R exceeds the critical threshold Rc = 8.505ɛ - 1 / 2 where ɛ is a material constant measuring the relative strength of second order viscous effects compared to inertial effects. At R =Rc, we find that the transition is either continuous or catastrophic and a small amplitude, time periodic flow with 3-fold azimuthal symmetry bifurcates. The time period of the bifurcated solution tends to infinity as R tends to Rc. Our numerical calculations suggest that for low ɛ values, the system prefers a catastrophic transition where the bifurcation is subcritical. We also show that there is a Reynolds number RE with RE
Electromagnetic effects in the stabilization of turbulence by sheared flow
NASA Astrophysics Data System (ADS)
Cole, M. D. J.; Newton, S. L.; Cowley, S. C.; Loureiro, N. F.; Dickinson, D.; Roach, C.; Connor, J. W.
2014-01-01
We have extended our study of the competition between the drive and stabilization of plasma microinstabilities by sheared flow to include electromagnetic effects at low plasma β (the ratio of plasma to magnetic pressure). The extended system of characteristic equations is formulated, for a dissipative fluid model developed from the gyrokinetic equation, using a twisting mode representation in sheared slab geometry and focusing on the ion temperature gradient mode. Perpendicular flow shear convects perturbations along the field at the speed we denote as Mcs (where cs is the sound speed). M \\gt 1/ \\sqrt{\\beta} is required to make the system characteristics unidirectional and inhibit eigenmode formation, leaving only transitory perturbations in the system. This typically represents a much larger flow shear than in the electrostatic case, which only needs M > 1. Numerical investigation of the region M \\lt 1/\\sqrt{\\beta} shows the driving terms can conflict, as in the electrostatic case, giving low growth rates over a range of parameters. Also, at modest drive strengths and low β values typical of experiments, including electromagnetic effects does not significantly alter the growth rates. For stronger flow shear and higher β, geometry characteristic of the spherical tokamak mitigates the effect of an instability of the shear Alfvén wave, driven by the parallel flow shear.
Progress in Creating Stabilized Gas Layers in Flowing Liquid Mercury
Wendel, Mark W; Felde, David K; Riemer, Bernie; Abdou, Ashraf A; D'Urso, Brian R; West, David L
2009-01-01
The Spallation Neutron Source (SNS) facility in Oak Ridge, Tennessee uses a liquid mercury target that is bombarded with protons to produce a pulsed neutron beam for materials research and development. In order to mitigate expected cavitation damage erosion (CDE) of the containment vessel, a two-phase flow arrangement of the target has been proposed and was earlier proven to be effective in significantly reducing CDE in non-prototypical target bodies. This arrangement involves covering the beam "window", through which the high-energy proton beam passes, with a protective layer of gas. The difficulty lies in establishing a stable gas/liquid interface that is oriented vertically with the window and holds up to the strong buoyancy force and the turbulent mercury flow field. Three approaches to establishing the gas wall have been investigated in isothermal mercury/gas testing on a prototypical geometry and flow: (1) free gas layer approach, (2) porous wall approach, and (3) surface-modified approach. The latter two of these approaches show success in that a stabilized gas layer is produced. Both of these successful approaches capitalize on the high surface energy of liquid mercury by increasing the surface area of the solid wall, thus increasing gas hold up at the wall. In this paper, a summary of these experiments and findings is presented as well as a description of the path forward toward incorporating the stabilized gas layer approach into a feasible gas/mercury SNS target design.
Stability of model flocks in a vortical flow
NASA Astrophysics Data System (ADS)
Baggaley, A. W.
2016-06-01
We investigate the stability of self-propelled particle flocks in the Taylor-Green vortex, a steady vortical flow. We consider a model in which particles align themselves to a combination of the orientation and the acceleration of particles within a critical radius. We identify two distinct regimes: If alignment with orientation is dominant, the particles tend to be expelled from regions of high vorticity. In contrast, if anticipation is dominant, the particles accumulate in areas of large vorticity. In both regimes, the relative order of the flock is reduced. However, we show that there can be a critical balance of the two effects that stabilizes the flock in the presence of external fluid forcing. This strategy could provide a mechanism for animal flocks to remain globally ordered in the presence of fluid forcing, and it may also have applications in the design of flocking autonomous drones and artificial microswimmers.
Stability of model flocks in a vortical flow.
Baggaley, A W
2016-06-01
We investigate the stability of self-propelled particle flocks in the Taylor-Green vortex, a steady vortical flow. We consider a model in which particles align themselves to a combination of the orientation and the acceleration of particles within a critical radius. We identify two distinct regimes: If alignment with orientation is dominant, the particles tend to be expelled from regions of high vorticity. In contrast, if anticipation is dominant, the particles accumulate in areas of large vorticity. In both regimes, the relative order of the flock is reduced. However, we show that there can be a critical balance of the two effects that stabilizes the flock in the presence of external fluid forcing. This strategy could provide a mechanism for animal flocks to remain globally ordered in the presence of fluid forcing, and it may also have applications in the design of flocking autonomous drones and artificial microswimmers. PMID:27415360
Symmetry and stability in Taylor-Couette flow
NASA Technical Reports Server (NTRS)
Golubitsky, M.; Stewart, I.
1986-01-01
The flow of a fluid between concentric rotating cylinders (the Taylor problem) is studied by exploiting the symmetries of the system. The Navier-Stokes equations, linearized about Couette flow, possess two zero and four purely imaginary eigenvalues at a suitable value of the speed of rotation of the outer cylinder. There is thus a reduced bifurcation equation on a six-dimensonal space which can be shown to commute with an action of the symmetry group 0(2) x S0(2). The group structure is used to analyze this bifurcation equation in the simplest (nondegenerate) case, and to compute the stabilities of solutions. In particular, when the outer cylinder is counterrotated, transitions which seem to agree with recent experiments of Andereck, Liu, and Swinney (1984) are obtained. It is also possible to obtain the 'main sequence' in this model. This sequence is normally observed in experiments when the outer cylinder is held fixed.
Stability theory applications to laminar-flow control
NASA Technical Reports Server (NTRS)
Malik, Mujeeb R.
1987-01-01
In order to design Laminar Flow Control (LFC) configurations, reliable methods are needed for boundary-layer transition predictions. Among the available methods, there are correlations based upon R sub e, shape factors, Goertler number and crossflow Reynolds number. The most advanced transition prediction method is based upon linear stability theory in the form of the e sup N method which has proven to be successful in predicting transition in two- and three-dimensional boundary layers. When transition occurs in a low disturbance environment, the e sup N method provides a viable design tool for transition prediction and LFC in both 2-D and 3-D subsonic/supersonic flows. This is true for transition dominated by either TS, crossflow, or Goertler instability. If Goertler/TS or crossflow/TS interaction is present, the e sup N will fail to predict transition. However, there is no evidence of such interaction at low amplitudes of Goertler and crossflow vortices.
Predicting the stability of a compressible periodic parallel jet flow
NASA Technical Reports Server (NTRS)
Miles, Jeffrey H.
1996-01-01
It is known that mixing enhancement in compressible free shear layer flows with high convective Mach numbers is difficult. One design strategy to get around this is to use multiple nozzles. Extrapolating this design concept in a one dimensional manner, one arrives at an array of parallel rectangular nozzles where the smaller dimension is omega and the longer dimension, b, is taken to be infinite. In this paper, the feasibility of predicting the stability of this type of compressible periodic parallel jet flow is discussed. The problem is treated using Floquet-Bloch theory. Numerical solutions to this eigenvalue problem are presented. For the case presented, the interjet spacing, s, was selected so that s/omega =2.23. Typical plots of the eigenvalue and stability curves are presented. Results obtained for a range of convective Mach numbers from 3 to 5 show growth rates omega(sub i)=kc(sub i)/2 range from 0.25 to 0.29. These results indicate that coherent two-dimensional structures can occur without difficulty in multiple parallel periodic jet nozzles and that shear layer mixing should occur with this type of nozzle design.
Stability of Inviscid Flow over Airfoils Admitting Multiple Numerical Solutions
NASA Astrophysics Data System (ADS)
Liu, Ya; Xiong, Juntao; Liu, Feng; Luo, Shijun
2012-11-01
Multiple numerical solutions at the same flight condition are found of inviscid transonic flow over certain airfoils (Jameson et al., AIAA 2011-3509) within some Mach number range. Both symmetric and asymmetric solutions exist for a symmetric airfoil at zero angle of attack. Global linear stability analysis of the multiple solutions is conducted. Linear perturbation equations of the Euler equations around a steady-state solution are formed and discretized numerically. An eigenvalue problem is then constructed using the modal analysis approach. Only a small portion of the eigen spectrum is needed and thus can be found efficiently by using Arnoldi's algorithm. The least stable or unstable mode corresponds to the eigenvalue with the largest real part. Analysis of the NACA 0012 airfoil indicates stability of symmetric solutions of the Euler equations at conditions where buffet is found from unsteady Navier-Stokes equations. Euler solutions of the same airfoil but modified to include the displacement thickness of the boundary layer computed from the Navier-Stokes equations, however, exhibit instability based on the present linear stability analysis. Graduate Student.
The inviscid stability of supersonic flow past a sharp cone
NASA Technical Reports Server (NTRS)
Duck, Peter W.; Shaw, Stephen J.
1990-01-01
The effects of lateral curvature on the development of supersonic laminar inviscid boundary-layer flow on a sharp cone with adiabatic wall conditions are investigated analytically, with a focus on the linear temporal inviscid stability properties. The derivation of the governing equations and of a 'triply generalized' inflexion condition is outlined, and numerical results for freestream Mach number 3.8 are presented in extensive graphs and characterized in detail. A third instability mode related to the viscous mode observed by Duck and Hall (1990) using triple-deck theory is detected and shown to be more unstable and to have larger growth rates than the second mode in some cases. It is found that the 'sonic' neutral mode is affected by the lateral curvature and becomes a supersonic neutral mode.
Stability analysis of traffic flow with extended CACC control models
NASA Astrophysics Data System (ADS)
Ya-Zhou, Zheng; Rong-Jun, Cheng; Siu-Ming, Lo; Hong-Xia, Ge
2016-06-01
To further investigate car-following behaviors in the cooperative adaptive cruise control (CACC) strategy, a comprehensive control system which can handle three traffic conditions to guarantee driving efficiency and safety is designed by using three CACC models. In this control system, some vital comprehensive information, such as multiple preceding cars’ speed differences and headway, variable safety distance (VSD) and time-delay effect on the traffic current and the jamming transition have been investigated via analytical or numerical methods. Local and string stability criterion for the velocity control (VC) model and gap control (GC) model are derived via linear stability theory. Numerical simulations are conducted to study the performance of the simulated traffic flow. The simulation results show that the VC model and GC model can improve driving efficiency and suppress traffic congestion. Project supported by the National Natural Science Foundation of China (Grant Nos. 71571107 and 11302110). The Scientific Research Fund of Zhejiang Province, China (Grant Nos. LY15A020007, LY15E080013, and LY16G010003). The Natural Science Foundation of Ningbo City (Grant Nos. 2014A610030 and 2015A610299), the Fund from the Government of the Hong Kong Administrative Region, China (Grant No. CityU11209614), and the K C Wong Magna Fund in Ningbo University, China.
Stability analysis of traffic flow with extended CACC control models
NASA Astrophysics Data System (ADS)
Ya-Zhou, Zheng; Rong-Jun, Cheng; Siu-Ming, Lo; Hong-Xia, Ge
2016-06-01
To further investigate car-following behaviors in the cooperative adaptive cruise control (CACC) strategy, a comprehensive control system which can handle three traffic conditions to guarantee driving efficiency and safety is designed by using three CACC models. In this control system, some vital comprehensive information, such as multiple preceding cars’ speed differences and headway, variable safety distance (VSD) and time-delay effect on the traffic current and the jamming transition have been investigated via analytical or numerical methods. Local and string stability criterion for the velocity control (VC) model and gap control (GC) model are derived via linear stability theory. Numerical simulations are conducted to study the performance of the simulated traffic flow. The simulation results show that the VC model and GC model can improve driving efficiency and suppress traffic congestion. Project supported by the National Natural Science Foundation of China (Grant Nos. 71571107 and 11302110). The Scientific Research Fund of Zhejiang Province, China (Grant Nos. LY15A020007, LY15E080013, and LY16G010003). The Natural Science Foundation of Ningbo City (Grant Nos. 2014A610030 and 2015A610299), the Fund from the Government of the Hong Kong Administrative Region, China (Grant No. CityU11209614), and the K C Wong Magna Fund in Ningbo University, China.
Hydroelastic response and stability of a hydrofoil in viscous flow
NASA Astrophysics Data System (ADS)
Ducoin, Antoine; Young, Yin L.
2013-04-01
The objective of this research is to investigate the hydroelastic response and stability of a flexible hydrofoil in viscous flow. The focus is on viscous effects, such as laminar to turbulent transition and stall, on the fluid-structure interaction (FSI) response and hydroelastic stability of flexible hydrofoils. The numerical approach is based on the coupling between a commercial Computational Fluid Dynamics (CFD) solver, CFX, and a simple two-degrees-of-freedom (2-DOF) system that simulates the tip section bend and twist deformations of a cantelivered, rectangular hydrofoil. The hydrodynamic loading is assumed to be uniform in the spanwise direction, and the hydrofoil is assumed to undergo bend and twist deformation along the spanwise direction only. The CFD solver is first validated by comparing numerical predictions with experimental measurements of the lift, drag, and moment coefficients of a rigid NACA0012 hydrofoil over a wide range of Reynolds numbers and angles of attack. The coupled viscous FSI solver is then validated by comparing numerical predictions with experimental measurements of (i) the lift coefficient of a rigid (stainless steel) NACA66 hydrofoil and (ii) the tip section displacement of a flexible (POM Polyacetate) NACA66 hydrofoil with the same initial (un-deformed) geometry. The hydrodynamic responses of the rigid and flexible NACA66 hydrodfoils are compared to identify FSI effects in viscous flow, including transition, stall, and static divergence. The results show that the flexible hydrofoil undergoes a clockwise twist deformation because the center of pressure is to the left of the elastic axis (center of twist), which increases the effective angle of attack and moves the center of pressure toward the leading edge; the resultant increase in lift and moment will further increase the effective angle of attack until the twist capacity is exceeded, i.e. static divergence or material failure occurs. The results show that viscous effects tend to
Stability Analysis of Large-Scale Incompressible Flow Calculations on Massively Parallel Computers
LEHOUCQ,RICHARD B.; ROMERO,LOUIS; SALINGER,ANDREW G.
1999-10-25
A set of linear and nonlinear stability analysis tools have been developed to analyze steady state incompressible flows in 3D geometries. The algorithms have been implemented to be scalable to hundreds of parallel processors. The linear stability of steady state flows are determined by calculating the rightmost eigenvalues of the associated generalize eigenvalue problem. Nonlinear stability is studied by bifurcation analysis techniques. The boundaries between desirable and undesirable operating conditions are determined for buoyant flow in the rotating disk CVD reactor.
The effect of asymmetric heating on flow stability and heat transfer for flow in a vertical tube
Tappan, C.H.
1987-11-01
This study presents experimental results of combined free and forced convection heat transfer in a vertical tube with a circumferentially nonuniform constant wall heat flux. The effect of an asymmetric wall heat flux on flow stability and on the rate of heat transfer for water flowing downward in a vertical tube was investigated. Experimental results were used to develop two stability maps which identify various flow regimes, corresponding to different thermal and hydraulic conditions. Heat transfer coefficients were also determined. Experimental results in the present investigation were compared to those with uniform heating in horizontal and vertical tube flow situations discussed in the literature. 23 refs., 12 figs., 1 tab.
On the stability and uniqueness of the flow of a fluid through a porous medium
NASA Astrophysics Data System (ADS)
Hill, A. A.; Rajagopal, K. R.; Vergori, L.
2016-06-01
In this short note, we study the stability of flows of a fluid through porous media that satisfies a generalization of Brinkman's equation to include inertial effects. Such flows could have relevance to enhanced oil recovery and also to the flow of dense liquids through porous media. In any event, one cannot ignore the fact that flows through porous media are inherently unsteady, and thus, at least a part of the inertial term needs to be retained in many situations. We study the stability of the rest state and find it to be asymptotically stable. Next, we study the stability of a base flow and find that the flow is asymptotically stable, provided the base flow is sufficiently slow. Finally, we establish results concerning the uniqueness of the flow under appropriate conditions, and present some corresponding numerical results.
A survey of the role of thermodynamic stability in viscous flow
NASA Technical Reports Server (NTRS)
Horne, W. C.; Smith, C. A.; Karamcheti, K.
1991-01-01
The stability of near-equilibrium states has been studied as a branch of the general field of nonequilibrium thermodynamics. By treating steady viscous flow as an open thermodynamic system, nonequilibrium principles such as the condition of minimum entropy-production rate for steady, near-equilibrium processes can be used to generate flow distributions from variational analyses. Examples considered in this paper are steady heat conduction, channel flow, and unconstrained three-dimensional flow. The entropy-production-rate condition has also been used for hydrodynamic stability criteria, and calculations of the stability of a laminar wall jet support this interpretation.
Stability of permeative flows in 1 dimensionally ordered systems
NASA Astrophysics Data System (ADS)
Prost, J.; Pomeau, Y.; Guyon, E.
1991-03-01
Layered structures are met in dissipative systems, such as Rayleigh Bénard rolls, as well as in liquid crystalline phases (smectics and cholesterics). We present here a general description, in the framework of phase dynamics, of the stability of these structures when submitted to an external force field (flow, electric field) acting perpendicular to the roll axis for various boundary conditions. The one-dimensional equilibrium solution with fixed boundary conditions leads to an effect, discovered experimentally by Pocheau and Croquette on Rayleigh-Bérnard rolls in the presence of a transverse flow, and involving the coexistence of compressed and dilated rolls; this effect has a known counterpart in cholesterics. Using the same boundary conditions, we generalize the well known undulation instability obtained under a dilative stress to the case of the action of a transverse force both from the point of view of linear stability and in the highly nonlinear limit. The possibility of observing fractal structures is indicated. For mixed boundary conditions, it is possible to have a sustained time dependent behavior involving the nucleation of new layers as also observed in the above mentioned experiments. On rencontre des structures en couches dans des systèmes dissipatifs tels que les rouleaux convectifs de Rayleigh-Bénard et dans les cristaux liquides (smectiques et cholestériques). Nous présentons ici une description générale de la stabilité de ces structures dans le cadre du formalisme de la diffusion de phase, lorsqu'elles sont soumises à un champ de force extérieur (écoulement, champ électrique) agissant à angle droit de la direction des rouleaux, en fonction des conditions aux limites. La solution unidimensionnelle d'équilibre avec des conditions aux limites rigides pour la phase conduit à un effet découvert par Pocheau et Croquette (P.C.) dans la convection de R.B. et mettant en jeu la coexistence de zones dilatée et comprimée. Cet effet a un
How does the flow within the boundary layer influence morphological stability of a vicinal face?
NASA Astrophysics Data System (ADS)
Chernov, A. A.
1992-04-01
Imagine parallel growth steps forming a vacinal face and moving in the same direction. Since the diffusion fields of these steps overlap, the steps decelerate one another and spontaneously form macroscopic bunches. Such instability is known always to develop in supersaturated solutions and supercooled melts despite capillarity. The corresponding stability problems were analyzed previously with the assumption that the fuid within the boundary layer is stagnant. In this paper, the effect of solution flow within the boundary layer on the stability is considered for the first time. The analytical solution found describes the drift of diffusion clouds (enriched or improverished regions of solution) surrounding spontaneously appearing slight step bunches. This drift turns out to enhance instability if the fluid flow direction is the same as the step motion direction. However, if these directions are antiparallel, the drift is a very strong stabilizing factor which keeps the interface stable up to large (many cm) size. This stability is provided by the drift, in cooperation with the growth rate anisotropy. For isotropic growth kinetics, this flow-kinetic stabilization is absent. The flow-kinetic stabilization is several orders of magnitude stronger than the stabilization by capillarity. In solutions, very low flow rates, just exceeding the step growth rates, are sufficient for the stabilization. In melts, the step motion is very fast and is equivalent to the opposite fluid flow thus providing kinetic stabilization per se. The analytical solution obtained may be used in other crystal growth problems.
Heaps of Shapes: Flow-Stabilized Solids with Non-Spherical Colloids
NASA Astrophysics Data System (ADS)
Lindauer, Scott; Shields, C. Wyatt, IV; Lopez, Gabriel P.; Daniels, Karen E.; Riehn, Robert
Flow-stabilized solids are a class of fragile matter that are formed when a dense suspension of hard colloids is accumulated against a semipermeable barrier. We build a microfluidic device to confine Brownian particles in a quasi-2D channel; a controlled flow rate above a critical value forms flow-stabilized solids against the barrier. We extend prior work on submicron spherical particles, to particles of size 2-5 microns, and of various shapes: circular, rectangular, hexagonal, and triangular prisms. We perform experiments on these flow-stabilized solids to observe the angle of repose, packing fraction, and orientational order as a function of flow rate. We vary the flow rate quasi-statically in order to conduct the experiment at steady state. We find a critical flow rate below which no pile forms. In general, particles with less-circular shape form more stable heaps.
The Cost of Stability in Network Flow Games
NASA Astrophysics Data System (ADS)
Resnick, Ezra; Bachrach, Yoram; Meir, Reshef; Rosenschein, Jeffrey S.
The core of a cooperative game contains all stable distributions of a coalition’s gains among its members. However, some games have an empty core, with every distribution being unstable. We allow an external party to offer a supplemental payment to the grand coalition, which may stabilize the game, if the payment is sufficiently high. We consider the cost of stability (CoS)—the minimal payment that stabilizes the game.
Impact of asymmetrical flow field-flow fractionation on protein aggregates stability.
Bria, Carmen R M; Williams, S Kim Ratanathanawongs
2016-09-23
The impact of asymmetrical flow field-flow fractionation (AF4) on protein aggregate species is investigated with the aid of multiangle light scattering (MALS) and dynamic light scattering (DLS). The experimental parameters probed in this study include aggregate stability in different carrier liquids, shear stress (related to sample injection), sample concentration (during AF4 focusing), and sample dilution (during separation). Two anti-streptavidin (anti-SA) IgG1 samples composed of low and high molar mass (M) aggregates are subjected to different AF4 conditions. Aggregates suspended and separated in phosphate buffer are observed to dissociate almost entirely to monomer. However, aggregates in citric acid buffer are partially stable with dissociation to 25% and 5% monomer for the low and high M samples, respectively. These results demonstrate that different carrier liquids change the aggregate stability and low M aggregates can behave differently than their larger counterparts. Increasing the duration of the AF4 focusing step showed no significant changes in the percent monomer, percent aggregates, or the average Ms in either sample. Syringe-induced shear related to sample injection resulted in an increase in hydrodynamic diameter (dh) as measured by batch mode DLS. Finally, calculations showed that dilution during AF4 separation is significantly lower than in size exclusion chromatography with dilution occurring mainly at the AF4 channel outlet and not during the separation. This has important ramifications when analyzing aggregates that rapidly dissociate (<∼2s) upon dilution as the size calculated by AF4 theory may be more accurate than that measured by online DLS. Experimentally, the dhs determined by online DLS generally agreed with AF4 theory except for the more well retained larger aggregates for which DLS showed smaller sizes. These results highlight the importance of using AF4 retention theory to understand the impacts of dilution on analytes. PMID
Heat transfer effects on the stability of low speed plane Couette-Poiseuille flow
NASA Astrophysics Data System (ADS)
Özgen, Serkan; Dursunkaya, Zafer; Ebrinç, Ali Aslan
2007-10-01
The stability problem of low-speed plane Couette-Poiseuille flow of air under heat transfer effects is solved numerically using the linear stability theory. Stability equations obtained from two-dimensional equations of motion and their boundary conditions result in an eigenvalue problem that is solved using an efficient shoot-search technique. Variable fluid properties are accounted for both in the basic flow and the perturbation (stability) equations. A parametric study is performed in order to assess the roles of moving wall velocity and heat transfer. It is found that the moving wall velocity and the location of the critical layers play decisive roles in the instability mechanism. The flow becomes unconditionally stable whenever the moving wall velocity exceeds half of the maximum velocity in the channel. With wall heating and Mach number effects included, the flow is stabilized.
Stability of parallel flows in a microchannel after a T junction.
Guillot, Pierre; Colin, Annie
2005-12-01
In this work, the flow of immiscible fluids in microchannels is studied. Flow pattern diagrams obtained in microfluidic chips are presented. Monodisperse droplets or parallel flows are obtained depending on the flow rate values of the aqueous phase and the oil phase. Transition from droplet regime to parallel flows cannot be described in terms of capillary numbers. Using confocal microscopy and high speed imaging, it was shown that droplets are formed through a blocking-pinching mechanism ruled by flow rate conservation. Conditions for parallel flow stability are quantified.
Stability of Poiseuille flow in a fluid overlying an anisotropic and inhomogeneous porous layer
NASA Astrophysics Data System (ADS)
Deepu, P.; Anand, Prateek; Basu, Saptarshi
2015-08-01
We present the linear stability analysis of horizontal Poiseuille flow in a fluid overlying a porous medium with anisotropic and inhomogeneous permeability. The generalized Darcy model is used to describe the flow in the porous medium with the Beavers-Joseph condition at the interface of the two layers and the eigenvalue problem is solved numerically. The effect of major system parameters on the stability characteristics is addressed in detail. It is shown that the anisotropic and inhomogeneous modulation of the permeability of the underlying porous layer provides an effective means for passive control of the flow stability.
Stability and angular-momentum transport of fluid flows between corotating cylinders.
Avila, M
2012-03-23
Turbulent transport of angular momentum is a necessary process to explain accretion in astrophysical disks. Although the hydrodynamic stability of disklike flows has been tested in experiments, results are contradictory and suggest either laminar or turbulent flow. Direct numerical simulations reported here show that currently investigated laboratory flows are hydrodynamically unstable and become turbulent at low Reynolds numbers. The underlying instabilities stem from the axial boundary conditions, affect the flow globally, and enhance angular-momentum transport.
Linear stability of circular Couette flow in the limit of small radius ratio
NASA Astrophysics Data System (ADS)
Pearlstein, Arne J.
2005-11-01
In the context of a detailed study of the linear stability of spiral Poiseuille flow at small radius ratio (Cotrell and Pearlstein, J. Fluid Mech., in press), we have shown that in the limiting case of no rotation, annular Poiseuille flow is linearly stable at all Re, provided that the radius ratio lies below a critical value. Here, we consider the other limiting case, of no axial flow, and report a numerical investigation of the stability of circular Couette flow for small radius ratio. The results are compared to experimental work of Theodorsen for a whirling shaft in an unbounded, otherwise quiescent fluid.
Stabilization of stationary excitation pulses in an open flow without long-range inhibition.
Kaern, Mads; Menzinger, Michael
2002-04-01
We study numerically and experimentally the stabilization of stationary excitation pulses in an open flow system. Since all the species have equal flow and diffusion coefficients, stabilization of stationary pulses by long-range inhibition is excluded. Upstream propagating pulses slow down as they approach the inflow boundary, where a constant forcing establishes a downstream extending subexcitable boundary layer. When the flow velocity is low, successive pulses vanish as they reach the subexcitable region. When the flow velocity is increased, the incoming pulses pile up near the inflow one after the other to form a stationary and space-periodic structure. This occurs in such a manner that the system remembers and stores the number of incoming pulses. We show that flow-induced stabilization of stationary pulses involves a mechanism by which the upstream subexcitable region and the flow cause the arrest of the pulse front and the pulse back, respectively. We discuss how the flow-stabilized structures compare to, and are different from those stabilized by a long-ranged, diffusive inhibition and from those observed in boundary-forced open flows of media showing relaxation-type oscillations.
Boundary Slip Effects on the Linear Stability of Circular and Spiral Poiseuille Flow
NASA Astrophysics Data System (ADS)
Cotrell, D.; McFadden, G.
2008-11-01
In this work, we consider the effect of boundary slip on the linear stability of various internal flows having boundary curvature. For the case of annular flow, slip can have a small to moderate affect on the linear stability analysis, with results showing that if the linear stability analysis gives a finite transition for no-slip boundary conditions, then the addition of slip can have either a stabilizing or destabilizing effect on the flow depending on the radius ratio. The results also show that for fixed Knudsen number, there is a value of the radius ratio for which there is no difference between linear stability results with and without slip, and that this value of the radius ratio changes with Reynolds number as does the number of crossings (i.e., one crossing for a Reynolds number of zero and two for a Reynolds number of 100). As for the annular special case (i.e., Taylor-Couette flow with μ>2̂), results show that relaxing the no-slip condition on the cylinder walls does not destabilize this flow (i.e., computations still give a critical value of infinity). Similar to these results, for circular Poiseuille flow (i.e., pipe flow) current results show that relaxing the no-slip boundary condition on the cylinder wall does not destabilize the flow.
On a modification of GLS stabilized FEM for solving incompressible viscous flows
NASA Astrophysics Data System (ADS)
Burda, P.; Novotný, J.; Ístek, J.
2006-07-01
We deal with 2D flows of incompressible viscous fluids with high Reynolds numbers. Galerkin Least Squares technique of stabilization of the finite element method is studied and its modification is described. We present a number of numerical results obtained by the developed method, showing its contribution to solving flows with high Reynolds numbers. Several recommendations and remarks are included. We are interested in positive as well as negative aspects of stabilization, which cannot be divorced.
On exponential stability of gravity driven viscoelastic flows
NASA Astrophysics Data System (ADS)
Jiang, Fei; Wu, Guochun; Zhong, Xin
2016-05-01
We investigate stability of an equilibrium state to a nonhomogeneous incompressible viscoelastic fluid driven by gravity in a bounded domain Ω ⊂R3 of class C3. First, we establish a critical number κC, which depends on the equilibrium density and the gravitational constant, and is a threshold of the elasticity coefficient κ for instability and stability of the linearized perturbation problem around the equilibrium state. Then we prove that the equilibrium state is exponential stability provided that κ >κC and the initial disturbance quantities around the equilibrium state satisfy some relations. In particular, if the equilibrium density ρ bar is a Rayleigh-Taylor (RT) type and ρbar‧ is a constant, our result strictly shows that the sufficiently large elasticity coefficient can prevent the RT instability from occurrence.
Vibrations and stability of a periodically supported rectangular plate immersed in axial flow
NASA Astrophysics Data System (ADS)
Tubaldi, E.; Amabili, M.
2013-05-01
Vibrations and stability of a thin rectangular plate, infinitely long and wide, periodically supported in both directions (so that it is composed by an infinite number of supported rectangular plates with slope continuity at the edges) and immersed in axial liquid flow on its upper side is studied theoretically. The flow is bounded by a rigid wall and the model is based on potential flow theory. The Galerkin method is applied to determine the expression of the flow perturbation potential. Then the Rayleigh-Ritz method is used to discretize the system. The stability of the coupled system is analyzed by solving the eigenvalue problem as a function of the flow velocity; divergence instability is detected. The convergence analysis is presented to determine the accuracy of the computed eigenfrequencies and stability limits. Finally, the effects of the plate aspect ratio and of the channel height ratio on the critical velocity giving divergence instability and vibration frequencies are investigated.
Boundary-Layer Stability Analysis of the Mean Flows Obtained Using Unstructured Grids
NASA Technical Reports Server (NTRS)
Liao, Wei; Malik, Mujeeb R.; Lee-Rausch, Elizabeth M.; Li, Fei; Nielsen, Eric J.; Buning, Pieter G.; Chang, Chau-Lyan; Choudhari, Meelan M.
2012-01-01
Boundary-layer stability analyses of mean flows extracted from unstructured-grid Navier- Stokes solutions have been performed. A procedure has been developed to extract mean flow profiles from the FUN3D unstructured-grid solutions. Extensive code-to-code validations have been performed by comparing the extracted mean ows as well as the corresponding stability characteristics to the predictions based on structured-grid solutions. Comparisons are made on a range of problems from a simple at plate to a full aircraft configuration-a modified Gulfstream-III with a natural laminar flow glove. The future aim of the project is to extend the adjoint-based design capability in FUN3D to include natural laminar flow and laminar flow control by integrating it with boundary-layer stability analysis codes, such as LASTRAC.
Acoustic Streaming in Microgravity: Flow Stability and Heat Transfer Enhancement
NASA Technical Reports Server (NTRS)
Trinh, E. H.
1999-01-01
Experimental results are presented for drops and bubbles levitated in a liquid host, with particular attention given to the effect of shape oscillations and capillary waves on the local flow fields. Some preliminary results are also presented on the use of streaming flows for the control of evaporation rate and rotation of electrostatically levitated droplets in 1 g. The results demonstrate the potential for the technological application of acoustic methods to active control of forced convection in microgravity.
Linear stability of general magnetically insulated electron flow
NASA Astrophysics Data System (ADS)
Swegle, J. A.; Mendel, C. W., Jr.; Seidel, D. B.; Quintenz, J. P.
1984-03-01
A linear stability theory for magnetically insulated systems was formulated by linearizing the general 3-D, time dependent theory of Mendel, Seidel, and Slut. It is found that, case of electron trajectories which are nearly laminar, with only small transverse motion, several suggestive simplifications occur in the eigenvalue equations.
Linear stability of general magnetically insulated electron flow
Swegle, J.A.; Mendel, C.W. Jr.; Seidel, D.B.; Quintenz, J.P.
1984-01-01
We have formulated a linear stability theory for magnetically insulated systems by linearizing the general 3-D, time-dependent theory of Mendel, Seidel, and Slutz. In the physically interesting case of electron trajectories which are nearly laminar, with only small transverse motion, we have found that several suggestive simplifications occur in the eigenvalue equations.
The Influence of Plant Root Systems on Subsurface Flow: Implications for Slope Stability
Although research has explained how plant roots mechanically stabilize soils, in this article we explore how root systems create networks of preferential flow and thus influence water pressures in soils to trigger landslides. Root systems may alter subsurface flow: Hydrological m...
The Hydrodynamic Stability of a Fluid-Particle Flow: Instabilities in Gas-Fluidized Beds
ERIC Educational Resources Information Center
Liu, Xue; Howley, Maureen A.; Johri, Jayati; Glasser, Benjamin J.
2008-01-01
A simplified model of an industrially relevant fluid-particle flow system is analyzed using linear stability theory. Instabilities of the uniform state of a fluidized bed are investigated in response to small flow perturbations. Students are expected to perform each step of the computational analysis, and physical insight into key mechanistic…
Kamchatnov, A. M.; Pitaevskii, L. P.
2008-04-25
The stability of dark solitons generated by supersonic flow of a Bose-Einstein condensate past an obstacle is investigated. It is shown that in the reference frame attached to the obstacle a transition occurs at some critical value of the flow velocity from absolute instability of dark solitons to their convective instability. This leads to the decay of disturbances of solitons at a fixed distance from the obstacle and the formation of effectively stable dark solitons. This phenomenon explains the surprising stability of the flow picture that has been observed in numerical simulations.
The stability of steady magnetohydrodynamic flows with current-vortex sheets
NASA Astrophysics Data System (ADS)
Ilin, K. I.; Trakhinin, Y. L.; Vladimirov, V. A.
2003-07-01
The stability of steady magnetohydrodynamic flows of an inviscid incompressible fluid with current-vortex sheets to small three-dimensional perturbations is studied. The energy method of Frieman and Rotenberg is extended to the case of steady flows with surfaces of tangential discontinuities across which the tangent velocity or the tangent magnetic field or both of them have jump discontinuities. Sufficient conditions for linear stability of some classes of steady flows with parallel velocity and magnetic field are obtained. Also, a sufficient condition for instability of a tubular current-vortex sheet is given.
Stability phenomena far beyond the Nusselt flow - Revealed by experimental asymptotics
NASA Astrophysics Data System (ADS)
Schörner, Mario; Reck, Daniel; Aksel, Nuri
2016-02-01
The present article contributes detailed experimental results on the linear stability of gravity-driven viscous films flowing down periodically corrugated inclines. We asymptotically left the well-known Nusselt flow by gradually increasing the topography's amplitude. Systematic variations of the channel's inclination and the fluid's viscosity followed. That way, we revealed non-trivial stability charts and phenomena far beyond the limits of the Nusselt regime. For the sake of understanding these phenomena, we thoroughly measured the steady-state free surfaces and velocity fields of the respective flows. This comprehensive approach provided us with the exceptional opportunity to unveil that the complex shape, which stability charts of film flows over strongly corrugated inclines exhibit, can be attributed to the simultaneous presence of stabilizing as well as destabilizing effects provoked by the topography. We proved that the stabilization of the flow due to an increased film thickness and the destabilization of the flow due to resonant standing waves are competing effects. Which one dominates in this competition depends on the amplitude and inclination of the substrate and on the viscosity of the fluid.
Stability Analysis of Non-Newtonian Rotational Flow with Hydromagnetic Effect
NASA Astrophysics Data System (ADS)
Ashrafi, Nariman
2014-11-01
Stability of the magnetorheological rotational flow in the presence of a magnetic excitation in the tangential direction is examined. The conservation of mass and momentum equations for an isothermal Carreau fluid between coaxial cylinders are numerically solved while mixed boundary conditions are assumed. In the absence of magnetic excitation, the base flow loses its radial flow stability to the vortex structure at a critical Taylor number. The emergence of the vortices corresponds to the onset of a supercritical bifurcation. The Taylor vortices, in turn, lose their stability as the Taylor number reaches a second critical number corresponding to the onset of a Hopf bifurcation. The tangential magnetic field turns out to be a controlling parameter as it alters the critical points throughout the bifurcation diagram. Also, the effect of the Hartmann number, the Deborah number and the fluid elasticity on the flow parameters were investigated.
Brown, Lynette; Green, Cherie L; Jones, Nicholas; Stewart, Jennifer J; Fraser, Stephanie; Howell, Kathy; Xu, Yuanxin; Hill, Carla G; Wiwi, Christopher A; White, Wendy I; O'Brien, Peter J; Litwin, Virginia
2015-03-01
The objective of this manuscript is to present an approach for evaluating specimen stability for flow cytometric methods used during drug development. While this approach specifically addresses stability assessment for assays to be used in clinical trials with centralized testing facilities, the concepts can be applied to any stability assessment for flow cytometric methods. The proposed approach is implemented during assay development and optimization, and includes suggestions for designing a stability assessment plan, data evaluation and acceptance criteria. Given that no single solution will be applicable in all scenarios, this manuscript offers the reader a roadmap for stability assessment and is intended to guide the investigator during both the method development phase and in the experimental design of the validation plan. PMID:25662815
Analyzing stability of compressible, swirling pipe flows using disturbance energy mechanisms
NASA Astrophysics Data System (ADS)
Samanta, Arnab
2015-11-01
We investigate the spatial stability of compressible, viscous pipe flows with radius-dependent mean density profiles, subjected to solid body rotations. Holding the flow Reynolds number fixed, as the Rossby number is lowered (increased swirl), flow usually transitions from being stable to convectively unstable, finally leading to absolute instability. In this work, the role of compressibility on flow stability is characterized via specifying stratified mean densities where for certain choices the flow appears to be unconditionally stable while for others the situation is more complex with an initially convectively unstable state becoming stable as rotational speeds are progressively raised. A disturbance energy-based method is used to obtain physical understanding of the instability mechanisms in such flows with special emphasis on the role of compressibility. We observe that mechanisms due to pressure energy redistribution and entropy perturbations dominate as primary instability mechanisms instead of the energy due to shear in axial velocity, the primary source of instability in incompressible flows. With reference to pipe flows, we quantify the complex interplay between the various energy mechanisms to provide physical insight into the stability of compressible swirling flows.
Stability results for multi-layer radial Hele-Shaw and porous media flows
NASA Astrophysics Data System (ADS)
Gin, Craig; Daripa, Prabir
2015-01-01
Motivated by stability problems arising in the context of chemical enhanced oil recovery, we perform linear stability analysis of Hele-Shaw and porous media flows in radial geometry involving an arbitrary number of immiscible fluids. Key stability results obtained and their relevance to the stabilization of fingering instability are discussed. Some of the key results, among many others, are (i) absolute upper bounds on the growth rate in terms of the problem data; (ii) validation of these upper bound results against exact computation for the case of three-layer flows; (iii) stability enhancing injection policies; (iv) asymptotic limits that reduce these radial flow results to similar results for rectilinear flows; and (v) the stabilizing effect of curvature of the interfaces. Multi-layer radial flows have been found to have the following additional distinguishing features in comparison to rectilinear flows: (i) very long waves, some of which can be physically meaningful, are stable; and (ii) eigenvalues can be complex for some waves depending on the problem data, implying that the dispersion curves for one or more waves can contact each other. Similar to the rectilinear case, these results can be useful in providing insight into the interfacial instability transfer mechanism as the problem data are varied. Moreover, these can be useful in devising smart injection policies as well as controlling the complexity of the long-term dynamics when drops of various immiscible fluids intersperse among each other. As an application of the upper bound results, we provide stabilization criteria and design an almost stable multi-layer system by adding many layers of fluid with small positive jumps in viscosity in the direction of the basic flow.
Albatsh, Fadi M; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M A
2015-01-01
This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches.
Albatsh, Fadi M; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M A
2015-01-01
This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches. PMID:25874560
Albatsh, Fadi M.; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M. A.
2015-01-01
This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches. PMID:25874560
Stability of a non-orthogonal stagnation flow to three dimensional disturbances
NASA Technical Reports Server (NTRS)
Lasseigne, D. G.; Jackson, T. L.
1991-01-01
A similarity solution for a low Mach number nonorthogonal flow impinging on a hot or cold plate is presented. For the constant density case, it is known that the stagnation point shifts in the direction of the incoming flow and that this shift increases as the angle of attack decreases. When the effects of density variations are included, a critical plate temperature exists; above this temperature the stagnation point shifts away from the incoming stream as the angle is decreased. This flow field is believed to have application to the reattachment zone of certain separated flows or to a lifting body at a high angle of attack. Finally, the stability of this nonorthogonal flow to self similar, 3-D disturbances is examined. Stability properties of the flow are given as a function of the parameters of this study; ratio of the plate temperature to that of the outer potential flow and angle of attack. In particular, it is shown that the angle of attack can be scaled out by a suitable definition of an equivalent wavenumber and temporal growth rate, and the stability problem for the nonorthogonal case is identical to the stability problem for the orthogonal case.
NASA Astrophysics Data System (ADS)
Zhang, Wen-Ming; Yan, Han; Jiang, Hui-Ming; Hu, Kai-Ming; Peng, Zhi-Ke; Meng, Guang
2016-04-01
In this paper, the dynamics of suspended microchannel resonators which convey internal flows with opposite directions are investigated. The fluid-structure interactions between the laminar fluid flow and oscillating cantilever are analyzed by comprehensively considering the effects of velocity profile, flow viscosity and added flowing particle. A new model is developed to characterize the dynamic behavior of suspended microchannel resonators with the fluid-structure interactions. The stability, frequency shift and energy dissipation of suspended microchannel resonators are analyzed and discussed. The results demonstrate that the frequency shifts induced by the added flowing particle which are obtained from the new model have a good agreement with the experimental data. The steady mean flow can cause the frequency shift and influence the stability of the dynamic system. As the flow velocity reaches the critical value, the coupled-mode flutter occurs via a Hamiltonian Hopf bifurcation. The perturbation flow resulted from the vibration of the microcantilever leads to energy dissipation, while the steady flow does not directly cause the damping which increases with the increasing of the flow velocity predicted by the classical model. It can also be found that the steady flow firstly changes the mode shape of the cantilever and consequently affects the energy dissipation.
Traffic behavior of mixed traffic flow with two kinds of different self-stabilizing control vehicles
NASA Astrophysics Data System (ADS)
Li, Zhipeng; Li, Wenzhong; Xu, Shangzhi; Qian, Yeqing; Sun, Jian
2015-10-01
In this paper, we propose a heterogeneous car following model in terms of an extension to the original optimal velocity model characterizing two classes of different self-stabilizing control vehicles. Linear stability analysis method is utilized to the extended model, for purpose to explore how the varying percentages of the vehicles with short-duration self-stabilizing control influence the stability of the heterogeneous traffic flow. We obtain the neutral stability lines for different percentages of two classes of vehicles, with finding that the traffic flow trends to stable with the decrease of the percentage for short-duration self-stabilizing control vehicles. Moreover, we explore a special case that the same numbers of two different classes of vehicles with self-stabilizing control. We theoretically derive the stability condition of the special case, and conclude the effect of the average value and the standard deviation of two time gaps, on the heterogeneous traffic stability. At last, direct simulations are conducted to verify the conclusion of theoretical analysis.
NASA Astrophysics Data System (ADS)
Müller, T.; Hoffmann, T.
2012-04-01
Debris flows play a crucial role in the coupling of hillslope-sediment sources and channels in mountain environments. In most landscape evolution models (LEMs), the sediment transport by debris flows is (if at all) often represented by simple empirical rules. This generally results from the mismatch of the coarse resolution of the LEMs and the small scale impacts of debris flow processes. To extend the accuracy and predictive power of LEMs, either a higher resolution of LEMs in combination with process-based debris flow models or a better parametrisation of subpixel scale debris flow processes is necessary. Furthermore, the simulation of sediment transport by debris flows is complicated by their episodic nature and unknown factors controlling the frequency and magnitude of events. Here, we present first results using a slope stability model (SINMAP) and an event-based debris flow routing model (SCIDDICA-S4c) to simulate the effects of debris flows in LEMs. The model was implemented in the XULU modelling platform developed by the Department of Computer Science at the University of Bonn. The combination of the slope stability model and the event-based routing and mass balance model enables us to simulate the triggering and routing of debris flow material through the iteration of single events over several thousand years. Although a detailed calibration and validation remains to be done, the resulting debris flow-affected areas in a test elevation model correspond well with data gained from a geomorphological mapping of the corresponding area, justifying our approach. The increased computation speed allows to run high resolution LEM in convenient short time at relatively low cost. This should encourage the development of more detailed LEMs, in which process-based models should be incorporated.
On three-dimensional linear stability of Poiseuille flow of Bingham fluids
NASA Astrophysics Data System (ADS)
Frigaard, Ian; Nouar, Cherif
2003-10-01
Plane channel Poiseuille flow of a Bingham fluid is characterized by the Bingham number, B, which describes the ratio of yield and viscous stresses. Unlike purely viscous non-Newtonian fluids, which modify hydrodynamic stability studies only through the dissipation and the basic flow, inclusion of a yield stress additionally results in a modified domain and boundary conditions for the stability problem. We investigate the effects of increasing B on the stability of the flow, using eigenvalue bounds that incorporate these features. As B→∞ we show that three-dimensional linear stability can be achieved for a Reynolds number bound of form Re=O(B3/4), for all wavelengths. For long wavelengths this can be improved to Re=O(B), which compares well with computed linear stability results for two-dimensional disturbances [J. Fluid Mech. 263, 133 (1994)]. It is also possible to find bounds of form Re=O(B1/2), which derive from purely viscous dissipation acting over the reduced domain and are comparable with the nonlinear stability bounds in J. Non-Newt. Fluid Mech. 100, 127 (2001). We also show that a Squire-like result can be derived for the plane channel flow. Namely, if the equivalent eigenvalue bounds for a Newtonian fluid yield a stability criterion, then the same stability criterion is valid for the Bingham fluid flow, but with reduced wavenumbers and Reynolds numbers. An application of these results is to bound the regions of parameter space in which computational methods need to be used.
Crossflow Stability and Transition Experiments in Swept-Wing Flow
NASA Technical Reports Server (NTRS)
Dagenhart, J. Ray; Saric, William S.
1999-01-01
An experimental examination of crossflow instability and transition on a 45deg swept wing was conducted in the Arizona State University Unsteady Wind Tunnel. The stationary-vortex pattern and transition location are visualized by using both sublimating chemical and liquid-crystal coatings. Extensive hot-wire measurements were obtained at several measurement stations across a single vortex track. The mean and travelling wave disturbances were measured simultaneously. Stationary crossflow disturbance profiles were determined by subtracting either a reference or a span-averaged velocity profile from the mean velocity data. Mean, stationary crossflow, and traveling wave velocity data were presented as local boundary layer profiles and contour plots across a single stationary crossflow vortex track. Disturbance mode profiles and growth rates were determined. The experimental data are compared with predictions from linear stability theory.
Stability of unsteady flow in a rotating torus
NASA Astrophysics Data System (ADS)
Hewitt, Richard; Hazel, Andrew; Clarke, Richard; Denier, James
2011-11-01
We consider the temporal evolution of a viscous incompressible fluid in a torus of finite curvature; a problem first investigated experimentally by Madden and Mullin (1994), herein referred to as MM. The system is initially in a state of rigid-body rotation (about the axis of rotational symmetry) and the container's rotation rate is then changed impulsively. We describe the transient flow that is induced at small values of the Ekman number, over a time scale that is comparable to one complete rotation of the container. We show that (rotationally symmetric) eruptive singularities (of the boundary layer) occur at the inner or outer bend of the pipe for a decrease or an increase in rotation rate respectively. Moreover, there is a ratio of initial-to-final rotation frequencies for which eruptive singularities can occur at both the inner and outer bend simultaneously. We also demonstrate that the flow is susceptible to non-axisymmetric inflectional instabilities. The inflectional instability arises as a consequence of the developing eruption and is shown to be in qualitative agreement with the experimental observations of MM. Detailed quantitative comparisons are made between asymptotic predictions and finite (but small) Ekman number Navier-Stokes computations using a finite-element method.
Stability of a jet in confined pressure-driven biphasic flows at low reynolds numbers.
Guillot, Pierre; Colin, Annie; Utada, Andrew S; Ajdari, Armand
2007-09-01
Motivated by its importance for microfluidic applications, we study the stability of jets formed by pressure-driven concentric biphasic flows in cylindrical capillaries. The specificity of this variant of the classical Rayleigh-Plateau instability is the role of the geometry which imposes confinement and Poiseuille flow profiles. We experimentally evidence a transition between situations where the flow takes the form of a jet and regimes where drops are produced. We describe this as the transition from convective to absolute instability, within a simple linear analysis using lubrication theory for flows at low Reynolds number, and reach remarkable agreement with the data.
Stability of a Soft Plate in Channel Flow
NASA Astrophysics Data System (ADS)
Tanida, Yoshimichi
The present paper gives a computational method for the flutter analysis of a soft plate placed in two-dimensional subsonic channel flow, remarking the palatal flutter in snoring. The computations were carried out first for the prelimanary case of a hard plate oscillating in windtunnel and then for the case of a soft plate oscillating with standing- or travelling-wave mode, simulating the palatal oscillation. The results obtained for a hard plate are in good agreement with those for the windtunnel wall effects, showing the validity of the present method. The results for a soft plate show that the palatal flutter can be caused by the oscillation of travelling-wave mode, and that the flutter is slightly promoted by the channel walls but slightly suppressed by the hard plate attached fore the soft plate. The effect of mechanical damping is also discussed.
TF34 engine compression system computer study. [simulation of flow stability
NASA Technical Reports Server (NTRS)
Hosny, W. M.; Steenken, W. G.
1979-01-01
The stability of the fan and the compressor components was examined individually using linearized and time dependent, one dimensional stability analysis techniques. The stability of the fan core integrated compression system was investigated using a two dimensional compression system model. The analytical equations on which this model was based satisfied the mass, axial momentum, radial momentum, and energy conservation equations for flow through a finite control volume. The results gave an accurate simulation of the flow through the compression system. The speed lines of the components were reproduced; the points of instability were accurately predicted; the locations where the instability was initiated in the fan and the core were indicated; and the variation of the bypass ratio during flow throttling was calculated. The validity of the analytical techniques was then established by comparing these results with test data and with results obtained from the steady state cycle deck.
NASA Astrophysics Data System (ADS)
Wang, Chao; Ji, Ming; Zhang, Ying; Jiang, Wentao; Lu, Xiaoyan; Wang, Jiaoying; Yang, Heng
2016-01-01
The electronic image stabilization technology based on improved optical-flow motion vector estimation technique can effectively improve the non normal shift, such as jitter, rotation and so on. Firstly, the ORB features are extracted from the image, a set of regions are built on these features; Secondly, the optical-flow vector is computed in the feature regions, in order to reduce the computational complexity, the multi resolution strategy of Pyramid is used to calculate the motion vector of the frame; Finally, qualitative and quantitative analysis of the effect of the algorithm is carried out. The results show that the proposed algorithm has better stability compared with image stabilization based on the traditional optical-flow motion vector estimation method.
A steady-state solver and stability calculator for nonlinear internal wave flows
NASA Astrophysics Data System (ADS)
Viner, Kevin C.; Epifanio, Craig C.; Doyle, James D.
2013-10-01
A steady solver and stability calculator is presented for the problem of nonlinear internal gravity waves forced by topography. Steady-state solutions are obtained using Newton's method, as applied to a finite-difference discretization in terrain-following coordinates. The iteration is initialized using a boundary-inflation scheme, in which the nonlinearity of the flow is gradually increased over the first few Newton steps. The resulting method is shown to be robust over the full range of nonhydrostatic and rotating parameter space. Examples are given for both nonhydrostatic and rotating flows, as well as flows with realistic upstream shear and static stability profiles. With a modest extension, the solver also allows for a linear stability analysis of the steady-state wave fields. Unstable modes are computed using a shifted-inverse method, combined with a parameter-space search over a set of realistic target values. An example is given showing resonant instability in a nonhydrostatic mountain wave.
Effects of additives on the stability of electrolytes for all-vanadium redox flow batteries
Zhang, Jianlu; Li, Liyu; Nie, Zimin; Chen, Baowei; Vijayakumar, M.; Kim, Soowhan; Wang, Wei; Schwenzer, Birgit; Liu, Jun; Yang, Zhenguo
2011-10-01
The stability of the electrolytes for all-vanadium redox flow battery was investigated with ex-situ heating/cooling treatment and in-situ flow-battery testing methods. The effects of inorganic and organic additives have been studied. The additives containing the ions of potassium, phosphate, and polyphosphate are not suitable stabilizing agents because of their reactions with V(V) ions, forming precipitates of KVSO6 or VOPO4. Of the chemicals studied, polyacrylic acid and its mixture with CH3SO3H are the most promising stabilizing candidates which can stabilize all the four vanadium ions (V2+, V3+, VO2+, and VO2+) in electrolyte solutions up to 1.8 M. However, further effort is needed to obtain a stable electrolyte solution with >1.8 M V5+ at temperatures higher than 40 °C.
An energy analysis of the stability of flexible filaments in coaxial flow
NASA Astrophysics Data System (ADS)
Iadikin, Iu. V.
1982-12-01
An energy-balance equation is obtained for flexible filaments of constant and variable lengths oscillating in coaxial flow. It is found that for any boundary conditions, the stability of a filament increases with internal and external damping, and decreases with hydrodynamic drag. It is also shown that tensile and gyroscopic forces applied to the free end of a filament increase the filament stability, whereas the centrifugal force of the associated liquid mass has the opposite effect.
The onset of absolute instability of rotating Hagen-Poiseuille flow: A spatial stability analysis
NASA Astrophysics Data System (ADS)
Fernandez-Feria, R.; del Pino, C.
2002-09-01
A spatial, viscous stability analysis of Poiseuille pipe flow with superimposed solid body rotation is considered. For each value of the swirl parameter (inverse Rossby number) L>0, there exists a critical Reynolds number Rec)(L above which the flow first becomes convectively unstable to nonaxisymmetric disturbances with azimuthal wave number n=-1. This neutral stability curve confirms previous temporal stability analyses. From this spatial stability analysis, we propose here a relatively simple procedure to look for the onset of absolute instability that satisfies the so-called Briggs-Bers criterion. We find that, for perturbations with n=-1, the flow first becomes absolutely unstable above another critical Reynolds number Ret)(L>Rec)(L, provided that L>0.38, with Ret[right arrow]Rec as L[right arrow]infinity. Other values of the azimuthal wave number n are also considered. For Re>Ret)(L, the disturbances grow both upstream and downstream of the source, and the spatial stability analysis becomes inappropriate. However, for Ret, the spatial analysis provides a useful description on how convectively unstable perturbations become absolutely unstable in this kind of flow.
The onset of absolute instability of rotating Hagen-Poiseuille flow: A spatial stability analysis
NASA Astrophysics Data System (ADS)
Fernandez-Feria, R.; del Pino, C.
2002-09-01
A spatial, viscous stability analysis of Poiseuille pipe flow with superimposed solid body rotation is considered. For each value of the swirl parameter (inverse Rossby number) L>0, there exists a critical Reynolds number Rec(L) above which the flow first becomes convectively unstable to nonaxisymmetric disturbances with azimuthal wave number n=-1. This neutral stability curve confirms previous temporal stability analyses. From this spatial stability analysis, we propose here a relatively simple procedure to look for the onset of absolute instability that satisfies the so-called Briggs-Bers criterion. We find that, for perturbations with n=-1, the flow first becomes absolutely unstable above another critical Reynolds number Ret(L)>Rec(L), provided that L>0.38, with Ret→Rec as L→∞. Other values of the azimuthal wave number n are also considered. For Re>Ret(L), the disturbances grow both upstream and downstream of the source, and the spatial stability analysis becomes inappropriate. However, for Re
Two-phase flow stability structure in a natural circulation system
Zhou, Zhiwei
1995-09-01
The present study reports a numerical analysis of two-phase flow stability structures in a natural circulation system with two parallel, heated channels. The numerical model is derived, based on the Galerkin moving nodal method. This analysis is related to some design options applicable to integral heating reactors with a slightly-boiling operation mode, and is also of general interest to similar facilities. The options include: (1) Symmetric heating and throttling; (2) Asymmetric heating and symmetric throttling; (3) Asymmetric heating and throttling. The oscillation modes for these variants are discussed. Comparisons with the data from the INET two-phase flow stability experiment have qualitatively validated the present analysis.
Thermonuclear dynamo inside ultracentrifuge with supersonic plasma flow stabilization
NASA Astrophysics Data System (ADS)
Winterberg, F.
2016-01-01
Einstein's general theory of relativity implies the existence of virtual negative masses in the rotational reference frame of an ultracentrifuge with the negative mass density of the same order of magnitude as the positive mass density of a neutron star. In an ultracentrifuge, the repulsive gravitational field of this negative mass can simulate the attractive positive mass of a mini-neutron star, and for this reason can radially confine a dense thermonuclear plasma placed inside the centrifuge, very much as the positive mass of a star confines its plasma by its own attractive gravitational field. If the centrifuge is placed in an externally magnetic field to act as the seed field of a magnetohydrodynamic generator, the configuration resembles a magnetar driven by the release of energy through nuclear fusion, accelerating the plasma to supersonic velocities, with the magnetic field produced by the thermomagnetic Nernst effect insulating the hot plasma from the cold wall of the centrifuge. Because of the supersonic flow and the high plasma density the configuration is stable.
Stability of the boundary layer flow on a long thin rotating cylinder
NASA Astrophysics Data System (ADS)
Herrada, M. A.; Del Pino, C.; Fernandez-Feria, R.
2008-03-01
The development and stability of the boundary layer flow over a long thin cylinder aligned with the main flow and which rotates around its axis is considered. Numerical results show that the introduction of rotation has an important effect on the behavior of the basic flow. When the swirl increases, the shear stress at the wall also increases due to the changes in the pressure distribution along the cylinder surface. A nonparallel linear stability analysis of the basic flow is performed using parabolized stability equations. Even at moderately low rotation, we find the existence of unstable centrifugal modes, in addition to the shear ones found in previous stability analysis of the boundary layer flow on a cylinder with no rotation. These centrifugal instabilities develop at Reynolds numbers, based on the cylinder radius and external axial velocity, much smaller than those required for the growing of the shear instabilities. Our analysis shows that nonparallel effects play a key role in the onset and development of these instabilities, being the spiral mode with azimuthal wavenumber n =1, the first to become unstable as the Reynolds number is increased in most cases of interest. We characterize the critical Reynolds number for convective instability as a function of the axial distance to the leading edge for several values of the swirl parameter.
Discharge stabilization studies of CO laser gas mixtures in quasi-steady supersonic flow
NASA Technical Reports Server (NTRS)
Srinivasan, G.; Smith, J. A.
1976-01-01
Experiments were conducted to study the applicability of a double discharge stabilization scheme in conditions appropriate for high energy CO lasers in supersonic flows. A Ludwieg tube impulse flow facility and a ballasted capacitor bank provided essentially steady flow and discharge conditions (d.c.) for times longer than ten electrode length-flow transit times. Steady, arc-free, volume discharges were produced in a Mach 3 test cavity using an auxiliary discharge to stabilize the main discharge in N2 and He/CO mixture. A signigicant result is the lack of observed plasma E/N changes in response to auxiliary discharge current changes. Also, where glow discharges were obtained, the energy loading achieved was very much less than the threshold level required for laser operation.
Gao, H.W.; French, T.R.
1988-04-01
To identify the optimal rheological characteristics for maintaining the dynamic stability of polymer solutions flowing through porous media, displacement tests with a Newtonian fluid and a non-Newtonian fluid were performed in a 4-ft Berea sandstone core. A solution of 63 wt pct gylcerin in 53 meg/1 NaCL and a solution of 1500 ppM Pusher 500 in 53 meq/1 NaCl were used as the Newtonian fluid and non-Newtonian fluid, respectively. Two flow rates one in the purely viscous regime and one in the viscoelastic flow regime of Pusher 500 in Berea sandstone, were used in the displacement tests. The effluents collected were analyzed to determine polymer and tracer concentrations. The viscosities of the effluents were also measured with a Contraves viscometer. By comparing the concentration profiles obtained in tests with Pusher 500 and in those with gylcerin, the effects of flow rate, mobility ratio, and rheological characteristics on the dynamic stability of polymer flow in porous media were determined. At both leading and trailing edges of the polymer slug, stability increases with decreasing mobility ratio. At both high and low flow rates, a Newtonian fluid gives a more stable displacement at the fluid front than does a non-Newtonian fluid. Measurements on the mixing lengths at the back edge show that the size of the mobility buffer bank required for a flow rate at reservior conditions (viscous flow regime) would be less for a Newtonian fluid than for a non-Newtonian fluid. At a flow rate in the viscoelastic flow regime, the required size of the mobility buffer bank is less for a non-Newtonian fluid than for a Newtonian fluid. 39 refs., 13 figs., 1 tab.
Study on interfacial stability and internal flow of a droplet levitated by ultrasonic wave.
Abe, Yutaka; Yamamoto, Yuji; Hyuga, Daisuke; Awazu, Shigeru; Aoki, Kazuyoshi
2009-04-01
For a microgravity environment, new and high-quality material is expected to be manufactured. However, the effect of surface instability and the internal flow become significant when the droplet becomes large. Elucidation of internal flow and surface instability on a levitated droplet is required for the quality improvement of new material manufacturing in a microgravity environment. The objectives of this study are to clarify the interfacial stability and internal flow of a levitated droplet. Surface instability and internal flow are investigated with a large droplet levitated by the ultrasonic acoustic standing wave. The experiment with a large droplet is conducted both under normal gravity and microgravity environments. In the experiment, at first, the characteristics of the levitated droplet are investigated; that is, the relationships among the levitated droplet diameter, the droplet aspect ratio, the displacement of the antinode of the standing wave, and the sound pressure are experimentally measured. As a result, it is clarified that the levitated droplet tends to be located at an optimal position with an optimal shape and diameter. Second, the border condition between the stable and the unstable levitation of the droplet is evaluated by using the existing stability theory. The experimental results qualitatively agree with the theory. It is suggested that the stability of the droplet can be evaluated with the stability theory. Finally, multidimensional visual measurement is conducted to investigate the internal flow structure in a levitated droplet. It is suggested that complex flow with the vortex is generated in the levitated droplet. Moreover, the effect of physical properties of the test fluid on the internal flow structure of the levitated droplet is investigated. As a result, the internal flow structure of the levitated droplet is affected by the surface tension and viscosity. PMID:19426319
Marietti, Y; Debierre, J M; Bock, T M; Kassner, K
2001-06-01
An asymptotic interface equation for directional solidification near the absolute stability limit is extended by a nonlocal term describing a shear flow parallel to the interface. In the long-wave limit considered, the flow acts destabilizing on a planar interface. Moreover, linear stability analysis suggests that the morphology diagram is modified by the flow near onset of the Mullins-Sekerka instability. Via numerical analysis, the bifurcation structure of the system is shown to change. Besides the known hexagonal cells, structures consisting of stripes arise. Due to its symmetry-breaking properties, the flow term induces a lateral drift of the whole pattern, once the instability has become active. The drift velocity is measured numerically and described analytically in the framework of a linear analysis. At large flow strength, the linear description breaks down, which is accompanied by a transition to flow-dominated morphologies which is described in the following paper. Small and intermediate flows lead to increased order in the lattice structure of the pattern, facilitating the elimination of defects. Locally oscillating structures appear closer to the instability threshold with flow than without.
NASA Astrophysics Data System (ADS)
Giribabu, D.; Shankar, V.
2016-07-01
The linear stability of plane Couette flow past a deformable solid is analyzed in the creeping-flow limit with an objective towards elucidating the consequences of employing two widely different formulations for the dissipative stresses in the deformable solid. One of the formulations postulates that the dissipative stress is proportional to the strain-rate tensor based on the left Cauchy-Green tensor, while in the other the dissipative stress in the solid is proportional to the rate-of-deformation tensor. However, it is well known in continuum mechanics that the rate-of-deformation tensor obeys the fundamental principle of material-frame indifference while the strain-rate-tensor formulation does not and hence it is more appropriate to employ the rate-of-deformation tensor in the description of dissipative stresses in deformable solids. In this work we consider the specific context of stability of plane Couette flow past a deformable solid and demonstrate that the results concerning the stability of the system from both models differ drastically. In the rate-of-deformation formulation for the dissipative stress, there is a range of solid-fluid thickness ratios (between 1.21 and 1.46) wherein the system is always stable for nonzero values of solid viscosity, unlike the strain-rate-tensor formulation wherein the system is unstable at all values of solid thickness. Further, for a solid-fluid thickness ratio less than 1, incorporation of dissipative effects in the solid using the rate-of-deformation formulation shows that the flow is more unstable compared to a purely elastic neo-Hookean solid, while for strain-rate-tensor formulation the flow is stabilized with an increase in viscosity of the solid. Using the fundamentally correct dissipative stress formulation, we also address the stability of pressure-driven flow in a deformable channel, wherein previous work carried out for an elastic neo-Hookean solid has shown that only the short-wave instability (driven by the
Stability of the flow in a soft tube deformed due to an applied pressure gradient.
Verma, M K S; Kumaran, V
2015-04-01
A linear stability analysis is carried out for the flow through a tube with a soft wall in order to resolve the discrepancy of a factor of 10 for the transition Reynolds number between theoretical predictions in a cylindrical tube and the experiments of Verma and Kumaran [J. Fluid Mech. 705, 322 (2012)]. Here the effect of tube deformation (due to the applied pressure difference) on the mean velocity profile and pressure gradient is incorporated in the stability analysis. The tube geometry and dimensions are reconstructed from experimental images, where it is found that there is an expansion and then a contraction of the tube in the streamwise direction. The mean velocity profiles at different downstream locations and the pressure gradient, determined using computational fluid dynamics, are found to be substantially modified by the tube deformation. The velocity profiles are then used in a linear stability analysis, where the growth rates of perturbations are calculated for the flow through a tube with the wall modeled as a neo-Hookean elastic solid. The linear stability analysis is carried out for the mean velocity profiles at different downstream locations using the parallel flow approximation. The analysis indicates that the flow first becomes unstable in the downstream converging section of the tube where the flow profile is more pluglike when compared to the parabolic flow in a cylindrical tube. The flow is stable in the upstream diverging section where the deformation is maximum. The prediction for the transition Reynolds number is in good agreement with experiments, indicating that the downstream tube convergence and the consequent modification in the mean velocity profile and pressure gradient could reduce the transition Reynolds number by an order of magnitude. PMID:25974574
Stability of the flow in a soft tube deformed due to an applied pressure gradient
NASA Astrophysics Data System (ADS)
Verma, M. K. S.; Kumaran, V.
2015-04-01
A linear stability analysis is carried out for the flow through a tube with a soft wall in order to resolve the discrepancy of a factor of 10 for the transition Reynolds number between theoretical predictions in a cylindrical tube and the experiments of Verma and Kumaran [J. Fluid Mech. 705, 322 (2012), 10.1017/jfm.2011.55]. Here the effect of tube deformation (due to the applied pressure difference) on the mean velocity profile and pressure gradient is incorporated in the stability analysis. The tube geometry and dimensions are reconstructed from experimental images, where it is found that there is an expansion and then a contraction of the tube in the streamwise direction. The mean velocity profiles at different downstream locations and the pressure gradient, determined using computational fluid dynamics, are found to be substantially modified by the tube deformation. The velocity profiles are then used in a linear stability analysis, where the growth rates of perturbations are calculated for the flow through a tube with the wall modeled as a neo-Hookean elastic solid. The linear stability analysis is carried out for the mean velocity profiles at different downstream locations using the parallel flow approximation. The analysis indicates that the flow first becomes unstable in the downstream converging section of the tube where the flow profile is more pluglike when compared to the parabolic flow in a cylindrical tube. The flow is stable in the upstream diverging section where the deformation is maximum. The prediction for the transition Reynolds number is in good agreement with experiments, indicating that the downstream tube convergence and the consequent modification in the mean velocity profile and pressure gradient could reduce the transition Reynolds number by an order of magnitude.
NASA Technical Reports Server (NTRS)
Al-Maaitah, Ayman A.; Nayfeh, Ali H.; Ragab, Saad A.
1989-01-01
The effect of suction on the stability of compressible flows over backward-facing steps is investigated. Mach numbers up to 0.8 are considered. The results show that continuous suction stabilizes the flow outside the separation bubble, but it destabilizes the flow inside it. Nevertheless, the overall N factor decreases as the suction level increases due to the considerable reduction of the separation bubble. For the same suction flow rate, properly distributed suction strips stabilize the flow more than continuous suction. The size of the separation bubble, and hence its effect on the instability can be considerably reduced by placing strips with high suction velocities in the separation region.
The stability of dissipative magnetohydrodynamic shear flow in a parallel magnetic field
NASA Technical Reports Server (NTRS)
Lerner, J.; Knobloch, E.
1985-01-01
The linear stability properties of dissipative field-aligned shear flow are described analytically. The results are used to calculate the decay bounds of linearized perturbations occurring in unbounded planes of Couette flow in a parallel magnetic field. It is shown that the perturbations associated with small-amplitude localized disturbances may take the form of rolls along the shear, and exhibit ordinary potential decay, while misaligned perturbations exhibit enhanced decay in the presence of dissipation. A decay criterion is established for MHD shear flow in an accretion disk on the basis of the analytical results.
Stability and dynamical properties of material flow systems on random networks
NASA Astrophysics Data System (ADS)
Anand, K.; Galla, T.
2009-04-01
The theory of complex networks and of disordered systems is used to study the stability and dynamical properties of a simple model of material flow networks defined on random graphs. In particular we address instabilities that are characteristic of flow networks in economic, ecological and biological systems. Based on results from random matrix theory, we work out the phase diagram of such systems defined on extensively connected random graphs, and study in detail how the choice of control policies and the network structure affects stability. We also present results for more complex topologies of the underlying graph, focussing on finitely connected Erdös-Réyni graphs, Small-World Networks and Barabási-Albert scale-free networks. Results indicate that variability of input-output matrix elements, and random structures of the underlying graph tend to make the system less stable, while fast price dynamics or strong responsiveness to stock accumulation promote stability.
The effects of viscosity on the stability of a trailing-line vortex in compressible flow
NASA Technical Reports Server (NTRS)
Stott, Jillian A. K.; Duck, Peter W.
1994-01-01
We consider the effects of viscosity on the inviscid stability of the Batchelor vortex in a compressible flow. The problem is tackled asymptotically, in the limit of large (streamwise and azimuthal) wavenumbers, together with large Mach numbers. Previous studies, with viscous effects neglected, found that the nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumber. This structure persists when viscous effects are included in the analysis. In the present study the mode present in the incompressible case ceases to be unstable at high Mach numbers and a center mode forms, whose stability characteristics are determined primarily by conditions close to the vortex axis. We find generally that viscosity has a stabilizing influence on the flow, while in the case of center modes, viscous effects become important at much larger Reynolds numbers than for the first class of disturbance.
The inviscid stability of supersonic flow past heated or cooled axisymmetric bodies
NASA Technical Reports Server (NTRS)
Shaw, Stephen J.; Duck, Peter W.
1992-01-01
The inviscid, linear, nonaxisymmetric, temporal stability of the boundary layer associated with the supersonic flow past axisymmetric bodies (with particular emphasis on long thin, straight circular cylinders), subject to heated or cooled wall conditions is investigated. The eigenvalue problem is computed in some detail for a particular Mach number or 3.8, revealing that the effect of curvature and the choice of wall conditions both have a significant effect on the stability of the flow. Both the asymptotic, large azimuthal wavenumber solution and the asymptotic, far downstream solution are obtained for the stability analysis and compared with numerical results. Additionally, asymptotic analyses valid for large radii of curvature with cooled/heated wall conditions are presented. In general, important differences were found to exist between the wall temperature conditions imposed and the adiabatic wall conditions considered previously.
The inviscid stability of supersonic flow past heated or cooled axisymmetric bodies
NASA Technical Reports Server (NTRS)
Shaw, Stephen J.; Duck, Peter W.
1990-01-01
The inviscid, linear, nonaxisymmetric, temporal stability of the boundary layer associated with the supersonic flow past axisymmetric bodies (with particular emphasis on long thin, straight circular cylinders), subject to heated or cooled wall conditions is investigated. The eigenvalue problem is computed in some detail for a particular Mach number or 3.8, revealing that the effect of curvature and the choice of wall conditions both have a significant effect on the stability of the flow. Both the asymptotic, large azimuthal wavenumber solution and the asymptotic, far downstream solution are obtained for the stability analysis and compared with numerical results. Additionally, asymptotic analyses valid for large radii of curvature with cooled/heated wall conditions, are presented. In general, important differences were found to exist between the wall temperature conditions imposed and the adiabatic wall conditions considered previously.
Asymptotic theory of neutral stability curve of the Couette flow of vibrationally excited gas
NASA Astrophysics Data System (ADS)
Grigor'ev, Yu N.; Ershov, I. V.
2016-06-01
The asymptotic theory of neutral stability curve of the supersonic plane Couette flow of vibrationally excited gas is constructed. The system of two-temperature viscous gas dynamics equations was used as original mathematical model. Spectral problem for an eighth order linear system of ordinary differential equations was obtained from the system within framework of classical theory of linear stability. Transformations of the spectral problem universal for all shear flows were carried along the classical Dunn — Lin scheme. As a result the problem was reduced to secular algebraic equation with a characteristic division on “inviscid” and “viscous” parts which was solved numerically. The calculated neutral stability curves coincide in limits of 10% with corresponding results of direct numerical solution of original spectral problem.
Stability Analysis of a natural circulation flow loop under supercritical condition
NASA Astrophysics Data System (ADS)
Jain, Rachna
2005-11-01
The stability of natural circulation flow loop geometry is under investigation in a specific thermo-dynamic region that encompasses the supercritical temperatures and pressures. This flow configuration is pertinent to the design of passive safety systems in some innovative reactor designs proposed for future generations of water-cooled nuclear reactors. Earlier studies employing both transient and linear stability approach considered supercritical natural circulation flow loop systems having a semi-closed boundary condition which required only the continuity in the pressure of the system around the loop. This is only true for loops that are connected to a large reservoir which theoretically can absorb any fluctuations in the flow velocity or temperatures and thus keep the inlet conditions fixed. A more realistic approach considered in the present study where a periodic boundary condition is imposed for such systems and requires continuity in the pressure, temperature and velocity as an essential boundary condition. With a highly non-linear equation of state specific to supercritical fluid and periodic boundary condition, the stability of this flow system is mathematically challenging to analyze.
The Effect of a Rotating Magnetic Field on Flow Stability During Crystal Growth
NASA Technical Reports Server (NTRS)
Volz, Martin P.; Mazuruk, K.
2000-01-01
The effect of a rotating magnetic field on the stability of flow in crystal growth configurations has been experimentally modeled using liquid gallium contained in a finite cylinder and heated from below. Several distinct flow regions were determined as a function of the Rayleigh and Hartmann numbers. At low values of the Rayleigh and Hartmann numbers, a region of stationary flow exists. As the rotating magnetic field is increased, the critical Rayleigh number bounding the stationary flow region can increase by a factor of 10. However, the rotating magnetic field itself induces an instability at a critical value of the Hartmann number independent of the Rayleigh number. In the stationary flow region, the rotating magnetic field can induce fluid motion with velocities several orders of magnitude larger than typical semiconductor crystal growth velocities. Thus, a rotating magnetic field can be used to achieve the benefits of forced convection without triggering deleterious instabilities.
The effect of stochastic modulations on the stability characteristics of hydrodynamic flows
NASA Astrophysics Data System (ADS)
Wulbrand, W.
The present study is concerned with the development of a model which can be employed to study the effect of temporal stochastic modulations of the boundary values on the stability of flows. The linearized equations of motion for the development of the disturbance of the basic flow have the form of stochastic differential equations with multiplicative 'external' noise. Equations for the first moment of the perturbation of the basic flow are derived for the formulation of an instability criterion. The Galerkin procedure is used for a calculation of the critical parameters. The considered method can be employed for all problems in which the basic flow can be calculated on the basis of the Navier-Stokes equations. An employment of the method to the Couette-Poiseuille flow is found to lead to equations which have to be evaluated numerically. On the other hand, in the case of convective instability, an approximate result can be obtained by means of an analytical calculation.
NASA Astrophysics Data System (ADS)
Luzzatto-Fegiz, Paolo
2011-11-01
Steady fluid solutions play a special role in the dynamics of a flow: stable states may be realized in practice, while unstable ones may act as attractors. Unfortunately, determining stability is often a process far more laborious than finding steady states; indeed, even for simple vortex or wave flows, stability properties have often been the subject of debate. We consider here a stability idea originating with Lord Kelvin (1876), which involves using the second variation of the energy, δ2 E , to establish bounds on a perturbation. However, for numerically obtained flows, computing δ2 E explicitly is often not feasible. To circumvent this issue, Saffman & Szeto (1980) proposed an argument linking changes in δ2 E to turning points in a bifurcation diagram, for families of steady flows. Later work has shown that this argument is unreliable; the two key issues are associated with the absence of a formal turning-point theory, and with the inability to detect bifurcations (Dritschel 1995, and references therein). In this work, we build on ideas from bifurcation theory, and link turning points in a velocity-impulse diagram to changes in δ2 E ; in addition, this diagram delivers the direction of the change of δ2 E , thereby providing information as to whether stability is gained or lost. To detect hidden solution branches, we introduce to these fluid problems concepts from imperfection theory. The resulting approach, involving ``imperfect velocity-impulse'' diagrams, leads us to new and surprising results for a wide range of fundamental vortex and wave flows; we mention here the calculation of the first steady vortices without any symmetry, and the uncovering of the complete solution structure for vortex pairs. In addition, we find precise agreement with available results from linear stability analysis. Doctoral work advised by C.H.K. Williamson at Cornell University.
Effects of tangential velocity distribution on flow stability in a draft tube
NASA Astrophysics Data System (ADS)
Dou, Huashu; Niu, Lin; Cao, Shuliang
2014-10-01
Numerical simulations of the flow in the draft tube of a Francis turbine are carried out in order to elucidate the effects of tangential velocity on flow stability. Influence of the location of the maximum tangential velocity is explored considering the equality of the total energy at the inlet of the draft tube. It is found that the amplitude of the pressure fluctuation decreases when the location of the maximum of the tangential velocity moves from the centre to the wall on the cross section. Thus, the stability of the flow in the draft tube increases with the moving of the location of the maximum tangential velocity. However, the relative hydraulic loss increases and the recovery coefficient of the draft tube decreases slightly.
The inviscid axisymmetric stability of the supersonic flow along a circular cylinder
NASA Technical Reports Server (NTRS)
Duck, Peter W.
1990-01-01
The supersonic flow past a thin straight circular cylinder is investigated. The associated boundary-layer flow (i.e. the velocity and temperature field) is computed; the asymptotic, far downstream solution is obtained, and compared with the full numerical results. The inviscid, linear, axisymmetric (temporal) stability of this boundary layer is also studied. A so-called 'doubly generalized' inflexion condition is derived, which is a condition for the existence of so-called 'subsonic' neutral modes. The eigenvalue problem (for the complex wavespeed) is computed for two free-stream Mach numbers (2.8 and 3.8), and this reveals that curvature has a profound effect on the stability of the flow. The first unstable inviscid mode is seen to disappear rapidly as curvature is introduced, while the second (and generally the most important) mode suffers a substantially reduced amplification rate.
The inviscid axisymmetric stability of the supersonic flow along a circular cylinder
NASA Technical Reports Server (NTRS)
Duck, Peter W.
1989-01-01
The supersonic flow past a thin straight circular cylinder is investigated. The associated boundary layer flow (i.e., the velocity and temperature field) is computed; the asymptotic, far downstream solution is obtained, and compared with the full numerical results. The inviscid, linear, axisymmetric (temporal) stability of this boundary layer is also studied. A so called doubly generalized inflexion condition is derived, which is a condition for the existence of so called subsonic neutral modes. The eigenvalue problem (for the complex wavespeed) is computed for two freestream Mach numbers (2.8 and 3.8), and this reveals that curvature has a profound effect on the stability of the flow. The first unstable inviscid mode is seen to rapidly disappear as curvature is introduced, while the second (and generally the most important) mode suffers a substantially reduced amplification rate.
Boundary layer stability analysis of a natural laminar flow glove on the F-111 TACT airplane
NASA Technical Reports Server (NTRS)
Runyan, L. J.; Steers, L. L.
1980-01-01
A natural laminar flow airfoil has been developed as a part of the aircraft energy efficiency program. A NASA flight program incorporating this airfoil into partial wing gloves on the F-111 TACT airplane was scheduled to start in May, 1980. In support of this research effort, an extensive boundary layer stability analysis of the partial glove has been conducted. The results of that analysis show the expected effects of wing leading-edge sweep angle, Reynolds number, and compressibility on boundary layer stability and transition. These results indicate that it should be possible to attain on the order of 60% laminar flow on the upper surface and 50% laminar flow on the lower surface for sweep angles of at least 20 deg, chord Reynolds numbers of 25 x 10 to the 6th and Mach numbers from 0.81 to 0.85.
Joh, S.; Evans, G.H.
1996-08-01
The flow and heat transfer in a vertical high-speed rotating disk/stagnation flow chemical vapor deposition (CVD) reactor is studied with particular emphasis on the effects of the spacing, {bar H}, between the stationary gas inlet and the rotating disk. A one-dimensional analysis is used to determine the effects of {bar H}, flow rate, and disk spin rate on the gas flow patterns and the heat transfer from the disk; the effects of buoyancy, reactor side walls, and finite disk geometry on these quantities are determined in a two-dimensional analysis. The Navier-Stokes and energy equations are solved for hydrogen over a range of gas flow rates, disk spin rates, axial and radial aspect ratios, for a pressure of 250 Torr, inlet gas temperature of 50 C, and disk temperature of 800 C. The 1D similarity solution results show that the dimensionless heat transfer from the rotating disk, Nu{sub 1D}, depends on SP and Re{sub w} to a much greater extent at smaller spacings than at larger spacings. For SP values of 0.92 and 4.5 and for both spacings studied, Nu{sub 1D} approaches the value for an infinite rotating disk for Re{sub w} {approx} 450, except for the case at SP = 4.5 and A = 0.54 where Nu{sub 1D} is significantly larger. The 1D results also show that for small SP (0.23) there is a significant flow toward r = 0 (the radial component of velocity is negative) which is larger for the smaller value of A. The 2D results show that the effect of inlet velocity (SP) on the radial variation of the disk heat transfer (Nu{sub 2D}) is greater for larger values of A; for both values of A there is greater radial variation of Nu{sub 2D} at the laser value of SP.
Paungmali, Aatit; Henry, Leonard Joseph; Sitilertpisan, Patraporn; Pirunsan, Ubon; Uthaikhup, Sureeporn
2016-01-01
[Purpose] This study investigated the effects of lumbopelvic stabilization training on tissue blood flow changes in the lumbopelvic region and lumbopelvic stability compared to placebo treatment and controlled intervention among patients with chronic non-specific low back pain. [Subjects and Methods] A total of 25 participants (7 males, 18 females; mean age, 33.3 ± 14.4 years) participated in this within-subject, repeated-measures, double-blind, placebo-controlled comparison trial. The participants randomly underwent three types of interventions that included lumbopelvic stabilization training, placebo treatment, and controlled intervention with 48 hours between sessions. Lumbopelvic stability and tissue blood flow were measured using a pressure biofeedback device and a laser Doppler flow meter before and after the interventions. [Results] The repeated-measures analysis of variance results demonstrated a significant increase in tissue blood flow over the lumbopelvic region tissues for post- versus pre-lumbopelvic stabilization training and compared to placebo and control interventions. A significant increase in lumbopelvic stability before and after lumbopelvic stabilization training was noted, as well as upon comparison to placebo and control interventions. [Conclusion] The current study supports an increase in tissue blood flow in the lumbopelvic region and improved lumbopelvic stability after core training among patients with chronic non-specific low back pain.
Paungmali, Aatit; Henry, Leonard Joseph; Sitilertpisan, Patraporn; Pirunsan, Ubon; Uthaikhup, Sureeporn
2016-01-01
[Purpose] This study investigated the effects of lumbopelvic stabilization training on tissue blood flow changes in the lumbopelvic region and lumbopelvic stability compared to placebo treatment and controlled intervention among patients with chronic non-specific low back pain. [Subjects and Methods] A total of 25 participants (7 males, 18 females; mean age, 33.3 ± 14.4 years) participated in this within-subject, repeated-measures, double-blind, placebo-controlled comparison trial. The participants randomly underwent three types of interventions that included lumbopelvic stabilization training, placebo treatment, and controlled intervention with 48 hours between sessions. Lumbopelvic stability and tissue blood flow were measured using a pressure biofeedback device and a laser Doppler flow meter before and after the interventions. [Results] The repeated-measures analysis of variance results demonstrated a significant increase in tissue blood flow over the lumbopelvic region tissues for post- versus pre-lumbopelvic stabilization training and compared to placebo and control interventions. A significant increase in lumbopelvic stability before and after lumbopelvic stabilization training was noted, as well as upon comparison to placebo and control interventions. [Conclusion] The current study supports an increase in tissue blood flow in the lumbopelvic region and improved lumbopelvic stability after core training among patients with chronic non-specific low back pain. PMID:27064327
Paungmali, Aatit; Henry, Leonard Joseph; Sitilertpisan, Patraporn; Pirunsan, Ubon; Uthaikhup, Sureeporn
2016-01-01
[Purpose] This study investigated the effects of lumbopelvic stabilization training on tissue blood flow changes in the lumbopelvic region and lumbopelvic stability compared to placebo treatment and controlled intervention among patients with chronic non-specific low back pain. [Subjects and Methods] A total of 25 participants (7 males, 18 females; mean age, 33.3 ± 14.4 years) participated in this within-subject, repeated-measures, double-blind, placebo-controlled comparison trial. The participants randomly underwent three types of interventions that included lumbopelvic stabilization training, placebo treatment, and controlled intervention with 48 hours between sessions. Lumbopelvic stability and tissue blood flow were measured using a pressure biofeedback device and a laser Doppler flow meter before and after the interventions. [Results] The repeated-measures analysis of variance results demonstrated a significant increase in tissue blood flow over the lumbopelvic region tissues for post- versus pre-lumbopelvic stabilization training and compared to placebo and control interventions. A significant increase in lumbopelvic stability before and after lumbopelvic stabilization training was noted, as well as upon comparison to placebo and control interventions. [Conclusion] The current study supports an increase in tissue blood flow in the lumbopelvic region and improved lumbopelvic stability after core training among patients with chronic non-specific low back pain. PMID:27064327
Effect of virtual mass on the characteristics and the numerical stability in two-phase flows
No, H.C.; Kazimi, M.S.
1981-04-01
It is known that the typical six equation two-fluid model of the two-phase flow possesses complex characteristics, exhibits unbounded instabilities in the short-wavelength limit and constitutes an ill-posed initial value problem. Among the suggestions to overcome these difficulties, one model for the virtual mass force terms were studied here, because the virtual mass represents real physical effects to accomplish the dissipation for numerical stability. It was found that the virtual mass has a profound effect upon the mathematical characteristic and numerical stability. Here a quantitative bound on the coefficient of the virtual mass terms was suggested for mathematical hyperbolicity and numerical stability. It was concluded that the finite difference scheme with the virtual mass model is restricted only by the convective stability conditions with the above suggested value.
Stability analysis for capillary channel flow: 1d and 3d computations
NASA Astrophysics Data System (ADS)
Grah, Aleksander; Klatte, Jörg; Dreyer, Michael E.
The subject of the presentation are numerical studies on capillary channel flow, based on results of the sounding rocket TEXUS experiments. The flow through a capillary channel is established by a gear pump at the outlet. The channel, consists of two parallel glass plates with a width of 25 mm, a gap of 10 mm and a length of 12 mm. The meniscus of a compensation tube maintains a constant system pressure. Steady and dynamic pressure effects in the system force the surfaces to bend inwards. A maximum flow rate is achieved when the free surface collapses and gas ingestion occurs at the outlet. This critical flow rate depends on the channel geometry, the flow regime and the liquid properties. The aim of the experiments is the determination of the free surface shape and to find the maximum flow rate. In order to study the unsteady liquid loop behavior, a dimensionless one-dimensional model and a corresponding three-dimensional model were developed. The one-dimensional model is based on the unsteady Bernoulli equation, the unsteady continuity equation and geometrical conditions for the surface curvature and the flow cross-section. The experimental and evaluated contour data show good agreement for a sequence of transient flow rate perturbations. In the case of steady flow at maximum flow rate, when the "choking" effect occurs, the surfaces collapse and cause gas ingestion into the channel. This effect is related to the Speed Index. At the critical flow rate the Speed Index reaches the value 1, in analogy to the Mach Number. Unsteady choking does not necessarily cause surface collapse. We show, that temporarily Speed Index values exceeding One may be achieved for a perfectly stable supercritical dynamic flow. As a supercritical criterion for the dynamic free surface stability we define a Dynamic Index considering the local capillary pressure and the convective pressure, which is a function of the local velocity. The Dynamic Index is below One for stable flow while D = 1
Stable structure in the interrupted z-pinch
Kubes, P.; Kravarik, J.; Hakr, J.; Kulhanek, P.; Pichal, J. . Faculty of Electrical Engineering)
1994-10-01
A low energy (500 J) discharge at relatively high pressure (kPa) between two cone-shaped electrodes has been studied. The discharge geometry enables the formation of two jets with filaments and a compact plasmoid in the center. The existence of the plasmoid was discovered in the experiments. Electron density and temperature were measured by the standard interferometric, schlieren, and spectroscopic methods. A turbulent structure of the jets and plasmoid was proposed for explanation of the measured values and some turbulent parameters were estimated.
Axial and Temporal Gradients in Mo Z Pinches
LePell, P D; Hansen, S B; Shlyaptseva, A S; Coverdale, C; Deeney, C; Apruzese, J P; Fournier, K B; Safronova, U I
2004-07-14
Three nested molybdenum wire arrays with initial outer diameters of 45, 50, and 55 mm were imploded by the {approx} 20 MA, 90 ns rise-time current pulse of Sandia's Z accelerator. The implosions generated Mo plasmas with approximately 10% of the array's initial mass reaching Ne-like and nearby ionization stages. These ions emitted 2 - 4 keV L-shell x-rays with radiative powers approaching 10 TW. Mo L-shell spectra with axial and temporal resolution were captured and have been analyzed using a non-LTE collisional-radiative model. We find significant axial variation in the plasma conditions, with electron densities increasing from the cathode ({approx} 3 x 10{sup 20}cm{sup -3}) to near the anode end of the plasma ({approx} 3 x 10{sup 21}cm{sup -3}) and electron temperatures decreasing slightly from the cathode ({approx} 1.7 keV) to the anode end ({approx} 1.5 keV). Time-resolved spectra indicate that the peak electron density is reached before the peak of the L-shell emission and decreases with time, while the electron temperature remains within 10% of 1.7 keV over the 20 - 30 ns L-shell radiation pulse. Finally, while the total yield, peak total power, and peak L-shell power all tended to decrease with increasing initial wire array diameters, the L-shell yield and the average plasma conditions varied little with the initial wire array diameter. Radiative cooling is likely to play an important role in the wire array plasma development.
Linear stability of spiral and annular Poiseuille flow for small radius ratio
NASA Astrophysics Data System (ADS)
Cotrell, David L.; Pearlstein, Arne J.
For the radius ratio η ≡ R_i/R_o = 0.1 and several rotation rate ratios μ ≡ Ω_o/Ω_i, we consider the linear stability of spiral Poiseuille flow (SPF) up to Re = 10^5, where R_i and R_o are the radii of the inner and outer cylinders, respectively, Re ≡ overline V_Z(R_o -R_i)/ν is the Reynolds number, Ω_i and Ω_o are the (signed) angular speeds of the inner and outer cylinders, respectively, ν is the kinematic viscosity, and overline V_Z is the mean axial velocity. The Re range extends more than three orders of magnitude beyond that considered in the previous μ = 0 work of Recktenwald et al. (Phys. Rev. E, vol. 48, 1993, p. 444). We show that in the non-rotating limit of annular Poiseuille flow, linear instability does not occur below a critical radius ratio hat η ≈ 0.115. We also establish the connection of the linear stability of annular Poiseuille flow for 0 < η ≤ hat η at all Re to the linear stability of circular Poiseuille flow (η = 0) at all Re. For the rotating case, with μ = -1, - 0.5, - 0.25, 0 and 0.2, the stability boundaries, presented in terms of critical Taylor number Ta ≡ Ω_i(R_o -R_i)^2/ν versus Re, show that the results are qualitatively different from those at larger η. For each μ, the centrifugal instability at small Re does not connect to a high-Re Tollmien Schlichting-like instability of annular Poiseuille flow, since the latter instability does not exist for η < hatη. We find a range of Re for which disconnected neutral curves exist in the k Ta plane, which for each non-zero μ considered, lead to a multi-valued stability boundary, corresponding to two disjoint ranges of stable Ta. For each counter-rotating (μ < 0) case, there is a finite range of Re for which there exist three critical values of Ta, with the upper branch emanating from the Re = 0 instability of Couette flow. For the co-rotating (μ = 0.2) case, there are two critical values of Ta for each Re in an apparently semi-infinite range of Re, with
Linear stability of plane Poiseuille flow in an infinite elastic medium and volcanic tremors
NASA Astrophysics Data System (ADS)
Sakuraba, Ataru; Yamauchi, Hatsuki
2014-12-01
The linear stability of a plane compressible laminar (Poiseuille) flow sandwiched between two semi-infinite elastic media was investigated with the aim of explaining the excitation of volcanic tremors. Our results show that there are several regimes of instability, and the nature of stability significantly depends on the symmetry of oscillatory fluid and solid motion. It has been shown that long-wave symmetric instability occurs at a very small value of the Reynolds number, but it is unlikely that this is the cause of volcanic tremors. We show that antisymmetric (flexural) instability also occurs, involving two parallel Rayleigh waves traveling against the Poiseuille flow, but the critical flow speed is faster than that of symmetric instability. However, if the basic flow profile is nonparabolic because of a nonuniform driving force or nonuniform viscosity, the critical flow speed of antisymmetric instability can be considerably slower than that of symmetric instability. Based on numerical calculations and analytical consideration, we conclude that this anomalous antisymmetric instability is possibly produced by a basaltic magma flow of a few meters per second through a dike with thickness of 1 m and extending for several kilometers; this origin can explain some of the characteristics of volcanic tremors.
Time-dependent rotating stratified shear flow: exact solution and stability analysis.
Salhi, A; Cambon, C
2007-01-01
A solution of the Euler equations with Boussinesq approximation is derived by considering unbounded flows subjected to spatially uniform density stratification and shear rate that are time dependent [S(t)= partial differentialU3/partial differentialx2]. In addition to vertical stratification with constant strength N(v)2, this base flow includes an additional, horizontal, density gradient characterized by N(h)2(t). The stability of this flow is then analyzed: When the vertical stratification is stabilizing, there is a simple harmonic motion of the horizontal stratification N(h)2(t) and of the shear rate S(t), but this flow is unstable to certain disturbances, which are amplified by a Floquet mechanism. This analysis may involve an additional Coriolis effect with Coriolis parameter f, so that governing dimensionless parameters are a modified Richardson number, R=[S(0)2+N(h)4(0)/N(v)2]1/2, and f(v)=f/N(v), as well as the initial phase of the periodic shear rate. Parametric resonance between the inertia-gravity waves and the oscillating shear is demonstrated from the dispersion relation in the limit R-->0. The parametric instability has connection with both baroclinic and elliptical flow instabilities, but can develop from a very different base flow.
Kuhlmann, Hendrik C.; Albensoeder, Stefan
2014-02-15
The stability of the steady flow in a lid-driven cube is investigated by a collocation method making use of asymptotic solutions for the singular edges of the cavity up- and downstream of the moving wall. Owing to the rapid convergence of the method high-accuracy critical data are obtained. To determine the critical point subcritical growth rates of small perturbations are extrapolated to zero. We find the bifurcation to be of Hopf-type and slightly subcritical. Above the critical point, the oscillatory flow is symmetric with respect to the symmetric midplane of the cavity and characterized by nearly streamwise vortices in the boundary layer on the wall upstream of the moving wall. The oscillation amplitude grows slowly and seems to saturate. On a long time scale, however, the constant-amplitude oscillations are unstable. The periodic oscillations are interrupted by short bursts during which the oscillation amplitude grows substantially and the spatial structure of the oscillating streamwise vortices changes. Towards the end of each burst the mirror symmetry of the oscillatory flow is lost, the flow returns to the vicinity of the unstable steady state and the growth of symmetric oscillations starts again leading to an intermittent chaotic flow.
NASA Astrophysics Data System (ADS)
Iyer, V.; Raj, A.; Annabattula, R. K.; Sen, A. K.
2015-07-01
This paper reports experimental and numerical studies of a passive microfluidic device that stabilizes a pulsating incoming flow and delivers a steady flow at the outlet. The device employs a series of chambers along the flow direction with a thin polymeric membrane (of thickness 75-250 µm) serving as the compliant boundary. The deformation of the membrane allows accumulation of fluid during an overflow and discharge of fluid during an underflow for flow stabilization. Coupled fluid-structure simulations are performed using Mooney-Rivlin formulations to account for a thin hyperelastic membrane material undergoing large deformations to accurately predict the device performance. The device was fabricated with PDMS as the substrate material and thin PDMS membrane as the compliant boundary. The performance of the device is defined in terms of a parameter called ‘Attenuation Factor (AF)’. The effect of various design parameters including membrane thickness, elastic modulus, chamber size and number of chambers in series as well as operating conditions including the outlet pressure, mean input flow rate, fluctuation amplitude and frequency on the device performance were studied using experiments and simulations. The simulation results successfully confront the experimental data (within 10%) which validates the numerical simulations. The device was used at the exit of a PZT actuated valveless micropump to take pulsating flow at the upstream and deliver steady flow downstream. The amplitude of the pulsating flow delivered by the micropump was significantly reduced (AF = 0.05 for a device with three 4 mm chambers) but at the expense of a reduction in the pressure capability (<20%). The proposed device could potentially be used for reducing flow pulsations in practical microfluidic circuits.
The stability of stratified spatially periodic shear flows at low Péclet number
Garaud, Pascale; Gallet, Basile
2015-08-15
This work addresses the question of the stability of stratified, spatially periodic shear flows at low Péclet number but high Reynolds number. This little-studied limit is motivated by astrophysical systems, where the Prandtl number is often very small. Furthermore, it can be studied using a reduced set of “low-Péclet-number equations” proposed by Lignières [“The small-Péclet-number approximation in stellar radiative zones,” Astron. Astrophys. 348, 933–939 (1999)]. Through a linear stability analysis, we first determine the conditions for instability to infinitesimal perturbations. We formally extend Squire’s theorem to the low-Péclet-number equations, which shows that the first unstable mode is always two-dimensional. We then perform an energy stability analysis of the low-Péclet-number equations and prove that for a given value of the Reynolds number, above a critical strength of the stratification, any smooth periodic shear flow is stable to perturbations of arbitrary amplitude. In that parameter regime, the flow can only be laminar and turbulent mixing does not take place. Finding that the conditions for linear and energy stability are different, we thus identify a region in parameter space where finite-amplitude instabilities could exist. Using direct numerical simulations, we indeed find that the system is subject to such finite-amplitude instabilities. We determine numerically how far into the linearly stable region of parameter space turbulence can be sustained.
Stability of plane Couette-Poiseuille flow of shear-thinning fluid
NASA Astrophysics Data System (ADS)
Nouar, Chérif; Frigaard, Ian
2009-06-01
A linear stability analysis of the combined plane Couette and Poiseuille flow of shear-thinning fluid is investigated. The rheological behavior of the fluid is described using the Carreau model. The linearized stability equations and their boundary conditions result in an eigenvalue problem that is solved numerically using a Chebyshev collocation method. A parametric study is performed in order to assess the roles of viscosity stratification and the Couette component. First of all, it is shown that for shear-thinning fluid, the critical Reynolds number for a two-dimensional perturbation is less than for a three dimensional. Therefore, it is sufficient to deal only with a modified Orr-Sommerfeld equation for the normal velocity component. The influence of the velocity of the moving wall on the critical conditions is qualitatively similar to that for a Newtonian fluid. Concerning the effect of the shear thinning, the computational results indicate that this behavior leads to a decrease in the phase velocity of the traveling waves and an increase in stability, when an appropriate viscosity is used in the definition of the Reynolds number. Using a long-wave version of the Orr-Sommerfeld equation, the cutoff velocity is derived. The mechanisms responsible for the changes in the flow stability are discussed in terms of the location of the critical layers, Reynolds stress distribution, and the exchange of energy between the base flow and the disturbance.
Stability and instability of equilibria in collisionless plasmas and ideal plane flows
NASA Astrophysics Data System (ADS)
Lin, Zhiwu
In this dissertation, I study instability and stability of steady solutions to the one-dimensional Vlasov-Poisson system (VP) and two-dimensional Euler equation of incompressible inviscid fluids (E). Some new methods are developed to find exponentially growing solutions (growing modes) to the linearized equation around the equilibrium. In order to obtain growing modes, I use several different methods, including the concept of neutral modes and of infinite determinant as well as continuation arguments. These methods are used to analyze a corresponding dispersion operator or the neutral mode equations (such as Rayleigh's classical equation). The new results obtained include: the proof of linear instability of any BGK waves of (VP) under multipy-periodic perturbations, new sufficient conditions for instability of plane shear flows and rotating flows for (E) and a criterion of finding purely growing modes for general steady ideal plane flows (E). These methods are flexible and might be applicable to study instability problems of other conservative systems in continuum physics. I also get some stability criteria for quite general ideal plane flows and compare the different types of stability in this case.
Linear stability of the Couette flow of a vibrationally excited gas. 2. viscous problem
NASA Astrophysics Data System (ADS)
Grigor'ev, Yu. N.; Ershov, I. V.
2016-03-01
Based on the linear theory, stability of viscous disturbances in a supersonic plane Couette flow of a vibrationally excited gas described by a system of linearized equations of two-temperature gas dynamics including shear and bulk viscosity is studied. It is demonstrated that two sets are identified in the spectrum of the problem of stability of plane waves, similar to the case of a perfect gas. One set consists of viscous acoustic modes, which asymptotically converge to even and odd inviscid acoustic modes at high Reynolds numbers. The eigenvalues from the other set have no asymptotic relationship with the inviscid problem and are characterized by large damping decrements. Two most unstable viscous acoustic modes (I and II) are identified; the limits of these modes were considered previously in the inviscid approximation. It is shown that there are domains in the space of parameters for both modes, where the presence of viscosity induces appreciable destabilization of the flow. Moreover, the growth rates of disturbances are appreciably greater than the corresponding values for the inviscid flow, while thermal excitation in the entire considered range of parameters increases the stability of the viscous flow. For a vibrationally excited gas, the critical Reynolds number as a function of the thermal nonequilibrium degree is found to be greater by 12% than for a perfect gas.
Experimental study of expansion and compression effects on the stability of Taylor vortex flow
NASA Astrophysics Data System (ADS)
Mansour, M.; Ali, M. H.; Abd El-Maksoud, R. M.
2016-08-01
The aim of the present experimental work is to determine the stability limits of Taylor cells by expanding and compressing the cells. The investigation was performed under laminar flow condition with a wide gap between an inner rotating cylinder and outer stationary cylinder. In order to allow the expansion and compression of the cells, the test rig was designed with a sliding upper end plate and a fixed lower end plate. The objectives are to determine the maximum and minimum size limits of each number of cells as well as the stability margin of them. Since, unstable cells have various oscillations and time dependent structures which change the behavior of the flow; the investigations of the stability limits is quite necessary to avoid the possible generation of unstable cells. In addition, the results are used to detect the number of cells that can be generated in the gap at different fluid column lengths. A stability map, locating the stability state of all possible numbers of cells, is assigned in the results. The map provides overlap zones between stable cells, in which the operating conditions will always lead to stable cells, even if the number of cells is changed by changing the initial conditions. Moreover, a rare phenomenon was observed during the compression process when the cells jumps unusually from six to two cells without passing through the four-cell mode.
Stability of viscosity stratified flows down an incline: Role of miscibility and wall slip
NASA Astrophysics Data System (ADS)
Ghosh, Sukhendu; Usha, R.
2016-10-01
The effects of wall velocity slip on the linear stability of a gravity-driven miscible two-fluid flow down an incline are examined. The fluids have the matched density but different viscosity. A smooth viscosity stratification is achieved due to the presence of a thin mixed layer between the fluids. The results show that the presence of slip exhibits a promise for stabilizing the miscible flow system by raising the critical Reynolds number at the onset and decreasing the bandwidth of unstable wave numbers beyond the threshold of the dominant instability. This is different from its role in the case of a single fluid down a slippery substrate where slip destabilizes the flow system at the onset. Though the stability properties are analogous to the same flow system down a rigid substrate, slip is shown to delay the surface mode instability for any viscosity contrast. It has a damping/promoting effect on the overlap modes (which exist due to the overlap of critical layer of dominant disturbance with the mixed layer) when the mixed layer is away/close from/to the slippery inclined wall. The trend of slip effect is influenced by the location of the mixed layer, the location of more viscous fluid, and the mass diffusivity of the two fluids. The stabilizing characteristics of slip can be favourably used to suppress the non-linear breakdown which may happen due to the coexistence of the unstable modes in a flow over a substrate with no slip. The results of the present study suggest that it is desirable to design a slippery surface with appropriate slip sensitivity in order to meet a particular need for a specific application.
Stagnation-point flow and heat transfer over an exponentially shrinking sheet: A stability analysis
NASA Astrophysics Data System (ADS)
Ismail, Nurul Syuhada; Arifin, Norihan Md.; Bachok, Norfifah; Mahiddin, Norhasimah
2016-06-01
Numerical solutions for the stagnation-point flow and heat transfer over an exponentially shrinking sheet have been investigated. The governing boundary layer equations are transformed into an ordinary differential equation using a non-similar transformation. By using the bvp4c solver in MATLAB, the results of the equations can be solved numerically. Numerical results indicate that in certain parameter, the non-unique solutions for the velocity and the temperature do exist. A linear stability analysis shows that only one solution is linearly stable otherwise is unstable. Then, the stability analysis is performed to identify which solution is stable between the two non-unique solutions.
NASA Technical Reports Server (NTRS)
Harvey, William D.; Harris, Charles D.; Brooks, Cuyler W., Jr.
1989-01-01
A swept, supercritical laminar flow control (LFC) airfoil designated NASA SCLFC(1)-0513F was tested at subsonic and transonic speeds in the NASA Langley eight-foot Transonic Pressure Tunnel. This paper examines Tollmien-Schlichting and crossflow disturbance amplification for this airfoil using the linear stability method. The design methodology using linear stability analysis is evaluated and the results of the incompressible and compressible methods are compared. Experimental data on the swept, supercritical LFC airfoil and reference wind tunnel and flight results are used to correlate and evaluate the N-factor method for transition prediction over a speed range M(infinity) from zero to one.
The Sobolev Stability Threshold for 2D Shear Flows Near Couette
NASA Astrophysics Data System (ADS)
Bedrossian, Jacob; Vicol, Vlad; Wang, Fei
2016-08-01
We consider the 2D Navier-Stokes equation on T × R , with initial datum that is ɛ -close in H^N to a shear flow (U(y), 0), where Vert U(y) - yVert _{H^{N+4}} ≪ 1 and N>1 . We prove that if ɛ ≪ ν ^{1/2} , where ν denotes the inverse Reynolds number, then the solution of the Navier-Stokes equation remains ɛ -close in H^1 to (e^{t ν partial _{yy}}U(y),0) for all t>0 . Moreover, the solution converges to a decaying shear flow for times t ≫ ν ^{-1/3} by a mixing-enhanced dissipation effect, and experiences a transient growth of gradients. In particular, this shows that the stability threshold in finite regularity scales no worse than ν ^{1/2} for 2D shear flows close to the Couette flow.
Preparative free-flow electrofocusing in a vortex-stabilized annulus.
Ivory, Cornelius F
2004-01-01
This paper describes the development of an annular chamber designed for preparative free-flow electrophoresis which can operate at voltages up to 20 kV, electric fields up to 65 kV/m, and power densities as high as 10 MW/m(3). This apparatus uses counter-rotating fluid vortices to stabilize the aqueous medium in the annulus against natural convection while improving heat and mass transfer over vortex-free Couette flow. The vortices are generated by rotating the inner surface of the annulus and, if the rotor and stator have complementary shapes, dispersion induced by electrokinetic and electrohydrodynamic flows can be mitigated even at the highest operating voltages. Following a brief overview of contemporary annular free-flow instrumentation, the theoretical principles for momentum and heat transport in the vortices are discussed in some detail and then the results of several electrofocusing experiments are provided to illustrate the resolving power of this instrument.
Preparative free-flow electrofocusing in a vortex-stabilized annulus.
Ivory, Cornelius F
2004-01-01
This paper describes the development of an annular chamber designed for preparative free-flow electrophoresis which can operate at voltages up to 20 kV, electric fields up to 65 kV/m, and power densities as high as 10 MW/m(3). This apparatus uses counter-rotating fluid vortices to stabilize the aqueous medium in the annulus against natural convection while improving heat and mass transfer over vortex-free Couette flow. The vortices are generated by rotating the inner surface of the annulus and, if the rotor and stator have complementary shapes, dispersion induced by electrokinetic and electrohydrodynamic flows can be mitigated even at the highest operating voltages. Following a brief overview of contemporary annular free-flow instrumentation, the theoretical principles for momentum and heat transport in the vortices are discussed in some detail and then the results of several electrofocusing experiments are provided to illustrate the resolving power of this instrument. PMID:14743489
On the stability of plane Couette-Poiseuille flow with uniform crossflow
NASA Astrophysics Data System (ADS)
Guha, Anirban; Frigaard, Ian A.
2010-06-01
We present a detailed study of the linear stability of plane Couette-Poiseuille flow in the presence of a cross-flow. The base flow is characterised by the cross flow Reynolds number, $R_{inj}$ and the dimensionless wall velocity, $k$. Squire's transformation may be applied to the linear stability equations and we therefore consider 2D (spanwise-independent) perturbations. Corresponding to each dimensionless wall velocity, $k\\in[0,1]$, two ranges of $R_{inj}$ exist where unconditional stability is observed. In the lower range of $R_{inj}$, for modest $k$ we have a stabilisation of long wavelengths leading to a cut-off $R_{inj}$. This lower cut-off results from skewing of the velocity profile away from a Poiseuille profile, shifting of the critical layers and the gradual decrease of energy production. Cross-flow stabilisation and Couette stabilisation appear to act via very similar mechanisms in this range, leading to the potential for robust compensatory design of flow stabilisation using either mechanism. As $R_{inj}$ is increased, we see first destabilisation and then stabilisation at very large $R_{inj}$. The instability is again a long wavelength mechanism. Analysis of the eigenspectrum suggests the cause of instability is due to resonant interactions of Tollmien-Schlichting waves. A linear energy analysis reveals that in this range the Reynolds stress becomes amplified, the critical layer is irrelevant and viscous dissipation is completely dominated by the energy production/negation, which approximately balances at criticality. The stabilisation at very large $R_{inj}$ appears to be due to decay in energy production, which diminishes like $R_{inj}^{-1}$. Our study is limited to two dimensional, spanwise independent perturbations.
Appearance and stability of vortices in Taylor-Couette flow of helium II
Swanson, C.J.
1992-01-01
The appearance and stability of vortices in helium II Taylor-Couette flow, flow between concentric rotating cylinder, has been studied. The two cylinders capable of independent rotation were first rotated as a solid body at slow speeds. Resonant second sound attenuation was used to examine the critical angular velocity for the onset of vorticity. The results are compared with previous experiments and theory in an attempt to understand which factors affect the first appearance of vortices. The most important factor is the existence of vorticity aligned perpendicular to the axis of rotation. This vorticity is created by acceleration and vibrational perturbation and renders detailed comparison to the theory impossible. Consequently it is also impossible to determine the size of the vortex core parameter from measurement of the critical angular velocity. It is argued, however, that the temperature dependence of the core parameter can be determined, and measurements of the temperature dependence agree well with expectations. Finally, studies of the prependicular component of the vorticity reveal that the parallel component of mutual friction B[double prime] is likely to be zero. A similar experiment was performed with the cylinders rotating at different speeds. Results are compared to theoretical predictions for shear flows in an annulus. It is found that the onset in this non-equilibrium flow does not agree well with the theory but instead exhibits an unexplained temperature dependence. Stability of the vortices was also studied at higher angular velocities. With the outer cylinder fixed and the inner cylinder increasing in speed, the helium undergoes a transition to unstable flow. An experimental study of the transition, again using second sound, was performed over a range of temperatures. The results agree with the stability analysis rigorously validating the helium II equations of flow.
Investigating motion and stability of particles in flows using numerical models
NASA Astrophysics Data System (ADS)
Khurana, Nidhi
The phenomenon of transport of particles in a fluid is ubiquitous in nature and a detailed understanding of its mechanism continues to remain a fundamental question for physicists. In this thesis, we use numerical methods to study the dynamics and stability of particles advected in flows. First, we investigate the dynamics of a single, motile particle advected in a two-dimensional chaotic flow. The particle can be either spherical or ellipsoidal. Particle activity is modeled as a constant intrinsic swimming velocity and stochastic fluctuations in both the translational and rotational motions are also taken into account. Our results indicate that interaction of swimming with flow structures causes a reduction in long-term transport at low speeds. Swimmers can get trapped at the transport barriers of the flow. We show that elongated swimmers respond more strongly to the dynamical structures of the flow field. At low speeds, their macroscopic transport is reduced even further than in the case of spherical swimmers. However, at high speeds these elongated swimmers tend to get attracted to the stable manifolds of hyperbolic fixed points, leading to increased transport. We then investigate the collective dynamics of a system of particles. The particles may interact both with each other and with the background flow. We focus on two different cases. In the fist case, we examine the stability of aggregation models in a turbulent-like flow. We use a simple aggregation model in which a point-like particle moves with a constant intrinsic speed while its velocity vector is reoriented according to the average direction of motion of its neighbors. We generate a strongly fluctuating, spatially correlated background flow using Kinematic Simulation, and show that flocks are highly sensitive to this background flow and break into smaller clusters. Our results indicate that such environmental perturbations must be taken into account for models which aim to capture the collective
Feedback stabilization of vortex flows in a finite-length straight pipe
NASA Astrophysics Data System (ADS)
Wang, S.; Gong, R.; Rusak, Z.; Xu, L.; Taylor, S.; Jeng, L.
2012-11-01
The properties of a recently proposed feedback stabilization method of swirling flows in a finite-length pipe are studied. In the natural case, when swirl is above a critical level, linearly unstable modes appear in sequence as swirl increases and evolve to a vortex breakdown state. Based on a long-wave approach, the feedback control methodology is shown to enforce decay of perturbation's kinetic energy and to quench all instability modes at above critical swirl. In the case of a solid-body rotation, the effectiveness of this control approach is further analyzed through a mode analysis of the full linearized flow control problem. We first establish the asymptotic decay of all modes with real growth rates. We then compute growth rates of all modes according to the linearized flow control problem for swirl up to 50% above critical level. Flow stabilization in the whole swirl range is demonstrated. However, control effectiveness is sensitive to choice of the control gain. An inadequate gain, either insufficient or excessive, could lead to a failure of control at high swirl levels. Predictions of controlled flow cases agree with numerical simulations using the full unsteady and axisymmetric Euler equations with fluidic actuation along the pipe wall. Rusak et al. JFM 2012.
Stability of pressure-driven creeping flows in channels lined with a nonlinear elastic solid
NASA Astrophysics Data System (ADS)
Gkanis, Vasileios; Kumar, Satish
2004-11-01
The effect of pressure gradients on the stability of creeping flows of Newtonian fluids in channels lined with an incompressible and impermeable neo-Hookean material is examined in this work. Three different configurations are considered: (i) pressure-driven flow between a rigid wall and a wall lined with a neo-Hookean material, (ii) pressure-driven flow between neo-Hookean-lined walls, and (iii) combined Couette-Poiseuille flow between a rigid wall and a neo-Hookean-lined wall. In each case, a first normal stress difference whose magnitude depends on depth arises in the base state for the solid, and linear stability analysis reveals that this leads to a shortwave instability that is removed by the presence of interfacial tension. For sufficiently thick solids, low wavenumber modes become unstable first as the applied strain increases above a critical value, whereas for sufficiently thin solids, high wavenumber modes becomes unstable first instead. Comparison of the dimensionless critical strains shows that configurations (i) and (ii) are more difficult to destabilize than Couette flow past a neo-Hookean solid. The mechanisms underlying the behavior of the critical strains are explained through an analysis of the interfacial boundary conditions.
Stability of pressure-driven creeping flows in channels lined with a nonlinear elastic solid
NASA Astrophysics Data System (ADS)
Gkanis, Vasileios; Kumar, Satish
2005-02-01
The effect of pressure gradients on the stability of creeping flows of Newtonian fluids in channels lined with an incompressible and impermeable neo-Hookean material is examined in this work. Three different configurations are considered: (i) pressure-driven flow between a rigid wall and a wall lined with a neo-Hookean material; (ii) pressure-driven flow between neo-Hookean-lined walls; and (iii) combined Couette-Poiseuille flow between a rigid wall and a neo-Hookean-lined wall. In each case, a first normal stress difference whose magnitude depends on depth arises in the base state for the solid, and linear stability analysis reveals that this leads to a short-wave instability which is removed by the presence of interfacial tension. For sufficiently thick solids, low-wavenumber modes become unstable first as the applied strain increases above a critical value, whereas for sufficiently thin solids, high-wavenumber modes becomes unstable first. Comparison of the dimensionless critical strains shows that configurations (i) and (ii) are more difficult to destabilize than Couette flow past a neo-Hookean solid. For configuration (iii), the nonlinear elasticity of the solid leads to two physically distinct critical conditions, in contrast to what happens when a linear elastic material is used. The mechanisms underlying the behaviour of the critical strains are explained through an analysis of the interfacial boundary conditions.
Nonlinear stability of cylindrical shells subjected to axial flow: Theory and experiments
NASA Astrophysics Data System (ADS)
Karagiozis, K. N.; Païdoussis, M. P.; Amabili, M.; Misra, A. K.
2008-01-01
This paper, is concerned with the nonlinear dynamics and stability of thin circular cylindrical shells clamped at both ends and subjected to axial fluid flow. In particular, it describes the development of a nonlinear theoretical model and presents theoretical results displaying the nonlinear behaviour of the clamped shell subjected to flowing fluid. The theoretical model employs the Donnell nonlinear shallow shell equations to describe the geometrically nonlinear structure. The clamped beam eigenfunctions are used to describe the axial variations of the shell deformation, automatically satisfying the boundary conditions and the circumferential continuity condition exactly. The fluid is assumed to be incompressible and inviscid, and the fluid-structure interaction is described by linear potential flow theory. The partial differential equation of motion is discretized using the Galerkin method and the final set of ordinary differential equations are integrated numerically using a pseudo-arclength continuation and collocation techniques and the Gear backward differentiation formula. A theoretical model for shells with simply supported ends is presented as well. Experiments are also described for (i) elastomer shells subjected to annular (external) air-flow and (ii) aluminium and plastic shells with internal water flow. The experimental results along with the theoretical ones indicate loss of stability by divergence with a subcritical nonlinear behaviour. Finally, theory and experiments are compared, showing good qualitative and reasonable quantitative agreement.
On a Model for Mixture Flows: Derivation, Dissipation and Stability Properties
NASA Astrophysics Data System (ADS)
Goudon, Thierry; Vasseur, Alexis
2016-04-01
We propose a new model describing mixture flows. The non linear system couples heterogeneous Navier-Stokes equations with a constraint on the mean volume velocity of the flow. The PDE system is obtained from a more microscopic viewpoint, involving a Vlasov-like equation describing the disperse phase, through a certain hydrodynamic limit. The model has remarkable dissipation properties, inherited from the structure of the fluid-kinetic description. Based on these properties, together with additional estimates that can be obtained in the one-dimension framework, we establish the stability of weak solutions.
NASA Astrophysics Data System (ADS)
Murata, H.; Matsuda, T.; Isaka, H.; Ohsugi, Y.; Boffin, H. M. J.
2008-08-01
We discuss the physical background of the molecular hydrodynamics method (MH), a new computational fluid dynamics (CFD) technique that we proposed recently, and further test it to simulate isothermal flows including those of zero temperature gas. The problems considered are a shock tube of an isothermal gas, a rotating cone test, a box shear flow test, and a Keplerian disc. We demonstrate that the MH is unconditionally stable in spite of the fact that the scheme is time-explicit. Because of this, we may choose any time step without losing stability. The only penalty for using a longer time step is a gradual degradation of the quality of the solution.
Stabilization of Taylor-Couette flow due to time-periodic outer cylinder oscillation
NASA Technical Reports Server (NTRS)
Murray, B. T.; Mcfadden, G. B.; Coriell, S. R.
1990-01-01
The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case when the inner cylinder is rotated at a constant angular velocity and the outer cylinder is driven sinusoidally in time with zero mean rotation. This configuration was studied experimentally by Walsh and Donnelly. The critical Reynolds numbers calculated from linear stability theory agree well with the experimental values, except at large modulation amplitudes and small frequencies. The theoretical values are obtained using Floquet theory implemented in two distinct approaches: a truncated Fourier series representation in time, and a fundamental solution matrix based on a Chebyshev pseudospectral representation in space. For large amplitude, low frequency modulation, the linear eigenfunctions are temporally complex, consisting of a quiescent region followed by rapid change in the perturbed flow velocities.
FLUT - A program for aeroelastic stability analysis. [of aircraft structures in subsonic flow
NASA Technical Reports Server (NTRS)
Johnson, E. H.
1977-01-01
A computer program (FLUT) that can be used to evaluate the aeroelastic stability of aircraft structures in subsonic flow is described. The algorithm synthesizes data from a structural vibration analysis with an unsteady aerodynamics analysis and then performs a complex eigenvalue analysis to assess the system stability. The theoretical basis of the program is discussed with special emphasis placed on some innovative techniques which improve the efficiency of the analysis. User information needed to efficiently and successfully utilize the program is provided. In addition to identifying the required input, the flow of the program execution and some possible sources of difficulty are included. The use of the program is demonstrated with a listing of the input and output for a simple example.
The stability of a trailing-line vortex in compressible flow
NASA Technical Reports Server (NTRS)
Stott, Jillian A. K.; Duck, Peter W.
1992-01-01
We consider the inviscid stability of the Batchelor (1964) vortex in a compressible flow. The problem is tackled numerically and also asymptotically, in the limit of large (aximuthal and streamwise) wavenumbers, together with large Mach numbers. The nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumbers. At very high wavenumbers and Mach numbers, the mode which is present in the incompressible case ceases to be unstable, while new 'center mode' forms, whose stability characteristics, are determined primarily by conditions close to the vortex axis. We find that generally the flow becomes less unstable as the Mach number increases, and that the regime of instability appears generally confined to disturbances in a direction counter to the direction of the rotation of the swirl of the vortex. Throughout the paper, comparison is made between our numerical results and results obtained from the various asymptotic theories.
Stability of flow of a thermoviscoelastic fluid between rotating coaxial circular cylinders
NASA Technical Reports Server (NTRS)
Ghandour, N. N.; Narasimhan, M. N. L.
1976-01-01
The stability problem of thermoviscoelastic fluid flow between rotating coaxial cylinders is investigated using nonlinear thermoviscoelastic constitutive equations due to Eringen and Koh. The velocity field is found to be identical with that of the classical viscous case and the case of the viscoelastic fluid, but the temperature and pressure fields are found to be different. By imposing some physically reasonable mechanical and geometrical restrictions on the flow, and by a suitable mathematical analysis, the problem is reduced to a characteristic value problem. The resulting problem is solved and stability criteria are obtained in terms of critical Taylor numbers. In general, it is found that thermoviscoelastic fluids are more stable than classical viscous fluids and viscoinelastic fluids under similar conditions.
Linear stability analysis and direct numerical simulation of a miscible two-fluid channel flow
NASA Astrophysics Data System (ADS)
Haapanen, Siina Ilona
The temporal evolution of an initially laminar two-fluid channel flow is investigated using linear stability analysis and direct numerical simulation. The stability of a two-fluid shear flow is encountered in numerous situations, including water wave generation by wind, atomization of fuels, aircraft deicing and nuclear reactor cooling. The application of particular interest in this study is liquefying hybrid combustion, for which the two-fluid channel flow is used as a model problem to characterize the relevant mixing and entrainment mechanisms. The two fluids are miscible with dissimilar densities and viscosities. The thickness of one of the fluid layers is much smaller than that of the other, with the denser and more viscous fluid comprising the thin layer. Linear stability analysis is used to identify possibly unstable modes in the two-fluid configuration. The analysis is considered for two different situations. In one case, the fluid density and viscosity change discontinuously across a sharp interface, while in the other, the fluids are separated by a finite thickness transition layer, over which the fluid properties vary continuously. In the sharp interface limit, the linear stability is governed by an Orr-Sommerfeld equation in each fluid layer, coupled by boundary conditions at the interface. A numerical solution of the system of equations is performed using a Chebyshev spectral collocation method. In the case where the fluids are separated by a finite thickness transition zone, an Orr-Sommerfeld-type equation is solved with the compound matrix method. The non-linear stages of the flow evolution are investigated by direct numerical simulation. In a temporal simulation, two of the three spatial dimensions are periodic. Fourier spectral discretization is used in these dimensions, while a compact finite difference scheme is utilized in the non-periodic direction. The time advancement is performed by a projection method with a third order Adams
Xiang, Yaolei; Xue, Yahui; Lv, Pengyu; Li, Dandan; Duan, Huiling
2016-05-14
Superhydrophobic surfaces have attracted great attention for drag reduction application. However, these surfaces are subject to instabilities, especially under fluid flow. In this work, we in situ examine the stability and wetting transition of underwater superhydrophobicity under laminar flow conditions by confocal microscopy. The absolute liquid pressure in the flow channel is regulated to acquire the pinned Cassie-Baxter and depinned metastable states. The subsequent dynamic evolution of the meniscus morphology in the two states under shear flow is monitored. It is revealed that fluid flow does not affect the pressure-mediated equilibrium states but accelerates the air exchange between entrapped air cavities and bulk water. A diffusion-based model with varying effective diffusion lengths is used to interpret the experimental data, which show a good agreement. The Sherwood number representing the convection-enhanced mass transfer coefficient is extracted from the data, and is found to follow a classic 1/3-power-law relation with the Reynolds number as has been discovered in channel flows with diffusive boundary conditions. The current work paves the way for designing durable superhydrophobic surfaces under flow conditions. PMID:27071538
Double-diffusive two-fluid flow in a slippery channel: A linear stability analysis
NASA Astrophysics Data System (ADS)
Ghosh, Sukhendu; Usha, R.; Sahu, Kirti Chandra
2014-12-01
The effect of velocity slip at the walls on the linear stability characteristics of two-fluid three-layer channel flow (the equivalent core-annular configuration in case of pipe) is investigated in the presence of double diffusive (DD) phenomenon. The fluids are miscible and consist of two solute species having different rates of diffusion. The fluids are assumed to be of the same density, but varying viscosity, which depends on the concentration of the solute species. It is found that the flow stabilizes when the less viscous fluid is present in the region adjacent to the slippery channel walls in the single-component (SC) system but becomes unstable at low Reynolds numbers in the presence of DD effect. As the mixed region of the fluids moves towards the channel walls, a new unstable mode (DD mode), distinct from the Tollman Schlichting (TS) mode, arises at Reynolds numbers smaller than the critical Reynolds number for the TS mode. We also found that this mode becomes more prominent when the mixed layer overlaps with the critical layer. It is shown that the slip parameter has nonmonotonic effect on the stability characteristics in this system. Through energy budget analysis, the dual role of slip is explained. The effect of slip is influenced by the location of mixed layer, the log-mobility ratio of the faster diffusing scalar, diffusivity, and the ratio of diffusion coefficients of the two species. Increasing the value of the slip parameter delays the first occurrence of the DD-mode. It is possible to achieve stabilization or destabilization by controlling the various physical parameters in the flow system. In the present study, we suggest an effective and realistic way to control three-layer miscible channel flow with viscosity stratification.
Stability of a Resonant System of Conservation Laws Modeling Polymer Flow with Gravitation
NASA Astrophysics Data System (ADS)
Klingenberg, Christian; Risebro, Nils Henrik
2001-03-01
We prove L1 uniqueness and stability for a resonant 2×2 system of conservation laws that arise as a model for two phase polymer flow in porous media. The analysis uses the equivalence of the Eulerian and Lagrangian formulation of this system, and the results are first established for an auxiliary scalar equation. Our methods are based on front tracking approximations for the auxiliary equation, and the Kružkov entropy condition for scalar conservation laws.
Stability analysis of stagnation-point flow over a stretching/shrinking sheet
NASA Astrophysics Data System (ADS)
Awaludin, I. S.; Weidman, P. D.; Ishak, Anuar
2016-04-01
The stagnation point flow over a linearly stretching or shrinking sheet is considered in the present study. The transformed ordinary differential equations are solved numerically. Dual solutions are possible for the shrinking case, while the solution is unique for the stretching case. For the shrinking case, a linear temporal stability analysis is performed to determine which one of the solution is stable and thus physically reliable.
de Croon, Guido C H E
2016-02-01
The visual cue of optical flow plays an important role in the navigation of flying insects, and is increasingly studied for use by small flying robots as well. A major problem is that successful optical flow control seems to require distance estimates, while optical flow is known to provide only the ratio of velocity to distance. In this article, a novel, stability-based strategy is proposed for monocular distance estimation, relying on optical flow maneuvers and knowledge of the control inputs (efference copies). It is shown analytically that given a fixed control gain, the stability of a constant divergence control loop only depends on the distance to the approached surface. At close distances, the control loop starts to exhibit self-induced oscillations. The robot can detect these oscillations and hence be aware of the distance to the surface. The proposed stability-based strategy for estimating distances has two main attractive characteristics. First, self-induced oscillations can be detected robustly by the robot and are hardly influenced by wind. Second, the distance can be estimated during a zero divergence maneuver, i.e., around hover. The stability-based strategy is implemented and tested both in simulation and on board a Parrot AR drone 2.0. It is shown that the strategy can be used to: (1) trigger a final approach response during a constant divergence landing with fixed gain, (2) estimate the distance in hover, and (3) estimate distances during an entire landing if the robot uses adaptive gain control to continuously stay on the 'edge of oscillation.' PMID:26740501
Design considerations of a thermally stabilized continuous flow electrophoresis chamber 2
NASA Technical Reports Server (NTRS)
Jandebeur, T. S.
1982-01-01
The basic adjustable parameters of a Beckman Continouous Particle Electrophoresis (CPE) Apparatus are investigated to determine the optimum conditions for ground based operation for comparison with space experiments. The possible application of electrically insulated copper/aluminum chamber walls is evaluated as a means to thermally stabilize or equilibrate lateral temperature gradients which exist on the walls of conventional plastic chambers and which distort the rectilinear base flow of buffer through the chamber, significantly affecting sample resolution.
de Croon, Guido C H E
2016-01-07
The visual cue of optical flow plays an important role in the navigation of flying insects, and is increasingly studied for use by small flying robots as well. A major problem is that successful optical flow control seems to require distance estimates, while optical flow is known to provide only the ratio of velocity to distance. In this article, a novel, stability-based strategy is proposed for monocular distance estimation, relying on optical flow maneuvers and knowledge of the control inputs (efference copies). It is shown analytically that given a fixed control gain, the stability of a constant divergence control loop only depends on the distance to the approached surface. At close distances, the control loop starts to exhibit self-induced oscillations. The robot can detect these oscillations and hence be aware of the distance to the surface. The proposed stability-based strategy for estimating distances has two main attractive characteristics. First, self-induced oscillations can be detected robustly by the robot and are hardly influenced by wind. Second, the distance can be estimated during a zero divergence maneuver, i.e., around hover. The stability-based strategy is implemented and tested both in simulation and on board a Parrot AR drone 2.0. It is shown that the strategy can be used to: (1) trigger a final approach response during a constant divergence landing with fixed gain, (2) estimate the distance in hover, and (3) estimate distances during an entire landing if the robot uses adaptive gain control to continuously stay on the 'edge of oscillation.'
Film stability in a vertical rotating tube with a core-gas flow.
NASA Technical Reports Server (NTRS)
Sarma, G. S. R.; Lu, P. C.; Ostrach, S.
1971-01-01
The linear hydrodynamic stability of a thin-liquid layer flowing along the inside wall of a vertical tube rotating about its axis in the presence of a core-gas flow is examined. The stability problem is formulated under the conditions that the liquid film is thin, the density and viscosity ratios of gas to liquid are small and the relative (axial) pressure gradient in the gas is of the same order as gravity. The resulting eigenvalue problem is first solved by a perturbation method appropriate to axisymmetric long-wave disturbances. The damped nature (to within the thin-film and other approximations made) of the nonaxisymmetric and short-wave disturbances is noted. In view of the limitations on a truncated perturbation solution when the disturbance wavenumber is not small, an initial value method using digital computer is presented. Stability characteristics of neutral, growing, and damped modes are presented showing the influences of rotation, surface tension, and the core-gas flow. Energy balance in a neutral mode is also illustrated.
Linear stability of Couette flow of vibrationally non-equilibrium gas
NASA Astrophysics Data System (ADS)
Grigor'ev, Yurii N.; Ershov, Igor'V.
2016-10-01
Stability of the supersonic plane Couette flow of a perfect gas and of a vibrationally excited gas is studied within the framework of the linear theory. In both cases two variants are studied. When the transport coeffcients are taken as con-stant, and when they are dependent on the flow static temperature. The Satherland's viscosity law was used as temperature dependence of the shear viscosity. The thermal conductivity coeffcients caused by the translational, rotational and vibra-tional motions of gas molecules are determined by the Eucken's relations. Detailed comparison of the characteristics of the stability of the acoustic modes I and II for both viscosity models is carried out for a perfect gas. It is shown that the "viscous" stratification significantly increases flow stability as compared with the case of the constant viscosity model. It is obtained that characteristic features of development of viscous disturbances noted for the Sutherland's model are conserved for more simple model of the constant viscosity. The dissipative effect of the excitation of the vibrational mode is preserved in the case of the temperature dependence of the transport coeffcients. The relative decrease in growth rates of viscous modes I and II at the vibrational excitation is practically the same for both viscosity models. The increase in the critical Reynolds number is approximately 12 % in both cases.
Nonmodal stability in Hagen-Poiseuille flow of a shear thinning fluid.
Liu, Rong; Liu, Qiu Sheng
2012-06-01
Linear stability in Hagen-Poiseuille flow of a shear-thinning fluid is considered. The non-Newtonian viscosity is described by the Carreau rheological law. The effects of shear thinning on the stability are investigated using the energy method and the nonmodal stability theory. The energy analysis shows that the nonaxisymmetric disturbance with the azimuthal wave number m=1 has the lowest critical energy Reynolds number for both the Newtonian and shear-thinning cases. With the increase of shear thinning, the critical energy Reynolds number decreases for both the axisymmetric and nonaxisymmetric cases. For the nonmodal stability, we focus on two problems: response to external excitations and response to initial conditions. The former is studied by examining the ε pseudospectrum, and the latter by examining the energy growth function G(t). For both Newtonian and shear-thinning fluids, it is found that there can be a rather large transient growth even though the linear operator of the Hagen-Poiseuille flow has no unstable eigenvalue. For the problem of response to external excitations, the optimal response is achieved by disturbance with m=1 for both the Newtonian and non-Newtonian cases. For the problem of response to initial conditions, the optimal disturbance is in the form of streamwise uniform streaks. Being different from the Newtonian case, the azimuthal wave number of the optimal disturbance may be greater than 1 for strongly shear-thinning cases.
Canonical fluid thermodynamics. [variational principles of stability for compressible adiabatic flow
NASA Technical Reports Server (NTRS)
Schmid, L. A.
1974-01-01
The space-time integral of the thermodynamic pressure plays in a certain sense the role of the thermodynamic potential for compressible adiabatic flow. The stability criterion can be converted into a variational minimum principle by requiring the molar free-enthalpy and temperature to be generalized velocities. In the fluid context, the definition of proper-time differentiation involves the fluid velocity expressed in terms of three particle identity parameters. The pressure function is then converted into a functional which is the Lagrangian density of the variational principle. Being also a minimum principle, the variational principle provides a means for comparing the relative stability of different flows. For boundary conditions with a high degree of symmetry, as in the case of a uniformly expanding spherical gas box, the most stable flow is a rectilinear flow for which the world-trajectory of each particle is a straight line. Since the behavior of the interior of a freely expanding cosmic cloud may be expected to be similar to that of the fluid in the spherical box of gas, this suggests that the cosmic principle is a consequence of the laws of thermodynamics, rather than just an ad hoc postulate.
Stability of Brillouin flow in the presence of slow-wave structure
NASA Astrophysics Data System (ADS)
Simon, D. H.; Lau, Y. Y.; Greening, G.; Wong, P.; Hoff, B.; Gilgenbach, R. M.
2016-09-01
Including a slow-wave structure (SWS) on the anode in the conventional, planar, and inverted magnetron, we systematically study the linear stability of Brillouin flow, which is the prevalent flow in crossed-field devices. The analytic treatment is fully relativistic and fully electromagnetic, and it incorporates the equilibrium density profile, flow profile, and electric field and magnetic field profiles in the linear stability analysis. Using parameters similar to the University of Michigan's recirculating planar magnetron, the numerical data show that the resonant interaction of the vacuum circuit mode and the corresponding smooth-bore diocotron-like mode is the dominant cause for instability. This resonant interaction is far more important than the intrinsic negative (positive) mass property of electrons in the inverted (conventional) magnetron geometry. It is absent in either the smooth-bore magnetron or under the electrostatic assumption, one or both of which was almost always adopted in prior analytical formulation. This resonant interaction severely restricts the wavenumber for instability to the narrow range in which the cold tube frequency of the SWS is within a few percent of the corresponding smooth bore diocotron-like mode in the Brillouin flow.
Dynamics and stability of two-potential flows in the porous media.
Markicevic, B; Bijeljic, B; Navaz, H K
2011-11-01
The experimental and numerical results of the capillary-force-driven climb of wetting liquid in porous media, which is opposed by the gravity force, are analyzed with respect to the emergence of a multiphase flow front and flow stability of the climbing liquid. Two dynamic characteristics are used: (i) the multiphase flow front thickness as a function of time, and (ii) the capillary number as a function of Bond number, where both numbers are calculated from the harmonic average of pores radii. Throughout the climb, the influence of capillary, gravity, and viscous force variations on the flow behavior is investigated for different porous media. For a specific porous medium, a unique flow front power law function of time is observed for the capillary flow climbs with or without gravity force. Distinct dynamic flow front power law functions are found for different porous media. However, for capillary climb in different porous media, one is able to predict a unique behavior for the wetting height (the interface between wetted and dry regions of porous medium) using the capillary and Bond number. It is found that these two numbers correlate as a unique exponential function, even for porous media whose permeabilities vary for two orders of magnitude. For climbs without the gravity force (capillary spreads), the initial climb dynamics follows this exponential law, but for later flow times and when a significant flow front is developed, one observes a constant value of the capillary number. Using this approach to describe the capillary climb, only the capillary versus Bond number correlation is needed, which is completely measureable from the experiments.
NASA Technical Reports Server (NTRS)
Wernet, Mark P.; Skoch, Gary J.; Wernet, Judith H.
1995-01-01
Laser anemometry enables the measurement of complex flow fields via the light scattered from small particles entrained in the flow. In the study of turbomachinery, refractory seed materials are required for seeding the flow due to the high temperatures encountered. In this work we present a pH stabilization technique commonly employed in ceramic processing to obtain stable dispersions for generating aerosols of refractory seed material. By adding submicron alumina particles to a preadjusted pH solution of ethanol, a stable dispersion is obtained which when atomized, produces a high quality aerosol. Commercial grade alumina powder is used with a moderate size distribution. Other metal oxide powders in various polar solvents could also be used once the point of zero charge (pH(pzc)) of the powder in the solvent has been determined. Laser anemometry measurements obtained using the new seeding technique are compared to measurements obtained using Polystyrene Latex (PSL) spheres as the seed material.
A neural network-based power system stabilizer using power flow characteristics
Park, Y.M.; Choi, M.S.; Lee, K.Y.
1996-06-01
A neural network-based Power System Stabilizer (Neuro-PSS) is designed for a generator connected to a multi-machine power system utilizing the nonlinear power flow dynamics. The uses of power flow dynamics provide a PSS for a wide range operation with reduced size neutral networks. The Neuro-PSS consists of two neutral networks: Neuro-Identifier and Neuro-Controller. The low-frequency oscillation is modeled by the Neuro-Identifier using the power flow dynamics, then a Generalized Backpropagation-Thorough-Time (GBTT) algorithm is developed to train the Neuro-Controller. The simulation results show that the Neuro-PSS designed in this paper performs well with good damping in a wide operation range compared with the conventional PSS.
On the stability of a solid-body-rotation flow in a finite-length pip
NASA Astrophysics Data System (ADS)
Wang, Shixiao; Rusak, Zvi; Gong, Rui; Liu, Feng
2015-11-01
The three-dimensional, inviscid and viscous flow instability modes that appear on a solid-body rotation flow in a finite-length, straight, circular pipe are analyzed. This study is a direct extension of the Wang & Rusak (1996) analysis of axisymmetric instabilities on inviscid swirling flows in a pipe. We study a general mode of perturbation that satisfies the inlet, outlet and wall conditions of a flow in a finite-length pipe with a fixed-in-time and in-space vortex generator ahead of it. The eigenvalue problem for the growth rate and the shape of the perturbations for any azimuthal wave number m is solved numerically for all azimuthal wave number m. In the inviscid flow case, the m = 1 modes are the first to become unstable as the swirl ratio is increased and dominate the perturbation's growth in a certain range of swirl levels. In the viscous flow case, the neutral stability line is presented in a Reynolds number (Re) versus swirl ratio (ω) diagram and can be used to predict the first appearance of of axisymmetric or spiral instabilities as a function of Re and L. We will discuss and demonstrate the physical mechanism and evidences of the onset of the instability.
Flow Dynamics and Stability of the NE Greenland Ice Stream from Active Seismics and Radar
NASA Astrophysics Data System (ADS)
Riverman, K. L.; Alley, R. B.; Anandakrishnan, S.; Christianson, K. A.; Peters, L. E.; Muto, A.
2015-12-01
We find that dilatant till facilitates rapid ice flow in central Greenland, and regions of dryer till limit the expansion of ice flow. The Northeast Greenland Ice Stream (NEGIS) is the largest ice stream in Greenland, draining 8.4% of the ice sheet's area. Fast ice flow initiates near the ice sheet summit in a region of high geothermal heat flow and extends some 700km downstream to three outlet glaciers along the NE Coast. The flow pattern and stability mechanism of this ice stream are unique to others in Greenland and Antarctica, and merit further study to ascertain the sensitivity of this ice stream to future climate change. In this study, we present the results of the first-ever ground-based geophysical survey of the initiation zone of NEGIS. Based on radar and preliminary seismic data, Christianson et al. (2014, EPSL) propose a flow mechanism for the ice stream based on topographically driven hydropotential lows which generate 'sticky' regions of the bed under the ice stream margins. We further test this hypothesis using a 40km reflection seismic survey across both ice stream margins. We find that regions of 'sticky' bed as observed by the radar survey are coincident with regions of the bed with seismic returns indicating drier subglacial sediments. These findings are further supported by five amplitude-verses-offset seismic surveys indicating dilatant till within the ice stream and consolidated sediments within its margins.