Turbulence Scattering of High Harmonic Fast Waves
M. Ono; J. Hosea; B. LeBlanc; J. Menard; C.K. Phillips; R. Wilson; P. Ryan; D. Swain; J. Wilgen; S. Kubota; and T.K. Mau
2001-05-31
Effect of scattering of high-harmonic fast-magnetosonic waves (HHFW) by low-frequency plasma turbulence is investigated. Due to the similarity of the wavelength of HHFW to that of the expected low-frequency turbulence in the plasma edge region, the scattering of HHFW can become significant under some conditions. The scattering probability increases with the launched wave parallel-phase-velocity as the location of the wave cut-off layer shifts toward the lower density edge. The scattering probability can be reduced significantly with higher edge plasma temperature, steeper edge density gradient, and magnetic field. The theoretical model could explain some of the HHFW heating observations on the National Spherical Torus Experiment (NSTX).
Numerical Modeling of High Harmonic Fast Wave Heating on NSTX
NASA Astrophysics Data System (ADS)
Phillips, C. K.; Hosea, J. C.; Bell, R. E.; Leblanc, B. P.; Parker, J. B.; Valeo, E. J.; Wilson, J. R.; Ryan, P. M.; Jaeger, E. F.; Wilgen, J. B.; Sabbagh, S. A.; Bonoli, P. T.; Wright, J. C.; Harvey, R. W.; Dumont, R. J.
2007-11-01
High harmonic fast wave (HHFW) heating and current drive processes, at frequencies up to 15 times the fundamental deuterium cyclotron frequency, are being studied on NSTX. Recent experiments indicate that the core heating efficiency depends strongly on the antenna phasing and plasma conditions [1]. The wave propagation and absorption characteristics for select NSTX discharges will be analyzed using a variety of rf modeling codes, including both ray tracing and full wave models. Both core power deposition profiles and rf power flow in the edge regions will be considered. The possibility of off-axis mode conversion of the HHFW to shorter wavelength modes and the subsequent impact on power deposition will be explored. [1] See invited talk by J. C. Hosea this meeting for details
High Harmonic Fast Wave Propagation and Heating on NSTX
NASA Astrophysics Data System (ADS)
Parker, J. B.; Phillips, C. K.; Hosea, J. C.; Valeo, E. J.; Wilson, J. R.; Harvey, R. W.
2007-11-01
Recent experiments on the National Spherical Torus Experiment (NSTX) show that the high harmonic fast wave (HHFW) core heating efficiency depends on the antenna phasing and plasma conditions. [1]. Power losses in the edge due to rf sheath formation or other parasitic absorption processes could occur if the waves propagate nearly parallel to the wall in the edge regions and intersect nearby vessel structures. To investigate this possibility, the 3D HHFW propagation in NSTX has been studied both analytically and numerically with the ray tracing code GENRAY. Initial calculations show that for certain values of the launched parallel wave number and magnetic field, the waves in NSTX are launched at a shallow angle to the vessel wall. In contrast, for ICRF heating in C-Mod or ITER, the initial ray trajectories tend to be more radially oriented. Comparisons of the GENRAY results with 2D TORIC full wave simulations for the power deposition will also be discussed. [1] See invited talk by J. C. Hosea this meeting.
Recent Results from High Harmonic Fast Wave Experiments on NSTX
NASA Astrophysics Data System (ADS)
Taylor, G.; Bell, R. E.; Hosea, J. C.; Leblanc, B. P.; Phillips, C. K.; Valeo, E. J.; Wilson, J. R.; Berry, L. A.; Jaeger, E. F.; Ryan, P. M.; Wilgen, J. B.; Bonoli, P. T.; Wright, J. C.; Harvey, R. W.; Yuh, H.
2008-11-01
30 MHz high harmonic fast wave (HHFW) heating and current drive experiments in NSTX at an axial toroidal field of 0.55 T show significantly improved core power deposition and heating efficiency at lower launched toroidal wavenumbers (k||) compared to operation at or below 0.45 T. In addition, lithium wall conditioning has been effectively used to reduce the edge density resulting in the first observation of HHFW core heating at k|| = 3 m-1 in a deuterium plasma. Record core electron temperatures of 5 keV were reached with 3.1 MW HHFW power, and for the first time core HHFW electron heating of NBI-driven deuterium H-mode plasmas was obtained. Motional Stark effect measurements of the current driven in 0.55 T L-mode helium plasmas are consistent with predictions from AORSA and TORIC full-wave simulations. These improved HHFW heating results are attributed to moving the onset density for perpendicular fast wave propagation in the plasma further from the wall [1]. [1] J.C. Hosea, et al., Phys. Plasmas 15, 056104 (2008)
Results of High Harmonic Fast Wave Heating Experiments on NSTX
J.C. Hosea; R.E. Bell; M. Bitter; P. Bonoli; M. Carter; D. Gates; B.P. LeBlanc; R. Majeski; T.K. Mau; J. Menard; D. Mueller; M. Ono; S. Paul; C.K. Phillips; R. Pinsker; A. Rosenberg; P. Ryan; S.A. Sabbagh; D. Stutman; D. Swain; Y. Takase; J. Wilgen; and J.R. Wilson
2001-08-09
The study of high-harmonic fast-wave (HHFW) heating and current drive is being conducted on the National Spherical Torus Experiment (NSTX) device to determine the physics of applying radio-frequency (rf) waves at high harmonics (approximately 10-20) of the ion cyclotron frequency in this high-beta plasma regime and to extend the performance of the NSTX plasma. The magnetic field of this low aspect ratio device is lower (less than or equal to 0.35 T for this work) than that for the typical moderate aspect ratio tokamak regime by about an order of magnitude and the plasma densities achieved are typically in the mid 10(superscript ''19'') m(superscript ''-3'') range. Thus, the dielectric constant of the plasma, epsilon always equals omega (subscript ''pe'')(superscript ''2'') divided by omega (subscript ''ce'')(superscript ''2''), is of order approximately 50-100 resulting in wave physics properties which favor electron heating by TTMP and Landau damping. Radio-frequency power is applied on NSTX at 3 0 MHz using an antenna array with 12 current straps aligned in the poloidal direction. The antenna can be phased to launch waves with toroidal wave numbers, k(subscript ''T'') between 2 m(superscript ''-1'') and 14 m(superscript ''-1'') and can be phased for current drive with peak toroidal directionality at 7 m(superscript ''-1''). To date most of the HHFW experiments have been carried out using k(subscript ''T'') = 14 m(superscript ''-1'') with 0-pi-0-pi-... phasing of the strap currents. The diagnostic complement on NSTX includes a 30-Hz, 10-spatial-channel Thomson scattering (MPTS) system for measuring profiles of electron temperature and density every 33 msec, and a charge-exchange recombination spectroscopy (CHERS) system for measuring profiles of the impurity ion temperature and toroidal rotation during a neutral-beam blip. Strong electron and ion heating are observed in helium discharges, whereas the heating efficiency is noticeably reduced for deuterium
High-harmonic Fast-wave Heating in NSTX
B.P. LeBlanc; R.E. Bell; P.T. Bonoli; J.C. Hosea; D.W. Johnson; T.K. Mau; J. Menard; D. Mueller; M. Ono; F. Paoletti; S. Paul; C.K. Phillips; R. Pinsker; A. Rosenberg; P.M. Ryan , S.A. Sabbagh; D. Stutman; D.W. Swain; Y. Takase; J.B. Wilgen; J.R. Wilson
2001-06-11
High-Harmonic Fast-Wave (HHFW), a radio-frequency technique scenario applicable to high-beta plasmas, has been selected as one of the main auxiliary heating systems on the National Spherical Torus Experiment (NSTX). The HHFW antenna assembly comprises 12 toroidally adjacent current elements, extending poloidally and centered on the equatorial plane. This paper reviews experimental results obtained with a symmetrical (vacuum) launching spectrum with k|| = 14 m(superscript ''-1'') at a frequency of 30 MHz. We describe results obtained when HHFW power is applied to helium and deuterium plasmas, during the plasma-current flattop period of the discharge. Application of 1.8-MW HHFW pulse to MHD quiescent plasmas resulted in strong electron heating, during which the central electron temperature T(subscript ''eo'') more than doubled from approximately 0.5 keV to 1.15 keV. In deuterium plasmas, HHFW heating was found less efficient, with a central electron temperature increase of the order of 40% during a 1.8-MW HHFW pulse, from approximately 400 eV to approximately 550 eV. (At HHFW power of 2.4 MW, central electron temperature increased by 60%, reaching 0.625 keV.) HHFW heating in presence of MHD activity is also discussed. A short neutral-beam pulse was applied to permit charge-exchange recombination spectroscopy (CHERS) measurement of the impurity ion temperature T(subscript ''i''). Preliminary CHERS analysis show that ion temperature approximately equals electron temperature during HHFW heating. Of special interest are deuterium discharges, where the application of HHFW power was done during the current ramp-up. We observe the creation of large density gradients in the edge region. In the latter case, the density rose spontaneously to n (subscript ''eo'') less than or equal to 8 x 10 (superscript ''13'') cm (superscript ''-3'').
High-Harmonic Fast-Wave heating in NSTX
NASA Astrophysics Data System (ADS)
LeBlanc, B. P.; Bell, R. E.; Bonoli, P. T.; Hosea, J. C.; Johnson, D. W.; Mau, T. K.; Menard, J.; Mueller, D.; Ono, M.; Paoletti, F.; Paul, S.; Phillips, C. K.; Pinsker, R.; Rosenberg, A.; Ryan, P. M.; Sabbagh, S. A.; Stutman, D.; Swain, D. W.; Takase, Y.; Wilgen, J. B.; Wilson, J. R.
2001-10-01
High-Harmonic Fast-Wave (HHFW), a radio-frequency technique scenario applicable to high-beta plasmas, has been selected as one of the main auxiliary heating systems on NSTX. The HHFW antenna assembly comprises 12 toroidally adjacent current elements, extending poloidally and centered on the equatorial plane. This paper reviews experimental results obtained with a symmetrical (vacuum) launching spectrum with k∥=14 m-1 at a frequency of 30 MHz. We describe results obtained when HHFW power is applied to helium and deuterium plasmas, during the plasma-current flattop period of the discharge. Application of 1.8-MW HHFW pulse to MHD quiescent plasmas resulted in strong electron heating, during which the central electron temperature, Teo more than doubled from ≈0.05 keV to 1.15 keV. In deuterium plasmas, HHFW heating was found less efficient, with a Teo increase of the order of 40% during a 1.8-MW HHFW pulse, from ≈400 eV to ≈550 eV. (At HHFW power of 2.4 MW, Teo increased by 60%, reaching 0.625 keV.) HHFW heating in presence of MHD activity is also discussed. A short neutral beam pulse was applied to permit charge-exchange recombination spectroscopy (CHERS) measurement of the impurity ion temperature Ti. Preliminary CHERS analysis show that Ti≈Te during HHFW heating. Of special interest are deuterium discharges, where the application of HHFW power was done during the current ramp-up. We observe the creation of large density gradients in the edge region. In the latter case, the density rose spontaneously to neo⩽8×1013 cm-3.
High Harmonic Fast Wave Heating Experiments on NSTX
Wilson, J. R.; Bell, R. E.; Bitter, M.; Bonoli, P.; Carter, Mark Dwain; Gates, D.; Hosea, Joel; LeBlanc, B; Majeski, R.; Mau, T. K.; Menard, J.; Mueller, D.; Paul, S.; Phillips, Cynthia; Pinsker, R.; Rosenberg, A.; Ryan, Philip Michael; Sabbagh, S. A.; Stutman, D.; Swain, David W; Takase, Y.; Wilgen, John B
2001-01-01
A radio frequency (rf) system has been installed on the National Spherical Torus Experiment (NSTX) with the aim of heating the plasma and driving plasma current. The system consists of six rf transmitters, a twelve element antenna and associated transmission line components to distribute and couple the power from the transmitters to the antenna elements in a fashion to allow control of the antenna toroidal wavenumber spectrum. To date, power levels up to 3.85 MW have been applied to the NSTX plasmas. The frequency and spectrum of the rf waves has been selected to heat electrons via Landau damping and transit time magnetic pumping. The electron temperature has been observed to increase from 400 to 900 eV with little change in plasma density resulting in a plasma stored energy of 59 kJ , a toroidal beta, βT , =10% and a normalized beta, βn = 2.7.
Reflectometer sensing of rf waves in front of the high harmonic fast wave antenna on NSTX
Wilgen, J. B.; Ryan, P. M.; Hanson, G. R.; Swain, D. W.; Bernabei, S. I.; Greenough, N.; DePasquale, S.; Phillips, C. K.; Hosea, J. C.; Wilson, J. R.
2006-10-15
The ability to measure rf driven waves in the edge of the plasma can help to elucidate the role that surface waves and parametric decay instabilities (PDIs) play in rf power losses on NSTX. A microwave reflectometer has recently been modified to monitor rf plasma waves in the scrape-off layer in front of the 30 MHz high harmonic fast wave antenna array on NSTX. In rf heated plasmas, the plasma-reflected microwave signal exhibits 30 MHz sidebands, due primarily to the modulation of the cutoff layer by the electrostatic component of the heating wave. Similarly, electrostatic parametric decay waves (when present) are detected at frequencies below the heating frequency, near 28, 26,... MHz, separated from the heating frequency by harmonics of the local ion cyclotron frequency of about 2 MHz. In addition, a corresponding frequency matched set of decay waves is also detected near the ion cyclotron harmonics at 2, 4,... MHz. The rf plasma-wave sensing capability is useful for determination of the PDI power threshold as a function of antenna array phasing (including toroidal wavelength), outer gap spacing, and various plasma parameters such as the magnetic field and the plasma current.
Fast ion absorption of the high harmonic fast wave in the National Spherical Torus Experiment
NASA Astrophysics Data System (ADS)
Rosenberg, A. L.; Menard, J. E.; Wilson, J. R.; Medley, S. S.; Andre, R.; Phillips, C. K.; Darrow, D. S.; LeBlanc, B. P.; Redi, M. H.; Fisch, N. J.; NSTX Team, Harvey, R. W.; Mau, T. K.; Jaeger, E. F.; Ryan, P. M.; Swain, D. W.; Sabbagh, S. A.; Egedal, J.
2004-05-01
Ion absorption of the high harmonic fast wave in a spherical torus [Y.-K. M. Peng et al., Nucl. Fusion 26, 769 (1986)] is of critical importance to assessing the viability of the wave as a means of heating and driving current. Analysis of recent National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 40, 557 (2000)] shots has revealed that under some conditions when neutral beam and rf power are injected into the plasma simultaneously, a fast ion population with energy above the beam injection energy is sustained by the wave. In agreement with modeling, these experiments find the rf-induced fast ion tail strength and neutron rate at lower B-fields to be less enhanced, likely due to a larger β profile, which promotes greater off-axis absorption where the fast ion population is small. Ion loss codes find the increased loss fraction with decreased B insufficient to account for the changes in tail strength, providing further evidence that this is a rf interaction effect. Though greater ion absorption is predicted with lower k∥, surprisingly little variation in the tail was observed, along with a neutron rate enhancement with higher k∥. Data from the neutral particle analyzer, neutron detectors, x-ray crystal spectrometer, and Thomson scattering are presented, along with results from the TRANSP [R. J. Hawryluk, Physics of Plasmas Close to Thermonuclear Conditions 1, 19 (1981); J. P. H. E. Ongena et al., Fusion Technol. 33, 181 (1998)] transport analysis code, ray-tracing codes HPRT [J. Menard et al., Phys. Plasmas 6, 2002 (1999)], and CURRAY [T. K. Mau et al., RF Power in Plasmas: 13th Topical Conference (1999), p. 148], full-wave code AORSA [E. F. Jaeger et al., RF Power in Plasmas: 14th Topical Conference, 2001, p. 369], quasilinear code CQL3D [R. W. Harvey et al., in Proceedings of the IAEA TCM on Advances in Simulation and Modeling of Thermonuclear Plasmas, 1992], and ion loss codes EIGOL [D. S. Darrow et al., in Proceedings of the 6th IAEA TCM on
Modeling of high harmonic fast wave current drive on EAST tokamak
Li, J. C.; Gong, X. Y. Li, F. Y.; Dong, J. Q.; Gao, Q. D.; Zhang, N.
2015-10-15
High harmonic fast waves (HHFW) are among the candidates for non-inductive current drive (CD), which is essential for long-pulse or steady-state operation of tokamaks. Current driven with HHFW in EAST tokamak plasmas is numerically studied. The HHFW CD efficiency is found to increase non-monotonically with the wave frequency, and this phenomenon is attributed to the multi-pass absorption of HHFW. The sensitivity of CD efficiency to the value of the parallel refraction index of the launched wave is confirmed. The quasilinear effects, assessed as significant in HHFW current drive with the GENRAY/CQL3D package, cause a significant increase in CD efficiency as RF power is increased, which is very different from helicon current drive. Simulations for a range of toroidal dc electric fields, in combination with a range of fast wave powers, are also presented and indicate that the presence of the DC field can also enhance the CD efficiency.
Modeling of high harmonic fast wave current drive on EAST tokamak
NASA Astrophysics Data System (ADS)
Li, J. C.; Gong, X. Y.; Dong, J. Q.; Gao, Q. D.; Zhang, N.; Li, F. Y.
2015-10-01
High harmonic fast waves (HHFW) are among the candidates for non-inductive current drive (CD), which is essential for long-pulse or steady-state operation of tokamaks. Current driven with HHFW in EAST tokamak plasmas is numerically studied. The HHFW CD efficiency is found to increase non-monotonically with the wave frequency, and this phenomenon is attributed to the multi-pass absorption of HHFW. The sensitivity of CD efficiency to the value of the parallel refraction index of the launched wave is confirmed. The quasilinear effects, assessed as significant in HHFW current drive with the GENRAY/CQL3D package, cause a significant increase in CD efficiency as RF power is increased, which is very different from helicon current drive. Simulations for a range of toroidal dc electric fields, in combination with a range of fast wave powers, are also presented and indicate that the presence of the DC field can also enhance the CD efficiency.
Advances in high-harmonic fast wave physics in the National Spherical Torus Experiment
Taylor, G.; Bell, R. E.; Hosea, J. C.; LeBlanc, B. P.; Phillips, C. K.; Podesta, M.; Valeo, E. J.; Wilson, J. R.; Ahn, J-W.; Chen, G.; Green, D. L.; Jaeger, E. F.; Maingi, R.; Ryan, P. M.; Wilgen, J. B.; Heidbrink, W. W.; Liu, D.; Bonoli, P. T.; Brecht, T.; Choi, M.
2010-05-15
Improved core high-harmonic fast wave (HHFW) heating at longer wavelengths and during start-up and plasma current ramp-up has now been obtained by lowering the edge density with lithium wall conditioning, thereby moving the critical density for perpendicular fast-wave propagation away from the vessel wall. Lithium conditioning allowed significant HHFW core electron heating of deuterium neutral beam injection (NBI) fuelled H-mode plasmas to be observed for the first time. Large edge localized modes were observed immediately after the termination of rf power. Visible and infrared camera images show that fast wave interactions can deposit considerable rf energy on the outboard divertor. HHFW-generated parametric decay instabilities were observed to heat ions in the plasma edge and may be the cause for a measured drag on edge toroidal rotation during HHFW heating. A significant enhancement in neutron rate and fast-ion profile was measured in NBI-fuelled plasmas when HHFW heating was applied.
Advances in High-harmonic Fast Wave Physics in the National Spherical Torus Experiment
Taylor, G; Hosea, J C; LeBlanc, B P; Phillips, C K; Podesta, M; Valeo, E J; Wilson, J R; Ahn, J -W; Chen, G; Green, D L; Jaeger, E F; Maingi, R; Ryan, P M; Wilgen, J B; Heidbrink, W W; Liu, D; Bonoli, P T; Brecht, T; Choi, M
2009-12-01
Improved core high-harmonic fast wave (HHFW) heating at longer wavelengths and during start-up and plasma current ramp-up, has now been obtained by lowering the edge density with lithium wall conditioning, thereby moving the critical density for perpendicular fast-wave propagation away from the vessel wall. Lithium conditioning allowed significant HHFW core electron heating of deuterium neutral beam injection (NBI) fuelled H-mode plasmas to be observed for the first time. Large edge localized modes were observed immediately after the termination of rf power. Visible and infrared camera images show that fast wave interactions can deposit considerable rf energy on the outboard divertor. HHFW-generated parametric decay instabilities were observed to heat ions in the plasma edge and may be the cause for a measured drag on edge toroidal rotation during HHFW heating. A significant enhancement in neutron rate and fast-ion profile were measured in NBI-fuelled plasmas when HHFW heating was applied. __________________________________________________
Exploration of High Harmonic Fast Wave Heating on the National Spherical Torus Experiment
J.R. Wilson; R.E. Bell; S. Bernabei; M. Bitter; P. Bonoli; D. Gates; J. Hosea; B. LeBlanc; T.K. Mau; S. Medley; J. Menard; D. Mueller; M. Ono; C.K. Phillips; R.I. Pinsker; R. Raman; A. Rosenberg; P. Ryan; S. Sabbagh; D. Stutman; D. Swain; Y. Takase; J. Wilgen; the NSTX Team
2003-02-11
High Harmonic Fast Wave (HHFW) heating has been proposed as a particularly attractive means for plasma heating and current drive in the high-beta plasmas that are achievable in spherical torus (ST) devices. The National Spherical Torus Experiment (NSTX) [Ono, M., Kaye, S.M., Neumeyer, S., et al., Proceedings, 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque, 1999, (IEEE, Piscataway, NJ (1999), p. 53.)] is such a device. An radio-frequency (rf) heating system has been installed on NSTX to explore the physics of HHFW heating, current drive via rf waves and for use as a tool to demonstrate the attractiveness of the ST concept as a fusion device. To date, experiments have demonstrated many of the theoretical predictions for HHFW. In particular, strong wave absorption on electrons over a wide range of plasma parameters and wave parallel phase velocities, wave acceleration of energetic ions, and indications of current drive for directed wave spectra have been observed. In addition HHFW heating has been used to explore the energy transport properties of NSTX plasmas, to create H-mode (high-confinement mode) discharges with a large fraction of bootstrap current and to control the plasma current profile during the early stages of the discharge.
Recent Developments in High-Harmonic Fast Wave Physics in NSTX
B.P. LeBlanc, R.E. Bell, P. Bonoli, R. Harvey, W.W. Heidbrink, J.C. Hosea, S.M. Kaye, D. Liu, R. Maingi, S.S. Medley, M. Ono, M. Podestà, C.K. Phillips, P.M. Ryan, A.L. Roquemore, G. Taylor, J.R. Wilson and the NSTX Team
2010-10-06
Understanding the interaction between ion cyclotron range of frequency (ICRF) fast waves and the fast-ions created by neutral beam injection (NBI) is critical for future devices such as ITER, which rely on a combination ICRF and NBI. Experiments in NSTX which use 30 MHz High-Harmonic Fast-Wave (HHFW) ICRF and NBI heating show a competition between electron heating via Landau damping and transit-time magnetic pumping, and radio-frequency wave acceleration of NBI generated fast ions. Understanding and mitigating some of the power loss mechanisms outside the last closed flux surface (LCFS) has resulted in improved HHFW heating inside the LCFS. Nevertheless a significant fraction of the HHFW power is diverted away from the enclosed plasma. Part of this power is observed locally on the divertor. Experimental observations point toward the radio-frequency (RF) excitation of surface waves, which disperse wave power outside the LCFS, as a leading loss mechanism. Lithium coatings lower the density at the antenna, thereby moving the critical density for perpendicular fast-wave propagation away from the antenna and surrounding material surfaces. Visible and infrared imaging reveal flows of RF power along open field lines into the divertor region. In L-mode -- low average NBI power -- conditions, the fast-ion D-alpha (FIDA) diagnostic measures a near doubling and broadening of the density profile of the upper energetic level of the fast ions concurrent with the presence of HHFW power launched with k// =-8m-1. We are able to heat NBI-induced H-mode plasmas with HHFW. The captured power is expected to be split between absorption by the electrons and absorption by the fast ions, based on TORIC calculation. In the case discussed here the Te increases over the whole profile when ~2MW of HHFW power with antenna k// =13m-1 is applied after the H-mode transition.. But somewhat unexpectedly fast-ion diagnostics do not observe a change between the HHFW heated NBI discharge and the
Transition From High Harmonic Fast Wave to Whistler/Helicon Regime in Tokamaks
NASA Astrophysics Data System (ADS)
Harris, S. P.; Pinsker, R. I.; Porkolab, M.
2014-10-01
Experiments are being prepared1 on DIII-D in which fast waves (FWs) at 0.5 GHz will be used to drive current noninductively in the mid-radius region. Previous DIII-D experiments used FWs at ~0.1 GHz to drive central current; in this work we examine the frequency dependence of wave propagation and damping in the 0.1-1.0 GHz range with the goal of identifying the optimum frequency range for a particular application. Strongly enhanced electron damping and reduced ion damping at higher frequencies must be weighed against increasing coupling difficulties at higher frequencies and more restrictive wave accessibility at low toroidal field. Wave propagation and accessibility is studied with ray tracing models in slab, cylindrical, and fully toroidal geometries. Analytic expressions for electron and ion damping will be derived with an emphasis on understanding the transition from the moderate-to-high ion cyclotron harmonic regime to the very high harmonic or ``whistler''/``helicon''/lower hybrid FW regime. Work supported in part by the National Undergraduate Fellowship Program in Plasma Physics and Fusion Energy Sciences and the US Department of Energy under DE-FC02-04ER54698.
Advances in High Harmonic Fast Wave Heating of NSTX H-mode Plasmas
Ryan, Philip Michael; Ahn, Joonwook; Bell, R. E.; Bonoli, P.; Chen, Guangye; Green, David L; Harvey, R. W.; Hosea, J.; Jaeger, Erwin Frederick; Kaye, S.; LeBlanc, B; Maingi, Rajesh; Phillips, Cynthia; Podesta, M.; Taylor, G.; Wilgen, John B; Wilson, J. R.
2010-01-01
High-harmonic fast wave (HHFW) heating and current drive is being developed in NSTX to provide bulk electron heating and q(0) control during non-inductively sustained Hmode plasmas fuelled by deuterium neutral-beam injection (NBI). In addition, it is used to assist the plasma current ramp-up. A major modification to increase the RF power limit was made in 2009; the original end-grounded, single end-powered current straps of the 12- element array were replaced with center-grounded, double end-powered straps. Greater than 3 MW have been coupled into NBI-driven, ELMy H-mode plasmas with this upgraded antenna. Improved core HHFW heating, particularly at longer wavelengths and during low-density start-up and plasma current ramp-up, has been obtained by lowering the edge density with lithium wall conditioning, thereby moving the critical density for fast-wave propagation away from the vessel wall [1]. Significant core electron heating of NBI-fuelled H-modes has been observed for the first time over a range of launched wavelengths and H-modes can be accessed by HHFW alone. Visible and IR camera images of the antenna and divertor indicate that fast wave interactions can deposit considerable RF energy on the outboard divertor plate, especially at longer wavelengths that begin to propagate closer to the vessel walls. Edge power loss can also arise from HHFWgenerated parametric decay instabilities; edge ion heating is observed that is wavelength dependent. During plasmas where HHFW is combined with NBI, there is a significant enhancement in neutron rate, and fast-ion D-alpha (FIDA) emission measurements clearly show broadening of the fast-ion profile in the plasma core. Large edge localized modes (ELMs) have been observed immediately following the termination of RF power, whether the power turn off is programmed or due to antenna arcing. Causality has not been established but new experiments are planned and will be reported. Fast digitization of the reflected power signal
Edge Ion Heating by Launched High Harmonic Fast Waves in NSTX
T.M. Biewer; R.E. Bell; S.J. Diem; C.K. Phillips; J.R. Wilson; P.M. Ryan
2004-12-01
A new spectroscopic diagnostic on the National Spherical Torus Experiment (NSTX) measures the velocity distribution of ions in the plasma edge simultaneously along both poloidal and toroidal views. An anisotropic ion temperature is measured during high-power high harmonic fast wave (HHFW) radio-frequency (rf) heating in helium plasmas, with the poloidal ion temperature roughly twice the toroidal ion temperature. Moreover, the measured spectral distribution suggests that two populations of ions are present and have temperatures of typically 500 eV and 50 eV with rotation velocities of -50 km/s and -10 km/s, respectively (predominantly perpendicular to the local magnetic field). This bi-modal distribution is observed in both the toroidal and poloidal views (for both He{sup +} and C{sup 2+} ions), and is well correlated with the period of rf power application to the plasma. The temperature of the hot component is observed to increase with the applied rf power, which was scanned between 0 and 4.3 MW . The 30 MHz HHFW launched by the NSTX antenna is expected and observed to heat core electrons, but plasma ions do not resonate with the launched wave, which is typically at >10th harmonic of the ion cyclotron frequency in the region of observation. A likely ion heating mechanism is parametric decay of the launched HHFW into an Ion Bernstein Wave (IBW). The presence of the IBW in NSTX plasmas during HHFW application has been directly confirmed with probe measurements. IBW heating occurs in the perpendicular ion distribution, consistent with the toroidal and poloidal observations. Calculations of IBW propagation indicate that multiple waves could be created in the parametric decay process, and that most of the IBW power would be absorbed in the outer 10 to 20 cm of the plasma, predominantly on fully stripped ions. These predictions are in qualitative agreement with the observations, and must be accounted for when calculating the energy budget of the plasma.
A.L. Rosenberg; J.E. Menard; J.R. Wilson; S. Medle; C.K. Phillips; R. Andre; D.S. Darro; R.J. Dumont; B.P. LeBlanc; M.H. Redi; T.K. Mau; E. F. Jaeger; P.M. Ryan; D.W. Swain; R.W. Harvey; J. Egedal; the NSTX Team
2003-08-19
Ion absorption of the high harmonic fast wave in a spherical torus is of critical importance to assessing the viability of the wave as a means of heating and driving current. Analysis of recent National Spherical Torus Experiment (NSTX) shots has revealed that under some conditions when neutral beam and radio-frequency (RF) power are injected into the plasma simultaneously, a fast ion population with energy above the beam injection energy is sustained by the wave. In agreement with modeling, these experiments find the RF-induced fast ion tail strength and neutron rate at lower B-fields to be less enhanced, likely due to a larger beta profile, which promotes greater off-axis absorption where the fast ion population is small. Ion loss codes find the increased loss fraction with decreased B insufficient to account for the changes in tail strength, providing further evidence that this is an RF interaction effect. Though greater ion absorption is predicted with lower k(sub)||, surprisingly little variation in the tail was observed, along with a small neutron rate enhancement with higher k(sub)||. Data from the neutral particle analyzer, neutron detectors, X-ray crystal spectrometer, and Thomson scattering is presented, along with results from the TRANSP transport analysis code, ray-tracing codes HPRT and CURRAY, full-wave code and AORSA, quasi-linear code CQL3D, and ion loss codes EIGOL and CONBEAM.
High-harmonic fast-wave power flow along magnetic field lines in the scrape-off layer of NSTX.
Perkins, R J; Hosea, J C; Kramer, G J; Ahn, J-W; Bell, R E; Diallo, A; Gerhardt, S; Gray, T K; Green, D L; Jaeger, E F; Jaworski, M A; LeBlanc, B P; McLean, A; Maingi, R; Phillips, C K; Roquemore, L; Ryan, P M; Sabbagh, S; Taylor, G; Wilson, J R
2012-07-27
A significant fraction of high-harmonic fast-wave (HHFW) power applied to NSTX can be lost to the scrape-off layer (SOL) and deposited in bright and hot spirals on the divertor rather than in the core plasma. We show that the HHFW power flows to these spirals along magnetic field lines passing through the SOL in front of the antenna, implying that the HHFW power couples across the entire width of the SOL rather than mostly at the antenna face. This result will help guide future efforts to understand and minimize these edge losses in order to maximize fast-wave heating and current drive. PMID:23006093
High-Harmonic Fast-Wave Power Flow Along Magnetic Field Lines in the Scrape-Off Layer of NSTX
Perkins, R. J.; Hosea, J.; Kramer, G.; Ahn, Joonwook; Bell, R. E.; Diallo, A.; Gerhardt, S.; Gray, T. K.; Green, David L; Jaeger, Erwin Frederick; Jaworski, M. A.; LeBlanc, B; McLean, Adam G; Maingi, Rajesh; Phillips, C. K.; Roquemore, L.; Ryan, Philip Michael; Sabbagh, S. A.; Taylor, G.; Wilson, J. R.
2012-01-01
A significant fraction of high-harmonic fast-wave (HHFW) power applied to NSTX can be lost to the scrape-off layer (SOL) and deposited in bright and hot spirals on the divertor rather than in the core plasma. We show that the HHFW power flows to these spirals along magnetic field lines passing through the SOL in front of the antenna, implying that the HHFW power couples across the entire width of the SOL rather than mostly at the antenna face. This result will help guide future efforts to understand and minimize these edge losses in order to maximize fast-wave heating and current drive.
HEATING AND CURRENT DRIVE IN NSTX WITH ELECTRON BERNSTEIN WAVES AND HIGH HARMONIC FAST WAVES
Ram, Abhay K
2010-06-14
A suitable theoretical and computational framework for studying heating and current drive by electron Bernstein waves in the National Spherical Torus Experiment has been developed. This framework can also be used to study heating and current drive by electron Bernstein waves in spherical tori and other magnetic confinement devices. It is also useful in studying the propagation and damping of electron cyclotron waves in the International Thermonuclear Experimental Reactor
Full Wave Modeling of High Harmonic Fast Wave Heating in NSTX
NASA Astrophysics Data System (ADS)
Phillips, C. K.; Bernabei, S.; Hosea, J.; Leblanc, B.; Wilson, J. R.; Bonoli, P. T.; Wright, J. C.; Jaeger, E. F.; Ryan, P.; Swain, D.
2004-11-01
Previous modeling of HHFW heating experiments predicted that the 2D nature of the magnetic equilibrium as well as the assumed antenna spectrum should strongly influence the wave propagation and power absorption in NSTX. Recently, a detailed series of HHFW heating experiments using modulated rf power waveforms have been performed on NSTX for a variety of antenna phasings and plasma conditions [1]. The power deposition profiles inferred from this experimental data will be compared to simulations obtained with the TORIC-HHFW [M. Brambilla, Pl. Phys. Controlled Fus. 44(2002)2423] and AORSA [E.F. Jaeger et al., Phys. Plasmas 8(2001)1573] full wave modeling codes. Though both the AORSA and TORIC-HHFW models make no assumptions about the relative size of the Larmor radius to the wavelength, AORSA solves the full integral wave equation, while TORIC-HHFW uses a generalized quasi-local approximation to effectively retain only the HHFW in the wave equation.1] See posters by. S. Bernabei et al and J. Hosea et al, this conference.
J. Hosea, R. E. Bell, B.P. LeBlanc, C.K. Phillips, G. Taylor, E. Valeo, J.R. Wilson, E.F. Jaeger, P.M. Ryan, J. Wilgen, H. Yuh, F. Levinton, S. Sabbagh, K. Tritz, J. Parker, P.T. Bonoli, R. Harvey, and the NSTX Team
2008-01-14
High harmonic fast wave heating and current drive (CD) are being developed on the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 41, 1435 (2001)] for supporting startup and sustainment of the ST plasma. Considerable enhancement of the core heating efficiency (η) from 44% to 65% has been obtained for CD phasing of the antenna (strap-to-strap φ = -90o, kφ = -8 m-1) by increasing the magnetic field from 4.5 kG to 5.5 kG. This increase in efficiency is strongly correlated to moving the location of the onset density for perpendicular fast wave propagation (nonset ∝ ΒΦ× k|| 2/w) away from the antenna face and wall, and hence reducing the propagating surface wave fields. RF waves propagating close to the wall at lower BΦ and k|| can enhance power losses from both the parametric decay instability (PDI) and wave dissipation in sheaths and structures around the machine. The improved efficiency found here is attributed to a reduction in the latter, as PDI losses are little changed at the higher magnetic field. Under these conditions of higher coupling efficiency, initial measurements of localized CD effects have been made and compared with advanced RF code simulations
Hosea, J.; Bell, R. E.; LeBlanc, B. P.; Phillips, C. K.; Taylor, G.; Valeo, E.; Wilson, J. R.; Jaeger, E. F.; Ryan, P. M.; Wilgen, J.; Yuh, H.; Levinton, F.; Sabbagh, S.; Tritz, K.; Parker, J.; Bonoli, P. T.; Harvey, R.
2008-05-15
High harmonic fast wave heating and current drive (CD) are being developed on the National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 41, 1435 (2001)] for supporting startup and sustainment of the spherical torus plasma. Considerable enhancement of the core heating efficiency ({eta}) from 44% to 65% has been obtained for CD phasing of the antenna (strap-to-strap {phi}=-90 deg., k{sub {phi}}=-8 m{sup -1}) by increasing the magnetic field from 4.5 to 5.5 kG. This increase in efficiency is strongly correlated to moving the location of the onset density for perpendicular fast wave propagation (n{sub onset}{proportional_to}Bxk{sub parallel}{sup 2}/{omega}) away from the antenna face and wall, and hence reducing the propagating surface wave fields. Radio frequency (RF) waves propagating close to the wall at lower B and k{sub parallel} can enhance power losses from both the parametric decay instability (PDI) and wave dissipation in sheaths and structures around the machine. The improved efficiency found here is attributed to a reduction in the latter, as PDI losses are little changed at the higher magnetic field. Under these conditions of higher coupling efficiency, initial measurements of localized CD effects have been made and compared with advanced RF code simulations.
Hosea, J.; Bell, R. E.; LeBlanc, B; Phillips, Cynthia; Taylor, G.; Valeo, Dr Ernest; Wilson, J. R.; Jaeger, Erwin Frederick; Ryan, Philip Michael; Wilgen, John B; Yuh, H.; Levinton, F.; Sabbagh, S. A.; Tritz, K.; Parker, J.; Bonoli, P.; Harvey, R. W.
2008-01-01
High harmonic fast wave heating and current drive CD are being developed on the National Spherical Torus Experiment M. Ono et al., Nucl. Fusion 41, 1435 2001 for supporting startup and sustainment of the spherical torus plasma. Considerable enhancement of the core heating efficiency from 44% to 65% has been obtained for CD phasing of the antenna strap-to-strap = 90 , k= 8 m 1 by increasing the magnetic field from 4.5 to 5.5 kG. This increase in efficiency is strongly correlated to moving the location of the onset density for perpendicular fast wave propagation nonsetBk 2 / away from the antenna face and wall, and hence reducing the propagating surface wave fields. Radio frequency RF waves propagating close to the wall at lower B and k can enhance power losses from both the parametric decay instability PDI and wave dissipation in sheaths and structures around the machine. The improved efficiency found here is attributed to a reduction in the latter, as PDI losses are little changed at the higher magnetic field. Under these conditions of higher coupling efficiency, initial measurements of localized CD effects have been made and compared with advanced RF code simulations.
NASA Astrophysics Data System (ADS)
Bertelli, N.; Jaeger, E. F.; Lau, C.; Blazevski, D.; Green, D. L.; Berry, L.; Bonoli, P. T.; Gerhardt, S.; Hosea, J. C.; LeBlanc, B.; Perkins, R. J.; Phillips, C. K.; Pinsker, R. I.; Prater, R.; Qin, C. M.; Ryan, P. M.; Taylor, G.; Valeo, E. J.; Wilson, J. R.; Wright, J. C.; Zhang, X. J.
2015-12-01
Several experiments on different machines and in different fast wave (FW) heating regimes, such as hydrogen minority heating and high harmonic fast waves, have found strong interactions between radio-frequency (RF) waves and the scrape-off layer (SOL) region. This paper examines the propagation and the power loss in the SOL by using the full wave code AORSA, in which the edge plasma beyond the last closed flux surface (LCFS) is included in the solution domain and a collisional damping parameter is used as a proxy to represent the real, and most likely nonlinear, damping processes. 3D AORSA results for the National Spherical Torus eXperiment (NSTX), where a full antenna spectrum is reconstructed, are shown, confirming the same behavior found for a single toroidal mode results in Bertelli et al, Nucl. Fusion, 54 083004, 2014, namely, a strong transition to higher SOL power losses (driven by the RF field) when the FW cut-off is moved away from in front of the antenna by increasing the edge density. Additionally, full wave simulations have been extended to "conventional" tokamaks with higher aspect ratios, such as the DIII-D, Alcator C-Mod, and EAST devices. DIII-D results show similar behavior found in NSTX and NSTX-U, consistent with previous DIII-D experimental observations. In contrast, a different behavior has been found for Alcator C-Mod and EAST, which operate in the minority heating regime unlike NSTX/NSTX-U and DIII-D, which operate in the mid/high harmonic regime. A substantial discussion of some of the main aspects, such as (i) the pitch angle of the magnetic field; (ii) minority heating vs. mid/high harmonic regimes is presented showing the different behavior of the RF field in the SOL region for NSTX-U scenarios with different plasma current. Finally, the preliminary results of the impact of the SOL region on the evaluation of the helicon current drive efficiency in DIII-D is presented for the first time and briefly compared with the different regimes
Bertelli, N. Gerhardt, S.; Hosea, J. C.; LeBlanc, B.; Perkins, R. J.; Phillips, C. K.; Taylor, G.; Valeo, E. J.; Wilson, J. R.; Jaeger, E. F.; Lau, C.; Blazevski, D.; Green, D. L.; Berry, L.; Ryan, P. M.; Bonoli, P. T.; Wright, J. C.; Pinsker, R. I.; Prater, R.; Qin, C. M.; and others
2015-12-10
Several experiments on different machines and in different fast wave (FW) heating regimes, such as hydrogen minority heating and high harmonic fast waves, have found strong interactions between radio-frequency (RF) waves and the scrape-off layer (SOL) region. This paper examines the propagation and the power loss in the SOL by using the full wave code AORSA, in which the edge plasma beyond the last closed flux surface (LCFS) is included in the solution domain and a collisional damping parameter is used as a proxy to represent the real, and most likely nonlinear, damping processes. 3D AORSA results for the National Spherical Torus eXperiment (NSTX), where a full antenna spectrum is reconstructed, are shown, confirming the same behavior found for a single toroidal mode results in Bertelli et al, Nucl. Fusion, 54 083004, 2014, namely, a strong transition to higher SOL power losses (driven by the RF field) when the FW cut-off is moved away from in front of the antenna by increasing the edge density. Additionally, full wave simulations have been extended to “conventional” tokamaks with higher aspect ratios, such as the DIII-D, Alcator C-Mod, and EAST devices. DIII-D results show similar behavior found in NSTX and NSTX-U, consistent with previous DIII-D experimental observations. In contrast, a different behavior has been found for Alcator C-Mod and EAST, which operate in the minority heating regime unlike NSTX/NSTX-U and DIII-D, which operate in the mid/high harmonic regime. A substantial discussion of some of the main aspects, such as (i) the pitch angle of the magnetic field; (ii) minority heating vs. mid/high harmonic regimes is presented showing the different behavior of the RF field in the SOL region for NSTX-U scenarios with different plasma current. Finally, the preliminary results of the impact of the SOL region on the evaluation of the helicon current drive efficiency in DIII-D is presented for the first time and briefly compared with the different regimes
Bertelli, Nicola; Jaeger, E. F.; Lau, Cornwall H; Blazevski, Dan; Green, David L; Berry, Lee Alan; Bonoli, P. T.; Gerhardt, S.P.; Hosea, J. C.; LeBlanc, B.; Perkins, R. J.; Phillips, Cynthia; Pinsker, R. I.; Prater, R.; Qin, C M; Ryan, P. M.; Taylor, G.; Valeo, E. J.; Wilson, Randy; Wright, J.; Zhang, X J
2015-01-01
Several experiments on different machines and in different fast wave (FW) heating regimes, such as hydrogen minority heating and high harmonic fast waves, have found strong interactions between radio-frequency (RF) waves and the scrape-off layer (SOL) region. This paper examines the propagation and the power loss in the SOL by using the full wave code AORSA, in which the edge plasma beyond the last closed flux surface (LCFS) is included in the solution domain and a collisional damping parameter is used as a proxy to represent the real, and most likely nonlinear, damping processes. 3D AORSA results for the National Spherical Torus eXperiment (NSTX), where a full antenna spectrum is reconstructed, are shown, confirming the same behavior found for a single toroidal mode results in Bertelli et al, Nucl. Fusion, 54 083004, 2014, namely, a strong transition to higher SOL power losses (driven by the RF field) when the FW cut-off is moved away from in front of the antenna by increasing the edge density. Additionally, full wave simulations have been extended to "conventional" tokamaks with higher aspect ratios, such as the DIII-D, Alcator C-Mod, and EAST devices. DIII-D results show similar behavior found in NSTX and NSTX-U, consistent with previous DIII-D experimental observations. In contrast, a different behavior has been found for Alcator C-Mod and EAST, which operate in the minority heating regime unlike NSTX/NSTX-U and DIII-D, which operate in the mid/high harmonic regime. A substantial discussion of some of the main aspects, such as (i) the pitch angle of the magnetic field; (ii) minority heating vs. mid/high harmonic regimes is presented showing the different behavior of the RF field in the SOL region for NSTX-U scenarios with different plasma current. Finally, the preliminary results of the impact of the SOL region on the evaluation of the helicon current drive efficiency in DIII-D is presented for the first time and briefly compared with the different regimes
NASA Astrophysics Data System (ADS)
Bertelli, N.; Jaeger, E. F.; Hosea, J. C.; Phillips, C. K.; Berry, L.; Bonoli, P. T.; Gerhardt, S. P.; Green, D.; LeBlanc, B.; Perkins, R. J.; Qin, C. M.; Pinsker, R. I.; Prater, R.; Ryan, P. M.; Taylor, G.; Valeo, E. J.; Wilson, J. R.; Wright, J. C.; Zhang, X. J.
2016-01-01
Several experiments on different machines and in different fast wave (FW) heating regimes, such as hydrogen minority heating and high harmonic fast waves (HHFW), have found strong interaction between radio-frequency (RF) waves and the scrape-off layer (SOL) region. This paper examines the propagation and the power loss in the SOL by using the full wave code AORSA, in which the edge plasma beyond the last closed flux surface (LCFS) is included in the solution domain and a collisional damping parameter is used as a proxy to represent the real, and most likely nonlinear, damping processes. 2D and 3D AORSA results for the National Spherical Torus eXperiment (NSTX) have shown a strong transition to higher SOL power losses (driven by the RF field) when the FW cut-off is removed from in front of the antenna by increasing the edge density. Here, full wave simulations have been extended for ‘conventional’ tokamaks with higher aspect ratios, such as the DIII-D, Alcator C-Mod, and EAST devices. DIII-D results in HHFW regime show similar behavior found in NSTX and NSTX-U, consistent with previous DIII-D experimental observations. In contrast, a different behavior has been found for C-Mod and EAST, which operate in the minority heating regime. This article is dedicated to the memory of Cynthia K. Phillips
Bertelli, N.; Jaeger, E. F.; Hosea, J. C.; Phillips, C. K.; Berry, L.; Bonoli, P. T.; Gerhardt, S. P.; Green, D.; LeBlanc, B.; Perkins, R. J.; Qin, C. M.; Pinsker, R. I.; Prater, R.; Ryan, P. M.; Taylor, G.; Valeo, E. J.; Wilson, J. R.; Wright, J. C.; Zhang, X. J.
2015-12-17
Several experiments on different machines and in different fast wave (FW) heating regimes, such as hydrogen minority heating and high harmonic fast waves (HHFW), have found strong interaction between radio-frequency (RF) waves and the scrape-off layer (SOL) region. This paper examines the propagation and the power loss in the SOL by using the full wave code AORSA, in which the edge plasma beyond the last closed flux surface (LCFS) is included in the solution domain and a collisional damping parameter is used as a proxy to represent the real, and most likely nonlinear, damping processes. 2D and 3D AORSA results for the National Spherical Torus eXperiment (NSTX) have shown a strong transition to higher SOL power losses (driven by the RF field) when the FW cut-off is removed from in front of the antenna by increasing the edge density. Here, full wave simulations have been extended for 'conventional' tokamaks with higher aspect ratios, such as the DIII-D, Alcator C-Mod, and EAST devices. DIII-D results in HHFW regime show similar behavior found in NSTX and NSTX-U, consistent with previous DIII-D experimental observations. In contrast, a different behavior has been found for C-Mod and EAST, which operate in the minority heating regime.
Bertelli, N.; Jaeger, E. F.; Hosea, J. C.; Phillips, C. K.; Berry, L.; Bonoli, P. T.; Gerhardt, S. P.; Green, D.; LeBlanc, B.; Perkins, R. J.; et al
2015-12-17
Here, several experiments on different machines and in different fast wave (FW) heating regimes, such as hydrogen minority heating and high harmonic fast waves (HHFW), have found strong interaction between radio-frequency (RF) waves and the scrape-off layer (SOL) region. This paper examines the propagation and the power loss in the SOL by using the full wave code AORSA, in which the edge plasma beyond the last closed flux surface (LCFS) is included in the solution domain and a collisional damping parameter is used as a proxy to represent the real, and most likely nonlinear, damping processes. 2D and 3D AORSAmore » results for the National Spherical Torus eXperiment (NSTX) have shown a strong transition to higher SOL power losses (driven by the RF field) when the FW cut-off is removed from in front of the antenna by increasing the edge density. Here, full wave simulations have been extended for 'conventional' tokamaks with higher aspect ratios, such as the DIII-D, Alcator C-Mod, and EAST devices. DIII-D results in HHFW regime show similar behavior found in NSTX and NSTX-U, consistent with previous DIII-D experimental observations. In contrast, a different behavior has been found for C-Mod and EAST, which operate in the minority heating regime.« less
Bertelli, N.; Jaeger, E. F.; Hosea, J. C.; Phillips, C. K.; Berry, L.; Bonoli, P. T.; Gerhardt, S. P.; Green, D.; LeBlanc, B.; Perkins, R. J.; Qin, C. M.; Pinsker, R. I.; Prater, R.; Ryan, P. M.; Taylor, G.; Valeo, E. J.; Wilson, J. R.; Wright, J. C.; Zhang, X. J.
2015-12-17
Here, several experiments on different machines and in different fast wave (FW) heating regimes, such as hydrogen minority heating and high harmonic fast waves (HHFW), have found strong interaction between radio-frequency (RF) waves and the scrape-off layer (SOL) region. This paper examines the propagation and the power loss in the SOL by using the full wave code AORSA, in which the edge plasma beyond the last closed flux surface (LCFS) is included in the solution domain and a collisional damping parameter is used as a proxy to represent the real, and most likely nonlinear, damping processes. 2D and 3D AORSA results for the National Spherical Torus eXperiment (NSTX) have shown a strong transition to higher SOL power losses (driven by the RF field) when the FW cut-off is removed from in front of the antenna by increasing the edge density. Here, full wave simulations have been extended for 'conventional' tokamaks with higher aspect ratios, such as the DIII-D, Alcator C-Mod, and EAST devices. DIII-D results in HHFW regime show similar behavior found in NSTX and NSTX-U, consistent with previous DIII-D experimental observations. In contrast, a different behavior has been found for C-Mod and EAST, which operate in the minority heating regime.
NASA Astrophysics Data System (ADS)
Carlsson, J. A.; Wilson, J. R.; Hosea, J. C.; Greenough, N. L.; Perkins, R. J.
2016-06-01
Third-order spectral analysis, in particular, the auto bicoherence, was applied to probe signals from high-harmonic fast-wave heating experiments in the National Spherical Torus Experiment. Strong evidence was found for parametric decay of the 30 MHz radio-frequency (RF) pump wave, with a low-frequency daughter wave at 2.7 MHz, the local majority-ion cyclotron frequency. The primary decay modes have auto bicoherence values around 0.85, very close to the theoretical value of one, which corresponds to total phase coherence with the pump wave. The threshold RF pump power for onset of parametric decay was found to be between 200 kW and 400 kW.
Taylor, G.; Hosea, J.; Kessel, C. E.; LeBlanc, B; Mueller, D.; Phillips, C. K.; Valeo, E. J.; Wilson, J. R.; Ryan, Philip Michael; Bonoli, P.; Harvey, R. W.
2012-01-01
A deuterium H-mode discharge with a plasma current of 300 kA, an axial toroidal magnetic field of 0.55 T, and a calculated non-inductive plasma current fraction of 0.7 1 has been generated in the National Spherical Torus Experiment by 1.4MW of 30MHz high-harmonic fast wave (HHFW) heating and current drive. Seventy-five percent of the non-inductive current was generated inside an internal transport barrier that formed at a normalized minor radius 0.4. Three quarters of the non-inductive current was bootstrap current, and the remaining non-inductive current was generated directly by HHFW power inside a normalized minor radius 0.2. VC 2012 American Institute of Physics.
NASA Astrophysics Data System (ADS)
Taylor, G.; Poli, F.; Bertelli, N.; Harvey, R. W.; Hosea, J. C.; Mueller, D.; Perkins, R. J.; Phillips, C. K.; Raman, R.
2015-12-01
A major challenge for spherical tokamak development is to start-up and ramp-up the plasma current (Ip) without using a central solenoid. Experiments in the National Spherical Torus eXperiment (NSTX) demonstrated that 1.4 MW of 30 MHz high-harmonic fast wave (HHFW) power could generate an Ip = 300 kA H-mode discharge with a non-inductive Ip fraction, fNI ˜ 0.7. The discharge had an axial toroidal magnetic field (BT(0)) of 0.55 T, the maximum BT(0) available on NSTX. NSTX has undergone a major upgrade (NSTX-U), that will eventually allow the generation of BT(0) ≤ 1 T and Ip ≤ 2 MA plasmas. Full wave simulations of 30 MHz HHFW and medium harmonic fast wave (MHFW) heating in NSTX-U predict significantly reduced FW power loss in the plasma edge at the higher BT(0) achievable in NSTX-U. HHFW experiments will aim to generate stable, fNI ˜ 1, Ip = 300 kA H-mode plasmas and to ramp Ip from 250 to 400 kA with FW power. Time-dependent TRANSP simulations are used to develop non-inductive Ip ramp-up and sustainment using 30 MHz FW power. This paper presents results from these RF simulations and plans for developing non-inductive plasmas heated by FW power.
G. Taylor, P.T. Bonoli, R.W. Harvey, J.C. hosea, E.F. Jaeger, B.P. LeBlanc, C.K. Phillisp, P.M. Ryan, E.J. Valeo, J.R. Wilson, J.C. Wright, and the NSTX Team
2012-07-25
A critical research goal for the spherical torus (ST) program is to initiate, ramp-up, and sustain a discharge without using the central solenoid. Simulations of non-solenoidal plasma scenarios in the National Spherical Torus Experiment (NSTX) [1] predict that high-harmonic fast wave (HHFW) heating and current drive (CD) [2] can play an important roll in enabling fully non-inductive (fNI {approx} 1) ST operation. The NSTX fNI {approx} 1 strategy requires 5-6 MW of HHFW power (PRF) to be coupled into a non-inductively generated discharge [3] with a plasma current, Ip {approx} 250-350 kA, driving the plasma into an HHFW H-mode with Ip {approx} 500 kA, a level where 90 keV deuterium neutral beam injection (NBI) can heat the plasma and provide additional CD. The initial approach on NSTX has been to heat Ip {approx} 300 kA, inductively heated, deuterium plasmas with CD phased HHFW power [2], in order to drive the plasma into an H-mode with fNI {approx} 1.
NASA Astrophysics Data System (ADS)
Perkins, R. J.; Ahn, J.-W.; Bortolon, A.; Brunkhorst, C.; Ellis, R.; Fredd, E.; Greenough, N.; Hosea, J. C.; Kung, C.; Miller, D.
2015-12-01
The twelve-strap high-harmonic fast-wave (HHFW) antenna on NSTX has exhibited a high-voltage standoff around 25 kV during previous experimental campaigns; this standoff needs to be improved for increased power coupling. During the recent NSTX-U upgrade period, a test-stand was set up with two antenna straps along with Faraday screens for testing purposes. Using a diagnostic suite consisting of a fast camera, a residual gas analyzer, a pressure gage, high-voltage probes, and an infrared camera, several interesting discoveries were made, leading to possible improvements of the antenna RF voltage operation level. First, arcing was observed outside the Faraday shields towards the low-voltage ("grounded") end of the straps (faraday shield box ends); this arcing was successfully eliminated by installing an additional grounding point between the Faraday shield box and the vessel wall. Second, considerable outgassing was observed during the RF pulse and the amount of outgassing was found to decrease with increasing RF power, possibly indicative of multipacting. Finally, infrared camera measurements of heating on the Faraday shield assembly suggest that the return currents on the Faraday shield box are highly localized at the box sides and possibly account for the pressure increase observed. Computations of these RF currents using Microwave Studio show qualitative agreement with the heated regions. New grounding points between the antenna box and the vessel have been implemented in NSTX-U, where future tests will be done to determine if the high-voltage standoff has improved. Further antenna improvements will be sought through future experiments on the test stand.
Perkins, R. J.; Ahn, J.W.; Bortolon, A.; Brunkhorst, C.; Ellis, R.; Fredd, E.; Greenough, Nevell; Hosea, J.; Kung, C. C.; Miller, D.
2015-01-01
The twelve-strap high-harmonic fast-wave (HHFW) antenna on NSTX has exhibited a high-voltage standoff around 25 kV during previous experimental campaigns; this standoff needs to be improved for increased power coupling. During the recent NSTX-U upgrade period, a test-stand was set up with two antenna straps along with Faraday screens for testing purposes. Using a diagnostic suite consisting of a fast camera, a residual gas analyzer, a pressure gage, high-voltage probes, and an infrared camera, several interesting discoveries were made, leading to possible improvements of the antenna RF voltage operation level. First, arcing was observed outside the Faraday shields towards the low-voltage ("grounded") end of the straps (faraday shield box ends); this arcing was successfully eliminated by installing an additional grounding point between the Faraday shield box and the vessel wall. Second, considerable outgassing was observed during the RF pulse and the amount of outgassing was found to decrease with increasing RF power, possibly indicative of multipacting. Finally, infrared camera measurements of heating on the Faraday shield assembly suggest that the return currents on the Faraday shield box are highly localized at the box sides and possibly account for the pressure increase observed. Computations of these RF currents using Microwave Studio show qualitative agreement with the heated regions. New grounding points between the antenna box and the vessel have been implemented in NSTX-U, where future tests will be done to determine if the high-voltage standoff has improved. Further antenna improvements will be sought through future experiments on the test stand.
NASA Astrophysics Data System (ADS)
Stefan, V. Alexander
2014-10-01
A novel method for alpha particle diagnostics is proposed. The theory of stimulated Raman scattering, SRS, of the fast wave and ion Bernstein mode, IBM, turbulence in multi-ion species plasmas, (Stefan University Press, La Jolla, CA, 2008). is utilized for the diagnostics of fast ions, (4)He (+2), in ITER plasmas. Nonlinear Landau damping of the IBM on fast ions near the plasma edge leads to the space-time changes in the turbulence level, (inverse alpha particle channeling). The space-time monitoring of the IBM turbulence via the SRS techniques may prove efficient for the real time study of the fast ion velocity distribution function, spatial distribution, and transport. Supported by Nikola Tesla Labs., La Jolla, CA 92037.
Semiclassical-wave-function perspective on high-harmonic generation
NASA Astrophysics Data System (ADS)
Mauger, François; Abanador, Paul M.; Lopata, Kenneth; Schafer, Kenneth J.; Gaarde, Mette B.
2016-04-01
We introduce a semiclassical-wave-function (SCWF) model for strong-field physics and attosecond science. When applied to high-harmonic generation (HHG), this formalism allows one to show that the natural time-domain separation of the contribution of ionization, propagation, and recollisions to the HHG process leads to a frequency-domain factorization of the harmonic yield into these same contributions, for any choice of atomic or molecular potential. We first derive the factorization from the natural expression of the dipole signal in the temporal domain by using a reference system, as in the quantitative rescattering (QRS) formalism [J. Phys. B 43, 122001 (2010), 10.1088/0953-4075/43/12/122001]. Alternatively, we show how the trajectory component of the SCWF can be used to express the factorization, which also allows one to attribute individual contributions to the spectrum to the underlying trajectories.
Perkins, R. J. Hosea, J. C.; Jaworski, M. A.; Diallo, A.; Bell, R. E.; Bertelli, N.; Gerhardt, S.; Kramer, G. J.; LeBlanc, B. P.; Phillips, C. K.; Podestà, M.; Roquemore, L.; Taylor, G.; Wilson, J. R.; Ahn, J.-W.; Gray, T. K.; McLean, A.; Sabbagh, S.
2015-04-15
The National Spherical Torus eXperiment (NSTX) can exhibit a major loss of high-harmonic fast wave (HHFW) power along scrape-off layer (SOL) field lines passing in front of the antenna, resulting in bright and hot spirals on both the upper and lower divertor regions. One possible mechanism for this loss is RF sheaths forming at the divertors. Here, we demonstrate that swept-voltage Langmuir probe characteristics for probes under the spiral are shifted relative to those not under the spiral in a manner consistent with RF rectification. We estimate both the magnitude of the RF voltage across the sheath and the sheath heat flux transmission coefficient in the presence of the RF field. Although precise comparison between the computed heat flux and infrared (IR) thermography cannot yet be made, the computed heat deposition compares favorably with the projections from IR camera measurements. The RF sheath losses are significant and contribute substantially to the total SOL losses of HHFW power to the divertor for the cases studied. This work will guide future experimentation on NSTX-U, where a wide-angle IR camera and a dedicated set of coaxial Langmuir probes for measuring the RF sheath voltage directly will quantify the contribution of RF sheath rectification to the heat deposition from the SOL to the divertor.
Two-wave regime of operation of the high-harmonic gyrotron
Savilov, A. V.; Denisov, G. G.; Kalynov, Yu. K.; Osharin, I. V.
2015-04-15
The use of the two-wave co-generation is proposed as a way to decrease the effective Q-factor of the operating near-cutoff wave of the gyrotron. In this two-wave regime, the operating wave represents a “hot” wave mode formed by two partial “cold” modes (near-cutoff and far-from-cutoff ones) coupled on the electron beam. It is shown that the use of this regime can provide a significant decrease of the Ohmic losses in low-relativistic high-harmonic gyrotrons operating in the THz frequency range.
Operation of a large-orbit high-harmonic gyro-traveling-wave tube amplifier
Furuno, D.S. ); McDermott, B.D.; Kou, C.S.; Luhmann, N.C. . Dept. of Electrical Engineering); Vitello, P. )
1990-06-01
The high-harmonic gyro-traveling wave tube (gyro-TWT) is a high-power ({>=} 1 kW) millimeter wave amplifier based on the synchronous interaction of a beam of large-orbit axis-encircling electrons with a high-order cylindrical waveguide mode. Since the interaction occurs at a high harmonic of the cyclotron frequency, the intense magnetic fields required for the conventional fundamental-mode gyro-TWT are not required. A proof-of-principle experiment designed to demonstrate the interaction of a 150-mA 350-keV electron beam with the TE{sub 81} ode of a cylindrical waveguide is described. Principal results include a small signal gain of 10 dB, an interaction bandwidth of 4.3 percent, and a saturated power transfer from electron beam to wave of 0.5 kW.
NASA Astrophysics Data System (ADS)
Stefan, V.
2006-10-01
A novel mechanism for the suppression of Weibel instabilities in the core of advanced fast ignition pellets is addressed. The propagation of generated suprathermal electron beam toward the core may lead to the appearance of colossal (˜10MG), small scale (L˜c/φpe, c---velocity of light, φpe---local electron plasma frequency) magnetic fields. The suppression synergy of high harmonic electron Bernstein, (EB), modes and Weibel modes, (WB), in the cone-attached laser fusion pellets is based on nonlinear mode-mode coupling. EB modes are excited by ignition, a cone guided, or implosion laser beams. High harmonic EB modes easily propagate to the core of the pellet whereby they nonlinearly interact with, and suppress, the WB. The suppression synergy is maximized at the simultaneous action of ignition and implosion lasers. E. S. Weibel, Phys. Rev. Lett., 2,83 (1959) in the core of advanced fast ignition pellets M. Tabak, J. Hammer, M.E. Glinsky, W.L. Kruer, S. C. Wilks, J. Woodworth, E. M. Campbell, and M.D. Perry, Phys. Plasmas 1 (5), 1626 (1994). V. Stefan, (a) Quasi-Stationary B-Fields due to Weibel Instability in FI Laser Fusion Pellets; (b) Pellet Core Heating Via High Harmonic EB Modes in FI Laser Fusion. 35th Annual A.A.C, 2005,
Taylor, G; Kessel, C E; LeBlanc, B P; Mueller, D; Phillips, D K; Valeo, E J; Wilson, J R; Ryan, P M; Bonoli, P T; Wright, J C
2012-02-13
1.4 MW of 30 MHz high-harmonic fast wave (HHFW) heating, with current drive antenna phasing, has generated a Ip = 300kA, BT (0) = 0.55T deuterium H-mode plasma in the National Spherical Torus Experiment that has a non-inductive plasma current fraction, fNI = 0.7-1. Seventy-five percent of the non-inductive current was generated inside an internal transport barrier that formed at a normalized minor radius, r/a {approx} 0.4 . Three quarters of the non-inductive current was bootstrap current and the remaining non-inductive current was generated directly by HHFW power inside r/a {approx} 0.2.
High Resolution Full Wave Modeling of Fast Waves in NSTX
NASA Astrophysics Data System (ADS)
Phillips, C. K.; Berk, L.; Hosea, J. C.; Leblanc, B. P.; Taylor, G.; Valeo, E. J.; Wilson, J. R.; Berry, L. A.; Jaeger, E. F.; Ryan, P. M.; Bonoli, P. T.; Wright, J. C.
2010-11-01
High Harmonic Fast Waves (HHFW) are being used in NSTX for plasma heating and noninductive current profile control. Numerical solutions for the wave fields obtained with the full wave TORIC and AORSA codes with ultrafine spatial resolution reveal the presence of a short wavelength feature that is predominantly polarized in the direction parallel to the equilibrium magnetic field and which is predicted by the codes to damp on electrons. A similar short wavelength mode also appears in simulations of the rf fields in C-Mod in the ICRF regime. Preliminary analysis indicates that the mode may be related to a slow mode that can propagate above the fundamental ion cyclotron frequency. The predicted power deposition profiles will be compared to those inferred from experimental measurements to see if the mode has a significant effect on the wave propagation and absorption. Possibilities for detecting the mode in NSTX and C-Mod will be discussed.
Spectral Effects on Fast Wave Core Heating and Current Drive
C.K. Phillips, R.E. Bell, L.A. Berry, P.T. Bonoli, R.W. Harvey, J.C. Hosea, E.F. Jaeger, B.P. LeBlanc, P.M. Ryan, G. Taylor, E.J. Valeo, J.R. Wilson, J.C. Wright, H. Yuh, and the NSTX Team
2009-05-11
Recent results obtained with high harmonic fast wave (HHFW) heating and current drive (CD) on NSTX strongly support the hypothesis that the onset of perpendicular fast wave propagation right at or very near the launcher is a primary cause for a reduction in core heating efficiency at long wavelengths that is also observed in ICRF heating experiments in numerous tokamaks. A dramatic increase in core heating efficiency was first achieved in NSTX L-mode helium majority plasmas when the onset for perpendicular wave propagation was moved away from the antenna and nearby vessel structures. Efficient core heating in deuterium majority L mode and H mode discharges, in which the edge density is typically higher than in comparable helium majority plasmas, was then accomplished by reducing the edge density in front of the launcher with lithium conditioning and avoiding operational points prone to instabilities. These results indicate that careful tailoring of the edge density profiles in ITER should be considered to limit rf power losses to the antenna and plasma facing materials. Finally, in plasmas with reduced rf power losses in the edge regions, the first direct measurements of high harmonic fast wave current drive were obtained with the motional Stark effect (MSE) diagnostic. The location and radial dependence of HHFW CD measured by MSE are in reasonable agreement with predictions from both full wave and ray tracing simulations.
NASA Astrophysics Data System (ADS)
Milanesio, D.; Maggiora, R.
2015-12-01
Ion Cyclotron (IC) antennas are routinely adopted in most of the existing nuclear fusion experiments, even though their main goal, i.e. to couple high power to the plasma (MW), is often limited by rather severe drawbacks due to high fields on the antenna itself and on the unmatched part of the feeding lines. In addition to the well exploited auxiliary ion heating during the start-up phase, some non-ohmic current drive (CD) at the IC range of frequencies may be explored in view of the DEMO reactor. In this work, we suggest and describe a compact high frequency DEMO relevant antenna, based on the high impedance surfaces concept. High-impedance surfaces are periodic metallic structures (patches) usually displaced on top of a dielectric substrate and grounded by means of vertical posts embedded inside the dielectric, in a mushroom-like shape. These structures present a high impedance, within a given frequency band, such that the image currents are in-phase with the currents of the antenna itself, thus determining a significant efficiency increase. After a general introduction on the properties of high impedance surfaces, we analyze, by means of numerical codes, a dielectric based and a full metal solution optimized to be tested and benchmarked on the FTU experiment fed with generators at 433MHz.
Progress on High Harmonic Fast Wave Heating and Current Drive on NSTX
NASA Astrophysics Data System (ADS)
Ryan, P. M.; Berry, L. A.; Jaeger, E. F.; Wilgen, J. B.; Bell, R. E.; Hosea, J. C.; Leblanc, B. P.; Phillips, C. K.; Taylor, G.; Valeo, E. J.; Wilson, J. R.; Yuh, H.
2008-11-01
The recent improvement of the 30 MHz HHFW heating efficiency at lower toroidal wavenumbers in helium plasmas [1] has been extended to deuterium operation at BT(0) = 0.55 T on NSTX. The key to effective power penetration of the edge plasma is the reduction of the plasma density near the Faraday screen/first wall [2]. For deuterium plasmas, it was necessary to use lithium wall conditioning to control the density rise that often accompanies high power RF operation, particularly at the lower toroidal wavenumbers achievable with the 12-element phased-array launcher. The HHFW power deposition at k|| = -8 m-1 is comparable to that of k|| = -14 m-1, and core heating at k|| = -3 m-1 has now been observed, albeit at lower efficiency. Central electron temperatures of 5 keV have been achieved in both deuterium and helium plasmas with 3.1 MW at k|| = -14 m-1 (-150^o relative phase shift). Central heating of NBI-driven H-mode plasmas has been observed for both k|| = 14 and 8 m-1. [1] Hosea, J. et al, Physics of Plasmas 15, 056104 (2008) [2] Hosea, J. et al, poster at this conference
Milanesio, D. Maggiora, R.
2015-12-10
Ion Cyclotron (IC) antennas are routinely adopted in most of the existing nuclear fusion experiments, even though their main goal, i.e. to couple high power to the plasma (MW), is often limited by rather severe drawbacks due to high fields on the antenna itself and on the unmatched part of the feeding lines. In addition to the well exploited auxiliary ion heating during the start-up phase, some non-ohmic current drive (CD) at the IC range of frequencies may be explored in view of the DEMO reactor. In this work, we suggest and describe a compact high frequency DEMO relevant antenna, based on the high impedance surfaces concept. High-impedance surfaces are periodic metallic structures (patches) usually displaced on top of a dielectric substrate and grounded by means of vertical posts embedded inside the dielectric, in a mushroom-like shape. These structures present a high impedance, within a given frequency band, such that the image currents are in-phase with the currents of the antenna itself, thus determining a significant efficiency increase. After a general introduction on the properties of high impedance surfaces, we analyze, by means of numerical codes, a dielectric based and a full metal solution optimized to be tested and benchmarked on the FTU experiment fed with generators at 433MHz.
NASA Astrophysics Data System (ADS)
Zürch, Michael; Foertsch, Stefan; Matzas, Mark; Pachmann, Katharina; Kuth, Rainer; Spielmann, Christian
2014-03-01
In cancer treatment it is highly desirable to identify and /or classify individual cancer cells in real time. Nowadays, the standard method is PCR which is costly and time-consuming. Here we present a different approach to rapidly classify cell types: we measure the pattern of coherently diffracted extreme ultraviolet radiation (XUV radiation at 38nm wavelength), allowing to distinguish different single breast cancer cell types. The output of our laser driven XUV light source is focused onto a single unstained and unlabeled cancer cell, and the resulting diffraction pattern is measured in reflection geometry. As we will further show, the outer shape of the object can be retrieved from the diffraction pattern with sub-micron resolution. For classification it is often not necessary to retrieve the image, it is only necessary to compare the diffraction patterns which can be regarded as a spatial fingerprint of the specimen. For a proof-of-principle experiment MCF7 and SKBR3 breast cancer cells were pipetted on gold-coated silica slides. From illuminating each single cell and measuring a diffraction pattern we could distinguish between them. Owing to the short bursts of coherent soft x-ray light, one could also image temporal changes of the specimen, i.e. studying changes upon drug application once the desired specimen is found by the classification method. Using a more powerful laser, even classifying circulating tumor cells (CTC) at a high throughput seems possible. This lab-sized equipment will allow fast classification of any kind of cells, bacteria or even viruses in the near future.
Recent Improvements in Fast Wave Heating in NSTX
G. Taylor, R.E. Bell, R.W. Harvey, J.C. Hosea, E.F. Jaeger, B.P. LeBlanc, C.K. Phillips, P.M. Ryan, E.J. Valeo, J.B. Wilgen, J.R. Wilson, and the NSTX Team
2009-06-26
Recent improvements in high-harmonic fast wave (HHFW) core heating in NSTX are attributed to using lithium conditioning, and other wall conditioning techniques, to move the onset density for perpendicular fast wave propagation further from the antenna. This has resulted in the first observation of HHFW core electron heating in deuterium plasma at a launched toroidal wavenumber, kφ = -3 m-1, NSTX record core electron temperatures of 5 keV in helium and deuterium discharges and, for the first time, significant HHFW core electron heating of deuterium neutral-beam-fuelled H-mode plasmas. Also, kφ = -8 m-1 heating of the plasma startup and plasma current ramp-up has resulted in significant core electron heating, even at central electron densities as low as ~ 4x1018 m-3.
Recent Improvements in Fast Wave Heating in NSTX
Taylor, G.; Bell, R. E.; Hosea, J. C.; LeBlanc, B. P.; Phillips, C. K.; Valeo, E. J.; Wilson, J. R.; Harvey, R. W.; Jaeger, E. F.; Ryan, P. M.; Wilgen, J. B.
2009-11-26
Recent improvements in high-harmonic fast wave (HHFW) core heating in NSTX are attributed to using lithium conditioning, and other wall conditioning techniques, to move the onset density for perpendicular fast wave propagation further from the antenna. This has resulted in the first observation of HHFW core electron heating in deuterium plasma at a launched toroidal wavenumber, k{phi} = -3 m{sup -1}, NSTX record core electron temperatures of 5 keV in helium and deuterium discharges and, for the first time, significant HHFW core electron heating of deuterium neutral-beam-fuelled H-mode plasmas. Also, k{phi} = -8 m{sup -1} heating of the plasma startup and plasma current ramp-up has resulted in significant core electron heating, even at central electron densities as low as {approx}4x10{sup 18} m-3.
Fast wave heating in the NSTX-Upgrade device
Bertelli, Nicola; Jaeger, E. F.; Berry, Lee Alan; Bonoli, P.; Budny, R. V.; Fu, GuoYong; Gerhardt, S.; Green, David L; Harvey, R. W.; Hosea, J.; Kramer, G.; LeBlanc, B; Perkins, R. J.; Phillips, C. K.; Ryan, Philip Michael; Taylor, G.; Valeo, E. J.; Wilson, J. R.; Wright, J.
2013-01-01
NSTX-Upgrade will operate with toroidal magnetic fields (B T) up to 1 T, nearly twice the value used in the experiments on NSTX, and the available NBI power will be doubled. The doubling of B T while retaining the 30 MHz RF source frequency has moved the heating regime from the high harmonic fast wave (HHFW) regime used in NSTX to the mid harmonic fast wave (MHFW) regime. By making use of the full wave code AORSA, this work shows that direct ion damping (mainly by thermal ions localized at the 5th harmonic resonance) might be significant in NSTX-Upgrade under TRANSP predicted full performance conditions and the electron and ion absorption is sensitive to the ratio of electron and ion temperature. Launching at high toroidal wave number appears to be one way to significantly reduce the ion damping. By using the extended AORSA code, which includes a detailed description of the scrape-off layer in the field solutions, we found a large electric field amplitude outside of the last closed flux surface as previously seen in NSTX from AORSA simulations (D. L. Green, et al, Phys. Rev. Lett. 107, 145001 (2011)). Preliminary results by introducing a collision damping in the scrape-off layer in the AORSA code to represent a damping process are presented, showing for the first time absorbed power in the scrape-off layer.
Spectral effects on fast wave core heating and current drive
Phillips, Cynthia; Bell, R. E.; Berry, Lee; Jaeger, Erwin Frederick; Ryan, Philip Michael; Wilgen, John B
2009-01-01
Recent results obtained with high harmonic fast wave (HHFW) heating and current drive (CD) on NSTX strongly support the hypothesis that the onset of perpendicular fast wave propagation right at or very near the launcher is a primary cause for a reduction in core heating efficiency at long wavelengths that is also observed in ICRF heating experiments in numerous tokamaks. A dramatic increase in core heating efficiency was first achieved in NSTX L-mode helium majority plasmas when the onset for perpendicular wave propagation was moved away from the antenna and nearby vessel structures. Efficient core heating in deuterium majority L-mode and H-mode discharges, in which the edge density is typically higher than in comparable helium majority plasmas, was then accomplished by reducing the edge density in front of the launcher with lithium conditioning and avoiding operational points prone to instabilities. These results indicate that careful tailoring of the edge density profiles in ITER should be considered to limit radio frequency (rf) power losses to the antenna and plasma facing materials. Finally, in plasmas with reduced rf power losses in the edge regions, the first direct measurements of HHFW CD were obtained with the motional Stark effect (MSE) diagnostic. The location and radial dependence of HHFW CD measured by MSE are in reasonable agreement with predictions from both full wave and ray tracing simulations.
Fast wave heating in the NSTX-Upgrade device
Bertelli, N.; Budny, R.; Fu, G.-Y.; Gerhardt, S.; Hosea, J. C.; Kramer, G. J.; LeBlanc, B.; Perkins, R. J.; Phillips, C. K.; Taylor, G.; Valeo, E. J.; Wilson, J. R.; Jaeger, E. F.; Berry, L.; Green, D. L.; Ryan, P.; Bonoli, P. T.; Wright, J. C.; Harvey, R. W.
2014-02-12
NSTX-Upgrade will operate with toroidal magnetic fields (B{sub T}) up to 1 T, nearly twice the value used in the experiments on NSTX, and the available NBI power will be doubled. The doubling of B{sub T} while retaining the 30 MHz RF source frequency has moved the heating regime from the high harmonic fast wave (HHFW) regime used in NSTX to the mid harmonic fast wave (MHFW) regime. By making use of the full wave code AORSA, this work shows that direct ion damping (mainly by thermal ions localized at the 5th harmonic resonance) might be significant in NSTX-Upgrade under TRANSP predicted full performance conditions and the electron and ion absorption is sensitive to the ratio of electron and ion temperature. Launching at high toroidal wave number appears to be one way to significantly reduce the ion damping. By using the extended AORSA code, which includes a detailed description of the scrape-off layer in the field solutions, we found a large electric field amplitude outside of the last closed flux surface as previously seen in NSTX from AORSA simulations (D. L. Green, et al, Phys. Rev. Lett. 107, 145001 (2011)). Preliminary results by introducing a collision damping in the scrape-off layer in the AORSA code to represent a damping process are presented, showing for the first time absorbed power in the scrape-off layer.
Cho, Suwon; Kwak, Jong-Gu
2014-04-15
The propagation and absorption of high harmonic fast waves is of interest for non-inductive current drives in fusion experiments. The fast wave can be coupled with the ion Bernstein wave that propagates in the high magnetic field side of an ion cyclotron harmonic resonance layer. This coupling and the absorption are analyzed using the hot plasma dispersion relation and a wave equation that was converted from an approximate dispersion relation for the case where λ{sub i}=k{sub ⊥}{sup 2}ρ{sub i}{sup 2}/2≳1 (where k{sub ⊥} is the perpendicular wave number and ρ{sub i} is the ion Larmor radius). It is found that both reflection and conversion may occur near the harmonic resonance layer but that they decrease rapidly, giving rise to a sharp increase in the absorption as the parallel wave number increases.
Fast magnetoacoustic wave trains in coronal holes
NASA Astrophysics Data System (ADS)
Pascoe, D. J.; Nakariakov, V. M.; Kupriyanova, E. G.
2014-08-01
Context. Rapidly propagating coronal EUV disturbances recently discovered in the solar corona are interpreted in terms of guided fast magnetoacoustic waves. Fast magnetoacoustic waves experience geometric dispersion in waveguides, which causes localised, impulsive perturbations to develop into quasi-periodic wave trains. Aims: We consider the formation of fast wave trains in a super-radially expanding coronal hole modelled by a magnetic funnel with a field-aligned density profile that is rarefied in comparison to the surrounding plasma. This kind of structure is typical of coronal holes, and it forms a fast magnetoacoustic anti-waveguide as a local maximum in the Alfvén speed. Methods: We performed 2D MHD numerical simulations for impulsively generated perturbations to the system. Both sausage and kink perturbations are considered and the role of the density contrast ratio investigated. Results: The anti-waveguide funnel geometry refracts wave energy away from the structure. However, in this geometry the quasi-periodic fast wave trains are found to appear, too, and so can be associated with the observed rapidly propagating coronal EUV disturbances. The wave trains propagate along the external edge of the coronal hole. The fast wave trains generated in coronal holes exhibit less dispersive evolution than in the case of a dense waveguide. Conclusions: We conclude that an impulsive energy release localised in a coronal plasma inhomogeneity develops into a fast wave train for both kink and sausage disturbances and for both waveguide and anti-waveguide transverse plasma profiles.
Fast wave power flow along SOL field lines in NSTX
NASA Astrophysics Data System (ADS)
Perkins, R. J.; Bell, R. E.; Diallo, A.; Gerhardt, S.; Hosea, J. C.; Jaworski, M. A.; Leblanc, B. P.; Kramer, G. J.; Phillips, C. K.; Roquemore, L.; Taylor, G.; Wilson, J. R.; Ahn, J.-W.; Gray, T. K.; Green, D. L.; McLean, A.; Maingi, R.; Ryan, P. M.; Jaeger, E. F.; Sabbagh, S.
2012-10-01
On NSTX, a major loss of high-harmonic fast wave (HHFW) power can occur along open field lines passing in front of the antenna over the width of the scrape-off layer (SOL). Up to 60% of the RF power can be lost and at least partially deposited in bright spirals on the divertor floor and ceiling [1,2]. The flow of HHFW power from the antenna region to the divertor is mostly aligned along the SOL magnetic field [3], which explains the pattern of heat deposition as measured with infrared (IR) cameras. By tracing field lines from the divertor back to the midplane, the IR data can be used to estimate the profile of HHFW power coupled to SOL field lines. We hypothesize that surface waves are being excited in the SOL, and these results should benchmark advanced simulations of the RF power deposition in the SOL (e.g., [4]). Minimizing this loss is critical optimal high-power long-pulse ICRF heating on ITER while guarding against excessive divertor erosion.[4pt] [1] J.C. Hosea et al., AIP Conf Proceedings 1187 (2009) 105. [0pt] [2] G. Taylor et al., Phys. Plasmas 17 (2010) 056114. [0pt] [3] R.J. Perkins et al., to appear in Phys. Rev. Lett. [0pt] [4] D.L. Green et al., Phys. Rev. Lett. 107 (2011) 145001.
Choi, M.; Pinsker, R. I.; Chan, V. S.; Muscatello, C. M.; Jaeger, E. F.
2011-12-23
In recent moderate to high harmonic fast wave heating and current drive experiments in DIII-D, a synergy effect was observed when the 6{sup th} harmonic 90 MHz fast wave power is applied to the plasma preheated by neutral beams and the 4{sup th} harmonic 60 MHz fast wave. In this paper, we investigate how the synergy can occur using ORBIT-RF coupled with AORSA. Preliminary simulations suggest that damping of 4{sup th} harmonic FW on beam ions accelerates them above the injection energy, which may allow significant damping of 6{sup th} harmonic FW on beam ion tails to produce synergy.
Observation of Electronic Structure Minima in High-Harmonic Generation
Woerner, Hans Jakob; Villeneuve, D. M.; Niikura, Hiromichi; Bertrand, Julien B.; Corkum, P. B.
2009-03-13
We report detailed measurements of the high-harmonic spectra generated from argon atoms. The spectra exhibit a deep minimum that is shown to be independent of the laser intensity, and is thus a clear measure of the electronic structure of the atom. We show that exact field-free continuum wave functions reproduce the minimum, but plane wave and Coulomb wave functions do not. This remarkable observation suggests that electronic structure can be accurately determined in high-harmonic experiments despite the presence of the strong laser field. Our results clarify the relation between high-harmonic generation and photoelectron spectroscopy. The use of exact continuum functions also resolves the ambiguity associated with the choice of the dispersion relation.
Fast wave current drive in neutral beam heated plasmas on DIII-D
Petty, C.C.; Forest, C.B.; Pinsker, R.I.
1997-04-01
The physics of non-inductive current drive and current profile control using the fast magnetosonic wave has been demonstrated on the DIII-D tokamak. In non-sawtoothing discharges formed by neutral beam injection (NBI), the radial profile of the fast wave current drive (FWCD) was determined by the response of the loop voltage profile to co, counter, and symmetric antenna phasings, and was found to be in good agreement with theoretical models. The application of counter FWCD increased the magnetic shear reversal of the plasma and delayed the onset of sawteeth, compared to co FWCD. The partial absorption of fast waves by energetic beam ions at high harmonics of the ion cyclotron frequency was also evident from a build up of fast particle pressure near the magnetic axis and a correlated increase in the neutron rate. The anomalous fast particle pressure and neutron rate increased with increasing NBI power and peaked when a harmonic of the deuterium cyclotron frequency passed through the center of the plasma. The experimental FWCD efficiency was highest at 2 T where the interaction between the fast waves and the beam ions was weakest; as the magnetic field strength was lowered, the FWCD efficiency decreased to approximately half of the maximum theoretical value.
High-harmonic gyrotron with sectioned cavity
Bandurkin, I. V.; Kalynov, Yu. K.; Savilov, A. V.
2010-07-15
High-harmonic large-orbit gyrotrons require long-length operating cavities because of both a weak electron-wave coupling and relatively low electron currents. Since diffraction Q factors of such cavities are very high, a large fraction of the radiated power is dissipated in Ohmic losses. A sectioned klystronlike cavity can be a way to combine a long electron-wave interaction region with a relatively low diffraction Q factor. In this paper, a design of a third-harmonic terahertz gyrotron is studied in detail and discussed. As compared to a regular cavity, the use of a sectioned microwave system provides an enhancement of the output rf power by several times along with the halving of the Ohmic losses.
Wave modes facilitating fast magnetic reconnection
NASA Astrophysics Data System (ADS)
Singh, N.
2011-12-01
Whistler and kinetic Alfven waves are often invoked to explain fast magnetic reconnection in collsionless plasmas. But how these wave modes facilitate the reconnection has remained unclear. An important unanswered question deals with the meaning of the wave frequency in the context of magnetic reconnection. New measurement on a fast explosive reconnection event in the Versatile Toroidal Facility (VTF) at MIT provides an interesting example of the meaning of the wave mode and the associated frequency directly related to the time scale of the impulsive reconnection. We examine the measurements in VTF in view of the whistler wave mode, showing that the explosive growth in the reconnection is related to the thinning of the current sheet to a few electron skin depths. We further demonstrate that the fastest measured time scale (~ 3 microseconds) and the largest normalized reconnection rate (~0.35) agree with those predicted from the whistler mode dispersion relation.
Fast Waves in Smooth Coronal Slab
NASA Astrophysics Data System (ADS)
Lopin, I.; Nagorny, I.
2015-03-01
This work investigates the effect of transverse density structuring in coronal slab-like waveguides on the properties of fast waves. We generalized previous results obtained for the exponential and Epstein profiles to the case of an arbitrary transverse density distribution. The criteria are given to determine the possible (trapped or leaky) wave regime, depending on the type of density profile function. In particular, there are plasma slabs with transverse density structuring that support pure trapped fast waves for all wavelengths. Their phase speed is nearly equal to the external Alfvén speed for the typical parameters of coronal loops. Our findings are obtained on the basis of Kneser’s oscillation theorem. To confirm the results, we analytically solved the wave equation evaluated at the cutoff point and the original wave equation for particular cases of transverse density distribution. We also used the WKB method and obtained approximate solutions of the wave equation at the cutoff point for an arbitrary transverse density profile. The analytic results were supplemented by numerical solutions of the obtained dispersion relations. The observed high-quality quasi-periodic pulsations of flaring loops are interpreted in terms of the trapped fundamental fast-sausage mode in a slab-like coronal waveguide.
High-harmonic generation in aligned water molecules
NASA Astrophysics Data System (ADS)
Wang, Song; Devin, Julien; Hoffmann, Matthias; Cryan, James; Kaldun, Andreas; Bucksbaum, Philip
2016-05-01
In recent years, the use of high harmonic generation (HHG) in aligned molecular vapors has become a powerful tool to study ultrafast dynamics of electronic and nuclear wave packets. In our new experimental setup, we are able to orient H2 O and D2 O molecules using a single cycle terahertz (THz) pulse. Aligning water is especially interesting as the highest occupied molecular orbital (HOMO) of water contains a node in the xz plane of the molecular frame, allowing us to perform HHG from second highest occupied molecular orbital (HOMO-1) only, by setting the polarization of the fundamental laser along the z-axis of the aligned water molecules. We are particularly interested in the HOMO-1 state, as there is fast motion of the H-O-H angle leading to sub-wavelength dynamics. On this poster we present our all-optical alignment setup where HHG and single-cycle THz generation take place in high-vacuum, where measurements with arbitrary polarization angles between the two are possible. In addition, we discuss the effects of the molecular orientation on HHG, including symmetry breaking that could produce even harmonics and isotope effects between H2 O and D2 O due to different vibrational energies. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.
Fast wave evanescence in filamentary boundary plasmas
Myra, J. R.
2014-02-15
Radio frequency waves for heating and current drive of plasmas in tokamaks and other magnetic confinement devices must first traverse the scrape-off-layer (SOL) before they can be put to their intended use. The SOL plasma is strongly turbulent and intermittent in space and time. These turbulent properties of the SOL, which are not routinely taken into account in wave propagation codes, can have an important effect on the coupling of waves through an evanescent SOL or edge plasma region. The effective scale length for fast wave (FW) evanescence in the presence of short-scale field-aligned filamentary plasma turbulence is addressed in this paper. It is shown that although the FW wavelength or evanescent scale length is long compared with the dimensions of the turbulence, the FW does not simply average over the turbulent density; rather, the average is over the exponentiation rate. Implications for practical situations are discussed.
Global wave modeling of electron interactions with fast magnetosonic waves
NASA Astrophysics Data System (ADS)
Jaeger, E. F.; Batchelor, D. B.; Murakami, M.
Electron interactions with fast magnetosonic waves are of interest for both direct electron heating and fast-wave current drive (FWCD) in tokamaks. Here the authors apply the full-wave ICRF code PICES to examples of both of these applications. To realistically account for the actual D-shaped magnetic geometry of present-day tokamaks, PICES is interfaced with the 3-D MHD equilibrium code VMEC. Likewise, to correctly model the real toroidal structure of both source and image currents in ICRF current drive antennas, PICES is interfaced with the 2-D recessed antenna impedance code RANT. Both current drive and electron heating by fast waves can be strongly altered through modification of the kappa(sub (parallel))-spectrum by the poloidal magnetic field. A poloidal mode expansion in PICES allows such variations in kappa(sub (parallel)) to be included correctly. In this paper, comparisons are made to observations of the direct electron heating profile on TFTR and to the FWCD efficiency on DIII-D. They also extrapolate to make predictions for future tokamaks such as TPX and ITER.
Bertelli, N; Jaeger, E F; Hosea, J C; Phillips, C K; Berry, L; Bonoli, P T; Gerhardt, S P; Green, D; LeBlanc, B; Perkins, R J; Ryan, P M; Taylor, G; Valeo, E J; Wilso, J R; Wright, J C
2014-07-01
Fast waves at harmonics of the ion cyclotron frequency, which have been used successfully on National Spherical Torus Experiment (NSTX), will also play an important role in ITER and are a promising candidate for the Fusion Nuclear Science Facility (FNSF) designs based on spherical torus (ST). Experimental studies of high harmonic fast waves (HHFW) heating on the NSTX have demonstrated that substantial HHFW power loss occurs along the open field lines in the scrape-off layer (SOL), but the mechanism behind the loss is not yet understood. The full wave RF code AORSA, in which the edge plasma beyond the last closed flux surface (LCFS) is included in the solution domain, is applied to specific NSTX discharges in order to predict the effects and possible causes of this power loss. In the studies discussed here, a collisional damping parameter has been implemented in AORSA as a proxy to represent the real, and most likely nonlinear, damping processes. A prediction for the NSTX Upgrade (NSTX-U) experiment, that will begin operation next year, is also presented, indicating a favorable condition for the experiment due to a wider evanescent region in edge density.*Research supported by the U.S. DOE under Contract No. DE-AC02-09CH11466 with Princeton University.
The Effects of Wave Escape on Fast Magnetosonic Wave Turbulence in Solar Flares
NASA Technical Reports Server (NTRS)
Pongkitiwanichakul, Peera; Chandran, Benjamin D. G.; Karpen, Judith T.; DeVore, C. Richard
2012-01-01
One of the leading models for electron acceleration in solar flares is stochastic acceleration by weakly turbulent fast magnetosonic waves ("fast waves"). In this model, large-scale flows triggered by magnetic reconnection excite large-wavelength fast waves, and fast-wave energy then cascades from large wavelengths to small wavelengths. Electron acceleration by large-wavelength fast-waves is weak, and so the model relies on the small-wavelength waves produced by the turbulent cascade. In order for the model to work, the energy cascade time for large-wavelength fast waves must be shorter than the time required for the waves to propagate out of the solar-flare acceleration region. To investigate the effects of wave escape, we solve the wave kinetic equation for fast waves in weak turbulence theory, supplemented with a homogeneous wave-loss term.We find that the amplitude of large-wavelength fast waves must exceed a minimum threshold in order for a significant fraction of the wave energy to cascade to small wavelengths before the waves leave the acceleration region.We evaluate this threshold as a function of the dominant wavelength of the fast waves that are initially excited by reconnection outflows.
THE EFFECTS OF WAVE ESCAPE ON FAST MAGNETOSONIC WAVE TURBULENCE IN SOLAR FLARES
Pongkitiwanichakul, Peera; Chandran, Benjamin D. G.; Karpen, Judith T.; DeVore, C. Richard E-mail: benjamin.chandran@unh.edu E-mail: devore@nrl.navy.mil
2012-09-20
One of the leading models for electron acceleration in solar flares is stochastic acceleration by weakly turbulent fast magnetosonic waves ({sup f}ast waves{sup )}. In this model, large-scale flows triggered by magnetic reconnection excite large-wavelength fast waves, and fast-wave energy then cascades from large wavelengths to small wavelengths. Electron acceleration by large-wavelength fast waves is weak, and so the model relies on the small-wavelength waves produced by the turbulent cascade. In order for the model to work, the energy cascade time for large-wavelength fast waves must be shorter than the time required for the waves to propagate out of the solar-flare acceleration region. To investigate the effects of wave escape, we solve the wave kinetic equation for fast waves in weak turbulence theory, supplemented with a homogeneous wave-loss term. We find that the amplitude of large-wavelength fast waves must exceed a minimum threshold in order for a significant fraction of the wave energy to cascade to small wavelengths before the waves leave the acceleration region. We evaluate this threshold as a function of the dominant wavelength of the fast waves that are initially excited by reconnection outflows.
Wavelength Scaling of High Harmonic Generation Efficiency
Shiner, A. D.; Trallero-Herrero, C.; Kajumba, N.; Corkum, P. B.; Villeneuve, D. M.; Bandulet, H.-C.; Comtois, D.; Legare, F.; Giguere, M.; Kieffer, J-C.
2009-08-14
Using longer wavelength laser drivers for high harmonic generation is desirable because the highest extreme ultraviolet frequency scales as the square of the wavelength. Recent numerical studies predict that high harmonic efficiency falls dramatically with increasing wavelength, with a very unfavorable lambda{sup -(5-6)} scaling. We performed an experimental study of the high harmonic yield over a wavelength range of 800-1850 nm. A thin gas jet was employed to minimize phase matching effects, and the laser intensity and focal spot size were kept constant as the wavelength was changed. Ion yield was simultaneously measured so that the total number of emitting atoms was known. We found that the scaling at constant laser intensity is lambda{sup -6.3+}-{sup 1.1} in Xe and lambda{sup -6.5+}-{sup 1.1} in Kr over the wavelength range of 800-1850 nm, somewhat worse than the theoretical predictions.
High harmonic generation from impulsively aligned SO2
NASA Astrophysics Data System (ADS)
Devin, Julien; Wang, Song; Kaldun, Andreas; Bucksbaum, Phil
2016-05-01
Previous work in high harmonics generation (HHG) in aligned molecular gases has mainly focused on rotational dynamics in order to determine the contributions of different orbitals to the ionization step. In our experiment, we focus on the shorter timescale of vibrational dynamics. We generate high harmonics from impulsively aligned SO2 molecules in a gas jet and record the emitted attosecond pulse trains in a home-built high resolution vacuum ultra violet (VUV) spectrometer. Using the high temporal resolution of our setup, we are able to map out the effects of vibrational wavepackets with a sub-femtosecond resolution. The target molecule, SO2 gas, is impulsively aligned by a near-infrared laser pulse and has accessible vibrations on the timescale of the short laser pulse used. We present first experimental results for the response to this excitation in high-harmonics. We observe both fast oscillations in the time domain as well as shifts of the VUV photon energy outside of the pulse overlaps. Research supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Chemical Sciences, Geosciences, and Biosciences Division and by the National Science Foundation Graduate Research Fellowship.
Multi-Orbital contributions in High Harmonic Generation
NASA Astrophysics Data System (ADS)
Guehr, Markus
2009-05-01
The high harmonic spectrum generated from atoms or molecules in a strong laser field contains information about the electronic structure of the generation medium. In the high harmonic generation (HHG) process, a free electron wave packet tunnel-ionizes from the molecular orbital in a strong laser field. After being accelerated by the laser electric field, the free electron wave packet coherently recombines to the orbital from which is was initially ionized, thereby emitting the harmonic spectrum. Interferences between the free electron wave packet and the molecular orbital will shape the spectrum in a characteristic way. These interferences have been used to tomographically image the highest occupied molecular orbital (HOMO) of N2 [1]. Molecular electronic states energetically below the HOMO should contribute to laser-driven high harmonic generation (HHG), but this behavior has not been observed previously. We have observed evidence of HHG from multiple orbitals in aligned N2 [2]. The tunneling ionization (and therefore the harmonic generation) is most efficient if the orbital has a large extension in the direction of the harmonic generation polarization. The HOMO with its σg symmetry therefore dominates the harmonic spectrum if the molecular axis is parallel to the harmonic generation polarization, the lower bound πu HOMO-1 dominates in the perpendicular case. The HOMO contributions appear as a regular plateau with a cutoff in the HHG spectrum. In contrast, the HOMO-1 signal is strongly peaked in the cutoff region. We explain this by semi-classical simulations of the recombination process that show constructive interferences between the HOMO-1 and the recombining wave packet in the cutoff region. The ability to monitor several orbitals opens the route to imaging coherent superpositions of electronic orbitals. [1] J. Itatani et al., Nature 432, 867 (2004)[2] B. K. McFarland, J. P. Farrell, P. H. Bucksbaum and M. Gühr, Science 322, 1232 (2008)
High efficiency off-axis current drive by high frequency fast waves
Prater, R.; Pinsker, R. I.; Moeller, C. P.; Porkolab, M.; Vdovin, V.
2014-02-12
Modeling work shows that current drive can be done off-axis with high efficiency, as required for FNSF and DEMO, by using very high harmonic fast waves (“helicons” or “whistlers”). The modeling indicates that plasmas with high electron beta are needed in order for the current drive to take place off-axis, making DIII-D a highly suitable test vehicle for this process. The calculations show that the driven current is not very sensitive to the launched value of n{sub ∥}, a result that can be understood from examination of the evolution of n{sub ∥} as the waves propagate in the plasma. Because of this insensitivity, relatively large values (∼3) of n{sub ∥} can be launched, thereby avoiding some of the problems with mode conversion in the boundary found in some previous experiments. Use of a traveling wave antenna provides a very narrow n{sub ∥} spectrum, which also helps avoid mode conversion.
Fast wave current drive: Experimental status and reactor prospects
Ehst, D.A.
1988-03-01
The fast wave is one of the two possible wave polarizations which propagate according to the basic theory of cold plasmas. It is distinguished from the other (slow wave) branch by having an electric field vector which is mainly orthogonal to the confining magnetic field of the plasma. The plasma and fast wave qualitatively assume different behavior depending on the frequency range of the launched wave. The high frequency fast wave (HFFW), with a frequency (..omega..2..pi.. )approximately) GHz) much higher than the ion cyclotron frequency (..cap omega../sub i/), suffers electron Landau damping and drives current by supplying parallel momentum to superthermal electrons in a fashion similar to lower hybrid (slow wave) current drive. In the simple theory the HFFW should be superior to the slow wave and can propagate to very high density and temperature without impediment. Experiments, however, have not conclusively shown that HFFW current drive can be achieved at densities above the slow wave current drive limit, possibly due to conversion of the launched fast waves into slow waves by density fluctuations. Alternatively, the low frequency fast wave (LFFW), with frequencies ()approxreverse arrowlt) 100 MHz) only a few times the ion cyclotron frequency, is damped by electron Landau damping and, in a hot plasma ()approxreverse arrowgt) 10 keV), by electron transit time magnetic pumping; current drive is achieved by pushing superthermal electrons, and efficiency is prediocted to be slightly better than for lower hybrid current drive. Most significantly, the slow wave does not propagate in high density plasma when ..omega.. )approximately) ..cap omega../sub i/, so parasitic coupling to the slow wave can be avoided, and no density and temperture limitations are foreseen. Experiments with fast wve current drive invariably find current drive efficiency as good as obtained in lower hybrid experiments at comparable, low temperatures. 45 refs., 4 figs., 1 tab
High-harmonic generation in cavitated plasmas
Schroeder, C. B.; Esarey, E.; Comier-Michel, E.; Leemans, W. P.
2008-05-15
A method is proposed for producing coherent x-rays via high-harmonic generation using ultraintense lasers interacting with highly stripped ions in cavitated plasmas. This method relies on plasma cavitation by the wake of an intense drive beam (laser or electron beam) to produce an ion cavity. An ultrashort pulse laser propagating in the plasma-electron-free ion cavity generates laser harmonics. The longitudinal electron motion, which inhibits high-harmonic generation at high laser intensities, can be suppressed by the space-charge field in the ion cavity or by using a counterpropagating laser pulse. Periodic suppression of the longitudinal electron motion may also be used to quasi-phase-match. This method enables harmonic generation to be extended to the sub-A regime.
High harmonic phase in molecular nitrogen
McFarland, Brian K.
2009-10-17
Electronic structure in atoms and molecules modulates the amplitude and phase of high harmonic generation (HHG). We report measurements of the high harmonic spectral amplitude and phase in N{sub 2}. The phase is measured interferometrically by beating the N{sub 2} harmonics with those of an Ar reference oscillator in a gas mixture. A rapid phase shift of 0.2{pi} is observed in the vicinity of the HHG spectral minimum, where a shift of {pi} had been presumed [J. Itatani et al., Nature 432, 867 (2004)]. We compare the phase measurements to a simulation of the HHG recombination step in N{sub 2} that is based on a simple interference model. The results of the simulation suggest that modifications beyond the simple interference model are needed to explain HHG spectra in molecules.
High Harmonic Generation at Long Wavelengths
Sheehy, B.; Martin, J. D. D.; DiMauro, L. F.; Agostini, P.; Schafer, K. J.; Gaarde, M. B.; Department of Physics, Lund Institute of Technology, P.O. Box 118, S-22100 Lund, ; Kulander, K. C.
1999-12-20
High harmonic radiation spectra up to 19th order in alkali metal vapors excited by an intense, picosecond mid-infrared (3-4 {mu} m ) laser are reported and compared to theory. The strong-field dynamics in the alkali metal atoms exhibit significant differences from all previously studied systems due to the strong coupling between their ground and first excited states. (c) 1999 The American Physical Society.
Wave-particle interactions on the FAST satellite
NASA Technical Reports Server (NTRS)
Temerin, M. A.; Carlson, C. W.; Cattell, C. A.; Ergun, R. E.; Mcfadden, J. P.
1990-01-01
NASA's Fast Auroral Snapshot, or 'FAST' satellite, scheduled for launch in 1993, will investigate the plasma physics of the low altitude auroral zone from a 3500-km apogee polar orbit. FAST will give attention to wave, double-layer, and soliton production processes due to electrons and ions, as well as to wave-wave interactions, and the acceleration of electrons and ions by waves and electric fields. FAST will employ an intelligent data-handling system capacle of data acquisition at rates of up to 1 Mb/sec, in addition to a 1-Gbit solid-state memory. The data need be gathered for only a few minutes during passes through the auroral zone, since the most interesting auroral phenomena occur in such narrow regions as auroral arcs, electrostatic shocks, and superthermal electron bursts.
Recent Fast Wave Coupling and Heating Studies on NSTX, with Possible Implications for ITER
J.C. Hosea, R.E. Bell, E. Feibush, R.W. Harvey, E.F. Jaeger, B.P LeBlanc, R. Maingi, C.K. Phillips, L. Roquemore, P.M. Ryan, G. Taylor, K. Tritz, E.J. Valeo, J. Wilgen, J.R. Wilson, and the NSTX Team
2009-07-21
The goal of the high harmonic fast wave (HHFW) research on NSTX is to maximize the coupling of RF power to the core of the plasma by minimizing the coupling of RF power to edge loss processes. HHFW core plasma heating efficiency in helium and deuterium L-mode discharges is found to improve markedly on NSTX when the density 2 cm in front of the antenna is reduced below that for the onset of perpendicular wave propagation (nonset ∝ B*k|| 2/ω). In NSTX, the observed RF power losses in the plasma edge are driven in the vicinity of the antenna as opposed to resulting from multi-pass edge damping. PDI surface losses through ion-electron collisions are estimated to be significant. Recent spectroscopic measurements suggest that additional PDI losses could be caused by the loss of energetic edge ions on direct loss orbits and perhaps result in the observed clamping of the edge rotation. Initial deuterium H-mode heating studies reveal that core heating is degraded at lower kφ (- 8 m-1 relative to 13 m-1) as for the Lmode case at elevated edge density. Fast visible camera images clearly indicate that a major edge loss process is occurring from the plasma scrape off layer (SOL) in the vicinity of the antenna and along the magnetic field lines to the lower outer divertor plate. Large type I ELMs, which are observed at both kφ values, appear after antenna arcs caused by precursor blobs, low level ELMs, or dust. For large ELMs without arcs, the source reflection coefficients rise on a 0.1 ms time scale, which indicates that the time derivative of the reflection coefficient can be used to discriminate between arcs and ELMs.
Recent Fast Wave Coupling and Heating Studies on NSTX, with Possible Implications for ITER
Hosea, J. C.; Bell, R. E.; Feibush, E.; LeBlanc, B. P.; Phillips, C. K.; Roquemore, L.; Taylor, G.; Valeo, E. J.; Wilson, J. R.; Harvey, R. W.; Jaeger, E. F.; Maingi, R.; Ryan, P. M.; Wilgen, J.; Tritz, K.
2009-11-26
The goal of the high harmonic fast wave (HHFW) research on NSTX is to maximize the coupling of RF power to the core of the plasma by minimizing the coupling of RF power to edge loss processes. HHFW core plasma heating efficiency in helium and deuterium L-mode discharges is found to improve markedly on NSTX when the density 2 cm in front of the antenna is reduced below that for the onset of perpendicular wave propagation (n{sub onset}{proportional_to}B*k{sub parallel}{sup 2}/{omega}). In NSTX, the observed RF power losses in the plasma edge are driven in the vicinity of the antenna as opposed to resulting from multi-pass edge damping. PDI surface losses through ion-electron collisions are estimated to be significant. Recent spectroscopic measurements suggest that additional PDI losses could be caused by the loss of energetic edge ions on direct loss orbits and perhaps result in the observed clamping of the edge rotation. Initial deuterium H-mode heating studies reveal that core heating is degraded at lower k{sub {phi}}(-8 m{sup -1} relative to 13 m{sup -1}) as for the L-mode case at elevated edge density. Fast visible camera images clearly indicate that a major edge loss process is occurring from the plasma scrape off layer (SOL) in the vicinity of the antenna and along the magnetic field lines to the lower outer divertor plate. Large type I ELMs, which are observed at both k{sub {phi}} values, appear after antenna arcs caused by precursor blobs, low level ELMs, or dust. For large ELMs without arcs, the source reflection coefficients rise on a 0.1 ms time scale, which indicates that the time derivative of the reflection coefficient can be used to discriminate between arcs and ELMs.
Fast magnetosonic waves of the magnetotail
NASA Astrophysics Data System (ADS)
Dmitrienko, Irina
Propagation of FMS waves in the cylindrical model of the magnetotail with plasma and current sheets are described. It is shown that the presence of the plasma sheet affects significantly the magnetotail transparency for FMS waves. Positions are calculated of reflecting cylindrical surfaces for the modes with different azimuthal numbers. It is also shown that the large azimuthal length FMS waves with sufficiently small longitudinal phase velocity penetrating into the magnetotail and propagating along the azimuthal coordinate concentrate in the lobes being very weak in the plasma sheet. Radial structures of FMS modes penetrating from the solar wind and those generating in the current sheet as well as the structures along PSBL of Alfven waves into which such FMS modes are mode converting and corresponding aurora are described.
Perkins, Roy
2013-06-21
Fast-wave heating and current drive efficiencies can be reduced by a number of processes in the vicinity of the antenna and in the scrape off layer (SOL). On NSTX from around 25% to more than 60% of the high-harmonic fast-wave power can be lost to the SOL regions, and a large part of this lost power flows along SOL magnetic field lines and is deposited in bright spirals on the divertor floor and ceiling. We show that field-line mapping matches the location of heat deposition on the lower divertor, albeit with a portion of the heat outside of the predictions. The field-line mapping can then be used to partially reconstruct the profile of lost fast-wave power at the midplane in front of the antenna, and the losses peak close to the last closed flux surface (LCFS) as well as the antenna. This profile suggests a radial standing-wave pattern formed by fast-wave propagation in the SOL, and this hypothesis will be tested on NSTX-U. Advanced RF codes must reproduce these results so that such codes can be used to understand this edge loss and to minimize RF heat deposition and erosion in the divertor region on ITER.
Parabolic approximation method for fast magnetosonic wave propagation in tokamaks
Phillips, C.K.; Perkins, F.W.; Hwang, D.Q.
1985-07-01
Fast magnetosonic wave propagation in a cylindrical tokamak model is studied using a parabolic approximation method in which poloidal variations of the wave field are considered weak in comparison to the radial variations. Diffraction effects, which are ignored by ray tracing mthods, are included self-consistently using the parabolic method since continuous representations for the wave electromagnetic fields are computed directly. Numerical results are presented which illustrate the cylindrical convergence of the launched waves into a diffraction-limited focal spot on the cyclotron absorption layer near the magnetic axis for a wide range of plasma confinement parameters.
Secondary Fast Magnetoacoustic Waves Trapped in Randomly Structured Plasmas
NASA Astrophysics Data System (ADS)
Yuan, Ding; Li, Bo; Walsh, Robert W.
2016-09-01
Fast magnetoacoustic waves are an important tool for inferring parameters of the solar atmosphere. We numerically simulate the propagation of fast wave pulses in randomly structured plasmas that mimic the highly inhomogeneous solar corona. A network of secondary waves is formed by a series of partial reflections and transmissions. These secondary waves exhibit quasi-periodicities in both time and space. Since the temporal and spatial periods are related simply through the speed of the fast wave, we quantify the properties of secondary waves by examining the dependence of the average temporal period (\\bar{p}) on the initial pulse width (w 0) and studying the density contrast ({δ }ρ ) and correlation length (L c ) that characterize the randomness of the equilibrium density profiles. For small-amplitude pulses, {δ }ρ does not alter \\bar{p} significantly. Large-amplitude pulses, on the other hand, enhance the density contrast when {δ }ρ is small but have a smoothing effect when {δ }ρ is sufficiently large. We found that \\bar{p} scales linearly with L c and that the scaling factor is larger for a narrower pulse. However, in terms of the absolute values of \\bar{p}, broader pulses generate secondary waves with longer periods, and this effect is stronger in random plasmas with shorter correlation lengths. Secondary waves carry the signatures of both the leading wave pulse and the background plasma. Our study may find applications in magnetohydrodynamic seismology by exploiting the secondary waves detected in the dimming regions after coronal mass ejections or extreme ultraviolet waves.
Fast Wave Current Drive in JET ITB-Plasma
Hellsten, T.; Laxaaback, M.; Bergkvist, T.; Johnson, T.; Brzozowski, J.; Rachlew, E.; Tennfors, E.; Mantsinen, M.; Matthews, G.; Tala, T.; Meo, F.; Nguyen, F.; Eriksson, L.-G.; Joffrin, E.; Noterdaeme, J.-M.; Petty, C.C.; Eester, D. van
2005-09-26
Fast wave current drive has been performed in JET plasmas with internal transport barriers, ITBs, and strongly reversed magnetic shear. Although the current drive efficiency of the power absorbed on the electrons is fairly high, only small effects are seen in the central current density. The main reasons are the parasitic absorption of RF power, the strongly inductive nature of the plasma and the interplay between the fast wave driven current and bootstrap current. The direct electron heating in the FWCD experiments is found to be strongly degraded compared to that with the dipole phasing.
NASA Astrophysics Data System (ADS)
Chanishvili, R.; Chagelishvili, G.; Uchava, E.; Kharshiladze, O.
2016-04-01
Our goal is to gain new insight into the physics of wave dynamics in ionospheric zonal shear flows. We study the shear flow non-normality induced linear coupling of planetary scale (slow) modified Rossby waves and westward propagating fast magnetized (Khantadze) waves using an approach different from the existing one to the linear wave dynamics. The performed analysis allows us to separate from each other different physical processes, grasp their interplay, and, by this way, construct the basic physics of the linear coupling of the slow and fast waves in an ionospheric zonal flow with linear shear of mean velocity, U0=(S y ,0 ) . It should be noted from the beginning that we consider incompressible flow and the classified "slow" and "fast" waves are not connected with the similarly labeled magnetosonic waves in compressible heliosphere. We show that: the modified Rossby waves generate fast magnetized waves due to the coupling for a quite wide range of ionospheric and shear flow parameters; the linear transient processes are highly anisotropic in wavenumber plane; the generation of the magnetized waves/oscillations is most efficient/optimal for S ≃0.1 (S is the shear rate normalized to the combination of the angular velocity and latitude, Ω0 cos θ0 ); the streamwise wave number of the optimally generated magnetized wave harmonics decreases (the length scale increases) with increasing the Hall parameter, α. At the end, we discuss nonlinear consequences of the described anisotropic linear dynamics—they should lead to an anisotropy of nonlinear cascade processes (in wavenumber plane). In turn, an interplay of the analyzed quite strong transient growth of the fast magnetic waves with anisotropic nonlinear processes should ensure self-sustenance of (stochastic or regular) magnetic perturbations.
Fast and Efficient Approach in Surface Wave Analysis
NASA Astrophysics Data System (ADS)
Kanli, A. I.
2010-12-01
Fast and Efficient Approach in Surface Wave Analysis Ali Ismet KANLI Istanbul University, Engineering Faculty, Department of Geophysical Engineering, 34320, Avcilar Campus, Istanbul-Turkey, E-mail: kanli@istanbul.edu.tr Abstract: A two-step surface wave analysis method is proposed including both the MASW (Multi-channel Analysis of Surface Waves) and Micro-tremor based techniques. This is an integrated approach and the MASW survey data are gathered to obtain the shear wave velocity-depth information up to at least 30 meters by using a special type active seismic source called as SR-II or Kangaroo. In the second step, the microtremor data which are based on surface waves from seismic noise at each site are used to determine the shear-wave velocity-depth profiles. In the second step of the process, the multichannel analysis of surface waves data are given as constraints in the microtremor inversion process. This proposed algorithm allows us to calculate shear wave velocity-depth information with all geotechnical parameters from near surface to bedrock depths very fast and efficiently.
Fast wave direct electron heating in TFTR
Murakami, M.; Jaeger, E.F.; Rimini, F.G.; Rasmussen, D.A.; Stevens, J.E.; Wilson, J.R.; Batchelor, D.B.; Bell, M.; Budny, R.; Fredrickson, E.; Goldfinger, R.C.; Hammett, G.; Hoffman, D.J.; Hosea, J.C.; Janos, A.; Majeski, R.; Mansfield, D.; Phillips, C.K.; Rogers, J.H.; Schilling, G.; Taylor, G.; Zamstorff, M.C. )
1994-10-15
Direct electron heating experiments were carried out in two regimes: B[sub T]=4.6 T with D[sup +] supershots; and B[sub T]=2.3 T with [sup 3]He majority. The electron power deposition profiles measured with modulation of RF power are found to be strongly peaked in the core with the total volume-integrated power of up to 80% of the modulated power. The magnitude and profile shape agree well with those predicted by a full-wave code.
Vacuum high-harmonic generation and electromagnetic shock
NASA Astrophysics Data System (ADS)
Böhl, P.; King, B.; Ruhl, H.
2016-04-01
> When one takes into account the presence of virtual charged states in the quantum vacuum, a nonlinear self-interaction can arise in the propagation of electromagnetic fields. This self-interaction is often referred to as `real photon-photon scattering'. When the centre-of-mass energy of colliding photons is much lower than the rest energy of an electron-positron pair, this quantum effect can be included in the classical field equations of motion as a vacuum current and charge density using the Heisenberg-Euler Lagrangian. Using analytical and numerical methods for subcritical fields, the intrinsic solution to Maxwell's equations has been found for counterpropagating probe and pump plane waves in the presence of vacuum four- and six-wave mixing. In the corresponding all-order solution for the scattered probe, a route to vacuum high-harmonic generation is identified in which a long phase length can compensate for the weakness of interacting fields. The resulting shocks in the probe carrier wave and envelope are studied for different parameter regimes and polarisation set-ups. In this special issue, we study two additional set-ups: that of a slowly varying single-cycle background to highlight the effect of an oscillating background on the probe harmonic spectrum, and that of a few-cycle probe to highlight the smoothing of the harmonic peaks produced by a wider spectrum of probe photons. We also correct sign errors in an earlier publication.
Fast wave current drive in DEMO
Lerche, E.; Van Eestera, D.; Messiaen, A.; Collaboration: EFDA-PPPT Contributors
2014-02-12
The ability to non-inductively drive a large fraction of the toroidal plasma current in magnetically confined plasmas is an essential requirement for steady state fusion reactors such as DEMO. Besides neutral beam injection (NBI), electron-cyclotron resonance heating (ECRH) and lower hybrid wave heating (LH), ion-cyclotron resonance heating (ICRH) is a promising candidate to drive current, in particular at the high temperatures expected in fusion plasmas. In this paper, the current drive (CD) efficiencies calculated with coupled ICRF wave / CD numerical codes for the DEMO-1 design case (R{sub 0}=9m, B{sub 0}=6.8T, a{sub p}=2.25m) [1] are presented. It will be shown that although promising CD efficiencies can be obtained in the usual ICRF frequency domain (20-100MHz) by shifting the dominant ion-cyclotron absorption layers to the high-field side, operation at higher frequencies (100-300MHz) has a stronger CD potential, provided the parasitic RF power absorption of the alpha particles can be minimized.
High-harmonic spectroscopy of molecular isomers
Wong, M. C. H.; Brichta, J.-P.; Bhardwaj, V. R.; Spanner, M.; Patchkovskii, S.
2011-11-15
We demonstrate that high-order-harmonic generation (HHG) spectroscopy can be used to probe stereoisomers of randomly oriented 1,2-dichloroethylene (C{sub 2}H{sub 2}Cl{sub 2}) and 2-butene (C{sub 4}H{sub 8}). The high-harmonic spectra of these isomers are distinguishable over a range of laser intensities and wavelengths. Time-dependent numerical calculations of angle-dependent ionization yields for 1,2-dichloroethylene suggest that the harmonic spectra of molecular isomers reflect differences in their strong-field ionization. The subcycle ionization yields for the cis isomer are an order of magnitude higher than those for the trans isomer. The sensitivity in discrimination of the harmonic spectra of cis- and trans- isomers is greater than 8 and 5 for 1,2-dichloroethylene and 2-butene, respectively. We show that HHG spectroscopy cannot differentiate the harmonic spectra of the two enantiomers of the chiral molecule propylene oxide (C{sub 3}H{sub 6}O).
Slow Magnetosonic Waves and Fast Flows in Active Region Loops
NASA Technical Reports Server (NTRS)
Ofman, L.; Wang, T. J.; Davila, J. M.
2012-01-01
Recent extreme ultraviolet spectroscopic observations indicate that slow magnetosonic waves are present in active region (AR) loops. Some of the spectral data were also interpreted as evidence of fast (approx 100-300 km/s) quasiperiodic flows. We have performed three-dimensional magnetohydrodynamic (3D MHD) modeling of a bipolar AR that contains impulsively generated waves and flows in coronal loops. The model AR is initiated with a dipole magnetic field and gravitationally stratified density, with an upflow-driven steadily or periodically in localized regions at the footpoints of magnetic loops. The resulting flows along the magnetic field lines of the AR produce higher density loops compared to the surrounding plasma by injection of material into the flux tubes and the establishment of siphon flow.We find that the impulsive onset of flows with subsonic speeds result in the excitation of damped slow magnetosonic waves that propagate along the loops and coupled nonlinearly driven fast-mode waves. The phase speed of the slow magnetosonic waves is close to the coronal sound speed. When the amplitude of the driving pulses is increased we find that slow shock-like wave trains are produced. When the upflows are driven periodically, undamped oscillations are produced with periods determined by the periodicity of the upflows. Based on the results of the 3D MHD model we suggest that the observed slow magnetosonic waves and persistent upflows may be produced by the same impulsive events at the bases of ARs.
SLOW MAGNETOSONIC WAVES AND FAST FLOWS IN ACTIVE REGION LOOPS
Ofman, L.; Wang, T. J.; Davila, J. M.
2012-08-01
Recent extreme ultraviolet spectroscopic observations indicate that slow magnetosonic waves are present in active region (AR) loops. Some of the spectral data were also interpreted as evidence of fast ({approx}100-300 km s{sup -1}) quasi-periodic flows. We have performed three-dimensional magnetohydrodynamic (3D MHD) modeling of a bipolar AR that contains impulsively generated waves and flows in coronal loops. The model AR is initiated with a dipole magnetic field and gravitationally stratified density, with an upflow-driven steadily or periodically in localized regions at the footpoints of magnetic loops. The resulting flows along the magnetic field lines of the AR produce higher density loops compared to the surrounding plasma by injection of material into the flux tubes and the establishment of siphon flow. We find that the impulsive onset of flows with subsonic speeds result in the excitation of damped slow magnetosonic waves that propagate along the loops and coupled nonlinearly driven fast-mode waves. The phase speed of the slow magnetosonic waves is close to the coronal sound speed. When the amplitude of the driving pulses is increased we find that slow shock-like wave trains are produced. When the upflows are driven periodically, undamped oscillations are produced with periods determined by the periodicity of the upflows. Based on the results of the 3D MHD model we suggest that the observed slow magnetosonic waves and persistent upflows may be produced by the same impulsive events at the bases of ARs.
Fast wave current drive in DIII-D
Petty, C.C.; Callis, R.W.; Chiu, S.C.; deGrassie, J.S.; Forest, C.B.; Freeman, R.L.; Gohil, P.; Harvey, R.W.; Ikezi, H.; Lin-Liu, Y.-R.
1995-02-01
The non-inductive current drive from fast Alfven waves launched by a directional four-element antenna was measured in the DIII-D tokamak. The fast wave frequency (60 MHz) was eight times the deuterium cyclotron frequency at the plasma center. An array of rf pickup loops at several locations around the torus was used to verify the directivity of the four-element antenna. Complete non-inductive current drive was achieved using a combination of fast wave current drive (FWCD) and electron cyclotron current drive (ECCD) in discharges for which the total plasma current was inductively ramped down from 400 to 170 kA. For discharges with steady plasma current, up to 110 kA of FWCD was inferred from an analysis of the loop voltage, with a maximum non-inductive current (FWCD, ECCD, and bootstrap) of 195 out of 310 kA. The FWCD efficiency increased linearly with central electron temperature. For low current discharges, the FWCD efficiency was degraded due to incomplete fast wave damping. The experimental FWCD was found to agree with predictions from the CURRAY ray-tracing code only when a parasitic loss of 4% per pass was included in the modeling along with multiple pass damping.
Real-time observation of interfering crystal electrons in high-harmonic generation.
Hohenleutner, M; Langer, F; Schubert, O; Knorr, M; Huttner, U; Koch, S W; Kira, M; Huber, R
2015-07-30
Acceleration and collision of particles has been a key strategy for exploring the texture of matter. Strong light waves can control and recollide electronic wavepackets, generating high-harmonic radiation that encodes the structure and dynamics of atoms and molecules and lays the foundations of attosecond science. The recent discovery of high-harmonic generation in bulk solids combines the idea of ultrafast acceleration with complex condensed matter systems, and provides hope for compact solid-state attosecond sources and electronics at optical frequencies. Yet the underlying quantum motion has not so far been observable in real time. Here we study high-harmonic generation in a bulk solid directly in the time domain, and reveal a new kind of strong-field excitation in the crystal. Unlike established atomic sources, our solid emits high-harmonic radiation as a sequence of subcycle bursts that coincide temporally with the field crests of one polarity of the driving terahertz waveform. We show that these features are characteristic of a non-perturbative quantum interference process that involves electrons from multiple valence bands. These results identify key mechanisms for future solid-state attosecond sources and next-generation light-wave electronics. The new quantum interference process justifies the hope for all-optical band-structure reconstruction and lays the foundation for possible quantum logic operations at optical clock rates. PMID:26223624
Real-time observation of interfering crystal electrons in high-harmonic generation
NASA Astrophysics Data System (ADS)
Hohenleutner, M.; Langer, F.; Schubert, O.; Knorr, M.; Huttner, U.; Koch, S. W.; Kira, M.; Huber, R.
2015-07-01
Acceleration and collision of particles has been a key strategy for exploring the texture of matter. Strong light waves can control and recollide electronic wavepackets, generating high-harmonic radiation that encodes the structure and dynamics of atoms and molecules and lays the foundations of attosecond science. The recent discovery of high-harmonic generation in bulk solids combines the idea of ultrafast acceleration with complex condensed matter systems, and provides hope for compact solid-state attosecond sources and electronics at optical frequencies. Yet the underlying quantum motion has not so far been observable in real time. Here we study high-harmonic generation in a bulk solid directly in the time domain, and reveal a new kind of strong-field excitation in the crystal. Unlike established atomic sources, our solid emits high-harmonic radiation as a sequence of subcycle bursts that coincide temporally with the field crests of one polarity of the driving terahertz waveform. We show that these features are characteristic of a non-perturbative quantum interference process that involves electrons from multiple valence bands. These results identify key mechanisms for future solid-state attosecond sources and next-generation light-wave electronics. The new quantum interference process justifies the hope for all-optical band-structure reconstruction and lays the foundation for possible quantum logic operations at optical clock rates.
Zabolotskii, A. A.
2009-11-15
An integrable Yajima-Oikawa system is solved in the case of a finite density, which corresponds to a slowly varying (long-wavelength) wave with finite amplitude at infinity and a localized fast-oscillating (short-wavelength) wave. Application of the results to spinor Bose-Einstein condensates and other physical systems is discussed.
Fast gravitational wave radiometry using data folding
NASA Astrophysics Data System (ADS)
Ain, Anirban; Dalvi, Prathamesh; Mitra, Sanjit
2015-07-01
Gravitational waves (GWs) from the early universe and unresolved astrophysical sources are expected to create a stochastic GW background (SGWB). The GW radiometer algorithm is well suited to probe such a background using data from ground-based laser interferometric detectors. Radiometer analysis can be performed in different bases, e.g., isotropic, pixel or spherical harmonic. Each of these analyses possesses a common temporal symmetry which we exploit here to fold the whole data set for every detector pair, typically a few hundred to a thousand days of data, to only one sidereal day, without any compromise in precision. We develop the algebra and a software pipeline needed to fold data, accounting for the effect of overlapping windows and nonstationary noise. We implement this on LIGO's fifth science run data and validate it by performing a standard anisotropic SGWB search on both folded and unfolded data. Folded data not only leads to orders of magnitude reduction in computation cost, but it results in a conveniently small data volume of few gigabytes, making it possible to perform an actual analysis on a personal computer, as well as easy movement of data. A few important analyses, yet unaccomplished due to computational limitations, will now become feasible. Folded data, being independent of the radiometer basis, will also be useful in reducing processing redundancies in multiple searches and provide a common ground for mutual consistency checks. Most importantly, folded data will allow vast amount of experimentation with existing searches and provide substantial help in developing new strategies to find unknown sources.
Effective ATI channels in high harmonic generation
NASA Astrophysics Data System (ADS)
Kuchiev, M. Yu; Ostrovsky, V. N.
2001-02-01
Harmonic generation by an atom in a laser field is described by the three-step mechanism as proceeding via above-threshold ionization (ATI) followed by electron propagation in the laser-dressed continuum and subsequent laser-assisted recombination (LAR). The amplitude of the harmonic production is given by the coherent sum of contributions from different intermediate ATI channels labelled by the number, m, of absorbed laser photons. The range of m-values that give a substantial contribution is explored and found to be rather broad for high harmonic generation. The coherence effects are of crucial importance as they are responsible for the characteristic pattern of harmonic intensities with a plateau domain followed by a cut-off region. Due to the multiphoton nature of the process, an efficient summation of m-contributions can be carried out within the framework of the saddle-point method. The saddle points correspond to some complex-valued labels m = mc associated with the intermediate effective ATI channels in the three-step harmonic generation process. The advantage of this approach stems from the fact that summation over a large number of conventional ATI m-channels is replaced by summation over a small number of effective mc-channels. The equation governing mc has a transparent physical meaning: the electron ejected from the atom on the first (ATI) stage should return to the core to make LAR possible. The effective channel labels m move along characteristic trajectories in the complex plane as the system parameters vary. In the cut-off region of the harmonic spectrum a single effective channel contributes. For lower harmonics, in the plateau domain, two effective ATI channels become essential. The interference of their contributions leads to an oscillatory pattern in the harmonic generation rates. The calculated rates are in good agreement with the results obtained by other approaches.
High Harmonic Generation from Rotationally Excited Molecules
NASA Astrophysics Data System (ADS)
Lock, Robynne M.
2011-12-01
High harmonic generation (HHG) is understood through a three-step model. A strong laser field ionizes an atom or molecule. The free electron propagates in the laser field and may recombine with the atom or molecule leading to the generation of extreme ultraviolet or soft x-ray light at odd harmonics of the fundamental. Since the wavelength of the recombining electron is on the order of internuclear distances in molecules, HHG acts as a probe of molecular structure and dynamics. Conversely, control of the molecules leads to control of the properties (intensity, phase, and polarization) of the harmonic emission. Rotationally exciting molecules provides field-free molecular alignment at time intervals corresponding to fractions of the rotational period of the molecule. Alignment is necessary for understanding how the harmonic emission depends on molecular structure and alignment. Additionally, HHG acts as a probe of the rotational wavepackets. This thesis reports three experiments on HHG from rotationally excited molecules. Before we can use HHG as a probe of complex molecular dynamics or control harmonic properties through molecules, the harmonic emission from aligned, linear molecules must first be understood. To that end, the first experiment measures the intensity and phase of harmonics generated from N 2O and N2 near times of strong alignment revealing interferences during recombination. The second experiment demonstrates HHG as a sensitive probe of rotational wavepacket dynamics in CO2 and N2O, revealing new revival features not detected by any other probe. The final experiment focuses on understanding and controlling the polarization state of the harmonic emission. Generating elliptically polarized harmonics would be very useful for probing molecular and materials systems. We observe an elliptical dichroism in polarization-resolved measurements of the harmonic emission from aligned N2 and CO2 molecules, revealing evidence for electron-hole dynamics between the
On Plasma Rotation Induced by Traveling Fast Alfvin Waves
F.W. Perkins; R.B. White; and V.S. Chan
2001-08-09
Absorption of fast Alfven waves by the minority fundamental ion-cyclotron resonance, coupled with finite banana width physics, generates torque distributions and ultimately rotational shear layers in the bulk plasma, even when the toroidal wavenumber k(subscript ''phi'') = n/R of the fast wave vanishes (n=0) and cyclotron absorption introduces no angular momentum nor canonical angular momentum [F.W. Perkins, R.B. White, P.T. Bonoli, and V.S. Chan, Phys. Plasmas 8 (2001) 2181]. The present work extends these results to travelling waves with non-zero n where heating directly introduces angular momentum. Since tokamak fast-wave antennas have approximately one wavelength per toroidal field coil, the toroidal mode number n lies in the range n = 10-20, independent of machine size. A zero-dimensional analysis shows that the rotation rate arising from direct torque is comparable to that of the rotational shear layer and has the same scaling. Nondimensional rotation profiles for n = (-10, 10) show modest changes from the n = 0 case in the expected direction. For a balanced antenna spectrum, the nondimensional rotational profile (averaged over n = -10, 10) lies quite close to the n = 0 profile.
Vorticity equation for MHD fast waves in geospace environment
NASA Technical Reports Server (NTRS)
Yamauchi, M.; Lundin, R.; Lui, A. T. Y.
1993-01-01
The MHD vorticity equation is modified in order to apply it to nonlinear MHD fast waves or shocks when their extent along the magnetic field is limited. Field-aligned current (FAC) generation is also discussed on the basis of this modified vorticity equation. When the wave normal is not aligned to the finite velocity convection and the source region is spatially limited, a longitudinal polarization causes a pair of plus and minus charges inside the compressional plane waves or shocks, generating a pair of FACs. This polarization is not related to the separation between the electrons and ions caused by their difference in mass, a separation which is inherent to compressional waves. The resultant double field-aligned current structure exists both with and without the contributions from curvature drift, which is questionable in terms of its contribution to vorticity change from the viewpoint of single-particle motion.
IBW and Fast Wave Launching and Damping on TFTR
First Author = J.C. Hosea
1997-01-01
Antennas to provide direct IBW (ion-Bernstein wave) excitation and to improve the launched spectrum and power handling for mode-coverted (MC) IBW excitation have been installed on TFTR (Tokamak Fusion Test Reactor) to support studies of transport barrier formation inside the TFTR plasma. Initial IBW launching/heating experiments have been performed at f(subscript) rf (nonsubsript) = 76 MHz and 50.6 MHz for several antenna and plasma positions, several mangetic fields [D, T, H, (superscript) 3 (nonsuperscript) He resonances], and with and without neutral-beam injection. Although the measured surface density profiles in front of the antenna should theoretically support IBW launching to the plasma core via EPW (electron plasma wave) excitation, loading resistance parameter dependence and heating results suggest that the wave energy is being deposited mostly in the plasma periphery. The potential roles of surface fast-wave and near-field excitation/damping on the IBW performance are discussed. Also MC IBW damping of the fast wave has been significantly improved through the removal of lithium 7 from the plasma.
Generation of sheet currents by high frequency fast MHD waves
NASA Astrophysics Data System (ADS)
Núñez, Manuel
2016-07-01
The evolution of fast magnetosonic waves of high frequency propagating into an axisymmetric equilibrium plasma is studied. By using the methods of weakly nonlinear geometrical optics, it is shown that the perturbation travels in the equatorial plane while satisfying a transport equation which enables us to predict the time and location of formation of shock waves. For plasmas of large magnetic Prandtl number, this would result into the creation of sheet currents which may give rise to magnetic reconnection and destruction of the original equilibrium.
Nonlinear fast sausage waves in homogeneous magnetic flux tubes
NASA Astrophysics Data System (ADS)
Mikhalyaev, Badma B.; Ruderman, Michael S.
2015-12-01
> We consider fast sausage waves in straight homogeneous magnetic tubes. The plasma motion is described by the ideal magnetohydrodynamic equations in the cold plasma approximation. We derive the nonlinear Schrödinger equation describing the nonlinear evolution of an envelope of a carrier wave. The coefficients of this equation are expressed in terms Bessel and modified Bessel functions. They are calculated numerically for various values of parameters. In particular, we show that the criterion for the onset of the modulational or Benjamin-Fair instability is satisfied. The implication of the obtained results for solar physics is discussed.
Time-resolving Attosecond Chiral Dynamics in Molecules with High Harmonic Spectroscopy
NASA Astrophysics Data System (ADS)
Smirnova, O.; Cireasa, R.; Boguslavskiy, A.; Pons, B.; Wong, M. C. H.; Descamps, D.; Petit, S.; Ruf, H.; Thire, N.; Ferre, A.; Suarez, J.; Schmidt, B. E.; Higuet, J.; Alharbi, A. F.; Legare, F.; Blanchet, V.; Fabre, B.; Patchkovskii, S.; Mairesse, Y.; Bhardwaj, R.
2015-05-01
We demonstrate extreme chiral sensitivity of high harmonic generation from randomly oriented ensemble of chiral molecules in elliptical mid-infrared fields, and explain the physical mechanism underlying this very strong chiro-optical response. We also use the high harmonic spectra to follow the electronic chiral response with 0.1 femtosecond resolution. We studied two chiral molecules, epoxypropane and fenchone in 1.8 μm, 50 fs, mid-1013 W/cm2 pulses. Very small ellipticity of the incident light, about 1% in the field, is sufficient to induce several percent difference between the high harmonic response of left and right enantiomers. The origin of this effect lies in chiral-sensitive dynamics of the hole created by strong field ionization. Small differences in this dynamics between ionization and recombination are recorded and amplified by several orders of magnitude in high harmonic spectra. Using time-energy mapping we reconstruct sub-femtosecond chiral dynamics and show that the standard measure of the chiral signal is directly proportional to the recombination amplitude to the chiral-sensitive component of the hole wave-packet.
Strongly Dispersive Transient Bragg Grating for High Harmonics
Farrell, J.; Spector, L.S.; Gaarde, M.B.; McFarland, B.K.; Bucksbaum, P.H.; Guhr, Markus; /SLAC, PULSE /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept.
2010-06-04
We create a transient Bragg grating in a high harmonic generation medium using two counterpropagating pulses. The Bragg grating disperses the harmonics in angle and can diffract a large bandwidth with temporal resolution limited only by the source size.
Single-shot fluctuations in waveguided high-harmonic generation.
Goh, S J; Tao, Y; van der Slot, P J M; Bastiaens, H J M; Herek, J; Biedron, S G; Danailov, M B; Milton, S V; Boller, K-J
2015-09-21
For exploring the application potential of coherent soft x-ray (SXR) and extreme ultraviolet radiation (XUV) provided by high-harmonic generation, it is important to characterize the central output parameters. Of specific importance are pulse-to-pulse (shot-to-shot) fluctuations of the high-harmonic output energy, fluctuations of the direction of the emission (pointing instabilities), and fluctuations of the beam divergence and shape that reduce the spatial coherence. We present the first single-shot measurements of waveguided high-harmonic generation in a waveguided (capillary-based) geometry. Using a capillary waveguide filled with Argon gas as the nonlinear medium, we provide the first characterization of shot-to-shot fluctuations of the pulse energy, of the divergence and of the beam pointing. We record the strength of these fluctuations vs. two basic input parameters, which are the drive laser pulse energy and the gas pressure in the capillary waveguide. In correlation measurements between single-shot drive laser beam profiles and single-shot high-harmonic beam profiles we prove the absence of drive laser beam-pointing-induced fluctuations in the high-harmonic output. We attribute the main source of high-harmonic fluctuations to ionization-induced nonlinear mode mixing during propagation of the drive laser pulse inside the capillary waveguide. PMID:26406689
Fokker-Planck/Ray Tracing for Electron Bernstein and Fast Wave Modeling in Support of NSTX
Harvey, R. W.
2009-11-12
This DOE grant supported fusion energy research, a potential long-term solution to the world's energy needs. Magnetic fusion, exemplified by confinement of very hot ionized gases, i.e., plasmas, in donut-shaped tokamak vessels is a leading approach for this energy source. Thus far, a mixture of hydrogen isotopes has produced 10's of megawatts of fusion power for seconds in a tokamak reactor at Princeton Plasma Physics Laboratory in New Jersey. The research grant under consideration, ER54684, uses computer models to aid in understanding and projecting efficacy of heating and current drive sources in the National Spherical Torus Experiment, a tokamak variant, at PPPL. The NSTX experiment explores the physics of very tight aspect ratio, almost spherical tokamaks, aiming at producing steady-state fusion plasmas. The current drive is an integral part of the steady-state concept, maintaining the magnetic geometry in the steady-state tokamak. CompX further developed and applied models for radiofrequency (rf) heating and current drive for applications to NSTX. These models build on a 30 year development of rf ray tracing (the all-frequencies GENRAY code) and higher dimensional Fokker-Planck rf-collisional modeling (the 3D collisional-quasilinear CQL3D code) at CompX. Two mainline current-drive rf modes are proposed for injection into NSTX: (1) electron Bernstein wave (EBW), and (2) high harmonic fast wave (HHFW) modes. Both these current drive systems provide a means for the rf to access the especially high density plasma--termed high beta plasma--compared to the strength of the required magnetic fields. The CompX studies entailed detailed modeling of the EBW to calculate the efficiency of the current drive system, and to determine its range of flexibility for driving current at spatial locations in the plasma cross-section. The ray tracing showed penetration into NSTX bulk plasma, relatively efficient current drive, but a limited ability to produce current over the whole
Fast Waves at the Base of the Cochlea
Recio-Spinoso, Alberto; Rhode, William S.
2015-01-01
Georg von Békésy observed that the onset times of responses to brief-duration stimuli vary as a function of distance from the stapes, with basal regions starting to move earlier than apical ones. He noticed that the speed of signal propagation along the cochlea is slow when compared with the speed of sound in water. Fast traveling waves have been recorded in the cochlea, but their existence is interpreted as the result of an experiment artifact. Accounts of the timing of vibration onsets at the base of the cochlea generally agree with Békésy’s results. Some authors, however, have argued that the measured delays are too short for consistency with Békésy’s theory. To investigate the speed of the traveling wave at the base of the cochlea, we analyzed basilar membrane (BM) responses to clicks recorded at several locations in the base of the chinchilla cochlea. The initial component of the BM response matches remarkably well the initial component of the stapes response, after a 4-μs delay of the latter. A similar conclusion is reached by analyzing onset times of time-domain gain functions, which correspond to BM click responses normalized by middle-ear input. Our results suggest that BM responses to clicks arise from a combination of fast and slow traveling waves. PMID:26062000
Frequency and damping rate of fast sausage waves
Farahani, S. Vasheghani; Van Doorsselaere, T.; Goossens, M.; Hornsey, C.
2014-02-01
We investigate the frequency and damping rate of fast axisymmetric waves that are subject to wave leakage for a one-dimensional magnetic cylindrical structure in the solar corona. We consider the ideal magnetohydrodynamic (MHD) dispersion relation for axisymmetric MHD waves superimposed on a straight magnetic cylinder in the zero β limit, similar to a jet or loop in the solar corona. An analytic study accompanied by numerical calculations has been carried out to model the frequency, damping rate, and phase speed of the sausage wave around the cut-off frequency and in the long wavelength limit. Analytic expressions have been obtained based on equations around the points of interest. They are linear approximations of the dependence of the sausage frequency on the wave number around the cut-off wavelength for both leaky and non-leaky regimes and in the long wavelength limit. Moreover, an expression for the damping rate of the leaky sausage wave has been obtained both around the cut-off frequency and in the long wavelength limit. These analytic results are compared with numerical computations. The expressions show that the complex frequencies are mainly dominated by the density ratio. In addition, it is shown that the damping eventually becomes independent of the wave number in the long wavelength limit. We conclude that the sausage mode damping directly depends on the density ratios of the internal and external media where the damping declines in higher density contrasts. Even in the long wavelength limit, the sausage mode is weakly damped for high-density contrasts. As such, sausage modes could be observed for a significant number of periods in high-density contrast loops or jets.
Non-collinear generation of angularly isolated circularly polarized high harmonics
NASA Astrophysics Data System (ADS)
Hickstein, Daniel D.; Dollar, Franklin J.; Grychtol, Patrik; Ellis, Jennifer L.; Knut, Ronny; Hernández-García, Carlos; Zusin, Dmitriy; Gentry, Christian; Shaw, Justin M.; Fan, Tingting; Dorney, Kevin M.; Becker, Andreas; Jaroń-Becker, Agnieszka; Kapteyn, Henry C.; Murnane, Margaret M.; Durfee, Charles G.
2015-11-01
We generate angularly isolated beams of circularly polarized extreme ultraviolet light through the first implementation of non-collinear high harmonic generation with circularly polarized driving lasers. This non-collinear technique offers numerous advantages over previous methods, including the generation of higher photon energies, the separation of the harmonics from the pump beam, the production of both left and right circularly polarized harmonics at the same wavelength and the capability of separating the harmonics without using a spectrometer. To confirm the circular polarization of the beams and to demonstrate the practicality of this new light source, we measure the magnetic circular dichroism of a 20 nm iron film. Furthermore, we explain the mechanisms of non-collinear high harmonic generation using analytical descriptions in both the photon and wave models. Advanced numerical simulations indicate that this non-collinear mixing enables the generation of isolated attosecond pulses with circular polarization.
Resonance absorption of propagating fast waves in a cold plasma
NASA Technical Reports Server (NTRS)
Hollweg, Joseph V.
1990-01-01
Absorption of propagating waves impinging on a surface in which the plasma and magnetic field may change is investigated by examining in depth the problem of a combination of cold plasma, uniform magnetic field and a surface density which varies linearly from zero at the left end to some finite value at the right end, beyond which the density is constant. Two cases are considered: one in which the plasma is a vacuum everywhere to the left of the surface (which may correspond to coronal conditions) and one in which the plasma density jumps to a very large value to the left of the surface (which may mimic the magnetosphere with the dense region at the left corresponding to the plasmasphere). A complete discussion of the resonance absorption of propagating fast waves for the case considered by Kiveloson and Southwood (1986) is presented, emphasizing approximate analytical results whenever possible; these results are then compared with exact numerical solutions.
Review of tokamak experiments on direct electron heating and current drive with fast waves
Pinsker, R.I.
1993-12-01
Results from tokamak experiments on direct electron interaction with the compressional Alfven wave ({open_quote}fast wave{close_quote}) are reviewed. Experiments aimed at electron heating as well as those in which fast wave electron current drive was investigated are discussed. A distinction is drawn between experiments employing the lower hybrid range of frequencies, where both the lower hybrid wave ({open_quote}slow wave{close_quote}) and the fast wave can propagate in much of the plasma, and those experiments using the fast wave in the range of moderate to high ion cyclotron harmonics, where only the fast wave can penetrate to the plasma core. Most of the early tokamak experiments were in the lower hybrid frequency regime, and the observed electron interaction appeared to be very similar to that obtained with the slow wave at the same frequency. In particular, electron interaction with the fast wave was observed only below a density limit nearly the same as the well known slow wave density limit. In the more recent lower frequency fast wave experiments, electron interaction (heating and current drive) is observed at the center of the discharge, where slow waves are not present.
High Harmonic Spectroscopy of the Cooper Minimum in Molecules
NASA Astrophysics Data System (ADS)
Wong, M. C. H.; Le, A.-T.; Alharbi, A. F.; Boguslavskiy, A. E.; Lucchese, R. R.; Brichta, J.-P.; Lin, C. D.; Bhardwaj, V. R.
2013-01-01
The Cooper minimum (CM) has been studied using high harmonic generation solely in atoms. Here, we present detailed experimental and theoretical studies on the CM in molecules probed by high harmonic generation using a range of near-infrared light pulses from λ=1.3 to 1.8μm. We demonstrate the CM to occur in CS2 and CCl4 at ˜42 and ˜40eV, respectively, by comparing the high harmonic spectra with the known partial photoionization cross sections of different molecular orbitals, confirmed by theoretical calculations of harmonic spectra. We use CM to probe electron localization in Cl-containing molecules (CCl4, CH2Cl2, and trans-C2H2Cl2) and show that the position of the minimum is influenced by the molecular environment.
Experimental observation of anomalous high harmonics at low intensities
NASA Astrophysics Data System (ADS)
Valentin, C.; Kazamias, S.; Douillet, D.; Grillon, G.; Lefrou, T.; Augé, F.; Sebban, S.; Balcou, P.
A variety of complex phenomena occurs when an ultra-short laser pulse interacts with atoms in the 1013 W/cm2 range: non-sequential ionisation, electron recollision, and Freeman resonances. We show that high-harmonic spectra obtained experimentally in this parameter range also display anomalous features, which are difficult to understand in the framework of the three-step, semiclassical model. The results of a systematic study of these high harmonics generated in argon, xenon, and krypton are presented. From the experimental curves, complex high-order harmonic generation phenomena are discussed.
Fast electronic resistance switching involving hidden charge density wave states
Vaskivskyi, I.; Mihailovic, I. A.; Brazovskii, S.; Gospodaric, J.; Mertelj, T.; Svetin, D.; Sutar, P.; Mihailovic, D.
2016-01-01
The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T–TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states. PMID:27181483
Gravitational wave asteroseismology with fast rotating neutron stars
Gaertig, Erich; Kokkotas, Kostas D.
2011-03-15
We investigate damping and growth times of the quadrupolar f mode for rapidly rotating stars and a variety of different polytropic equations of state in the Cowling approximation. This is the first study of the damping/growth time of these types of oscillations for fast-rotating neutron stars in a relativistic treatment where the spacetime degrees of freedom of the perturbations are neglected. We use these frequencies and damping/growth times to create robust empirical formulae which can be used for gravitational-wave asteroseismology. The estimation of the damping/growth time is based on the quadrupole formula and our results agree very well with Newtonian ones in the appropriate limit.
Technology of fast-wave current drive antennas
Hoffman, D.J.; Baity, F.W.; Goulding, R.H.; Haste, G.R.; Ryan, P.M.; Taylor, D.J.; Swain, D.W.; Mayberry, M.J.; Yugo, J.J.; General Atomics, San Diego, CA; Oak Ridge National Lab., TN )
1989-01-01
The design of fast-wave current drive (FWCD) antennas combines the usual antenna considerations (e.g., the plasma/antenna interface, disruptions, high currents and voltages, and thermal loads) with new requirements for spectral shaping and phase control. The internal configuration of the antenna array has a profound effect on the spectrum and the ability to control phasing. This paper elaborates on these considerations, as epitomized by a proof-of-principle (POP) experiment designed for the DIII-D tokamak. The extension of FWCD for machines such as the International Thermonuclear Engineering Reactor (ITER) will require combining ideas implemented in the POP experiment with reactor-relevant antenna concepts, such as the folded waveguide. 6 refs., 8 figs.
Fast electronic resistance switching involving hidden charge density wave states
NASA Astrophysics Data System (ADS)
Vaskivskyi, I.; Mihailovic, I. A.; Brazovskii, S.; Gospodaric, J.; Mertelj, T.; Svetin, D.; Sutar, P.; Mihailovic, D.
2016-05-01
The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T-TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states.
Fast electronic resistance switching involving hidden charge density wave states.
Vaskivskyi, I; Mihailovic, I A; Brazovskii, S; Gospodaric, J; Mertelj, T; Svetin, D; Sutar, P; Mihailovic, D
2016-01-01
The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T-TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states. PMID:27181483
Fast calcium wave inhibits excessive apoptosis during epithelial wound healing.
Justet, Cristian; Hernández, Julio A; Torriglia, Alicia; Chifflet, Silvia
2016-08-01
Successful wound closure is mainly the result of two cellular processes: migration and proliferation. Apoptosis has also been suggested to play a role in the mechanisms of wound healing. The fast calcium wave (FCW), triggered immediately after a wound is produced, has been proposed to be involved in determining healing responses in epithelia. We have explored the effects of the reversible inhibition of FCW on the apoptotic and proliferative responses of healing bovine corneal endothelial (BCE) cells in culture. The most important findings of this study are that caspase-dependent apoptosis occurs during the healing process, that the amount of apoptosis has a linear dependence on the migrated distance, and that FCW inhibition greatly increases the apoptotic index. We have further been able to establish that FCW plays a role in the control of cell proliferation during BCE wound healing. These results indicate that one of the main roles of the wave is to inhibit an excessive apoptotic response of the healing migrating cells. This property might represent a basic mechanism to allow sufficient migration and proliferation of the healing cells to assure proper restitution of the injured tissue. PMID:26987821
High frequency fast wave current drive for DEMO
Koch, R.; Lerche, E.; Van Eester, D.
2011-12-23
A steady-state tokamak reactor (SSTR) requires a high efficiency current drive system, from plug to driven mega-amps. RF systems working in the ion-cyclotron range of frequencies (ICRF) have high efficiency from plug to antenna but a limited current drive (CD) efficiency and centrally peaked CD profiles. The latter feature is not adequate for a SSTR where the current should be sufficiently broad to keep the central safety factor (possibly significantly) above 1. In addition, the fact that the fast wave (FW) is evanescent at the edge limits coupling, requiring high voltage operation, which makes the system dependent on plasma edge properties and prone to arcing, reducing its reliability. A possible way to overcome these weaknesses is to operate at higher frequency (10 times or more the cyclotron frequency). The advantages are: (1) The coupling can be much better (waves propagate in vacuum) if the parallel refractive index n{sub ||} is kept below one, (2) The FW group velocity tends to align to the magnetic field, so the power circumnavigates the magnetic axis and can drive off-axis current, (3) Due to the latter property, n{sub ||} can be upshifted along the wave propagation path, allowing low n{sub ||} launch (hence good coupling, large CD efficiency) with ultimately good electron absorption (which requires higher n{sub ||}. Note however that the n{sub ||} upshift is a self-organized feature, that electron absorption is in competition with {alpha}-particle absorption and that uncoupling of the FW from the lower hybrid resonance at the edge requires n{sub ||} slightly above one. The latter possibly counterproductive features might complicate the picture. The different aspects of this potentially attractive off-axis FWCD scheme are discussed.
Fast T Wave Detection Calibrated by Clinical Knowledge with Annotation of P and T Waves
Elgendi, Mohamed; Eskofier, Bjoern; Abbott, Derek
2015-01-01
Background There are limited studies on the automatic detection of T waves in arrhythmic electrocardiogram (ECG) signals. This is perhaps because there is no available arrhythmia dataset with annotated T waves. There is a growing need to develop numerically-efficient algorithms that can accommodate the new trend of battery-driven ECG devices. Moreover, there is also a need to analyze long-term recorded signals in a reliable and time-efficient manner, therefore improving the diagnostic ability of mobile devices and point-of-care technologies. Methods Here, the T wave annotation of the well-known MIT-BIH arrhythmia database is discussed and provided. Moreover, a simple fast method for detecting T waves is introduced. A typical T wave detection method has been reduced to a basic approach consisting of two moving averages and dynamic thresholds. The dynamic thresholds were calibrated using four clinically known types of sinus node response to atrial premature depolarization (compensation, reset, interpolation, and reentry). Results The determination of T wave peaks is performed and the proposed algorithm is evaluated on two well-known databases, the QT and MIT-BIH Arrhythmia databases. The detector obtained a sensitivity of 97.14% and a positive predictivity of 99.29% over the first lead of the validation databases (total of 221,186 beats). Conclusions We present a simple yet very reliable T wave detection algorithm that can be potentially implemented on mobile battery-driven devices. In contrast to complex methods, it can be easily implemented in a digital filter design. PMID:26197321
Can a Fast-Mode EUV Wave Generate a Stationary Front?
NASA Astrophysics Data System (ADS)
Chen, P. F.; Fang, C.; Chandra, R.; Srivastava, A. K.
2016-06-01
The discovery of stationary "EIT waves" about 16 years ago posed a big challenge to the then favorite fast-mode wave model for coronal "EIT waves". It encouraged various non-wave models and played an important role in convergence of the opposing viewpoints toward the recent consensus that there are two types of EUV waves. However, it was recently discovered that a stationary wave front can also be generated when a fast-mode wave passes through a magnetic quasi-separatrix layer (QSL). In this article, we perform a magnetohydrodynamic (MHD) numerical simulation of the interaction between a fast-mode wave and a magnetic QSL, and a stationary wave front is reproduced. The analysis of the numerical results indicates that near the plasma beta {˜} 1 layer in front of the magnetic QSL, part of the fast-mode wave is converted to a slow-mode MHD wave, which is then trapped inside the magnetic loops, forming a stationary wave front. Our results imply that we have to be cautious in identifying the nature of a wave, since there may be mode conversion during the propagation of the waves driven by solar eruptions.
60 MHz fast wave current drive experiment for DIII-D
Mayberry, M.J.; Chiu, S.C.; Porkolab, M.; Chan, V.; Freeman, R.; Harvey, R.; Pinsker, R. )
1989-07-01
The DIII-D facility provides an opportunity to test fast wave current drive appoach. Efficient FWCD is achieved by direct electron absorption due to Landa damping and transit time magnetic pumping. To avoid competing damping mechamisms we seek to maximize the single-pass asorption of the fast waves by electrons. (AIP)
Kwon, Ryun-Young; Ofman, Leon; Kramar, Maxim; Olmedo, Oscar; Davila, Joseph M.; Thompson, Barbara J.; Cho, Kyung-Suk
2013-03-20
We report white-light observations of a fast magnetosonic wave associated with a coronal mass ejection observed by STEREO/SECCHI/COR1 inner coronagraphs on 2011 August 4. The wave front is observed in the form of density compression passing through various coronal regions such as quiet/active corona, coronal holes, and streamers. Together with measured electron densities determined with STEREO COR1 and Extreme UltraViolet Imager (EUVI) data, we use our kinematic measurements of the wave front to calculate coronal magnetic fields and find that the measured speeds are consistent with characteristic fast magnetosonic speeds in the corona. In addition, the wave front turns out to be the upper coronal counterpart of the EIT wave observed by STEREO EUVI traveling against the solar coronal disk; moreover, stationary fronts of the EIT wave are found to be located at the footpoints of deflected streamers and boundaries of coronal holes, after the wave front in the upper solar corona passes through open magnetic field lines in the streamers. Our findings suggest that the observed EIT wave should be in fact a fast magnetosonic shock/wave traveling in the inhomogeneous solar corona, as part of the fast magnetosonic wave propagating in the extended solar corona.
Vibrational Quantum Beats and High Harmonic Generation in SF6
NASA Astrophysics Data System (ADS)
Walters, Zachary B.; Tonzani, Stefano; Greene, Chris H.
2007-06-01
Although HHG is commonly understood as an electronic process, vibrational degrees of freedom in molecules allow for phenomena which have no analogue in atomic systems. This was recently demonstrated in experiments performed with SF6 (Wagner et al, PNAS 103 13279, 2006). If a HHG laser pulse is preceded by a weaker pulse which stimulates Raman-active vibrations, the harmonic intensity oscillates with the interpulse delay time at the frequencies of the stimulated modes. We explain this modulation as quantum interference between adjacent vibrational states of the molecule, which are mixed during the high harmonic process. We present an improved version of the three-step model, which uses nonperturbative electron-ion scattering wavefunctions to find the recombination dipole, and which tracks the vibrational wavefunction of the molecule throughout the high harmonic process.
Role of Many-Electron Dynamics in High Harmonic Generation
Gordon, Ariel; Kaertner, Franz X.; Rohringer, Nina; Santra, Robin
2006-06-09
High harmonic generation (HHG) in many-electron atoms is studied theoretically. The breakdown of the frozen-core single active electron approximation is demonstrated, as it predicts roughly the same radiation amplitude in all noble gases. This is in contradiction with experiments, where heavier noble gases are known to emit much stronger HHG radiation than lighter ones. This experimental behavior of the noble gases can be qualitatively reproduced when many-electron dynamics, within a simple approximation, is taken into account.
Energy and energy flux in axisymmetric slow and fast waves
NASA Astrophysics Data System (ADS)
Moreels, M. G.; Van Doorsselaere, T.; Grant, S. D. T.; Jess, D. B.; Goossens, M.
2015-06-01
Aims: We aim to calculate the kinetic, magnetic, thermal, and total energy densities and the flux of energy in axisymmetric sausage modes. The resulting equations should contain as few parameters as possible to facilitate applicability for different observations. Methods: The background equilibrium is a one-dimensional cylindrical flux tube model with a piecewise constant radial density profile. This enables us to use linearised magnetohydrodynamic equations to calculate the energy densities and the flux of energy for axisymmetric sausage modes. Results: The equations used to calculate the energy densities and the flux of energy in axisymmetric sausage modes depend on the radius of the flux tube, the equilibrium sound and Alfvén speeds, the density of the plasma, the period and phase speed of the wave, and the radial or longitudinal components of the Lagrangian displacement at the flux tube boundary. Approximate relations for limiting cases of propagating slow and fast sausage modes are also obtained. We also obtained the dispersive first-order correction term to the phase speed for both the fundamental slow body mode under coronal conditions and the slow surface mode under photospheric conditions. Appendix A is available in electronic form at http://www.aanda.org
Gus’kov, S. Yu.; Nicolai, Ph.; Ribeyre, X.; Tikhonchuk, V. T.
2015-09-15
An exact analytic solution is found for the steady-state distribution function of fast electrons with an arbitrary initial spectrum irradiating a planar low-Z plasma with an arbitrary density distribution. The solution is applied to study the heating of a material by fast electrons of different spectra such as a monoenergetic spectrum, a step-like distribution in a given energy range, and a Maxwellian spectrum, which is inherent in laser-produced fast electrons. The heating of shock- and fast-ignited precompressed inertial confinement fusion (ICF) targets as well as the heating of a target designed to generate a Gbar shock wave for equation of state (EOS) experiments by laser-produced fast electrons with a Maxwellian spectrum is investigated. A relation is established between the energies of two groups of Maxwellian fast electrons, which are responsible for generation of a shock wave and heating the upstream material (preheating). The minimum energy of the fast and shock igniting beams as well as of the beam for a Gbar shock wave generation increases with the spectral width of the electron distribution.
Ultraviolet surprise: Efficient soft x-ray high-harmonic generation in multiply ionized plasmas
NASA Astrophysics Data System (ADS)
Popmintchev, Dimitar; Hernández-García, Carlos; Dollar, Franklin; Mancuso, Christopher; Pérez-Hernández, Jose A.; Chen, Ming-Chang; Hankla, Amelia; Gao, Xiaohui; Shim, Bonggu; Gaeta, Alexander L.; Tarazkar, Maryam; Romanov, Dmitri A.; Levis, Robert J.; Gaffney, Jim A.; Foord, Mark; Libby, Stephen B.; Jaron-Becker, Agnieszka; Becker, Andreas; Plaja, Luis; Murnane, Margaret M.; Kapteyn, Henry C.; Popmintchev, Tenio
2015-12-01
High-harmonic generation is a universal response of matter to strong femtosecond laser fields, coherently upconverting light to much shorter wavelengths. Optimizing the conversion of laser light into soft x-rays typically demands a trade-off between two competing factors. Because of reduced quantum diffusion of the radiating electron wave function, the emission from each species is highest when a short-wavelength ultraviolet driving laser is used. However, phase matching—the constructive addition of x-ray waves from a large number of atoms—favors longer-wavelength mid-infrared lasers. We identified a regime of high-harmonic generation driven by 40-cycle ultraviolet lasers in waveguides that can generate bright beams in the soft x-ray region of the spectrum, up to photon energies of 280 electron volts. Surprisingly, the high ultraviolet refractive indices of both neutral atoms and ions enabled effective phase matching, even in a multiply ionized plasma. We observed harmonics with very narrow linewidths, while calculations show that the x-rays emerge as nearly time-bandwidth-limited pulse trains of ~100 attoseconds.
The Ultraviolet Surprise. Efficient Soft X-Ray High Harmonic Generation in Multiply-Ionized Plasmas
Popmintchev, Dimitar; Hernandez-Garcia, Carlos; Dollar, Franklin; Mancuso, Christopher; Perez-Hernandez, Jose A.; Chen, Ming-Chang; Hankla, Amelia; Gao, Xiaohui; Shim, Bonggu; Gaeta, Alexander L.; Tarazkar, Maryam; Romanov, Dmitri A.; Levis, Robert J.; Gaffney, Jim A.; Foord, Mark; Libby, Stephen B.; Jaron-Becker, Agnieskzka; Becker, Andreas; Plaja, Luis; Muranane, Margaret M.; Kapteyn, Henry C.; Popmintchev, Tenio
2015-12-04
High-harmonic generation is a universal response of matter to strong femtosecond laser fields, coherently upconverting light to much shorter wavelengths. Optimizing the conversion of laser light into soft x-rays typically demands a trade-off between two competing factors. Reduced quantum diffusion of the radiating electron wave function results in emission from each species which is highest when a short-wavelength ultraviolet driving laser is used. But, phase matching—the constructive addition of x-ray waves from a large number of atoms—favors longer-wavelength mid-infrared lasers. We identified a regime of high-harmonic generation driven by 40-cycle ultraviolet lasers in waveguides that can generate bright beams in the soft x-ray region of the spectrum, up to photon energies of 280 electron volts. Surprisingly, the high ultraviolet refractive indices of both neutral atoms and ions enabled effective phase matching, even in a multiply ionized plasma. We observed harmonics with very narrow linewidths, while calculations show that the x-rays emerge as nearly time-bandwidth–limited pulse trains of ~100 attoseconds.
The Ultraviolet Surprise. Efficient Soft X-Ray High Harmonic Generation in Multiply-Ionized Plasmas
Popmintchev, Dimitar; Hernandez-Garcia, Carlos; Dollar, Franklin; Mancuso, Christopher; Perez-Hernandez, Jose A.; Chen, Ming-Chang; Hankla, Amelia; Gao, Xiaohui; Shim, Bonggu; Gaeta, Alexander L.; et al
2015-12-04
High-harmonic generation is a universal response of matter to strong femtosecond laser fields, coherently upconverting light to much shorter wavelengths. Optimizing the conversion of laser light into soft x-rays typically demands a trade-off between two competing factors. Reduced quantum diffusion of the radiating electron wave function results in emission from each species which is highest when a short-wavelength ultraviolet driving laser is used. But, phase matching—the constructive addition of x-ray waves from a large number of atoms—favors longer-wavelength mid-infrared lasers. We identified a regime of high-harmonic generation driven by 40-cycle ultraviolet lasers in waveguides that can generate bright beams inmore » the soft x-ray region of the spectrum, up to photon energies of 280 electron volts. Surprisingly, the high ultraviolet refractive indices of both neutral atoms and ions enabled effective phase matching, even in a multiply ionized plasma. We observed harmonics with very narrow linewidths, while calculations show that the x-rays emerge as nearly time-bandwidth–limited pulse trains of ~100 attoseconds.« less
Investigate the effect of bounce resonance between fast magnetosonic waves and energetic electrons
NASA Astrophysics Data System (ADS)
Maldonado, A.; Chen, L.
2014-12-01
Equatorial noises are fast magnetosonic wave emissions that are nearly perpendicular propagating and confined near the geomagnetic equator within several degrees. We investigate the effect of bounce resonance between a fast magnetosonic wave and equatorially mirroring electrons using test particle simulation. Bounce resonance occurs when wave frequency matches multiple of electron bounce frequency. We find that the bounce resonance can lead to nonlinear oscillation of equatorially trapped electrons when wave frequency is near first few harmonics of electron bounce frequency. When in bounce resonance, the oscillation amplitude increases for larger wave amplitude, smaller wave normal angle, or larger plasma density. This oscillation is important for dynamics of equatorially mirroring electrons above 100 keV, because it can produce finite vz, which could enable gyro-resonance interaction with other waves such as whistler mode waves.
Using dynamic interferometric synthetic aperature radar (InSAR) to image fast-moving surface waves
Vincent, Paul
2005-06-28
A new differential technique and system for imaging dynamic (fast moving) surface waves using Dynamic Interferometric Synthetic Aperture Radar (InSAR) is introduced. This differential technique and system can sample the fast-moving surface displacement waves from a plurality of moving platform positions in either a repeat-pass single-antenna or a single-pass mode having a single-antenna dual-phase receiver or having dual physically separate antennas, and reconstruct a plurality of phase differentials from a plurality of platform positions to produce a series of desired interferometric images of the fast moving waves.
Fast Magnetoacoustic Wave Trains of Sausage Symmetry in Cylindrical Waveguides of the Solar Corona
NASA Astrophysics Data System (ADS)
Shestov, S.; Nakariakov, V. M.; Kuzin, S.
2015-12-01
Fast magnetoacoustic waves guided along the magnetic field by plasma non-uniformities, in particular coronal loops, fibrils, and plumes, are known to be highly dispersive, which lead to the formation of quasi-periodic wave trains excited by a broadband impulsive driver, e.g., a solar flare. We investigated the effects of cylindrical geometry on the fast sausage wave train formation. We performed magnetohydrodynamic numerical simulations of fast magnetoacoustic perturbations of a sausage symmetry, propagating from a localized impulsive source along a field-aligned plasma cylinder with a smooth radial profile of the fast speed. The wave trains are found to have pronounced period modulation, with the longer instant period seen in the beginning of the wave train. The wave trains also have a pronounced amplitude modulation. Wavelet spectra of the wave trains have characteristic tadpole features, with the broadband large-amplitude heads preceding low-amplitude quasi-monochromatic tails. The mean period of the wave train is about the transverse fast magnetoacoustic transit time across the cylinder. The mean parallel wavelength is about the diameter of the wave-guiding plasma cylinder. Instant periods are longer than the sausage wave cutoff period. The wave train characteristics depend on the fast magnetoacoustic speed in both the internal and external media, the smoothness of the transverse profile of the equilibrium quantities, and also the spatial size of the initial perturbation. If the initial perturbation is localized at the axis of the cylinder, the wave trains contain higher radial harmonics that have shorter periods.
Groopman, Amber M.; Katz, Jonathan I.; Holland, Mark R.; Fujita, Fuminori; Matsukawa, Mami; Mizuno, Katsunori; Wear, Keith A.; Miller, James G.
2015-01-01
Conventional, Bayesian, and the modified least-squares Prony's plus curve-fitting (MLSP + CF) methods were applied to data acquired using 1 MHz center frequency, broadband transducers on a single equine cancellous bone specimen that was systematically shortened from 11.8 mm down to 0.5 mm for a total of 24 sample thicknesses. Due to overlapping fast and slow waves, conventional analysis methods were restricted to data from sample thicknesses ranging from 11.8 mm to 6.0 mm. In contrast, Bayesian and MLSP + CF methods successfully separated fast and slow waves and provided reliable estimates of the ultrasonic properties of fast and slow waves for sample thicknesses ranging from 11.8 mm down to 3.5 mm. Comparisons of the three methods were carried out for phase velocity at the center frequency and the slope of the attenuation coefficient for the fast and slow waves. Good agreement among the three methods was also observed for average signal loss at the center frequency. The Bayesian and MLSP + CF approaches were able to separate the fast and slow waves and provide good estimates of the fast and slow wave properties even when the two wave modes overlapped in both time and frequency domains making conventional analysis methods unreliable. PMID:26328678
High harmonic terahertz confocal gyrotron with nonuniform electron beam
NASA Astrophysics Data System (ADS)
Fu, Wenjie; Guan, Xiaotong; Yan, Yang
2016-01-01
The harmonic confocal gyrotron with nonuniform electron beam is proposed in this paper in order to develop compact and high power terahertz radiation source. A 0.56 THz third harmonic confocal gyrotron with a dual arc section nonuniform electron beam has been designed and investigated. The studies show that confocal cavity has extremely low mode density, and has great advantage to operate at high harmonic. Nonuniform electron beam is an approach to improve output power and interaction efficiency of confocal gyrotron. A dual arc beam magnetron injection gun for designed confocal gyrotron has been developed and presented in this paper.
Lateral shearing interferometry of high-harmonic wavefronts.
Austin, Dane R; Witting, Tobias; Arrell, Christopher A; Frank, Felix; Wyatt, Adam S; Marangos, Jon P; Tisch, John W G; Walmsley, Ian A
2011-05-15
We present a technique for frequency-resolved wavefront characterization of high harmonics based on lateral shearing interferometry. Tilted replicas of the driving laser pulse are produced by a Mach-Zehnder interferometer, producing separate focii in the target. The interference of the resulting harmonics on a flat-field extreme ultraviolet spectrometer yields the spatial phase derivative. A comprehensive set of spatial profiles, resolved by harmonic order, validate the technique and reveal the interplay of single-atom and macroscopic effects. PMID:21593877
Attosecond Probing of Vibrational Dynamics with High-Harmonic Generation
NASA Astrophysics Data System (ADS)
Lein, Manfred
2005-02-01
The numerical solution of the time-dependent Schrödinger equation for vibrating hydrogen molecules in few-cycle laser pulses shows that high-harmonic generation is sensitive to the laser-induced vibrational motion. More intense harmonics are generated in heavier isotopes, the difference increasing with the harmonic frequency. Analytical theory reveals a dependence of the harmonics on the vibrational autocorrelation function. With the help of a genetic algorithm, the nuclear motion can be reconstructed from the harmonic spectra with sub-fs time resolution.
Quantitative Modeling of Single Atom High Harmonic Generation
Gordon, Ariel; Kaertner, Franz X.
2005-11-25
It is shown by comparison with numerical solutions of the Schroedinger equation that the three step model (TSM) of high harmonic generation (HHG) can be improved to give a quantitatively reliable description of the process. Excellent agreement is demonstrated for the H atom and the H{sub 2}{sup +} molecular ion. It is shown that the standard TSM heavily distorts the HHG spectra, especially of H{sub 2}{sup +}, and an explanation is presented for this behavior. Key to the improvement is the use of the Ehrenfest theorem in the TSM.
High Harmonic Generation from Multiple Orbitals in N2
McFarland, B.; Farrell, Joseph P.; Bucksbaum, Philip H.; Guehr, Markus; /SLAC, Pulse /Stanford U., Phys. Dept.
2009-03-05
Molecular electronic states energetically below the highest occupied molecular orbital (HOMO) should contribute to laser-driven high harmonic generation (HHG), but this behavior has not been observed previously. Our measurements of the HHG spectrum of N{sub 2} molecules aligned perpendicular to the laser polarization showed a maximum at the rotational half-revival. This feature indicates the influence of electrons occupying the orbital just below the N{sub 2} HOMO, referred to as the HOMO-1. Such observations of lower-lying orbitals are essential to understanding subfemtosecond/subangstrom electronic motion in laser-excited molecules.
Control of Laser High-Harmonic Generation with Counterpropagating Light
NASA Astrophysics Data System (ADS)
Voronov, S. L.; Kohl, I.; Madsen, J. B.; Simmons, J.; Terry, N.; Titensor, J.; Wang, Q.; Peatross, J.
2001-09-01
Relatively weak counterpropagating light is shown to disrupt the emission of laser high-harmonic generation. Harmonic orders ranging from the teens to the low thirties produced by a 30-femtosecond pulse in a narrow argon jet are ``shut down'' with a contrast as high as 2 orders of magnitude by a chirped 1-picosecond counterpropagating laser pulse (60 times less intense). Alternatively, under poor phase-matching conditions, the counterpropagating light boosts harmonic production by similar contrast through quasiphase matching where out-of-phase emission is suppressed.
High harmonic generation by novel fiber amplifier based sources.
Hädrich, S; Rothhardt, J; Krebs, M; Tavella, F; Willner, A; Limpert, J; Tünnermann, A
2010-09-13
Significant progress in high repetition rate ultrashort pulse sources based on fiber technology is presented. These systems enable operation at a high repetition rate of up to 500 kHz and high average power in the extreme ultraviolet wavelength range via high harmonic generation in a gas jet. High average power few-cycle pulses of a fiber amplifier pumped optical parametric chirped pulse amplifier are used to produce µW level average power for the strongest harmonic at 42.9 nm at a repetition rate of 96 kHz. PMID:20940915
Karttunen, S.J.; Paettikangas, T.J.; Tala, T.J.; Cairns, R.A.
1997-09-01
Fast electron generation near the cutoff of an electrostatic plasma wave is investigated by particle-in-cell simulations and test particle calculations. Intense electron plasma waves which are excited in an underdense plasma region propagate up the density gradient until they are reflected from the cutoff layer. The density gradient affects the fast electron generation by the wave considerably. At low densities, the phase velocity is fairly close to the thermal distribution, which leads to wave-particle interactions with a large electron population. The trapped electrons are accelerated by the electron plasma wave with increasing phase velocity resulting in a very large and energetic population behind the cutoff layer. Since the accelerating electrons receive energy, the wave must be damped. A simple model based on the conservation of the energy of the wave and the trapped electrons is developed to describe the damping mechanism. {copyright} {ital 1997} {ital The American Physical Society}
High harmonics from solids probe Angstrom scale structure
NASA Astrophysics Data System (ADS)
You, Yong Sing; Reis, David; Ghimire, Shambhu
2016-05-01
The basic microscopic mechanism for the high harmonics generation (HHG) in isolated atoms and molecules has been understood in the 90's. Since then the gas harmonics have been utilized widely in ultrafast x-ray science, from attosecond pulse generation to imaging molecular orbitals of the target molecule. In contrast, the solid-state harmonic generation mechanism is currently being investigated following the recent experimental discovery in zinc oxide crystal. In particular, because of the fundamental differences, attributed to the high density and periodicity of the crystal, it was not clear if the solid-state harmonics could be used to reveal bonding structures in crystals. Here we report our experimental results on generation of XUV harmonics in single crystal MgO subjected to the field strengths on the order of 1V/Å without damage. High harmonics in MgO show strong crystal orientation dependence as well as a strong laser ellipticity dependence. By exploiting these unique characteristics, we demonstrate that XUV harmonics from bulk crystals can probe Angstrom scale electronic structure of the crystal.
High harmonic generation in underdense plasmas by intense laser pulses with orbital angular momentum
Mendonça, J. T.; Vieira, J.
2015-12-15
We study high harmonic generation produced by twisted laser pulses, with orbital angular momentum in the relativistic regime, for pulse propagation in underdense plasma. We consider fast time scale processes associated with an ultra-short pulse, where the ion motion can be neglected. We use both analytical models and numerical simulations using a relativistic particle-in-cell code. The present description is valid for relativistic laser intensities, when the normalized field amplitude is much larger than one, a ≫ 1. We also discuss two distinct processes associated with linear and circular polarization. Using both analytical solutions and particle-in-cell simulations, we are able to show that, for laser pulses in a well defined Laguerre-Gauss mode, angular momentum conservation is observed during the process of harmonic generation. Intensity modulation of the harmonic spectrum is also verified, as imposed by the nonlinear time-scale for energy transfer between different harmonics.
High harmonic generation in underdense plasmas by intense laser pulses with orbital angular momentum
NASA Astrophysics Data System (ADS)
Mendonça, J. T.; Vieira, J.
2015-12-01
We study high harmonic generation produced by twisted laser pulses, with orbital angular momentum in the relativistic regime, for pulse propagation in underdense plasma. We consider fast time scale processes associated with an ultra-short pulse, where the ion motion can be neglected. We use both analytical models and numerical simulations using a relativistic particle-in-cell code. The present description is valid for relativistic laser intensities, when the normalized field amplitude is much larger than one, a ≫ 1. We also discuss two distinct processes associated with linear and circular polarization. Using both analytical solutions and particle-in-cell simulations, we are able to show that, for laser pulses in a well defined Laguerre-Gauss mode, angular momentum conservation is observed during the process of harmonic generation. Intensity modulation of the harmonic spectrum is also verified, as imposed by the nonlinear time-scale for energy transfer between different harmonics.
MODELING SUPER-FAST MAGNETOSONIC WAVES OBSERVED BY SDO IN ACTIVE REGION FUNNELS
Ofman, L.; Liu, W.; Title, A.; Aschwanden, M.
2011-10-20
Recently, quasi-periodic, rapidly propagating waves have been observed in extreme ultraviolet by the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) instrument in about 10 flare/coronal mass ejection (CME) events thus far. A typical example is the 2010 August 1 C3.2 flare/CME event that exhibited arc-shaped wave trains propagating in an active region (AR) magnetic funnel with {approx}5% intensity variations at speeds in the range of 1000-2000 km s{sup -1}. The fast temporal cadence and high sensitivity of AIA enabled the detection of these waves. We identify them as fast magnetosonic waves driven quasi-periodically at the base of the flaring region and develop a three-dimensional MHD model of the event. For the initial state we utilize the dipole magnetic field to model the AR and include gravitationally stratified density at coronal temperature. At the coronal base of the AR, we excite the fast magnetosonic wave by periodic velocity pulsations in the photospheric plane confined to a funnel of magnetic field lines. The excited fast magnetosonic waves have similar amplitude, wavelength, and propagation speeds as the observed wave trains. Based on the simulation results, we discuss the possible excitation mechanism of the waves, their dynamical properties, and the use of the observations for coronal MHD seismology.
High-harmonic generation in a quantum electron gas trapped in a nonparabolic and anisotropic well
NASA Astrophysics Data System (ADS)
Hurst, Jérôme; Lévêque-Simon, Kévin; Hervieux, Paul-Antoine; Manfredi, Giovanni; Haas, Fernando
2016-05-01
An effective self-consistent model is derived and used to study the dynamics of an electron gas confined in a nonparabolic and anisotropic quantum well. This approach is based on the equations of quantum hydrodynamics, which incorporate quantum and nonlinear effects in an approximate fashion. The effective model consists of a set of six coupled differential equations (dynamical system) for the electric dipole and the size of the electron gas. Using this model we show that: (i) high harmonic generation is related to the appearance of chaos in the phase space, as attested to by related Poincaré sections; (ii) higher order harmonics can be excited efficiently and with relatively weak driving fields by making use of chirped electromagnetic waves.
Attosecond control of electron-ion recollision in high harmonic generation
NASA Astrophysics Data System (ADS)
Gademann, G.; Kelkensberg, F.; Siu, W. K.; Johnsson, P.; Gaarde, M. B.; Schafer, K. J.; Vrakking, M. J. J.
2011-03-01
We show that high harmonic generation driven by an intense near-infrared (IR) laser can be temporally controlled when an attosecond pulse train (APT) is used to ionize the generation medium, thereby replacing tunnel ionization as the first step in the well-known three-step model. New harmonics are formed when the ionization occurs at a well-defined time within the optical cycle of the IR field. The use of APT-created electron wave packets affords new avenues for the study and application of harmonic generation. In the present experiment, this makes it possible to study harmonic generation at IR intensities where tunnel ionization does not give a measurable signal.
3D WKB solution for fast magnetoacoustic wave behaviour around an X-line
NASA Astrophysics Data System (ADS)
McLaughlin, J. A.; Botha, G. J. J.; Régnier, S.; Spoors, D. L.
2016-06-01
Context. We study the propagation of a fast magnetoacoustic wave in a 3D magnetic field created from two magnetic dipoles. The magnetic topology contains an X-line. Aims: We aim to contribute to the overall understanding of MHD wave propagation within inhomogeneous media, specifically around X-lines. Methods: We investigate the linearised, 3D MHD equations under the assumptions of ideal and cold plasma. We utilise the WKB approximation and Charpit's method during our investigation. Results: It is found that the behaviour of the fast magnetoacoustic wave is entirely dictated by the local, inhomogeneous, equilibrium Alfvén speed profile. All parts of the wave experience refraction during propagation, where the magnitude of the refraction effect depends on the location of an individual wave element within the inhomogeneous magnetic field. The X-line, along which the Alfvén speed is identically zero, acts as a focus for the refraction effect. There are two main types of wave behaviour: part of the wave is either trapped by the X-line or escapes the system, and there exists a critical starting region around the X-line that divides these two types of behaviour. For the set-up investigated, it is found that 15.5% of the fast wave energy is trapped by the X-line. Conclusions: We conclude that linear, β = 0 fast magnetoacoustic waves can accumulate along X-lines and thus these will be specific locations of fast wave energy deposition and thus preferential heating. The work here highlights the importance of understanding the magnetic topology of a system. We also demonstrate how the 3D WKB technique described in this paper can be applied to other magnetic configurations.
High harmonic generation in the undulators for free electron lasers
NASA Astrophysics Data System (ADS)
Zhukovsky, K.
2015-10-01
We present the analysis of the undulator radiation (UR) with account for major sources of the spectral line broadening. For relativistic electrons we obtain the analytical expressions for the UR spectrum, the intensity and the emission line shape with account for the finite size of the beam, the emittance and the energy spread. Partial compensation of the divergency by properly imposed weak constant magnetic component is demonstrated in the analytical form. Considering the examples of radiation from single and double frequency undulators, we study high harmonic generation with account for all major sources of homogeneous and inhomogeneous broadening with account for the characteristics of the electrons beam. We apply our analysis to free electron laser (FEL) calculations and we compare the obtained results with the radiation of a FEL on the supposition of the ideal undulator.
Ptychographic hyperspectral spectromicroscopy with an extreme ultraviolet high harmonic comb.
Zhang, Bosheng; Gardner, Dennis F; Seaberg, Matthew H; Shanblatt, Elisabeth R; Porter, Christina L; Karl, Robert; Mancuso, Christopher A; Kapteyn, Henry C; Murnane, Margaret M; Adams, Daniel E
2016-08-01
We report a proof-of-principle demonstration of a new scheme of spectromicroscopy in the extreme ultraviolet (EUV) spectral range, where the spectral response of the sample at different wavelengths is imaged simultaneously. This scheme is enabled by combining ptychographic information multiplexing (PIM) with a tabletop EUV source based on high harmonic generation, where four spectrally narrow harmonics near 30 nm form a spectral comb structure. Extending PIM from previously demonstrated visible wavelengths to the EUV/X-ray wavelengths promises much higher spatial resolution and a more powerful spectral contrast mechanism, making PIM an attractive spectromicroscopy method in both microscopy and spectroscopy aspects. In addition to spectromicroscopy, this method images the multicolor EUV beam in situ, making this a powerful beam characterization technique. In contrast to other methods, the techniques described here use no hardware to separate wavelengths, leading to efficient use of the EUV radiation. PMID:27505837
Creating High-Harmonic Beams with Controlled Orbital Angular Momentum
NASA Astrophysics Data System (ADS)
Boyd, Robert W.
A beam of light with an angle-dependent phase Φ = lϕ , where ϕ is the azimuthal coordinate, about the beam axis carries an orbital angular momentum (OAM) of lℏ per photon. Such beams have been exploited to provide superresolution in visible-light microscopy. The ability to create extreme ultraviolet or soft-x-ray beams with controllable OAM would be a critical step towards extending superresolution methods to extremely small feature size. Here we show that OAM is conserved during the process of high-harmonic generation (HHG). Experimentally, we use a fundamental beam with l = 1 and interferometrically determine that the q-th harmonic has an OAM quantum number l equal to its harmonic order q. We also show theoretically how to couple an arbitrary low value of the OAM quantum number l to any harmonic order q in a controlled manner. Our results open a route to microscopy on the molecular, or even submolecular, scale.
Polarization gating of high harmonic generation in the water window
NASA Astrophysics Data System (ADS)
Li, Jie; Ren, Xiaoming; Yin, Yanchun; Cheng, Yan; Cunningham, Eric; Wu, Yi; Chang, Zenghu
2016-06-01
We implement the polarization gating (PG) technique with a two-cycle, 1.7 μm driving field to generate an attosecond supercontinuum extending to the water window spectral region. The ellipticity dependence of the high harmonic yield over a photon energy range much broader than previous work is measured and compared with a semi-classical model. When PG is applied, the carrier-envelope phase (CEP) is swept to study its influence on the continuum generation. PG with one-cycle (5.7 fs) and two-cycle (11.3 fs) delay are tested, and both give continuous spectra spanning from 50 to 450 eV under certain CEP values, strongly indicating the generation of isolated attosecond pulses in the water window region.
Direct electron heating by 60 MHz fast waves on DIII-D
Petty, C.C.; Pinsker, R.I.; Mayberry, M.J.; Chiu, S.C.; Luce, T.C.; Prater, R. ); Porkolab, M.; Bonoli, P.T. . Plasma Fusion Center); de Haas, J.C.M.; James, R.A. ); Baity, F.W.; Goulding, R.H.; Hoffman, D.J. (Oak Ridge National Lab., TN (United St
1991-10-01
Efficient direct electron heating by fast waves has been observed on the DIII-D tokamak. A four strap antenna with (0,{pi},0,{pi}) phasing launched up to 1.6 MW of fast wave power with {vert bar}n{sub {parallel}}{vert bar} {approx} 11. This {vert bar}n{sub {parallel}}{vert bar} is suitable for strong electron interaction in ohmic target plasmas (T{sub e} {le} 2 keV). Ion cyclotron absorption was minimized by keeping the hydrogen fraction low ({lt}3%) in deuterium discharges and by operating at high ion cyclotron harmonics ({omega} = 4{Omega}{sub H} = 8{Omega}{sub D} at 1T). The fast wave electron heating was weak for central electron temperatures below 1 keV, but improved substantially with increasing T{sub e}. Although linear theory predicts a strong inverse magnetic field scaling of the first pass absorption, the measured fast-wave heating efficiency was independent of magnetic field. Multiple pass absorption of the fast waves appears to be occurring since at 2.1 T nearly 100% efficient plasma heating is observed while the calculated first pass absorption is 6% to 8%. The central electron temperature during fast wave heating also increased with magnetic field. The improved electron heating at higher magnetic fields may be due in part to a peaking of the ohmic plasma current and the ohmic electron temperature profiles. Centrally peaked deposition profiles were measured by modulating the fast wave power at 10 Hz and observing the local electron temperature response across the plasma. 11 refs., 10 figs.
Extreme ultraviolet high-harmonic spectroscopy of solids
NASA Astrophysics Data System (ADS)
Luu, T. T.; Garg, M.; Kruchinin, S. Yu.; Moulet, A.; Hassan, M. Th.; Goulielmakis, E.
2015-05-01
Extreme ultraviolet (EUV) high-harmonic radiation emerging from laser-driven atoms, molecules or plasmas underlies powerful attosecond spectroscopy techniques and provides insight into fundamental structural and dynamic properties of matter. The advancement of these spectroscopy techniques to study strong-field electron dynamics in condensed matter calls for the generation and manipulation of EUV radiation in bulk solids, but this capability has remained beyond the reach of optical sciences. Recent experiments and theoretical predictions paved the way to strong-field physics in solids by demonstrating the generation and optical control of deep ultraviolet radiation in bulk semiconductors, driven by femtosecond mid-infrared fields or the coherent up-conversion of terahertz fields to multi-octave spectra in the mid-infrared and optical frequencies. Here we demonstrate that thin films of SiO2 exposed to intense, few-cycle to sub-cycle pulses give rise to wideband coherent EUV radiation extending in energy to about 40 electronvolts. Our study indicates the association of the emitted EUV radiation with intraband currents of multi-petahertz frequency, induced in the lowest conduction band of SiO2. To demonstrate the applicability of high-harmonic spectroscopy to solids, we exploit the EUV spectra to gain access to fine details of the energy dispersion profile of the conduction band that are as yet inaccessible by photoemission spectroscopy in wide-bandgap dielectrics. In addition, we use the EUV spectra to trace the attosecond control of the intraband electron motion induced by synthesized optical transients. Our work advances lightwave electronics in condensed matter into the realm of multi-petahertz frequencies and their attosecond control, and marks the advent of solid-state EUV photonics.
A fast algorithm for the simulation of arterial pulse waves
NASA Astrophysics Data System (ADS)
Du, Tao; Hu, Dan; Cai, David
2016-06-01
One-dimensional models have been widely used in studies of the propagation of blood pulse waves in large arterial trees. Under a periodic driving of the heartbeat, traditional numerical methods, such as the Lax-Wendroff method, are employed to obtain asymptotic periodic solutions at large times. However, these methods are severely constrained by the CFL condition due to large pulse wave speed. In this work, we develop a new numerical algorithm to overcome this constraint. First, we reformulate the model system of pulse wave propagation using a set of Riemann variables and derive a new form of boundary conditions at the inlet, the outlets, and the bifurcation points of the arterial tree. The new form of the boundary conditions enables us to design a convergent iterative method to enforce the boundary conditions. Then, after exchanging the spatial and temporal coordinates of the model system, we apply the Lax-Wendroff method in the exchanged coordinate system, which turns the large pulse wave speed from a liability to a benefit, to solve the wave equation in each artery of the model arterial system. Our numerical studies show that our new algorithm is stable and can perform ∼15 times faster than the traditional implementation of the Lax-Wendroff method under the requirement that the relative numerical error of blood pressure be smaller than one percent, which is much smaller than the modeling error.
NASA Astrophysics Data System (ADS)
Liang, J.; Ni, B.; Cully, C. M.; Donovan, E. F.; Thorne, R. M.; Angelopoulos, V.
2012-03-01
In this study we perform a statistical survey of the extremely-low-frequency wave activities associated with fast earthward flows in the mid-tail central plasma sheet (CPS) based upon THEMIS measurements. We reveal clear trends of increasing wave intensity with flow enhancement over a broad frequency range, from below fLH (lower-hybrid resonant frequency) to above fce (electron gyrofrequency). We mainly investigate two electromagnetic wave modes, the lower-hybrid waves at frequencies below fLH, and the whistler-mode waves in the frequency range fLH < f < fce. The waves at f < fLH dramatically intensify during fast flow intervals, and tend to contain strong electromagnetic components in the high-plasma-beta CPS region, consistent with the theoretical expectation of the lower-hybrid drift instability in the center region of the tail current sheet. ULF waves with very large perpendicular wavenumber might be Doppler-shifted by the flows and also partly contribute to the observed waves in the lower-hybrid frequency range. The fast flow activity substantially increases the occurrence rate and peak magnitude of the electromagnetic waves in the frequency range fLH < f < fce, though they still tend to be short-lived and sporadic in occurrence. We also find that the electron pitch-angle distribution in the mid-tail CPS undergoes a variation from negative anisotropy (perpendicular temperature smaller than parallel temperature) during weak flow intervals, to more or less positive anisotropy (perpendicular temperature larger than parallel temperature) during fast flow intervals. The flow-related electromagnetic whistler-mode wave tends to occur in conjunction with positive electron anisotropy.
Direct electron heating and current drive with fast waves in DIII-D
Pinsker, R.I.; Petty, C.C.; Callis, R.W.; Cary, W.P.; Chiu, S.C.; Freeman, R.L.; deGrassie, J.S.; Harvey, R.W.; Luce, T.C.; Mayberry, M.J.; Prater, R.; Porkolab, M.; Bonoli, P.T.; Baity, F.W.; Goulding, R.H.; Hoffmann, D.J.; James, R.A.; Kawashima, H.
1992-09-01
Experiments on the DIII-D tokamak have been performed to evaluate noninductive current drive with direct electron absorption of the fast Alfven wave (FW) in the ion cyclotron range of frequencies. These experiments have employed a 2 MW 60 NM transmitter connected to a four-element toroidally phased array of loop antennas located at the outside midplane of the DIII-D vacuum vessel. Efficient direct electron heating was obtained with (0, {pi}, 0, {pi}) antenna phasing; H-mode confinement was obtained with direct electron absorption of the fast wave as the sole source of auxiliary heating. Current drive experiments were performed with (0,{pi}/2,{pi},3{pi}/2) antenna phasing at fast wave power levels up to 1.2 MW. Preheating with 60 GHz ECH was used to increase the single-pass absorption of the fast wave with a directive spectrum. When the fast wave is lunched in the direction that aids the inductively driven current (co-current drive), up to 40% of the 0.4 MA plasma current is sustained noninductively. Counter-current drive strongly affects the sawtoothing behavior, and results in highly peaked electron temperature profiles (T{sub e}(0) {approx_lt} 6 keV) but much smaller driven currents.
Direct electron heating and current drive with fast waves in DIII-D
Pinsker, R.I.; Petty, C.C.; Callis, R.W.; Cary, W.P.; Chiu, S.C.; Freeman, R.L.; deGrassie, J.S.; Harvey, R.W.; Luce, T.C.; Mayberry, M.J.; Prater, R. ); Porkolab, M.; Bonoli, P.T. ); Baity, F.W.; Goulding, R.H.; Hoffmann, D.J. ); James, R.A. (Lawrence Livermor
1992-09-01
Experiments on the DIII-D tokamak have been performed to evaluate noninductive current drive with direct electron absorption of the fast Alfven wave (FW) in the ion cyclotron range of frequencies. These experiments have employed a 2 MW 60 NM transmitter connected to a four-element toroidally phased array of loop antennas located at the outside midplane of the DIII-D vacuum vessel. Efficient direct electron heating was obtained with (0, [pi], 0, [pi]) antenna phasing; H-mode confinement was obtained with direct electron absorption of the fast wave as the sole source of auxiliary heating. Current drive experiments were performed with (0,[pi]/2,[pi],3[pi]/2) antenna phasing at fast wave power levels up to 1.2 MW. Preheating with 60 GHz ECH was used to increase the single-pass absorption of the fast wave with a directive spectrum. When the fast wave is lunched in the direction that aids the inductively driven current (co-current drive), up to 40% of the 0.4 MA plasma current is sustained noninductively. Counter-current drive strongly affects the sawtoothing behavior, and results in highly peaked electron temperature profiles (T[sub e](0) [approx lt] 6 keV) but much smaller driven currents.
Resonant Alfven wave instabilities driven by streaming fast particles
Zachary, A.
1987-05-08
A plasma simulation code is used to study the resonant interactions between streaming ions and Alfven waves. The medium which supports the Alfven waves is treated as a single, one-dimensional, ideal MHD fluid, while the ions are treated as kinetic particles. The code is used to study three ion distributions: a cold beam; a monoenergetic shell; and a drifting distribution with a power-law dependence on momentum. These distributions represent: the field-aligned beams upstream of the earth's bow shock; the diffuse ions upstream of the bow shock; and the cosmic ray distribution function near a supernova remnant shock. 92 refs., 31 figs., 12 tabs.
Detonation models of fast combustion waves in nanoscale Al-MoO3 bulk powder media
NASA Astrophysics Data System (ADS)
Shaw, Benjamin D.; Pantoya, Michelle L.; Dikici, Birce
2013-02-01
The combustion of nanometric aluminum (Al) powder with an oxidiser such as molybdenum trioxide (MoO3) is studied analytically. This study focuses on detonation wave models and a Chapman-Jouget detonation model provides reasonable agreement with experimentally-observed wave speeds provided that multiphase equilibrium sound speeds are applied at the downstream edge of the detonation wave. The results indicate that equilibrium sound speeds of multiphase mixtures can play a critical role in determining speeds of fast combustion waves in nanoscale Al-MoO3 powder mixtures.
Fast wave current drive experiment on the DIII-D tokamak
Petty, C.C.; Pinsker, R.I.; Chiu, S.C.; deGrassie, J.S.; Harvey, R.W.; Lohr, J.; Luce, T.C.; Mayberry, M.J.; Prater, R. ); Porkolab, M. ); Baity, F.W.; Goulding, R.H.; Hoffman, J.D. ); James, R.A. ); Kawash
1992-06-01
One method of radio-frequency heating which shows theoretical promise for both heating and current drive in tokamak plasmas is the direct absorption by electrons of the fast Alfven wave (FW). Electrons can directly absorb fast waves via electron Landau damping and transit-time magnetic pumping when the resonance condition {omega} {minus} {kappa}{sub {parallel}e}{upsilon}{sup {parallel}e} = O is satisfied. Since the FW accelerates electrons traveling the same toroidal direction as the wave, plasma current can be generated non-inductively by launching FW which propagate in one toroidal direction. Fast wave current drive (FWCD) is considered an attractive means of sustaining the plasma current in reactor-grade tokamaks due to teh potentially high current drive efficiency achievable and excellent penetration of the wave power to the high temperature plasma core. Ongoing experiments on the DIII-D tokamak are aimed at a demonstration of FWCD in the ion cyclotron range of frequencies (ICRF). Using frequencies in the ICRF avoids the possibility of mode conversion between the fast and slow wave branches which characterized early tokamak FWCD experiments in the lower hybrid range of frequencies. Previously on DIII-D, efficient direct electron heating by FW was found using symmetric (non-current drive) antenna phasing. However, high FWCD efficiencies are not expected due to the relatively low electron temperatures (compared to a reactor) in DIII-D.
Initial fast wave heating and current drive experiments on the DIII-D tokamak
Prater, R.; Mayberry, M.J.; Petty, C.C.; Pinsker, R.I.; Chiu, S.C.; Harvey, R.W.; Luce, T.C.; Porkolab, M.; Bonoli, P.; James, R.A.; Kawashima, H.; Baity, F.W.; Goulding, R.H.; Hoffman, D.J.; Becoulet, A.; Moreau, D.; Trukhin, V.
1991-12-01
Heating and current drive experiments have been performed on the DIII-D tokamak using a 4-strap fast wave antenna at power up to 1.7 MW at 30--60 MHz. Minority heating experiments using D(H) showed effective wave absorption, confirming that the antenna was launching the fast wave. Experiments on the direct absorption of fast waves by electrons through Landau damping and transit-time magnetic pumping were performed at 60 MHz. These experiments showed effective heating of electrons, with a global heating efficiency comparable to that of neutral injection, even when the calculated single-pass dumping was as small as 5%. It is believed that effective multiple-pass damping is taking place. Fast wave current drive experiments were performed with a toroidally directional spectrum obtained by {pi}/2-phasing of the antenna straps. Although non-inductive currents of up to 160 kA were found, the magnitude of the non-inductive current did not decrease when the wave spectrum was reversed. These results are presently under investigation.
NASA Astrophysics Data System (ADS)
Fu, S.
2015-12-01
There are many energetic electrons in the radiation belt of Earth. When the geomagnetic activity becomes stronger, the energy flux of energetic electrons will increase to more than ten times in the outer radiation belt, therefore it is very important to study how the energetic electrons generate and the lifetime of energetic electrons for space weather research. The acceleration of electrons in radiation belt is mainly depending on wave-particle interaction: the whistler mode chorus is the main driver for local acceleration mechanism, which could accelerate and loss energetic electrons; the geomagnetic pulsation ULF wave will cause energetic electron inward radial diffusion which will charge the electrons; recently observation results show us that the fast magnetosonic waves may also accelerate energetic electrons. For the reason that we try to study the wave-particle interaction between fast Magnetosonic and energetic electrons based on numerical simulation, in which the most important past is at the storm time the combination of highly warped Earth magnetic field and fast magnetosonic wave field will be applied for the electromagnetic environment of moving test particles. The energy, pitch angle and cross diffusion coefficients will be calculated respectively in this simulation to study how the electrons receive energy from fast magnetosonic wave. The diffusion coefficients within different dipole Earth magnetic field and non-dipole storm magnetic field are compared, while dynamics of electrons at selected initial energys are shown in our study.
Acceleration of the Fast Solar Wind by Solitary Waves in Coronal Holes
NASA Technical Reports Server (NTRS)
Ofman, Leon
2001-01-01
The purpose of this investigation is to develop a new model for the acceleration of the fast solar wind by nonlinear. time-dependent multidimensional MHD simulations of waves in solar coronal holes. Preliminary computational studies indicate that nonlinear waves are generated in coronal holes by torsional Alfv\\'{e}n waves. These waves in addition to thermal conduction may contribute considerably to the accelerate the solar wind. Specific goals of this proposal are to investigate the generation of nonlinear solitary-like waves and their effect on solar wind acceleration by numerical 2.5D MHD simulation of coronal holes with a broad range of plasma and wave parameters; to study the effect of random disturbances at the base of a solar coronal hole on the fast solar wind acceleration with a more advanced 2.5D MHD model and to compare the results with the available observations; to extend the study to a full 3D MHD simulation of fast solar wind acceleration with a more realistic model of a coronal hole and solar boundary conditions. The ultimate goal of the three year study is to model the, fast solar wind in a coronal hole, based on realistic boundary conditions in a coronal hole near the Sun, and the coronal hole structure (i.e., density, temperature. and magnetic field geometry,) that will become available from the recently launched SOHO spacecraft.
Acceleration of the Fast Solar Wind by Solitary Waves in Coronal Holes
NASA Technical Reports Server (NTRS)
Ofman, Leon
2000-01-01
The purpose of this investigation is to develop a new model for the acceleration of the fast solar wind by nonlinear, time-dependent multidimensional MHD simulations of waves in solar coronal holes. Preliminary computational studies indicate that solitary-like waves are generated in coronal holes nonlinearly by torsional Alfven waves. These waves in addition to thermal conduction may contribute considerably to the accelerate the solar wind. Specific goals of this proposal are to investigate the generation of nonlinear solitary-like waves and their effect on solar wind acceleration by numerical 2.5D MHD simulation of coronal holes with a broad range of plasma and wave parameters; to study the effect of random disturbances at the base of a solar coronal hole on the fast solar wind acceleration with a more advanced 2.5D MHD model and to compare the results with the available observations; to extend the study to a full 3D MHD simulation of fast solar wind acceleration with a more realistic model of a coronal hole and solar boundary conditions. The ultimate goal of the three year study is to model the fast solar wind in a coronal hole, based on realistic boundary conditions in a coronal hole near the Sun, and the coronal hole structure (i.e., density, temperature, and magnetic field geometry) that will become available from the recently launched SOHO spacecraft.
Full Wave Modeling of Wave -- Plasma Interactions in NSTX.
NASA Astrophysics Data System (ADS)
Phillips, C. K.; Bernabei, S.; Fredrickson, E.; Gorelenkov, N.; Hosea, J. C.; Leblanc, B.; Valeo, E. J.; Wilson, J. R.; Bonoli, P. T.; Wright, J. C.; Ryan, P. M.; Wilgen, J. B.
2006-10-01
Wave plasma interactions play an important role in the dynamics of NSTX plasmas in a wide range of frequencies. High harmonic fast waves (HHFW), with frequencies significantly above the fundamental ion cyclotron frequency, are used to heat and drive noninductive currents in NSTX plasmas. Fast ions from neutral beam injection can excite compressional and / or global Alfven eigenmodes (CAE/GAE) with frequencies near the fundamental ion cyclotron frequency. Simulations of power deposition profiles obtained with the full wave code, TORIC, will be compared to the observations from recent HHFW experiments that show that the wave propagation and absorption depend strongly on the antenna phasing and plasma conditions [i]. The issue of mode conversion of the HHFWs to shorter wavelength modes will be revisited. Initial simulations of driven eigenmodes in the CAE / GAE frequency range will also be discussed. [i] See contributed Oral Talk by J. C. Hosea et al this conference
Current drive with fast waves, electron cyclotron waves, and neutral injection in the DIII-D tokamak
Prater, R.; Petty, C.C.; Pinsker, R.I.; Chiu, S.C.; deGrassie, J.S.; Harvey, R.W.; Ikel, H.; Lin-Liu, Y.R.; Luce, T.C. ); James, R.A. ); Porkolab, M. ); Baity, F.W.; Goulding, R.H.; Hoffmann, D.J. ); Kawash
1992-09-01
Current drive experiments have been performed on the DIII-D tokamak using fast waves, electron cyclotron waves, and neutral injection. Fast wave experiments were performed using a 4-strap antenna with 1 MW of power at 60 MHz. These experiments showed effective heating of electrons, with a global heating efficiency equivalent to that of neutral injection even when the single pass damping was calculated to be as small as 5%. The damping was probably due to the effect of multiple passes of the wave through the plasma. Fast wave current drive experiments were performed with a toroidally directional phasing of the antenna straps. Currents driven by fast wave current drive (FWCD) in the direction of the main plasma current of up to 100 kA were found, not including a calculated 40 kA of bootstrap current. Experiments with FWCD in the counter current direction showed little current drive. In both cases, changes in the sawtooth behavior and the internal inductance qualitatively support the measurement of FWCD. Experiments on electron cyclotron current drive have shown that 100 kA of current can be driven by 1 MW of power at 60 GHz. Calculations with a Fokker-Planck code show that electron cyclotron current drive (ECCD) can be well predicted when the effects of electron trapping and of the residual electric field are included. Experiments on driving current with neutral injection showed that effective current drive could be obtained and discharges with full current drive were demonstrated. Interestingly, all of these methods of current drive had about the same efficiency, 0.015 {times} 10{sup 20} MA/MW/m{sup 2}.
Analytical estimates of electron quasi-linear diffusion by fast magnetosonic waves
NASA Astrophysics Data System (ADS)
Mourenas, D.; Artemyev, A. V.; Agapitov, O. V.; Krasnoselskikh, V.
2013-06-01
Quantifying the loss of relativistic electrons from the Earth's radiation belts requires to estimate the effects of many kinds of observed waves, ranging from ULF to VLF. Analytical estimates of electron quasi-linear diffusion coefficients for whistler-mode chorus and hiss waves of arbitrary obliquity have been recently derived, allowing useful analytical approximations for lifetimes. We examine here the influence of much lower frequency and highly oblique, fast magnetosonic waves (also called ELF equatorial noise) by means of both approximate analytical formulations of the corresponding diffusion coefficients and full numerical simulations. Further analytical developments allow us to identify the most critical wave and plasma parameters necessary for a strong impact of fast magnetosonic waves on electron lifetimes and acceleration in the simultaneous presence of chorus, hiss, or lightning-generated waves, both inside and outside the plasmasphere. In this respect, a relatively small frequency over ion gyrofrequency ratio appears more favorable, and other propitious circumstances are characterized. This study should be useful for a comprehensive appraisal of the potential effect of fast magnetosonic waves throughout the magnetosphere.
FAST TRACK COMMUNICATION Quasi self-adjoint nonlinear wave equations
NASA Astrophysics Data System (ADS)
Ibragimov, N. H.; Torrisi, M.; Tracinà, R.
2010-11-01
In this paper we generalize the classification of self-adjoint second-order linear partial differential equation to a family of nonlinear wave equations with two independent variables. We find a class of quasi self-adjoint nonlinear equations which includes the self-adjoint linear equations as a particular case. The property of a differential equation to be quasi self-adjoint is important, e.g. for constructing conservation laws associated with symmetries of the differential equation.
Fast neural solution of a nonlinear wave equation
NASA Technical Reports Server (NTRS)
Toomarian, Nikzad; Barhen, Jacob
1992-01-01
A neural algorithm for rapidly simulating a certain class of nonlinear wave phenomena using analog VLSI neural hardware is presented and applied to the Korteweg-de Vries partial differential equation. The corresponding neural architecture is obtained from a pseudospectral representation of the spatial dependence, along with a leap-frog scheme for the temporal evolution. Numerical simulations demonstrated the robustness of the proposed approach.
A new equation in two dimensional fast magnetoacoustic shock waves in electron-positron-ion plasmas
Masood, W.; Jehan, Nusrat; Mirza, Arshad M.
2010-03-15
Nonlinear properties of the two dimensional fast magnetoacoustic waves are studied in a three-component plasma comprising of electrons, positrons, and ions. In this regard, Kadomtsev-Petviashvili-Burger (KPB) equation is derived using the small amplitude perturbation expansion method. Under the condition that the electron and positron inertia are ignored, Burger-Kadomtsev-Petviashvili (Burger-KP) for a fast magnetoacoustic wave is derived for the first time, to the best of author's knowledge. The solutions of both KPB and Burger-KP equations are obtained using the tangent hyperbolic method. The effects of positron concentration, kinematic viscosity, and plasma beta are explored both for the KPB and the Burger-KP shock waves and the differences between the two are highlighted. The present investigation may have relevance in the study of nonlinear electromagnetic shock waves both in laboratory and astrophysical plasmas.
Commensal searches for microhertz gravitational waves and fast radio bursts: A pilot study
NASA Astrophysics Data System (ADS)
Shannon, Ryan; Hobbs, George; Ravi, Vikram
2014-04-01
In this pilot observing programme, we propose to observe at high cadence the transient gravitational-wave and radio-wave Universe. The goals of these observations are threefold: 1) To improve the timing precision of secondary pulsars in the Parkes Pulsar Timing Array (PPTA) to accelerate the detection of gravitational waves; 2) To characterise the gravitational wave universe in the hitherto unexplored microhertz frequency band; and 3) To develop methods and search for fast radio bursts (FRBs) while conducting precision time experiments. To achieve these goals, we request 120 hours of observations with the Parkes multibeam system, divided into 10 epochs comprising 12-hour LST days. This pilot project acts as a feasibility study for modifications to both the PPTA project and the International Pulsar Timing Array (IPTA), the consortium coordinating timing array observations in Australia, Europe, and North America, and assess the feasibility of searching for fast radio bursts while conduction precision timing observations.
Fast algorithm for calculation of the moving tsunami wave height
NASA Astrophysics Data System (ADS)
Krivorotko, Olga; Kabanikhin, Sergey
2014-05-01
One of the most urgent problems of mathematical tsunami modeling is estimation of a tsunami wave height while a wave approaches to the coastal zone. There are two methods for solving this problem, namely, Airy-Green formula in one-dimensional case ° --- S(x) = S(0) 4 H(0)/H (x), and numerical solution of an initial-boundary value problem for linear shallow water equations ( { ηtt = div (gH (x,y)gradη), (x,y,t) ∈ ΩT := Ω ×(0,T); ( η|t=0 = q(x,y), ηt|t=0 = 0, (x,y ) ∈ Ω := (0,Lx)× (0,Ly ); (1) η|δΩT = 0. Here η(x,y,t) is the free water surface vertical displacement, H(x,y) is the depth at point (x,y), q(x,y) is the initial amplitude of a tsunami wave, S(x) is a moving tsunami wave height at point x. The main difficulty problem of tsunami modeling is a very big size of the computational domain ΩT. The calculation of the function η(x,y,t) of three variables in ΩT requires large computing resources. We construct a new algorithm to solve numerically the problem of determining the moving tsunami wave height which is based on kinematic-type approach and analytical representation of fundamental solution (2). The wave is supposed to be generated by the seismic fault of the bottom η(x,y,0) = g(y) ·θ(x), where θ(x) is a Heaviside theta-function. Let τ(x,y) be a solution of the eikonal equation 1 τ2x +τ2y = --, gH (x,y) satisfying initial conditions τ(0,y) = 0 and τx(0,y) = (gH (0,y))-1/2. Introducing new variables and new functions: ° -- z = τ(x,y), u(z,y,t) = ηt(x,y,t), b(z,y) = gH(x,y). We obtain an initial-boundary value problem in new variables from (1) ( 2 2 (2 bz- ) { utt = uzz + b uyy + 2b τyuzy + b(τxx + τyy) + 2b + 2bbyτy uz+ ( +2b(bzτy + by)uy, z,y- >2 0,t > 0,2 -1/2 u|t 0,t > 0. Then after some mathematical transformation we get the structure of the function u(x,y,t) in the form u(z,y,t) = S(z,y)·θ(t - z) + ˜u(z,y,t). (2) Here Å©(z,y,t) is a smooth function, S(z,y) is the solution of the problem: { S + b2τ S + (1b2(τ +
Calculation of coupling to slow and fast waves in the LHRF from phased waveguide arrays
Pinsker, R.I.; Duvall, R.E.; Fortgang, C.M.; Colestock, P.L.
1986-04-01
A previously reported algorithm for solving the problem of coupling electromagnetic energy in the LHRF from a phased array of identical rectangular waveguides to a plane-stratified, magnetized cold plasma is numerically implemented. The resulting computer codes are sufficiently general to allow for an arbitrary number of waveguides with finite dimensions in both poloidal and toroidal directions, and are thus capable of computing coupling to both slow and fast waves in the plasma. Some of the details of the implementation and the extension of the algorithm to allow study of the Fourier spectrum of slow and fast waves launched by the array are discussed. Good agreement is found with previously reported, less general work for the slow wave launching case. The effect of phasing multirow arrays in the poloidal direction is studied, and an asymmetry between phasing 'up' and 'down' is found that persists in the case where the plasma adjacent to the array is uniform. A 4 x 3 array designed to launch fast waves of high phase velocity is studied. By using the optimal poloidal phasing, low reflection coefficients (absolute value of R/sup 2/ less than or equal to 20%) are found under some not unrealistic edge plasma conditions, but most of the input power is trapped in the outermost layer of the plasma. Implications of our results for fast wave current drive experiments are discussed.
High-harmonic generation from an atomically thin semiconductor
NASA Astrophysics Data System (ADS)
Liu, Hanzhe; Li, Yilei; Ghimire, Shambhu; Heinz, Tony; Reis, David
The process of high-harmonic generation (HHG) from ultrashort laser pulses has recently been observed in bulk solids, complementing the well-established process in the gas phase. HHG is of interest both as a source of ultrashort pulses in the attosecond regime that has photon energies extending up to the soft x-ray region and as a method of probing material response outside the regime of perturbative nonlinear optics. In this paper, we present the observation of HHG from a single atomic layer of MoS2 driven by a strong infrared pulse of 100 fs duration and 0.3 eV photon energy. We observe distinct harmonics up to the 13th order of the infrared excitation. The non-perturbative nature of the HHG process is demonstrated by the weak power dependence of the harmonic intensities. To gain further insight into the process, we have investigated the variation of the HHG signal with sample orientation and the ellipticity of pump excitation. We compare and contrast the process with that from the bulk MoS2 crystal. We find significant differences in the response for the monolayer and bulk crystal, which can be understood in terms of the distinct crystallographic symmetries in the two cases.
Avalanche of stimulated forward scattering in high harmonic generation.
Serrat, Carles; Roca, David; Budesca, Josep M; Seres, Jozsef; Seres, Enikoe; Aurand, Bastian; Hoffmann, Andreas; Namba, Shinichi; Kuehl, Thomas; Spielmann, Christian
2016-04-18
Optical amplifiers in all ranges of the electromagnetic spectrum exhibit an essential characteristic, namely the input signal during the propagation in the amplifier medium is multiplied by the avalanche effect of the stimulated emission to produce exponential growth. We perform a theoretical study motivated and supported by experimental data on a He gas amplifier driven by intense 30-fs-long laser pulses and seeded with attosecond pulse trains generated in a separated Ne gas jet. We demonstrate that the strong-field theory in the frame of high harmonic generation fully supports the appearance of the avalanche effect in the amplification of extreme ultraviolet attosecond pulse trains. We theoretically separate and identify different physical processes taking part in the interaction and we demonstrate that X-ray parametric amplification dominates over others. In particular, we identify strong-field mediated intrapulse X-ray parametric processes as decisive for amplification at the single-atom level. We confirm that the amplification takes place at photon energies where the amplifier is seeded and when the seed pulses are perfectly synchronized with the driving strong field in the amplifier. Furthermore, propagation effects, phase matching and seed synchronization can be exploited to tune the amplified spectral range within the seed bandwidth. PMID:27137242
EUV off-axis focusing using a high harmonic source
NASA Astrophysics Data System (ADS)
Mills, B.; Rogers, E. T. F.; Grant-Jacob, J.; Stebbings, S. L.; Praeger, M.; de Paula, A. M.; Froud, C. A.; Chapman, R. T.; Butcher, T. J.; Brocklesby, W. S.; Frey, J. G.
2009-05-01
High Harmonic Generation is a well established technique for generating Extreme Ultraviolet radiation. It is a promising technique for both structure and spectroscopic imaging due to both the high flux and coherence of the source, and the existence of multiple absorption edges at the generated wavelengths. To increase the flux, a focussing device can be used. Here we present focussing results for a Mo/Si spherical mirror that has been used in an off-axis arrangement, and give extensive analysis of the resulting astigmatic focus and its consequence on diffractive imaging. The astigmatic beam exists as a vertical and horizontal focus, separated by a circle of least confusion. With the help of a theoretical model we show that the most intense part of the beam is always the second line foci and that the phase at the focus is strongly saddle-shaped. However, this phase distortion cannot explain the significant interference peak splitting that is experimentally observed in our diffraction patterns. Instead we propose that the beam quality is degraded upon reflection from the multilayer mirror and it is this asymmetric phase distortion that causes the diffraction peak splitting.
High harmonic generation from Bloch electron in Solids
NASA Astrophysics Data System (ADS)
Wu, Mengxi; Ghimire, Shambhu; Reis, David; Schafer, Kenneth; Gaarde, Mette
2015-05-01
We study the generation of high harmonic radiation by Bloch electrons in a model solid driven by a strong mid-infrared laser field. We solve the single-electron time-dependent Schrödinger equation (TDSE) using a velocity-gauge method [New J. Phys. 15, 013006 (2013)]. The resulting harmonic spectrum exhibits a primary plateau due to the coupling of the valence band to the first conduction band, with a cutoff energy that scales linearly with field strength and laser wavelength. We also find a weaker second plateau due to coupling to higher-lying conduction bands, with a cutoff that is also approximately linear in the field strength. To facilitate the analysis of the time-frequency characteristics of the emitted harmonics, we also solve the TDSE in the Houston states [Phys. Rev. B 33, 5494 (1986)], which allows us to separate inter- and intra-band contributions to the current. We find that the inter- and intra-band contributions display very different time-frequency characteristics. We show that solutions in these two bases are equivalent under an unitary transformation but that, unlike the velocity gauge method, the Houston state treatment is numerically unstable when more than a few low lying energy bands are used.
The preplasma effect on the properties of the shock wave driven by a fast electron beam
NASA Astrophysics Data System (ADS)
Llor Aisa, E.; Ribeyre, X.; Gus'kov, S. Yu.; Tikhonchuk, V. T.
2016-08-01
Strong shock wave generation by a mono-energetic fast electron beam in a plasma with an increasing density profile is studied theoretically. The proposed analytical model describes the shock wave characteristics for a homogeneous plasma preceded by a low density precursor. The shock pressure and the time of shock formation depend on the ratio of the electron stopping length to the preplasma areal density and on the initial energy of injected electrons. The conclusions of theoretical model are confirmed in numerical simulations.
Preliminary study of slow and fast ultrasonic waves using MR images of trabecular bone phantom
NASA Astrophysics Data System (ADS)
Solis-Najera, S. E.; Neria-Pérez, J. A.; Medina, L.; Garipov, R.; Rodríguez, A. O.
2014-11-01
Cancellous bone is a complex tissue that performs physiological and biomechanical functions in all vertebrates. It is made up of trabeculae that, from a simplified structural viewpoint, can be considered as plates and beams in a hyperstatic structure that change with time leading to osteoporosis. Several methods has been developed to study the trabecular bone microstructure among them is the Biot's model which predicts the existence of two longitudinal waves in porous media; the slow and the fast waves, that can be related to porosity of the media. This paper is focused on the experimental detection of the two Biot's waves of a trabecular bone phantom, consisting of a trabecular network of inorganic hydroxyapatite. Experimental measurements of both waves were performed using through transmission ultrasound. Results had shown clearly that the propagation of two waves propagation is transversal to the trabecular alignment. Otherwise the waves are overlapped and a single wave seems to be propagated. To validate these results, magnetic resonance images were acquired to assess the trabecular direction, and to assure that the pulses correspond to the slow and fast waves. This approach offers a methodology for non-invasive studies of trabecular bones.
Preliminary study of slow and fast ultrasonic waves using MR images of trabecular bone phantom
Solis-Najera, S. E. E-mail: angel.perez@ciencias.unam.mx Neria-Pérez, J. A. E-mail: angel.perez@ciencias.unam.mx Medina, L. E-mail: angel.perez@ciencias.unam.mx; Garipov, R.; Rodríguez, A. O.
2014-11-07
Cancellous bone is a complex tissue that performs physiological and biomechanical functions in all vertebrates. It is made up of trabeculae that, from a simplified structural viewpoint, can be considered as plates and beams in a hyperstatic structure that change with time leading to osteoporosis. Several methods has been developed to study the trabecular bone microstructure among them is the Biot’s model which predicts the existence of two longitudinal waves in porous media; the slow and the fast waves, that can be related to porosity of the media. This paper is focused on the experimental detection of the two Biot’s waves of a trabecular bone phantom, consisting of a trabecular network of inorganic hydroxyapatite. Experimental measurements of both waves were performed using through transmission ultrasound. Results had shown clearly that the propagation of two waves propagation is transversal to the trabecular alignment. Otherwise the waves are overlapped and a single wave seems to be propagated. To validate these results, magnetic resonance images were acquired to assess the trabecular direction, and to assure that the pulses correspond to the slow and fast waves. This approach offers a methodology for non-invasive studies of trabecular bones.
Inspection of Samples using a fast Millimetre Wave Scanner
NASA Astrophysics Data System (ADS)
Hommes, A.; Nüssler, D.; Warok, P.; Krebs, C.; Heinen, S.; Essen, H.
2011-08-01
Millimeterwaves and terahertz sensors can cover a broad field of applications ranging from production control to security scanners. The outstanding features are the transparency of many materials like textiles, paper and plastics in this frequency region, the good contrast of any humid or dense dielectric material and the capability to employ miniaturized RF systems and small antenna apertures or dielectric probes. A stand-alone-millimetre-wave-imager, SAMMY, was developed and built, to demonstrate the outstanding features of this part of the electromagnetic spectrum for material inspection.
Simultaneous realization of negative group velocity, fast and slow acoustic waves in a metamaterial
NASA Astrophysics Data System (ADS)
Li, Xiao-juan; Xue, Cheng; Fan, Li; Zhang, Shu-yi; Chen, Zhe; Ding, Jin; Zhang, Hui
2016-06-01
An acoustic metamaterial is designed based on a simple and compact structure of one string of side pipes arranged along a waveguide, in which diverse group velocities are achieved. Owing to Fabry-Perot resonance of the side pipes, a negative phase time is achieved, and thus, acoustic waves transmitting with negative group velocities are produced near the resonant frequency. In addition, both fast and slow acoustic waves are also observed in the vicinity of the resonance frequency. The extraordinary group velocities can be explained based on spectral rephasing induced by anomalous dispersion on the analogy of Lorentz dispersion in electromagnetic waves.
High-harmonic generation from Bloch electrons in solids
NASA Astrophysics Data System (ADS)
Wu, Mengxi; Ghimire, Shambhu; Reis, David A.; Schafer, Kenneth J.; Gaarde, Mette B.
2015-04-01
We study the generation of high-harmonic radiation by Bloch electrons in a model transparent solid driven by a strong midinfrared laser field. We solve the single-electron time-dependent Schrödinger equation (TDSE) using a velocity-gauge method [M. Korbman et al., New J. Phys. 15, 013006 (2013), 10.1088/1367-2630/15/1/013006] that is numerically stable as the laser intensity and number of energy bands are increased. The resulting harmonic spectrum exhibits a primary plateau due to the coupling of the valence band to the first conduction band, with a cutoff energy that scales linearly with field strength and laser wavelength. We also find a weaker second plateau due to coupling to higher-lying conduction bands, with a cutoff that is also approximately linear in the field strength. To facilitate the analysis of the time-frequency characteristics of the emitted harmonics, we also solve the TDSE in a time-dependent basis set, the Houston states [J. B. Krieger and G. J. Iafrate, Phys. Rev. B 33, 5494 (1986), 10.1103/PhysRevB.33.5494], which allows us to separate interband and intraband contributions to the time-dependent current. We find that the interband and intraband contributions display very different time-frequency characteristics. We show that solutions in these two bases are equivalent under a unitary transformation but that, unlike the velocity-gauge method, the Houston state treatment is numerically unstable when more than a few low-lying energy bands are used.
Fast wave stabilization/destabilization of drift waves in a plasma
Kumar, Pawan; Tripathi, V. K.
2013-03-15
Four wave-nonlinear coupling of a large amplitude whistler with low frequency drift wave and whistler wave sidebands is examined. The pump and whistler sidebands exert a low frequency ponderomotive force on electrons introducing a frequency shift in the drift wave. For whistler pump propagating along the ambient magnetic field B{sub s}z-caret with wave number k(vector sign){sub 0}, drift waves of wave number k(vector sign)=k(vector sign){sub Up-Tack }+k{sub ||}z-caret see an upward frequency shift when k{sub Up-Tack }{sup 2}/k{sub 0}{sup 2}>4k{sub ||}/k{sub 0} and are stabilized once the whistler power exceeds a threshold value. The drift waves of low transverse wavelength tend to be destabilized by the nonlinear coupling. Oblique propagating whistler pump with transverse wave vector parallel to k(vector sign){sub Up-Tack} is also effective but with reduced effectiveness.
Partial Reflection and Trapping of a Fast-mode Wave in Solar Coronal Arcade Loops
NASA Astrophysics Data System (ADS)
Kumar, Pankaj; Innes, D. E.
2015-04-01
We report on the first direct observation of a fast-mode wave propagating along and perpendicular to cool (171 Å) arcade loops observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA). The wave was associated with an impulsive/compact flare near the edge of a sunspot. The EUV wavefront expanded radially outward from the flare center and decelerated in the corona from 1060 to 760 km s-1 within ˜3-4 minutes. Part of the EUV wave propagated along a large-scale arcade of cool loops and was partially reflected back to the flare site. The phase speed of the wave was about 1450 km s-1, which is interpreted as a fast-mode wave. A second overlying loop arcade, orientated perpendicular to the cool arcade, is heated and becomes visible in the AIA hot channels. These hot loops sway in time with the EUV wave, as it propagated to and fro along the lower loop arcade. We suggest that an impulsive energy release at one of the footpoints of the arcade loops causes the onset of an EUV shock wave that propagates along and perpendicular to the magnetic field.
Structured mass density slab as a waveguide of fast magnetoacoustic waves
NASA Astrophysics Data System (ADS)
Jelínek, P.; Karlický, M.
Coronal loops are waveguides for magnetohydrodynamic (MHD) waves. These loops are expected to be structured. Therefore, in the present paper, we numerically studied the propagation of the fast MHD waves in the structured density slab (composed from a broad density slab with one axisymmetric narrow sub-slab superposed), and analysed the wave signals. Then, this structured slab was divided into its components, i.e., to simple broad and narrow slabs and the same analysis was made. We compared results of both these cases. For the calculations we adopted a two-dimensional (2D) magnetohydrodynamic (MHD) model, in which we solved a full set of ideal time-dependent MHD equations using the FLASH code, applying the adaptive mesh refinement (AMR) method. To initiate the fast sausage magnetoacoustic waves, we used axisymmetric Gaussian velocity perturbation. Wave signals were detected in different locations along the slab and as a diagnostic tool of these waves, the wavelet analysis method has been used. We found that for the structured density slab with sufficiently sharp boundaries, i.e., for good quality waveguides (without an energy leakage), the guided waves in the structured slab behave similarly as in its separated (simple slab) components.
NASA Astrophysics Data System (ADS)
Garnett Marques Brum, C.; Abdu, M. A.; Batista, P. P.; Gurubaran, S.; Pancheva, D.; Bageston, J. V.; Batista, I. S.; Takahashi, H.
2014-12-01
In this paper we investigate the role of eastward and upward propagating Fast (FK) and Ultrafast Kelvin (UFK) waves in the day-to-day variability of equatorial evening prereversal vertical drift and post sunset generation of spread F/plasma bubbles irregularities. Meteor wind data from Cariri and Cachoeira Paulista (Brazil) and medium Frequency (MF) radar wind data from Tirunelveli (India) are analyzed together with TIMED/SABER temperature in the 40 km - 100 km region to characterize the zonal and vertical propagations of these waves. Also analyzed are the F region evening vertical drift and spread F (ESF) development features as diagnosed by Digisondes operated at Fortaleza and Sao Luis in Brazil. The SABER temperature data permitted determination of the upward propagation characteristics of the FK (E1) waves with propagation speed in the range of 4 km/day. The radar Mesosphere and Lower Thermosphere (MLT) winds in the widely separated longitude sectors have yielded the eastward phase velocity of the both the FK and UFK waves. The vertical propagation of these waves cause strong oscillation in the F region evening prereversal vertical drift, observed for the first time at both FK and UFK periodicities. A delay of a few (~10) days is observed in the F region vertical drift perturbation with respect to the corresponding FK/UFK zonal wind oscillations, or temperature oscillations in the MLT region, which has permitted a direct identification of the sunset electro dynamic coupling process as responsible for the generation of the FK/UFK induced vertical drift oscillation. The vertical drift oscillations are found to cause significant modulation in the spread F/ plasma bubble irregularity development. The overall results highlight the role of FK/UFK waves in the day-to-day variability of the ESF in its occurrence season.
NASA Astrophysics Data System (ADS)
He, Xiao; Hu, Hengshan; Guan, Wei
2010-04-01
Dipole acoustic fields in an arbitrarily deviated well penetrating a homogeneous as well as a stratified transversely isotropic formation are simulated using a 3-D finite-difference time-domain algorithm in cylindrical coordinates. The modelling results show that a dipole source can excite a fast- and a slow-flexural mode due to the shear wave anisotropy when the borehole is inclined with respect to the symmetry axis of transverse isotropy. Both flexural slownesses change with the wellbore deviation angle. The splitting of flexural modes is prominent in full wave arrays when the shear anisotropy is strong enough. It is revealed that the dipole orientation influences the relative amplitudes of the fast- and slow-flexural waves but it has no effect on their slownesses or phases. In a vertical well parallel to the symmetry axis, the two flexural waves degenerate and propagate at the same speed. The degenerated flexural wave travels approximately at the shear speed along the borehole wall except in a few formations. Our study shows, for example, that it is about 10 per cent slower than the shear wave in Mesaverde clayshale 5501. Even in that kind of formations, however, extraction of the fast- and slow-shear velocities from the flexural modes is still possible if the borehole deviation is large enough. To examine the effect of layering, we modelled the full waves in a formation with a sandwich. When the well is perpendicular to the layer interfaces, reflection is obvious and can be recognized. It becomes weaker or even invisible as the deviation angle increases, so it is difficult to detect a thin layer embedded in a formation directly from reflected waves. The sandwich can, instead, be recognized from the irregularity in the spectra of the full waveforms displayed versus depth. [Correction added after online publication 25th February 2009; the original spelling of `homogenous' in the title has been corrected to `homogeneous'.[
Fast and accurate analytical model to solve inverse problem in SHM using Lamb wave propagation
NASA Astrophysics Data System (ADS)
Poddar, Banibrata; Giurgiutiu, Victor
2016-04-01
Lamb wave propagation is at the center of attention of researchers for structural health monitoring of thin walled structures. This is due to the fact that Lamb wave modes are natural modes of wave propagation in these structures with long travel distances and without much attenuation. This brings the prospect of monitoring large structure with few sensors/actuators. However the problem of damage detection and identification is an "inverse problem" where we do not have the luxury to know the exact mathematical model of the system. On top of that the problem is more challenging due to the confounding factors of statistical variation of the material and geometric properties. Typically this problem may also be ill posed. Due to all these complexities the direct solution of the problem of damage detection and identification in SHM is impossible. Therefore an indirect method using the solution of the "forward problem" is popular for solving the "inverse problem". This requires a fast forward problem solver. Due to the complexities involved with the forward problem of scattering of Lamb waves from damages researchers rely primarily on numerical techniques such as FEM, BEM, etc. But these methods are slow and practically impossible to be used in structural health monitoring. We have developed a fast and accurate analytical forward problem solver for this purpose. This solver, CMEP (complex modes expansion and vector projection), can simulate scattering of Lamb waves from all types of damages in thin walled structures fast and accurately to assist the inverse problem solver.
Nonlinear interaction of fast particles with Alfven waves in toroidal plasmas
Candy, J.; Borba, D.; Huysmans, G.T.A.; Kerner, W.; Berk, H.L.
1996-12-17
A numerical algorithm to study the nonlinear, resonant interaction of fast particles with Alfven waves in tokamak geometry has been developed. The scope of the formalism is wide enough to describe the nonlinear evolution of fishbone modes, toroidicity-induced Alfven eigenmodes and ellipticity-induced Alfven eigenmodes, driven by both passing and trapped fast ions. When the instability is sufficiently weak, it is known that the wave-particle trapping nonlinearity will lead to mode saturation before wave-wave nonlinearities are appreciable. The spectrum of linear modes can thus be calculated using a magnetohydrodynamic normal-mode code, then nonlinearly evolved in time in an efficient way according to a two-time-scale Lagrangian dynamical wave model. The fast particle kinetic equation, including the effect of orbit nonlinearity arising from the mode perturbation, is simultaneously solved of the deviation, {delta}f = f {minus} f{sub 0}, from an initial analytic distribution f{sub 0}. High statistical resolution allows linear growth rates, frequency shifts, resonance broadening effects, and nonlinear saturation to be calculated quickly and precisely. The results have been applied to an ITER instability scenario. Results show that weakly-damped core-localized modes alone cause negligible alpha transport in ITER-like plasmas--even with growth rates one order of magnitude higher than expected values. However, the possibility of significant transport in reactor-type plasmas due to weakly unstable global modes remains an open question.
Fast ion loss diagnostic plans for NSTX
D. S. Darrow; R. Bell; D. W. Johnson; H. Kugel; J. R. Wilson; F. E. Cecil; R. Maingi; A. Krasilnikov; A. Alekseyev
2000-06-13
The prompt loss of neutral beam ions from the National Spherical Torus Experiment (NSTX) is expected to be between 12% and 42% of the total 5 MW of beam power. There may, in addition, be losses of fast ions arising from high harmonic fast wave (HHFW) heating. Most of the lost ions will strike the HHFW antenna or the neutral beam dump. To measure these losses in the 2000 experimental campaign, thermocouples in the antenna, several infrared camera views, and a Faraday cup lost ion probe will be employed. The probe will measure loss of fast ions with E > 1 keV at three radial locations, giving the scrape-off length of the fast ions.
Heikkinen, J.A.; Sipilae, S.K.
1995-10-01
The direction and magnitude of power and momentum exchange between fast ions and electrostatic waves in slab and toroidal systems are obtained from global Monte Carlo simulations that include the quasilinear wave-induced ion diffusion both in velocity space and through a radially localized (lower hybrid) wave structure with propagation in one preferential poloidal direction in tokamaks. The model considers a full linearized collision model, finite fast ion orbits, and losses in toroidal geometry, and can properly treat the boundary effects on the particle--wave interaction in the configuration space. For an isotropic steady ion source, reduction of wave Landau damping but no wave amplification by wave localization is found for a Gaussian wave intensity distribution in radius, irrespective of the steepness of the radial gradient of the fast ion source rate. Enhanced wave-driven fast ion current, with magnitude, direction, and profile determined by the boundary conditions, net power transfer, and fast ion radial transport, is found to follow from the asymmetry in the parallel wave number spectrum created by the finite poloidal magnetic field. In the presence of intense well-penetrated waves the current carried by fusion {alpha} particles can be controlled by the choice of the poloidal wave number spectrum and the total current can greatly exceed the neoclassical bootstrap current of the {alpha} particles in a reactor. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Fast and slow magnetosonic waves in two-dimensional spin-1/2 quantum plasma
Mushtaq, A.; Vladimirov, S. V.
2010-10-15
Using the spin-1/2 resistive quantum magnetohydrodynamics model, linear and nonlinear relations for slow and fast magnetosonic modes are derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. The plasma resistivity is shown to play a role of dissipation in the system. With the aid of tanh method the traveling wave solution of Kadomstev-Petviashvili-Burgers is obtained. The solution shows a general shock wave profile superposed by a perturbative solitary-wave contribution. The dynamics of fast and slow magnetosonic shock and soliton, respectively, in the presence and absence of dissipation is investigated with respect to electron spin magnetization, quantum diffraction, and plasma statistic. It is found that results obtained from the spin quantum plasmas differ significantly from the nonspin quantum plasmas. The relevance of the present work to dense astrophysical plasmas such as pulsar magnetosphere is pointed out.
Tomographic errors from wave front healing: more than just a fast bias
NASA Astrophysics Data System (ADS)
Malcolm, Alison E.; Trampert, Jeannot
2011-04-01
Wave front healing, in which diffractions interfere with directly travelling waves causing a reduction in recorded traveltime delays, has been postulated to cause a bias towards faster estimated earth models. This paper reviews the theory from the mathematical physics community that explains the properties of diffractions and applies it to a suite of increasingly complicated numerical examples. We focus in particular on the elastic case and on the differences between P and S healing. We find that rather than introducing a systemic fast bias, wave front healing gives a more complicated bias in the results of traveltime tomography, with fast anomalies even manifesting themselves as slow anomalies in some situations. Of particular interest, we find that a negative correlation between the bulk and shear or compressional velocities may result to a large extend from healing.
Fast multiscale Gaussian beam methods for wave equations in bounded convex domains
Bao, Gang; Lai, Jun; Qian, Jianliang
2014-03-15
Motivated by fast multiscale Gaussian wavepacket transforms and multiscale Gaussian beam methods which were originally designed for pure initial-value problems of wave equations, we develop fast multiscale Gaussian beam methods for initial boundary value problems of wave equations in bounded convex domains in the high frequency regime. To compute the wave propagation in bounded convex domains, we have to take into account reflecting multiscale Gaussian beams, which are accomplished by enforcing reflecting boundary conditions during beam propagation and carrying out suitable reflecting beam summation. To propagate multiscale beams efficiently, we prove that the ratio of the squared magnitude of beam amplitude and the beam width is roughly conserved, and accordingly we propose an effective indicator to identify significant beams. We also prove that the resulting multiscale Gaussian beam methods converge asymptotically. Numerical examples demonstrate the accuracy and efficiency of the method.
Full wave simulations of fast wave heating losses in the scrape-off layer of NSTX and NSTX-U
Bertelli, Nicola; Jaeger, E. F.; Hosea, J.; Phillips, C. K.; Berry, Lee Alan; Gerhardt, S.; Green, David L; LeBlanc, B; Perkins, R. J.; Ryan, Philip Michael; Taylor, G.; Valeo, E. J.; Wilson, J. R.
2014-01-01
Full wave simulations of fusion plasmas show a direct correlation between the location of the fast-wave cut-off, radiofrequency (RF) field amplitude in the scrape-off layer (SOL) and the RF power losses in the SOL observed in the National Spherical Torus eXperiment (NSTX). In particular, the RF power losses in the SOL increase significantly when the launched waves transition from evanescent to propagating in that region. Subsequently, a large amplitude electric field occurs in the SOL, driving RF power losses when a proxy collisional loss term is added. A 3D reconstruction of absorbed power in the SOL is presented showing agreement with the RF experiments in NSTX. Loss predictions for the future experiment NSTX-Upgrade (NSTX-U) are also obtained and discussed.
Tweten, Dennis J; Okamoto, Ruth J; Schmidt, John L; Garbow, Joel R; Bayly, Philip V
2015-11-26
This paper describes a method to estimate mechanical properties of soft, anisotropic materials from measurements of shear waves with specific polarization and propagation directions. This method is applicable to data from magnetic resonance elastography (MRE), which is a method for measuring shear waves in live subjects or in vitro samples. Here, we simulate MRE data using finite element analysis. A nearly incompressible, transversely isotropic (ITI) material model with three parameters (shear modulus, shear anisotropy, and tensile anisotropy) is used, which is appropriate for many fibrous, biological tissues. Both slow and fast shear waves travel concurrently through such a material with speeds that depend on the propagation direction relative to fiber orientation. A three-parameter estimation approach based on directional filtering and isolation of slow and fast shear wave components (directional filter inversion, or DFI) is introduced. Wave speeds of each isolated shear wave component are estimated using local frequency estimation (LFE), and material properties are calculated using weighted least squares. Data from multiple finite element simulations are used to assess the accuracy and reliability of DFI for estimation of anisotropic material parameters. PMID:26476762
Fast particles-wave interaction in the Alfven frequency range on the Joint European Torus tokamak
Fasoli, A.; Borba, D.; Association EURATOM Breizman, B.; Gormezano, C.; Heeter, R. F.; Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543 ; Juan, A.; Mantsinen, M.; Sharapov, S.; Testa, D.
2000-05-01
Wave-particle interaction phenomena in the Alfven Eigenmode (AE) frequency range are investigated at the Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)] using active and passive diagnostic methods. Fast particles are generated by neutral beam injection, ion cyclotron resonance heating, and fusion reactions. External antennas are used to excite stable AEs and measure fast particle drive and damping separately. Comparisons with numerical calculations lead to an identification of the different damping mechanisms. The use of the active AE diagnostic system to generate control signals based on the proximity to marginal stability limits for AE and low-frequency magnetohydrodynamic (MHD) modes is explored. Signatures of the different nonlinear regimes of fast particle driven AE instabilities predicted by theory are found in the measured spectra. The diagnostic use of AE measurements to get information both on the plasma bulk and the fast particle distribution is assessed. (c) 2000 American Institute of Physics.
Fast Wave Trains Associated with Solar Eruptions: Insights from 3D Thermodynamic MHD Simulations
NASA Astrophysics Data System (ADS)
Downs, C.; Liu, W.; Torok, T.; Linker, J.; Mikic, Z.; Ofman, L.
2015-12-01
EUV imaging observations during the SDO/AIA era have provided new insights into a variety of wave phenomena occurring in the low solar corona. One example is the observation of quasi-periodic, fast-propagating wave trains that are associated with solar eruptions, including flares and CMEs. While there has been considerable progress in understanding such waves from both an observational and theoretical perspective, it remains a challenge to pin down their physical origin. In this work, we detail our results from a case-study 3D thermodynamic MHD simulation of a coronal mass ejection where quasi-periodic wave trains are generated during the simulated eruption. We find a direct correlation between the onset of non-steady reconnection in the flare current sheet and the generation of quasi-periodic wave train signatures when patchy, collimated downflows interact with the flare arcade. Via forward modeling of SDO/AIA observables, we explore how the appearance of the wave trains is affected by line-of-sight integration and the multi-thermal nature of the coronal medium. We also examine how the wave trains themselves are channeled by natural waveguides formed in 3D by the non-uniform background magnetic field. While the physical association of the reconnection dynamics to the generation of quasi-periodic wave trains appears to be a compelling result, unanswered questions posed from recent observations as well as future prospects will be discussed.
The structure of fast sausage waves in current-carrying coronal loops
NASA Astrophysics Data System (ADS)
Bembitov, D. B.; Mikhalyaev, B. B.; Ruderman, M. S.
2014-09-01
We study fast sausage waves in a model coronal loop that consists of a cylindrical core with axial magnetic field and coaxial annulus with purely azimuthal magnetic field. The magnetic field is discontinuous at the tube and core boundaries, and there are surface currents with the opposite directions on these boundaries. The principal mode of fast sausage waves in which the magnetic pressure perturbation has no nodes in the radial direction can exist for arbitrary wavelength. The results for the fundamental radial mode of sausage waves are applied to the interpretation of observed periodic pulsations of microwave emission in flaring loops with periods of a few tens of seconds. Radial plasma motion has opposite directions at the tube and core boundaries. This leads to the periodic contraction and expansion of the annulus. We assume that the principal mode of fast sausage waves in the current-carrying coronal loops is able to produce a current sheet. However, the nonlinear analysis is needed to confirm this conjecture.
Full-wave calculation of fast-wave current drive in tokamaks including k sub parallel variations
Jaeger, E.F; Batchelor, D.B.
1991-01-01
When fast waves propagate inward from the edge of a tokamak toward the plasma center, the k{perpendicular} spectrum produced by the antenna is not maintained but is shifted and deformed due to the presence of the finite poloidal magnetic field. This k{perpendicular} shift causes a variation in the parallel phase speed of the wave and can therefore have a strong effect on electron damping and current drive efficiency. In this paper, we include this effect in a new full-wave calculation (PICES) which represents the wave fields as a superposition of poloidal modes, thereby reducing k{perpendicular} to an algebraic operator. The wave equation is solved in general flux coordinates, including a full (non-perturbative) solution for E{perpendicular} and a reduced-order dielectric formulation to eliminate short-wavelength ion Bernstein modes. A simplified current drive model which includes particle trapping is used to estimate the effect of the k{perpendicular} shift on current drive efficiency in ITER and D3-D. Results suggest that when single-pass absorption is weak, reflected power may drive current nearly as efficiently as that absorbed on the first pass. 15 refs., 5 figs.
Wear, Keith; Nagatani, Yoshiki; Mizuno, Katsunori; Matsukawa, Mami
2014-10-01
Fast and slow waves were detected in a bovine cancellous bone sample for thicknesses ranging from 7 to 12 mm using bandlimited deconvolution and the modified least-squares Prony's method with curve fitting (MLSP + CF). Bandlimited deconvolution consistently isolated two waves with linear-with-frequency attenuation coefficients as evidenced by high correlation coefficients between attenuation coefficient and frequency: 0.997 ± 0.002 (fast wave) and 0.986 ± 0.013 (slow wave) (mean ± standard deviation). Average root-mean-squared (RMS) differences between the two algorithms for phase velocities were 5 m/s (fast wave, 350 kHz) and 13 m/s (slow wave, 750 kHz). Average RMS differences for signal loss were 1.6 dB (fast wave, 350 kHz) and 0.4 dB (slow wave, 750 kHz). Phase velocities for thickness = 10 mm were 1726 m/s (fast wave, 350 kHz) and 1455 m/s (slow wave, 750 kHz). Results show support for the model of two waves with linear-with frequency attenuation, successful isolation of fast and slow waves, good agreement between bandlimited deconvolution and MLSP + CF as well as with a Bayesian algorithm, and potential variations of fast and/or slow wave properties with bone sample thickness. PMID:25324100
Nonlinear fast growth of surface gravity waves under the action of wind
NASA Astrophysics Data System (ADS)
Brunetti, Maura; Marchiando, Nadège; Berti, Nicolas; Kasparian, Jérôme
2014-05-01
The generation of ocean waves by wind is a highly nonlinear problem where the physical processes at the air-water interface are difficult to measure and to model for the presence of turbulence in both fluids. Direct field measurements of the induced pressure by airflow on waves are rare and difficult to perform, thus the underlying mechanisms leading to wave amplification are still unclear. We consider here the Miles' mechanism, which is characterised by growth rates, ΓM/f, in the range from 10-3-10-2 for fast-moving waves and in the range 10-2-1 for slow-moving waves and waves in laboratory tank experiments. This prompted us to investigate the case with Miles' growth rates of first order in the wave steepness, ΓM/f = O(ɛ), instead of the usually considered one, ΓM/f = O(ɛ2), where ɛ is the wave steepness which both in ocean and tank experiments can be of the order of 0.1. We use the method of multiple scales for deriving the nonlinear Schrödinger (NLS) equation with wave growth rate of first order in the wave steepness. We find that a simple coordinate transformation reduces the wind-forced NLS equation into the standard NLS equation with constant coefficients. Thus, we show how the Peregrine, Akhmediev and Kuznetsov-Ma solutions are modified in the presence of this first-order wind. In particular, the lifetime of both the Peregrine and the Akhmediev solitons increases for large growth rates and the maximum amplitude of these solitons slightly increases for growth rates larger than a certain value. The enhancement of both lifetime and maximum amplitude of rogue waves under the action of wind has been observed in tank experiments and numerical simulations of dispersive focusing, thus confirming the relevance in this context of the case ΓM/f = O(ɛ) considered in the present study.
Lloyd’s mirror interference lithography with EUV radiation from a high-harmonic source
NASA Astrophysics Data System (ADS)
Kim, Hyun-su; Baksh, Peter; Odstrcil, Michal; Miszczak, Magdalena; Frey, Jeremy G.; Juschkin, Larissa; Brocklesby, William S.
2016-07-01
We demonstrate interference lithography using a high-harmonic source. Extreme ultraviolet (EUV) radiation is produced by high-harmonic generation with 800 nm light from a femtosecond Ti:sapphire laser (40 fs pulses, 1 kHz, 2 W average power) in argon gas. Interference patterns created using Lloyd’s mirror setup and monochromatized radiation at the 27th harmonic (29 nm) are recorded using a ZEP-520A photoresist, producing features with <200 nm pitch. The effect of the use of femtosecond pulsed EUV radiation on the recorded pattern is investigated. The capability of the high-harmonic source for high-resolution patterning is discussed.
Enhanced loss of fast ions during mode conversion ion Bernstein wave heating in TFTR
Darrow, D.S.; Majeski, R.; Fisch, N.J.; Heeter, R.F.; Herrmann, H.W.; Herrmann, M.C.; Zarnstorff, M.C.; Zweben, S.J.
1995-12-01
A strong interaction of fast ions with ion Bernstein waves has been observed in TFTR. It results in a large increase in the fast ion loss rate, and heats the lost particles to several MeV. The lost ions are observed at the passing/trapped boundary and appear to be either DD fusion produced tritons or accelerated D neutral beam ions. Under some conditions, enhanced loss of DT alpha particles is also seen. The losses provide experimental support for some of the elements required for alpha energy channeling.
Effect of surface modes on coupling to fast waves in the LHRF
Pinsker, R.I.; Colestock, P.L.
1990-09-16
The effect of surface modes of propagation on coupling to fast waves in the LHRF is studied theoretically and experimentally. The previously reported up-down' poloidal phasing asymmetry for coupling to a uniform plasma is shown to be due to the properties of a mode which carries energy along the plasma-conducting wall interface. Comparison of the theory with coupling experiments performed on the PLT tokamak with a phased array of twelve dielectric-loaded waveguides at 800 MHz shows that the observed dependence of the net reflection coefficient on toroidal phase angle can be explained only if the surface wave is taken into account. 43 refs., 10 figs.
Heikkinen, J.A.; Pavlov, I.P.
1996-02-01
The fairly large poloidal directivity of a radiated fast wave spectrum related to the wave polarization relative to the ion gyration can be further enhanced by the nonperpendicular angle between the antenna current strap and the magnetic field. The latter is shown to be responsible also for the asymmetry in the parallel wavenumber spectrum of an unphased antenna, and can lead to deviations of order {le}30{percent} in the corresponding spectrum of a phased antenna array. The consequences of the observed effects to the antenna performance in the current drive applications as well as in excitation of poloidally asymmetric spectra are discussed. {copyright} {ital 1996 American Institute of Physics.}
NASA Astrophysics Data System (ADS)
Kichigin, G. N.
2016-01-01
Solutions describing solitary fast magnetosonic (FMS) waves (FMS solitons) in cold magnetized plasma are obtained by numerically solving two-fluid hydrodynamic equations. The parameter domain within which steady-state solitary waves can propagate is determined. It is established that the Mach number for rarefaction FMS solitons is always less than unity. The restriction on the propagation velocity leads to the limitation on the amplitudes of the magnetic field components of rarefaction solitons. It is shown that, as the soliton propagates in plasma, the transverse component of its magnetic field rotates and makes a complete turn around the axis along which the soliton propagates.
ITER equilibrium with bootstrap currents, lower hybrid current drive and fast wave current drive
Ehst, D.A.
1989-03-01
A current drive system is proposed for the technology phase of ITER which relies on rf power and bootstrap currents. The rf/bootstrap system permits operation at high safety factor, and we consider the axial value to be q/sub a/ approx. = 1.9, which minimizes the need for seed current near the magnetic axis. Lower hybrid power (/approximately/30 MW) provides current density near the surface, ICRF (/approximately/65 MHz, /approximately/30 MW) fast waves generate current near the axis, and high frequency fast waves (/approximately/250 MHz, /approximately/74 MW) supply the remaining current density. The system is not yet optimized but appears to offer great flexibility (ion heating for ignition, current rampup, etc.) with relatively inexpensive and well developed technology. 29 refs., 16 figs., 1 tab.
Modeling of fast wave current drive experiments on DIII-D
Luce, T.C.; Chiu, S.C.; Harvey, R.W.; Mayberry, M.J.; Petty, C.C.; Pinsker, R.I.; Prater, R.; Tsunoda, S.I.
1991-09-01
Modeling of fast wave current drive experiments for D3-D has been improved to include calculation of target temperature profiles consistent with the D3-D database and more accurate modeling of the launched spectrum. The calculations indicate that a measurable current will be driven by fast wave in the near-term (30--200 kA). Modeling of the long-range goal of 2 MA non-inductive at high {beta} indicates the proposed 18 MW of rf power will be adequate. The optimum frequency for the intermediate scenario is 120 MHz; this frequency selection is also adequate for the long-term goals. 8 refs., 2 figs., 2 tabs.
First results on fast wave current drive in advanced tokamak discharges in DIII-D
Prater, R.; Cary, W.P.; Baity, F.W.
1995-07-01
Initial experiments have been performed on the DIII-D tokamak on coupling, direct electron heating, and current drive by fast waves in advanced tokamak discharges. These experiments showed efficient central heating and current drive in agreement with theory in magnitude and profile. Extrapolating these results to temperature characteristic of a power plant (25 keV) gives current drive efficiency of about 0.3 MA/m{sup 2}.
Fast P wave propagation in subducted Pacific lithosphere: Refraction from the plate
NASA Astrophysics Data System (ADS)
Smith, Gideon; Gubbins, David; Mao, Weijian
1994-12-01
P waves traveling from events in the Tonga-Kermadec seismic zone to stations in New Zealand are very fast with highly emergent, dispersed waveforms. Ray tracing has shown the waves to travel close to the subducted Pacific plate throughout their length, and synthetic seismogram calculations have shown the dispersion requires a very thin (8-12 km) fast layer. Previous work has been based on data from analog records and one digital, single-component short-period instrument; no polarization analysis was possible, and measurements of dispersion were limited by the bandwidth. From January 1991 to August 1992 we deployed nine broad band, three-component seismometers in good sites for observing these arrivals; the data are augmented by three-component, short-period digital records from new stations of the New Zealand National Network. In this study we analyze 1191 broad-band and 2076 short period seismograms from 71 events for polarization of the initial P wave. The polarization directions are found to be up to 30 deg off the great circle path and consistently steep (20 deg from vertical). They are too steep to be explained by standard ray paths or refraction from a fast horizontal layer. We invert the polarization directions for a tilted interface beneath the array and use arrival times to control the depth to the interface, which is found to lie close to the top of the subducted plate inferred from the seismicity. We conclude that these precursive, emergent P waves have traveled through a fast layer close to the top of the subducted plate and refract upward to the station. A second arrival, with lower dominant frequency near 1 Hz and normal travel time, is occasionally seen on both broad band and short-time stations. Its polarization direction is similarly steep but difficult to measure; the evidence suggests that it also travels within the plate with similar ray path to the precursor.
Hybrid Metameterials Enable Fast Electrical Modulation Of Freely Propagating Terahertz Waves
Chen, Hou-tong; O' Hara, John F; Taylor, Antoinette J
2008-01-01
We demonstrate fast electrical modulation of freely propagating THz waves at room temperature using hybrid metamaterial devices. the devices are planar metamaterials fabricated on doped semiconducor epitaxial layers, which form hybrid metamaterial - Schottky diode structures. With an applied ac voltage bias, we show modulation of THz radiation at inferred frequencies over 2 MHz. The modulation speed is limited by the device depletion capacitance which may be reduced for even faster operation.
Schmidt, Jürgen; Guggenmos, Alexander; Hofstetter, Michael; Chew, Soo Hoon; Kleineberg, Ulf
2015-12-28
High harmonic radiation is meanwhile nearly extensively used for the spectroscopic investigation of electron dynamics with ultimate time resolution. The majority of high harmonic beamlines provide linearly polarized radiation created in a gas target. However, circular polarization greatly extends the spectroscopic possibilities for high harmonics, especially in the analysis of samples with chirality or prominent spin polarization. We produced a free-standing multilayer foil as a transmission EUV quarter waveplate and applied it for the first time to high harmonic radiation. We measured a broadband (4.6 eV FWHM) ellipticity of 75% at 66 eV photon energy with a transmission efficiency of 5%. The helicity is switchable and the ellipticity can be adjusted to lower values by angle tuning. As a single element it can be easily integrated in any existing harmonic beamline without major changes. PMID:26832020
Influence of High Harmonics of Magnetic Fields on Trapped Magnetic Fluxes in HTS Bulk
NASA Astrophysics Data System (ADS)
Yamagishi, K.; Miyagi, D.; Tsukamoto, O.
Various kinds of HTS bulk motors are proposed and have been developed. Generally, those motors are driven by semiconductor inverters and currents fed to the armature windings contain high harmonics. Therefore, the bulks are exposed to high harmonics magnetic fields and AC losses are produced in the bulks. The AC losses deteriorate the efficiency of the motors and cause temperature rise of the bulks which decrease the trapped magnetic fluxes of the bulks. Usually, electro-magnetic shielding devices are inserted between the bulks and armature windings. However, the shielding devices degrade compactness of the motors. Therefore, it is important to have knowledge of the influence of the high harmonics magnetic fields on the AC losses and trapped magnetic fluxes of the bulk for optimum design of the shielding devices. In this work, the authors experimentally study the influence of high harmonics magnetic fields.
Variational full wave calculation of fast wave current drive in DIII-D using the ALCYON code
Becoulet, A.; Moreau, D.
1992-04-01
Initial fast wave current drive simulations performed with the ALCYON code for the 60 MHz DIII-D experiment are presented. Two typical shots of the 1991 summer campaign were selected with magnetic field intensities of 1 and 2 teslas respectively. The results for the wave electromagnetic field in the plasma chamber are displayed. They exhibit a strong enrichment of the poloidal mode number m-spectrum which leads to the upshift of the parallel wavenumber, {kappa}{perpendicular}, and to the wave absorption. The m-spectrum is bounded when the local poloidal wavenumber reaches the Alfven wavenumber and the {kappa}{perpendicular} upshifts do not destroy the wave directionality. Linear estimations of the driven current are made. The current density profiles are found to be peaked and we find that about 88 kA can be driven in the 1 tesla/1.7 keV phase with 1.7 MW coupled to the electrons. In the 2 tesla/3.4 keV case, 47 kA are driven with a total power of 1.5 MW, 44% of which are absorbed on the hydrogen minority, through the second harmonic ion cyclotron resonance. The global efficiency is then 0.18 {times} 10{sup 19} A m{sup {minus}2}W{sup {minus}1} if one considers only the effective power going to the electrons.
Realistic Modeling of SDO/AIA-discovered Coronal Fast MHD Wave Trains in Active Regions
NASA Astrophysics Data System (ADS)
Ofman, Leon; Liu, Wei
2016-05-01
High-resolution EUV observations by space telescopes have provided plenty of evidence for coronal MHD waves in active regions. In particular, SDO/AIA discovered quasi-periodic, fast-mode propagating MHD wave trains (QFPs), which can propagate at speeds of ~1000 km/s perpendicular to the magnetic field. Such waves can provide information on the energy release of their associated flares and the magnetized plasma structure of the active regions. Before we can use these waves as tools for coronal seismology, 3D MHD modeling is required for disentangling observational ambiguities and improving the diagnostic accuracy. We present new results of observationally contained models of QFPs using our recently upgraded radiative, thermally conductive, visco-resistive 3D MHD code. The waves are excited by time-depended boundary conditions constrained by the spatial (localized) and quasi-periodic temporal evolution of a C-class flare typically associated with QFPs. We investigate the excitation, propagation, and damping of the waves for a range of key model parameters, such as the background temperature, density, magnetic field structure, and the location of the flaring site within the active region. We synthesize EUV intensities in multiple AIA channels and then obtain the model parameters that best reproduce the properties of observed QFPs. We discuss the implications of our model results for the seismological application of QFPs and for understanding the dynamics of their associated flares.
Fast wave propagation in auditory cortex of an awake cat using a chronic microelectrode array
NASA Astrophysics Data System (ADS)
Witte, Russell S.; Rousche, Patrick J.; Kipke, Daryl R.
2007-06-01
We investigated fast wave propagation in auditory cortex of an alert cat using a chronically implanted microelectrode array. A custom, real-time imaging template exhibited wave dynamics within the 33-microwire array (3 mm2) during ten recording sessions spanning 1 month post implant. Images were based on the spatial arrangement of peri-stimulus time histograms at each recording site in response to auditory stimuli consisting of tone pips between 1 and 10 kHz at 75 dB SPL. Functional images portray stimulus-locked spiking activity and exhibit waves of excitation and inhibition that evolve during the onset, sustained and offset period of the tones. In response to 5 kHz, for example, peak excitation occurred at 27 ms after onset and again at 15 ms following tone offset. Variability of the position of the centroid of excitation during ten recording sessions reached a minimum at 31 ms post onset (σ = 125 µm) and 18 ms post offset (σ = 145 µm), suggesting a fine place/time representation of the stimulus in the cortex. The dynamics of these fast waves also depended on stimulus frequency, likely reflecting the tonotopicity in auditory cortex projected from the cochlea. Peak wave velocities of 0.2 m s-1 were also consistent with those purported across horizontal layers of cat visual cortex. The fine resolution offered by microimaging may be critical for delivering optimal coding strategies used with an auditory prosthesis. Based on the initial results, future studies seek to determine the relevance of these waves to sensory perception and behavior. The work was performed at Department of Bioengineering, Arizona State University, ECG 334 MS-9709 Arizona State University, Tempe, AZ 85287-9709, USA.
Fast wave propagation in auditory cortex of an awake cat using a chronic microelectrode array.
Witte, Russell S; Rousche, Patrick J; Kipke, Daryl R
2007-06-01
We investigated fast wave propagation in auditory cortex of an alert cat using a chronically implanted microelectrode array. A custom, real-time imaging template exhibited wave dynamics within the 33-microwire array (3 mm(2)) during ten recording sessions spanning 1 month post implant. Images were based on the spatial arrangement of peri-stimulus time histograms at each recording site in response to auditory stimuli consisting of tone pips between 1 and 10 kHz at 75 dB SPL. Functional images portray stimulus-locked spiking activity and exhibit waves of excitation and inhibition that evolve during the onset, sustained and offset period of the tones. In response to 5 kHz, for example, peak excitation occurred at 27 ms after onset and again at 15 ms following tone offset. Variability of the position of the centroid of excitation during ten recording sessions reached a minimum at 31 ms post onset (sigma = 125 microm) and 18 ms post offset (sigma = 145 microm), suggesting a fine place/time representation of the stimulus in the cortex. The dynamics of these fast waves also depended on stimulus frequency, likely reflecting the tonotopicity in auditory cortex projected from the cochlea. Peak wave velocities of 0.2 m s(-1) were also consistent with those purported across horizontal layers of cat visual cortex. The fine resolution offered by microimaging may be critical for delivering optimal coding strategies used with an auditory prosthesis. Based on the initial results, future studies seek to determine the relevance of these waves to sensory perception and behavior. PMID:17409481
NASA Technical Reports Server (NTRS)
Stark, B. A.; Musielak, Z. E.
1993-01-01
This study analytically examines conditions for reflection of MHD fast-mode waves propagating upward in an isothermal atmosphere. A new method of transforming the linearized wave equation into Klein-Gordon form is utilized to calculate a local cutoff (critical) frequency for these waves. This critical frequency determines the height in the atmosphere at which reflection dominates and above which wave propagation is effectively cut off. Comparison of our results to those previously obtained shows that earlier calculations of the critical frequency for MHD fast mode waves were done incorrectly. The results may be helpful in explaining the short-period end of the spectrum of the solar global p-mode oscillations. They may also be important in studies of wave propagation and wave trapping in highly magnetized stellar atmospheres.
Heating and Acceleration of the Fast Solar Wind by Alfvén Wave Turbulence
NASA Astrophysics Data System (ADS)
van Ballegooijen, A. A.; Asgari-Targhi, M.
2016-04-01
We present numerical simulations of reduced magnetohydrodynamic (RMHD) turbulence in a magnetic flux tube at the center of a polar coronal hole. The model for the background atmosphere is a solution of the momentum equation and includes the effects of wave pressure on the solar wind outflow. Alfvén waves are launched at the coronal base and reflect at various heights owing to variations in Alfvén speed and outflow velocity. The turbulence is driven by nonlinear interactions between the counterpropagating Alfvén waves. Results are presented for two models of the background atmosphere. In the first model the plasma density and Alfvén speed vary smoothly with height, resulting in minimal wave reflections and low-energy dissipation rates. We find that the dissipation rate is insufficient to maintain the temperature of the background atmosphere. The standard phenomenological formula for the dissipation rate significantly overestimates the rate derived from our RMHD simulations, and a revised formula is proposed. In the second model we introduce additional density variations along the flux tube with a correlation length of 0.04 R⊙ and with relative amplitude of 10%. These density variations simulate the effects of compressive MHD waves on the Alfvén waves. We find that such variations significantly enhance the wave reflection and thereby the turbulent dissipation rates, producing enough heat to maintain the background atmosphere. We conclude that interactions between Alfvén and compressive waves may play an important role in the turbulent heating of the fast solar wind.
Fast electron flux driven by lower hybrid wave in the scrape-off layer
Li, Y. L.; Xu, G. S.; Wang, H. Q.; Wan, B. N.; Chen, R.; Wang, L.; Gan, K. F.; Yang, J. H.; Zhang, X. J.; Liu, S. C.; Li, M. H.; Ding, S.; Yan, N.; Zhang, W.; Hu, G. H.; Liu, Y. L.; Shao, L. M.; Li, J.; Chen, L.; Zhao, N.; and others
2015-02-15
The fast electron flux driven by Lower Hybrid Wave (LHW) in the scrape-off layer (SOL) in EAST is analyzed both theoretically and experimentally. The five bright belts flowing along the magnetic field lines in the SOL and hot spots at LHW guard limiters observed by charge coupled device and infrared cameras are attributed to the fast electron flux, which is directly measured by retarding field analyzers (RFA). The current carried by the fast electron flux, ranging from 400 to 6000 A/m{sup 2} and in the direction opposite to the plasma current, is scanned along the radial direction from the limiter surface to the position about 25 mm beyond the limiter. The measured fast electron flux is attributed to the high parallel wave refractive index n{sub ||} components of LHW. According to the antenna structure and the LHW power absorbed by plasma, a broad parallel electric field spectrum of incident wave from the antennas is estimated. The radial distribution of LHW-driven current density is analyzed in SOL based on Landau damping of the LHW. The analytical results support the RFA measurements, showing a certain level of consistency. In addition, the deposition profile of the LHW power density in SOL is also calculated utilizing this simple model. This study provides some fundamental insight into the heating and current drive effects induced by LHW in SOL, and should also help to interpret the observations and related numerical analyses of the behaviors of bright belts and hot spots induced by LHW.
Fast and accurate inference on gravitational waves from precessing compact binaries
NASA Astrophysics Data System (ADS)
Smith, Rory; Field, Scott E.; Blackburn, Kent; Haster, Carl-Johan; Pürrer, Michael; Raymond, Vivien; Schmidt, Patricia
2016-08-01
Inferring astrophysical information from gravitational waves emitted by compact binaries is one of the key science goals of gravitational-wave astronomy. In order to reach the full scientific potential of gravitational-wave experiments, we require techniques to mitigate the cost of Bayesian inference, especially as gravitational-wave signal models and analyses become increasingly sophisticated and detailed. Reduced-order models (ROMs) of gravitational waveforms can significantly reduce the computational cost of inference by removing redundant computations. In this paper, we construct the first reduced-order models of gravitational-wave signals that include the effects of spin precession, inspiral, merger, and ringdown in compact object binaries and that are valid for component masses describing binary neutron star, binary black hole, and mixed binary systems. This work utilizes the waveform model known as "IMRPhenomPv2." Our ROM enables the use of a fast reduced-order quadrature (ROQ) integration rule which allows us to approximate Bayesian probability density functions at a greatly reduced computational cost. We find that the ROQ rule can be used to speed-up inference by factors as high as 300 without introducing systematic bias. This corresponds to a reduction in computational time from around half a year to half a day for the longest duration and lowest mass signals. The ROM and ROQ rules are available with the main inference library of the LIGO Scientific Collaboration, LALInference.
Pavlov, I.P.; Heikkinen, J.A.
1995-10-01
Asymmetry in the transverse wave number spectrum of the radiated power of a screenless fast wave antenna at an ion cyclotron range of frequencies is calculated with a model that takes into account the nonsymmetry of the plasma surface impedance matrix for an inhomogeneous tokamak plasma in front of the antenna. The directivity of the wave number spectrum transverse to the ambient magnetic field caused by the asymmetry in the surface impedance is found to be strongly asymmetric with respect to the parallel wave number by the effect of the nonperpendicular angle between the antenna current strap and the magnetic field. The latter is shown to be responsible also for the asymmetry in the parallel wave number spectrum of an undirected antenna, and can lead to deviations of order {le}30% in the corresponding spectrum of a phased antenna array with directivity. The consequences of the observed effects to the antenna performance in the current drive applications as well as in excitation of poloidally asymmetric spectra are discussed. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Resonant Absorption of Solar Wind-Generated Fast Magnetosonic Waves in the Magnetosphere
NASA Astrophysics Data System (ADS)
Kozlov, Daniil
Resonant transformation of fast magnetosonic (FMS) waves into Alfven and slow magnetosonic (SMS) oscillations during their propagation from the solar wind to the magnetosphere is inves-tigated. The one-dimensionally inhomogeneous medium model with non-isothermal plasma is used to describe the day-side magnetosphere. In order to determine integrated properties of the FMS wave absorption after their transformation into resonant Alfven and SMS oscillations, we use the Kolmogorov spectrum typical of waves in turbulent plasma of the solar wind. Spatial distribution of energy dissipation rate of FMS oscillations penetrating into the magnetosphere from the solar wind is studied. The FMS wave energy dissipation rate caused by magnetosonic resonance excitation is shown to be several orders of magnitude greater than that caused by the Alfven resonance excitation at the same surface. It is connected with the spectrum of incident FMS waves. Magnitude of the Fourier harmonics exciting resonant Alfven oscillations is much smaller than that of the harmonics driving lower-frequency magnetosonic resonance. Being a low-frequency extension of ion-sound branch, SMS oscillations strongly interact with background ions. We estimate efficiency of the magnetospheric plasma heating via absorption of resonant SMS oscillations. The additional temperature related to such a heating turns out to be four orders of magnitude smaller than the background temperature.
Fast solution of elliptic partial differential equations using linear combinations of plane waves.
Pérez-Jordá, José M
2016-02-01
Given an arbitrary elliptic partial differential equation (PDE), a procedure for obtaining its solution is proposed based on the method of Ritz: the solution is written as a linear combination of plane waves and the coefficients are obtained by variational minimization. The PDE to be solved is cast as a system of linear equations Ax=b, where the matrix A is not sparse, which prevents the straightforward application of standard iterative methods in order to solve it. This sparseness problem can be circumvented by means of a recursive bisection approach based on the fast Fourier transform, which makes it possible to implement fast versions of some stationary iterative methods (such as Gauss-Seidel) consuming O(NlogN) memory and executing an iteration in O(Nlog(2)N) time, N being the number of plane waves used. In a similar way, fast versions of Krylov subspace methods and multigrid methods can also be implemented. These procedures are tested on Poisson's equation expressed in adaptive coordinates. It is found that the best results are obtained with the GMRES method using a multigrid preconditioner with Gauss-Seidel relaxation steps. PMID:26986436
NASA Astrophysics Data System (ADS)
Zheng, Chang-Jun; Chen, Hai-Bo; Chen, Lei-Lei
2013-04-01
This paper presents a novel wideband fast multipole boundary element approach to 3D half-space/plane-symmetric acoustic wave problems. The half-space fundamental solution is employed in the boundary integral equations so that the tree structure required in the fast multipole algorithm is constructed for the boundary elements in the real domain only. Moreover, a set of symmetric relations between the multipole expansion coefficients of the real and image domains are derived, and the half-space fundamental solution is modified for the purpose of applying such relations to avoid calculating, translating and saving the multipole/local expansion coefficients of the image domain. The wideband adaptive multilevel fast multipole algorithm associated with the iterative solver GMRES is employed so that the present method is accurate and efficient for both lowand high-frequency acoustic wave problems. As for exterior acoustic problems, the Burton-Miller method is adopted to tackle the fictitious eigenfrequency problem involved in the conventional boundary integral equation method. Details on the implementation of the present method are described, and numerical examples are given to demonstrate its accuracy and efficiency.
Fast solution of elliptic partial differential equations using linear combinations of plane waves
NASA Astrophysics Data System (ADS)
Pérez-Jordá, José M.
2016-02-01
Given an arbitrary elliptic partial differential equation (PDE), a procedure for obtaining its solution is proposed based on the method of Ritz: the solution is written as a linear combination of plane waves and the coefficients are obtained by variational minimization. The PDE to be solved is cast as a system of linear equations A x =b , where the matrix A is not sparse, which prevents the straightforward application of standard iterative methods in order to solve it. This sparseness problem can be circumvented by means of a recursive bisection approach based on the fast Fourier transform, which makes it possible to implement fast versions of some stationary iterative methods (such as Gauss-Seidel) consuming O (N logN ) memory and executing an iteration in O (N log2N ) time, N being the number of plane waves used. In a similar way, fast versions of Krylov subspace methods and multigrid methods can also be implemented. These procedures are tested on Poisson's equation expressed in adaptive coordinates. It is found that the best results are obtained with the GMRES method using a multigrid preconditioner with Gauss-Seidel relaxation steps.
Fast Magnetosonic Waves and Global Coronal Seismology in the Extended Solar Corona
NASA Astrophysics Data System (ADS)
Kwon, Ryun Young; Zhang, J.; Kramar, M.; Wang, T.; Ofman, L.; Davila, J. M.
2013-07-01
We present global coronal seismology, for the first time, that allows us to determine inhomogeneous magnetic field strengths in a wide range of the extended solar corona. We use observations of propagating disturbance associated with a coronal mass ejection observed on 2011 August 4 by the COR1 inner coronagraphs on board the STEREO spacecraft. We establish that the disturbance is in fact a fast magnetosonic wave as the upper coronal counterpart of the EIT wave observed by STEREO EUVI and travels across magnetic field lines with inhomogeneous speeds, passing through various coronal regions such as quiet/active corona, coronal holes, and streamers. We derive magnetic field strengths along the azimuthal trajectories of the fronts at heliocentric distances 2.0, 2.5, and 3.0 Rs, using the varying speeds and electron densities. The derived magnetic field strengths are consistent with values determined with a potential field source surface model and reported in previous works. The ranges of the magnetic field strengths at these heliocentric distances are 0.44 ± 0.29, 0.23 ± 0.15, and 0.26 ± 0.14 G, respectively. The uncertainty in determining magnetic field strengths is about 40 %. This work demonstrates that observations of fast magnetosonic waves by white-light coronagraphs can provide us with a unique way to diagnose magnetic field strength of an inhomogeneous medium in a wide spatial range of the extended solar corona.
Fast-mode Coronal Wave Trains Detected by SDO/AIA: Recent Observational Progress
NASA Astrophysics Data System (ADS)
Liu, Wei; Downs, Cooper; Ofman, Leon
2016-05-01
Quasi-periodic Fast Propagating wave trains (QFPs) are a new observational phenomenon discovered by SDO/AIA in extreme ultraviolet (EUV). They are fast-mode magnetosonic waves, closely related to quasi-periodic pulsations in solar flare emission ranging from radio to X-ray wavelengths. The significance of QFPs lies in their diagnostic potential, because they can provide critical clues to flare energy release and serve as new tools for coronal seismology. In this presentation, we report recent advances in observing QFPs. In particular, using differential emission measure (DEM) inversion, we found clear evidence of heating and cooling cycles that are consistent with alternating compression and rarefaction expected for magnetosonic wave pulses. We also found that different local magnetic and plasma environments can lead to two distinct types of QFPs located in different spatial domains with respect to their accompanying coronal mass ejections (CMEs). Moreover, recent IRIS observations of QFP source regions revealed sawtooth-like flare ribbon motions, indicative of pulsed magnetic reconnection, that are correlated with QFP excitation. More interestingly, from a statistical survey of over 100 QFP events, we found a preferential association with eruptive flares rather than confined flares. We will discuss the implications of these results and the potential roles of QFPs in coronal heating, energy transport, and solar eruptions.
Anticorrelated Emission of High Harmonics and Fast Electron Beams From Plasma Mirrors
NASA Astrophysics Data System (ADS)
Bocoum, Maïmouna; Thévenet, Maxence; Böhle, Frederik; Beaurepaire, Benoît; Vernier, Aline; Jullien, Aurélie; Faure, Jérôme; Lopez-Martens, Rodrigo
2016-05-01
We report for the first time on the anticorrelated emission of high-order harmonics and energetic electron beams from a solid-density plasma with a sharp vacuum interface—plasma mirror—driven by an intense ultrashort laser pulse. We highlight the key role played by the nanoscale structure of the plasma surface during the interaction by measuring the spatial and spectral properties of harmonics and electron beams emitted by a plasma mirror. We show that the nanoscale behavior of the plasma mirror can be controlled by tuning the scale length of the electron density gradient, which is measured in situ using spatial-domain interferometry.
Gaussian-Schell analysis of the transverse spatial properties of high-harmonic beams.
Lloyd, David T; O'Keeffe, Kevin; Anderson, Patrick N; Hooker, Simon M
2016-01-01
High harmonic generation (HHG) is an established means of producing coherent, short wavelength, ultrafast pulses from a compact set-up. Table-top high-harmonic sources are increasingly being used to image physical and biological systems using emerging techniques such as coherent diffraction imaging and ptychography. These novel imaging methods require coherent illumination, and it is therefore important to both characterize the spatial coherence of high-harmonic beams and understand the processes which limit this property. Here we investigate the near- and far-field spatial properties of high-harmonic radiation generated in a gas cell. The variation with harmonic order of the intensity profile, wavefront curvature, and complex coherence factor is measured in the far-field by the SCIMITAR technique. Using the Gaussian-Schell model, the properties of the harmonic beam in the plane of generation are deduced. Our results show that the order-dependence of the harmonic spatial coherence is consistent with partial coherence induced by both variation of the intensity-dependent dipole phase as well as finite spatial coherence of the driving radiation. These findings are used to suggest ways in which the coherence of harmonic beams could be increased further, which would have direct benefits to imaging with high-harmonic radiation. PMID:27465654
Gaussian-Schell analysis of the transverse spatial properties of high-harmonic beams
NASA Astrophysics Data System (ADS)
Lloyd, David T.; O’Keeffe, Kevin; Anderson, Patrick N.; Hooker, Simon M.
2016-07-01
High harmonic generation (HHG) is an established means of producing coherent, short wavelength, ultrafast pulses from a compact set-up. Table-top high-harmonic sources are increasingly being used to image physical and biological systems using emerging techniques such as coherent diffraction imaging and ptychography. These novel imaging methods require coherent illumination, and it is therefore important to both characterize the spatial coherence of high-harmonic beams and understand the processes which limit this property. Here we investigate the near- and far-field spatial properties of high-harmonic radiation generated in a gas cell. The variation with harmonic order of the intensity profile, wavefront curvature, and complex coherence factor is measured in the far-field by the SCIMITAR technique. Using the Gaussian-Schell model, the properties of the harmonic beam in the plane of generation are deduced. Our results show that the order-dependence of the harmonic spatial coherence is consistent with partial coherence induced by both variation of the intensity-dependent dipole phase as well as finite spatial coherence of the driving radiation. These findings are used to suggest ways in which the coherence of harmonic beams could be increased further, which would have direct benefits to imaging with high-harmonic radiation.
Gaussian-Schell analysis of the transverse spatial properties of high-harmonic beams
Lloyd, David T.; O’Keeffe, Kevin; Anderson, Patrick N.; Hooker, Simon M.
2016-01-01
High harmonic generation (HHG) is an established means of producing coherent, short wavelength, ultrafast pulses from a compact set-up. Table-top high-harmonic sources are increasingly being used to image physical and biological systems using emerging techniques such as coherent diffraction imaging and ptychography. These novel imaging methods require coherent illumination, and it is therefore important to both characterize the spatial coherence of high-harmonic beams and understand the processes which limit this property. Here we investigate the near- and far-field spatial properties of high-harmonic radiation generated in a gas cell. The variation with harmonic order of the intensity profile, wavefront curvature, and complex coherence factor is measured in the far-field by the SCIMITAR technique. Using the Gaussian-Schell model, the properties of the harmonic beam in the plane of generation are deduced. Our results show that the order-dependence of the harmonic spatial coherence is consistent with partial coherence induced by both variation of the intensity-dependent dipole phase as well as finite spatial coherence of the driving radiation. These findings are used to suggest ways in which the coherence of harmonic beams could be increased further, which would have direct benefits to imaging with high-harmonic radiation. PMID:27465654
Synergy in Two-Frequency Fast Wave Cyclotron Harmonic Absorption in DIII-D
Pinsker, R. I.; Choi, M.; Heidbrink, W. W.; Zhu, Y.; Porkolab, M.; Baity, F. W.; Hosea, J. C.
2009-11-26
Fast waves (FWs) at 60 MHz and at 90 MHz are coupled to DIII-D discharges for central heating and current drive at net FW power up to 3.5 MW. The primary absorption mechanism is intended to be direct electron damping in the plasma core. In discharges at B = 2 T with fast deuteron populations from neutral beam injection, 4th and 6th deuterium cyclotron harmonic absorption on the fast ions competes with direct electron damping. Previous experiments have shown that the 6{omega}{sub D} absorption of the 90 MHz FWs is weaker than the 4{omega}{sub D} absorption of 60 MHz FWs, in agreement with a model that includes unspecified edge losses. Recent experiments have shown that if the fast deuterons are accelerated by absorption of 60 MHz (4{omega}{sub D}) FWs, adding 90 MHz power (6{omega}{sub D}) can increase the fusion neutron rate by a larger increment than is obtained with 90 MHz power alone. Details of this synergy between 4{omega}{sub D} and 6{omega}{sub D} absorption are presented.
Love-Wave Sensors Combined with Microfluidics for Fast Detection of Biological Warfare Agents
Matatagui, Daniel; Fontecha, José Luis; Fernández, María Jesús; Gràcia, Isabel; Cané, Carles; Santos, José Pedro; Horrillo, María Carmen
2014-01-01
The following paper examines a time-efficient method for detecting biological warfare agents (BWAs). The method is based on a system of a Love-wave immunosensor combined with a microfluidic chip which detects BWA samples in a dynamic mode. In this way a continuous flow-through of the sample is created, promoting the reaction between antigen and antibody and allowing a fast detection of the BWAs. In order to prove this method, static and dynamic modes have been simulated and different concentrations of BWA simulants have been tested with two immunoreactions: phage M13 has been detected using the mouse monoclonal antibody anti-M13 (AM13), and the rabbit immunoglobulin (Rabbit IgG) has been detected using the polyclonal antibody goat anti-rabbit (GAR). Finally, different concentrations of each BWA simulants have been detected with a fast response time and a desirable level of discrimination among them has been achieved. PMID:25029282
Love-wave sensors combined with microfluidics for fast detection of biological warfare agents.
Matatagui, Daniel; Fontecha, José Luis; Fernández, María Jesús; Gràcia, Isabel; Cané, Carles; Santos, José Pedro; Horrillo, María Carmen
2014-01-01
The following paper examines a time-efficient method for detecting biological warfare agents (BWAs). The method is based on a system of a Love-wave immunosensor combined with a microfluidic chip which detects BWA samples in a dynamic mode. In this way a continuous flow-through of the sample is created, promoting the reaction between antigen and antibody and allowing a fast detection of the BWAs. In order to prove this method, static and dynamic modes have been simulated and different concentrations of BWA simulants have been tested with two immunoreactions: phage M13 has been detected using the mouse monoclonal antibody anti-M13 (AM13), and the rabbit immunoglobulin (Rabbit IgG) has been detected using the polyclonal antibody goat anti-rabbit (GAR). Finally, different concentrations of each BWA simulants have been detected with a fast response time and a desirable level of discrimination among them has been achieved. PMID:25029282
Gravitational-wave Constraints on the Progenitors of Fast Radio Bursts
NASA Astrophysics Data System (ADS)
Callister, Thomas; Kanner, Jonah; Weinstein, Alan
2016-07-01
The nature of fast radio bursts (FRBs) remains enigmatic. Highly energetic radio pulses of millisecond duration, FRBs are observed with dispersion measures consistent with an extragalactic source. A variety of models have been proposed to explain their origin. One popular class of theorized FRB progenitor is the coalescence of compact binaries composed of neutron stars and/or black holes. Such coalescence events are strong gravitational-wave emitters. We demonstrate that measurements made by the LIGO and Virgo gravitational-wave observatories can be leveraged to severely constrain the validity of FRB binary coalescence models. Existing measurements constrain the binary black hole rate to approximately 5% of the FRB rate, and results from Advanced LIGO’s O1 and O2 observing runs may place similarly strong constraints on the fraction of FRBs due to binary neutron star and neutron star–black hole progenitors.
Lee, Jeong Yong; Hwang, Ji Won; Jung, Hyun Wook; Kim, Sung Hyun; Lee, Seong Jae; Yoon, Kisun; Weitz, David A
2013-01-22
The fast dynamics generated by the Brownian motion of particles in colloidal drops, and the related relaxation during drying, which play key roles in suspension systems, were investigated incorporating multispeckle diffusing wave spectroscopy (MSDWS). MSDWS equipment was implemented to analyze the relaxation properties of suspensions under a nonergodic and nonstationary drying process, which cannot be elucidated by conventional light scattering methods, such as dynamic light scattering and diffusing wave spectroscopy. Rapid particle movement can be identified by the characteristic relaxation time, which is closely related to the Brownian motion due to thermal fluctuations of the particles. In the compacting stage of the drying process, the characteristic relaxation time increased gradually with the drying time because the particles in the colloidal drop were constrained by themselves. Moreover, variations of the initial concentration and particle size considerably affected the complete drying time and characteristic relaxation time, producing a shorter relaxation time for a low concentrated suspension with small particles. PMID:23281633
Towards a fast-running method for blast-wave mitigation by a prismatic blast wall
NASA Astrophysics Data System (ADS)
Éveillard, Sébastien; Lardjane, Nicolas; Vinçont, Jean-Yves; Sochet, Isabelle
A procedure aimed at developing a fast-running method for blast-wave effects characterization behind a protection barrier is presented. Small-scale experiments of a hemispherical gaseous charge (stoichiometric propane-oxygen mixture) without and with a prismatic protective barrier are used to validate the use of an in-house CFD code for gaseous detonation. From numerical experiments, pressure loss of a blast wave at a corner is quantified. These fits, in conjunction with TM5-1300 reflection charts, are used to estimate the maximum overpressure around a protective barrier through geometrical and empirical laws. The results show good agreement with numerical and experimental data from the ANR-BARPPRO research project.
De-trapping Magnetic Mirror Confined Fast Electrons by Shear Alfvén Waves
NASA Astrophysics Data System (ADS)
Wang, Y.; Gekelman, W. N.; Pribyl, P.; Papadopoulos, K.
2013-12-01
found. Research is supported by an ONR MURI award, and conducted at the Basic Plasma Science Facility at UCLA funded by DoE and NSF. A schematic plot of the experiment, with measured Alfvén wave magnetic field vector over-plotted. The plot shows a plane transverse to the background magnetic mirror field, in which a population of fast electrons is trapped and formed a hot electron ring. It has been observed the shear Alfvén wave can effectively de-trap the mirror confined fast electrons.
Shock-wave generation in transparent media from ultra-fast lasers
NASA Astrophysics Data System (ADS)
Bernath, R.; Brown, C. G.; Aspiotis, J.; Fisher, M.; Richardson, M.
2006-05-01
Laser interactions with bulk transparent media have long been investigated for material processing applications involving ablation and shock wave generation in both the nanosecond and femtosecond pulse width regimes1. Shock waves have been studied in fused silica and other optical glasses but previously have been characterized by the morphology of the concurrent ablation. We perform ablation at distances of 30 meters using the non-linear self-channeling effect. Using silicon wafers as targets because of their clearly defined ablation zones, we examine the effect that the filament has on the thin SiO II layer coating the wafer's surface. It is observed that the surface layer experiences a shock wave resulting from the explosive forces produced by the plasma. The use of several laser pulses in burst mode operation leads to the observation of multiple shock fronts in the material, and the possibility of shock wave addition for higher damage. Optical interferometry will be used to characterize the shock wave dynamics, using both traditional means of focusing in the near field and at 30 meters using propagating self-channeled femtosecond pulses. The novelty of using self-channeling laser pulses for shock wave generation has many implications for military applications. These experiments are to be performed in our secure test range using intensities of 10 14W/cm2 and higher incident on various transparent media. Interferometry is performed using a harmonic of the pump laser frequency. Experiments also include burst-mode operation, where a train of ultra-fast pulses, closely spaced in time, and novel new beam distributions, strike the sample.
One dimensional full wave analysis of slow-to-fast mode conversion in lower hybrid frequencies
Jia, Guo-Zhang; Gao, Zhe
2014-12-15
The linear conversion from the slow wave to the fast wave in the lower hybrid range of frequencies is analyzed numerically by using the set of field equations describing waves in a cold plane-stratified plasma. The equations are solved as a two-point boundary value problem, where the polarizations of each mode are set consistently in the boundary conditions. The scattering coefficients and the field patterns are obtained for various density profiles. It is shown that, for large density scale length, the results agree well with the traditional cognitions. In contrast, the reflected component and the probable transmitted-converted component from the conversion region, which are neglected in the usual calculations, become significant when the scale length is smaller than the wavelength of the mode. The inclusion of these new components will improve the accuracy of the simulated propagation and deposition for the injected rf power when the conversion process is involved within a sharp-varying density profile. Meanwhile, the accessibility of the incident slow wave for the low frequency case is also affected by the scale length of the density profile.
Kwon, Ryun-Young; Kramar, Maxim; Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.; Chae, Jongchul; Zhang, Jie
2013-10-10
We present global coronal seismology for the first time, which allows us to determine inhomogeneous magnetic field strength in the extended corona. From the measurements of the propagation speed of a fast magnetosonic wave associated with a coronal mass ejection (CME) and the coronal background density distribution derived from the polarized radiances observed by the STEREO SECCHI COR1, we determined the magnetic field strengths along the trajectories of the wave at different heliocentric distances. We found that the results have an uncertainty less than 40%, and are consistent with values determined with a potential field model and reported in previous works. The characteristics of the coronal medium we found are that (1) the density, magnetic field strength, and plasma β are lower in the coronal hole region than in streamers; (2) the magnetic field strength decreases slowly with height but the electron density decreases rapidly so that the local fast magnetosonic speed increases while plasma β falls off with height; and (3) the variations of the local fast magnetosonic speed and plasma β are dominated by variations in the electron density rather than the magnetic field strength. These results imply that Moreton and EIT waves are downward-reflected fast magnetosonic waves from the upper solar corona, rather than freely propagating fast magnetosonic waves in a certain atmospheric layer. In addition, the azimuthal components of CMEs and the driven waves may play an important role in various manifestations of shocks, such as type II radio bursts and solar energetic particle events.
Controlling the Interference of Multiple Molecular Orbitals in High-Harmonic Generation
Woerner, H. J.; Bertrand, J. B.; Hockett, P.; Corkum, P. B.; Villeneuve, D. M.
2010-06-11
We demonstrate a new method to investigate the origin of spectral structures in high-harmonic generation. We report detailed measurements of high-harmonic spectra in aligned nitrogen and carbon dioxide molecules. Varying the wavelength and intensity of the generating laser field, we show that the minimum in aligned N{sub 2} molecules is nearly unaffected, whereas the minimum in aligned CO{sub 2} molecules shifts over more than 15 eV. Our quantitative analysis shows that both the interference of multiple orbitals and their structural characteristics affect the position of the minimum. Our method provides a simple approach to the investigation of the high-harmonic generation process in more complex molecules.
Axis-dependence of molecular high harmonic emission in three dimensions.
Spector, Limor S; Artamonov, Maxim; Miyabe, Shungo; Martinez, Todd; Seideman, Tamar; Guehr, Markus; Bucksbaum, Philip H
2014-01-01
High-order harmonic generation in an atomic or molecular gas is a promising source of sub-femtosecond vacuum ultraviolet coherent radiation for transient scattering, absorption, metrology and imaging applications. High harmonic spectra are sensitive to Ångstrom-scale structure and motion of laser-driven molecules, but interference from radiation produced by random molecular orientations obscures this in all but the simplest cases, such as linear molecules. Here we show how to extract full body-frame high harmonic generation information for molecules with more complicated geometries by utilizing the methods of coherent transient rotational spectroscopy. To demonstrate this approach, we obtain the relative strength of harmonic emission along the three principal axes in the asymmetric-top sulphur dioxide. This greatly simplifies the analysis task of high harmonic spectroscopy and extends its usefulness to more complex molecules. PMID:24504181
Multielectron Correlation in High-Harmonic Generation: A 2D Model Analysis
Sukiasyan, Suren; McDonald, Chris; Destefani, Carlos; Brabec, Thomas; Ivanov, Misha Yu.
2009-06-05
We analyze the role of multielectron dynamics in high-harmonic generation spectroscopy, using an example of a two-electron system. We identify and systematically quantify the importance of correlation and exchange effects. One of the main sources for correlation is identified to be the polarization of the ion by the recombining continuum electron. This effect, which plays an important qualitative and quantitative role, seriously undermines the validity of the standard approaches to high-harmonic generation, which ignore the contribution of excited ionic states to the radiative recombination of the continuum electron.
NASA Technical Reports Server (NTRS)
Liu, Wei; Ofman, Leon; Nitta, Nariaki; Aschwanden, Markus J.; Schrijver, Carolus J.; Title, Alan M.; Tarbell, Theodore D.
2012-01-01
We present the first unambiguous detection of quasi-periodic wave trains within the broad pulse of a global EUV wave (so-called EIT wave) occurring on the limb. These wave trains, running ahead of the lateral coronal mass ejection (CME) front of 2-4 times slower, coherently travel to distances greater than approximately solar radius/2 along the solar surface, with initial velocities up to 1400 kilometers per second decelerating to approximately 650 kilometers per second. The rapid expansion of the CME initiated at an elevated height of 110 Mm produces a strong downward and lateral compression, which may play an important role in driving the primary EUV wave and shaping its front forwardly inclined toward the solar surface. The wave trains have a dominant 2 minute periodicity that matches the X-ray flare pulsations, suggesting a causal connection. The arrival of the leading EUV wave front at increasing distances produces an uninterrupted chain sequence of deflections and/or transverse (likely fast kink mode) oscillations of local structures, including a flux-rope coronal cavity and its embedded filament with delayed onsets consistent with the wave travel time at an elevated (by approximately 50%) velocity within it. This suggests that the EUV wave penetrates through a topological separatrix surface into the cavity, unexpected from CME-caused magnetic reconfiguration. These observations, when taken together, provide compelling evidence of the fast-mode MHD wave nature of the primary (outer) fast component of a global EUV wave, running ahead of the secondary (inner) slow component of CME-caused restructuring.
Liu Wei; Nitta, Nariaki V.; Aschwanden, Markus J.; Schrijver, Carolus J.; Title, Alan M.; Tarbell, Theodore D.; Ofman, Leon
2012-07-01
We present the first unambiguous detection of quasi-periodic wave trains within the broad pulse of a global EUV wave (so-called EIT wave) occurring on the limb. These wave trains, running ahead of the lateral coronal mass ejection (CME) front of 2-4 times slower, coherently travel to distances {approx}> R{sub Sun }/2 along the solar surface, with initial velocities up to 1400 km s{sup -1} decelerating to {approx}650 km s{sup -1}. The rapid expansion of the CME initiated at an elevated height of 110 Mm produces a strong downward and lateral compression, which may play an important role in driving the primary EUV wave and shaping its front forwardly inclined toward the solar surface. The wave trains have a dominant 2 minute periodicity that matches the X-ray flare pulsations, suggesting a causal connection. The arrival of the leading EUV wave front at increasing distances produces an uninterrupted chain sequence of deflections and/or transverse (likely fast kink mode) oscillations of local structures, including a flux-rope coronal cavity and its embedded filament with delayed onsets consistent with the wave travel time at an elevated (by {approx}50%) velocity within it. This suggests that the EUV wave penetrates through a topological separatrix surface into the cavity, unexpected from CME-caused magnetic reconfiguration. These observations, when taken together, provide compelling evidence of the fast-mode MHD wave nature of the primary (outer) fast component of a global EUV wave, running ahead of the secondary (inner) slow component of CME-caused restructuring.
Fast wave heating and current drive in tokamak plasmas with negative central shear
Forest, C.B.; Petty, C.C.; Baity, F.W.
1996-07-01
Fast waves provide an excellent tool for heating electrons and driving current in the central region of tokamak plasmas. In this paper, we report the use of centrally peaked electron heating and current drive to study transport in plasmas with negative central shear (NCS). Tokamak plasmas with NCS offer the potential of reduced energy transport and improved MHD stability properties, but will require non-inductive current drive to maintain the required current profiles. Fast waves, combined with neutral beam injection, provide the capability to change the central current density evolution and independently vary {ital T{sub e}}, and {ital T{sub i}} for transport studies in these plasmas. Electron heating also reduces the collisional heat exchange between electrons and ions and reduces the power deposition from neutral beams into electrons, thus improving the certainty in the estimate of the electron heating. The first part of this paper analyzes electron and ion heat transport in the L-mode phase of NCS plasmas as the current profile resistively evolves. The second part of the paper discusses the changes that occur in electron as well as ion energy transport in this phase of improved core confinement associated with NCS.
NASA Astrophysics Data System (ADS)
Emelina, A. S.; Emelin, M. Yu.; Ryabikin, M. Yu.
2016-04-01
Using the theoretical description beyond the dipole approximation, we examine the impact of the electron magnetic drift caused by a strong midinfrared laser field on the feasibility and ultimate limitations of the method proposed recently [C. Hernández-García et al., Phys. Rev. Lett. 111, 033002 (2013), 10.1103/PhysRevLett.111.033002] as a route to the generation of zeptosecond x-ray waveforms; this method relies on the interference of high-harmonic emission from multiple reencounters of the electron wave packet with the ion. We show that the electron magnetic drift serves as the spectral filter changing the relative weights of the contributions to the high-harmonic signal from different rescattering events. For a range of driving wavelengths in the midinfrared, the use of the control of the carrier-envelope phase, occasionally in combination with the spectral filtering, to cope with the magnetic drift effect is shown to facilitate the production of intense high-contrast keV beats of durations shorter than 0.8 attosecond. The limitations on the laser wavelengths usable for implementing this approach are determined by the growing unamendable imbalance between the contributions of interfering paths and by an overall decline in the efficiency of high-harmonic generation at longer driving wavelengths.
Excitation of kinetic Alfvén waves by fast electron beams
Chen, L.; Wu, D. J.; Zhao, G. Q.; Tang, J. F.; Huang, J. E-mail: djwu@pmo.ac.cn E-mail: jftang@xao.ac.cn
2014-09-20
Energetic electron beams, which are ubiquitous in a large variety of active phenomena in space and astrophysical plasmas, are one of the most important sources that drive plasma instabilities. In this paper, taking account of the return-current effect of fast electron beams, kinetic Alfvén wave (KAW) instability driven by a fast electron beam is investigated in a finite-β plasma of Q < β < 1 (where β is the kinetic-to-magnetic pressure ratio and Q ≡ m{sub e} /m{sub i} is the mass ratio of electrons to ions). The results show that the kinetic resonant interaction of beam electrons is the driving source for KAW instability, unlike the case driven by a fast ion beam, where both the kinetic resonant interaction of beam ions and the return-current are the driving source for the KAW instability. KAW instability has a nonzero growth rate in the range of the perpendicular wave number, 0
Absorption of Fast Waves at Moderate to High Ion Cyclotron Harmonics on DIII-D
Pinsker, R.I.; Petty, C.C.; Prater, R.; Choi, M.; Porkolab, M.; Heidbrink, W.W.; Luo, Y.; Baity, F.W.; Murakami, M.; Fredd, E.; Hosea, J.C.; Harvey, R.W.; Smirnov, A.P.; Van Zeeland, M.A.
2005-09-26
The absorption of fast Alfven waves (FW) by ion cyclotron harmonic damping in the range of harmonics from fourth to eighth is studied theoretically and with experiments in the DIII-D tokamak. A formula for linear ion cyclotron absorption on Maxwellian ion species is used to estimate the single-pass damping for various cases of experimental interest. It is found that damping on fast ions from neutral beam injection can be significant even at the eighth harmonic if the fast ion beta and the background plasma density are both high enough. The predictions are tested in several L-mode experiments in DIII-D with FW power at 60 MHz and at 116 MHz. It is found that 4th and 5th harmonic absorption of the 60 MHz power on the beam ions can be quite strong, but 8th harmonic absorption of the 116 MHz power appears to be weaker than expected. Possible explanations of the discrepancy are discussed.
Transverse instability of a plane front of fast impact ionization waves
Kyuregyan, A. S.
2012-05-15
The transverse instability of a plane front of fast impact ionization waves in p{sup +}-n-n{sup +} semiconductor structures with a finite concentration of donors N in the n layer has been theoretically analyzed. It is assumed that the high velocity u of impact ionization waves is ensured owing to the avalanche multiplication of the uniform background of electrons and holes whose concentration {sigma}{sub b} ahead of the front is high enough for the continuum approximation to be applicable. The problem of the calculation of the growth rate s of a small harmonic perturbation with wavenumber k is reduced to the eigenvalue problem for a specific homogeneous Volterra equation of the second kind containing the sum of double and triple integrals of an unknown eigenfunction. This problem has been solved by the method of successive approximations. It has been shown that the function s(k) for small k values increases monotonically in agreement with the analytical theory reported in Thermal Engineering 58 (13), 1119 (2011), reaches a maximum s{sub M} at k = k{sub M}, then decreases, and becomes negative at k > k{sub 01}. This behavior of the function s(k) for short-wavelength perturbations is due to a decrease in the distortion of the field owing to a finite thickness of the space charge region of the front and 'smearing' of perturbation of concentrations owing to the transverse transport of charge carriers. The similarity laws for perturbations with k Greater-Than-Or-Equivalent-To k{sub M} have been established: at fixed {sigma}{sub b} values and the maximum field strength on the front E{sub 0M}, the growth rate s depends only on the ratio k/N and the boundary wavenumber k{sub 01} {proportional_to} N. The parameters s{sub M}, k{sub M}, and k{sub 01}, which determine the perturbation growth dynamics and the upper boundary of the instability region for impact ionization waves, have been presented as functions of E{sub 0M}. These dependences indicate that the model of a plane
Observational and Theoretical Challenges to Wave or Turbulence Accelerations of the Fast Solar Wind
NASA Technical Reports Server (NTRS)
Roberts, D. Aaron
2008-01-01
We use both observations and theoretical considerations to show that hydromagnetic waves or turbulence cannot produce the acceleration of the fast solar wind and the related heating of the open solar corona. Waves do exist as shown by Hinode and other observations, and can play a role in the differential heating and acceleration of minor ions but their amplitudes are not sufficient to power the wind, as demonstrated by extrapolation of magnetic spectra from Helios and Ulysses observations. Dissipation mechanisms invoked to circumvent this conclusion cannot be effective for a variety of reasons. In particular, turbulence does not play a strong role in the corona as shown by both eclipse observations of coronal striations and theoretical considerations of line-tying to a nonturbulent photosphere, nonlocality of interactions, and the nature of kinetic dissipation. In the absence of wave heating and acceleration, the chromosphere and transition region become the natural source of open coronal energization. We suggest a variant of the velocity filtration approach in which the emergence and complex churning of the magnetic flux in the chromosphere and transition region continuously and ubiquitously produces the nonthermal distributions required. These particles are then released by magnetic carpet reconnection at a wide range of scales and produce the wind as described in kinetic approaches. Since the carpet reconnection is not the main source of the energization of the plasma, there is no expectation of an observable release of energy in nanoflares.
Measurement of the wave-front aberration of the eye by a fast psychophysical procedure
He, J.C.; Marcos, S.; Webb, R.H.; Burns, S.A.
1998-09-01
We used a fast psychophysical procedure to determine the wave-front aberrations of the human eye {ital in vivo}. We measured the angular deviation of light rays entering the eye at different pupillary locations by aligning an image of a point source entering the pupil at different locations to the image of a fixation cross entering the pupil at a fixed location. We fitted the data to a Zernike series to reconstruct the wave-front aberrations of the pupil. With this technique the repeatability of the measurement of the individual coefficients was 0.019 {mu}m. The standard deviation of the overall wave-height estimation across the pupil is less than 0.3 {mu}m. Since this technique does not require the administration of pharmacological agents to dilate the pupil, we were able to measure the changes in the aberrations of the eye during accommodation. We found that administration of even a mild dilating agent causes a change in the aberration structure of the eye. {copyright} 1998 Optical Society of America
Experimental investigation of the shock wave in a fast discharge with cylindrical geometry
Antsiferov, P. S.; Dorokhin, L. A.
2013-08-15
The work is devoted to the registration and the study of the properties of cylindrical shock waves generated in the fast discharge (dI/dt ∼ 10{sup 12} A/s) inside the ceramic tube (Al{sub 2}O{sub 3}) filled by argon at pressures of 100 and 300 Pa. The shock wave appears at the inner wall of the insulator and moves to the discharge axis with a velocity of about (3−4) × 10{sup 6} cm/s with subsequent cumulation. The plasma behind the front is heated enough to produce radiation in the vacuum ultraviolet (VUV) region, which makes it possible to study its structure by means of a pinhole camera with a microchannel plate detector. The time resolution of the registration system was 10 ns. The analysis of VUV spectra of the plasma shows that the electron temperature behind the shock wave front is about several eV; after the moment of cumulation, its temperature increases to 20–30 eV.
Modeling of Discharges with Fast Wave Power in DIII-D
Prater, R.; Choi, M.; Petty, C.C.; Pinsker, R.I.; Harvey, R.W.; Hosea, J.C.; Porkolab, M.; Smirnov, A.P.
2005-09-26
In order to facilitate the planning and analysis of experiments in which fast wave power is applied to discharges in DIII-D, a code has been developed to run conveniently a ray tracing code (GENRAY) and/or a full wave code (TORIC) for experimental or planned conditions. The code gathers information about the kinetic profiles (Te, Ti, ne, Zeff) and the neutral beam injection and calls the ONETWO transport code to obtain the density and equivalent Maxwellian temperature profiles of the energetic beam ions. Using all these data and the wave frequency and toroidal and poloidal spectra characteristic of any DIII-D antenna, GENRAY or TORIC can be run. For ray tracing some self-consistency checks on the absorption and current drive physics may be made using the output files, and comparisons with analytic expressions have been made. A goal of this program is the development and validation against experiment of computational models for FWCD which will be suitable for use on ITER.
Experimental Study of RF Sheath Formation on a Fast Wave Antenna and Limiter in the LAPD
NASA Astrophysics Data System (ADS)
Martin, Michael; Gekelman, Walter; Pribyl, Patrick; van Compernolle, Bart; Carter, Troy
2015-11-01
Ion cyclotron resonance heating (ICRH) will be an essential component of heating power in ITER. During ICRH, radio frequency (RF) sheaths may form both at the exciting antenna and further away, e.g. in the divertor region, and may cause wall material sputtering and decreased RF power coupling to the plasma. It is important to do detailed laboratory experiments that fully diagnose the sheaths and wave fields. This is not possible in fusion devices. A new RF system has recently been constructed for performing such studies in the LAPD plasma column (ne ~1012 -1013cm-3 , Te ~ 1 - 10 eV ,B0 ~ 400 - 2000 G , diameter ~ 60cm , length ~ 18 m) . The RF system is capable of pulsing at the 1 Hz rep. rate of the LAPD plasma and operating between 2-6 MHz (1st - 9th harmonic of fci in H) with a power output of 200 kW. First results of this system driving a single-strap fast wave antenna will be presented. Emissive and Langmuir probe measurements in the vicinity of both the antenna and a remote limiter and wave coupling measured by magnetic pickup loops will be presented.
NASA Astrophysics Data System (ADS)
Hollweg, Joseph V.; Markovskii, S. A.
2002-06-01
There is a growing consensus that cyclotron resonances play important roles in heating protons and ions in coronal holes where the fast solar wind originates and throughout interplanetary space as well. Most work on cyclotron resonant interactions has concentrated on the special, but unrealistic, case of propagation along the ambient magnetic field, B0, because of the great simplification it gives. This paper offers a physical discussion of how the cyclotron resonances behave when the waves propagate obliquely to B0. We show how resonances at harmonics of the cyclotron frequency come about, and how the physics can be different depending on whether E⊥ is in or perpendicular to the plane containing k and B0 (k is wave vector, and E⊥ is the component of the wave electric field perpendicular to B0). If E⊥ is in the k-B0 plane, the resonances are analogous to the Landau resonance and arise because the particle tends to stay in phase with the wave during the part of its orbit when it is interacting most strongly with E⊥. If E⊥ is perpendicular to the k-B0 plane, then the resonances depend on the fact that the particle is at different positions during the parts of its orbit when it is interacting most strongly with E⊥. Our main results are our
Carrier-envelope phase- and spectral control of fractional high-harmonic combs
NASA Astrophysics Data System (ADS)
Raith, Philipp; Ott, Christian; Meyer, Kristina; Kaldun, Andreas; Laux, Martin; Ceci, Matteo; Anderson, Christopher P.; Pfeifer, Thomas
2013-11-01
We experimentally and numerically control high-harmonic generation (HHG) by time delaying variable segments of a few-cycle driving laser spectrum. In this configuration combs of fractional high harmonics can be produced by interference of two temporally spaced attosecond pulse trains. We explain the observed beating of the high-harmonic intensity with the time delay and study the influence of the spectral segmentation on the high harmonics. By the implementation of additional carrier-envelope phase (CEP) control, we extend the control configuration and demonstrate independent multi-parameter controllability of HHG purely enabled by the CEP and the time delay between two spectral segments. We present how specific properties of the fractional harmonics can be optimized. Analyzing the measured fractional harmonic combs by a spectral interferometry method, we find that the relative phase between the two contributing attosecond pulse trains can be freely set by the CEP of the driving laser field. We also discuss how, in the future, this method can be applied to simultaneously measure transient dispersion and absorption in the extreme ultraviolet spectral region.
Initial Testing of Optical Arc Detector Inside 285/300 Fast Wave Antenna Box on DIII-D
Diem, Stephanie J; Fehling, Dan T; Hillis, Donald Lee; Horton, Anthony R; Unterberg, E. A.; Nagy, A.; Pinsker, R.
2013-01-01
Locating arcs within the fast wave current drive system is necessary to improve antenna performance and coupling to the plasma. Previously, there had been no way to observe arcs inside the vacuum vessel in an ICRF antenna on DIII-D. A new diagnostic that uses photomultiplier tubes has been installed for the 2012 run campaign on the 285/300 antenna of the fast wave system. The diagnostic has top and bottom views of the back of the four antenna straps and uses narrow-bandpass visible filters to isolate emission lines of copper (577 nm) and deuterium (656.1 nm). This diagnostic is based on the ORNL filterscope system currently in use on multiple devices. The system will be used to guide fast wave antenna conditioning, plasma operation and provide insight into future antenna upgrades on DIII-D.
Joint European Torus results with both fast and lower-hybrid wave consequences for future devices
Jacquinot, J.; Bures, M. ); the JET Team
1992-07-01
Heating and current drive studies were performed during the JET (Phys Fluids B {bold 3}, 2209 (1991)) 1990/91 operation using two large systems capable of generating either fast waves in the ion cyclotron range of frequencies (ICRF) or slow waves at a frequency above the lower-hybrid resonance (LH). The maximum wave power coupled to the torus reached 22 MW for ICRH and 2.4 MW for LH. The results obtained in plasma heating experiments qualify ICRH as a prime candidate for heating reactor grade plasmas. A centrally localized deposition profile in the cyclotron damping regime was demonstrated in a wide range of plasma density resulting in (i) record value {ital n}{sub {ital d}} {tau}{sub {ital E}} {ital T}{sub {ital i}0} {congruent} 7.8 {times} 10{sup 20} m{sup {minus}3} sec keV in thermal'' conditions {ital T}{sub {ital i}} = {ital T}{sub {ital e}} {congruent} 11 keV at high central densities generated by pellet injection; (ii) large normalized confinement 2.5 {le} {tau}{sub {ital E}}/{tau}{sub Goldston}{le}4. The large values of {tau}{sub {ital E}}/{tau}{sub Goldston} are reached in H-mode discharges ({ital I}{le}1.5 MA) with large bootstrap current fraction {ital I}{sub BS}/{ital I} {le} 0.7 {plus minus} 0.2; (iii) the highest to date D--{sup 3}He fusion power (140 kW) generated with 10--14 MW of ICRH in the L-mode regime at the {sup 3}He cyclotron frequency. All specific impurity generations have been reduced to negligible levels by proper antenna design and the generic difficulty of wave--plasma coupling has been greatly reduced using feedback loops controlling in real time the antenna circuits and the plasma position.
Fast dropouts of multi-MeV electrons due to combined effects of EMIC and whistler mode waves
NASA Astrophysics Data System (ADS)
Mourenas, D.; Artemyev, A. V.; Ma, Q.; Agapitov, O. V.; Li, W.
2016-05-01
We investigate how whole populations of 2-6 MeV electrons can be quickly lost from the Earth's outer radiation belt at L= 3-6 through precipitation into the atmosphere due to quasi-linear pitch angle scattering by combined electromagnetic ion cyclotron (EMIC) and whistler mode waves of realistic intensities occurring at the same or different local times. We provide analytical estimates of the corresponding relativistic electron lifetimes, emphasizing that the combined effects of both waves can lead to very fast (2-10 h) dropouts. Scaling laws for the loss timescales are derived, allowing us to determine the various plasma and wave parameter domains potentially leading to strong and fast dropouts. The analysis reveals that the fastest MeV electron dropouts occur at approximately the same rate over some high energy range and almost independently of EMIC wave amplitudes above a certain threshold. These results should help to better understand the dynamic variability of the radiation belts.
State-Space Realization of the Wave-Radiation Force within FAST: Preprint
Duarte, T.; Sarmento, A.; Alves, M.; Jonkman, J.
2013-06-01
Several methods have been proposed in the literature to find a state-space model for the wave-radiation forces. In this paper, four methods were compared, two in the frequency domain and two in the time domain. The frequency-response function and the impulse response of the resulting state-space models were compared against the ones derived by the numerical code WAMIT. The implementation of the state-space module within the FAST offshore wind turbine computer-aided engineering (CAE) tool was verified, comparing the results against the previously implemented numerical convolution method. The results agreed between the two methods, with a significant reduction in required computational time when using the state-space module.
Millimeter-wave center of curvature test for a fast paraboloid.
Goldberg, Samuel; Padin, Stephen
2012-01-20
We describe a technique for measuring the surface profile of a radio telescope with a fast paraboloidal primary. The technique uses a sensor, at the center of curvature of the primary, consisting of a millimeter-wave source and an array of receivers to measure the field in the caustic. The sensor is mounted on the telescope enclosure and it moves with the telescope, so the measurements can be used for continuous, slow, closed-loop control of the surface. Sensor decenter and despace errors, due to wind buffeting and thermal deformation of the sensor support, do not compromise the surface measurements because they result in profile errors that are mainly translation, which has no effect on astronomical observations, or tilt and defocus, which can be measured using astronomical sources. If the position of the sensor is known to 20 μm rms, the surface can be measured to ~1 μm rms at λ=3 mm. PMID:22270658
Mézière, F; Juskova, P; Woittequand, J; Muller, M; Bossy, E; Boistel, Renaud; Malaquin, L; Derode, A
2016-02-01
In this paper, ultrasound measurements of 1:1 scale three-dimensional (3D) printed trabecular bone phantoms are reported. The micro-structure of a trabecular horse bone sample was obtained via synchrotron x-ray microtomography, converted to a 3D binary data set, and successfully 3D-printed at scale 1:1. Ultrasound through-transmission experiments were also performed through a highly anisotropic version of this structure, obtained by elongating the digitized structure prior to 3D printing. As in real anisotropic trabecular bone, both the fast and slow waves were observed. This illustrates the potential of stereolithography and the relevance of such bone phantoms for the study of ultrasound propagation in bone. PMID:26936578
Design Concepts For A Long Pulse Upgrade For The DIII-D Fast Wave Antenna Array
Ryan, Philip Michael; Baity Jr, F Wallace; Caughman, John B; Goulding, Richard Howell; Hosea, J.; Greenough, Nevell; Nagy, Alex; Pinsker, R.; Rasmussen, David A
2009-01-01
A goal in the 5-year plan for the fast wave program on DIII-D is to couple a total of 3.6 MW of RF power into a long pulse, H-mode plasma for central electron heating. The present short-pulse 285/300 antenna array would need to be replaced with one capable of at least 1.2 MW, 10 s operation at 60 MHz into an H-mode (low resistive loading) plasma condition. The primary design under consideration uses a poloidally-segmented strap (3 sections) for reduced strap voltage near the plasma/Faraday screen region. Internal capacitance makes the antenna structure self-resonant at 60 MHz, strongly reducing peak E-fields in the vacuum coax and feed throughs.
Design Concepts For A Long Pulse Upgrade For The DIII-D Fast Wave Antenna Array
Ryan, P. M.; Baity, F. W.; Caughman, J. B. O.; Goulding, R. H.; Rasmussen, D. A.; Hosea, J. C.; Greenough, N. L.; Nagy, A.; Pinsker, R. I.
2009-11-26
A goal in the 5-year plan for the fast wave program on DIII-D is to couple a total of 3.6 MW of RF power into a long pulse, H-mode plasma for central electron heating. The present short-pulse 285/300 antenna array would need to be replaced with one capable of at least 1.2 MW, 10 s operation at 60 MHz into an H-mode (low resistive loading) plasma condition. The primary design under consideration uses a poloidally-segmented strap (3 sections) for reduced strap voltage near the plasma/Faraday screen region. Internal capacitance makes the antenna structure self-resonant at 60 MHz, strongly reducing peak E-fields in the vacuum coax and feed throughs.
Investigations of Low and Moderate Harmonic Fast Wave Physics on CDX-U
J. Spaleta; R. Majeski; C.K. Phillips; R.J. Dumont; R. Kaita; V. Soukhanovskii; L. Zakharov
2003-07-14
Third harmonic hydrogen cyclotron fast wave heating studies are planned in the near term on CDX-U to investigate the potential for bulk ion heating. In preparation for these studies, the available radio-frequency power in CDX-U has been increased to 0.5 MW. The operating frequency of the CDX-U radio-frequency transmitter was lowered to operate in the range of 8-10 MHz, providing access to the ion harmonic range 2* {approx} 4* in hydrogen. A similar regime is accessible for the 30 MHz radio-frequency system on the National Spherical Torus Experiment (NSTX), at 0.6 Tesla in hydrogen. Preliminary computational studies over the plasma regimes of interest for NSTX and CDX-U indicate the possibility of strong localized absorption on bulk ion species.
Development of a fast traveling-wave beam chopper for the National Spallation Neutron Source
Kurennoy, S.S.; Jason, A.J.; Krawczyk, F.L.; Power, J.
1997-10-01
High current and severe restrictions on beam losses, below 1 nA/m, in the designed linac for the National Spallation Neutron Source (NSNS) require clean and fast--with the rise time from 2% to 98% less than 2.5 ns to accommodate a 402.5-MHz beam structure--beam chopping in its front end, at the beam energy 2.5 MeV. The R and D program includes both modification of the existing LANSCE coax-plate chopper to reduce parasitic coupling between adjacent plates, and development of new traveling-wave deflecting structures, in particular, based on a meander line. Using analytical methods and three-dimensional time-domain computer simulations the authors study transient effects in such structures to choose an optimal chopper design.
NASA Astrophysics Data System (ADS)
Vackář, Jiří; Zahradník, Jiří; Sokos, Efthimios
2014-01-01
The January 18, 2010, shallow earthquake in the Corinth Gulf, Greece ( M w 5.3) generated unusually strong long-period waves (periods 4-8 s) between the P and S wave arrival. These periods, being significantly longer than the source duration, indicated a structural effect. The waves were observed in epicentral distances 40-250 km and were significant on radial and vertical component. None of existing velocity models of the studied region provided explanation of the waves. By inverting complete waveforms, we obtained an 1-D crustal model explaining the observation. The most significant feature of the best-fitting model (as well as the whole suite of models almost equally well fitting the waveforms) is a strong velocity step at depth about 4 km. In the obtained velocity model, the fast long-period wave was modeled by modal summation and identified as a superposition of several leaking modes. In this sense, the wave is qualitatively similar to P long or Pnl waves, which however are usually reported in larger epicentral distances. The main innovation of this paper is emphasis to smaller epicentral distances. We studied properties of the wave using synthetic seismograms. The wave has a normal dispersion. Azimuthal and distance dependence of the wave partially explains its presence at 46 stations of 70 examined. Depth dependence shows that the studied earthquake was very efficient in the excitation of these waves just due to its shallow centroid depth (4.5 km).
Lerche, Ernesto; Van Eester, Dirk
2011-12-23
Fourier analysis in the poloidal direction is a standard ingredient in present-day 2D wave equation solvers describing radio frequency waves in hot tokamak plasmas. Although a powerful and elegant technique, Fourier analysis has the disadvantage that a large number of modes is needed to describe the field pattern on a magnetic surface if a short wavelength mode exists on any - even very small - subpart of the particle trajectory. The present paper examines the potential of a method that does not suffer from this drawback: a finite element technique relying on simple linear or cubic area base functions that are defined on irregular elementary surfaces of triangular shape. The wave equation is solved in its weak Galerkin variational form and for realistic 2D tokamak geometry, accounting for the toroidal curvature but assuming the toroidal angle is ignorable, allowing to study the wave pattern for each of the independent toroidal modes excited by the antenna individually.The locally uniform full hot plasma dielectric tensor to all orders in finite Larmor radius was adopted. As the main intended application is the study of fast wave behavior (heating and current drive) at arbitrary harmonics, the wave vector complex amplitude appearing in the dielectric tensor is determined through a local dispersion root evaluation. High frequency fast wave propagation and damping is provided as an illustration in view of possible application of this type of current drive in future high density reactor-like tokamaks.
A fast neuronal signal-sensitive continuous-wave near-infrared imaging system
NASA Astrophysics Data System (ADS)
Zhang, Zhongxing; Sun, Bailei; Gong, Hui; Zhang, Lei; Sun, Jinyan; Wang, Bangde; Luo, Qingming
2012-09-01
We have developed a continuous-wave near-infrared imaging system to measure fast neuronal signals. We used a simultaneous sampling method with a separate high-speed analog-to-digital converter for each input channel, which provides a much larger point sample in a digital lock-in algorithm, higher temporal resolution, and lower crosstalk among detected channels. Without any analog filter, digital lock-in detection with a large point sample suppresses noise excellently, making the system less complex and offering better flexibility. In addition, using a custom-made collimator, more photons can reach the brain tissue due to the smaller divergence angle. Performance analysis shows high detection sensitivity (on the order of 0.1 pW) and high temporal resolution (˜50 Hz, 48 channels). Simulation experiments show that intensity changes on the order of 0.01% can be resolved by our instrument when averaging over approximately 500 stimuli. In vivo experiments over the motor cortex show that our instrument can detect fast neuronal signals in the human brain.
A fast neuronal signal-sensitive continuous-wave near-infrared imaging system.
Zhang, Zhongxing; Sun, Bailei; Gong, Hui; Zhang, Lei; Sun, Jinyan; Wang, Bangde; Luo, Qingming
2012-09-01
We have developed a continuous-wave near-infrared imaging system to measure fast neuronal signals. We used a simultaneous sampling method with a separate high-speed analog-to-digital converter for each input channel, which provides a much larger point sample in a digital lock-in algorithm, higher temporal resolution, and lower crosstalk among detected channels. Without any analog filter, digital lock-in detection with a large point sample suppresses noise excellently, making the system less complex and offering better flexibility. In addition, using a custom-made collimator, more photons can reach the brain tissue due to the smaller divergence angle. Performance analysis shows high detection sensitivity (on the order of 0.1 pW) and high temporal resolution (~50 Hz, 48 channels). Simulation experiments show that intensity changes on the order of 0.01% can be resolved by our instrument when averaging over approximately 500 stimuli. In vivo experiments over the motor cortex show that our instrument can detect fast neuronal signals in the human brain. PMID:23020395
A square-wave adsorptive stripping voltammetric method for determination of fast green dye.
Al-Ghamdi, Ali F
2009-01-01
Square-wave adsorptive stripping voltammetric (SW-AdSV) determinations of trace concentrations of the coloring agent fast green were described. The analytical methodology used was based on the adsorptive preconcentration of the dye on the hanging mercury drop electrode, and then a negative sweep was initiated. In pH 10 carbonate supporting electrolyte, fast green gave a well-defined and sensitive SW-AdSV peak at -1220 mV. The electroanalytical determination of this dye was found to be optimized in carbonate buffer (pH 10) with the following experimental conditions: accumulation time (120 s); accumulation potential (-0.8 V); scan rate (800 mV/s); pulse amplitude (90 mV); frequency (90 Hz); surface area of the working electrode (0.6 mm2); and the convection rate (2000 rpm). Under these optimized conditions, the AdSV peak current was proportional over the concentration range 2 x 10(-8) -6 x 10(-7) M (r = 0.999), with an LOD of 1.63 x 10(-10) M (0.132 ppb). This analytical approach possessed more enhanced sensitivity than conventional chromatography or spectrophotometry, and was simple and quick. The precision of the method in terms of RSD was 0.17%, whereas the accuracy was evaluated via the mean recovery of 99.6%. Possible interferences by several substances usually present as food additive azo dyes (E110, E102, E123, and E129), natural and artificial sweeteners, and antioxidants were also investigated. Applicability of the developed electroanalysis method was illustrated via the determination of fast green in ice cream and soft drink samples. PMID:20166589
Fast methods for computing scene raw signals in millimeter-wave sensor simulations
NASA Astrophysics Data System (ADS)
Olson, Richard F.; Reynolds, Terry M.; Satterfield, H. Dewayne
2010-04-01
Modern millimeter wave (mmW) radar sensor systems employ wideband transmit waveforms and efficient receiver signal processing methods for resolving accurate measurements of targets embedded in complex backgrounds. Fast Fourier Transform processing of pulse return signal samples is used to resolve range and Doppler locations, and amplitudes of scattered RF energy. Angle glint from RF scattering centers can be measured by performing monopulse arithmetic on signals resolved in both delta and sum antenna channels. Environment simulations for these sensors - including all-digital and hardware-in-the-loop (HWIL) scene generators - require fast, efficient methods for computing radar receiver input signals to support accurate simulations with acceptable execution time and computer cost. Although all-digital and HWIL simulations differ in their representations of the radar sensor (which is itself a simulation in the all-digital case), the signal computations for mmW scene modeling are closely related for both types. Engineers at the U.S. Army Aviation and Missile Research, Development and Engineering Center (AMRDEC) have developed various fast methods for computing mmW scene raw signals to support both HWIL scene projection and all-digital receiver model input signal synthesis. These methods range from high level methods of decomposing radar scenes for accurate application of spatially-dependent nonlinear scatterer phase history, to low-level methods of efficiently computing individual scatterer complex signals and single precision transcendental functions. The efficiencies of these computations are intimately tied to math and memory resources provided by computer architectures. The paper concludes with a summary of radar scene computing performance on available computer architectures, and an estimate of future growth potential for this computational performance.
Fast-wave slotted-waveguide coupler on Versator-II
NASA Astrophysics Data System (ADS)
Colborn, J. A.; Parker, R. R.; Chen, K.-I.; Luckhardt, S. C.; Porkolab, M.
1987-09-01
A slotted-waveguide fast-wave coupler has been constructed, without the use of dielectric, and used to drive current on the Versator-II tokamak. Up to 35 kW of net rf power at 2.45 GHz has been radiated into plasmas with 2×1012 cm-3≤n¯e≤1.2×1013 cm-3 and Btor≊1.0 T. The launched spectrum has a peak near N∥=2 and a large peak near N∥=-0.8 Radiating efficiency of the antenna is roughly independent of antenna position except when the antenna is at least 0.2 cm outside the limiter, in which case the radiating efficiency slightly improves as the antenna is moved farther outside. When the coupler is inside the limiter, radiating efficiency improves moderately with increased n¯e. Current-drive efficiency is comparable to that of the slow-wave, and is not affected when the antenna spectrum is reversed.
Fast simulated annealing inversion of surface waves on pavement using phase-velocity spectra
Ryden, N.; Park, C.B.
2006-01-01
The conventional inversion of surface waves depends on modal identification of measured dispersion curves, which can be ambiguous. It is possible to avoid mode-number identification and extraction by inverting the complete phase-velocity spectrum obtained from a multichannel record. We use the fast simulated annealing (FSA) global search algorithm to minimize the difference between the measured phase-velocity spectrum and that calculated from a theoretical layer model, including the field setup geometry. Results show that this algorithm can help one avoid getting trapped in local minima while searching for the best-matching layer model. The entire procedure is demonstrated on synthetic and field data for asphalt pavement. The viscoelastic properties of the top asphalt layer are taken into account, and the inverted asphalt stiffness as a function of frequency compares well with laboratory tests on core samples. The thickness and shear-wave velocity of the deeper embedded layers are resolved within 10% deviation from those values measured separately during pavement construction. The proposed method may be equally applicable to normal soil site investigation and in the field of ultrasonic testing of materials. ?? 2006 Society of Exploration Geophysicists.
The gradient waves of perturbations as an instability factor in fast-flow lasers
NASA Astrophysics Data System (ADS)
Fedoseev, A. I.; Mushenkov, A. V.; Odintsov, A. I.; Smirnov, A. P.
2016-07-01
We study the mechanism of the self-oscillation instability associated with the nonlinear interaction of radiation with a moving active medium in a fast-flow gas laser. The results of our analytical and numerical calculations of the frequencies and increments of the small self-oscillation perturbations in an unstable cavity of the laser with a non-uniform pumping rate are presented. In the analytical model the small perturbations of the gain in each point of the flow consist of two parts. The first part includes the ‘local’ perturbations that are not related to a motion of the medium. The second part includes the ‘flow’ perturbations that arise upstream of the flow due to the gradients of the pumping rate and the laser field intensity. These perturbations are carried by the flow in the form of traveling waves. The interference of the ‘gradient’ waves of the flow perturbations results in the resonant properties of the feedback produced by the flow. It is demonstrated that it is feasible to control the lasing regime based on these resonant properties of the feedback. The simulation of the nonlinear lasing regimes demonstrates that the conversion of continuous lasing into the periodical self-pulsing regime is not accompanied by a significant reduction in the average power output.
60 MHz fast wave current drive experiments for DIII-D
Mayberry, M.J.; Chiu, S.C.; Porkolab, M.; Chan, V.; Freeman, R.; Harvey, R.; Pinsker, R.
1989-05-01
Non-inductive current drive is an essential element of the ITER program because it enhances high fluence nuclear testing during the technology phase of operations. By using fast waves in the ion cyclotron range of frequencies (ICRF), current drive efficiencies comparable to lower-hybrid current drive can be obtained with good penetration of wave power to the high temperature plasma core. An additional advantage of the low frequency scheme is its technological simplicity due to the present availability of efficient, multi-megawatt rf sources in the ICRF. The DIII-D facility provides an excellent opportunity to test the feasibility of the low frequency FWCD approach. By combining with high power (2 MW) ECH injection at 60 GHz, it should be possible to generate plasmas with central electron temperatures of T/sub e0/ approx. = 4 keV, and by operating at a reduced toroidal field (B = 1T) to increase the electron ..beta.., strong single-pass absorption (/eta//sub abs/ greater than or equal to 0.3) can be achieved. The availability of a wide port recess (1m toroidal by 0.5m poloidal) will enable a travelling wave spectrum to be launched with N/sub parallel/ approx. = 5--7 at 60 MHz, which should be optimum for strong electron interaction. The resulting current drive efficiency should be sufficiently high to demonstrate FWCD at the /approximately/ 0.25--0.5 MA level at moderate densities (/bar n/ approx. = 1.3 /times/ 10/sup 19/ m/sup /minus/3/) using the existing 2 MW ICRF transmitter. 7 refs., 5 figs.
Mode conversion of fast Alfv{acute e}n waves at the ion{endash}ion hybrid resonance
Ram, A.K.; Bers, A.; Schultz, S.D.; Fuchs, V.
1996-05-01
Substantial radio-frequency power in the ion-cyclotron range of frequencies can be effectively coupled to a tokamak plasma from poloidal current strap antennas at the plasma edge. If there exists an ion{endash}ion hybrid resonance inside the plasma, then some of the power from the antenna, delivered into the plasma by fast Alfv{acute e}n waves, can be mode converted to ion-Bernstein waves. In tokamak confinement fields the mode-converted ion-Bernstein waves can damp effectively and locally on electrons [A. K. Ram and A. Bers, Phys. Fluids B {bold 3}, 1059 (1991)]. The usual mode-conversion analysis that studies the propagation of fast Alfv{acute e}n waves in the immediate vicinity of the ion{endash}ion hybrid resonance is extended to include the propagation and reflection of the fast Alfv{acute e}n waves on the high magnetic-field side of the ion{endash}ion hybrid resonance. It is shown that there exist plasma conditions for which the entire fast Alfv{acute e}n wave power incident on the ion{endash}ion hybrid resonance can be converted to ion-Bernstein waves. In this extended analysis of the mode conversion process, the fast Alfv{acute e}n waves can be envisioned as being coupled to an internal plasma resonator. This resonator extends from the low magnetic-field cutoff near the ion{endash}ion hybrid resonance to the high magnetic-field cutoff. The condition for 100{percent} mode conversion corresponds to a critical coupling of the fast Alfv{acute e}n waves to this internal resonator. As an example, the appropriate plasma conditions for 100{percent} mode conversion are determined for the Tokamak Fusion Test Reactor (TFTR) [R. Majeski {ital et} {ital al}., {ital Proceedings} {ital of} {ital the} 11{ital th} {ital Topical} {ital Conference} {ital on} {ital RF} {ital Power} {ital in} {ital Plasmas}, Palm Springs (American Institute of Physics, New York, 1995), Vol. 355, p. 63] experimental parameters. {copyright} {ital 1996 American Institute of Physics.}
Tomographic reconstruction of circularly polarized high-harmonic fields: 3D attosecond metrology
Chen, Cong; Tao, Zhensheng; Hernández-García, Carlos; Matyba, Piotr; Carr, Adra; Knut, Ronny; Kfir, Ofer; Zusin, Dimitry; Gentry, Christian; Grychtol, Patrik; Cohen, Oren; Plaja, Luis; Becker, Andreas; Jaron-Becker, Agnieszka; Kapteyn, Henry; Murnane, Margaret
2016-01-01
Bright, circularly polarized, extreme ultraviolet (EUV) and soft x-ray high-harmonic beams can now be produced using counter-rotating circularly polarized driving laser fields. Although the resulting circularly polarized harmonics consist of relatively simple pairs of peaks in the spectral domain, in the time domain, the field is predicted to emerge as a complex series of rotating linearly polarized bursts, varying rapidly in amplitude, frequency, and polarization. We extend attosecond metrology techniques to circularly polarized light by simultaneously irradiating a copper surface with circularly polarized high-harmonic and linearly polarized infrared laser fields. The resulting temporal modulation of the photoelectron spectra carries essential phase information about the EUV field. Utilizing the polarization selectivity of the solid surface and by rotating the circularly polarized EUV field in space, we fully retrieve the amplitude and phase of the circularly polarized harmonics, allowing us to reconstruct one of the most complex coherent light fields produced to date. PMID:26989782
NASA Astrophysics Data System (ADS)
Wang, Chang-Ming; Ho, Tak-San; Chu, Shih-I.
2016-05-01
The study of high harmonic generation in solid driven by intense laser fields is a subject of much current interest. Recently we introduce a new optimization method to directly reconstruct the band structure of the crystal from the power spectrum of strong-field generated high harmonics. Without loss of generality, the reconstruction is formulated for a one-dimensional single band model as a minimization problem and solved by a derivative-free unconstrained optimization algorithm-NEWUOA. The method can be readily generalized to treat multi-band problems. Numerical simulations are presented to demonstrate the applicability of the method, and the reconstructed band structure is found to be in excellent agreement with the exact one. It is also shown that our optimization method remains robust and efficient even starting from the poorly guessed band structure.
Tomographic Reconstruction of Circularly Polarized High Harmonic Fields: 3D Attosecond Metrology
NASA Astrophysics Data System (ADS)
Chen, Cong; Tao, Zhensheng; Hernández-García, Carlos; Matyba, Piotr; Carr, Adra; Knut, Ronny; Kfir, Ofer; Zusin, Dimitry; Gentry, Christian; Grychtol, Patrick; Cohen, Oren; Plaja, Lius; Becker, Andreas; Jaron-Becker, Agnieszka; Kapteyn, Henry; Murnane, Margaret
Bright, circularly polarized, extreme ultraviolet (EUV) and soft X-ray high harmonic beams can now be produced using counter-rotating circularly polarized driving laser fields. In the time domain, the field is predicted to emerge as a complex series of rotating linearly polarized bursts, varying rapidly in amplitude, frequency and polarization. Here, we extend attosecond metrology techniques to circularly polarized light for the first time by simultaneously irradiating a copper surface with circularly polarized high harmonic and linearly polarized infrared laser fields. The resulting temporal modulation of the photoelectron spectra carries essential phase information about the EUV field. Utilizing the polarization selectivity of the solid surface and by rotating the circularly polarized EUV field in space, we fully retrieve the amplitude and phase of the circularly polarized harmonics, allowing us to reconstruct one of the most complex coherent light fields produced to date.
Single-pass high-harmonic generation at 20.8 MHz repetition rate.
Vernaleken, Andreas; Weitenberg, Johannes; Sartorius, Thomas; Russbueldt, Peter; Schneider, Waldemar; Stebbings, Sarah L; Kling, Matthias F; Hommelhoff, Peter; Hoffmann, Hans-Dieter; Poprawe, Reinhart; Krausz, Ferenc; Hänsch, Theodor W; Udem, Thomas
2011-09-01
We report on single-pass high-harmonic generation (HHG) with amplified driving laser pulses at a repetition rate of 20.8 MHz. An Yb:YAG Innoslab amplifier system provides 35 fs pulses with 20 W average power at 1030 nm after external pulse compression. Following tight focusing into a xenon gas jet, we observe the generation of high-harmonic radiation of up to the seventeenth order. Our results show that state-of-the-art amplifier systems have become a promising alternative to cavity-assisted HHG for applications that require high repetition rates, such as frequency comb spectroscopy in the extreme UV. PMID:21886233
Using the third state of matter: high harmonic generation from liquid targets
NASA Astrophysics Data System (ADS)
Heissler, P.; Lugovoy, E.; Hörlein, R.; Waldecker, L.; Wenz, J.; Heigoldt, M.; Khrennikov, K.; Karsch, S.; Krausz, F.; Abel, B.; Tsakiris, G. D.
2014-11-01
High harmonic generation on solid and gaseous targets has been proven to be a powerful platform for the generation of attosecond pulses. Here we demonstrate a novel technique for the XUV generation on a smooth liquid surface target in vacuum, which circumvents the problem of low repetition rate and limited shot numbers associated with solid targets, while it maintains some of its merits. We employed atomically smooth, continuous liquid jets of water, aqueous salt solutions and ethanol that allow uninterrupted high harmonic generation due to the coherent wake emission mechanism for over 8 h. It has been found that the mechanism of plasma generation is very similar to that for smooth solid target surfaces. The vapor pressure around the liquid target in our setup has been found to be very low such that the presence of the gas phase around the liquid jet could be neglected.
Intense sub-2 optical cycle laser pulses at 1.8 micron for high harmonic generation
NASA Astrophysics Data System (ADS)
Legare, Francois; Schmidt, Bruno E.; Béejot, Pierre; Giguère, Mathieu; Shiner, Andrew D.; Trallero-Herrero, Carlos; Bisson, Éric; Kasparian, Jerome; Wolf, Jean-Pierre; Villeneuve, David M.; Kieffer, Jean-Claude; Corkum, Paul B.
2010-03-01
Shortening of attosecond pulse duration utilizing high harmonic generation (HHG) requires access to few cycle pulses in the infrared spectral range because the cut-off shifts towards higher photon energies proportional to the square of the driving field wavelength. Furthermore, the ability of performing time-resolved molecular orbital tomography of polyatomic molecules will benefit from longer wavelengths compared to 800 nm because of their low ionization potential. A simple scheme for generating 0.4 mJ 11.5 fs pulses at 1.8 μm is presented. Optical parametric amplified pulses were spectrally broadened in a hollow-core fiber and subsequently compressed by utilizing linear propagation through bulk material. The physical origin of the pulse compression scheme will be confirmed with numerical simulations of nonlinear propagation in the hollow-core fiber. Finally, high harmonic generation of noble gas atoms will be reported.
High-harmonic XUV source for time- and angle-resolved photoemission spectroscopy
Dakovski, Georgi L; Li, Yinwan; Durakiewicz, Tomasz; Rodriguez, George
2009-01-01
We present a laser-based apparatus for visible pump/XUV probe time- and angle-resolved photoemission spectroscopy (TRARPES) utilizing high-harmonic generation from a noble gas. Femtosecond temporal resolution for each selected harmonic is achieved by using a time-delay-compensated monochromator (TCM). The source has been used to obtain photoemission spectra from insulators (UO{sub 2}) and ultrafast pump/probe processes in semiconductors (GaAs).
Quasi-phase-matched high harmonic generation in hollow core photonic crystal fibers.
Ren, H; Nazarkin, A; Nold, J; Russell, P St J
2008-10-13
The potential of hollow core photonic crystal fiber as a nonlinear gas cell for efficient high harmonic generation is discussed. The feasibility of phase-matching this process by modulating the phase of ionization electrons using a counter-propagating laser field is shown. In this way, harmonics with energies of several hundreds of eV can be produced using fs-laser pump pulses of microJ energy. PMID:18852815
Pressure optimization of high harmonic generation in a differentially pumped Ar or H2 gas jet
NASA Astrophysics Data System (ADS)
Sayrac, M.; Kolomenskii, A. A.; Anumula, S.; Boran, Y.; Hart, N. A.; Kaya, N.; Strohaber, J.; Schuessler, H. A.
2015-04-01
We experimentally studied the dependence of high harmonic generation in argon and molecular hydrogen on pressure changes in a gas jet that cause variations of the phase matching conditions and absorption. The study was performed at a peak laser intensity of ˜1.5 × 1014 W/cm2. To enable measurements over a wide range of pressures, we employed differential pumping with an additional cell (˜20 cm3 volume) enclosing the gas jet. By increasing the pressure in the gas jet up to a maximum of 1.5 bars with argon or 0.5 bars with hydrogen, we observed an increase in the high harmonic (HH) yield until an optimum pressure of 0.2 bars was reached for Ar, beyond which the output began decreasing. For H2, we observed an increase of the HH output up to the maximum pressure of 0.5 bars. This pressure-dependence study allowed us to achieve a tenfold enhancement in the high harmonic yield at the optimum pressure.
Opportunities for chiral discrimination using high harmonic generation in tailored laser fields
NASA Astrophysics Data System (ADS)
Smirnova, Olga; Mairesse, Yann; Patchkovskii, Serguei
2015-12-01
Chiral discrimination with high harmonic generation (cHHG method) has been introduced in the recent work by R Cireasa et al (2015 Nat. Phys. 11 654-8). In its original implementation, the cHHG method works by detecting high harmonic emission from randomly oriented ensemble of chiral molecules driven by elliptically polarized field, as a function of ellipticity. Here we discuss future perspectives in the development of this novel method, the ways of increasing chiral dichroism using tailored laser pulses, new detection schemes involving high harmonic phase measurements, and concentration-independent approaches. Using the example of the epoxypropane molecule CH3CHCH2O (also known as 1,2-propylene oxide), we show theoretically that application of two-color counter-rotating elliptically polarized laser fields yields an order of magnitude enhancement of chiral dichroism compared to single color elliptical fields. We also describe how one can introduce a new functionality to cHHG: concentration-independent measurement of the enatiomeric excess in a mixture of randomly oriented left-handed and right-handed molecules. Finally, for arbitrary configurations of laser fields, we connect the observables of the cHHG method to the amplitude and phase of chiral response, providing a basis for reconstructing wide range of chiral dynamics from cHHG measurements, with femtosecond to sub-femtosecond temporal resolution.
Pongkitiwanichakul, Peera; Chandran, Benjamin D. G.
2014-11-20
We develop a model for stochastic acceleration of electrons in solar flares. As in several previous models, the electrons are accelerated by turbulent fast magnetosonic waves ({sup f}ast waves{sup )} via transit-time-damping (TTD) interactions. (In TTD interactions, fast waves act like moving magnetic mirrors that push the electrons parallel or anti-parallel to the magnetic field). We also include the effects of Coulomb collisions and the waves' parallel electric fields. Unlike previous models, our model is two-dimensional in both momentum space and wavenumber space and takes into account the anisotropy of the wave power spectrum F{sub k} and electron distribution function f {sub e}. We use weak turbulence theory and quasilinear theory to obtain a set of equations that describes the coupled evolution of F{sub k} and f {sub e}. We solve these equations numerically and find that the electron distribution function develops a power-law-like non-thermal tail within a restricted range of energies E in (E {sub nt}, E {sub max}). We obtain approximate analytic expressions for E {sub nt} and E {sub max}, which describe how these minimum and maximum energies depend upon parameters such as the electron number density and the rate at which fast-wave energy is injected into the acceleration region at large scales. We contrast our results with previous studies that assume that F{sub k} and f {sub e} are isotropic, and we compare one of our numerical calculations with the time-dependent hard-X-ray spectrum observed during the 1980 June 27 flare. In our numerical calculations, the electron energy spectra are softer (steeper) than in models with isotropic F{sub k} and f {sub e} and closer to the values inferred from observations of solar flares.
NASA Astrophysics Data System (ADS)
Thoen, D. J.; Bongers, W. A.; Westerhof, E.; Oosterbeek, J. W.; de Baar, M. R.; van den Berg, M. A.; van Beveren, V.; Bürger, A.; Goede, A. P. H.; Graswinckel, M. F.; Hennen, B. A.; Schüller, F. C.
2009-10-01
A fast Fourier transform (FFT) based wide range millimeter wave diagnostics for spectral characterization of scattered millimeter waves in plasmas has been successfully brought into operation. The scattered millimeter waves are heterodyne downconverted and directly digitized using a fast analog-digital converter and a compact peripheral component interconnect computer. Frequency spectra are obtained by FFT in the time domain of the intermediate frequency signal. The scattered millimeter waves are generated during high power electron cyclotron resonance heating experiments on the TEXTOR tokamak and demonstrate the performance of the diagnostics and, in particular, the usability of direct digitizing and Fourier transformation of millimeter wave signals. The diagnostics is able to acquire 4 GHz wide spectra of signals in the range of 136-140 GHz. The rate of spectra is tunable and has been tested between 200 000 spectra/s with a frequency resolution of 100 MHz and 120 spectra/s with a frequency resolution of 25 kHz. The respective dynamic ranges are 52 and 88 dB. Major benefits of the new diagnostics are a tunable time and frequency resolution due to postdetection, near-real time processing of the acquired data. This diagnostics has a wider application in astrophysics, earth observation, plasma physics, and molecular spectroscopy for the detection and analysis of millimeter wave radiation, providing high-resolution spectra at high temporal resolution and large dynamic range.
Thoen, D J; Bongers, W A; Westerhof, E; Oosterbeek, J W; de Baar, M R; van den Berg, M A; van Beveren, V; Bürger, A; Goede, A P H; Graswinckel, M F; Hennen, B A; Schüller, F C
2009-10-01
A fast Fourier transform (FFT) based wide range millimeter wave diagnostics for spectral characterization of scattered millimeter waves in plasmas has been successfully brought into operation. The scattered millimeter waves are heterodyne downconverted and directly digitized using a fast analog-digital converter and a compact peripheral component interconnect computer. Frequency spectra are obtained by FFT in the time domain of the intermediate frequency signal. The scattered millimeter waves are generated during high power electron cyclotron resonance heating experiments on the TEXTOR tokamak and demonstrate the performance of the diagnostics and, in particular, the usability of direct digitizing and Fourier transformation of millimeter wave signals. The diagnostics is able to acquire 4 GHz wide spectra of signals in the range of 136-140 GHz. The rate of spectra is tunable and has been tested between 200,000 spectra/s with a frequency resolution of 100 MHz and 120 spectra/s with a frequency resolution of 25 kHz. The respective dynamic ranges are 52 and 88 dB. Major benefits of the new diagnostics are a tunable time and frequency resolution due to postdetection, near-real time processing of the acquired data. This diagnostics has a wider application in astrophysics, earth observation, plasma physics, and molecular spectroscopy for the detection and analysis of millimeter wave radiation, providing high-resolution spectra at high temporal resolution and large dynamic range. PMID:19895061
Schmidt, J L; Tweten, D J; Benegal, A N; Walker, C H; Portnoi, T E; Okamoto, R J; Garbow, J R; Bayly, P V
2016-05-01
Mechanical anisotropy is an important property of fibrous tissues; for example, the anisotropic mechanical properties of brain white matter may play a key role in the mechanics of traumatic brain injury (TBI). The simplest anisotropic material model for small deformations of soft tissue is a nearly incompressible, transversely isotropic (ITI) material characterized by three parameters: minimum shear modulus (µ), shear anisotropy (ϕ=µ1µ-1) and tensile anisotropy (ζ=E1E2-1). These parameters can be determined using magnetic resonance elastography (MRE) to visualize shear waves, if the angle between the shear-wave propagation direction and fiber direction is known. Most MRE studies assume isotropic material models with a single shear (µ) or tensile (E) modulus. In this study, two types of shear waves, "fast" and "slow", were analyzed for a given propagation direction to estimate anisotropic parameters µ, ϕ, and ζ in two fibrous soft materials: turkey breast ex vivo and aligned fibrin gels. As expected, the speed of slow shear waves depended on the angle between fiber direction and propagation direction. Fast shear waves were observed when the deformations due to wave motion induced stretch in the fiber direction. Finally, MRE estimates of anisotropic mechanical properties in turkey breast were compared to estimates from direct mechanical tests. PMID:26920505
Fast determination of earthquake magnitude and fault extent from real-time P-wave recordings
NASA Astrophysics Data System (ADS)
Colombelli, Simona; Zollo, Aldo
2015-08-01
This work is aimed at the automatic and fast characterization of the extended earthquake source, through the progressive measurement of the P-wave displacement amplitude along the recorded seismograms. We propose a straightforward methodology to quickly characterize the earthquake magnitude and the expected length of the rupture, and to provide an approximate estimate of the average stress drop to be used for Earthquake Early Warning and rapid response purposes. We test the methodology over a wide distance and magnitude range using a massive Japan earthquake, accelerogram data set. Our estimates of moment magnitude, source duration/length and stress drop are consistent with the ones obtained by using other techniques and analysing the whole seismic waveform. In particular, the retrieved source parameters follow a self-similar, constant stress-drop scaling (median value of stress drop = 0.71 MPa). For the M 9.0, 2011 Tohoku-Oki event, both magnitude and length are underestimated, due to limited, available P-wave time window (PTWs) and to the low-frequency cut-off of analysed data. We show that, in a simulated real-time mode, about 1-2 seconds would be required for the source parameter determination of M 4-5 events, 3-10 seconds for M 6-7 and 30-40 s for M 8-8.5. The proposed method can also provide a rapid evaluation of the average slip on the fault plane, which can be used as an additional discriminant for tsunami potential, associated to large magnitude earthquakes occurring offshore.
NASA Astrophysics Data System (ADS)
Turnbull, A. D.; Choi, M.; Lao, L. L.; Chan, V. S.; Chu, M. S.; Jeon, Y. M.; Li, G.; Ren, Q.; Gorelenkov, N.
2007-11-01
Validation of a predictive sawtooth model is important for burning plasma experiments such as ITER. The Porcelli model using simplified expressions for the key contributions has been found to predict average sawtooth periods reasonably well in existing tokamaks. We evaluate this model using realistic models for the ideal MHD contribution from GATO, and a nonisotropic fast ion contribution using ORBIT-RF and TORIC for the rf-modified fast-ion pressure. Application to the first giant sawtooth cycle in a DIII-D discharge where beam ions accelerated by fast waves modify the sawteeth shows the model can predict the crash time consistent with the experimental crash. The stabilizing contributions depend strongly on uncertainties in the magnetic shear at q=1 and the fast ion poloidal beta. The model will be also applied to other sawteeth in the same discharge and compared to predictions from the more complete NOVA-K stability code with full anistropy.
Fast ion loss diagnostic plans for the National Spherical Torus Experiment
Darrow, D. S.; Bell, R.; Johnson, D. W.; Kugel, H.; Wilson, J. R.; Cecil, F. E.; Maingi, R.; Krasilnikov, A.; Alekseyev, A.
2001-01-01
The prompt loss of neutral beam ions from the National Spherical Torus Experiment is expected to be between 12% and 42% of the total 5 MW of beam power. There may, in addition, be losses of fast ions arising from high harmonic fast wave (HHFW) heating. Most of the lost ions will strike the HHFW antenna or the neutral beam dump. To measure these losses in the 2000 experimental campaign, thermocouples in the antenna, several infrared camera views, and a Faraday cup lost ion probe will be employed. The probe will measure loss of fast ions with E>1 keV at three radial locations, giving the scrape-off length of the fast ions.
Arpin, P.; Popmintchev, T.; Kapteyn, H. C.; Murnane, M. M.; Wagner, N. L.; Cohen, O.
2009-10-02
By combining laser pulse self-compression and high harmonic generation within a single waveguide, we demonstrate high harmonic emission from multiply charged ions for the first time. This approach enhances the laser intensity and counteracts ionization-induced defocusing, extending the cutoff photon energy in argon above 500 eV for the first time, with higher spectral intensity and cutoff energy than He for the same input laser parameters. This Letter demonstrates a pathway for extending high harmonic emission to very high photon energies using large, multiply charged, ions with high ionization potentials.
High resolution fast wave reflectometry: JET design and implications for ITER.
Cupido, L; Cardinali, A; Igreja, R; Serra, F; Manso, M E; Murari, A
2008-10-01
The measurement of the fuel mixture remains a very difficult task in thermonuclear plasmas, where the hydrogen isotopes are fully stripped and do not emit line radiation. On the other hand, direct determination of the ion species mix will be essential in the reactor to keep the mixture close to 50/50 and maximize the fusion output. In this paper, the design of fast wave reflectometry for JET is reviewed to show the potential of such a method in the perspective of ITER. The main design elements of the antenna and the detection system, based on vectorial measurements, are reported. The main challenges to such a diagnostic, mainly the intrinsic ion cyclotron emission from the plasma and the extensive use of ion cyclotron radiofrequencies as additional heating, are addressed in detail. The overall design indicates that the proposed system would be able to provide a measurement of the fuel ratio with spatial resolution in the range of few centimeters and temporal resolution in the range of 1 ms in the vast majority of JET scenarios. PMID:19068526
Recent Results on Coupling Fast Waves to High Performance Plasmas on DIII-D
Pinsker, R. I.; Luce, T. C.; Politzer, P. A.; Porkolab, M.; Goulding, R. H.; Hanson, G. R.; Ryan, P. M.; Hosea, J. C.; Nagy, A.; Wilson, J. R.; Maggiora, R.; Milanesio, D.; Zeng, L.
2011-12-23
Fast Waves (FWs) at 60 MHz and 90 MHz are used in DIII-D for central electron heating and current drive. Coupling of FWs to high-performance discharges is limited by low antenna loading in these regimes. To extend the application of high-power FWs to such regimes, methods of increasing the antenna loading in these regimes are needed. A systematic study of loading enhancement techniques has been carried out in DIII-D, including reduction of the antenna/plasma distance, gas puffing into the far scrape-off layer (SOL), and control of other parameters that affect the particle balance in the far SOL. Quantitative understanding of the physics of the loading resistance and its dependence on edge density profiles is demonstrated. The core FW heating efficiency appeared to be {approx}100% in the Advanced Inductive regime, consistent with the high first-pass direct electron absorption of {approx}75% that is predicted by the ray-tracing code GENRAY in this high electron beta regime.
High resolution fast wave reflectometry: JET design and implications for ITER
Cupido, L.; Igreja, R.; Serra, F.; Manso, M. E.; Cardinali, A.; Murari, A.
2008-10-15
The measurement of the fuel mixture remains a very difficult task in thermonuclear plasmas, where the hydrogen isotopes are fully stripped and do not emit line radiation. On the other hand, direct determination of the ion species mix will be essential in the reactor to keep the mixture close to 50/50 and maximize the fusion output. In this paper, the design of fast wave reflectometry for JET is reviewed to show the potential of such a method in the perspective of ITER. The main design elements of the antenna and the detection system, based on vectorial measurements, are reported. The main challenges to such a diagnostic, mainly the intrinsic ion cyclotron emission from the plasma and the extensive use of ion cyclotron radiofrequencies as additional heating, are addressed in detail. The overall design indicates that the proposed system would be able to provide a measurement of the fuel ratio with spatial resolution in the range of few centimeters and temporal resolution in the range of 1 ms in the vast majority of JET scenarios.
Generation of plasma rotation in a tokamak by ion-cyclotron absorption of fast Alfven waves
F.W. Perkins; R.B. White; P. Bonoli
2000-06-13
Control of rotation in tokamak plasmas provides a method for suppressing fine-scale turbulent transport by velocity shear and for stabilizing large-scale magnetohydrodynamic instabilities via a close-fitting conducting shell. The experimental discovery of rotation in a plasma heated by the fast-wave minority ion cyclotron process is important both as a potential control method for a fusion reactor and as a fundamental issue, because rotation arises even though this heating process introduces negligible angular momentum. This paper proposes and evaluates a mechanism which resolves this apparent conflict. First, it is assumed that angular momentum transport in a tokamak is governed by a diffusion equation with a no-slip boundary condition at the plasma surface and with a torque-density source that is a function of radius. When the torque density source consists of two separated regions of positive and negative torque density, a non-zero central rotation velocity results, even when the total angular momentum input vanishes. Secondly, the authors show that localized ion-cyclotron heating can generate regions of positive and negative torque density and consequently central plasma rotation.
Gravitational Waves from Rotating Neutron Stars and Evaluation of fast Chirp Transform Techniques
NASA Technical Reports Server (NTRS)
Strohmayer, Tod E.; White, Nicholas E. (Technical Monitor)
2000-01-01
X-ray observations suggest that neutron stars in low mass X-ray binaries (LMXB) are rotating with frequencies from 300 - 600 Hz. These spin rates are significantly less than the break-up rates for essentially all realistic neutron star equations of state, suggesting that some process may limit the spin frequencies of accreting neutron stars to this range. If the accretion induced spin up torque is in equilibrium with gravitational radiation losses, these objects could be interesting sources of gravitational waves. I present a brief summary of current measurements of neutron star spins in LMXBs based on the observations of high-Q oscillations during thermonuclear bursts (so called 'burst oscillations'). Further measurements of neutron star spins will be important in exploring the gravitational radiation hypothesis in more detail. To this end I also present a study of fast chirp transform (FCT) techniques as described by Jenet and Prince in the context of searching for the chirping signals observed during X-ray bursts.
GPU-based beamformer: fast realization of plane wave compounding and synthetic aperture imaging.
Yiu, Billy Y S; Tsang, Ivan K H; Yu, Alfred C H
2011-08-01
Although they show potential to improve ultrasound image quality, plane wave (PW) compounding and synthetic aperture (SA) imaging are computationally demanding and are known to be challenging to implement in real-time. In this work, we have developed a novel beamformer architecture with the real-time parallel processing capacity needed to enable fast realization of PW compounding and SA imaging. The beamformer hardware comprises an array of graphics processing units (GPUs) that are hosted within the same computer workstation. Their parallel computational resources are controlled by a pixel-based software processor that includes the operations of analytic signal conversion, delay-and-sum beamforming, and recursive compounding as required to generate images from the channel-domain data samples acquired using PW compounding and SA imaging principles. When using two GTX-480 GPUs for beamforming and one GTX-470 GPU for recursive compounding, the beamformer can compute compounded 512 x 255 pixel PW and SA images at throughputs of over 4700 fps and 3000 fps, respectively, for imaging depths of 5 cm and 15 cm (32 receive channels, 40 MHz sampling rate). Its processing capacity can be further increased if additional GPUs or more advanced models of GPU are used. PMID:21859591
NASA Astrophysics Data System (ADS)
Boardsen, S. A.; Hospodarsky, G. B.; Kletzing, C.; Santolik, O.; Wygant, J. R.; MacDonald, E.; Pfaff, R. F., Jr.; Kurth, W. S.; Khazanov, G. V.
2015-12-01
The fast magnetosonic mode, also referred to as equatorial noise, occurs at frequencies mainly between the proton cyclotron frequency (fcp) and the lower hybrid frequency. The wave properties of this mode are characterized by a strong magnetic compressional component. These waves are observed around the magnetic equator in the Earth's inner magnetosphere. Case studies of the spectra of these waves have found the emissions to be composed of 1) harmonics, usually with spacing near the local fcp, 2) broad band hiss-like structure, or 3) a superposition of the two spectral types. No statistical studies of the frequency structure of these waves have been made. Using ~600,000 burst mode wave captures from the EMFISIS Wave Form Receiver and the EFW instrument on the Van Allen Probes spacecraft this mode will be identified in the high resolution frequency spectra and its frequency structure will be characterized. The variation of the frequency structure will be investigated as a function of normalized frequency, location, and geomagnetic conditions, and with spacecraft separation. The frequency structure will be compared with path integrated gain using proton ring distributions as the wave source. Recently the modulation of the fast magnetosonic mode has been reported, with modulation periods in the range of 30s to 240s. It has been proposed that frequency drift observed during each modulation is due to strong inward diffusion in energy of the proton ring distributions that generate these waves. As the inner edge of the ring distribution diffuses towards lower energies the band of unstable harmonics increases in frequency. If in the source region, for modulations with periods greater than say 100s, the inward energy diffusion should be observable in the HOPE proton data which has a cycle time of 24s.
NASA Astrophysics Data System (ADS)
Wang, Jun; Zhao, Jianlin; Di, Jianglei; Jiang, Biqiang
2015-04-01
A scheme for recording fast process at nanosecond scale by using digital holographic interferometry with continuous wave (CW) laser is described and demonstrated experimentally, which employs delayed-time fibers and angular multiplexing technique and can realize the variable temporal resolution at nanosecond scale and different measured depths of object field at certain temporal resolution. The actual delay-time is controlled by two delayed-time fibers with different lengths. The object field information in two different states can be simultaneously recorded in a composite hologram. This scheme is also suitable for recording fast process at picosecond scale, by using an electro-optic modulator.
NASA Astrophysics Data System (ADS)
Imamura, Takeshi; Watanabe, Ayuka; Maejima, Yasumitsu
2016-03-01
Generation of gravity waves by convection was studied using a nonlinear two-dimensional model. A boundary-layer convection forced by a horizontally-uniform heating and a plume forced by a localized heating representing a local dust storm were tested. The results suggest that vigorous convection occurs due to the low density of the martian atmosphere and that short-period waves having frequencies near the buoyancy frequency can be preferentially generated. The propagation of those gravity waves to thermospheric heights was studied using a linearized one-dimensional model. Because of the fast vertical propagation the waves attain large amplitudes in the lower thermosphere, being consistent with Mars Global Surveyor and Mars Odyssey's accelerometer measurements and MAVEN's neutral and ion measurements. The heating and cooling caused by the waves are expected to be significant in the energy budget of the thermosphere, and the vertical mixing induced by those gravity waves should influence the homopause height. Since the thermospheric densities of light, minor species increase with the lowering of the homopause, a lower homopause may have enhanced the escape of such species to space for early Mars, where slower, weaker gravity waves should dominate.
Wave Driven Fast Ion Loss in the National Spherical Torus Experiment
E.D. Fredrickson; C.Z. Cheng; D. Darrow; G. Fu; N.N. Gorelenkov; G. Kramer; S.S. Medley; J. Menard; L. Roquemore; D. Stutman; R.B. White
2003-01-28
Spherical tokamaks, with their relatively low toroidal field, extend fast-ion-driven instability physics to parameter ranges not normally accessed in conventional tokamaks. The low field means that both the fast-ion Larmor radius normalized to the plasma minor radius and the ratio of the fast-ion velocity to the Alfven speed are relatively large. The large Larmor radius of the ions enhances their interaction with instability modes, influencing the structure of the unstable mode spectrum. The relatively large fast-ion velocity allows for a larger population of fast ions to be in resonance with the mode, increasing the drive. It is therefore an important goal of the present proof-of-principle spherical tokamaks to evaluate the role of fast-ion-driven instabilities in fast-ion confinement. This paper presents the first observations of fast-ion losses resulting from toroidal Alfven eigenmodes and a new, fishbone-like, energetic particle mode.
Hahn, M.; Savin, D. W.
2013-10-20
We present a measurement of the energy carried and dissipated by Alfvén waves in a polar coronal hole. Alfvén waves have been proposed as the energy source that heats the corona and drives the solar wind. Previous work has shown that line widths decrease with height in coronal holes, which is a signature of wave damping, but have been unable to quantify the energy lost by the waves. This is because line widths depend on both the non-thermal velocity v{sub nt} and the ion temperature T{sub i}. We have implemented a means to separate the T{sub i} and v{sub nt} contributions using the observation that at low heights the waves are undamped and the ion temperatures do not change with height. This enables us to determine the amount of energy carried by the waves at low heights, which is proportional to v{sub nt}. We find the initial energy flux density present was 6.7 ± 0.7 × 10{sup 5} erg cm{sup –2} s{sup –1}, which is sufficient to heat the coronal hole and accelerate the solar wind during the 2007-2009 solar minimum. Additionally, we find that about 85% of this energy is dissipated below 1.5 R{sub ☉}, sufficiently low that thermal conduction can transport the energy throughout the coronal hole, heating it and driving the fast solar wind. The remaining energy is roughly consistent with what models show is needed to provide the extended heating above the sonic point for the fast solar wind. We have also studied T{sub i}, which we found to be in the range of 1-2 MK, depending on the ion species.
NASA Astrophysics Data System (ADS)
Liu, Wei; Ofman, Leon; Broder, Brittany; Karlický, Marian; Downs, Cooper
2016-03-01
Quasi-periodic, fast-mode, propagating wave trains (QFPs) are a new observational phenomenon recently discovered in the solar corona by the Solar Dynamics Observatory with extreme ultraviolet (EUV) imaging observations. They originate from flares and propagate at speeds up to ˜2000 km s-1 within funnel-shaped waveguides in the wakes of coronal mass ejections (CMEs). QFPs can carry suffcient energy fluxes required for coronal heating during their occurr ences. They can provide new diagnostics for the solar corona and their associated flares. We present recent observations of QFPs focusing on their spatio-temporal properties, temperature dependence, and statistical correlation with flares and CMEs. Of particular interest is the 2010-Aug-01 C3.2 flare with correlated QFPs and drifting zebra and fiber radio bursts, which might be different manifestations of the same fast-mode wave trains. We also discuss the potential roles of QFPs in accelerating and/or modulating the solar wind.
Strong-Field Perspective on High-Harmonic Radiation from Bulk Solids
NASA Astrophysics Data System (ADS)
Higuchi, Takuya; Stockman, Mark I.; Hommelhoff, Peter
2014-11-01
Mechanisms of high-harmonic generation from crystals are described by treating the electric field of a laser as a quasistatic strong field. Under the quasistatic electric field, electrons in periodic potentials form dressed states, known as Wannier-Stark states. The energy differences between the dressed states determine the frequencies of the radiation. The radiation yield is determined by the magnitudes of the interband and intraband current matrix elements between the dressed states. The generation of attosecond pulses from solids is predicted. Ramifications for strong-field physics are discussed.
Interferences induced by spatially nonhomogeneous fields in high-harmonic generation
NASA Astrophysics Data System (ADS)
Ebadi, H.
2014-05-01
The high-harmonic spectrum simulated in a few-cycle laser pulse with spatially nonhomogeneous field presents two types of interferences, which characterize different plateaus in the spectrum. One of these plateaus is discernible with the nonequidistant peaks due to the interference of short and long trajectories, while another one is distinguished by a periodicity much larger than the laser frequency arising from trajectories modified by the nonhomogeneous field. Beside, the continuum-continuum harmonic generation appears in the spectrogram in the tunneling regime of the laser parameters. These features bear the tracking of classical trajectories and the complete characterization of emission spectrum, when using nanostructures in attoscience.
NASA Astrophysics Data System (ADS)
Lin, Ming-Fu
XUV light from high harmonic generation is an emerging new tool for studying ultrafast dynamics. Such sources have intrinsic ``spatial chirp'' that can cause significant periodic artifacts in absorption spectra of inhomogeneous samples. We show that a uniform thin-film morphology is required in order to obtain harmonic-structure free absorption spectra, especially for organometallic complexes that have strong non-resonant absorption features from the organic ligands. Demonstration of several static absorption spectra of different organometallic complexes and perovskite materials reveals elemental, oxidation state, and band structure specificity in agreement with theoretical results.
Lensless Diffractive Imaging Using Tabletop Coherent High-Harmonic Soft-X-Ray Beams
Sandberg, Richard L.; Paul, Ariel; Raymondson, Daisy A.; Haedrich, Steffen; Gaudiosi, David M.; Holtsnider, Jim; Tobey, Ra'anan I.; Cohen, Oren; Murnane, Margaret M.; Kapteyn, Henry C.; Song, Changyong; Miao Jianwei; Liu Yanwei; Salmassi, Farhad
2007-08-31
We present the first experimental demonstration of lensless diffractive imaging using coherent soft x rays generated by a tabletop soft-x-ray source. A 29 nm high harmonic beam illuminates an object, and the subsequent diffraction is collected on an x-ray CCD camera. High dynamic range diffraction patterns are obtained by taking multiple exposures while blocking small-angle diffraction using beam blocks of varying size. These patterns reconstruct to images with 214 nm resolution. This work demonstrates a practical tabletop lensless microscope that promises to find applications in materials science, nanoscience, and biology.
Calero, Venancio; García-Martínez, Pascuala; Albero, Jorge; Sánchez-López, María M; Moreno, Ignacio
2013-11-15
Unusually large phase modulation in a commercial liquid crystal spatial light modulator (LCSLM) is reported. Such a situation is obtained by illuminating with visible light a device designed to operate in the infrared range. The phase modulation range reaches 6π radians in the red region of the visible spectrum and 10π radians in the blue region. Excellent diffraction efficiency in high harmonic orders is demonstrated despite a concomitant and non-negligible Fabry-Perot interference effect. This type of SLM opens the possibility to implement diffractive elements with reduced chromatic dispersion or chromatic control. PMID:24322100
Ellipticity dependence of high harmonic yield in intense laser field: case of s-valence electron
NASA Astrophysics Data System (ADS)
Sarantseva, T. S.; Silaev, A. A.; Vvedenskii, N. V.; Frolov, M. V.; Manakov, N. L.
2016-04-01
Having solved numerically the time-dependent Schrödinger equation, we have analysed the dependence of the high harmonic generation yield on the ellipticity of an intense laser field. For the case of a zero angular momentum of an initial state, it has been shown that the ellipticity dependence of the HHG yield is affected by the harmonic number. The numerical results are interpreted in the framework of our recently developed quasi-classical analytical model for HHG. In the quasi-classical approximation, the difference in the ellipticity dependence of the HHG yield for different harmonics is shown to be caused by the interference effects of quantum orbits.
High Harmonic Spectroscopy of Multichannel Dynamics in Strong-Field Ionization
Mairesse, Y.; Higuet, J.; Fabre, B.; Mevel, E.; Constant, E.; Dudovich, N.; Shafir, D.; Patchkovskii, S.; Walters, Z.; Smirnova, O.; Ivanov, M. Yu.
2010-05-28
We perform high harmonic generation spectroscopy of aligned nitrogen molecules to characterize the attosecond dynamics of multielectron rearrangement during strong-field ionization. We use the spectrum and ellipticity of the harmonic light to reconstruct the relative phase between different ionization continua participating in the ionization, and thus determine the shape and location of the hole left in the molecule by strong-field ionization. Our interferometric technique uses transitions between the ionic states, induced by the laser field on the subcycle time scale.
Time and Space Resolved High Harmonic Imaging of Electron Tunnelling from Molecules
NASA Astrophysics Data System (ADS)
Smirnova, O.
2009-05-01
High harmonic generation in intense laser fields carries the promise of combining sub-Angstrom spatial and attosecond temporal resolution of electronic structures and dynamics in molecules, see e.g. [1-3]. High harmonic emission occurs when an electron detached from a molecule by an intense laser field recombines with the parent ion [4]. Similar to Young's double-slit experiment, recombination to several ``lobes'' of the same molecular orbital can produce interference minima and maxima in harmonic intensities [1]. These minima (maxima) carry structural information -- they occur when the de-Broglie wavelength of the recombining electron matches distances between the centers. We demonstrate both theoretically and experimentally that amplitude minima (maxima) in the harmonic spectra can also have dynamical origin, reflecting multi-electron dynamics in the molecule. We use high harmonic spectra to record this dynamics and reconstruct the position of the hole left in the molecule after ionization. Experimental data are consistent with the hole starting in different places as the ionization dynamics changes from tunnelling to the multi-photon regime. Importantly, hole localization and subsequent attosecond dynamics are induced even in the tunnelling limit. Thus, even ``static'' tunnelling induced by a tip of a tunnelling microscope will generate similar attosecond dynamics in a sample. We anticipate that our approach will become standard in disentangling spatial and temporal information from high harmonic spectra of molecules.[4pt] In collaboration with Serguei Patchkovskii, National Research Council, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada; Yann Mairesse, NRC Canada and CELIA, Universit'e Bordeaux I, UMR 5107 (CNRS, Bordeaux 1, CEA), 351 Cours de la Lib'eration, 33405 Talence Cedex, France; Nirit Dudovich, NRC Canada and Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100, Israel; David Villeneuve, Paul Corkum, NRC Canada
NASA Astrophysics Data System (ADS)
Aknoun, Sherazade; Bon, Pierre; Savatier, Julien; Monneret, Serge; Wattellier, Benoit F.
2016-03-01
We describe the use of polarized spatially coherent illumination to perform linear retardance imaging and measurements of semi-transparent biological samples using a quantitative phase imaging technique [1]. Quantitative phase imaging techniques [2-5] are used in microscopy for the imaging of semi-transparent samples and gives information about the optical path difference (OPD). The strength of those techniques is their non-invasive (the sample is not labelled) and fast approach. However, this high contrast is non-specific and cannot be linked to specific properties of the sample. To overcome this limitation, we propose to use polarized light in combination with QPI. Indeed, anisotropy has been used to reveal ordered fibrous structures in biological samples without any staining or labelling with polarized light microscopy [6-8]. Recent studies have shown polarimetry as a potential diagnostic tool for various dermatological diseases on thick tissue samples [9]. Particularly, specific collagen fibers spatial distribution has been demonstrated to be a signature for the optical diagnosis and prognosis of cancer in tissues [10]. In this paper, we describe a technical improvement of our technique based on high-resolution quadri-wave lateral shearing interferometry (QWLSI) and liquid crystal retarder to perform quantitative linear birefringence measurements on biological samples. The system combines a set of quantitative phase images with different excitation polarizations to create birefringence images. These give information about the local retardance and orientation of biological anisotropic components. We propose using a commercial QWLSI [11] (SID4Bio, Phasics SA, Saint Aubin, France) directly plugged onto a lateral video port of an inverted microscope (TE2000-U, Nikon, Japan). We are able to take retardance images in less than 1 second which allows us to record dynamic phenomena (living cells study) and make high speed acquisitions to reconstruct tissues virtual
4 MW upgrade to the DIII-D fast wave current drive system
deGrassie, J.S.; Pinsker, R.I.; Cary, W.P.
1993-10-01
The DIII-D fast wave current drive (FWCD) system is being upgraded by an additional 4 MW in the 30 to 120 MHz frequency range. This capability adds to the existing 2 MW 30 to 60 MHz system. Two new ABB transmitters of the type that are in use on the ASDEX-Upgrade tokamak in Garching will be used to drive two new water-cooled four-strap antennas to be installed in DIII-D in early 1994. The transmission and tuning system for each antenna will be similar to that now in use for the first 2 MW system on DIII-D, but with some significant improvements. One improvement consists of adding a decoupler element to counter the mutual coupling between the antenna straps which results in large imbalances in the power to a strap for the usual current drive intrastrap phasing of 90{degrees}. Another improvement is to utilize pressurized, ceramic-insulated transmission lines. The intrastrap phasing will again be controlled in pairs, with a pair of straps coupled in a resonant loop configuration, locking their phase difference at either 0 or 180{degrees}, depending upon the length of line installed. These resonant loops will incorporate a phase shifter so that they will be able to be tuned to resonance at several frequencies in the operating band of the transmitter. With the frequency change capability of the ABB generators, the FWCD frequency will thus be selectable on a shot-to-shot basis, from this preselected set of frequencies. The schedule is for experiments to begin with this added 4 MW capability in mid-1994. The details of the system are described.
Mishra, K.; Kulkarni, S.; Rathi, D.; Varia, A.; Jadav, H.; Parmar, K.; Kadia, B.; Joshi, R.; Srinivas, Y.; Singh, R.; Kumar, S.; Dani, S.; Gayatri, A.; Yogi, R.; Singh, M.; Joisa, Y.; Rao, C.; Kumar, S.; Jha, R.; Manchanda, R.
2011-12-23
Fast wave electron heating experiments are carried out on Aditya tokamak [R = 0.75 m, a = 0.25m,Bt = 0.75T,ne{approx}1-3E13/cc,Te{approx}250eV] with the help of indigenously developed 200 kW, 20-40 MHz RF heating system. Significant direct electron heating is observed by fast waves in hydrogen plasma with prompt rise in electron temperature with application of RF power and it increases linearly with RF power. A corresponding increase in plasma beta and hence increase in stored diamagnetic energy is also observed in presence of RF. We observe an improvement of energy confinement time from 2-4msec during ohmic heating phase to 3-6msec in RF heating phase. This improvement is within the ohmic confinement regime for the present experiments. The impurity radiation and electron density do not escalate significantly with RF power. The direct electron heating by fast wave in Aditya is also predicted by ion cyclotron resonance heating code TORIC.
Slow Wave Excitation in the ICRF and HHFW Regimes
Phillips, C. K.; Valeo, E. J.; Hosea, J. C.; LeBlanc, B. P.; Wilson, J. R.; Jaeger, E. F.; Berry, L. A.; Ryan, P. M.; Bonoli, P. T.; Wright, J. C.; Smithe, D. N.
2011-12-23
Theoretical considerations and high spatial resolution numerical simulations of radio frequency (rf) wave heating in tokamaks and in spherical toruses (ST) indicate that fast waves launched into tokamaks in the ion cyclotron range of frequencies (ICRF) or into spherical toruses in the high harmonic fast wave (HHFW) regime may excite a short wavelength slow mode inside of the plasma discharge due to the presence of hot electrons that satisfy the condition {omega}
Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism
Fan, Tingting; Grychtol, Patrik; Knut, Ronny; Hernández-García, Carlos; Hickstein, Daniel D.; Zusin, Dmitriy; Gentry, Christian; Dollar, Franklin J.; Mancuso, Christopher A.; Hogle, Craig W.; Kfir, Ofer; Legut, Dominik; Carva, Karel; Ellis, Jennifer L.; Dorney, Kevin M.; Chen, Cong; Shpyrko, Oleg G.; Fullerton, Eric E.; Cohen, Oren; Oppeneer, Peter M.; Milošević, Dejan B.; Becker, Andreas; Jaroń-Becker, Agnieszka A.; Popmintchev, Tenio; Murnane, Margaret M.; Kapteyn, Henry C.
2015-01-01
We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform. PMID:26534992
Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism.
Fan, Tingting; Grychtol, Patrik; Knut, Ronny; Hernández-García, Carlos; Hickstein, Daniel D; Zusin, Dmitriy; Gentry, Christian; Dollar, Franklin J; Mancuso, Christopher A; Hogle, Craig W; Kfir, Ofer; Legut, Dominik; Carva, Karel; Ellis, Jennifer L; Dorney, Kevin M; Chen, Cong; Shpyrko, Oleg G; Fullerton, Eric E; Cohen, Oren; Oppeneer, Peter M; Milošević, Dejan B; Becker, Andreas; Jaroń-Becker, Agnieszka A; Popmintchev, Tenio; Murnane, Margaret M; Kapteyn, Henry C
2015-11-17
We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform. PMID:26534992
Generation of bright phase-matched circularly-polarized extreme ultraviolet high harmonics
NASA Astrophysics Data System (ADS)
Kfir, Ofer; Grychtol, Patrik; Turgut, Emrah; Knut, Ronny; Zusin, Dmitriy; Popmintchev, Dimitar; Popmintchev, Tenio; Nembach, Hans; Shaw, Justin M.; Fleischer, Avner; Kapteyn, Henry; Murnane, Margaret; Cohen, Oren
2015-02-01
Circularly-polarized extreme ultraviolet and X-ray radiation is useful for analysing the structural, electronic and magnetic properties of materials. To date, such radiation has only been available at large-scale X-ray facilities such as synchrotrons. Here, we demonstrate the first bright, phase-matched, extreme ultraviolet circularly-polarized high harmonics source. The harmonics are emitted when bi-chromatic counter-rotating circularly-polarized laser pulses field-ionize a gas in a hollow-core waveguide. We use this new light source for magnetic circular dichroism measurements at the M-shell absorption edges of Co. We show that phase-matching of circularly-polarized harmonics is unique and robust, producing a photon flux comparable to linearly polarized high harmonic sources. This work represents a critical advance towards the development of table-top systems for element-specific imaging and spectroscopy of multiple elements simultaneously in magnetic and other chiral media with very high spatial and temporal resolution.
Parametric Excitations of Fast Plasma Waves by Counter-propagating Laser Beams
G. Shvets; N.J. Fisch
2001-03-19
Short- and long-wavelength plasma waves can become strongly coupled in the presence of two counter-propagating laser pump pulses detuned by twice the cold plasma frequency. What makes this four-wave interaction important is that the growth rate of the plasma waves occurs much faster than in the more obvious co-propagating geometry.
Current-drive on the Versator-2 tokamak with a slotted-waveguide fast-wave coupler
NASA Astrophysics Data System (ADS)
Colborn, J. A.
1987-11-01
A slotted-waveguide fast-wave coupler has been constructed, without dielectric, and used to drive current on the Versator-2 tokamak. Up to 35 kW of net microwave power at 2.45 GHz has been radiated into plasmas with 2 x 10 to the 12th/cu cm less than or equal to mean of n(sub e) less than or equal to 1.2 x 10 to the 13th/cu cm and B(sub tor) approx. = 1.0 T. The launched spectrum had a peak near N(sub parallel) = -2.0 and a larger peak near N(sub parallel) = 0.7. Radiating efficiency of the antenna was roughly independent of antenna position except when the antenna was at least 0.2 cm outside the limiter, in which case the radiating efficiency slightly improved as the antenna was moved farther outside. When the coupler was inside the limiter, radiating efficiency improved moderately with increased mean of n(sub e). Current-drive efficiency was comparable to that of the slow wave and was not affected when the antenna spectrum was reversed; however, no current was driven for mean of n(sub e) less than or equal to 2 x 10 to the 12th/cu cm. These results indicate the fast wave was launched, but a substantial part of the power may have been mode-converted to the slow wave, possible via a downshift in N(sub parallel), and these slow waves may have been responsible for most of the driven current. Relevant theory for waves in plasma, current-drive efficiency, and coupling of the slotted-waveguide is discussed, the antenna design method is explained, and future work, including the construction of a much-improved probe-fed antenna, is described.
Kinetic effects in the conversion of fast waves in pre-heated, low aspect ratio tokamak plasmas
NASA Astrophysics Data System (ADS)
Kommoshvili, K.; Cuperman, S.; Bruma, C.
2003-03-01
Kinetic effects in the conversion of fast waves to Alfvèn waves and their subsequent deposition in low aspect ratio (spherical) tokamaks (LARTs) have been investigated theoretically. More specifically, we have considered the consequences of incorporation of kinetic effects in the electron parallel (to the ambient magnetic field) dynamics derived by following the drift-tearing mode analysis of Chen et al (Chen L, Rutherford P H and Tang W M 1977 Phys. Rev. Lett. 39 460), and particle-conserving Krook collision operator for the passing electrons involved (Mett R R and Mahajan S M 1992 Phys. Fluids B 4 2885). The perpendicular plasma dynamics is described by a quite general resistive two-fluid (2F) model based dielectric tensor-operator (Cuperman S, Bruma C and Komoshvili K 2002 Solution of the resistive 2F wave equations for Alfvènic modes in spherical tokamak plasmas J. Plasma Phys. accepted for publication). The full-wave electromagnetic equations, formulated in terms of the vector and scalar potentials, have been solved by the aid of an advanced finite elements numerical code (Sewell G 1993 Adv. Eng. Software 17 105). Detailed solutions of the full-wave equations are obtained and compared with those corresponding to a pure resistive 2F model, this, for the illustrative pre-heated START-type device (Sykes 1994). Our results quantitatively confirm the general theory of the conversion of fast waves with subsequent power dissipation for the conditions of spherical tokamaks thus providing the required auxilliary energy source for the succesful operation of LARTs. Moreover, these results indicate the absolute necessity of using a full model for the parallel electron dynamics, i.e. including both kinetic and collisional effects.
NASA Astrophysics Data System (ADS)
Love, H.; LeGood, M.; Stuart, G.; Reyners, M.; Eberhart-Phillips, D. E.; Gubbins, D.
2015-08-01
Seismic tomography has revealed very high P-wave velocities, over 8.5 km s-1, at shallow depths, 30-100 km, beneath New Zealand. Here we study fast, high-frequency arrivals at North and South Island stations that contain additional information about the crust and mantle structure. These arrivals, which are from earthquakes within or close to the land mass, have a characteristic high-frequency precursor followed by a lower frequency, larger amplitude, main phase. Precursors were seen on at least one station from 262 of 306 candidate events; the best-recorded 76 events were analysed for wave speed, frequency content and polarization. Time-distance plots are consistent with two phases travelling at 8.38 ± 0.03 and 6.93 ± 0.05 km s-1. The precursor has typical frequencies 4-9 Hz, the second arrival 2-4 Hz. Polarizations are off-azimuth by 30° and steeper than predicted by ray tracing through a smooth 3-D tomographic model. These results are explained by propagation through a dipping layer of order 10 km thick with seismic velocity around 8.5 km s-1; it is too thin to propagate frequencies below 4 Hz and waves refract from it at a steep, out-of-plane angle, explaining the anomalous polarization. Ray paths cover a region coinciding with the subducted Hikurangi Plateau; the fast layer is interpreted as the lowest section of the plateau that has transformed to eclogite, which has the same fast seismic velocity that we observe. Unlike the fast, eclogitic layers identified in subduction zones such as the Kermadecs, this layer is shallower, at 30 km, than the eclogite transformation; we therefore propose that it formed at the base of the thick plateau prior to subduction.
On the Estimation of T-Wave Alternans Using the Spectral Fast Fourier Transform Method
Armoundas, Antonis A; Mela, Theofanie; Merchant, Faisal M
2012-01-01
BACKGROUND T-wave alternans (TWA), has been associated with increased vulnerability to ventricular tachyarrhythmias and sudden cardiac death (SCD). However, both random (white) noise and (patho)physiologic processes (i.e. premature ventricular contractions [PVCs], heart and respiration rates) may hamper TWA estimation and therefore, lessen its clinical utility for risk stratification. OBJECTIVE To investigate the effect of random noise and certain (patho)physiologic processes on the estimation of TWA using the Fast Fourier Transform (FFT) method and to develop methods to overcome these potential sources of error. METHODS We used a combination of human electrocardiogram data and computer simulations to assess the effects of a PVC, random and colored noise on the accuracy of TWA estimation. RESULTS We quantitatively demonstrate that replacing a “bad” beat with an odd/even median beat is a more accurate approach than replacing it with the overall average or the overall median beat. We also show that phase resetting may have a significant effect on alternans estimation and that estimation of alternans using frequencies greater than 0.4922 cycles/beat in a 128-point FFT provides the most accurate approach for estimating the alternans when phase resetting is likely to occur. Additionally, our data demonstrate that the number of indeterminate TWA tests due to high levels of noise can be reduced when the alternans voltage exceeds a new higher threshold. Also, the amplitude of random noise has a significant effect on alternans estimation and should be considered to adjust the alternans voltage threshold for noise levels greater than 1.8 μV. Finally, we quantitatively demonstrate that colored noise may lead to a false positive or a false negative result. We propose methods to estimate the effect of these (patho)physiologic processes on the alternans estimation in order to determine whether a TWA test is likely to be a true positive or a true negative. CONCLUSION This
Kohno, H.; Myra, J. R.; D'Ippolito, D. A.
2015-07-15
Interactions between propagating fast waves and radio-frequency (RF) sheaths in the ion cyclotron range of frequencies are numerically investigated based on a cold fluid plasma model coupled with a sheath boundary condition. In this two-dimensional study, the capability of the finite element code rfSOL, which was developed in previous numerical work, is extended to analyze self-consistent RF sheath-plasma interaction problems in a tokamak with a non-circular cross-section. It is found that a large sheath voltage is generated near the edges of the limiter-shaped deformation as a result of the conversion from fast to slow waves on the sheaths. The sheath voltage associated with this conversion is particularly significant in the localized region where the contact angle between the magnetic field line and the conducting wall varies rapidly along the curved sheath surface, which is consistent with the results in previous one-dimensional theoretical work. The dependences of the RF sheaths on various parameters in plasma such as the toroidal wavenumber, edge plasma density, and the degree of the RF wave absorption in the core region are also examined in detail.
NASA Astrophysics Data System (ADS)
Liu, W.; Ofman, L.; Downs, C.; Cheung, C. M. M.; Broder, B.; De Pontieu, B.
2015-12-01
Quasi-periodic Fast Propagating wave trains (QFPs) are a new observational phenomenon discovered in extreme ultraviolet (EUV) by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). They are fast-mode magnetosonic waves, closely related to quasi-periodic pulsations in solar flare emission ranging from radio to X-ray wavelengths. The significance of QFPs lies in their diagnostic potential, because they can provide critical clues to flare energy release and serve as new tools for coronal seismology. In this presentation, we report recent advances in observing and modeling QFPs. For example, using differential emission measure (DEM) inversion, we found clear evidence of heating and cooling cycles that are consistent with alternating compression and rarefaction expected for magnetosonic wave pulses. Moreover, recent IRIS observations of QFP source regions revealed sawtooth-like flare ribbon motions, indicative of pulsed magnetic reconnection, that are correlated with QFP excitation. More interestingly, from a survey of over 100 QFP events, we found a preferential association with eruptive flares rather than confined flares. We will discuss the implications of these results and the potential roles of QFPs in coronal heating, energy transport, and solar eruptions.
NASA Astrophysics Data System (ADS)
Ren, Xiaoming; Makhija, Varun; Le, Anh-Thu; Troß, Jan; Mondal, Sudipta; Jin, Cheng; Kumarappan, Vinod; Trallero-Herrero, Carlos
2013-10-01
We exploit the relationship between high harmonic generation (HHG) and the molecular photorecombination dipole to extract the molecular-frame differential photoionization cross section (PICS) in the extreme ultraviolet (XUV) for molecular nitrogen. A shape resonance and a Cooper-type minimum are reflected in the pump-probe time delay measurements of different harmonic orders, where high-order rotational revivals are observed in N2. We observe the energy- and angle-dependent Cooper minimum and shape resonance directly in the laboratory-frame HHG yield by achieving a high degree of alignment,
Reconstruction of correlation-driven electron-hole dynamics by high-harmonic-generation spectroscopy
NASA Astrophysics Data System (ADS)
Leeuwenburgh, Jonathan; Cooper, Bridgette; Averbukh, Vitali; Marangos, Jonathan P.; Ivanov, Misha
2014-09-01
We present detailed analysis of the recently proposed technique of high-order-harmonic generation spectroscopy of correlation-driven electron hole dynamics in atoms and molecules. This novel technique resolves Auger-type processes with attosecond-scale resolution by clocking the decay process with high-harmonic generation. The harmonic generation is driven by an attosecond, XUV pump pulse and a long-duration, infrared pulse. We present the strong-field-approximation-based theory of such an XUV-initiated high-order-harmonic generation process. We detail different ways of recovering the hole survival probability by altering experimental parameters to change the time-energy mapping of the harmonics. The various reconstruction methods are then simulated for M4,5NN Auger decay in krypton and molecular-orbital breakdown dynamics in trans-butadiene and propanal.
Development of high harmonic generation spectroscopy of organic molecules and biomolecules
NASA Astrophysics Data System (ADS)
Marangos, J. P.
2016-07-01
In this review we will discuss the topic of high order harmonic generation (HHG) from samples of organic and bio-molecules. The possibility to extract useful dynamical and structural information from the measurement of the HHG emission, a technique termed high harmonic generation spectroscopy (HHGS), will be the special focus of our discussions. We will begin by introducing the salient facts of HHG from atoms and simple molecules and explaining the principles behind HHGS. Next the technical difficulties associated with HHG from samples of organic molecules and biomolecules, principally the low sample density and the low ionization potential, will be examined. Then we will present some recent experiments where HHG spectra from samples of these molecules have been measured and discuss what has been learned from these measurements. Finally we will look at the future prospects for HHG spectroscopy of organic molecules, discussing some of the technical and in principle limits of the technique and methods that may ameliorate these limits.
Ganeev, R. A.; Abdelrahman, Z. Frank, F.; Witting, T.; Okell, W. A.; Fabris, D.; Hutchison, C.; Marangos, J. P.; Tisch, J. W. G.
2014-01-13
We present measurements of the spatial coherence of the high-order harmonics generated in laser-produced ablation plumes. Harmonics were generated using 4 fs, 775 nm pulses with peak intensity 3 × 10{sup 14} W cm{sup −2}. Double-slit fringe visibilities in the range of ≈0.6–0.75 were measured for non-resonant harmonics in carbon and resonantly enhanced harmonics in zinc and indium. These are somewhat higher than the visibility obtained for harmonics generated in argon gas under similar conditions. This is attributed to lower time-dependent ionization of the plasma ablation targets compared to argon during the high harmonics generation process.
Nonlinear Resonant Excitation of Fast Sausage Waves in Current-Carrying Coronal Loops
NASA Astrophysics Data System (ADS)
Mikhalyaev, B. B.; Bembitov, D. B.
2014-11-01
We consider a model of a coronal loop that is a cylindrical magnetic tube with two surface electric currents. Its principal sausage mode has no cut-off in the long-wavelength limit. For typical coronal conditions, the period of the mode is between one and a few minutes. The sausage mode of flaring loops could cause long-period pulsations observed in microwave and hard X-ray ranges. There are other examples of coronal oscillations: long-period pulsations of active-region quiet loops in the soft X-ray emission are observed. We assume that these can also be caused by sausage waves. The question arises of how the sausage waves are generated in quiet loops. We assume that they can be generated by torsional oscillations. This process can be described in the framework of the nonlinear three-wave interaction formalism. The periods of interacting torsional waves are similar to the periods of torsional oscillations observed in the solar atmosphere. The timescale of the sausage-wave excitation is not much longer than the periods of interacting waves, so that the sausage wave is excited before torsional waves are damped.
Wave Driven Fast Ion Loss in the National Spherical Torus Experiment
E.D. Fredrickson; C.Z. Cheng; D. Darrow; G. Fu; N.N. Gorelenkov; G. Kramer; S.S. Medley; J. Menard; L. Roquemore; D. Stutman; R.B. White
2003-08-05
The study of fast ion instabilities in conventional aspect ratio tokamaks is motivated in large part by their potential to negatively impact the ignition threshold in fusion reactors by causing fast ion losses. Spherical tokamak's (ST), with intrinsically low magnetic fields, are particularly susceptible to fast ion driven instabilities. The 3.5 MeV alpha's from the D-T [deuterium-tritium] fusion reaction in proposed ST reactors will have velocities much higher than the Alfven speed. The Larmor radius of the fusion alphas, normalized to the plasma size, will also be larger than for conventional aspect ratio tokamak reactors. The resulting longer wavelengths of the *AE instabilities will be more effective in driving fast ion loss. The change in magnetic topology also influences the mode structure, as in the case of the Compressional Alfven Eigenmodes (CAE) seen on NSTX.
Fast and Slow Mode Solitary Waves in a Five Component Plasma
NASA Astrophysics Data System (ADS)
Sebastian, Sijo; Michael, Manesh; Varghese, Anu; Sreekala, G.; Venugopal, Chandu
2016-07-01
We have investigated fast and slow mode solitary profiles in a five component plasma consisting of positively and negatively charged pair ions, hydrogen ions and hotter and colder electrons. Of these, the heavier ions and colder photo-electrons are of cometary origin while the other components are of solar origin; the electrons being described by kappa distributions. The Zakharov-Kuznetzov (ZK) equation is derived and solutions for fast and slow mode solitary structures are plotted for parameters relevant to that of comet Halley. From the figures, it is seen that the presence of hydrogen ion determines the polarity of fast and slow mode solitary structures. Also different pair ions like He, C and O have significant effect on the width of the fast and slow mode solitary structures.
Goh, S J; Reinink, J; Tao, Y; van der Slot, P J M; Bastiaens, H J M; Herek, J L; Biedron, S G; Milton, S V; Boller, K-J
2016-01-25
We experimentally investigate spectral control of high-harmonic generation in a wide-diameter (508 μm) capillary that allows using significantly lower gas pressures coupled with elevated drive laser energies to achieve higher harmonic energies. Using phase shaping to change the linear chirp of the drive laser pulses, we observe wavelength tuning of the high-harmonic output to both larger and smaller values. Comparing tuning via the gas pressure with the amount of blue shift in the transmitted drive laser spectrum, we conclude that both adiabatic and non-adiabatic effects cause pulse-shaping induced tuning of high harmonics. We obtain a fractional wavelength tuning, Δλ/λ, in the range from -0.007 to + 0.01, which is comparable to what is achieved with standard capillaries of smaller diameter and higher pressures. PMID:26832538
Emelin, M Yu; Ryabikin, M Yu
2013-03-31
The influence of the magnetic field of a laser pulse and the depletion of bound levels of working-medium atoms on the generation of high harmonics of mid-IR laser radiation in gases is investigated using numerical quantum-mechanical calculations. The maximum attainable spectral widths of high harmonics are estimated for model atoms with different ionisation potentials taking into account the aforementioned limiting effects. It is shown (within a two-dimensional model) that high harmonics with wavelengths to several angstroms can be generated by irradiating helium atoms with high-power femtosecond pulses of a laser [5] with a centre wavelength of 3.9 {mu}m. The possibility of observing experimentally relativistic effects using modern desktop mid-IR laser sources is demonstrated. (extreme light fields and their applications)
Bierbach, Jana; Yeung, Mark; Eckner, Erich; Roedel, Christian; Kuschel, Stephan; Zepf, Matt; Paulus, Gerhard G.
2015-05-01
Surface high-harmonic generation in the relativistic regime is demonstrated as a source of extreme ultra-violet (XUV) pulses with extended operation time. Relativistic high-harmonic generation is driven by a frequency-doubled high-power Ti:Sapphire laser focused to a peak intensity of 3·1019 W/cm2 onto spooling tapes. We demonstrate continuous operation over up to one hour runtime at a repetition rate of 1 Hz. Harmonic spectra ranging from 20 eV to 70 eV (62 nm to 18 nm) were consecutively recorded by an XUV spectrometer. An average XUV pulse energy in the µJ range is measured. With the presented setup, relativistic surface high-harmonic generation becomes a powerful source of coherent XUV pulses that might enable applications in, e.g. attosecond laser physics and the seeding of free-electron lasers, when the laser issues causing 80-% pulse energy fluctuations are overcome.
Xuan, Weipeng; He, Mei; Meng, Nan; He, Xingli; Wang, Wenbo; Chen, Jinkai; Shi, Tianjin; Hasan, Tawfique; Xu, Zhen; Xu, Yang; Luo, J. K.
2014-01-01
We report ZnO/glass surface acoustic wave (SAW) humidity sensors with high sensitivity and fast response using graphene oxide sensing layer. The frequency shift of the sensors is exponentially correlated to the humidity change, induced mainly by mass loading effect rather than the complex impedance change of the sensing layer. The SAW sensors show high sensitivity at a broad humidity range from 0.5%RH to 85%RH with < 1 sec rise time. The simple design and excellent stability of our GO-based SAW humidity sensors, complemented with full humidity range measurement, highlights their potential in a wide range of applications. PMID:25425458
NASA Astrophysics Data System (ADS)
Shprits, Yuri Y.; Runov, Andrei; Ni, Binbin
2013-02-01
In the current study, we perform statistical analysis of the magnetosonic (MS) waves (also often referred to as extremely low frequency (ELF) equatorial noise) in the range between the ion cyclotron frequency and the lower hybrid resonance frequency within 10° of the magnetic equator. Observations were made between 2 and 9 RE using THEMIS Filter Bank (FBK) data. ELF waves with spectral power exceeding 10-6 nT2/Hz are registered in ~3% of all samples in the inner magnetosphere. The survey has shown that, during the solar minimum, the average amplitude of equatorial ELF waves is less than 0.025 nT. Interpreting ELF events as MS waves, we have evaluated the corresponding wave-induced resonant scattering coefficients of radiation belt energetic electrons. We also study the effect of heavy ions on the scattering rates. The analysis reveals that the scattering by magnetosonic waves for various plasma compositions during geomagnetically quiet times is by up to two orders of magnitude slower than was previously reported and cannot significantly contribute to the long-term dynamics of the radiation belts. Computed electron scattering rates by magnetosonic waves extends to higher αeq when the fraction of H+ in the plasma decreases, while the range of pitch angles for which resonance occurs remains relatively insensitive to the plasma composition. While inclusion of multi-ion species into the wave dispersion relation produces noticeable changes in bounce-averaged scattering rates, the average rates are still significantly below typical scattering rates of chorus or hiss waves.
NASA Astrophysics Data System (ADS)
Abdu, Mangalathayil A.; Brum, Christiano GM; Batista, Paulo P.; Gurubaran, Subramanian; Pancheva, Dora; Bageston, Jose V.; Batista, Inez S.; Takahashi, Hisao
2015-01-01
In this paper, we investigate the role of eastward and upward propagating fast (FK) and ultrafast Kelvin (UFK) waves in the day-to-day variability of equatorial evening prereversal vertical drift and post sunset generation of spread F/plasma bubble irregularities. Meteor wind data from Cariri and Cachoeira Paulista (Brazil) and medium frequency (MF) radar wind data from Tirunelveli (India) are analyzed together with Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) temperature in the 40- to 100-km region to characterize the zonal and vertical propagations of these waves. Also analyzed are the F region evening vertical drift and spread F (ESF) development features as diagnosed by Digisonde (Lowell Digisonde International, LLC, Lowell, MA, USA) operated at Fortaleza and Sao Luis in Brazil. The SABER temperature data permitted determination of the upward propagation characteristics of the FK (E1) waves with propagation speed in the range of 4 km/day. The radar mesosphere and lower thermosphere (MLT) winds in the widely separated longitude sectors have yielded the eastward phase velocity of both the FK and UFK waves. The vertical propagation of these waves cause strong oscillation in the F region evening prereversal vertical drift, observed for the first time at both FK and UFK periodicities. A delay of a few (approximately 10) days is observed in the F region vertical drift perturbation with respect to the corresponding FK/UFK zonal wind oscillations, or temperature oscillations in the MLT region, which has permitted a direct identification of the sunset electrodynamic coupling process as being responsible for the generation of the FK/UFK-induced vertical drift oscillation. The vertical drift oscillations are found to cause significant modulation in the spread F/plasma bubble irregularity development. The overall results highlight the role of FK/UFK waves in the day
NASA Astrophysics Data System (ADS)
Degeling, A. W.; Rankin, R.; Zong, Q.-G.
2014-11-01
We investigate the magnetospheric MHD and energetic electron response to a Storm Sudden Commencement (SSC) and subsequent magnetopause buffeting, focusing on an interval following an SSC event on 25 November 2001. We find that the electron flux signatures observed by LANL, Cluster, and GOES spacecraft during this event can largely be reproduced using an advective kinetic model for electron phase space density, using externally prescribed electromagnetic field inputs, (herein described as a "test-kinetic model") with electromagnetic field inputs provided by a 2-D linear ideal MHD model for ULF waves. In particular, we find modulations in electron flux phase shifted by 90° from the local azimuthal ULF wave electric field (Eφ) and a net enhancement in electron flux after 1.5 h for energies between 500 keV and 1.5 MeV near geosynchronous orbit. We also demonstrate that electrons in this energy range satisfy the drift resonance condition for the ULF waves produced by the MHD model. This confirms the conclusions reached by Tan et al. (2011), that the energization process in this case is dominated by drift-resonant interactions between electrons and MHD fast mode waves, produced by fluctuations in solar wind dynamic pressure.
NASA Astrophysics Data System (ADS)
Ham, Suyun; Popovics, John S.
2015-03-01
Ultrasonic techniques provide an effective non-destructive evaluation (NDE) method to monitor concrete structures, but the need to perform rapid and accurate structural assessment requires evaluation of hundreds, or even thousands, of measurement datasets. Use of a fully contactless ultrasonic system can save time and labor through rapid implementation, and can enable automated and controlled data acquisition, for example through robotic scanning. Here we present results using a fully contactless ultrasonic system. This paper describes our efforts to develop a contactless ultrasonic guided wave NDE approach to detect and characterize delamination defects in concrete structures. The developed contactless sensors, controlled scanning system, and employed Multi-channel Analysis of Surface Waves (MASW) signal processing scheme are reviewed. Then a guided wave interpretation approach for MASW data is described. The presence of delamination is interpreted by guided plate wave (Lamb wave) behavior, where a shift in excited Lamb mode phase velocity, is monitored. Numerically simulated and experimental ultrasonic data collected from a concrete sample with simulated delamination defects are presented, where the occurrence of delamination is shown to be associated with a mode shift in Lamb wave energy.
NASA Astrophysics Data System (ADS)
Ren, Hongwu; Dekany, Richard
2004-07-01
Large degree-of-freedom real-time adaptive optics (AO) control requires reconstruction algorithms that are computationally efficient and readily parallelized for hardware implementation. In particular, we find the wave-front reconstruction for the Hudgin and Fried geometry can be cast into a form of the well-known Sylvester equation using the Kronecker product properties of matrices. We derive the filters and inverse filtering formulas for wave-front reconstruction in two-dimensional (2-D) Discrete Cosine Transform (DCT) domain for these two geometries using the Hadamard product concept of matrices and the principle of separable variables. We introduce a recursive filtering (RF) method for the wave-front reconstruction on an annular aperture, in which, an imbedding step is used to convert an annular-aperture wave-front reconstruction into a squareaperture wave-front reconstruction, and then solving the Hudgin geometry problem on the square aperture. We apply the Alternating Direction Implicit (ADI) method to this imbedding step of the RF algorithm, to efficiently solve the annular-aperture wave-front reconstruction problem at cost of order of the number of degrees of freedom, O(n). Moreover, the ADI method is better suited for parallel implementation and we describe a practical real-time implementation for AO systems of order 3,000 actuators.
NASA Astrophysics Data System (ADS)
McLaughlin, J. A.; De Moortel, I.; Hood, A. W.; Brady, C. S.
2009-01-01
Context: This paper extends the models of Craig & McClymont (1991, ApJ, 371, L41) and McLaughlin & Hood (2004, A&A, 420, 1129) to include finite β and nonlinear effects. Aims: We investigate the nature of nonlinear fast magnetoacoustic waves about a 2D magnetic X-point. Methods: We solve the compressible and resistive MHD equations using a Lagrangian remap, shock capturing code (Arber et al. 2001, J. Comp. Phys., 171, 151) and consider an initial condition in {v}×{B} \\cdot {hat{z}} (a natural variable of the system). Results: We observe the formation of both fast and slow oblique magnetic shocks. The nonlinear wave deforms the X-point into a “cusp-like” point which in turn collapses to a current sheet. The system then evolves through a series of horizontal and vertical current sheets, with associated changes in connectivity, i.e. the system exhibits oscillatory reconnection. Our final state is non-potential (but in force balance) due to asymmetric heating from the shocks. Larger amplitudes in our initial condition correspond to larger values of the final current density left in the system. Conclusions: The inclusion of nonlinear terms introduces several new features to the system that were absent from the linear regime. A movie is available in electronic form at http://www.aanda.org
Alfvénic waves with sufficient energy to power the quiet solar corona and fast solar wind.
McIntosh, Scott W; De Pontieu, Bart; Carlsson, Mats; Hansteen, Viggo; Boerner, Paul; Goossens, Marcel
2011-07-28
Energy is required to heat the outer solar atmosphere to millions of degrees (refs 1, 2) and to accelerate the solar wind to hundreds of kilometres per second (refs 2-6). Alfvén waves (travelling oscillations of ions and magnetic field) have been invoked as a possible mechanism to transport magneto-convective energy upwards along the Sun's magnetic field lines into the corona. Previous observations of Alfvénic waves in the corona revealed amplitudes far too small (0.5 km s(-1)) to supply the energy flux (100-200 W m(-2)) required to drive the fast solar wind or balance the radiative losses of the quiet corona. Here we report observations of the transition region (between the chromosphere and the corona) and of the corona that reveal how Alfvénic motions permeate the dynamic and finely structured outer solar atmosphere. The ubiquitous outward-propagating Alfvénic motions observed have amplitudes of the order of 20 km s(-1) and periods of the order of 100-500 s throughout the quiescent atmosphere (compatible with recent investigations), and are energetic enough to accelerate the fast solar wind and heat the quiet corona. PMID:21796206
Co-counter asymmetry in fast wave heating and current drive
Jaeger, E.F.; Carter, M.D.; Berry, L.A.; Batchelor, D.B.; Forest, C.B.; Weitzner, H.
1997-04-01
Full wave ICRF coupling models show differences in plasma response when antenna arrays are phase to drive currents and counter to the plasma current. The source of this difference lies in the natural up- sown asymmetry of the antenna`s radiated power spectrum. This asymmetry is due to Hall terms in the wave equation, and occurs even without a poloidal magnetic field. When a poloidal field is included, the up-down asymmetry acquires a toroidal component. The result is that plasma absorption (i.e. antenna loading) is shifted or skewed toward the co-current drive direction, independent of the direction of the magnetic field. When wave are launched to drive current counter the plasma current , electron heating an current profiles are more peaked on axis, and this peaking becomes more pronounce a lower toroidal magnetic fields.
Noise-like pulses generated at high harmonics in a partially-mode-locked km-long Raman fiber laser
NASA Astrophysics Data System (ADS)
Boucon, A.; Barviau, B.; Fatome, J.; Finot, C.; Sylvestre, T.; Lee, M. W.; Grelu, P.; Millot, G.
2012-02-01
We present a 5-km-long Raman fiber laser that delivers pulses at high harmonics of the fundamental cavity repetition rate, up to 1 GHz. The observed nanosecond pulses that propagate in an anomalous dispersion regime possess a complex noise-like structure with a coherence time of around 1 picosecond.
NASA Astrophysics Data System (ADS)
Verma, Kanika; Baliyan, Sweta; Sajal, Vivek; Kumar, Ravindra; Sharma, Navneet K.
2016-07-01
The parametric decay of large amplitude non-resonant beating mode of counter-propagating lasers (having a frequency difference ≥ 2 ω p ) into a pair of upper hybrid waves is studied in magnetized plasma. One of the excited upper hybrid waves (known as fast wave) having phase velocity close to c , can be utilized for electron acceleration. The coupled mode equations of fast and slow upper hybrid waves are modelled by solving equation of motion and continuity equation simultaneously (using the density perturbation technique) to derive the dispersion relation for two plasmon decay process. The growth rate of the present excitation process using right circularly polarized beating lasers is higher as compared with the growth rates of the excitation processes using ordinary and extraordinary beating lasers. However, the growth rate is not significant in the case of left circularly polarized beating lasers. The growth rate ˜ 0.15 ω p s - 1 is achieved for right circularly polarized beating lasers having v 1 , 2 / c = 0.1 for scattering angle θ s ˜ 160 ° and applied magnetic field ˜ 90 T. The growth rate of fast upper hybrid wave was reduced with the applied axial magnetic field in the present case. The present work is not only significant for the electron acceleration by fast upper hybrid wave but also for diagnostic purpose.
NASA Astrophysics Data System (ADS)
Levko, Dmitry; Raja, Laxminarayan L.
2016-04-01
The influence of field emission of electrons from surfaces on the fast ionization wave (FIW) propagation in high-voltage nanosecond pulse discharge in the atmospheric-pressure nitrogen is studied by a one-dimensional Particle-in-Cell Monte Carlo Collisions model. A strong influence of field emission on the FIW dynamics and plasma parameters is obtained. Namely, the accounting for the field emission makes possible the bridging of the cathode-anode gap by rather dense plasma (˜1013 cm-3) in less than 1 ns. This is explained by the generation of runaway electrons from the field emitted electrons. These electrons are able to cross the entire gap pre-ionizing it and promoting the ionization wave propagation. We have found that the propagation of runaway electrons through the gap cannot be accompanied by the streamer propagation, because the runaway electrons align the plasma density gradients. In addition, we have obtained that the field enhancement factor allows controlling the speed of ionization wave propagation.
Angular and Intensity Dependent Spectral Modulations in High Harmonics from N2
NASA Astrophysics Data System (ADS)
McFarland, Brian; Farrell, Joseph; Bucksbaum, Philip; Guehr, Markus
2009-05-01
The spectral amplitude and phase modulation of high harmonics (HHG) in molecules provides important clues to molecular structure and dynamics in strong laser fields. We have studied these effects in aligned N2. Earlier results of HHG experiments claimed that the spectral amplitude modulation was predominantly due to geometrical interference between the recombining electron and the highest occupied molecular orbital (HOMO) [1]. We report evidence that contradicts this simple view. We observe a phase jump accompanied by a spectral minimum for HHG in aligned N2. The minimum shifts to lower harmonics as the angle between the molecular axis and harmonic generation polarization increases, and shifts to higher harmonics with increasing harmonic generation intensity. The features observed cannot be fully explained by a geometrical model. We discuss alternative explanations involving multi orbital effects [2]. [0pt] [1] Lein et al., Phys. Rev. A, 66, 023805 (2002) [2] B. K. McFarland, J. P. Farrell, P. H. Bucksbaum and M. Gühr, Science 322, 1232 (2008)
Iikubo, Ryo; Fujiwara, Takehisa; Sekikawa, Taro; Harabuchi, Yu; Satoh, Sota; Taketsugu, Tetsuya; Kayanuma, Yosuke
2015-07-01
Using 42 nm high harmonic pulses, the dissociation dynamics of 1,2-butadiene was investigated by time-resolved photoelectron spectroscopy (TRPES), enabling us to observe dynamical changes of multiple molecular orbitals (MOs) with higher temporal resolution than conventional light sources. Because each lower-lying occupied MO has particular spatial electron distribution, the structural dynamics of photochemical reaction can be revealed. On the femtosecond time scale, a short-lived excited state with a lifetime of 37 ± 15 fs and the coherent oscillation of the photoelectron yield stimulated by Hertzberg-Teller coupling were observed. Ab initio molecular dynamics simulations in the electronically excited state find three relaxation pathways from the vertically excited structure in S1 to the ground state, and one of them is the dominant relaxation pathway, observed as the short-lived excited state. On the picosecond time scale, the photoelectron yields related to the C-C bond decreased upon photoexcitation, indicating C-C bond cleavage. PMID:26266720
A Theory of Dynamic Imaging of Coherent Molecular Rotations by High Harmonic Generation
NASA Astrophysics Data System (ADS)
Faisal, F. H. M.; Abdurrouf, A.
A dynamic theory of mapping coherent molecular motions from high harmonic generation signals is presented. Application to mapping of coherent rotational motions of linear molecules is made. Results of concrete calculations for N2, O2 and CO2 are analyzed both in time and frequency domains. A "magic angle" for the polarization geometry is predicted at which the HHG signals for all pump-probe delay times become equal for linear molecules of σg orbital symmetry. In contrast only a "crossing neighborhood" near the magic angle is predicted for molecules with orbitals of π symmetry. They are expected to help in identifying the orbital symmetry in the inverse problem of orbital reconstruction from experimental data. Comparison with available experimental data show remarkable agreement with all the salient properties of dynamic HHG signals of linear diatomic molecules, N2 and O2, and some simple organic molecules. Additional results for the triatomic molecule CO2 are discussed that might help to test the theory further.
Data Acquisition in a High Harmonic Generation Lab and at LCLS
Hirokawa, Takako; /U. Colorado, Boulder /SLAC
2011-06-22
In this paper, we examine data acquisition in a high harmonic generation (HHG) lab and preliminary data analysis with the Cyclohexadiene Collaboration at the Linac Coherent Lightsource (LCLS) at SLAC National Accelerator Laboratory. HHG experiments have a large number of parameters that need to be monitored constantly. In particular, the pressure of the target is critical to HHG yield. However, this pressure can fluctuate wildly and without a tool to monitor it, it is difficult to analyze the correlation between HHG yield and the pressure. I used the Arduino microcontroller board and created a complementary MATLAB graphical user interface (GUI), thereby enhancing the ease with which users can acquire time-stamped parameter data. Using the Arduino, it is much easier to match the pressure to the corresponding HHG yield. Collecting data by using the Arduino and the GUI is flexible, user-friendly, and cost-effective. In the future, we hope to be able to control and monitor parts of the lab with the Arduino alone. While more parameter information is needed in the HHG lab, we needed to reduce the amount of data during the cyclohexadiene collaboration. This was achieved by sorting the data into bins and filtering out unnecessary details. This method was highly effective in that it minimized the amount of data without losing any valuable information. This effective preliminary data analysis technique will continue to be used to decrease the size of the collected data.
Designs and numerical calculations for echo-enabled harmonic generation at very high harmonics
NASA Astrophysics Data System (ADS)
Penn, G.; Reinsch, M.
2011-09-01
The echo-enabled harmonic generation (EEHG) scheme for driving an FEL using two seeded energy modulations at much longer wavelengths than the output wavelength is a promising concept for future seeded FELs. There are many competing requirements in the design of an EEHG beamline which need careful optimization. Furthermore, revised simulation tools and methods are necessary because of both the high harmonic numbers simulated and the complicated nature of the phase space manipulations which are intrinsic to the scheme. This paper explores the constraints on performance and the required tolerances for reaching wavelengths well below 1/100th of that of the seed lasers, and describes some of the methodology for designing such a beamline. Numerical tools, developed both for the GENESIS and GINGER FEL codes, are presented and used here for more accurate study of the scheme beyond a time-averaged model. In particular, the impact of the local structure in peak current and bunching, which is an inherent part of the EEHG scheme, is evaluated.
Ultrafast high harmonics for probing the fastest spin and charge dynamics in magnetic materials
NASA Astrophysics Data System (ADS)
Grychtol, Patrick
2015-03-01
Ultrafast light based on the high-harmonic up-conversion of femtosecond laser pulses have been successfully employed to access resonantly enhanced magnetic contrast at the Mabsorption edges of the 3d ferromagnets Fe, Co and Ni in a table-top setup. Thus, it has been possible to study element-specific dynamics in magnetic materials at femtosecond time scales in a laboratory environment, providing a wealth of opportunities for a greater fundamental understanding of correlated phenomena in solid-state matter. However, these investigations have so far been limited to linear polarized harmonics, since most techniques by which circular soft x-rays can be generated are highly inefficient reducing the photon flux to a level unfit for scientific applications. Besides presenting key findings of our ultrafast studies on charge and spin dynamics, we introduce a simple setup which allows for the efficient generation of circular harmonics bright enough for XMCD experiments. Our work thus represents a critical advance that enables element-specific imaging and spectroscopy of multiple elements simultaneously in magnetic and other chiral media with very high spatial and temporal resolution on the tabletop. In collboration with Ronny Knut, Emrah Turgut, Dmitriy Zusin, Christian Gentry, Henry Kapteyn, Margaret Murnane, JILA, University of Colorado, Boulder; Justin Shaw, Hans Nembach, Tom Silva, Electromagnetics Division, NIST, Boulder, CO; and Ofer Kfir, Avner Fleischer, Oren Cohen, Extreme Nonlinear Optics Group, Solid State Institute, Technion, Israel.
Lamb waves based fast subwavelength imaging using a DORT-MUSIC algorithm
NASA Astrophysics Data System (ADS)
He, Jiaze; Yuan, Fuh-Gwo
2016-02-01
A Lamb wave-based, subwavelength imaging algorithm is developed for damage imaging in large-scale, plate-like structures based on a decomposition of the time-reversal operator (DORT) method combined with the multiple signal classification (MUSIC) algorithm in the space-frequency domain. In this study, a rapid, hybrid non-contact scanning system was proposed to image an aluminum plate using a piezoelectric linear array for actuation and a laser Doppler vibrometer (LDV) line-scan for sensing. The physics of wave propagation, reflection, and scattering that underlies the response matrix in the DORT method is mathematically formulated in the context of guided waves. The singular value decomposition (SVD) and MUSIC-based imaging condition enable quantifying the damage severity by a `reflectivity' parameter and super-resolution imaging. With the flexibility of this scanning system, a considerably large area can be imaged using lower frequency Lamb waves with limited line-scans. The experimental results showed that the hardware system with a signal processing tool such as the DORT-MUSIC (TR-MUSIC) imaging technique can provide rapid, highly accurate imaging results as well as damage quantification with unknown material properties.
Hansen, Shelley C.; Cally, Paul S. E-mail: paul.cally@monash.edu
2012-05-20
Alfven waves may be difficult to excite at the photosphere due to low-ionization fraction and suffer near-total reflection at the transition region (TR). Yet they are ubiquitous in the corona and heliosphere. To overcome these difficulties, we show that they may instead be generated high in the chromosphere by conversion from reflecting fast magnetohydrodynamic waves, and that Alfvenic TR reflection is greatly reduced if the fast reflection point is within a few scale heights of the TR. The influence of mode conversion on the phase of the reflected fast wave is also explored. This phase can potentially be misinterpreted as a travel speed perturbation with implications for the practical seismic probing of active regions.
Fast Acceleration of 2D Wave Propagation Simulations Using Modern Computational Accelerators
Wang, Wei; Xu, Lifan; Cavazos, John; Huang, Howie H.; Kay, Matthew
2014-01-01
Recent developments in modern computational accelerators like Graphics Processing Units (GPUs) and coprocessors provide great opportunities for making scientific applications run faster than ever before. However, efficient parallelization of scientific code using new programming tools like CUDA requires a high level of expertise that is not available to many scientists. This, plus the fact that parallelized code is usually not portable to different architectures, creates major challenges for exploiting the full capabilities of modern computational accelerators. In this work, we sought to overcome these challenges by studying how to achieve both automated parallelization using OpenACC and enhanced portability using OpenCL. We applied our parallelization schemes using GPUs as well as Intel Many Integrated Core (MIC) coprocessor to reduce the run time of wave propagation simulations. We used a well-established 2D cardiac action potential model as a specific case-study. To the best of our knowledge, we are the first to study auto-parallelization of 2D cardiac wave propagation simulations using OpenACC. Our results identify several approaches that provide substantial speedups. The OpenACC-generated GPU code achieved more than speedup above the sequential implementation and required the addition of only a few OpenACC pragmas to the code. An OpenCL implementation provided speedups on GPUs of at least faster than the sequential implementation and faster than a parallelized OpenMP implementation. An implementation of OpenMP on Intel MIC coprocessor provided speedups of with only a few code changes to the sequential implementation. We highlight that OpenACC provides an automatic, efficient, and portable approach to achieve parallelization of 2D cardiac wave simulations on GPUs. Our approach of using OpenACC, OpenCL, and OpenMP to parallelize this particular model on modern computational accelerators should be applicable to other computational models of wave propagation in
Study of Spurious Response near the Fast Shear Wave in SiO2/Al/LiNbO3 Structure
NASA Astrophysics Data System (ADS)
Goto, Rei; Fujiwara, Joji; Nakamura, Hiroyuki; Tsurunari, Tetsuya; Nakanishi, Hidekazu; Hamaoka, Yosuke
2013-07-01
The shear horizontal (SH) mode on the SiO2/Al/LiNbO3 structure is studied because of its sufficient electromechanical coupling factor (K2) and good temperature coefficient of frequency (TCF). The authors proposed a method of suppressing the spurious response of the Rayleigh mode and the transverse mode for narrow duplex gap applications. For the narrow duplex gap application, the SiO2 thickness must be increased to achieve good TCF characteristics. However, another spurious response appears near the fast shear wave with increasing SiO2 thickness. In this paper, we discuss the suppression mechanism of the spurious response near the fast shear wave.
Zheng Ruisheng; Jiang Yunchun; Hong Junchao; Yang Jiayan; Bi Yi; Yang Liheng; Yang Dan
2011-10-01
'Extreme ultraviolet (EUV) waves' are large-scale wavelike transients often associated with coronal mass ejections (CMEs). In this Letter, we present a possible detection of a fast-mode EUV wave associated with a mini-CME observed by the Solar Dynamics Observatory. On 2010 December 1, a small-scale EUV wave erupted near the disk center associated with a mini-CME, which showed all the low corona manifestations of a typical CME. The CME was triggered by the eruption of a mini-filament, with a typical length of about 30''. Although the eruption was tiny, the wave had the appearance of an almost semicircular front and propagated at a uniform velocity of 220-250 km s{sup -1} with very little angular dependence. The CME lateral expansion was asymmetric with an inclination toward north, and the southern footprints of the CME loops hardly shifted. The lateral expansion resulted in deep long-duration dimmings, showing the CME extent. Comparing the onset and the initial speed of the CME, the wave was likely triggered by the rapid expansion of the CME loops. Our analysis confirms that the small-scale EUV wave is a true wave, interpreted as a fast-mode wave.
Grimes, Morad; Bouhadjera, Abdelmalek; Haddad, Sofiane; Benkedidah, Toufik
2012-07-01
In testing cancellous bone using ultrasound, two types of longitudinal Biot's waves are observed in the received signal. These are known as fast and slow waves and their appearance depend on the alignment of bone trabeculae in the propagation path and the thickness of the specimen under test (SUT). They can be used as an effective tool for the diagnosis of osteoporosis because wave propagation behavior depends on the bone structure. However, the identification of these waves in the received signal can be difficult to achieve. In this study, ultrasonic wave propagation in a 4mm thick bovine cancellous bone in the direction parallel to the trabecular alignment is considered. The observed Biot's fast and slow longitudinal waves are superimposed; which makes it difficult to extract any information from the received signal. These two waves can be separated using the space alternating generalized expectation maximization (SAGE) algorithm. The latter has been used mainly in speech processing. In this new approach, parameters such as, arrival time, center frequency, bandwidth, amplitude, phase and velocity of each wave are estimated. The B-Scan images and its associated A-scans obtained through simulations using Biot's finite-difference time-domain (FDTD) method are validated experimentally using a thin bone sample obtained from the femoral-head of a 30 months old bovine. PMID:22284937
Fast detection and automatic parameter estimation of a gravitational wave signal with a novel method
NASA Astrophysics Data System (ADS)
Wang, Yan
2015-12-01
The detection of gravitational wave usually requires to match the measurement data with a large number of templates, which is computationally very expensive. Compressed sensing methods allow one to match the data with a small number of templates and interpolate the rest. However, the interpolation process is still computationally expensive. In this article, we designed a novel method that only requires to match the data with a few templates, yet without needing any interpolation process. The algorithm worked well for signals with relatively high SNRs. It also showed promise for low SNRs signals.
Fiber-optic evanescent-wave spectroscopy for fast multicomponent analysis of human blood
NASA Astrophysics Data System (ADS)
Simhi, Ronit; Gotshal, Yaron; Bunimovich, David; Katzir, Abraham; Sela, Ben-Ami
1996-07-01
A spectral analysis of human blood serum was undertaken by fiber-optic evanescent-wave spectroscopy (FEWS) by the use of a Fourier-transform infrared spectrometer. A special cell for the FEWS measurements was designed and built that incorporates an IR-transmitting silver halide fiber and a means for introducing the blood-serum sample. Further improvements in analysis were obtained by the adoption of multivariate calibration techniques that are already used in clinical chemistry. The partial least-squares algorithm was used to calculate the concentrations of cholesterol, total protein, urea, and uric acid in human blood serum. The estimated prediction errors obtained (in percent from the average value) were 6% for total protein, 15% for cholesterol, 30% for urea, and 30% for uric acid. These results were compared with another independent prediction method that used a neural-network model. This model yielded estimated prediction errors of 8.8% for total protein, 25% for cholesterol, and 21% for uric acid. spectroscopy, fiber-optic evanescent-wave spectroscopy, Fourier-transform infrared spectrometer, blood, multivariate calibration, neural networks.
NASA Astrophysics Data System (ADS)
Zhao, Wen; Zhang, Yang; You, Xiao-Peng; Zhu, Zong-Hong
2013-06-01
Measurement of pulsar timing residuals provides a direct way to detect relic gravitational waves at the frequency f˜1/yr. In this paper, we investigate the constraints on the inflationary parameters, the tensor-to-scalar ratio r, and the tensor spectral index nt, by the current and future pulsar timing arrays. We find that the Five-hundred-meter Aperture Spherical Radio Telescope in China and the planned Square Kilometre Array projects have fairly strong abilities to test the phantomlike inflationary models. If r=0.1, then Five-hundred-meter Aperture Spherical Radio Telescope could give the constraint on the spectral index nt<0.56 and Square Kilometre Array could give nt<0.32, while an observation with total time T=20yr, pulsar noise level σw=30ns, and monitored pulsar number n=200 could even constrain nt<0.07. These are much tighter than those inferred from the current results of the Parkes Pulsar Timing Array, European Pulsar Timing Array, and North American Nanohertz Observatory for Gravitational Waves. By studying the effects of various observational factors on the sensitivities of pulsar timing arrays, we find that compared with σw and n, the total observation time T has the most significant effect.
Simulations of fast-wave current drive in pulsed and steady-state DEMO designs
NASA Astrophysics Data System (ADS)
Bilato, R.; Brambilla, M.; Fable, E.
2014-11-01
Electromagnetic waves in the ion-cyclotron (IC) range of frequencies are presently investigated as possible current drive (CD) systems in fusion reactors. Among many physical and technical issues, an accurate description of radio-frequency (RF) power absorption by fusion- born alpha particles is of special importance, since RF heating of these particles is not only detrimental for the CD efficiency, but might worsen the operative conditions by increasing their prompt losses. The capability of the full-wave TORIC code has been recently augmented to account for RF absorption by fusion-born alpha particles, calculated to all-orders in finite Larmor radius and with a realistic distribution function. Here, we present simulation with TORIC addressing the sensitivity of current drive efficiency on the design of a future reactor, in particular density and temperature profiles, magnetic field intensity, and plasma dimensions. For this purpose, we have investigated possible frequency windows for CD for two proposed versions of the DEMO reactor, namely its pulsed and its more ambitious steady-state design. The important role of the antenna for a realistic estimate of the CD efficiency is pointed out.
Slow, large scales from fast, small ones in dispersive wave turbulence
NASA Astrophysics Data System (ADS)
Smith, Leslie; Waleffe, Fabian
2000-11-01
Dispersive wave turbulence in systems of geophysical interest (beta-plane, rotating, stratified and rotating-stratified flows) has been simulated with random, isotropic small scale forcing and hyper-viscosity. This can be thought of as a Langevin model of the small space-time scales only with potential implications for climate modeling. In all cases, slow, coherent large scales are generated after long times of 2nd order in the nonlinear time scale. These slow, large scales ultimately dominate the flows. Beta-plane and rotating flow results were reported earlier [PoF 11, 1608]. In stratified flows, the energy accumulates in a 1D vertically sheared flow at selected large scales. As the rotation rate is increased, a progressive transition toward generation of all large scale vortical zero modes (quasi-geostrophic 3D flow) is observed. For yet higher rotation rate, energy accumulates primarily in a 2D quasi-geostrophic flow (cyclonic vortices) at all large scales.
Tunable compression of template banks for fast gravitational-wave detection and localization
NASA Astrophysics Data System (ADS)
Chua, Alvin J. K.; Gair, Jonathan R.
2016-06-01
One strategy for reducing the online computational cost of matched-filter searches for gravitational waves is to introduce a compressed basis for the waveform template bank in a grid-based search. In this paper, we propose and investigate several tunable compression schemes for a general template bank. Through offline compression, such schemes are shown to yield faster detection and localization of signals, along with moderately improved sensitivity and accuracy over coarsened banks at the same level of computational cost. This is potentially useful for any search involving template banks, and especially in the analysis of data from future space-based detectors such as eLISA, for which online grid searches are difficult due to the long-duration waveforms and large parameter spaces.
Optical emission from a fast shock wave - The remnants of Tycho's supernova and SN 1006
NASA Technical Reports Server (NTRS)
Chevalier, R. A.; Raymond, J. C.
1978-01-01
The faint optical filaments in Tycho's supernova remnant appear to be emission from a shock front moving at 5600 km/s. The intensity of the hydrogen lines, the absence of forbidden lines of heavy elements in the spectrum, and the width of the filaments are explained by a model in which a collisionless shock wave is moving into partially neutral gas. The presence of the neutral gas can be used to set an upper limit of approximately 5 x 10 to the 47th power ergs to the energy in ionizing radiation emitted by a Type I supernova. The patchy neutral gas is probably part of the warm neutral component of the interstellar medium. The existing information on the remnant of SN 1006 indicates that its emission is similar in nature to that from Tycho's remnant.
Fast plane wave density functional theory molecular dynamics calculations on multi-GPU machines
Jia, Weile; University of Chinese Academy of Sciences, Beijing ; Fu, Jiyun; University of Chinese Academy of Sciences, Beijing ; Cao, Zongyan; Wang, Long; Chi, Xuebin; Gao, Weiguo; MOE Key Laboratory of Computational Physical Sciences, Fudan University, Shanghai ; Wang, Lin-Wang
2013-10-15
Plane wave pseudopotential (PWP) density functional theory (DFT) calculation is the most widely used method for material simulations, but its absolute speed stagnated due to the inability to use large scale CPU based computers. By a drastic redesign of the algorithm, and moving all the major computation parts into GPU, we have reached a speed of 12 s per molecular dynamics (MD) step for a 512 atom system using 256 GPU cards. This is about 20 times faster than the CPU version of the code regardless of the number of CPU cores used. Our tests and analysis on different GPU platforms and configurations shed lights on the optimal GPU deployments for PWP-DFT calculations. An 1800 step MD simulation is used to study the liquid phase properties of GaInP.
Bierbach, Jana; Yeung, Mark; Eckner, Erich; Roedel, Christian; Kuschel, Stephan; Zepf, Matt; Paulus, Gerhard G.
2015-05-01
Surface high-harmonic generation in the relativistic regime is demonstrated as a source of extreme ultra-violet (XUV) pulses with extended operation time. Relativistic high-harmonic generation is driven by a frequency-doubled high-power Ti:Sapphire laser focused to a peak intensity of 3·1019 W/cm2 onto spooling tapes. We demonstrate continuous operation over up to one hour runtime at a repetition rate of 1 Hz. Harmonic spectra ranging from 20 eV to 70 eV (62 nm to 18 nm) were consecutively recorded by an XUV spectrometer. An average XUV pulse energy in the µJ range is measured. With the presented setup, relativistic surface high-harmonic generationmore » becomes a powerful source of coherent XUV pulses that might enable applications in, e.g. attosecond laser physics and the seeding of free-electron lasers, when the laser issues causing 80-% pulse energy fluctuations are overcome.« less
Fast acoustic streaming in standing waves: generation of an additional outer streaming cell.
Reyt, Ida; Daru, Virginie; Bailliet, Hélène; Moreau, Solène; Valière, Jean-Christophe; Baltean-Carlès, Diana; Weisman, Catherine
2013-09-01
Rayleigh streaming in a cylindrical acoustic standing waveguide is studied both experimentally and numerically for nonlinear Reynolds numbers from 1 to 30 [Re(NL)=(U0/c0)(2)(R/δν)(2), with U0 the acoustic velocity amplitude at the velocity antinode, c0 the speed of sound, R the tube radius, and δν the acoustic boundary layer thickness]. Streaming velocity is measured by means of laser Doppler velocimetry in a cylindrical resonator filled with air at atmospheric pressure at high intensity sound levels. The compressible Navier-Stokes equations are solved numerically with high resolution finite difference schemes. The resonator is excited by shaking it along the axis at imposed frequency. Results of measurements and of numerical calculation are compared with results given in the literature and with each other. As expected, the axial streaming velocity measured and calculated agrees reasonably well with the slow streaming theory for small ReNL but deviates significantly from such predictions for fast streaming (ReNL>1). Both experimental and numerical results show that when ReNL is increased, the center of the outer streaming cells are pushed toward the acoustic velocity nodes until counter-rotating additional vortices are generated near the acoustic velocity antinodes. PMID:23967913
[Research on fast experimental measurement method for atmosphere downward long-wave radiance].
Hu, Ju-Yang; Tang, Shi-Hao; Dong, Li-Xin; Li, Xiang
2012-06-01
Direct measurement of the sky radiation in the direction of a special zenith angle as the average downward radiation is the fastest instantaneous downward radiation measurement. But this method has not been widely used, because there is no accu rate method for determining special zenith angle. The present paper analyzed the special angle with the variation of the aerosol optical thickness and atmospheric temperature and humidity through simulation by radiative transfer model. The results show that the special angles will be affected none by aerosols in clear skies, very little by atmospheric temperature, but significantly by atmospheric water vapor content. Therefore, the special angle could be determined only by atmospheric water vapor content in downward radiance infrared spectroscopy measurements in clear sky conditions. The downward radiation measurements results in western desert region indicate that the special angles determined by local atmospheric water vapor content are the same as experimental results. Besides, the error caused by taking the radiance at the special angle as the integral radiance meets the accuracy requirements. Accordingly, this fast measurement method can be widely used in field experiments while the special angle can be determined by atmospheric water vapor of the study area, since it can measure instantaneous downward radiance conveniently and accurately. PMID:22870647
Maneva, Y. G.; Araneda, J. A.; Marsch, E.
2014-03-10
We study the preferential heating and differential acceleration of minor ions by dissipation of ion-acoustic waves (IAWs) generated by parametric instabilities of a finite-amplitude monochromatic Alfvén-cyclotron pump wave. We consider the associated kinetic effects of Landau damping and nonlinear pitch-angle scattering of protons and α particles in the tenuous plasma of coronal holes and the fast solar wind. Various data collected by Wind spacecraft show signatures for a local transverse heating of the minor ions, presumably by Alfvén-cyclotron wave dissipation, and an unexpected parallel heating by a so far unknown mechanism. Here, we present the results from a set of 1.5 dimensional hybrid simulations in search for a plausible explanation for the observed field-aligned kinetic features in the fast solar wind minor ions. We investigate the origin and regulation of ion relative drifts and temperature anisotropies in low plasma β, fast solar wind conditions. Depending on their initial drifts, both ion species can heat up not only transversely through cyclotron resonance and non-resonant wave-particle interactions, but also strongly in the parallel direction by Landau damping of the daughter IAWs. We discuss the dependence of the relative ion drifts and temperature anisotropies on the plasma β of the individual species and we describe the effect of the pump wave amplitude on the ion heating and acceleration.
Fast control of semiconductor qubits beyond the rotating-wave approximation
NASA Astrophysics Data System (ADS)
Song, Yang; Kestner, J. P.; Wang, Xin; Das Sarma, S.
2016-07-01
We present a theoretical study of single-qubit operations by oscillatory fields on various semiconductor platforms. We explicitly show how to perform faster gate operations by going beyond the universally used rotating-wave approximation (RWA) regime, while using only two sinusoidal pulses. We first show for specific published experiments how much error is currently incurred by implementing pulses designed using standard RWA. We then show that an even modest increase in gate speed would cause problems in using RWA for gate design in the singlet-triplet (ST) and resonant-exchange (RX) qubits. We discuss the extent to which analytically keeping higher orders in the perturbation theory would address the problem. More strikingly, we give a new prescription for gating with strong coupling far beyond the RWA regime. We perform numerical calculations for the phases and the durations of two consecutive pulses to realize the key Hadamard and π/8 gates with coupling strengths up to several times the qubit splitting. Working in this manifestly non-RWA regime, the gate operation speeds up by two to three orders of magnitude and nears the quantum speed limit without requiring complicated pulse shaping or optimal control sequences.
NASA Astrophysics Data System (ADS)
Picolloto, A. M.; Mariucci, V. V. G.; Szpak, W.; Medina, A. N.; Baesso, M. L.; Astrath, N. G. C.; Astrath, F. B. G.; Santos, A. D.; Moraes, J. C. S.; Bento, A. C.
2013-11-01
The thermal wave method is applied for thermal properties measurement in fast endodontic cement (CER). This new formula is developed upon using Portland cement in gel and it was successfully tested in mice with good biocompatibility and stimulated mineralization. Recently, thermal expansion and setting time were measured, conferring to this material twice faster hardening than the well known Angelus Mineral trioxide aggregate (MTA) the feature of fast hardening (˜7 min) and with similar thermal expansion (˜12 μstrain/ °C). Therefore, it is important the knowledge of thermal properties like thermal diffusivity, conductivity, effusivity in order to match thermally the tissue environment upon its application in filling cavities of teeth. Photothermal radiometry technique based on Xe illumination was applied in CER disks 600 μm thick for heating, with prepared in four particle sizes (25, 38, 45, and 53) μm, which were added microemulsion gel with variation volumes (140, 150, 160, and 170) μl. The behavior of the thermal diffusivity CER disks shows linear decay for increase emulsion volume, and in contrast, thermal diffusivity increases with particles sizes. Aiming to compare to MTA, thermal properties of CER were averaged to get the figure of merit for thermal diffusivity as (44.2 ± 3.6) × 10-3 cm2/s, for thermal conductivity (228 ± 32) mW/cm K, the thermal effusivity (1.09 ± 0.06) W s0.5/cm2 K and volume heat capacity (5.2 ± 0.7) J/cm3 K, which are in excellent agreement with results of a disk prepared from commercial MTA-Angelus (grain size < 10 μm using 57 μl of distilled water).
Picolloto, A. M.; Mariucci, V. V. G.; Szpak, W.; Medina, A. N.; Baesso, M. L.; Astrath, N. G. C.; Astrath, F. B. G.; Bento, A. C.; Santos, A. D.; Moraes, J. C. S.
2013-11-21
The thermal wave method is applied for thermal properties measurement in fast endodontic cement (CER). This new formula is developed upon using Portland cement in gel and it was successfully tested in mice with good biocompatibility and stimulated mineralization. Recently, thermal expansion and setting time were measured, conferring to this material twice faster hardening than the well known Angelus Mineral trioxide aggregate (MTA) the feature of fast hardening (∼7 min) and with similar thermal expansion (∼12 μstrain/ °C). Therefore, it is important the knowledge of thermal properties like thermal diffusivity, conductivity, effusivity in order to match thermally the tissue environment upon its application in filling cavities of teeth. Photothermal radiometry technique based on Xe illumination was applied in CER disks 600 μm thick for heating, with prepared in four particle sizes (25, 38, 45, and 53) μm, which were added microemulsion gel with variation volumes (140, 150, 160, and 170) μl. The behavior of the thermal diffusivity CER disks shows linear decay for increase emulsion volume, and in contrast, thermal diffusivity increases with particles sizes. Aiming to compare to MTA, thermal properties of CER were averaged to get the figure of merit for thermal diffusivity as (44.2 ± 3.6) × 10{sup −3} cm{sup 2}/s, for thermal conductivity (228 ± 32) mW/cm K, the thermal effusivity (1.09 ± 0.06) W s{sup 0.5}/cm{sup 2} K and volume heat capacity (5.2 ± 0.7) J/cm{sup 3} K, which are in excellent agreement with results of a disk prepared from commercial MTA-Angelus (grain size < 10 μm using 57 μl of distilled water)
NASA Astrophysics Data System (ADS)
Lu, Wangtao; Qian, Jianliang; Burridge, Robert
2016-05-01
In some applications, it is reasonable to assume that geodesics (rays) have a consistent orientation so that the Helmholtz equation can be viewed as an evolution equation in one of the spatial directions. With such applications in mind, starting from Babich's expansion, we develop a new high-order asymptotic method, which we dub the fast Huygens sweeping method, for solving point-source Helmholtz equations in inhomogeneous media in the high-frequency regime and in the presence of caustics. The first novelty of this method is that we develop a new Eulerian approach to compute the asymptotics, i.e. the traveltime function and amplitude coefficients that arise in Babich's expansion, yielding a locally valid solution, which is accurate close enough to the source. The second novelty is that we utilize the Huygens-Kirchhoff integral to integrate many locally valid wavefields to construct globally valid wavefields. This automatically treats caustics and yields uniformly accurate solutions both near the source and remote from it. The third novelty is that the butterfly algorithm is adapted to accelerate the Huygens-Kirchhoff summation, achieving nearly optimal complexity O (Nlog N), where N is the number of mesh points; the complexity prefactor depends on the desired accuracy and is independent of the frequency. To reduce the storage of the resulting tables of asymptotics in Babich's expansion, we use the multivariable Chebyshev series expansion to compress each table by encoding the information into a small number of coefficients. The new method enjoys the following desired features. First, it precomputes the asymptotics in Babich's expansion, such as traveltime and amplitudes. Second, it takes care of caustics automatically. Third, it can compute the point-source Helmholtz solution for many different sources at many frequencies simultaneously. Fourth, for a specified number of points per wavelength, it can construct the wavefield in nearly optimal complexity in terms
Weatherford, Brandon R. E-mail: zax@esi-group.com E-mail: mjkush@umich.edu; Barnat, E. V. E-mail: zax@esi-group.com E-mail: mjkush@umich.edu; Xiong, Zhongmin E-mail: zax@esi-group.com E-mail: mjkush@umich.edu; Kushner, Mark J. E-mail: zax@esi-group.com E-mail: mjkush@umich.edu
2014-09-14
Fast ionization waves (FIWs), often generated with high voltage pulses over nanosecond timescales, are able to produce large volumes of ions and excited states at moderate pressures. The mechanisms of FIW propagation were experimentally and computationally investigated to provide insights into the manner in which these large volumes are excited. The two-dimensional structure of electron and metastable densities produced by short-pulse FIWs sustained in helium were measured using laser-induced fluorescence and laser collision-induced fluorescence diagnostics for times of 100–120 ns after the pulse, as the pressure was varied from 1 to 20 Torr. A trend of center-peaked to volume-filling to wall-peaked electron density profiles was observed as the pressure was increased. Instantaneous FIW velocities, obtained from plasma-induced emission, ranged from 0.1 to 3×10⁹cm s⁻¹, depending on distance from the high voltage electrode and pressure. Predictions from two-dimensional modeling of the propagation of a single FIW correlated well with the experimental trends in electron density profiles and wave velocity. Results from the model show that the maximum ionization rate occurs in the wavefront, and the discharge continues to propagate forward after the removal of high voltage from the powered electrode due to the potential energy stored in the space charge. As the pressure is varied, the radial distribution of the ionization rate is shaped by changes in the electron mean free path, and subsequent localized electric field enhancement at the walls or on the centerline of the discharge.
NASA Astrophysics Data System (ADS)
Weatherford, Brandon R.; Xiong, Zhongmin; Barnat, E. V.; Kushner, Mark J.
2014-09-01
Fast ionization waves (FIWs), often generated with high voltage pulses over nanosecond timescales, are able to produce large volumes of ions and excited states at moderate pressures. The mechanisms of FIW propagation were experimentally and computationally investigated to provide insights into the manner in which these large volumes are excited. The two-dimensional structure of electron and metastable densities produced by short-pulse FIWs sustained in helium were measured using laser-induced fluorescence and laser collision-induced fluorescence diagnostics for times of 100-120 ns after the pulse, as the pressure was varied from 1 to 20 Torr. A trend of center-peaked to volume-filling to wall-peaked electron density profiles was observed as the pressure was increased. Instantaneous FIW velocities, obtained from plasma-induced emission, ranged from 0.1 to 3 × 109 cm s-1, depending on distance from the high voltage electrode and pressure. Predictions from two-dimensional modeling of the propagation of a single FIW correlated well with the experimental trends in electron density profiles and wave velocity. Results from the model show that the maximum ionization rate occurs in the wavefront, and the discharge continues to propagate forward after the removal of high voltage from the powered electrode due to the potential energy stored in the space charge. As the pressure is varied, the radial distribution of the ionization rate is shaped by changes in the electron mean free path, and subsequent localized electric field enhancement at the walls or on the centerline of the discharge.
High harmonic generation in a gas-filled hollow-core photonic crystal fiber
NASA Astrophysics Data System (ADS)
Heckl, O. H.; Baer, C. R. E.; Kränkel, C.; Marchese, S. V.; Schapper, F.; Holler, M.; Südmeyer, T.; Robinson, J. S.; Tisch, J. W. G.; Couny, F.; Light, P.; Benabid, F.; Keller, U.
2009-10-01
High harmonic generation (HHG) of intense infrared laser radiation (Ferray et al., J. Phys. B: At. Mol. Opt. Phys. 21:L31, 1988; McPherson et al., J. Opt. Soc. Am. B 4:595, 1987) enables coherent vacuum-UV (VUV) to soft-X-ray sources. In the usual setup, energetic femtosecond laser pulses are strongly focused into a gas jet, restricting the interaction length to the Rayleigh range of the focus. The average photon flux is limited by the low conversion efficiency and the low average power of the complex laser amplifier systems (Keller, Nature 424:831, 2003; Südmeyer et al., Nat. Photonics 2:599, 2008; Röser et al., Opt. Lett. 30:2754, 2005; Eidam et al., IEEE J. Sel. Top. Quantum Electron. 15:187, 2009) which typically operate at kilohertz repetition rates. This represents a severe limitation for many experiments using the harmonic radiation in fields such as metrology or high-resolution imaging. Driving HHG with novel high-power diode-pumped multi-megahertz laser systems has the potential to significantly increase the average photon flux. However, the higher average power comes at the expense of lower pulse energies because the repetition rate is increased by more than a thousand times, and efficient HHG is not possible in the usual geometry. So far, two promising techniques for HHG at lower pulse energies were developed: external build-up cavities (Gohle et al., Nature 436:234, 2005; Jones et al., Phys. Rev. Lett. 94:193, 2005) and resonant field enhancement in nanostructured targets (Kim et al., Nature 453:757, 2008). Here we present a third technique, which has advantages in terms of ease of HHG light extraction, transverse beam quality, and the possibility to substantially increase conversion efficiency by phase-matching (Paul et al., Nature 421:51, 2003; Ren et al., Opt. Express 16:17052, 2008; Serebryannikov et al., Phys. Rev. E (Stat. Nonlinear Soft Matter Phys.) 70:66611, 2004; Serebryannikov et al., Opt. Lett. 33:977, 2008; Zhang et al., Nat. Phys. 3
NASA Astrophysics Data System (ADS)
Kwon, Jae-Min; McCune, Douglas; Chang, C. S.
2007-11-01
The Monte-Carlo package NUBEAM for time-dependent modeling of fast ions in a tokamak geometry has been upgraded to simulate the effects of ICRF heating on the fast ions. The RF-wave field data is provided by executing TORIC5 inside TRANSP and passed to NUBEAM. An iterative algorithm has been implemented to match the RF-power absorption value calculated by NUBEAM with the level predicted by TORIC5. The effects of RF-wave fields on the fast ions are modeled by evaluating Monte-Carlo kicks based on the quasi-linear theory. Because of the unique feature of NUBEAM, the so called ``goosing'' which enables an order of magnitude faster calculation, special care needs to be taken in the Monte-Carlo simulation. The modification of the goose algorithm in the presence of RF-wave fields will be presented. Also, the necessary features of NUBEAM for future application to self-consistent coupling with an ICRF full wave code will be discussed.
Pinsker, R. I.; Jackson, G. L.; Luce, T. C.; Politzer, P. A.; Austin, M. E.; Diem, S. J.; Kaufman, M. C.; Ryan, P. M.; Doyle, E. J.; Zeng, L.; Grierson, B. A.; Hosea, J. C.; Nagy, A.; Perkins, R.; Solomon, W. M.; Taylor, G.; Maggiora, R.; Milanesio, D.; Porkolab, M.; Turco, F.
2014-02-12
Fast Wave (FW) heating and electron cyclotron heating (ECH) are used in the DIII-D tokamak to study plasmas with low applied torque and dominant electron heating characteristic of burning plasmas. FW heating via direct electron damping has reached the 2.5 MW level in high performance ELMy H-mode plasmas. In Advanced Inductive (AI) plasmas, core FW heating was found to be comparable to that of ECH, consistent with the excellent first-pass absorption of FWs predicted by ray-tracing models at high electron beta. FW heating at the ∼2 MW level to ELMy H-mode discharges in the ITER Baseline Scenario (IBS) showed unexpectedly strong absorption of FW power by injected neutral beam (NB) ions, indicated by significant enhancement of the D-D neutron rate, while the intended absorption on core electrons appeared rather weak. The AI and IBS discharges are compared in an effort to identify the causes of the different response to FWs.
Comparison of 3-D Modeling With Experimental Results on Fast Wave Antenna Loading in DIII-D
NASA Astrophysics Data System (ADS)
Pinsker, R. I.; Ryan, P. M.; Goulding, R. H.; Hanson, G. R.; Milanesio, D.; Maggiora, R.; Hosea, J. C.; Nagy, A.; Porkolab, M.; Zeng, L.
2011-10-01
In DIII-D and other tokamaks, with a fixed system voltage limit, the parameter that limits the ICRF power that can be coupled to H-mode plasmas is the antenna loading resistance RL. For a fixed antenna geometry and excitation (phasing), RL is determined by the electron density profile in the antenna near-field region. Quantitative understanding of the coupling physics is obtained by comparing the resistive (RL) and reactive components of the antenna loading, without and with plasma, to predictions of 3-D models of the antenna and the edge plasma (Microwave Studio and TOPICA). When measured density profiles from reflectometers are used, good agreement between predicted and measured values of RL is obtained without any adjustable parameters in the model. The improved understanding is applied to enhancement of RL in advanced scenarios in DIII-D to increase the coupled fast wave power. Supported in part by US DOE under DE-FC02-04ER54698, DE-AC05-00OR22725, DE-AC02-09CH11466, DE-FG02-08ER54984.
Enhanced loss of magnetic-mirror-trapped fast electrons by a shear Alfvén wave
Wang, Y.; Gekelman, W.; Pribyl, P.; Papadopoulos, K.
2014-05-15
Laboratory observations of enhanced loss of magnetic mirror trapped fast electrons irradiated by a shear Alfvén Wave (SAW) are reported. The experiment is performed in the quiescent after-glow plasma in the Large Plasma Device [Gekelman et al., Rev. Sci. Instrum. 62(12), 2875–2883 (1991)]. A trapped energetic electron population (>100 keV) is generated in a magnetic mirror section (mirror ratio ≈ 2, length = 3.5 m) by an X-mode high power microwave pulse, and forms a hot electron ring due to the grad-B and curvature drift. SAWs of arbitrary polarization are launched externally by a Rotating Magnetic Field source (δB/B{sub 0} ≈ 0.1%, λ{sub ∥} ≈ 9 m). Irradiated by a right-handed circularly polarized SAW, the loss of electrons, in both the radial and the axial direction of the mirror field, is significantly enhanced and is modulated at f{sub Alfvén}. The periodical loss continues even after the termination of the SAW. Experimental observations suggest that a spatial distortion of the ring is formed in the SAW field and creates a collective mode of the hot electron population that degrades its confinement and leads to electron loss from the magnetic mirror. The results could have implications on techniques of radiation belt remediation.
NASA Astrophysics Data System (ADS)
Chai, Kil-Byoung; Zhai, Xiang; Bellan, Paul M.
2016-03-01
A spatially localized energetic extreme ultra-violet (EUV) burst is imaged at the presumed position of fast magnetic reconnection in a plasma jet produced by a coaxial helicity injection source; this EUV burst indicates strong localized electron heating. A circularly polarized high frequency magnetic field perturbation is simultaneously observed at some distance from the reconnection region indicating that the reconnection emits whistler waves and that Hall dynamics likely governs the reconnection. Spectroscopic measurement shows simultaneous fast ion heating. The electron heating is consistent with Ohmic dissipation, while the ion heating is consistent with ion trajectories becoming stochastic.
NASA Astrophysics Data System (ADS)
Wakui, Kentaro; Hayasaka, Kazuhiro; Ido, Tetsuya
2014-09-01
Vacuum ultraviolet (VUV) radiation around 159 nm is obtained toward direct excitation of a single trapped ^{115}{In}+ ion. An efficient fluoride-based VUV output coupler is employed for intracavity high-harmonic generation of a Ti:S oscillator. Using this coupler, where we measured its reflectance to be about 90 %, an average power reaching 6.4 \\upmu W is coupled out from a modest fundamental power of 650 mW. When a single comb component out of 1.9 × 105 teeth is resonant to the atomic transition, 100s of fluorescence photons per second will be detectable under a realistic condition.
NASA Astrophysics Data System (ADS)
Zhong, Huiying; Guo, Jing; Feng, Wei; Li, Peng-Cheng; Liu, Xue-Shen
2016-01-01
The high harmonic generation (HHG) from 3D hydrogen (H) atom in three kinds of inhomogeneous fields are investigated by solving the time-dependent Schrödinger equation (TDSE) accurately with time-dependent generalized pseudospectral method (TDGPS), and compared together. The corresponding time-frequency and three-step model is also presented to explain the differences between three cases. We will also calculate the ionization probability and electron wavepacket as functions of time to further illustrate this phenomenon. By superposing a series of properly selected harmonics, the isolated attosecond pulses can be obtained straightforwards the shortest of which is 64 as.
NASA Astrophysics Data System (ADS)
Sanz, Javier; Debayle, Arnaud; Mima, K.
2012-11-01
An analytical study of the relativistic interaction of a linearly-polarized laser-field of ω frequency with highly overdense plasma is presented. Very intense high harmonics are generated produced by relativistic mirrors effects due to the relativistic electron plasma oscillation. Also, in agreement with 1D Particle-In-Cell Simulations (PICS), the model self-consistently explains the transition between the sheath inverse bremsstrahlung (SIB) absorption regime and the J×B heating (responsible for the 2ω electron bunches), as well as the mean electron energy.
NASA Astrophysics Data System (ADS)
Wakui, Kentaro; Hayasaka, Kazuhiro; Ido, Tetsuya
2014-12-01
Vacuum ultraviolet (VUV) radiation around 159 nm is obtained toward direct excitation of a single trapped ion. An efficient fluoride-based VUV output coupler is employed for intracavity high-harmonic generation of a Ti:S oscillator. Using this coupler, where we measured its reflectance to be about 90 %, an average power reaching 6.4 W is coupled out from a modest fundamental power of 650 mW. When a single comb component out of 1.9 10 teeth is resonant to the atomic transition, 100s of fluorescence photons per second will be detectable under a realistic condition.
Plans for Electron Bernstein Wave and Electron Cyclotron Heating in NSTX
Taylor, G.; Diem, S. J.; Ellis, R. A.; Fredd, E. H.; Greenough, N. L.; Hosea, J. C.; Bigelow, T. S.; Caughman, J. B.; Rasmussen, D. A.; Ryan, P. M.; Wilgen, J. B.; Ershov, N. M.; Harvey, R. W.; Smirnov, A. P.; Preinhaelter, J.; Urban, J.; Ram, A. K.
2007-09-28
A 200 kW, 28 GHz system for electron cyclotron heating (ECH) and electron Bernstein wave heating (EBWH) is being installed on NSTX to assist solenoid-free startup, high harmonic fast wave heated current ramp up, and to support initial EBW coupling and heating studies. This system will provide on-axis second harmonic ECH/EBWH in NSTX. Fundamental on-axis heating may also be possible at 15.3 GHz by operating the gyrotron in a lower order TE01 cavity mode. Sufficient power supply capability will be provided to provide up to 1 MW of gyrotron power for future proof-of-principle EBWH experiments on NSTX. Initial modeling of an NSTX startup discharge with 28 GHz ECH is presented.
NASA Astrophysics Data System (ADS)
le Roux, J. A.
2012-12-01
It has been argued that the acceleration of SEPS at a quasi-parallel CME-driven shock to GeV energies in the corona only occurs if strong wave-excitation by SEPs ahead of the shock reduces the parallel mean free path upstream, thus boosting the rate of diffusive shock acceleration. To investigate this issue, we modeled SEP acceleration at a fast parallel traveling shock in the corona with an existing time-dependent focused transport model. The model has been expanded recently to also feature time-dependent self-excitation and damping of Alfvén waves by SEP anisotropies ahead of the shock based on standard quasi-linear theory. Alfvén wave propagation near the traveling shock is modeled based on standard theory for wave transport in a slowly varying non-uniform plasma medium. Preliminary results will be shown to illustrate the increase in wave power driven by SEP anisotropies upstream, the effect of the shock wave in shortening the wave length and increasing the wave amplitude of Alfvén waves, and the associated acceleration of SEPs by 1st order Fermi acceleration to high energies. The role of the acceleration of the cross-shock solar wind flow, which was found to create a downstream population of shock pre-heated particles which forms an additional source for injection into 1st order Fermi acceleration, will be discussed in terms of how it affects self-excitation of Alfvén waves and the formation of high-energy SEPs by 1st order Fermi acceleration.
Vacuum high-harmonic generation in the shock regime and photon-photon scattering dynamics
NASA Astrophysics Data System (ADS)
King, B.; Böhl, P.; Ruhl, H.
2016-02-01
The presence of charged quantum virtual states permits a nonlinear self-interaction of the electromagnetic field in vacuum. This interaction can be described as real photon-photon scattering. This effect has been calculated for the case of colliding plane waves, when the centre- of-mass energy is much less than the electron rest energy. The quantum effect is included in the classical electromagnetic field equations of motion by a standard effective approach based upon a weak-field expansion of the Heisenberg-Euler Lagrangian. Solving for the resultant electromagnetic field indicates a signal for real photon-photon scattering when the plane waves overlap, which can be significantly larger than the usually-considered asymptotic values that reach detectors. By considering arbitrary numbers of four- and six-photon scattering, the process of vacuum higher harmonic generation has been studied both analytically and numerically. A route to prolific harmonic generation is identified that does not depend on field strengths being necessarily close to the Schwinger limit. The resulting vacuum electromagnetic shock wave has been studied and a nonlinear shock parameter identified.
Route to optimal generation of soft X-ray high harmonics with synthesized two-color laser pulses
Jin, Cheng; Wang, Guoli; Le, Anh-Thu; Lin, C. D.
2014-01-01
High harmonics extending to X-rays have been generated from gases by intense lasers. To establish these coherent broadband radiations as an all-purpose tabletop light source for general applications in science and technology, new methods are needed to overcome the present low conversion efficiencies. Here we show that the conversion efficiency may be drastically increased with an optimized two-color pulse. By employing an optimally synthesized 2-µm mid-infrared laser and a small amount of its third harmonic, we show that harmonic yields from sub- to few-keV energy can be increased typically by ten-fold over the optimized single-color one. By combining with favorable phase-matching and together with the emerging high-repetition MHz mid-infrared lasers, we anticipate efficiency of harmonic yields can be increased by four to five orders in the near future, thus paving the way for employing high harmonics as useful broadband tabletop light sources from the extreme ultraviolet to the X-rays, as well as providing new tools for interrogating ultrafast dynamics of matter at attosecond timescales. PMID:25400015
Ishii, Nobuhisa; Kaneshima, Keisuke; Kitano, Kenta; Kanai, Teruto; Watanabe, Shuntaro; Itatani, Jiro
2014-01-01
High harmonic generation (HHG) using waveform-controlled, few-cycle pulses from Ti:sapphire lasers has opened emerging researches in strong-field and attosecond physics. However, the maximum photon energy of attosecond pulses via HHG remains limited to the extreme ultraviolet region. Long-wavelength light sources with carrier-envelope phase stabilization are promising to extend the photon energy of attosecond pulses into the soft X-ray region. Here we demonstrate carrier-envelope phase-dependent HHG in the water window using sub-two-cycle optical pulses at 1,600 nm. Experimental and simulated results indicate the confinement of soft X-ray emission in a single recombination event with a bandwidth of 75 eV around the carbon K edge. Control of high harmonics by the waveform of few-cycle infrared pulses is a key milestone to generate soft X-ray attosecond pulses. We measure a dependence of half-cycle bursts on the gas pressure, which indicates subcycle deformation of the waveform of the infrared drive pulses in the HHG process. PMID:24535006
Reflectometer Sensing of RF Waves in front of the HHFW antenna on NSTX
Wilgen, John B; Ryan, Philip Michael; Hanson, Gregory R; Swain, David W; Bernabei, Stefano; Greenough, Nevell; DePasquale, Steve; Phillips, Cynthia; Hosea, Joel; Wilson, Randy
2006-01-01
The ability to measure RF driven waves in the edge of the plasma can help to elucidate the role that surface waves and Parametric Decay Instabilities (PDI) play in RF power losses on NSTX. A microwave reflectometer has recently been modified to monitor RF plasma waves in the scrape-off layer in front of the 30 MHz High Harmonic Fast Wave (HHFW) antenna array on NSTX. In RF heated plasmas, the plasma-reflected microwave signal exhibits 30 MHz sidebands, due to the modulation of the cutoff layer by the electrostatic component of the heating wave. Similarly, electrostatic parametric decay waves (when present) are detected at frequencies below the heating frequency, near 28, 26, MHz, separated from the heating frequency by harmonics of the local ion cyclotron frequency of about 2 MHz. In addition, a corresponding frequency matched set of decay waves is also detected near the ion cyclotron harmonics, at 2, 4, MHz. The RF plasma-wave sensing capability is useful for determination of the PDI power threshold as a function of antenna array phasing (including toroidal wavelength), outer gap spacing, and various plasma parameters such as the magnetic field and the plasma current.
NASA Astrophysics Data System (ADS)
Mathijssen, T.; Gallo, M.; Casati, E.; Nannan, N. R.; Zamfirescu, C.; Guardone, A.; Colonna, P.
2015-10-01
This paper describes the commissioning of the flexible asymmetric shock tube (FAST), a novel Ludwieg tube-type facility designed and built at Delft University of Technology, together with the results of preliminary experiments. The FAST is conceived to measure the velocity of waves propagating in dense vapours of organic fluids, in the so-called non-ideal compressible fluid dynamics (NICFD) regime, and can operate at pressures and temperatures as high as 21 bar and 400°C, respectively. The set-up is equipped with a special fast-opening valve, separating the high-pressure charge tube from the low-pressure plenum. When the valve is opened, a wave propagates into the charge tube. The wave speed is measured using a time-of-flight technique employing four pressure transducers placed at known distances from each other. The first tests led to the following results: (1) the leakage rate of 5 × {10}^{-4} {mbar l s^{-1}} for subatmospheric and 5 × {10}^{-2} {mbar l s^{-1}} for a superatmospheric pressure is compatible with the purpose of the conceived experiments, (2) the process start-up time of the valve has been found to be between 2.1 and 9.0 ms, (3) preliminary rarefaction wave experiments in the dense vapour of siloxane {D}_6 (dodecamethylcyclohexasiloxane, an organic fluid) were successfully accomplished up to temperatures of 300°C, and (4) a method for the estimation of the speed of sound from wave propagation experiments is proposed. Results are found to be within 2.1 % of accurate model predictions for various gases. The method is then applied to estimate the speed of sound of {D}_6 in the NICFD regime.
NASA Astrophysics Data System (ADS)
Pischiutta, M.; Pastori, M.; Improta, L.; Salvini, F.; Rovelli, A.
2014-01-01
polarization is investigated using 200 seismograms recorded by a network of 20 stations installed on rock outcrops in the Val d'Agri region that hosts the largest oil fields in the southern Apennines (Italy). Polarization is assessed both in the frequency and time domains through the individual-station horizontal-to-vertical spectral ratio and covariance-matrix analysis, respectively. We find that most of the stations show a persistent horizontal polarization of waveforms, with a NE-SW predominant trend. This direction is orthogonal to the general trend of Quaternary normal faults in the region and to the maximum horizontal stress related to the present extensional regime. According to previous studies in other areas, such a directional effect is interpreted as due to the presence of fault-related fracture fields, polarization being orthogonal to their predominant direction. A comparison with S wave anisotropy inferred from shear wave splitting indicates an orthogonal relation between horizontal polarization and fast S wave direction. This suggests that wavefield polarization and fast velocity direction are effects of the same cause: The existence of an anisotropic medium represented by fractured rocks where shear wave velocity is larger in the crack-parallel component and compliance is larger perpendicularly to the crack strike. The latter is responsible for the observed anisotropic pattern of amplitudes of horizontal ground motion in the study area.
Emelina, Anna S; Emelin, Mikhail Yu; Ganeev, Rashid A; Suzuki, Masayuki; Kuroda, Hiroto; Strelkov, Vasily V
2016-06-27
The high-order harmonic generation (HHG) in silver, gold, and zinc plasma plumes irradiated by orthogonally polarized two-color field is studied theoretically and experimentally. We find an increase of the HHG efficiency in comparison with the single-color case, which essentially depends on the plasma species and harmonic order. An increase of more than an order of magnitude is observed for silver plasma, whereas for gold and zinc it is lower; these results are reproduced in our calculations that include both propagation and microscopic response studies. We show that the widely used theoretical approach assuming the 1s ground state of the generating particle fails to reproduce the experimental results; the agreement is achieved in our theory using the actual quantum numbers of the outer electron of the generating particles. Moreover, our theoretical studies highlight the redistribution of the electronic density in the continuum wave packet as an important aspect of the HHG enhancement in the two-color orthogonally polarized fields with comparable intensities: in the single-color field the electronic trajectories with almost zero return energy are the most populated ones; in the two-color case the total field maximum can be shifted in time so that the trajectories with high return energies (in particular, the cut-off trajectory) become the most populated ones. PMID:27410560
Molecular Self-Probing Spectroscopy with High Harmonic Generation at Long Wavelengths
NASA Astrophysics Data System (ADS)
Camper, A.; Schoun, S. B.; Agostini, P.; Salieres, Pascal; Caillat, J.; Lucchese, R. R.; Dimauro, L.
2015-05-01
We used laser driven sub-femtosecond electronic wave packet (EWP) recollision to generate high-order harmonics (HHG) of a 1.3 μm laser pulse in aligned molecules. We performed a tomographic investigation of N2 [ItataniNature2004, HaesslerNatPhys2010, VozziNatPhys2011, DivekiNJP2012] by characterizing the HHG yield and spectral phase of the attosecond emission for different recollision angles of EWP with respect to the main axis of the angular distribution of the molecules. Thanks to the high degree of alignment and to the fine spectral sampling, our XUV quantum phase measurements [SchounPRL2014] reveal subtle features in the recombination dipole moment of N2. We interpret the latter within the Quantitative Rescattering Theory [LePRA2009] and emphasize the effect of the EWP scattering on the ion Coulombic potential and of the shape resonance in the X channel of N2 on HHG [LucchesePRA1982]. Compared to previous results at 800 nm, our experiment is deeper into the tunneling regime and only one ionization channel is enough to explain what we observed. Our results shine a new light on imaging molecular orbitals using laser-driven photo-recombination processes.
NASA Astrophysics Data System (ADS)
Kanai, Tsuneto; Takahashi, Eiji J.; Nabekawa, Yasuo; Midorikawa, Katsumi
2008-02-01
We probe the attosecond dynamics of nuclear wavepackets in H2 and D2 molecules by measuring the relative phase of high harmonics generated in each molecule by using a novel method with a mixed gas of H2 and D2. We find that not only the single molecule responses but also the propagation effects of harmonics differ between the two isotopes and we conclude that in order to discuss the dynamics of molecules in the single molecule responses, the propagation effects need to be excluded from the raw harmonic signals. The measured relative phase as well as the intensity ratio are found to be monotonic functions of the harmonic order and are successfully reproduced by applying Feynman's path integral method fully to the dynamics of the nuclei and electrons in the molecules.
Xiang, D.; Colby, E.; Dunning, M.; Gilevich, S.; Hast, C.; Jobe, K.; McCormick, D.; Nelson, J.; Raubenheimer, T.O.; Soong, K.; Stupakov, G.; Szalata, Z.; Walz, D.; Weathersby, S.; Woodle, M.; /SLAC
2012-02-15
Echo-enabled harmonic generation free electron lasers hold great promise for the generation of fully coherent radiation in x-ray wavelengths. Here we report the first evidence of high harmonics from the echo-enabled harmonic generation technique in the realistic scenario where the laser energy modulation is comparable to the beam slice energy spread. In this experiment, coherent radiation at the seventh harmonic of the second seed laser is generated when the energy modulation amplitude is about 2-3 times the slice energy spread. The experiment confirms the underlying physics of echo-enabled harmonic generation and may have a strong impact on emerging seeded x-ray free electron lasers that are capable of generating laserlike x rays which will advance many areas of science.
Improving the efficiency of high harmonic generation (HHG) by Ne-admixing into a pure Ar gas medium
NASA Astrophysics Data System (ADS)
Seo, Hyun Ook; Arion, Tiberiu; Roth, Friedrich; Ramm, Daniel; Lupulescu, Cosmin; Eberhardt, Wolfgang
2016-04-01
Laser-based higher-order harmonic generation has been investigated extensively in the past two decades. The current manuscript deals with the high harmonic generation (HHG) outputs from a gas-filled waveguide when using mixtures of two rare gases (Ar and Ne) as nonlinear media. We find that the efficiency of the HHG process can be optimized by changing the pressure or alternatively the mixing ratio of the two gases. This is attributed to the fact that both of these parameters have an effect on the phase-matching in the waveguide. These observations are especially useful when phase matching in a gas jet is concerned, where the absolute local pressure of the gas media cannot be controlled as readily as in a capillary-based HHG setup.
NASA Astrophysics Data System (ADS)
Weber, S. J.; Manschwetus, B.; Billon, M.; Böttcher, M.; Bougeard, M.; Breger, P.; Géléoc, M.; Gruson, V.; Huetz, A.; Lin, N.; Picard, Y. J.; Ruchon, T.; Salières, P.; Carré, B.
2015-03-01
We describe the versatile features of the attosecond beamline recently installed at CEA-Saclay on the PLFA kHz laser. It combines a fine and very complete set of diagnostics enabling high harmonic spectroscopy (HHS) through the advanced characterization of the amplitude, phase, and polarization of the harmonic emission. It also allows a variety of photo-ionization experiments using magnetic bottle and COLTRIMS (COLd Target Recoil Ion Momentum Microscopy) electron spectrometers that may be used simultaneously, thanks to a two-foci configuration. Using both passive and active stabilization, special care was paid to the long term stability of the system to allow, using both experimental approaches, time resolved studies with attosecond precision, typically over several hours of acquisition times. As an illustration, applications to multi-orbital HHS and electron-ion coincidence time resolved spectroscopy are presented.
Weber, S. J. Manschwetus, B.; Billon, M.; Bougeard, M.; Breger, P.; Géléoc, M.; Gruson, V.; Lin, N.; Ruchon, T.; Salières, P.; Carré, B.
2015-03-15
We describe the versatile features of the attosecond beamline recently installed at CEA-Saclay on the PLFA kHz laser. It combines a fine and very complete set of diagnostics enabling high harmonic spectroscopy (HHS) through the advanced characterization of the amplitude, phase, and polarization of the harmonic emission. It also allows a variety of photo-ionization experiments using magnetic bottle and COLTRIMS (COLd Target Recoil Ion Momentum Microscopy) electron spectrometers that may be used simultaneously, thanks to a two-foci configuration. Using both passive and active stabilization, special care was paid to the long term stability of the system to allow, using both experimental approaches, time resolved studies with attosecond precision, typically over several hours of acquisition times. As an illustration, applications to multi-orbital HHS and electron-ion coincidence time resolved spectroscopy are presented.
Weber, S J; Manschwetus, B; Billon, M; Böttcher, M; Bougeard, M; Breger, P; Géléoc, M; Gruson, V; Huetz, A; Lin, N; Picard, Y J; Ruchon, T; Salières, P; Carré, B
2015-03-01
We describe the versatile features of the attosecond beamline recently installed at CEA-Saclay on the PLFA kHz laser. It combines a fine and very complete set of diagnostics enabling high harmonic spectroscopy (HHS) through the advanced characterization of the amplitude, phase, and polarization of the harmonic emission. It also allows a variety of photo-ionization experiments using magnetic bottle and COLTRIMS (COLd Target Recoil Ion Momentum Microscopy) electron spectrometers that may be used simultaneously, thanks to a two-foci configuration. Using both passive and active stabilization, special care was paid to the long term stability of the system to allow, using both experimental approaches, time resolved studies with attosecond precision, typically over several hours of acquisition times. As an illustration, applications to multi-orbital HHS and electron-ion coincidence time resolved spectroscopy are presented. PMID:25832212
NASA Astrophysics Data System (ADS)
Gardner, Dennis F.; Porter, Christina L.; Shanblatt, Elisabeth R.; Mancini, Giulia F.; Karl, Robert; Tanksalvala, Michael; Bevis, Charles; Kapteyn, Henry C.; Murnane, Margaret M.; Adams, Daniel E.
2016-03-01
We use EUV coherent microscopy to obtain high-resolution images of buried interfaces, with chemical specificity, in 2+1 dimensions. We perform reflection mode, ptychographic, coherent diffractive imaging with tabletop EUV light, at 29nm, produced by high harmonic generation. Our damascene-style samples consist of copper structures inlaid in SiO2, polished nearly flat with chemical mechanical polishing. We obtain images of both an unaltered damascene as well as one buried below a 100nm thick layer of evaporated aluminum. The aluminum is opaque to visible light and thick enough that neither optical microscopy, SEM, nor AFM can access the buried interface. EUV microscopy is able to image the buried structures, non-destructively, in conditions where other techniques cannot.
NASA Astrophysics Data System (ADS)
Carrera, Juan J.; Son, Sang-Kil; Chu, Shih-I.
2007-06-01
We present an ab initio quantum investigation of the frequency comb structure formed within each high harmonic generation (HHG) power spectrum driven by a train of equal- spacing short laser pulses. The HHG power spectrum of atomic hydrogen is calculated by solving the time-dependent Schr"o dinger equation accurately and efficiently by means of the time- dependent generalized pseudospectral method. We found that the frequency comb structure is preserved within each harmonic. In addition, the repetition frequency of the comb laser depends upon the pulse separation τ and the spectral width of each individual comb fringe is inversely proportional to the number of pulses (n) used. However, the global HHG power spectrum pattern depends only upon the laser frequency and intensity used and is not sensitive to the τ and n parameters. Finally, the frequency comb structure persists even in the presence of appreciable ionization.
Couling, A. J.; Goupee, A. J.; Robertson, A. N.; Jonkman, J. M.
2013-06-01
To better access the abundant offshore wind resource, efforts across the world are being undertaken to develop and improve floating offshore wind turbine technologies. A critical aspect of creating reliable, mature floating wind turbine technology is the development, verification, and validation of efficient computer-aided-engineering (CAE) tools that can be relied upon in the design process. The National Renewable Energy Laboratory (NREL) has created a comprehensive, coupled analysis CAE tool for floating wind turbines, FAST, which has been verified and utilized in numerous floating wind turbine studies. Several efforts are currently underway that leverage the extensive 1/50th-scale DeepCwind wind/wave basin model test dataset, obtained at the Maritime Research Institute Netherlands (MARIN) in 2011, to validate the floating platform functionality of FAST to complement its already validated aerodynamic and structural simulation capabilities. In this paper, further work is undertaken to continue this validation. In particular, the ability of FAST to replicate global response behaviors associated with dynamic wind forces, second-order difference-frequency wave-diffraction forces and their interaction with one another are investigated.
Nonlinear Reflection Process of Linearly Polarized, Broadband Alfvén Waves in the Fast Solar Wind
NASA Astrophysics Data System (ADS)
Shoda, M.; Yokoyama, T.
2016-04-01
Using one-dimensional numerical simulations, we study the elementary process of Alfvén wave reflection in a uniform medium, including nonlinear effects. In the linear regime, Alfvén wave reflection is triggered only by the inhomogeneity of the medium, whereas in the nonlinear regime, it can occur via nonlinear wave-wave interactions. Such nonlinear reflection (backscattering) is typified by decay instability. In most studies of decay instabilities, the initial condition has been a circularly polarized Alfvén wave. In this study we consider a linearly polarized Alfvén wave, which drives density fluctuations by its magnetic pressure force. For generality, we also assume a broadband wave with a red-noise spectrum. In the data analysis, we decompose the fluctuations into characteristic variables using local eigenvectors, thus revealing the behaviors of the individual modes. Different from the circular-polarization case, we find that the wave steepening produces a new energy channel from the parent Alfvén wave to the backscattered one. Such nonlinear reflection explains the observed increasing energy ratio of the sunward to the anti-sunward Alfvénic fluctuations in the solar wind with distance against the dynamical alignment effect.
He Jiansen; Tu Chuanyi; Marsch, Eckart; Yao Shuo
2012-01-20
To determine the wave modes prevailing in solar wind turbulence at kinetic scales, we study the magnetic polarization of small-scale fluctuations in the plane perpendicular to the data sampling direction (namely, the solar wind flow direction, V{sub SW}) and analyze its orientation with respect to the local background magnetic field B{sub 0,local}. As an example, we take only measurements made in an outward magnetic sector. When B{sub 0,local} is quasi-perpendicular to V{sub SW}, we find that the small-scale magnetic-field fluctuations, which have periods from about 1 to 3 s and are extracted from a wavelet decomposition of the original time series, show a polarization ellipse with right-handed orientation. This is consistent with a positive reduced magnetic helicity, as previously reported. Moreover, for the first time we find that the major axis of the ellipse is perpendicular to B{sub 0,local}, a property that is characteristic of an oblique Alfven wave rather than oblique whistler wave. For an oblique whistler wave, the major axis of the magnetic ellipse is expected to be aligned with B{sub 0,local}, thus indicating significant magnetic compressibility, and the polarization turns from right to left handedness as the wave propagation angle ({theta}{sub kB}) increases toward 90 Degree-Sign . Therefore, we conclude that the observation of a right-handed polarization ellipse with orientation perpendicular to B{sub 0,local} seems to indicate that oblique Alfven/ion-cyclotron waves rather than oblique fast-mode/whistler waves dominate in the 'dissipation' range near the break of solar wind turbulence spectra occurring around the proton inertial length.
Yang, Ying-Ying; Scrinzi, Armin; Husakou, Anton; Li, Qian-Guang; Stebbings, Sarah L; Süßmann, Frederik; Yu, Hai-Juan; Kim, Seungchul; Rühl, Eckart; Herrmann, Joachim; Lin, Xue-Chun; Kling, Matthias F
2013-01-28
Coherent XUV sources, which may operate at MHz repetition rate, could find applications in high-precision spectroscopy and for spatio-time-resolved measurements of collective electron dynamics on nanostructured surfaces. We theoretically investigate utilizing the enhanced plasmonic fields in an ordered array of gold nanoparticles for the generation of high-harmonic, extreme-ultraviolet (XUV) radiation. By optimization of the chirp of ultrashort laser pulses incident on the array, our simulations indicate a potential route towards the temporal shaping of the plasmonic near-field and, in turn, the generation of single attosecond pulses. The inherent effects of inhomogeneity of the local fields on the high-harmonic generation are analyzed and discussed. While taking the inhomogeneity into account does not affect the optimal chirp for the generation of a single attosecond pulse, the cut-off energy of the high-harmonic spectrum is enhanced by about a factor of two. PMID:23389200
La-O-Vorakiat, Chan; Siemens, Mark; Murnane, Margaret M; Kapteyn, Henry C; Mathias, Stefan; Aeschlimann, Martin; Grychtol, Patrik; Adam, Roman; Schneider, Claus M; Shaw, Justin M; Nembach, Hans; Silva, T J
2009-12-18
We use few-femtosecond soft x-ray pulses from high-harmonic generation to extract element-specific demagnetization dynamics and hysteresis loops of a compound material for the first time. Using a geometry where high-harmonic beams are reflected from a magnetized Permalloy grating, large changes in the reflected intensity of up to 6% at the M absorption edges of Fe and Ni are observed when the magnetization is reversed. A short pump pulse is used to destroy the magnetic alignment, which allows us to measure the fastest, elementally specific demagnetization dynamics, with 55 fs time resolution. The use of high harmonics for probing magnetic materials promises to combine nanometer spatial resolution, elemental specificity, and femtosecond-to-attosecond time resolution, making it possible to address important fundamental questions in magnetism. PMID:20366281
Podesta, M.; Heidbrink, W. W.; Liu, D.; Ruskov, E.; Bell, R. E.; Darrow, D. S.; Fredrickson, E. D.; Gorelenkov, N. N.; Kramer, G. J.; LeBlanc, B. P.; Medley, S. S.; Roquemore, A. L.; Crocker, N. A.; Kubota, S.; Yuh, H.
2009-05-15
Fast-ion transport induced by Alfven eigenmodes (AEs) is studied in beam-heated plasmas on the National Spherical Torus Experiment [Ono et al., Nucl. Fusion 40, 557 (2000)] through space, time, and energy resolved measurements of the fast-ion population. Fast-ion losses associated with multiple toroidicity-induced AEs (TAEs), which interact nonlinearly and terminate in avalanches, are characterized. A depletion of the energy range >20 keV, leading to sudden drops of up to 40% in the neutron rate over 1 ms, is observed over a broad spatial range. It is shown that avalanches lead to a relaxation of the fast-ion profile, which in turn reduces the drive for the instabilities. The measured radial eigenmode structure and frequency of TAEs are compared with the predictions from a linear magnetohydrodynamics stability code. The partial disagreement suggests that nonlinearities may compromise a direct comparison between experiment and linear theory.
Perkins, R. J.; Hosea, J. C.; Bertelli, N.; Taylor, G.; Wilson, J. R.
2016-07-01
Heating magnetically confined plasmas using waves in the ion-cyclotron range of frequencies typically requires coupling these waves over a steep density gradient. Furthermore, this process has produced an unexpected and deleterious phenomenon on the National Spherical Torus eXperiment (NSTX): a prompt loss of wave power along magnetic field lines in front of the antenna to the divertor. Understanding this loss may be key to achieving effective heating and expanding the operational space of NSTX-Upgrade. Here, we propose that a new type of mode, which conducts a significant fraction of the total wave power in the low-density peripheral plasma, is drivingmore » these losses. We demonstrate the existence of such modes, which are distinct from surface modes and coaxial modes, in a cylindrical cold-plasma model when a half wavelength structure fits into the region outside the core plasma. The latter condition generalizes the previous hypothesis regarding the occurence of the edge losses and may explain why full-wave simulations predict these losses in some cases but not others. If valid, this condition implies that outer gap control is a potential strategy for mitigating the losses in NSTX-Upgrade in addition to raising the magnetic field or influencing the edge density.« less
NASA Astrophysics Data System (ADS)
Perkins, R. J.; Hosea, J. C.; Bertelli, N.; Taylor, G.; Wilson, J. R.
2016-07-01
Heating magnetically confined plasmas using waves in the ion-cyclotron range of frequencies typically requires coupling these waves over a steep density gradient. This process has produced an unexpected and deleterious phenomenon on the National Spherical Torus eXperiment (NSTX): a prompt loss of wave power along magnetic field lines in front of the antenna to the divertor. Understanding this loss may be key to achieving effective heating and expanding the operational space of NSTX-Upgrade. Here, we propose that a new type of mode, which conducts a significant fraction of the total wave power in the low-density peripheral plasma, is driving these losses. We demonstrate the existence of such modes, which are distinct from surface modes and coaxial modes, in a cylindrical cold-plasma model when a half wavelength structure fits into the region outside the core plasma. The latter condition generalizes the previous hypothesis regarding the occurrence of the edge losses and may explain why full-wave simulations predict these losses in some cases but not others. If valid, this condition implies that outer gap control is a potential strategy for mitigating the losses in NSTX-Upgrade in addition to raising the magnetic field or influencing the edge density.
NASA Astrophysics Data System (ADS)
Elboudali, F.; Joulakian, B.
2001-12-01
The (e, 2e) ionization of diatomic lithium Li2 by fast electrons is studied by applying, for the slow ejected electron, an asymptotically exact partial-wave description, which takes into account the diatomic nature of the problem. The ionization is considered as a vertical transition from the lowest vibrational and rotational level of the fundamental electronic state 1Σg+ of Li2 to the fundamental 2Σg+ state of Li2+. After verification of the procedure on the (e, 2e) ionization of diatomic hydrogen H2 for which experimental and theoretical results exist we present the particularities and favourable directions for Li2 targets.
Gosain, S.; Foullon, C.
2012-12-20
We analyze flare-associated transverse oscillations in a quiescent solar prominence on 2010 September 8-9. Both the flaring active region and the prominence were located near the west limb, with a favorable configuration and viewing angle. The full-disk extreme ultraviolet (EUV) images of the Sun obtained with high spatial and temporal resolution by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory show flare-associated lateral oscillations of the prominence sheet. The STEREO-A spacecraft, 81.{sup 0}5 ahead of the Sun-Earth line, provides an on-disk view of the flare-associated coronal disturbances. We derive the temporal profile of the lateral displacement of the prominence sheet by using the image cross-correlation technique. The displacement curve was de-trended and the residual oscillatory pattern was derived. We fit these oscillations with a damped cosine function with a variable period and find that the period is increasing. The initial oscillation period (P{sub 0}) is {approx}28.2 minutes and the damping time ({tau}{sub D}) {approx} 44 minutes. We confirm the presence of fast and slow EUV wave components. Using STEREO-A observations, we derive a propagation speed of {approx}250 km s{sup -1} for the slow EUV wave by applying the time-slice technique to the running difference images. We propose that the prominence oscillations are excited by the fast EUV wave while the increase in oscillation period of the prominence is an apparent effect, related to a phase change due to the slow EUV wave acting as a secondary trigger. We discuss implications of the dual trigger effect for coronal prominence seismology and scaling law studies of damping mechanisms.
Heating of ions by high frequency electromagnetic waves in magnetized plasmas
Zestanakis, P. A.; Kominis, Y.; Hizanidis, K.; Ram, A. K.
2013-07-15
The heating of ions by high frequency electrostatic waves in magnetically confined plasmas has been a paradigm for studying nonlinear wave-particle interactions. The frequency of the waves is assumed to be much higher than the ion cyclotron frequency and the waves are taken to propagate across the magnetic field. In fusion type plasmas, electrostatic waves, like the lower hybrid wave, cannot access the core of the plasma. That is a domain for high harmonic fast waves or electron cyclotron waves—these are primarily electromagnetic waves. Previous studies on heating of ions by two or more electrostatic waves are extended to two electromagnetic waves that propagate directly across the confining magnetic field. While the ratio of the frequency of each wave to the ion cyclotron frequency is large, the frequency difference is assumed to be near the ion cyclotron frequency. The nonlinear wave-particle interaction is studied analytically using a two time-scale canonical perturbation theory. The theory elucidates the effects of various parameters on the gain in energy by the ions—parameters such as the amplitudes and polarizations of the waves, the ratio of the wave frequencies to the cyclotron frequency, the difference in the frequency of the two waves, and the wave numbers associated with the waves. For example, the ratio of the phase velocity of the envelope formed by the two waves to the phase velocity of the carrier wave is important for energization of ions. For a positive ratio, the energy range is much larger than for a negative ratio. So waves like the lower hybrid waves will impart very little energy to ions. The theoretical results are found to be in good agreement with numerical simulations of the exact dynamical equations. The analytical results are used to construct mapping equations, simplifying the derivation of the motion of ions, which are, subsequently, used to follow the evolution of an ion distribution function. The heating of ions can then be
NASA Astrophysics Data System (ADS)
Lilley, M. K.; Breizman, B. N.; Sharapov, S. E.
2009-05-01
The nonlinear evolution of waves excited by the resonant interaction with energetic particles, just above the instability threshold, is shown to depend on the type of relaxation process that restores the unstable distribution function. When dynamical friction dominates over diffusion in the phase space region surrounding the wave-particle resonance, an explosive evolution of the wave is found to be the only solution. This is in contrast with the case of dominant diffusion when the wave may exhibit steady-state, amplitude modulation, chaotic and explosive regimes near marginal stability. The experimentally observed differences between Alfvénic instabilities driven by neutral beam injection and those driven by ion-cyclotron resonance heating are interpreted.
Direct measurement of density oscillation induced by a radio-frequency wave.
Yamada, T; Ejiri, A; Shimada, Y; Oosako, T; Tsujimura, J; Takase, Y; Kasahara, H
2007-08-01
An O-mode reflectometer at a frequency of 25.85 GHz was applied to plasmas heated by the high harmonic fast wave (21 MHz) in the TST-2 spherical tokamak. An oscillation in the phase of the reflected microwave in the rf range was observed directly for the first time. In TST-2, the rf (250 kW) induced density oscillation depends mainly on the poloidal rf electric field, which is estimated to be about 0.2 kV/m rms by the reflectometer measurement. Sideband peaks separated in frequency by ion cyclotron harmonics from 21 MHz, and peaks at ion cyclotron harmonics which are suggested to be quasimodes generated by parametric decay, were detected. PMID:17764321
The K(a)-band 10-kW continuous wave gyrotron with wide-band fast frequency sweep.
Glyavin, M; Luchinin, A; Morozkin, M
2012-07-01
The dual-frequency gyrotron with fast 2% frequency sweep at about 28 GHz is designed to power an electron cyclotron resonance ion source (ECRIS). Operation with an output power of up to 10 kW in CW mode and efficiency of 20% was demonstrated at both frequencies. Frequency manipulation has a characteristic time of about 1 ms and is based on magnetic field variation with an additional low-power coil. Fast frequency sweep will supposedly increase the ion current and the average ion charge of ECRIS. The possibility of 100% power modulation is demonstrated using the same control method. PMID:22852711
The Ka-band 10-kW continuous wave gyrotron with wide-band fast frequency sweep
NASA Astrophysics Data System (ADS)
Glyavin, M.; Luchinin, A.; Morozkin, M.
2012-07-01
The dual-frequency gyrotron with fast 2% frequency sweep at about 28 GHz is designed to power an electron cyclotron resonance ion source (ECRIS). Operation with an output power of up to 10 kW in CW mode and efficiency of 20% was demonstrated at both frequencies. Frequency manipulation has a characteristic time of about 1 ms and is based on magnetic field variation with an additional low-power coil. Fast frequency sweep will supposedly increase the ion current and the average ion charge of ECRIS. The possibility of 100% power modulation is demonstrated using the same control method.
NASA Astrophysics Data System (ADS)
Jia, Guozhang; Xiang, Nong; Wang, Xueyi; Huang, Yueheng; Lin, Yu
2016-01-01
The propagation and mode conversion of lower hybrid waves in an inhomogeneous plasma are investigated by using the nonlinear δf algorithm in a two-dimensional particle-in-cell simulation code based on the gyrokinetic electron and fully kinetic ion (GeFi) scheme [Lin et al., Plasma Phys. Controlled Fusion 47, 657 (2005)]. The characteristics of the simulated waves, such as wavelength, frequency, phase, and group velocities, agree well with the linear theoretical analysis. It is shown that a significant reflection component emerges in the conversion process between the slow mode and the fast mode when the scale length of the density variation is comparable to the local wavelength. The dependences of the reflection coefficient on the scale length of the density variation are compared with the results based on the linear full wave model for cold plasmas. It is indicated that the mode conversion for the waves with a frequency of 2.45 GHz (ω ˜ 3ωLH, where ωLH represents the lower hybrid resonance) and within Tokamak relevant amplitudes can be well described in the linear scheme. As the frequency decreases, the modification due to the nonlinear term becomes important. For the low-frequency waves (ω ˜ 1.3ωLH), the generations of the high harmonic modes and sidebands through nonlinear mode-mode coupling provide new power channels and thus could reduce the reflection significantly.
Phelps, D.A.; Ikezi, H.; Moeller, C.P.
1995-10-01
The impact of a contemplated conversion of the directly driven high power antenna arrays in DIII-D to externally tuned and coupled traveling wave antennas (TWAs) is evaluated based on empirical modeling, computer simulation and low power experiments. A regime of operation is predicted within the TWA passband in which the reflected power from the TWA approaches 0.1% during ELM-free H-mode. Furthermore, this reflected power does not exceed 1% and the optimum phase velocity produced by the TWA decreases less than 5% during ELMs. This resilient operating regime is phase shifted using external tuning stubs, thus providing considerable experimental flexibility. Over 90% plasma coupling efficiency is achieved by recovering the TWA output power using a novel traveling wave recirculator. Combining the above attributes with efficient plasma coupling even at large antenna-plasma distances and the lack of need for dynamic tuning, TWAs appear to offer great promise for ITER.
Chen, Bao-Qin; Zhang, Chao; Hu, Chen-Yang; Liu, Rong-Juan; Li, Zhi-Yuan
2015-08-21
Nonlinear frequency conversion offers an effective way to expand the laser wavelength range based on birefringence phase matching (BPM) or quasi-phase-matching (QPM) techniques in nonlinear crystals. So far, efficient high-harmonic generation is enabled only via multiple cascaded crystals because of the extreme difficulty to simultaneously satisfy BPM or QPM for multiple nonlinear up-conversion processes within a single crystal. Here we report the design and fabrication of a chirped periodic poled lithium niobate (CPPLN) nonlinear crystal that offers controllable multiple QPM bands to support 2nd-8th harmonic generation (HG) simultaneously. Upon illumination of a mid-IR femtosecond pulse laser, we observe the generation of an ultrabroadband visible white light beam corresponding to 5th-8th HG with a record high conversion efficiency of 18%, which is high compared to conventional supercontinuum generation, especially in the HG parts. Our CPPLN scheme opens up a new avenue to explore and engineer novel nonlinear optical interactions in solid state materials for application in ultrafast lasers and broadband laser sources. PMID:26340190
High harmonic generation based time resolved ARPES at 30 eV with 50 meV energy resolution
NASA Astrophysics Data System (ADS)
Rohwer, Timm; Sie, Edbert J.; Mahmood, Fahad; Gedik, Nuh
Angle-resolved photoelectron spectroscopy (ARPES) has emerged as a leading technique in identifying equilibrium properties of complex electronic systems as well as their correlated dynamics. By using femtosecond high harmonic generation (HHG) pulses, this technique can be extended to monitor ultrafast changes in the electronic structure in response to an optical excitation. However, the broad bandwidth of the HHG pulses has been a major experimental limitation. In this contribution, we combine the HHG source with an off-axis Czerny-Turner XUV monochromator and a three-dimensional ``ARTOF'' photoelectron detector to achieve an unrivaled overall energy resolution of 50 meV in multiple harmonic energies. Moreover, the use of a stack of different gratings enables us to fine control both the photon energy and time vs. energy resolution to its particular needs. The performance of our setup is demonstrated by studies on the transition metal dichalcogenide IrTe2 which undergoes a first-order structural transition and accompanied reconstruction of the band structure upon cooling without the characteristic opening of an energy gap.
Seres, J.; Seres, E.; Landgraf, B.; Ecker, B.; Aurand, B.; Kuehl, T.; Spielmann, C.
2014-01-01
We report, for the first time, the generation of high-order harmonics in a spectral range between 200 eV and 1 keV with an unusual spectral property: only every 4th (4i + 1, i∈ℵ) harmonic line appears, whereas the usual high-harmonic spectra consist of every odd (2i + 1) harmonic. We attribute this unique property to the quantum path interference of two extended electron trajectories that experience multiple re-scattering. In the well-established theory, electrons emitted via tunnel ionisation are accelerated by a laser field, return to the ion and recombine. The acceleration typically lasts for less than one optical cycle, and the electrons radiate in the extreme ultraviolet range at recombination. In contrast, for extended trajectories, electrons are accelerated over two or more optical cycles. Here, we demonstrate that two sets of trajectories dominate and provide substantial contributions to the generated soft X-ray radiation because they fulfil the resonance condition for X-ray parametric amplification. PMID:24577220
High-peak-power surface high-harmonic generation at extreme ultra-violet wavelengths from a tape
Shaw, B. H.; Tilborg, J. van; Sokollik, T.; Schroeder, C. B.; McKinney, W. R.; Artemiev, N. A.; Yashchuk, V. V.; Gullikson, E. M.; Leemans, W. P.
2013-07-28
Solid-based surface high-harmonic generation from a tape is experimentally studied. By operating at mildly relativistic normalized laser strengths a{sub 0}≲0.2, harmonics up to the 17th order are efficiently produced in the coherent wake emission (CWE) regime. CWE pulse properties, such as divergence, energy, conversion efficiency, and spectrum, are investigated for various tape materials and drive laser conditions. A clear correlation between surface roughness and harmonic beam divergence is found. At the measured pulse properties for the 15th harmonic (conversion efficiency ∼6.5×10{sup −7}, divergence ∼7−15 mrad), the 100-mJ-level drive laser produces several MWs of extreme ultra-violet pulses. The spooling tape configuration enables multi-Hz operation over thousands of shots, making this source attractive as a seed to the few-Hz laser-plasma-accelerator-driven free-electron laser (FEL). Models indicate that these CWE pulses with MW level powers are sufficient for seed-induced bunching and FEL gain.
NASA Astrophysics Data System (ADS)
Chen, Bao-Qin; Zhang, Chao; Hu, Chen-Yang; Liu, Rong-Juan; Li, Zhi-Yuan
2015-08-01
Nonlinear frequency conversion offers an effective way to expand the laser wavelength range based on birefringence phase matching (BPM) or quasi-phase-matching (QPM) techniques in nonlinear crystals. So far, efficient high-harmonic generation is enabled only via multiple cascaded crystals because of the extreme difficulty to simultaneously satisfy BPM or QPM for multiple nonlinear up-conversion processes within a single crystal. Here we report the design and fabrication of a chirped periodic poled lithium niobate (CPPLN) nonlinear crystal that offers controllable multiple QPM bands to support 2nd-8th harmonic generation (HG) simultaneously. Upon illumination of a mid-IR femtosecond pulse laser, we observe the generation of an ultrabroadband visible white light beam corresponding to 5th-8th HG with a record high conversion efficiency of 18%, which is high compared to conventional supercontinuum generation, especially in the HG parts. Our CPPLN scheme opens up a new avenue to explore and engineer novel nonlinear optical interactions in solid state materials for application in ultrafast lasers and broadband laser sources.
NASA Astrophysics Data System (ADS)
Castro, Alberto; Rubio, Angel; Gross, Eberhard K. U.
2015-08-01
High harmonic generation (HHG) provides a flexible framework for the development of coherent light sources in the extreme-ultraviolet and soft X-ray regimes. However it suffers from low conversion efficiencies as the control of the HHG spectral and temporal characteristics requires manipulating electron trajectories on attosecond time scale. The phase matching mechanism has been employed to selectively enhance specific quantum paths leading to HHG. A few important fundamental questions remain open, among those how much of the enhancement can be achieved by the single-emitter and what is the role of correlations (or the electronic structure) in the selectivity and control of HHG generation. Here we address those questions by examining computationally the possibility of optimizing the HHG spectrum of isolated hydrogen and helium atoms by shaping the slowly varying envelope of a 800 nm, 200-cycles long laser pulse. The spectra are computed with a fully quantum mechanical description, by explicitly computing the time-dependent dipole moment of the systems using a time-dependent density-functional approach (or the single-electron Schrödinger equation for the case of H), on top of a one-dimensional model. The sought optimization corresponds to the selective enhancement of single harmonics, which we find to be significant. This selectivity is entirely due to the single atom response, and not to any propagation or phase-matching effect. Moreover, we see that the electronic correlation plays a role in the determining the degree of optimization that can be obtained.
Fast one-dimensional wave-front propagation for x-ray differential phase-contrast imaging
Wolf, Johannes; Malecki, Andreas; Sperl, Jonathan; Chabior, Michael; Schüttler, Markus; Bequé, Dirk; Cozzini, Cristina; Pfeiffer, Franz
2014-01-01
Numerical wave-optical simulations of X-ray differential phase-contrast imaging using grating interferometry require the oversampling of gratings and object structures in the range of few micrometers. Consequently, fields of view of few millimeters already use large amounts of a computer’s main memory to store the propagating wave front, limiting the scope of the investigations to only small-scale problems. In this study, we apply an approximation to the Fresnel-Kirchhoff diffraction theory to overcome these restrictions by dividing the two-dimensional wave front up into 1D lines, which are processed separately. The approach enables simulations with samples of clinically relevant dimensions by significantly reducing the memory footprint and the execution time and, thus, allows the qualitative comparison of different setup configurations. We analyze advantages as well as limitations and present the simulation of a virtual mammography phantom of several centimeters of size. PMID:25360386
Fast one-dimensional wave-front propagation for x-ray differential phase-contrast imaging.
Wolf, Johannes; Malecki, Andreas; Sperl, Jonathan; Chabior, Michael; Schüttler, Markus; Bequé, Dirk; Cozzini, Cristina; Pfeiffer, Franz
2014-10-01
Numerical wave-optical simulations of X-ray differential phase-contrast imaging using grating interferometry require the oversampling of gratings and object structures in the range of few micrometers. Consequently, fields of view of few millimeters already use large amounts of a computer's main memory to store the propagating wave front, limiting the scope of the investigations to only small-scale problems. In this study, we apply an approximation to the Fresnel-Kirchhoff diffraction theory to overcome these restrictions by dividing the two-dimensional wave front up into 1D lines, which are processed separately. The approach enables simulations with samples of clinically relevant dimensions by significantly reducing the memory footprint and the execution time and, thus, allows the qualitative comparison of different setup configurations. We analyze advantages as well as limitations and present the simulation of a virtual mammography phantom of several centimeters of size. PMID:25360386
High harmonics focusing undulator
Varfolomeev, A.A.; Hairetdinov, A.H.; Smirnov, A.V.; Khlebnikov, A.S.
1995-12-31
It was shown in our previous work that there exist a possibility to enhance significantly the {open_quote}natural{close_quote} focusing properties of the hybrid undulator. Here we analyze the actual undulator configurations which could provide such field structure. Numerical simulations using 2D code PANDIRA were carried out and the enhanced focusing properties of the undulator were demonstrated. The obtained results provide the solution for the beam transport in a very long (short wavelength) undulator schemes.
NASA Astrophysics Data System (ADS)
Boardsen, Scott A.; Hospodarsky, George B.; Kletzing, Craig A.; Engebretson, Mark J.; Pfaff, Robert F.; Wygant, John R.; Kurth, William S.; Averkamp, Terrance F.; Bounds, Scott R.; Green, Jim L.; De Pascuale, Sebastian
2016-04-01
We present a statistical survey of the latitudinal structure of the fast magnetosonic wave mode detected by the Van Allen Probes spanning the time interval of 21 September 2012 to 1 August 2014. We show that statistically, the latitudinal occurrence of the wave frequency (f) normalized by the local proton cyclotron frequency (fcP) has a distinct funnel-shaped appearance in latitude about the magnetic equator similar to that found in case studies. By comparing the observed E/B ratios with the model E/B ratio, using the observed plasma density and background magnetic field magnitude as input to the model E/B ratio, we show that this mode is consistent with the extra-ordinary (whistler) mode at wave normal angles (θk) near 90°. Performing polarization analysis on synthetic waveforms composed from a superposition of extra-ordinary mode plane waves with θk randomly chosen between 87 and 90°, we show that the uncertainty in the derived wave normal is substantially broadened, with a tail extending down to θk of 60°, suggesting that another approach is necessary to estimate the true distribution of θk. We find that the histograms of the synthetically derived ellipticities and θk are consistent with the observations of ellipticities and θk derived using polarization analysis. We make estimates of the median equatorial θk by comparing observed and model ray tracing frequency-dependent probability occurrence with latitude and give preliminary frequency dependent estimates of the equatorial θk distribution around noon and 4 RE, with the median of ~4 to 7° from 90° at f/fcP = 2 and dropping to ~0.5° from 90° at f/fcP = 30. The occurrence of waves in this mode peaks around noon near the equator at all radial distances, and we find that the overall intensity of these waves increases with AE*, similar to findings of other studies.
NASA Astrophysics Data System (ADS)
Rothhardt, J.; Hädrich, S.; Demmler, S.; Krebs, M.; Winters, D. F. A.; Kühl, Th; Stöhlker, Th; Limpert, J.; Tünnermann, A.
2015-11-01
We present novel high photon flux XUV and soft x-ray sources based on high harmonic generation (HHG). The sources employ femtosecond fiber lasers, which can be operated at very high (MHz) repetition rate and average power (>100 W). HHG with such lasers results in ˜1013 photons s-1 within a single harmonic line at ˜40 nm (˜30 eV) wavelength, a photon flux comparable to what is typically available at synchrotron beam lines. In addition, resonant enhancement of HHG can result in narrow-band harmonics with high spectral purity—well suited for precision spectroscopy. These novel light sources will enable seminal studies on electronic transitions in highly-charged ions. For example, at the experimental storage ring 2s1/2-2p1/2 transitions in Li-like ions can be excited up to Z = 47 (˜100 eV transition energy), which provides unique sensitivity to quantum electro-dynamical effects and nuclear corrections. We estimate fluorescence count rates of the order of tens per second, which would enable studies on short-lived isotopes as well. In combination with the Doppler up-shift available in head-on excitation at future heavy-ion storage rings, such as the high energy storage ring, even multi-keV transitions can potentially be excited. Pump-probe experiments with femtosecond resolution could also be feasible and access the lifetime of short-lived excited states, thus providing novel benchmarks for atomic structure theory.
NASA Astrophysics Data System (ADS)
Lin, Ming-Fu; Verkamp, Max A.; Ryland, Elizabeth S.; Benke, Kristin; Zhang, Kaili; Carlson, Michaela; Vura-Weis, Josh
2015-06-01
Extreme ultraviolet (XUV) light source from high-order harmonic generation has been shown to be a powerful tool for core-level spectroscopy. In addition, this light source provides very high temporal resolution (10-18 s to 10-15 s) for time-resolved transient absorption spectroscopy. Most applications of the light source have been limited to the studies of atomic and molecular systems, with technique development focused on optimizing for shorter pulses (i.e. tens of attoseconds) or higher XUV energy (i.e. ~keV range). For the application to general molecular systems in solid and liquid forms, however, the XUV photon flux and stability are highly demanded due to the strong absorption by substrates and solvents. In this case, the main limitation is due to the stability of the high order generation process and the limited bandwidth of the XUV source that gives only discrete even/odd order peaks. Consequently, this results in harmonic artifact noise that overlaps with the resonant signal. In our current study, we utilize a semi-infinite cell for high harmonic generation from two quantum trajectories (i.e. short and long) at over-driven NIR power. This condition, produces broad XUV spectrum without using complicated optics (e.g. hollow-core fibers and double optical gating). This light source allows us to measure the static absorption spectrum of the iron M-edge from a Fe(acac)3 molecular solid film, which shows a resonant feature of 0.01 OD (~2.3% absorption). Moreover, we also investigate how sample roughness affects the static absorption spectrum. We are able to make smooth solar cell precursor materials (i.e. PbI2 and PbBr2) by spin casting and observe iodine (50 eV) and bromine (70 eV) absorption edges in the order of 0.05 OD with minimal harmonic artifact noise.
Low-harmonic magnetosonic waves observed by the Van Allen Probes
NASA Astrophysics Data System (ADS)
Posch, J. L.; Engebretson, M. J.; Olson, C. N.; Thaller, S. A.; Breneman, A. W.; Wygant, J. R.; Boardsen, S. A.; Kletzing, C. A.; Smith, C. W.; Reeves, G. D.
2015-08-01
Purely compressional electromagnetic waves (fast magnetosonic waves), generated at multiple harmonics of the local proton gyrofrequency, have been observed by various types of satellite instruments (fluxgate and search coil magnetometers and electric field sensors), but most recent studies have used data from search coil sensors, and many have been restricted to high harmonics. We report here on a survey of low-harmonic waves, based on electric and magnetic field data from the Electric Fields and Waves double probe and Electric and Magnetic Field Instrument Suite and Integrated Science fluxgate magnetometer instruments, respectively, on the Van Allen Probes spacecraft during its first full precession through all local times, from 1 October 2012 to 13 July 2014. These waves were observed both inside and outside the plasmapause (PP), at L shells from 2.4 to ~6 (the spacecraft apogee), and in regions with plasma number densities ranging from 10 to >1000 cm-3. Consistent with earlier studies, wave occurrence was sharply peaked near the magnetic equator. Waves appeared at all local times but were more common from noon to dusk, and often occurred within 3 h after substorm injections. Outside the PP occurrence maximized broadly across noon, and inside the PP occurrence maximized in the dusk sector, in an extended plasmasphere. We confirm recent ray-tracing studies showing wave refraction and/or reflection at PP-like boundaries. Comparison with waveform receiver data indicates that in some cases these low-harmonic magnetosonic wave events occurred independently of higher-harmonic waves; this indicates the importance of including this population in future studies of radiation belt dynamics.
Fast estimation from above of the maximum wave speed in the Riemann problem for the Euler equations
NASA Astrophysics Data System (ADS)
Guermond, Jean-Luc; Popov, Bojan
2016-09-01
This paper is concerned with the construction of a fast algorithm for computing the maximum speed of propagation in the Riemann solution for the Euler system of gas dynamics with the co-volume equation of state. The novelty in the algorithm is that it stops when a guaranteed upper bound for the maximum speed is reached with a prescribed accuracy. The convergence rate of the algorithm is cubic and the bound is guaranteed for gasses with the co-volume equation of state and the heat capacity ratio γ in the range (1 , 5 / 3 ].
Oh, Se Yeon
2015-01-01
Fast gas chromatography-surface acoustic wave sensor (GC/SAW) has been applied for the detection of the pharmacological volatiles emanated from Houttuynia cordata Thunb which is from South Korea. H. cordata Thunb with unpleasant and fishy odors shows a variety of pharmacological activities such as anti-microbial, anti-inflammatory, anti-cancer, and insect repellent. The aim of this study is to show a novel quality control by GC/SAW methodology for the discrimination of the three different parts of the plant such as leaves, aerial stems, and underground stems for H. cordata Thunb. Sixteen compounds were identified. β-Myrcene, cis-ocimene and decanal are the dominant volatiles for leaves (71.0%) and aerial stems (50.1%). While, monoterpenes (74.6%) are the dominant volatiles for underground stems. 2-Undecanone (1.3%) and lauraldehyde (3.5%) were found to be the characteristic components for leaves. Each part of the plant has its own characteristic fragrance pattern owing to its individual chemical compositions. Moreover, its individual characteristic fragrance patterns are conducive to discrimination of the three different parts of the plant. Consequently, fast GC/SAW can be a useful analytical method for quality control of the different parts of the plant with pharmacological volatiles as it provides second unit analysis, a simple and fragrant pattern recognition. PMID:26046325
NASA Astrophysics Data System (ADS)
Zaleśny, Jarosław; Galant, Grzegorz; Lisak, Mietek; Berczyński, Paweł; Berczyński, Stefan
2011-12-01
In this paper the Berk-Breizman (BB) model of plasma wave instability arising on the stability threshold is considered. An interesting although physically unacceptable feature of the model is the explosive behaviour occurring in the regime of small values of the collision frequency parameter. We present an analytical description of the explosive solution, based on a fitting to the numerical solution of the BB equation with the collision parameter equal to zero. We find that the chaotic behaviour taking place for small but non-zero values of the collision parameter is absent in this case; therefore, chaotic behaviour seems to be an independent phenomenon not directly related to the blow-up regime. The time and the velocity dependence of the distribution function are found numerically and plotted to better understand what actually happens in the model. It allows us to obtain a good qualitative understanding of the time evolution of the mode amplitude including the linear growth of the amplitude, reaching its maximum and then decreasing towards the zero value. Nevertheless, we have no satisfactory physical explanation of the amplitude evolution when the amplitude vanishes at some time and then revives but with an opposite phase.
NASA Astrophysics Data System (ADS)
Zeng, Zhihui; Liu, Menglong; Xu, Hao; Liu, Weijian; Liao, Yaozhong; Jin, Hao; Zhou, Limin; Zhang, Zhong; Su, Zhongqing
2016-06-01
Inspired by an innovative sensing philosophy, a light-weight nanocomposite sensor made of a hybrid of carbon black (CB)/polyvinylidene fluoride (PVDF) has been developed. The nanoscalar architecture and percolation characteristics of the hybrid were optimized in order to fulfil the in situ acquisition of dynamic elastic disturbance from low-frequency vibration to high-frequency ultrasonic waves. Dynamic particulate motion induced by elastic disturbance modulates the infrastructure of the CB conductive network in the sensor, with the introduction of the tunneling effect, leading to dynamic alteration in the piezoresistivity measured by the sensor. Electrical analysis, morphological characterization, and static/dynamic electromechanical response interrogation were implemented to advance our insight into the sensing mechanism of the sensor, and meanwhile facilitate understanding of the optimal percolation threshold. At the optimal threshold (∼6.5 wt%), the sensor exhibits high fidelity, a fast response, and high sensitivity to ultrafast elastic disturbance (in an ultrasonic regime up to 400 kHz), yet with an ultralow magnitude (on the order of micrometers). The performance of the sensor was evaluated against a conventional strain gauge and piezoelectric transducer, showing excellent coincidence, yet a much greater gauge factor and frequency-independent piezoresistive behavior. Coatable on a structure and deployable in a large quantity to form a dense sensor network, this nanocomposite sensor has blazed a trail for implementing in situ sensing for vibration- or ultrasonic-wave-based structural health monitoring, by striking a compromise between ‘sensing cost’ and ‘sensing effectiveness’.
Artem'ev, K V; Berezhetskaya, N K; Kazantsev, S Yu; Kononov, N G; Kossyi, I A; Popov, N A; Tarasova, N M; Filimonova, E A; Firsov, K N
2015-08-13
Results are presented from experimental studies of the initiation of combustion in a stoichiometric methane-oxygen mixture by a freely localized laser spark and by a high-current multispark discharge in a closed chamber. It is shown that, preceding the stage of 'explosive' inflammation of a gas mixture, there appear two luminous objects moving away from the initiator along an axis: a relatively fast and uniform wave of 'incomplete combustion' under laser spark ignition and a wave with a brightly glowing plasmoid behind under ignition from high-current slipping surface discharge. The gas mixtures in both the 'preflame' and developed-flame states are characterized by a high degree of ionization as the result of chemical ionization (plasma density n(e)≈10(12) cm(-3)) and a high frequency of electron-neutral collisions (ν(en)≈10(12) s(-1)). The role of chemical ionization in constructing an adequate theory for the ignition of a gas mixture is discussed. The feasibility of the microwave heating of both the preflame and developed-flame plasma, supplementary to a chemical energy source, is also discussed. PMID:26170426
Artem'ev, K. V.; Berezhetskaya, N. K.; Kazantsev, S. Yu.; Kononov, N. G.; Kossyi, I. A.; Popov, N. A.; Tarasova, N. M.; Filimonova, E. A.; Firsov, K. N.
2015-01-01
Results are presented from experimental studies of the initiation of combustion in a stoichiometric methane–oxygen mixture by a freely localized laser spark and by a high-current multispark discharge in a closed chamber. It is shown that, preceding the stage of ‘explosive’ inflammation of a gas mixture, there appear two luminous objects moving away from the initiator along an axis: a relatively fast and uniform wave of ‘incomplete combustion’ under laser spark ignition and a wave with a brightly glowing plasmoid behind under ignition from high-current slipping surface discharge. The gas mixtures in both the ‘preflame’ and developed-flame states are characterized by a high degree of ionization as the result of chemical ionization (plasma density ne≈1012 cm−3) and a high frequency of electron–neutral collisions (νen≈1012 s−1). The role of chemical ionization in constructing an adequate theory for the ignition of a gas mixture is discussed. The feasibility of the microwave heating of both the preflame and developed-flame plasma, supplementary to a chemical energy source, is also discussed. PMID:26170426
NASA Astrophysics Data System (ADS)
Archer, M. O.; Hartinger, M. D.; Walsh, B. M.; Plaschke, F.; Angelopoulos, V.
2015-12-01
Coupled fast mode resonances (cFMRs) in the outer magnetosphere, between the magnetopause and a turning point, are often invoked to explain observed discrete frequency field line resonances. We quantify their frequency variability, applying cFMR theory to a realistic magnetic field model and magnetospheric density profiles observed over almost half a solar cycle. Our calculations show that cFMRs are most likely around dawn, since the plasmaspheric plumes and extended plasmaspheres often found at noon and dusk can preclude their occurrence. The relative spread (median absolute deviation divided by the median) in eigenfrequencies is estimated to be 28%, 72%, and 55% at dawn, noon, and dusk, respectively, with the latter two chiefly due to density. Finally, at dawn we show that the observed bimodal density distribution results in bimodal cFMR frequencies, whereby the secondary peaks are consistent with the so-called "CMS" frequencies that have previously been attributed to cFMRs.
Kramer, G.J.; Budny, R.V.; Bortolon, A.; Fredrickson, E.D.; Fu, G.Y.; Heidbrink, W.W.; Nazikian, R.; Valeo, E.; Van Zeeland, M.A.
2012-07-27
The numerical methods used in the full particle-orbit following SPIRAL code are described and a number of physics studies performed with the code are presented to illustrate its capabilities. The SPIRAL code is a test-particle code and is a powerful numerical tool to interpret and plan fast-ion experiments in Tokamaks. Gyro-orbit effects are important for fast ions in low-field machines such as NSTX and to a lesser extent in DIII-D. A number of physics studies are interlaced between the description of the code to illustrate its capabilities. Results on heat loads generated by a localized error-field on the DIII-D wall are compared to measurements. The enhanced Triton losses caused by the same localized error-field are calculated and compared to measured neutron signals. MHD activity such as tearing modes and Toroidicity-induced Alfven Eigenmodes (TAEs) have a profound effect on the fast-ion content of Tokamak plasmas and SPIRAL can calculate the effects of MHD activity on the confined and lost fast-ion population as illustrated for a burst of TAE activity in NSTX. The interaction between Ion Cyclotron Range of Frequency (ICRF) heating and fast ions depends solely on the gyro-motion of the fast ions and is captured exactly in the SPIRAL code. A calculation of ICRF absorption on beam ions in ITER is presented. The effects of high harmonic fast wave heating on the beam-ion slowing-down distribution in NSTX is also studied.
ERIC Educational Resources Information Center
Frashure, K. M.; Chen, R. F.; Stephen, R. A.; Bolmer, T.; Lavin, M.; Strohschneider, D.; Maichle, R.; Micozzi, N.; Cramer, C.
2007-01-01
Demonstrating wave processes quantitatively in the classroom using standard classroom tools (such as Slinkys and wave tanks) can be difficult. For example, waves often travel too fast for students to actually measure amplitude or wavelength. Also, when teaching propagating waves, reflections from the ends set up standing waves, which can confuse…
NASA Astrophysics Data System (ADS)
Zhang, Bing
2016-08-01
The discoveries of GW150914, GW151226, and LVT151012 suggest that double black hole (BH–BH) mergers are common in the universe. If at least one of the two merging black holes (BHs) carries a certain amount of charge, possibly retained by a rotating magnetosphere, the inspiral of a BH–BH system would drive a global magnetic dipole normal to the orbital plane. The rapidly evolving magnetic moment during the merging process would drive a Poynting flux with an increasing wind power. The magnetospheric activities during the final phase of the merger would make a fast radio burst (FRB) if the BH charge can be as large as a factor of \\hat{q}∼ ({10}-9{--}{10}-8) of the critical charge Q c of the BH. At large radii, dissipation of the Poynting flux energy in the outflow would power a short-duration high-energy transient, which would appear as a detectable short-duration gamma-ray burst (GRB) if the charge can be as large as \\hat{q}∼ ({10}-5{--}{10}-4). The putative short GRB coincident with GW150914 recorded by Fermi GBM may be interpreted with this model. Future joint GW/GRB/FRB searches would lead to a measurement or place a constraint on the charges carried by isolate BHs.
NASA Astrophysics Data System (ADS)
Wei, Jian-Gong; Peng, Zhen; Lee, Jin-Fa
2012-10-01
The implementation details of a fast direct solver is described herein for solving dense matrix equations from the application of surface integral equation methods for electromagnetic field scatterings from non-penetrable targets. The proposed algorithm exploits the smoothness of the far field and computes a low rank decomposition of the off-diagonal coupling blocks of the matrices through a set of skeletonization processes. Moreover, an artificial surface (the Huygens' surface) is introduced for each clustering group to efficiently account for the couplings between well-separated groups. Furthermore, a recursive multilevel version of the algorithm is presented. Although asymptotically the algorithm would not alter the bleak outlook of the complexity of the worst case scenario,O(N3) for required CPU time where N denotes the number of unknowns, for electrically large electromagnetic (EM) problems; through numerical examples, we found that the proposed multilevel direct solver can scale as good as O(N1.3) in memory consumption and O(N1.8) in CPU time for moderate-sized EM problems. Note that our conclusions are drawn based on a few sample examples that we have conducted and should not be taken as a true complexity analysis for general electrodynamic applications. However, for the fixed frequency (h-refinement) scenario, where the discretization size decreases, the computational complexities observed agree well with the theoretical predictions. Namely, the algorithm exhibits O(N) and O(N1.5) complexities for memory consumption and CPU time, respectively.
NASA Astrophysics Data System (ADS)
Zhang, Bing
2016-08-01
The discoveries of GW150914, GW151226, and LVT151012 suggest that double black hole (BH–BH) mergers are common in the universe. If at least one of the two merging black holes (BHs) carries a certain amount of charge, possibly retained by a rotating magnetosphere, the inspiral of a BH–BH system would drive a global magnetic dipole normal to the orbital plane. The rapidly evolving magnetic moment during the merging process would drive a Poynting flux with an increasing wind power. The magnetospheric activities during the final phase of the merger would make a fast radio burst (FRB) if the BH charge can be as large as a factor of \\hat{q}˜ ({10}-9{--}{10}-8) of the critical charge Q c of the BH. At large radii, dissipation of the Poynting flux energy in the outflow would power a short-duration high-energy transient, which would appear as a detectable short-duration gamma-ray burst (GRB) if the charge can be as large as \\hat{q}˜ ({10}-5{--}{10}-4). The putative short GRB coincident with GW150914 recorded by Fermi GBM may be interpreted with this model. Future joint GW/GRB/FRB searches would lead to a measurement or place a constraint on the charges carried by isolate BHs.
Sun, Dongning; Dong, Yi; Shi, Hongxiao; Xia, Zongyang; Liu, Zhangweiyi; Wang, Siwei; Xie, Weilin; Hu, Weisheng
2014-05-15
We demonstrate a phase-stabilized remote distribution of 100.04 GHz millimeter wave signal over 60 km optical fiber. The phase error of the remote millimeter wave signal induced by fiber transmission delay variations is detected by dual-heterodyne phase error transfer and corrected with a feedback system based on a fast response acousto-optic frequency shifter. The phase noise within the bandwidth of 300 Hz is effectively suppressed; thus, the fast transmission delay variations can be compensated. The residual phase noise of the remote 100.04 GHz signal reaches -56 dBc/Hz at 1 Hz frequency offset from the carrier, and long-term stability of 1.6×10(-16) at 1000 s averaging time is achieved. The fast phase-noise-correcting capability is evaluated by vibrating part of the transmission fiber link. PMID:24978219
NASA Astrophysics Data System (ADS)
MacFarlane, Tyler L.
The Montney Formation of western Canada is one of the largest economically viable gas resource plays in North America with reserves of 449TCF. As an unconventional tight gas play, the well development costs are high due to the hydraulic stimulations necessary for economic success. The Pouce Coupe research project is a multidisciplinary collaboration between the Reservoir Characterization Project (RCP) and Talisman Energy Inc. with the objective of understanding the reservoir to enable the optimization of well placement and completion design. The work in this thesis focuses on identifying the natural fractures in the reservoir that act as the delivery systems for hydrocarbon flow to the wellbore. Characterization of the Montney Formation at Pouce Coupe is based on time-lapse multicomponent seismic surveys that were acquired before and after the hydraulic stimulation of two horizontal wells. Since shear-wave velocities and amplitudes of the PS-waves are known to be sensitive to near-vertical fractures, I utilize isotropic simultaneous seismic inversions on azimuthally-sectored PS1 and PS2 data sets to obtain measurements of the fast and slow shear-velocities. Specifically, I analyze two orthogonal azimuths that are parallel and perpendicular to the strike of the dominant fracture system in the field. These volumes are used to approximate the shear-wave splitting parameter (gamma(s*)) that is closely related to crack density. Since crack density has a significant impact on defining the percolation zone, the work presented in this thesis provides information that can be utilized to reduce uncertainty in the reservoirs fracture model. Isotropic AVO inversion of azimuthally limited PS-waves demonstrates sufficient sensitivity to detect contrast between the anisotropic elastic properties of the reservoir and is capable of identifying regions with high crack density. This is supported by integration with spinner production logs, hydraulic stimulation history of the field
Oliveira, Thiago da Costa; Freitas, Jhonys Machado; Abarza Munoz, Rodrigo Alejandro; Richter, Eduardo Mathias
2016-05-15
In this work, a batch-injection analysis system with square-wave voltammetric (BIA-SWV) detection was applied for the first time to the simultaneous determination of inorganic (zinc) and organic (naphazoline) species. Both compounds were detected in a single run (70 injections h(-1)) with a small injection volume (∼100µL). The calibration curves exhibited linear response range between 3.0 and 21.0μmolL(-1) (r=0.999) for naphazoline and between 10.0 and 60.0μmolL(-1) (r=0.992) for zinc. The detection limits were 0.13 and 0.04μmolL(-1) for zinc and naphazoline, respectively. Good reproducibility was achieved for multiple measurements of a solution containing both species (RSD<1.0%; n=20). The results obtained with the BIA-SWV method for the simultaneous determination of naphazoline and zinc were compared to those obtained by HPLC (naphazoline) and by FAAS (zinc); no statistically significant differences were observed (95% confidence level). PMID:26992525
Bellan, Paul M.
2014-10-15
If either finite electron inertia or finite resistivity is included in 2D magnetic reconnection, the two-fluid equations become a pair of second-order differential equations coupling the out-of-plane magnetic field and vector potential to each other to form a fourth-order system. The coupling at an X-point is such that out-of-plane even-parity electric and odd-parity magnetic fields feed off each other to produce instability if the scale length on which the equilibrium magnetic field changes is less than the ion skin depth. The instability growth rate is given by an eigenvalue of the fourth-order system determined by boundary and symmetry conditions. The instability is a purely growing mode, not a wave, and has growth rate of the order of the whistler frequency. The spatial profile of both the out-of-plane electric and magnetic eigenfunctions consists of an inner concave region having extent of the order of the electron skin depth, an intermediate convex region having extent of the order of the equilibrium magnetic field scale length, and a concave outer exponentially decaying region. If finite electron inertia and resistivity are not included, the inner concave region does not exist and the coupled pair of equations reduces to a second-order differential equation having non-physical solutions at an X-point.
Study of nonlinear MHD equations governing the wave propagation in twisted coronal loops
NASA Technical Reports Server (NTRS)
Parhi, S.; DeBruyne, P.; Goossens, M.; Zhelyazkov, I.
1995-01-01
The solar corona, modelled by a low beta, resistive plasma slab, sustains MHD wave propagations due to shearing footpoint motions in the photosphere. By using a numerical algorithm the excitation and nonlinear development of MHD waves in twisted coronal loops are studied. The plasma responds to the footpoint motion by sausage waves if there is no twist. The twist in the magnetic field of the loop destroys initially developed sausage-like wave modes and they become kinks. The transition from sausage to kink modes is analyzed. The twist brings about mode degradation producing high harmonics and this generates more complex fine structures. This can be attributed to several local extrema in the perturbed velocity profiles. The Alfven wave produces remnants of the ideal 1/x singularity both for zero and non-zero twist and this pseudo-singularity becomes less pronounced for larger twist. The effect of nonlinearity is clearly observed by changing the amplitude of the driver by one order of magnitude. The magnetosonic waves also exhibit smoothed remnants of ideal logarithmic singularities when the frequency of the driver is correctly chosen. This pseudo-singularity for fast waves is absent when the coronal loop does not undergo any twist but becomes pronounced when twist is included. On the contrary, it is observed for slow waves even if there is no twist. Increasing the twist leads to a higher heating rate of the loop. The larger twist shifts somewhat uniformly distributed heating to layers inside the slab corresponding to peaks in the magnetic field strength.
NASA Astrophysics Data System (ADS)
Michel, N.; Stoitsov, M. V.
2008-04-01
The fast computation of the Gauss hypergeometric function F12 with all its parameters complex is a difficult task. Although the F12 function verifies numerous analytical properties involving power series expansions whose implementation is apparently immediate, their use is thwarted by instabilities induced by cancellations between very large terms. Furthermore, small areas of the complex plane, in the vicinity of z=e, are inaccessible using F12 power series linear transformations. In order to solve these problems, a generalization of R.C. Forrey's transformation theory has been developed. The latter has been successful in treating the F12 function with real parameters. As in real case transformation theory, the large canceling terms occurring in F12 analytical formulas are rigorously dealt with, but by way of a new method, directly applicable to the complex plane. Taylor series expansions are employed to enter complex areas outside the domain of validity of power series analytical formulas. The proposed algorithm, however, becomes unstable in general when |a|, |b|, |c| are moderate or large. As a physical application, the calculation of the wave functions of the analytical Pöschl-Teller-Ginocchio potential involving F12 evaluations is considered. Program summaryProgram title: hyp_2F1, PTG_wf Catalogue identifier: AEAE_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEAE_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 6839 No. of bytes in distributed program, including test data, etc.: 63 334 Distribution format: tar.gz Programming language: C++, Fortran 90 Computer: Intel i686 Operating system: Linux, Windows Word size: 64 bits Classification: 4.7 Nature of problem: The Gauss hypergeometric function F12, with all its parameters complex, is uniquely
Jafari, Safiye; Faridbod, Farnoush; Norouzi, Parviz; Dezfuli, Amin Shiralizadeh; Ajloo, Davood; Mohammadipanah, Fatemeh; Ganjali, Mohammad Reza
2015-10-01
A new strategy was introduced for ssDNA immobilization on a modified glassy carbon electrode. The electrode surface was modified using polyaniline and chemically reduced graphene oxide decorated cerium oxide nanoparticles (CeO2NPs-RGO). A single-stranded DNA (ssDNA) probe was immobilized on the modified electrode surface. Fast Fourier transform square wave voltammetry (FFT-SWV) was applied as detection technique and [Ru(bpy)3](2+/3+) redox signal was used as electrochemical marker. The hybridization of ssDNA with its complementary target caused a dramatic decrease in [Ru(bpy)3](2+/3+) FFT-SW signal. The proposed electrochemical biosensor was able to detect Aeromonas hydrophila DNA oligonucleotide sequence encoding aerolysin protein. Under optimal conditions, the biosensor showed excellent selectivity toward complementary sequence in comparison with noncomplementary and two-base mismatch sequences. The dynamic linear range of this electrochemical DNA biosensor for detecting 20-mer oligonucleotide sequence of A. hydrophila was from 1 × 10(-15) to 1 × 10(-8) mol L(-1). The proposed biosensor was successfully applied for the detection of DNA extracted from A. hydrophila in fish pond water up to 0.01 μg mL(-1) with RSD of 5%. Besides, molecular docking was applied to consider the [Ru(bpy)3](2+/3+) interaction with ssDNA before and after hybridization. PMID:26454462
NASA Astrophysics Data System (ADS)
Lin, Yuanqing; Lech, Gwen; Nioka, Shoko; Intes, Xavier; Chance, Britton
2002-08-01
This article focuses on optimizing the signal to noise ratio (SNR) of a three-wavelength light-emitting diode (LED) near-infrared continuous-wave (cw) imager and its application to in vivo muscle metabolism measurement. The shot-noise limited SNR is derived and calculated to be 2 x104 for the physiological blood concentrations of muscle. Aiming at shot-noise limited SNR performance and fast imaging, we utilize sample and hold circuits to reduce high-frequency noise. These circuits have also been designed to be parallel integrating, through which SNR of 2 x103 and 2 Hz imaging acquisition rate have been achieved when the probe is placed on a muscle model. The noise corresponds to 2 x10-4 optical density error, which suggests an in vitro resolution of 15. 4 nM blood volume and 46.8 nM deoxygenation changes. A 48 dB digital gain control circuit with 256 steps is employed to enlarge the dynamic range of the imager. We utilize cuff ischemia as a living model demonstration and its results are reported. The instrument is applied during exercise to measure the changes of blood volume and deoxygenation, which provides important information about muscle metabolism. We find that the primary source of noise encountered during exercise experiment is from the random motion of muscle. The results demonstrate that the LED cw imager is ideal for the noninvasive study of muscle metabolism.
Rothhardt, Jan; Hädrich, Steffen; Shamir, Yariv; Tschnernajew, Maxim; Klas, Robert; Hoffmann, Armin; Tadesse, Getnet K; Klenke, Arno; Gottschall, Thomas; Eidam, Tino; Limpert, Jens; Tünnermann, Andreas; Boll, Rebecca; Bomme, Cedric; Dachraoui, Hatem; Erk, Benjamin; Di Fraia, Michele; Horke, Daniel A; Kierspel, Thomas; Mullins, Terence; Przystawik, Andreas; Savelyev, Evgeny; Wiese, Joss; Laarmann, Tim; Küpper, Jochen; Rolles, Daniel
2016-08-01
Unraveling and controlling chemical dynamics requires techniques to image structural changes of molecules with femtosecond temporal and picometer spatial resolution. Ultrashort-pulse x-ray free-electron lasers have significantly advanced the field by enabling advanced pump-probe schemes. There is an increasing interest in using table-top photon sources enabled by high-harmonic generation of ultrashort-pulse lasers for such studies. We present a novel high-harmonic source driven by a 100 kHz fiber laser system, which delivers 10^{11} photons/s in a single 1.3 eV bandwidth harmonic at 68.6 eV. The combination of record-high photon flux and high repetition rate paves the way for time-resolved studies of the dissociation dynamics of inner-shell ionized molecules in a coincidence detection scheme. First coincidence measurements on CH_{3}I are shown and it is outlined how the anticipated advancement of fiber laser technology and improved sample delivery will, in the next step, allow pump-probe studies of ultrafast molecular dynamics with table-top XUV-photon sources. These table-top sources can provide significantly higher repetition rates than the currently operating free-electron lasers and they offer very high temporal resolution due to the intrinsically small timing jitter between pump and probe pulses. PMID:27505779
NASA Astrophysics Data System (ADS)
Dundas, Daniel
2012-05-01
A mixed quantum-classical approach is introduced which allows the dynamical response of molecules driven far from equilibrium to be modeled. This method is applied to the interaction of molecules with intense, short-duration laser pulses. The electronic response of the molecule is described using time-dependent density functional theory (TDDFT) and the resulting Kohn-Sham equations are solved numerically using finite difference techniques in conjunction with local and global adaptations of an underlying grid in curvilinear coordinates. Using this approach, simulations can be carried out for a wide range of molecules and both all-electron and pseudopotential calculations are possible. The approach is applied to the study of high harmonic generation in N2 and benzene using linearly polarized laser pulses and, to the best of our knowledge, the results for benzene represent the first TDDFT calculations of high harmonic generation in benzene using linearly polarized laser pulses. For N2 an enhancement of the cut-off harmonics is observed whenever the laser polarization is aligned perpendicular to the molecular axis. This enhancement is attributed to the symmetry properties of the Kohn-Sham orbital that responds predominantly to the pulse. In benzene we predict that a suppression in the cut-off harmonics occurs whenever the laser polarization is aligned parallel to the molecular plane. We attribute this suppression to the symmetry-induced response of the highest-occupied molecular orbital.
Manschwetus, Bastian; Lin, Nan; Rothhardt, Jan; Guichard, Roland; Auguste, Thierry; Camper, Antoine; Breger, Pierre; Caillat, Jérémie; Géléoc, Marie; Ruchon, Thierry; Taïeb, Richard; Carré, Bertrand; Salières, Pascal
2015-06-11
We present characterizations of the attosecond pulse train produced in the high harmonic generation (HHG) from SF6 molecules irradiated by a strong pulsed laser field at 800 nm. At harmonic order 17, we observe a minimum in the amplitude of the emitted spectrum and a corresponding distortion in the phase. Our experimental results are compared to two models: a multicenter interference model focused on the effect of the structure of the SF6 molecule in HHG and a model focused on the interferences between multiple ionization channels in HHG. We find that the experimental results agree very well with the multiple ionization channels model, illustrating that HHG in molecules can be very complex and that it provides insights of the intramolecular electron dynamics during the interaction process. PMID:25812633
Liu Wei; Title, Alan M.; Schrijver, Carolus J.; Aschwanden, Markus J.; De Pontieu, Bart; Tarbell, Theodore D.; Zhao Junwei; Ofman, Leon
2011-07-20
Quasi-periodic propagating fast mode magnetosonic waves in the solar corona were difficult to observe in the past due to relatively low instrument cadences. We report here evidence of such waves directly imaged in EUV by the new Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory. In the 2010 August 1 C3.2 flare/coronal mass ejection event, we find arc-shaped wave trains of 1%-5% intensity variations (lifetime {approx}200 s) that emanate near the flare kernel and propagate outward up to {approx}400 Mm along a funnel of coronal loops. Sinusoidal fits to a typical wave train indicate a phase velocity of 2200 {+-} 130 km s{sup -1}. Similar waves propagating in opposite directions are observed in closed loops between two flare ribbons. In the k-{omega} diagram of the Fourier wave power, we find a bright ridge that represents the dispersion relation and can be well fitted with a straight line passing through the origin. This k-{omega} ridge shows a broad frequency distribution with power peaks at 5.5, 14.5, and 25.1 mHz. The strongest signal at 5.5 mHz (period 181 s) temporally coincides with quasi-periodic pulsations of the flare, suggesting a common origin. The instantaneous wave energy flux of (0.1-2.6) x 10{sup 7} erg cm{sup -2} s{sup -1} estimated at the coronal base is comparable to the steady-state heating requirement of active region loops.
NASA Astrophysics Data System (ADS)
Adcock, T. A. A.; Taylor, P. H.
2016-01-01
The non-linear Schrödinger equation and its higher order extensions are routinely used for analysis of extreme ocean waves. This paper compares the evolution of individual wave-packets modelled using non-linear Schrödinger type equations with packets modelled using fully non-linear potential flow models. The modified non-linear Schrödinger Equation accurately models the relatively large scale non-linear changes to the shape of wave-groups, with a dramatic contraction of the group along the mean propagation direction and a corresponding extension of the width of the wave-crests. In addition, as extreme wave form, there is a local non-linear contraction of the wave-group around the crest which leads to a localised broadening of the wave spectrum which the bandwidth limited non-linear Schrödinger Equations struggle to capture. This limitation occurs for waves of moderate steepness and a narrow underlying spectrum.
Kuwahata, A.; Igami, H.; Kawamori, E.; Kogi, Y.; Inomoto, M.; Ono, Y.
2014-10-15
We report the observation of electromagnetic radiation at high harmonics of the electron cyclotron frequency that was considered to be converted from electrostatic waves called electron Bernstein waves (EBWs) during magnetic reconnection in laboratory overdense plasmas. The excitation of EBWs was attributed to the thermalization of electrons accelerated by the reconnection electric field around the X-point. The radiative process discussed here is an acceptable explanation for observed radio waves pulsation associated with major flares.
NASA Astrophysics Data System (ADS)
Raghuvanshi, Nimisha; Singh, Avinash
2010-10-01
Spin waves in the (0, π) and (0, π, π) ordered spin-density-wave (SDW) states of the t-t' Hubbard model are investigated at finite doping. In the presence of small t', these composite ferro-antiferromagnetic (F-AF) states are found to be strongly stabilized at finite hole doping due to enhanced carrier-induced ferromagnetic spin couplings as in metallic ferromagnets. Anisotropic spin-wave velocities, a spin-wave energy scale of around 200 meV, reduced magnetic moment and rapid suppression of magnetic order with electron doping x (corresponding to F substitution of O atoms in LaO1 - xFxFeAs or Ni substitution of Fe atoms in BaFe2 - xNixAs2) obtained in this model are in agreement with observed magnetic properties of doped iron pnictides.
NASA Astrophysics Data System (ADS)
Chu, Xi; Groenenboom, Gerrit C.
2013-01-01
A minimum at ˜39 eV is observed in the high-harmonic-generation spectra of N2 for several laser intensities and frequencies. This minimum appears to be invariant for different molecular orientations. We reproduce this minimum for a set of laser parameters and orientations in time-dependent density-functional-theory calculations, which also render orientation-dependent maxima at 23-26 eV. Photon energies of these maxima overlap with ionization potentials of excited states observed in photoelectron spectra. Time profile analysis shows that these maxima are caused by resonance-enhanced multiphoton excitation. We propose a four-step mechanism, in which an additional excitation step is added to the well-accepted three-step model. Excitation to a linear combination of Rydberg states c4'1Σu+ and c31Πu gives rise to an orientation-invariant minimum analogous to the “Cooper minimum” in argon. When the molecular axis is parallel to the polarization direction of the field, a radial node goes through the atomic centers, and hence the Cooper-like minimum coincides with the minimum predicted by a modified two-center interference model that considers the de-excitation of the ion and symmetry of the Rydberg orbital.
The K{sub a}-band 10-kW continuous wave gyrotron with wide-band fast frequency sweep
Glyavin, M.; Luchinin, A.; Morozkin, M.
2012-07-15
The dual-frequency gyrotron with fast 2% frequency sweep at about 28 GHz is designed to power an electron cyclotron resonance ion source (ECRIS). Operation with an output power of up to 10 kW in CW mode and efficiency of 20% was demonstrated at both frequencies. Frequency manipulation has a characteristic time of about 1 ms and is based on magnetic field variation with an additional low-power coil. Fast frequency sweep will supposedly increase the ion current and the average ion charge of ECRIS. The possibility of 100% power modulation is demonstrated using the same control method.
Luppi, Eleonora; Head-Gordon, Martin
2013-10-28
We study the role of Rydberg bound-states and continuum levels in the field-induced electronic dynamics associated with the High-Harmonic Generation (HHG) spectroscopy of the hydrogen atom. Time-dependent configuration-interaction (TD-CI) is used with very large atomic orbital (AO) expansions (up to L= 4 with sextuple augmentation and off-center functions) to describe the bound Rydberg levels, and some continuum levels. To address the lack of ionization losses in TD-CI with finite AO basis sets, we employed a heuristic lifetime for energy levels above the ionization potential. The heuristic lifetime model is compared against the conventional atomic orbital treatment (infinite lifetimes), and a third approximation which is TD-CI using only the bound levels (continuum lifetimes go to zero). The results suggest that spectra calculated using conventional TD-CI do not converge with increasing AO basis set size, while the zero lifetime and heuristic lifetime models converge to qualitatively similar spectra, with implications for how best to apply bound state electronic structure methods to simulate HHG. The origin of HHG spectral features including the cutoff and extent of interference between peaks is uncovered by separating field-induced coupling between different types of levels (ground state, bound Rydberg levels, and continuum) in the simulated electronic dynamics. Thus the origin of deviations between the predictions of the semi-classical three step model and the full simulation can be associated with particular physical contributions, which helps to explain both the successes and the limitations of the three step model.
NASA Technical Reports Server (NTRS)
Correia, E.; Kaufmann, P.; Costa, J. E. R.; Vaz, A. M. Z.; Dennis, B. R.
1986-01-01
The solar burst of 21 May 1984 presented a number of unique features. The time profile consisted of seven major structures (seconds), with a turnover frequency or approx. 90 GHz, well correlated in time to hard X-ray emission. Each structure consisted of multiple fast pulses (.1 seconds), which were analyzed in detail. A proportionality between the repetition rate of the pulses and the burst fluxes at 90 GHz and or approx. 100 keV hard X-rays, and an inverse proportionality between repetition rates and hard X-rays power law indices have been found. A synchrotron/inverse Compton model has been applied to explain the emission of the fast burst structures, which appear to be possible for the first three or four structures.
NASA Technical Reports Server (NTRS)
Correia, E.; Kaufmann, P.; Costa, J. E. R.; Zodivaz, A. M.; Dennis, B. R.
1986-01-01
The solar burst of 21 May 1984, presented a number of unique features. The time profile consisted of seven major structures (seconds), with a turnover frequency of greater than or approximately 90 GHz, well correlated in time to hard X-ray emission. Each structure consisted of multiple fast pulses (0.1 seconds), which were analyzed in detail. A proportionality between the repetition rate of the pulses and the burst fluxes at 90 GHz and greater than or approximately 100 keV hard X-rays, and an inverse proportionality between repetition rates and hard X-ray power law indices were found. A synchrotron/inverse Compton model was applied to explain the emission of the fast burst structures, which appear to be possible for the first three or four structures.
[The design of handheld fast ECG detector].
Shi, Bo; Zhang, Genxuan; Tsau, Young
2013-03-01
A new handheld fast ECG detector based on low gain amplifier, the high resolution analog to digital converter, the real-time digital filter, fast P-QRS-T wave detection and abstraction algorithm was designed. The results showed that the ECG detector can meet the requirements of fast detecting heart rate and ECG P-QRS-T waveforms. PMID:23777065
NASA Astrophysics Data System (ADS)
Kim, E.-H.; Boardsen, S. A.; Johnson, J. R.; Slavin, J. A.
2016-02-01
This chapter provides a brief overview of the observed characteristics of ultra-low-frequency (ULF) waves at Mercury. It shows how field-aligned propagating ULF waves at Mercury can be generated by externally driven fast compressional waves (FWs) via mode conversion at the ion-ion hybrid resonance. Then, the chapter reviews the interpretation that the strong magnetic compressional waves near and its harmonics observed with 20 of Mercury's magnetic equator could be the ion Bernstein wave (IBW) mode. A recent statistical study of ULF waves at Mercury based on MESSENGER data reported the occurrence and polarization of the detected waves. The chapter further introduces the field line resonance and the electromagnetic ion Bernstein waves to explain such waves, and shows that both theories can partially explain the observations.
NASA Astrophysics Data System (ADS)
Yan, Limei; He, Jiansen; Zhang, Lei; Tu, Chuanyi; Marsch, Eckart; Chen, Christopher H. K.; Wang, Xin; Wang, Linghua; Wicks, Robert T.
2016-01-01
Intensive studies have been conducted to understand the anisotropy of solar wind turbulence. However, the anisotropy of Elsässer variables ({{\\boldsymbol{Z}}}+/- ) in 2D wave-vector space has yet to be investigated. Here we first verify the transformation based on the projection-slice theorem between the power spectral density {{PSD}}2{{D}}({k}\\parallel ,{k}\\perp ) and the spatial correlation function {{CF}}2{{D}}({r}\\parallel ,{r}\\perp ). Based on the application of the transformation to the magnetic field and the particle measurements from the WIND spacecraft, we investigate the spectral anisotropy of Elsässer variables ({{\\boldsymbol{Z}}}+/- ), and the distribution of residual energy {E}{{R}}, Alfvén ratio {R}{{A}}, and Elsässer ratio {R}{{E}} in the ({k}\\parallel ,{k}\\perp ) space. The spectra {{PSD}}2{{D}}({k}\\parallel ,{k}\\perp ) of {\\boldsymbol{B}}, {\\boldsymbol{V}}, and {{\\boldsymbol{Z}}}{major} (the larger of {{\\boldsymbol{Z}}}+/- ) show a similar pattern that {{PSD}}2{{D}}({k}\\parallel ,{k}\\perp ) is mainly distributed along a ridge inclined toward the k⊥ axis. This is probably the signature of the oblique Alfvénic fluctuations propagating outwardly. Unlike those of {\\boldsymbol{B}}, {\\boldsymbol{V}}, and {{\\boldsymbol{Z}}}{major}, the spectrum {{PSD}}2{{D}}({k}\\parallel ,{k}\\perp ) of {{\\boldsymbol{Z}}}{minor} is distributed mainly along the k⊥ axis. Close to the k⊥ axis, | {E}{{R}}| becomes larger while {R}{{A}} becomes smaller, suggesting that the dominance of magnetic energy over kinetic energy becomes more significant at small k∥. {R}{{E}} is larger at small k∥, implying that {{PSD}}2{{D}}({k}\\parallel ,{k}\\perp ) of {{\\boldsymbol{Z}}}{minor} is more concentrated along the k⊥ direction as compared to that of {{\\boldsymbol{Z}}}{major}. The residual energy condensate at small k∥ is consistent with simulation results in which {E}{{R}} is spontaneously generated by Alfvén wave interaction.
Two-wave propagation in in vitro swine distal ulna
NASA Astrophysics Data System (ADS)
Mano, Isao; Horii, Kaoru; Matsukawa, Mami; Otani, Takahiko
2015-07-01
Ultrasonic transmitted waves were obtained in an in vitro swine distal ulna specimen, which mimics a human distal radius, that consists of interconnected cortical bone and cancellous bone. The transmitted waveforms appeared similar to the fast waves, slow waves, and overlapping fast and slow waves measured in the specimen after removing the surface cortical bone (only cancellous bone). In addition, the circumferential waves in the cortical bone and water did not affect the fast and slow waves. This suggests that the fast-and-slow-wave phenomenon can be observed in an in vivo human distal radius.
NASA Astrophysics Data System (ADS)
Simoniello, R.; Finsterle, W.; García, R. A.; Salabert, D.; Jiménez, A.; Elsworth, Y.; Schunker, H.
2010-06-01
We used long duration, high quality, unresolved (Sun-as-a star) observations collected by the ground based network BiSON and by the instruments GOLF and VIRGO on board the ESA/NASA SOHO satellite to search for solar-cycle-related changes in mode characteristics in velocity and continuum intensity for the frequency range between 2.5 mHz <ν< 6.8 mHz. Over the ascending phase of solar cycle 23 we found a suppression in the p-mode amplitudes both in the velocity and intensity data between 2.5 mHz <ν< 4.5 mHz with a maximum suppression for frequencies in the range between 2.5 mHz <ν< 3.5 mHz. The size of the amplitude suppression is 13 ± 2 per cent for the velocity and 9 ± 2 per cent for the intensity observations. Over the range of 4.5 mHz <ν< 5.5 mHz the findings hint within the errors to a null change both in the velocity and intensity amplitudes. At still higher frequencies, in the so called High-frequency Interference Peaks (HIPs) between 5.8 mHz <ν< 6.8 mHz, we found an enhancement in the velocity amplitudes with the maximum 36 ± 7 per cent occurring for 6.3 mHz <ν< 6.8 mHz. However, in intensity observations we found a rather smaller enhancement of about 5 ± 2 per cent in the same interval. There is evidence that the frequency dependence of solar-cycle velocity amplitude changes is consistent with the theory behind the mode conversion of acoustic waves in a non-vertical magnetic field, but there are some problems with the intensity data, which may be due to the height in the solar atmosphere at which the VIRGO data are taken.
NASA Astrophysics Data System (ADS)
Tanaka, Keiichi; Hayashi, Masato; Ohtsuki, Mitsuhiko; Harada, Kensuke; Tanaka, Takehiko
2010-06-01
Ortho-para mixing interaction due to the coupling of nuclear and electron spins was detected for the first time by millimeter-wave spectroscopy of deuterated vinyl radicals, H_2CCD and D_2CCD, of which the ground states are split by the tunneling motion of the α deuteron into two components 0^+ and 0^-, whose separations have been determined to be Δ E_0 = 1186.644(16) and 771.978(18) MHz, respectively. The observed tunneling-rotation spectra are significantly perturbed by the othro-para mixing interaction expressed by < 0^± |H'|0^mprangle = (δ aF(β)/2) S \\cdot(I_β 1-I_β 2), where I_β 1 and I_β 2 are spins of the two hydrogen nuclei in the β position and S is the electron spin, which connects rotational levels in the 0^+ and 0^- states, one being an ortho level and the other a para level. The δ aF(β) constants for H_2CCD and D_2CCD have been determined to be 68.06(53) and 10.63(94) MHz, respectively, consistent each other within the isotopic mass relation. The othro and para states are mixed by about 0.097% and 0.0123% due to this interaction. The δ aF constant for H_2CCH should be similar to that for H_2CCD because of the same probability density of the unpaired electron at the β protons, but could not be determined independently in our previous study. It is because the mixing of para- and ortho-levels of about 0.00044% is much smaller than that for H_2CCD due to the large tunneling splitting of Δ E_0=16271.8429(59) MHz. The rate constant of para to ortho (I_β = 0 → 1) conversion is predicted as 1.2× 10^5 s-1 torr-1 for H_2CCD, suggesting extremely rapid mutual conversion between ortho and para nuclear spin isomers of H_2CCD, which is more than 106 times faster compared with that in closed shell molecules such as H_2CO and H_2CCH_2. K. Tanaka, M. Hayashi, M. Ohtsuki, K. Harada, T. Tanaka, J. Chem. Phys., 131, 111101 (2009). K. Tanaka, M. Toshimitsu, K. Harada, T. Tanaka, J. Chem. Phys., 120, 3604 (2004).
Emelina, A S; Emelin, M Yu; Ryabikin, M Yu
2014-05-30
Based on the analytical quantum-mechanical description in the framework of the modified strong-field approximation, we have investigated high harmonic generation of mid-IR laser radiation in neutral gases taking into account the depletion of bound atomic levels of the working medium and the electron magnetic drift in a high-intensity laser field. The possibility is shown to generate high-order harmonics with photon energies greater than 10 keV under irradiation of helium atoms by intense femtosecond laser pulses with a centre wavelength of 8 – 10.6 μm. (interaction of radiation with matter)
Cosmology: Home of a fast radio burst
NASA Astrophysics Data System (ADS)
Lorimer, Duncan
2016-02-01
Our understanding of fast radio bursts -- intense pulses of radio waves -- and their use as cosmic probes promises to be transformed now that one burst has been associated with a galaxy of known distance from Earth. See Letter p.453
El-Shenawee, M; Rappaport, C; Silevitch, M
2001-12-01
We present a statistical study of the electric field scattered from a three-dimensional penetrable object buried under a two-dimensional random rough surface. Monte Carlo simulations using the steepest-descent fast multipole method (SDFMM) are conducted to calculate the average and the standard deviation of the near-zone scattered fields. The SDFMM, originally developed at the University of Illinois at Urbana-Champaign, has been modified to calculate the unknown surface currents both on the rough ground and on the buried object that are due to excitation by a tapered Gaussian beam. The rough ground medium used is an experimentally measured typical dry Bosnian soil with 3.8% moisture, while the buried object represents a plastic land mine modeled as an oblate spheroid with dimensions and burial depth smaller than the free-space wavelength. Both vertical and horizontal polarizations for the incident waves are studied. The numerical results show that the TNT mine signature is almost 5% of the total field scattered from the ground. Moreover, relatively recognizable object signatures are observed even when the object is buried under the tail of the incident beam. Interestingly, even for the small surface roughness parameters considered, the standard deviation of the object signature is almost 30% of the signal itself, indicating significant clutter distortion that is due to the roughness of the ground. PMID:11760205
Van Dyke, William J.
1992-01-01
A fast valve is disclosed that can close on the order of 7 milliseconds. It is closed by the force of a compressed air spring with the moving parts of the valve designed to be of very light weight and the valve gate being of wedge shaped with O-ring sealed faces to provide sealing contact without metal to metal contact. The combination of the O-ring seal and an air cushion create a soft final movement of the valve closure to prevent the fast air acting valve from having a harsh closing.
Van Dyke, W.J.
1992-04-07
A fast valve is disclosed that can close on the order of 7 milliseconds. It is closed by the force of a compressed air spring with the moving parts of the valve designed to be of very light weight and the valve gate being of wedge shaped with O-ring sealed faces to provide sealing contact without metal to metal contact. The combination of the O-ring seal and an air cushion create a soft final movement of the valve closure to prevent the fast air acting valve from having a harsh closing. 4 figs.
ERIC Educational Resources Information Center
Essexville-Hampton Public Schools, MI.
Described are components of Project FAST (Functional Analysis Systems Training) a nationally validated project to provide more effective educational and support services to learning disordered children and their regular elementary classroom teachers. The program is seen to be based on a series of modules of delivery systems ranging from mainstream…
Impulsively generated fast coronal pulsations
NASA Technical Reports Server (NTRS)
Edwin, P. M.; Roberts, B.
1986-01-01
Rapid oscillations in the corona are discussed from a theoretical standpoint, developing some previous work on ducted, fast magnetoacoustic waves in an inhomogeneous medium. In the theory, impulsively (e.g., flare) generated mhd (magnetohydrodynamic) waves are ducted by regions of low Alfven speed (high density) such as coronal loops. Wave propagation in such ducts is strongly dispersive and closely akin to the behavior of Love waves in seismology, Pekeris waves in oceanography and guided waves in fiber optics. Such flare-generated magnetoacoustic waves possess distinctive temporal signatures consisting of periodic, quasi-periodic and decay phases. The quasi-periodic phase possesses the strongest amplitudes and the shortest time scales. Time scales are typically of the order of a second for inhomogeneities (coronal loop width) of 1000 km and Alfven speeds of 1000/kms, and pulse duration times are of tens of seconds. Quasi-periodic signatures have been observed in radio wavelengths for over a decade and more recently by SMM. It is hoped that the theoretical ideas outlined may be successfully related to these observations and thus aid the interpretation of oscillatory signatures recorded by SMM. Such signatures may also provide a diagnostic of coronal conditions. New aspects of the ducted mhd waves, for example their behavior in smoothly varying as opposed to tube-like inhomogeneities, are currently under investigation. The theory is not restricted to loops but applied equally to open field regions.
Prof. Henry C. Kapteyn
2005-05-03
In this project, we use coherent short-wavelength light generated using high-order harmonic generation as a probe of laser-plasma dynamics and phase transitions on femtosecond time-scales. The interaction of ultrashort laser pulses with materials and plasmas is relevant to stockpile stewardship, to understanding the equation of state of matter at high pressures and temperatures, and to plasma concepts such as the fast-ignitor ICF fusion concept and laser-based particle acceleration. Femtosecond laser technology makes it possible to use a small-scale setup to generate 20fs pulses with average power >10W at multiple kHz repetition rates, that can be focused to intensities in excess of 1017W/cm2. These lasers can be used either to rapidly heat materials to initiate phase transitions, or to create laser plasmas over a wide parameter space. These lasers can also be used to generate fully spatially coherent XUV beams with which to probe these materials and plasma systems. We are in process of implementing imaging studies of plasma hydrodynamics and warm, dense matter. The data will be compared with simulation codes of laser-plasma interactions, making it possible to refine and validate these codes.