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Title: Kinetic enhancement of Raman backscatter, and electron acoustic Thomson scatter

Abstract

One-dimensional Eulerian Vlasov-Maxwell simulations are presented that show kinetic enhancement of stimulated Raman backscatter (SRBS) due to electron trapping in regimes of heavy linear Landau damping. The conventional Raman Langmuir wave is transformed into a set of beam acoustic modes [L. Yin et al., Phys. Rev. E 73, 025401 (2006)]. A low phase velocity electron acoustic wave (EAW) is seen developing from the self-consistent Raman physics. Backscatter of the pump laser off the EAW fluctuations is reported and referred to as electron acoustic Thomson scatter. This light is similar in wavelength to, although much lower in amplitude than, the reflected light between the pump and SRBS wavelengths observed in single-hot-spot experiments, and previously interpreted as stimulated electron acoustic scatter [D. S. Montgomery et al., Phys. Rev. Lett. 87, 155001 (2001)]. The EAW observed in our simulations is strongest well below the phase-matched frequency for electron acoustic scatter, and therefore the EAW is not produced by it. The beating of different beam acoustic modes is proposed as the EAW excitation mechanism, and is called beam acoustic decay. Supporting evidence for this process, including bispectral analysis, is presented. The linear electrostatic modes, found by projecting the numerical distribution function onto a Gauss-Hermitemore » basis, include beam acoustic modes (some of which are unstable even without parametric coupling to light waves) and a strongly damped EAW similar to the observed one. This linear EAW results from non-Maxwellian features in the electron distribution, rather than nonlinearity due to electron trapping.« less

Authors:
; ; ;  [1];  [2]
  1. Lawrence Livermore National Laboratory, University of California, Livermore, California 94550 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20960119
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 1; Other Information: DOI: 10.1063/1.2431161; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BEAMS; DISTRIBUTION FUNCTIONS; ELECTRON PLASMA WAVES; ELECTRONS; EXCITATION; HOT SPOTS; LANDAU DAMPING; NONLINEAR PROBLEMS; ONE-DIMENSIONAL CALCULATIONS; PHASE VELOCITY; PLASMA; PLASMA SIMULATION; TRAPPING; WAVELENGTHS

Citation Formats

Strozzi, D. J., Williams, E. A., Langdon, A. B., Bers, A., and Massachusetts Institute of Technology, Cambridge, Massachusetts 02139. Kinetic enhancement of Raman backscatter, and electron acoustic Thomson scatter. United States: N. p., 2007. Web. doi:10.1063/1.2431161.
Strozzi, D. J., Williams, E. A., Langdon, A. B., Bers, A., & Massachusetts Institute of Technology, Cambridge, Massachusetts 02139. Kinetic enhancement of Raman backscatter, and electron acoustic Thomson scatter. United States. doi:10.1063/1.2431161.
Strozzi, D. J., Williams, E. A., Langdon, A. B., Bers, A., and Massachusetts Institute of Technology, Cambridge, Massachusetts 02139. Mon . "Kinetic enhancement of Raman backscatter, and electron acoustic Thomson scatter". United States. doi:10.1063/1.2431161.
@article{osti_20960119,
title = {Kinetic enhancement of Raman backscatter, and electron acoustic Thomson scatter},
author = {Strozzi, D. J. and Williams, E. A. and Langdon, A. B. and Bers, A. and Massachusetts Institute of Technology, Cambridge, Massachusetts 02139},
abstractNote = {One-dimensional Eulerian Vlasov-Maxwell simulations are presented that show kinetic enhancement of stimulated Raman backscatter (SRBS) due to electron trapping in regimes of heavy linear Landau damping. The conventional Raman Langmuir wave is transformed into a set of beam acoustic modes [L. Yin et al., Phys. Rev. E 73, 025401 (2006)]. A low phase velocity electron acoustic wave (EAW) is seen developing from the self-consistent Raman physics. Backscatter of the pump laser off the EAW fluctuations is reported and referred to as electron acoustic Thomson scatter. This light is similar in wavelength to, although much lower in amplitude than, the reflected light between the pump and SRBS wavelengths observed in single-hot-spot experiments, and previously interpreted as stimulated electron acoustic scatter [D. S. Montgomery et al., Phys. Rev. Lett. 87, 155001 (2001)]. The EAW observed in our simulations is strongest well below the phase-matched frequency for electron acoustic scatter, and therefore the EAW is not produced by it. The beating of different beam acoustic modes is proposed as the EAW excitation mechanism, and is called beam acoustic decay. Supporting evidence for this process, including bispectral analysis, is presented. The linear electrostatic modes, found by projecting the numerical distribution function onto a Gauss-Hermite basis, include beam acoustic modes (some of which are unstable even without parametric coupling to light waves) and a strongly damped EAW similar to the observed one. This linear EAW results from non-Maxwellian features in the electron distribution, rather than nonlinearity due to electron trapping.},
doi = {10.1063/1.2431161},
journal = {Physics of Plasmas},
number = 1,
volume = 14,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}