Kinetic enhancement of Raman backscatter, and electron acoustic Thomson scatter

Journal Article · Mon Jan 15 04:00:00 EST 2007 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2431161· OSTI ID:20960119

Strozzi, D J; Williams, E A; Langdon, A B; Bers, A ^[1]

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1. Lawrence Livermore National Laboratory, University of California, Livermore, California 94550 (United States)

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.

• OSTI ID: 20960119
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 1 Vol. 14; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

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