Kinetic Enhancement of Raman Backscatter, and Electron Acoustic Thomson Scatter

Journal Article · Fri Sep 01 04:00:00 EDT 2006 · Physics of Plasmas

OSTI ID:902311

Strozzi, D J; Williams, E A; Langdon, A B; Bers, A

1-D Eulerian Vlasov-Maxwell simulations are presented which 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)]. For the first time, 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.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 902311
• Report Number(s): UCRL-JRNL-224816
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Vol. 14; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ACOUSTICS
AMPLITUDES
DECAY
DISTRIBUTION FUNCTIONS
ELECTRON PLASMA WAVES
ELECTRONS
ELECTROSTATICS
EXCITATION
FLUCTUATIONS
HOT SPOTS
KINETICS
LANDAU DAMPING
LASERS
PHASE VELOCITY
PHYSICS
TRAPPING
WAVELENGTHS