Nonlinear backward stimulated Raman scattering from electron beam acoustic modes in the kinetic regime

Journal Article · Sat Jul 15 00:00:00 EDT 2006 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2210929· OSTI ID:20860136

Yin, L; Daughton, W; Albright, B J; Bowers, K J; Montgomery, D S; Kline, J L; Fernandez, J C; Roper, Q ^[1]

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1. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

The backward stimulated Raman scattering (BSRS) of a laser from electron beam acoustic modes (BAM) in the presence of self-consistent non-Maxwellian velocity distributions is examined by linear theory and particle-in-cell (PIC) simulations in one and two dimensions (1D and 2D). The BAM evolve from Langmuir waves (LW) as electron trapping modifies the distribution to a non-Maxwellian form that exhibits a beam component. Linear dispersion relations using the nonlinearly modified distribution from simulations are solved for the electrostatic modes involved in the parametric coupling. Results from linear analysis agree well with electrostatic spectra from simulations. It is shown that the intersection of the Stokes root with BAM (instead of LW) determines the matching conditions for BSRS at a nonlinear stage. As the frequency of the unstable Stokes mode decreases with increasing wave number, the damping rate and the phase velocity of BAM decreases with the phase velocity of the Stokes mode, providing a self-consistently evolving plasma linear response that favors continuation of the nonlinear frequency shift. Coincident with the emergence of BAM is a rapid increase in BSRS reflectivity. The details of the wave-particle interaction region in the electron velocity distribution determine the growth/damping rate of these electrostatic modes and the nonlinear frequency shift; in modeling this behavior, the use of sufficiently large numbers of particles in the simulations is crucial. Both the reflectivity scaling with laser intensity and the spectral features from simulations are discussed and are consistent with recent Trident experiments.

• OSTI ID: 20860136
• Journal Information: Physics of Plasmas, Vol. 13, Issue 7; Other Information: DOI: 10.1063/1.2210929; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BEAM-PLASMA SYSTEMS
COUPLING
DAMPING
DISPERSION RELATIONS
DISTRIBUTION
ELECTRON BEAMS
ELECTRONS
ION ACOUSTIC WAVES
LASERS
LIGHT TRANSMISSION
NONLINEAR PROBLEMS
PARAMETRIC INSTABILITIES
PHASE VELOCITY
PLASMA
PLASMA SIMULATION
RADIATION TRANSPORT
RAMAN EFFECT
REFLECTIVITY
TRAPPING