On the dominant and subdominant behavior of stimulated Raman and Brillouin scattering driven by nonuniform laser beams

Journal Article · Tue Dec 01 04:00:00 EST 1998 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.873171· OSTI ID:664695

Berger, R L; Still, C H; Williams, E A; Langdon, A B ^[1]

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1. Lawrence Livermore National Laboratory, University of California, Livermore, California 94551 (United States)

In a number of experiments, stimulated Brillouin (SBS) or Raman backscattering (SRS) has been observed to be much more vigorous than the other although the expectations based on linear gain exponents are that they should both be reflecting large amounts of incident light. Multidimensional fluid simulations of the growth and saturation of these two instabilities driven by a nonuniform incident laser beam are presented. On the fast time scale, the nonlinear saturation occurs via an anomalous damping inspired by fundamental studies of Langmuir turbulence [D. F. DuBois {ital et al.}, Bull. Am. Phys. Soc. {bold 41}, 1531 (1996)] and acoustic wave turbulence [B. I. Cohen {ital et al.}, Phys. Plasmas {bold 4}, 956 (1997)]. Over a longer time scale, SRS and SBS are limited by quasilinear processes such as flows induced by the transfer of momentum from the light to the plasma and ion temperature increases caused by a loss of light energy in SBS. The simulations show a reduction of the SBS reflectivity under conditions of strong SRS reflectivity even if the laser energy is not depleted. The recent observations of decreasing SBS reflectivity with increasing plasma density [D. S. Montgomery, Phys. Plasmas {bold 5}, 1973 (1998)] are shown to be consistent with linear theory and nonlinear simulations of SBS provided the increasing levels of SRS are included. Because the reflectivity is produced by scattering in intense hotspots, where the local reflectivity can be very large, the SBS and SRS can be anticorrelated even when the total scattering is quite modest. {copyright} {ital 1998 American Institute of Physics.}

• OSTI ID: 664695
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 12 Vol. 5; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BACKSCATTERING
BEAM-PLASMA SYSTEMS
BRILLOUIN EFFECT
LASER RADIATION
PLASMA INSTABILITY
PLASMA SIMULATION
PLASMA WAVES
RAMAN EFFECT
REFLECTIVITY
SATURATION
TURBULENCE
WAVE PROPAGATION