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Title: Nonlinear plasma response to a slowly varying electrostatic wave, and application to stimulated Raman scattering

Abstract

The nonlinear electronic susceptibility induced by an electrostatic wave slowly varying in space and time, which is the key parameter for the kinetic modeling of stimulated Raman scattering (SRS), is derived analytically. When calculating the real part of the susceptibility, by making the adiabatic approximation, account is taken of the amplitude dependence of the wave frequency. Then, the 'loss of resonance' of a plasma wave is found to occur at much larger amplitudes than has been predicted by Rose and Russel [H. A. Rose and D. A. Russell, Phys. Plasmas 11, 4784 (2001)] using the constant-frequency approximation. The imaginary part of the susceptibility, from which is deduced the Landau damping rate of the plasma wave, is derived using two different approaches (perturbative or not) depending on the wave amplitude. It is shown to be a nonlocal function of the wave amplitude, which underlines the importance of interspeckle interactions in SRS.

Authors:
;  [1]
  1. Departement de Physique Theorique et Appliquee, CEA/DAM Ile-de-France, Boite Postale 12, 91680 Bruyeres-Le-Chatel Cedex (France)
Publication Date:
OSTI Identifier:
20974925
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 4; Other Information: DOI: 10.1063/1.2711819; (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; ADIABATIC APPROXIMATION; AMPLITUDES; INTERACTIONS; LANDAU DAMPING; LIGHT TRANSMISSION; NONLINEAR PROBLEMS; PLASMA; PLASMA WAVES; RAMAN EFFECT; RESONANCE; SIMULATION; STRONTIUM SULFIDES

Citation Formats

Benisti, Didier, and Gremillet, Laurent. Nonlinear plasma response to a slowly varying electrostatic wave, and application to stimulated Raman scattering. United States: N. p., 2007. Web. doi:10.1063/1.2711819.
Benisti, Didier, & Gremillet, Laurent. Nonlinear plasma response to a slowly varying electrostatic wave, and application to stimulated Raman scattering. United States. doi:10.1063/1.2711819.
Benisti, Didier, and Gremillet, Laurent. Sun . "Nonlinear plasma response to a slowly varying electrostatic wave, and application to stimulated Raman scattering". United States. doi:10.1063/1.2711819.
@article{osti_20974925,
title = {Nonlinear plasma response to a slowly varying electrostatic wave, and application to stimulated Raman scattering},
author = {Benisti, Didier and Gremillet, Laurent},
abstractNote = {The nonlinear electronic susceptibility induced by an electrostatic wave slowly varying in space and time, which is the key parameter for the kinetic modeling of stimulated Raman scattering (SRS), is derived analytically. When calculating the real part of the susceptibility, by making the adiabatic approximation, account is taken of the amplitude dependence of the wave frequency. Then, the 'loss of resonance' of a plasma wave is found to occur at much larger amplitudes than has been predicted by Rose and Russel [H. A. Rose and D. A. Russell, Phys. Plasmas 11, 4784 (2001)] using the constant-frequency approximation. The imaginary part of the susceptibility, from which is deduced the Landau damping rate of the plasma wave, is derived using two different approaches (perturbative or not) depending on the wave amplitude. It is shown to be a nonlocal function of the wave amplitude, which underlines the importance of interspeckle interactions in SRS.},
doi = {10.1063/1.2711819},
journal = {Physics of Plasmas},
number = 4,
volume = 14,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • The kinetic nonlinear dispersion relation, and frequency shift {delta}{omega}{sub srs}, of a plasma wave driven by stimulated Raman scattering (SRS) are presented. Our theoretical calculations are fully electromagnetic, and use an adiabatic expression for the electron susceptibility which accounts for the change in phase velocity as the wave grows. When k{lambda}{sub D} {approx}> 0.35 (k being the plasma wave number and {lambda}{sub D} the Debye length), {delta}{omega}{sub srs} is significantly larger than could be inferred by assuming that the wave is freely propagating. Our theory is in excellent agreement with 1-D Eulerian Vlasov-Maxwell simulations when 0.3 {le} k{lambda}{sub D} {le}more » 0.58, and allows discussion of previously proposed mechanisms for Raman saturation. In particular, we find that no 'loss of resonance' of the plasma wave would limit the Raman growth rate, and that saturation through a phase detuning between the plasma wave and the laser drive is mitigated by wave number shifts.« less
  • The kinetic nonlinear dispersion relation, and frequency shift {delta}{omega}{sub srs}, of a plasma wave driven by stimulated Raman scattering are presented. Our theoretical calculations are fully electromagnetic, and use an adiabatic expression for the electron susceptibility which accounts for the change in phase velocity as the wave grows. When k{lambda}{sub D} > or approx. 0.35 (k being the plasma wave number and {lambda}{sub D} the Debye length), {delta}{omega}{sub srs} is significantly larger than could be inferred by assuming that the wave is freely propagating. Our theory is in excellent agreement with 1D Eulerian Vlasov-Maxwell simulations when 0.3{<=}k{lambda}{sub D}{<=}0.58, and allowsmore » discussion of previously proposed mechanisms for Raman saturation. In particular, we find that no ''loss of resonance'' of the plasma wave would limit the Raman growth rate, and that saturation through a phase detuning between the plasma wave and the laser drive is mitigated by wave number shifts.« less
  • The parametric coupling involving backward stimulated scattering of a laser and electron beam acoustic modes (BAM) is described as observed in particle-in-cell (PIC) simulations. The BAM modes evolve from Langmuir waves (LW) as the electron velocity distribution is nonlinearly modified to be non-Maxwellian by backward stimulated Raman scattering (BSRS). With a marginal damping rate, BAM can be easily excited and allow an extended chirping in frequency to occur as later SRS pulses encounter modified distributions. Coincident with the emergence of this non-Maxwellian distribution is a rapid increase in BSRS reflectivities with laser intensities. Both the reflectivity scaling with laser intensitymore » and the observed spectral features from PIC simulations are consistent with recent Trident experiments.« less
  • We have used temporally and spectrally resolved Thomson scattering in a CO/sub 2/-laser--plasma interaction experiment to identify electron plasma waves driven by stimulated Raman scattering in a low-density preformed plasma. Plasma waves were observed in a Gaussian-shaped plasma whose peak density was in the range (0.01--0.05)n/sub c/, in qualitative agreement with threshold calculations using a convective amplification model. The plasma waves were observed only during the early part of the pump pulse, and disappeared coincidentally with the onset of ion waves driven by stimulated Brillouin scattering.
  • Experimental evidence for the evolution of stimulated Raman backscatter instability of laser light into stimulated Compton scattering in an initially cold plasma is presented using time and wave number resolved spectra, [ital w]([ital t]) and [ital w]([ital k]), of Thomson scattered light from plasma fluctuations. Supporting particle simulations show that the key to the spectral evolution is wave breaking of Raman plasmons, which accelerates some electrons up to 4 times the phase velocity, and the consequent return current of the bulk plasma electrons in the opposite direction.