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Title: Stimulated scattering in laser driven fusion and high energy density physics experiments

Abstract

In laser driven fusion and high energy density physics experiments, one often encounters a kλ{sub D} range of 0.15 < kλ{sub D} < 0.5, where stimulated Raman scattering (SRS) is active (k is the initial electron plasma wave number and λ{sub D} is the Debye length). Using particle-in-cell simulations, the SRS reflectivity is found to scale as ∼ (kλ{sub D}){sup −4} for kλ{sub D} ≳ 0.3 where electron trapping effects dominate SRS saturation; the reflectivity scaling deviates from the above for kλ{sub D} < 0.3 when Langmuir decay instability (LDI) is present. The SRS risk is shown to be highest for kλ{sub D} between 0.2 and 0.3. SRS re-scattering processes are found to be unimportant under conditions relevant to ignition experiments at the National Ignition Facility (NIF). Large-scale simulations of the hohlraum plasma show that the SRS wavelength spectrum peaks below 600 nm, consistent with most measured NIF spectra, and that nonlinear trapping in the presence of plasma gradients determines the SRS spectral peak. Collisional effects on SRS, stimulated Brillouin scattering (SBS), LDI, and re-scatter, together with three dimensional effects, are examined. Effects of collisions are found to include de-trapping as well as cross-speckle electron temperature variation from collisional heating, the latter of which reduces gain, introducesmore » a positive frequency shift that counters the trapping-induced negative frequency shift, and affects SRS and SBS saturation. Bowing and breakup of ion-acoustic wavefronts saturate SBS and cause a dramatic, sharp decrease in SBS reflectivity. Mitigation of SRS and SBS in the strongly nonlinear trapping regime is discussed.« less

Authors:
; ; ; ; ; ; ;  [1]; ;  [2]
  1. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
  2. Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
Publication Date:
OSTI Identifier:
22303646
Resource Type:
Journal Article
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 21; Journal Issue: 9; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1070-664X
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BRILLOUIN EFFECT; COLLISIONAL HEATING; DEBYE LENGTH; DECAY INSTABILITY; ELECTRON PLASMA WAVES; ELECTRONS; ENERGY DENSITY; LASERS; NONLINEAR PROBLEMS; REFLECTIVITY; SIMULATION; STRONTIUM SULFIDES; TRAPPING

Citation Formats

Yin, L., E-mail: lyin@lanl.gov, Albright, B. J., Rose, H. A., Montgomery, D. S., Kline, J. L., Finnegan, S. M., Bergen, B., Bowers, K. J., Kirkwood, R. K., and Milovich, J. Stimulated scattering in laser driven fusion and high energy density physics experiments. United States: N. p., 2014. Web. doi:10.1063/1.4895504.
Yin, L., E-mail: lyin@lanl.gov, Albright, B. J., Rose, H. A., Montgomery, D. S., Kline, J. L., Finnegan, S. M., Bergen, B., Bowers, K. J., Kirkwood, R. K., & Milovich, J. Stimulated scattering in laser driven fusion and high energy density physics experiments. United States. doi:10.1063/1.4895504.
Yin, L., E-mail: lyin@lanl.gov, Albright, B. J., Rose, H. A., Montgomery, D. S., Kline, J. L., Finnegan, S. M., Bergen, B., Bowers, K. J., Kirkwood, R. K., and Milovich, J. Mon . "Stimulated scattering in laser driven fusion and high energy density physics experiments". United States. doi:10.1063/1.4895504.
@article{osti_22303646,
title = {Stimulated scattering in laser driven fusion and high energy density physics experiments},
author = {Yin, L., E-mail: lyin@lanl.gov and Albright, B. J. and Rose, H. A. and Montgomery, D. S. and Kline, J. L. and Finnegan, S. M. and Bergen, B. and Bowers, K. J. and Kirkwood, R. K. and Milovich, J.},
abstractNote = {In laser driven fusion and high energy density physics experiments, one often encounters a kλ{sub D} range of 0.15 < kλ{sub D} < 0.5, where stimulated Raman scattering (SRS) is active (k is the initial electron plasma wave number and λ{sub D} is the Debye length). Using particle-in-cell simulations, the SRS reflectivity is found to scale as ∼ (kλ{sub D}){sup −4} for kλ{sub D} ≳ 0.3 where electron trapping effects dominate SRS saturation; the reflectivity scaling deviates from the above for kλ{sub D} < 0.3 when Langmuir decay instability (LDI) is present. The SRS risk is shown to be highest for kλ{sub D} between 0.2 and 0.3. SRS re-scattering processes are found to be unimportant under conditions relevant to ignition experiments at the National Ignition Facility (NIF). Large-scale simulations of the hohlraum plasma show that the SRS wavelength spectrum peaks below 600 nm, consistent with most measured NIF spectra, and that nonlinear trapping in the presence of plasma gradients determines the SRS spectral peak. Collisional effects on SRS, stimulated Brillouin scattering (SBS), LDI, and re-scatter, together with three dimensional effects, are examined. Effects of collisions are found to include de-trapping as well as cross-speckle electron temperature variation from collisional heating, the latter of which reduces gain, introduces a positive frequency shift that counters the trapping-induced negative frequency shift, and affects SRS and SBS saturation. Bowing and breakup of ion-acoustic wavefronts saturate SBS and cause a dramatic, sharp decrease in SBS reflectivity. Mitigation of SRS and SBS in the strongly nonlinear trapping regime is discussed.},
doi = {10.1063/1.4895504},
journal = {Physics of Plasmas},
issn = {1070-664X},
number = 9,
volume = 21,
place = {United States},
year = {2014},
month = {9}
}