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Onset and saturation of backward stimulated Raman scattering of laser in trapping regime in three spatial dimensions

Phys. Plasmas 16, 113101 (2009); doi:10.1063/1.3250928

Published 2 November 2009

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L. Yin, B. J. Albright, H. A. Rose, K. J. Bowers, B. Bergen, D. S. Montgomery, J. L. Kline, and J. C. Fernández
Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
A suite of three-dimensional (3D) VPIC [K. J. Bowers et al., Phys. Plasmas 15, 055703 (2008)] particle-in-cell simulations of backward stimulated Raman scattering (SRS) in inertial confinement fusion hohlraum plasma has been performed on the heterogeneous multicore supercomputer, Roadrunner, presently the world's most powerful supercomputer. These calculations reveal the complex nonlinear behavior of SRS and point to a new era of “at scale” 3D modeling of SRS in solitary and multiple laser speckles. The physics governing nonlinear saturation of SRS in a laser speckle in 3D is consistent with that of prior two-dimensional (2D) studies [L. Yin et al., Phys. Rev. Lett. 99, 265004 (2007)], but with important differences arising from enhanced diffraction and side loss in 3D compared with 2D. In addition to wave front bowing of electron plasma waves (EPWs) due to trapped electron nonlinear frequency shift and amplitude-dependent damping, we find for the first time that EPW self-focusing, which evolved from trapped particle modulational instability [H. A. Rose and L. Yin, Phys. Plasmas 15, 042311 (2008)], also exhibits loss of angular coherence by formation of a filament necklace, a process not available in 2D. These processes in 2D and 3D increase the side-loss rate of trapped electrons, increase wave damping, decrease source coherence for backscattered light, and fundamentally limit how much backscatter can occur from a laser speckle. For both SRS onset and saturation, the nonlinear trapping induced physics is not captured in linear gain modeling of SRS. A simple metric is described for using single-speckle reflectivities obtained from VPIC simulations to infer the total reflectivity from the population of laser speckles of amplitude sufficient for significant trapping-induced nonlinearity to arise. ©2009 American Institute of Physics
History: Received 29 April 2009; accepted 29 September 2009; published 2 November 2009
Permalink: http://link.aip.org/link/?PHPAEN/16/113101/1
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KEYWORDS and PACS

Keywords
PACS
  • 52.38.Bv
    Rayleigh scattering; stimulated Brillouin and Raman scattering in plasmas
  • 52.65.-y
    Plasma simulation
  • 52.57.-z
    Laser inertial confinement
  • 52.50.Jm
    Plasma production and heating by laser beams
  • 52.35.Py
    Plasma macroinstabilities (hydromagnetic)
  • 52.35.Mw
    Nonlinear phenomena: plasma waves, wave propagation and other interactions
  • YEAR: 2009

PUBLICATION DATA

ISSN:
1070-664X (print)   1089-7674 (online)
Publisher:
AIP is a member of CrossRef AIP

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