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Measurements of the effects of an external B-field on backscattered Stimulated Raman Scattering(SRS) reflectivity

POSTER

Abstract



Laser-plasma instabilities such as Stimulated Raman Scattering (SRS) play a detrimental role in inertial confinement fusion. SRS leads to a loss of energy due to light scattering and preheating of the fuel by suprathermal electrons generated through the decay of electron plasma waves. Recent numerical work has shown that a moderate external magnetic field can mitigate SRS through its influence on wave-particle interactions. A novel platform at the OMEGA-EP laser was developed to study the effect of a 25 T perpendicular magnetic field (using MIFEDS coils) on the backscattered SRS (BSRS) light spectrum from an Argon gas jet target. The Sub-Aperture Backward Scatter diagnostic was fielded to measure the BSRS spectra with a time resolution that enables probing of different plasma conditions on the same shot, via the use of a train of short pulses for the excitation beam. The results attest to a kinetic effect that the B-field has on BSRS reflectivity: (i) when ne<11%ncr, the BSRS reflectivity is enhanced, and (ii) when ne >11%ncr, the B-field reduces the BSRS reflectivity. The X-ray spectrometry confirms that the BSRS occurs in the expected kinetic regime ( kλD ~ 0.2-0.3).

Publication: B. J. Winjum, F. S. Tsung, and W. B. Mori, "Mitigation of stimulated Raman scattering in the kinetic regime by external magnetic fields", Phys. Rev. E 98, 043208 (2018).<br>

Presenters

  • Alemayehu Bogale

    University of California, San Diego

Authors

  • Alemayehu Bogale

    University of California, San Diego

  • Mathieu Bailly-Grandvaux

    UCSD, University of California, San Diego

  • Simon Bolanos

    UCSD, University of California, San Diego

  • Mario Manuel

    General Atomics - San Diego

  • Benjamin J Winjum

    University of California, Los Angeles

  • Christopher A Walsh

    Lawrence Livermore National Laboratory, LLNL, Lawrence Livermore Natl Lab

  • Jacob Saret

    UCSD, University of California, San Diego

  • Roman Lee

    University of California, Los Angeles

  • Frank S Tsung

    University of California, Los Angeles

  • Warren B Mori

    University of California, Los Angeles, Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA

  • Dustin Froula

    University of Rochester, Laboratory for Laser Energetics, Laboratory for Laser Energetics, U. of Rochester, Laboratory for Laser Energetics, University of Rochester

  • T. Filkins

    LLE, Lab for Laser Energetics, Laboratory for Laser Energetics, University of Rochester, Rochester, New York, USA, University of Rochester, Laboratory for Laser Energetics, University of Rochester

  • Farhat N Beg

    University of California, San Diego