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).

*The experiment was conducted at the Omega Laser Facility at the University of Rochester’s Laboratory for Laser Energetics with the beam time through the National Laser Users’ Facility (NLUF) program. This material is based upon work supported by the Department of Energy, National Nuclear Security Administration under Award Numbers DE-NA0003842 and DE-NA0003856, the University of Rochester, and the New York State Energy Research and Development Authority.

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).

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