• High Power Laser Science and Engineering
  • Vol. 4, Issue 3, 03000e23 (2016)
C. Riconda1、* and S. Weber2
Author Affiliations
  • 1LULI-UPMC Universit′e Paris 6: Sorbonne Universit′es, CNRS, Ecole Polytechnique, CEA: Universit′e Paris-Saclay, 75252 Paris, France
  • 2Institute of Physics of the ASCR, ELI-Beamlines, 18221 Prague, Czech Republic
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    Abstract

    The co-existence of the Raman and Brillouin backscattering instability is an important issue for inertial confinement fusion. The present paper presents extensive one-dimensional (1D) particle-in-cell (PIC) simulations for a wide range of parameters extending and complementing previous findings. PIC simulations show that the scenario of reflectivity evolution and saturation is very sensitive to the temperatures, intensities, size of plasma and boundary conditions employed. The Langmuir decay instability is observed for rather small kepwD but has no influence on the saturation of Brillouin backscattering, although there is a clear correlation of Langmuir decay instability modes and ion-fractional decay for certain parameter ranges. Raman backscattering appears at any intensity and temperature but is only a transient phenomenon. In several configurations forward as well as backward Raman scattering is observed. For the intensities considered, I2oabove 1015 W mm2=cm2, Raman is always of bursty nature. A particular setup allows the simulation of multi-speckle aspects in which case it is found that Raman is self-limiting due to strong modifications of the distribution function. Kinetic effects are of prime importance for Raman backscattering at high temperatures. No unique scenario for the saturation of Raman scattering or Raman–Brillouin competition does exist. The main effect in the considered parameter range is pump depletion because of large Brillouin backscattering. However, in the low kepwD regime the presence of ion-acoustic waves due to the Langmuir decay instability from the Raman created electron plasma waves can seed the ion-fractional decay and affect the Brillouin saturation.0.0/15-008/0000162) from European Regional Development.

    1 Introduction

    A major task of the laser–plasma interaction (LPI) community is to develop predictive means for the envisaged inertial confinement fusion (ICF) experiments such as National Ignition Facility (NIF)[13], Laser MegaJoule (LMJ)[4] and ShengGuang (SG)[5]. Among the dominant problems is an accurate evaluation of backscatter reflectivities, Brillouin (SBS) and Raman (SRS), for plasmas having an electron temperature of a few kilo electronvolts. Due to the complexity of the interaction numerical simulations should be the obvious means in order to understand fusion plasmas. However, the calculated reflectivity data do not always agree with the experimental data. A detailed comprehension of SBS and SRS is therefore necessary. First-principle simulations like the particle-in-cell (PIC) approach (mobile ions as well as electrons) should give a correct answer but cannot be performed for millimetre-cube plasmas and interaction times of several hundred picoseconds as they are too demanding for present-day computers. Nevertheless the kinetic approach is the most reasonable one as it can be expected that eventually models can be derived for the saturation of the parametric instabilities which in turn are incorporated in macroscopic, fluid-type, simulations of fusion plasmas.

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    C. Riconda, S. Weber. Raman–Brillouin interplay for inertial confinement fusion relevant laser–plasma interaction[J]. High Power Laser Science and Engineering, 2016, 4(3): 03000e23
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    Received: Apr. 15, 2016
    Accepted: May. 18, 2016
    Published Online: Nov. 7, 2016
    The Author Email: C. Riconda (caterina.riconda@upmc.fr)