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Title: Stimulated Brillouin scattering reduction induced by self-focusing for a single laser speckle interacting with an expanding plasma

The origin of the low level of stimulated Brillouin scattering (SBS) observed in laser-plasma experiments carried out with a single laser speckle is investigated by means of three-dimensional simulations and modeling in the limit when the laser beam power P is well above the critical power for ponderomotive self-focusing We find that the order of magnitude of the time averaged reflectivities, together with the temporal and spatial SBS localization observed in our simulations, are correctly reproduced by our modeling. It is observed that, after a short transient stage, SBS reaches a significant level only (i) as long as the incident laser pulse is increasing in amplitude and (ii) in a single self-focused speckle located in the low-density front part of the plasma. In order to describe self-focusing in an inhomogeneous expanding plasma, we have derived a new Lagrangian density describing this process. Using then a variational approach, our model reproduces the position and the peak intensity of the self-focusing hot spot in the front part of the plasma density profile as well as the local density depletion in this hot spot. The knowledge of these parameters then makes it possible to estimate the spatial amplification of SBS as a functionmore » of the laser beam power and consequently to explain the experimentally observed SBS reflectivity, considerably reduced with respect to standard theory in the regime of large laser beam power.« less
Authors:
; ;  [1] ; ;  [2] ;  [3] ;  [4]
  1. CEA, DAM, DIF, F-91297 Arpajon Cedex (France)
  2. Centre de Physique Théorique (CPHT), CNRS, École Polytechnique, 91128 Palaiseau Cedex (France)
  3. LULI, CNRS, Université Pierre et Marie Curie, École Polytechnique, 91128 Palaiseau Cedex (France)
  4. Institut National de la Recherche Scientifique (INRS), Varennes, Québec J3X1S2 (Canada)
Publication Date:
OSTI Identifier:
22251956
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 3; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ACCIDENTS; AMPLIFICATION; AMPLITUDES; BEAMS; BRILLOUIN EFFECT; FOCUSING; HOT SPOTS; LAGRANGIAN FUNCTION; LASERS; PLASMA DENSITY; PONDEROMOTIVE FORCE; REFLECTIVITY; SIMULATION; THREE-DIMENSIONAL CALCULATIONS; VARIATIONAL METHODS