Raman backscattering saturation due to coupling between ωp and 2ωp modes in plasma

G Raj,S Yoffe,D A Jaroszynski,Min Sup Hur,B Ersfeld,R A Cairns,G Vieux

doi:10.1088/1367-2630/17/10/103026

Abstract

Raman backscattering (RBS) in plasma is the basis of plasma-based amplifiers and is important in laser-driven fusion experiments. We show that saturation can arise from nonlinearities due to coupling between the fundamental and harmonic plasma wave modes for sufficiently intense pump and seed pulses. We present a time-dependent analysis that shows that plasma wave phase shifts reach a maximum close to wavebreaking. The study contributes to a new understanding of RBS saturation for counter-propagating laser pulses.

Highlights

Homogeneous Raman backscattering (RBS) is the fastest growing of the Raman scattering instabilities that frequently occurs when a very long laser pulse propagates through plasma, such as in Raman amplification [1,2,3,4,5] and in laser driven inertial confinement fusion experiments, such as the National Ignition Facility (NIF)[6, 7] where it has a role in preheating the fuel pellet and degrading the implosion symmetry
We investigate nonlinear growth and saturation of RBS in a parameter regime characterized by high density, cold, homogeneous and underdense plasma with intense initial seed and pump laser pulses
In this paper, using 1D simulations for the laser-plasma parameters relevant to Raman amplifiers operating in the nonlinear RBS regime [2, 26], we show the existence of plasma wave harmonic modes in the leading edge region (LER) of the seed pulse

Summary

14 October 2015

Raman backscattering saturation due to coupling between ωp and 2ωp modes in plasma. G Raj, B Ersfeld, G Vieux, S Yoffe, Min Sup Hur, R A Cairns and D A Jaroszynski.

Introduction

Theoretical model

Numerical and simulation results

Conclusions