Absolute instability modes due to rescattering of stimulated Raman scattering in a large nonuniform plasma

TL;DR

This paper investigates the development of absolute instability modes caused by rescattering of stimulated Raman scattering in large nonuniform plasmas, revealing their growth, nonlinear effects, and potential impact on inertial confinement fusion experiments.

Contribution

It provides a theoretical and numerical analysis of absolute SRS modes due to rescattering, highlighting their characteristics and significance in plasma physics and fusion research.

Findings

Absolute SRS modes develop high phase velocity Langmuir waves.

Weak Landau damping allows the growth of absolute SRS in linear stage.

Nonlinear regime heats electrons to hundreds of keV.

Abstract

Absolute instability modes due to rescattering of SRS in a large nonuniform plasma are studied theoretically and numerically. The backscattered light of convective SRS can be considered as a pump light with a finite bandwidth. The different frequency components of the backscattered light can be coupled to develop absolute stimulated Raman scattering (SRS) and two plasmon decay (TPD) instability near their quarter-critical densities via rescattering process. The absolute SRS mode develops a Langmuir wave with a high phase velocity about $c/\sqrt{3}$ with $c$ the light speed in vacuum. Given that most electrons are at low velocities in the linear stage, the absolute SRS mode grows with much weak Landau damping. When the interaction evolves into the nonlinear regime, the Langmuir wave can heat abundant electrons up to a few hundred keV. Our theoretical model is validated by particle-in-cell simulations. The absolute instabilities may play a considerable role in the experiments of inertial confined fusion.