Nonlinear kinetic modeling of stimulated Raman scattering in a multidimensional geometry

TL;DR

This paper develops nonlinear kinetic envelope equations for stimulated Raman scattering in multi-dimensional plasmas, incorporating effects like Landau damping reduction, wave trapping, and self-focusing, validated through simulations.

Contribution

It introduces a comprehensive set of nonlinear envelope equations for SRS in multidimensional geometry, including effects like damping reduction and wave trapping, and validates them with PIC simulations.

Findings

BRAMA accurately predicts Raman reflectivity evolution.

The model determines the correct laser threshold for SRS.

Simulations match experimental and PIC results for key parameters.

Abstract

In this paper, we derive coupled envelope equations modeling the growth of stimulated Raman scattering (SRS) in a multi-dimensional geometry, and accounting for nonlinear kinetic effects. In particular, our envelope equations allow for the nonlinear reduction of the Landau damping rate, whose decrease with the plasma wave amplitude depends on the rate of side-loss. Account is also made of the variations in the extent of the plasma wave packet entailed by the collisionless dissipation due to trapping. The dephasing between the electron plasma wave (EPW) and the laser drive, as well as the self-focussing of the plasma wave, both induced by the EPW nonlinear frequency shift, are also included in our envelope equations. These equations are solved in a multi-dimensional geometry using our code dubbed BRAMA, whose predictions regarding the evolution of Raman reflectivity as a function of the laser intensity are compared against previously published PIC results, thus illustrating the ability of BRAMA simulations to provide the correct laser threshold intensity for SRS, as well as the right order of magnitude of Raman reflectivity above threshold.