Investigation of Langdon effect on the nonlinear evolution of SRS from the early-stage inflation to the late-stage development of secondary instabilities

TL;DR

This paper investigates how the Langdon effect, which causes super-Gaussian electron energy distributions, influences the nonlinear evolution and saturation of stimulated backward Raman scattering (SRS) in laser-irradiated plasmas through simulations.

Contribution

It provides new insights into the impact of the Langdon effect on SRS growth, saturation, and secondary instabilities across different plasma conditions.

Findings

Langdon effect widens the parameter range for SRS absolute growth.

It shortens the time to reach SRS saturation within certain parameters.

The effect influences secondary processes like decay and rescattering of plasma waves.

Abstract

In a laser-irradiated plasma, the Langdon effect can result in a super-Gaussian electron energy distribution function (EEDF), imposing significant influences on the stimulated backward Raman scattering (SRS). In this work, the influence of a super-Gaussian EEDF on the nonlinear evolution of SRS is investigated by three wave model simulation and Vlasov-Maxwell simulation for plasma parameters covering a wide range of k{\lambda}De from 0.19 to 0.48 at both high and low intensity laser drives. In the early-stage of SRS evolution, it is found that besides the kinetic effects due to electron trapping [Phys. Plasmas 25, 100702 (2018)], the Langdon effect can also significantly widen the parameter range for the absolute growth of SRS, and the time for the absolute SRS to reach saturation is greatly shorten by Langdon effect within certain parameter region. In the late-stage of SRS, when secondary instabilities such as decay of the electron plasma wave to beam acoustic modes, rescattering, and Langmuir decay instability become important, the Langdon effect can influence the reflectivity of SRS by affecting the secondary processes. The comprehension of Langdon effect on nonlinear evolution and saturation of SRS would contribute to a better understanding and prediction of SRS in inertial confinement fusion.