Density modulation-induced absolute laser-plasma-instabilities: simulations and theory

TL;DR

This paper demonstrates through simulations and theory that sinusoidal density modulations can convert convective laser-plasma instabilities into absolute ones, impacting energy deposition in inertial confinement fusion.

Contribution

It provides a theoretical and simulation-based analysis of how density modulations induce absolute instabilities, with an analytical threshold expression based on the density gradient change.

Findings

Density modulations can turn convective instabilities into absolute ones.

A threshold for the gradient change is derived analytically.

Implications for hot electron generation and energy deposition in fusion.

Abstract

Fluid simulations show that when a sinusoidal density modulation is superimposed on a linear density profile, convective instabilities can become absolutely unstable. This conversion can occur for two-plasmon-decay and stimulated Raman Scattering instabilities under realistic direct-drive inertial confinement fusion conditions and can affect hot electron generation and laser energy deposition. Analysis of the three-wave model shows that a sufficiently large change of the density gradient in a linear density profile can turn convective instabilities into absolute ones. An analytical expression is given for the threshold of the gradient change, which depends on the convective gain only.