Magnetized Laser-Plasma Interactions in High-Energy-Density Systems: Parallel Propagation

TL;DR

This paper explores how external magnetic fields influence laser-plasma interactions in high-energy-density systems, deriving dispersion relations and identifying a new scattering process called stimulated whistler scattering.

Contribution

It introduces a comprehensive theoretical framework for parametric processes in magnetized plasmas, including the novel stimulated whistler scattering mechanism.

Findings

Faraday rotation can be significant in HED conditions.

Raman and Brillouin spectra are slightly modified by magnetic fields.

Stimulated whistler scattering occurs only with an external B field.

Abstract

We investigate parametric processes in magnetised plasmas, driven by a large-amplitude pump light wave. Our focus is on laser-plasma interactions relevant to high-energy-density (HED) systems, such as the National Ignition Facility and the Sandia MagLIF concept. We derive dispersion relations for three-wave interactions in a multi-species plasma using Maxwell's equations, the warm-fluid momentum equation and the continuity equation. The application of an external B field causes right and left polarised light waves to propagate with differing phase velocities. This leads to Faraday rotation of the polarisation, which can be significant in HED conditions. Raman and Brilllouin scattering have modified spectra due to the background B field, though this effect is usually small in systems of current practical interest. We identify a scattering process we call stimulated whistler scattering, where a light wave decays to an electromagnetic whistler wave ($\omega \lesssim \omega_{ce}$) and a Langmuir wave. This only occurs in the presence of an external B field, which is required for the whistler wave to exist. We compute the scattered wavelengths for Raman, Brillouin, and whistler scattering.