Magnetised Thermal Self-focusing and Filamentation of Long-Pulse Lasers in Plasmas Relevant to Magnetised ICF Experiments

TL;DR

This study investigates how magnetic fields influence laser self-focusing and filamentation in plasmas, revealing that magnetised thermal conductivity reduces self-focal length and enhances filamentation growth, impacting inertial fusion experiments.

Contribution

It provides the first combined analytic and simulation analysis of magnetised thermal effects on laser propagation in plasmas, emphasizing the importance of extended electron transport in modeling.

Findings

Magnetic fields shorten the laser self-focal length in plasma.

Magnetised plasmas increase filamentation growth rates.

External magnetic fields significantly affect laser propagation in fusion experiments.

Abstract

In this paper we study the influence of the magnetised thermal conductivity on the propagation of a nanosecond $10^{14} \mathrm{Wcm}^{-2}$ laser in an underdense plasma by performing simulations of a paraxial model laser in a plasma with the full Braginskii magnetised transport coefficients. Analytic theory and simulations show the shortening of the self-focal length of a laser beam in a plasma as a result of the reduction of the plasma thermal conductivity in a magnetic field. Furthermore the filamentation of a laser via the thermal mechanism is found to have an increased spatial growth rate in a magnetised plasma. We discuss the effect of these results on recent magnetised inertial fusion experiments where filamentation can be detrimental to laser propagation and uniform laser heating. We conclude the application of external magnetic fields to laser-plasma experiments requires the inclusion of the extended electron transport terms in simulations of laser propagation.