Emission of electromagnetic waves as a stopping mechanism for nonlinear collisionless ionization waves in a high-$\beta$ regime

TL;DR

This paper investigates how electromagnetic wave emission acts as a stopping mechanism for nonlinear collisionless ionization waves in high-beta plasmas, revealing magnetic field-induced energy loss of electrons that halts wave propagation.

Contribution

It demonstrates that in high-beta regimes, magnetic fields cause energetic electrons to emit electromagnetic waves, stopping ionization wave propagation and expelling magnetic fields from the plasma.

Findings

Magnetic fields halt ionization waves by causing electron energy loss through electromagnetic emission.

Electromagnetic wave emission leads to magnetic field expulsion from the plasma.

The mechanism can mitigate rapid plasma expansion in applications like neutron production.

Abstract

A high energy density plasma embedded in a neutral gas is able to launch an outward-propagating nonlinear electrostatic ionization wave that traps energetic electrons. The trapping maintains a strong sheath electric field, enabling rapid and long-lasting wave propagation aided by field ionization. Using 1D3V kinetic simulations, we examine the propagation of the ionization wave in the presence of a transverse MG-level magnetic field with the objective to identify qualitative changes in a regime where the initial thermal pressure of the plasma exceeds the pressure of the magnetic field ($\beta>1$). Our key finding is that the magnetic field stops the propagation by causing the energetic electrons sustaining the wave to lose their energy by emitting an electromagnetic wave. The emission is accompanied by the magnetic field expulsion from the plasma and an increased electron loss from the trapping wave structure. The described effect provides a mechanism mitigating rapid plasma expansion for those applications that involve an embedded plasma, such as high-flux neutron production from laser-irradiated deuterium gas jets.