Shock creation and particle acceleration driven by plasma expansion into a rarefied medium

TL;DR

This study models plasma expansion into a rarified medium using 1D Particle-In-Cell simulations, revealing shock formation, wave phenomena, and efficient proton acceleration with velocities up to 60 times thermal speed.

Contribution

It introduces a detailed simulation of plasma expansion into a rarefied medium, highlighting nonlinear phenomena and proton acceleration mechanisms.

Findings

Formation of strong ion-acoustic shock waves.

Detection of secondary structures driven by drift instability.

Protons accelerated up to 60 times initial thermal speed.

Abstract

The expansion of a dense plasma through a more rarefied ionised medium is a phenomenon of interest in various physics environments ranging from astrophysics to high energy density laser- matter laboratory experiments. Here this situation is modeled via a 1D Particle-In-Cell simulation; a jump in the plasma density of a factor of 100 is introduced in the middle of an otherwise equally dense electron-proton plasma with an uniform proton and electron temperature of 10eV and 1keV respectively. The diffusion of the dense plasma, through the rarified one, triggers the onset of different nonlinear phenomena such as a strong ion-acoustic shock wave and a rarefaction wave. Secondary structures are detected, some of which are driven by a drift instability of the rarefaction wave. Efficient proton acceleration occurs ahead of the shock, bringing the maximum proton velocity up to 60 times the initial ion thermal speed.