One-dimensional thermal pressure-driven expansion of a pair cloud into an electron-proton plasma

TL;DR

This study uses one-dimensional PIC simulations to explore how a hot pair cloud expands into an electron-proton plasma, leading to electron phase space holes that can accelerate protons to MeV energies, relevant for laboratory and astrophysical contexts.

Contribution

It demonstrates that a thermal pair cloud can drive instabilities that accelerate protons, a novel insight into plasma dynamics and particle acceleration mechanisms.

Findings

Electron phase space holes form during cloud expansion.

Some protons are accelerated to MeV energies.

Laser-generated pair clouds could enable proton acceleration.

Abstract

Recently a filamentation instability was observed when a laser-generated pair cloud interacted with an ambient plasma. The magnetic field it drove was strong enough to magnetize and accelerate the ambient electrons. It is of interest to determine if and how pair cloud-driven instabilities can accelerate ions in the laboratory or in astrophysical plasma. For this purpose, the expansion of a localized pair cloud with the temperature 400 keV into a cooler ambient electron-proton plasma is studied by means of one-dimensional particle-in-cell (PIC) simulations. The cloud's expansion triggers the formation of electron phase space holes that accelerate some protons to MeV energies. Forthcoming lasers might provide the energy needed to create a cloud that can accelerate protons.