Electron acceleration during three-dimensional relaxation of an electron beam-return current plasma system in a magnetic field

TL;DR

This study uses 3D particle-in-cell simulations to show that during electron beam relaxation in magnetized plasma, a significant portion of electrons are accelerated, impacting solar flare electron population interpretations.

Contribution

It demonstrates the occurrence of electron acceleration during non-linear beam-plasma relaxation in a magnetic field using detailed 3D simulations, highlighting its importance in solar flare analysis.

Findings

Accelerated electrons can contain 10-30% of initial beam energy.

Electron acceleration occurs despite energy loss to thermal plasma.

Collective plasma effects influence non-thermal electron population estimates.

Abstract

We investigate the effects of acceleration during non-linear electron-beam relaxation in magnetized plasma in the case of electron transport in solar flares. The evolution of electron distribution functions is computed using a three-dimensional particle-in-cell electromagnetic code. Analytical estimations under simplified assumptions are made to provide comparisons. We show that, during the non-linear evolution of the beam-plasma system, the accelerated electron population appears. We found that, although the electron beam loses its energy efficiently to the thermal plasma, a noticeable part of the electron population is accelerated. For model cases with initially monoenergetic beams in uniform plasma, we found that the amount of energy in the accelerated electrons above the injected beam-electron energy varies depending the plasma conditions and could be around 10-30% of the initial beam energy. This type of acceleration could be important for the interpretation of non-thermal electron populations in solar flares. Its neglect could lead to the over-estimation of accelerated electron numbers. The results emphasize that collective plasma effects should not be treated simply as an additional energy-loss mechanism, when hard X-ray emission in solar flares is interpreted, notably in the case of RHESSI data.