Wave emission of non-thermal electron beams generated by magnetic reconnection

TL;DR

This study uses kinetic simulations to investigate how non-thermal electron beams generated by magnetic reconnection produce radio waves, revealing specific plasma instabilities and wave emissions relevant to solar flare diagnostics.

Contribution

It demonstrates the generation of multiple harmonic plasma and electromagnetic waves from distinct electron velocity distributions in magnetic reconnection regions.

Findings

Electron/ion streaming instabilities produce ion acoustic and Langmuir waves.

Perpendicular crescent EVDFs cause electromagnetic electron cyclotron waves.

Results help diagnose plasma conditions in solar flare reconnection sites.

Abstract

Magnetic reconnection in solar flares can efficiently generate non-thermal electron beams. The energetic electrons can, in turn, cause radio waves through microscopic plasma instabilities as they propagate through the ambient plasma along the magnetic field lines. We aim at investigating the wave emission caused by fast moving electron beams (FEBs) with characteristic non-thermal electron velocity distribution functions (EVDFs) generated by kinetic magnetic reconnection: two-streaming EVDFs along the separatrices and in the diffusion region, and perpendicular crescent-shaped EVDFs closer to the diffusion region. For this purpose, we utilized 2.5D fully kinetic Particle-In-Cell (PIC) code simulations in this study. We found that:(1) the two-streaming EVDFs plus the background ions are unstable to electron/ion (streaming) instabilities which cause ion acoustic waves and Langmuir waves due to the net current. This can lead to multiple harmonic plasma emission in the diffusion region and the separatrices of reconnection. (2) The perpendicular crescent-shaped EVDFs can cause multiple harmonic electromagnetic electron cyclotron waves through the electron cyclotron maser instabilities in the diffusion region of reconnection. Our results are applicable to diagnose the plasma parameters which control magnetic reconnection in solar flares by means of radio waves observations.