# Scattering of energetic electrons by heat-flux-driven whistlers in flares

## TL;DR

This study uses particle-in-cell simulations to investigate how heat-flux-driven whistler waves scatter energetic electrons in solar flares, revealing potential confinement mechanisms for high-energy particles.

## Contribution

It demonstrates that heat-flux-driven whistlers can effectively scatter energetic electrons, contributing to their confinement in flare environments, a novel insight into flare particle transport.

## Key findings

- Whistler waves are driven by heat flux and cold return currents.
- Energetic electrons resonate with whistlers and are scattered within a hundred electron cyclotron times.
- Electron scattering reduces heat flux and increases perpendicular energy, aiding confinement.

## Abstract

The scattering of electrons by heat-flux-driven whistler waves is explored with a particle-in-cell (PIC) simulation relevant to the transport of energetic electrons in flares. The simulation is initiated with a large heat flux that is produced using a kappa distribution of electrons with positive velocity and a cold return current beam. This system represents energetic electrons escaping from a reconnection-driven energy release site. This heat flux system drives large amplitude oblique whistler waves propagating both along and against the heat flux, as well as electron acoustic waves. While the waves are dominantly driven by the low energy electrons, including the cold return current beam, the energetic electrons resonate with and are scattered by the whistlers on time scales of the order of a hundred electron cyclotron times. Peak whistler amplitudes of $\tilde{B} / B_{0} \sim 0.125$ and angles of $\sim 60 \degree$ with respect to the background magnetic field are observed. Electron perpendicular energy is increased while the field-aligned electron heat flux is suppressed. The resulting scattering mean-free-paths of energetic electrons are small compared with the typical scale size of energy release sites in flares, which might lead to the effective confinement of energetic electrons that is required for the production of very energetic particles.