Wave generation and energetic electron scattering in solar flares

TL;DR

This study uses particle-in-cell simulations to explore how self-generated electromagnetic waves scatter energetic electrons in solar flares, revealing key parameters that influence heat flux reduction and electron isotropization.

Contribution

It introduces a scaling law for electron scattering rates based on drift speed relative to the electron Alfvén speed, advancing understanding of electron transport in solar flares.

Findings

Higher drift speeds lead to stronger wave fluctuations and greater heat flux reduction.

Reducing electron density by 50% does not significantly change scattering rates.

A scaling law relates scattering rate to the ratio of drift speed to Alfvén speed.

Abstract

We conduct two-dimensional particle-in-cell simulations to investigate the scattering of electron heat flux by self-generated oblique electromagnetic waves. The heat flux is modeled as a bi-kappa distribution with a T_parallel > T_perp temperature anisotropy maintained by continuous injection at the boundaries. The anisotropic distribution excites oblique whistler waves and filamentary-like Weibel instabilities. Electron velocity distributions taken after the system has reached a steady state show that these in stabilities inhibit the heat flux and drive the total distributions towards isotropy. Electron trajectories in velocity space show a circular-like diffusion along constant energy surfaces in the wave frame. The key parameter controlling the scattering rate is the average speed, or drift speed vd, of the heat flux compared with the electron Alfven speed vAe, with higher drift speeds producing stronger fluctua tions and a more significant reduction of the heat flux. Reducing the density of the electrons carrying the heat flux by 50% does not significantly affect the scattering rate. A scaling law for the electron scattering rate versus vd/vAe is deduced from the simulations. The implications of these results for understanding energetic electron transport during solar flare energy release are discussed.