Parallel Velocity Mixing Yielding Enhanced Electron Heating During Magnetic Pumping

TL;DR

This paper investigates how magnetic trapping and pitch angle scattering mechanisms combine to enhance electron heating during magnetic pumping in space plasmas, with implications for solar wind and Earth's bow shock environments.

Contribution

It introduces a model showing how trapping/detrapping of energetic electrons and pitch angle scattering jointly increase electron heating rates beyond previous theories.

Findings

Parallel velocity diffusion is caused by trapping/detrapping of electrons.

Pitch angle scattering with Whistler waves enhances heating.

Combined mechanisms outperform previous magnetic pumping predictions.

Abstract

Magnetic wave perturbations are observed in the solar wind and in the vicinity of Earth's bow shock. For such environments, recent work on magnetic pumping with electrons trapped in the magnetic perturbations have demonstrated the possibility of efficient energization of superthermal electrons. Here we also analyze the energization of such energetic electrons for which the transit time through the system is short compared to time scales associated with the magnetic field evolution. In particular, considering an idealized magnetic configuration we show how trapping/detrapping of energetic magnetized electrons can cause effective parallel velocity diffusion. This parallel diffusion, combined with naturally occurring mechanisms known to cause pitch angle scattering, such as Whistler waves, produces enhanced heating rates for magnetic pumping. We find that at low pitch angle scattering rates the combined mechanism enhances the heating beyond the predictions of the recent theory for magnetic pumping with trapped electrons.