Two-Stage Bulk Electron Heating in the Diffusion Region of Anti-Parallel Symmetric Reconnection

TL;DR

This paper investigates the two-stage process of electron heating during magnetic reconnection, combining theoretical analysis, simulations, and observations to understand how electrons gain energy in the diffusion region.

Contribution

It provides a simplified control-volume analysis that accurately estimates electron heating scaling, aligning with kinetic simulations and spacecraft data.

Findings

Electron heating occurs in two stages: trapping and energization by electric fields, then gain from reconnection electric field.

The analysis matches simulation and spacecraft observations, validating the simplified model.

Electron velocity distributions become highly structured during the process.

Abstract

Electron bulk energization in the diffusion region during anti-parallel symmetric reconnection entails two stages. First, the inflowing electrons are adiabatically trapped and energized by an ambipolar parallel electric field. Next, the electrons gain energy from the reconnection electric field as they undergo meandering motion. These collisionless mechanisms have been decribed previously, and they lead to highly-structured electron velocity distributions. Nevertheless, a simplified control-volume analysis gives estimates for how the net effective heating scales with the upstream plasma conditions in agreement with fully kinetic simulations and spacecraft observations.