The Physical Foundation of the Reconnection Electric Field

TL;DR

This paper combines simulations and theory to reveal that the reconnection electric field primarily sustains current density through thermal effects, highlighting the importance of particle interactions and thermalization in magnetic reconnection.

Contribution

It provides a self-consistent explanation of the reconnection electric field's role, emphasizing thermal effects over convection or magnetic field rotation, with testable predictions for laboratory and satellite studies.

Findings

Current dissipation results from thermal effects, not convection.

Reconnection electric field redirects acceleration into thermal motion.

Thermalization increases the plasma's thermal energy.

Abstract

We report on computer simulations and analytic theory to provide a self-consistent understanding of the role of the reconnection electric field, which extends substantially beyond the simple change of magnetic connections. Rather, we find that the reconnection electric field is essential to maintaining the current density in the diffusion region, which would otherwise be dissipated by a set of processes. Natural candidates for current dissipation are the average convection of current carriers away from the reconnection region by the outflow of accelerated particles, or the average rotation of the current density by the magnetic field reversal in the vicinity. Instead, we show here that the current dissipation is the result of thermal effects, underlying the statistical interaction of current-carrying particles with the adjacent magnetic field. We find that this interaction serves to redirect the directed acceleration of the reconnection electric field to thermal motion. This thermalization manifests itself in form of quasi-viscous terms in the thermal energy balance of the current layer. These quasi-viscous terms act to increase the average thermal energy. Our predictions regarding current and thermal energy balance are readily amenable to exploration in the laboratory or by satellite missions, in particular, by NASAs Magnetospheric Multiscale mission.