Parallel electric fields are inefficient drivers of energetic electrons in magnetic reconnection

TL;DR

This study uses kinetic simulations to show that parallel electric fields mainly accelerate electrons without producing energetic populations in strong guide field magnetic reconnection, highlighting the importance of Fermi acceleration in weaker guide fields.

Contribution

It demonstrates that parallel electric fields are inefficient at generating energetic electrons in strong guide field reconnection, emphasizing the role of Fermi acceleration in weaker guide fields.

Findings

Parallel electric fields drive electron energy gain in strong guide fields.

Fermi acceleration is responsible for energetic electrons in weak guide fields.

Parallel electric fields do not produce energetic electrons in strong guide field regimes.

Abstract

We present two-dimensional kinetic simulations, with a broad range of initial guide fields, that isolate the role of parallel electric fields ($E_\parallel$) in energetic electron production during collisionless magnetic reconnection. In the strong guide field regime, $E_\parallel$ drives essentially all of the electron energy gain, yet fails to generate an energetic component. We suggest that this is due to the weak energy scaling of particle acceleration from $E_\parallel$ compared to that of a Fermi-type mechanism responsible for energetic electron production in the weak guide-field regime. This result has important implications for energetic electron production in astrophysical systems and reconnection-driven dissipation in turbulence.