Energy transfer and electron energization in collisionless magnetic reconnection for different guide-field intensities

Abstract

Electron dynamics and energization are one of the key components of magnetic field dissipation in collisionless reconnection. In 2D numerical simulations of magnetic reconnection, the main mechanism that limits the current density and provides an effective dissipation is most probably the electron pressure tensor term, which has been shown to break the frozen-in condition at the x-point. In addition, the electron-meandering-orbit scale controls the width of the electron dissipation region, where the electron temperature has been observed to increase both in recent Magnetospheric Multiple-Scale (MMS) observations and in laboratory experiments, such as the Magnetic Reconnection Experiment (MRX). By means of two-dimensional full-particle simulations in an open system, we investigate how the energy conversion and particle energization depend on the guide field intensity. We study the energy transfer from the magnetic field to the plasma in the vicinity of the x-point and close downstream regions, and E·J and the threshold guide field separating two regimes where either the parallel component, E||J||, or the perpendicular component, E⊥·J⊥, dominate the energy transfer, confirming recent MRX results and also consistent with MMS observations. We calculate the energy partition between fields and kinetic and thermal energies of different species, from electron to ion scales, showing that there is no significant variation for different guide field configurations. Finally, we study possible mechanisms for electron perpendicular heating by examining electron distribution functions and self-consistently evolved particle orbits in high guide field configurations.