Numerical study of non-gyrotropic electron pressure effects in collisionless magnetic reconnection

TL;DR

This study uses a hybrid simulation to explore how non-gyrotropic electron pressure influences magnetic reconnection, revealing that pressure anisotropies can lead to bifurcated current sheets and affect reconnection rates.

Contribution

It demonstrates the role of electron pressure anisotropy and isotropization in the evolution of magnetic reconnection, highlighting the impact on current sheet structure and reconnection efficiency.

Findings

Electron pressure anisotropy causes current sheet bifurcation.

Isotropization related to electron heat flux stabilizes pressure tensor components.

Bifurcated current sheets have smaller reconnection rates.

Abstract

We investigate the time evolution of the six-component electron pressure tensor in a hybrid code studying consequences for the two-dimensional reconnection process in an initially perturbed Harris sheet. We put forward that two tensor components (a diagonal and a non-diagonal one) grow in an unstable way unless an isotropization operator is considered. This isotropization term is physically associated with an electron heat flux. As a consequence, we put forward that an enhanced value of a diagonal component is observed in the very middle of field reversal at sub-ion scale. Because of the increase of the kinetic pressure, the magnetic field is decreased in this electron layer, hence increasing the associated out-of-plane current at its edges and leading to its bifurcation. The bifurcation mechanism is based on the presence of electron pressure anisotropy, related to the gradient of inflow electron bulk velocity. The gradient in the inflow direction of the enhanced diagonal electron pressure tensor component results in the deceleration of the ions entering the X-point region. We suggest that bifurcated current sheets resulting from the anisotropies/agyrotropies of the six-component electron pressure tensor correspond to smaller reconnection rates comparing to non-bifurcated ones.