Magnetic reconnection during collisionless, stressed, X-point collapse using Particle-in-Cell simulation

TL;DR

This study uses Particle-in-Cell simulations to analyze magnetic reconnection during collisionless, stressed X-point collapse, revealing how stress levels influence reconnection rates, energy conversion, and particle acceleration.

Contribution

It provides new insights into how different stress levels affect reconnection dynamics and energy conversion in collisionless plasmas, relevant to solar and space physics.

Findings

Reconnection rate peaks at 0.11 in weak stress and 2.5 in strong stress cases.

Strong stress accelerates reconnection by a factor of 3.4.

Significant magnetic energy converts into heat and particle energy during reconnection.

Abstract

Two cases of weakly and strongly stressed X-point collapse were considered. Here descriptors weakly and strongly refer to 20 % and 124 % unidirectional spatial compression of the X-point, respectively. In the weakly stressed case, the reconnection rate, defined as the out-of-plane electric field in the X-point (the magnetic null) normalised by the product of external magnetic field and Alfv\'en speeds, peaks at 0.11, with its average over 1.25 Alfv\'en times being 0.04. Electron energy distribution in the current sheet, at the high energy end of the spectrum, shows a power law distribution with the index varying in time, attaining a maximal value of -4.1 at the final simulation time step (1.25 Alfv\'en times). In the strongly stressed case, magnetic reconnection peak occurs 3.4 times faster and is more efficient. The peak reconnection rate now attains value 2.5, with the average reconnection rate over 1.25 Alfv\'en times being 0.5. The power law energy spectrum for the electrons in the current sheet attains now a steeper index of -5.5, a value close to the ones observed in the vicinity of X-type region in the Earth's magneto-tail. Within about one Alfv\'en time, 2% and 20% of the initial magnteic energy is converted into heat and accelerated particle energy in the case of weak and strong stress, respectively. In the both cases, during the peak of the reconnection, the quadruple out-of-plane magnetic field is generated, hinting possibly to the Hall regime of the reconnection. These results strongly suggest the importance of the collionless, stressed X-point collapse as a possible contributing factor to the solution of the solar coronal heating problem or more generally, as an efficient mechanism of converting magnetic energy into heat and super-thermal particle energy.