Effects of a Velocity Shear on Double Current Sheet Systems: Explosive Reconnection and Particle Acceleration

TL;DR

This study investigates how a parallel velocity shear influences explosive magnetic reconnection and particle acceleration in double current sheet systems within a 2D resistive MHD framework, revealing shear-dependent reconnection rates and particle energy spectra modifications.

Contribution

It demonstrates the impact of velocity shear on reconnection dynamics, particle acceleration mechanisms, and energy spectra, providing new insights into shear effects in magnetic reconnection processes.

Findings

Reconnection rate scales with shear when measured at similar island sizes.

Lower shear leads to larger magnetic islands and higher reconnection rates.

Flow modifies the high-energy tail of particle spectra without affecting the power-law index.

Abstract

The effect of a parallel velocity shear on the explosive phase of a double current sheet system is investigated within the 2D resistive magnetohydrodynamic (MHD) framework. We further explore the effect of this shear on acceleration of test particles. The general evolution pattern of the double current sheets is similar for all sub-Alfv\'enic shears with respect to the initial transient phase, the onset of the plasmoid instability and the final relaxation phase. We find that the theoretical scaling of the reconnection rate with shear holds if the rate is measured when the islands have a similar size. The larger island widths for lower shears greatly enhance the reconnection rate during the explosive phase. We have further examined the modification of the energy spectrum of the accelerated particles in the presence of a shear. Our results also show that the flow only modifies the high energy tail of the particle spectrum and has negligible effect on the power-law index. Individual particle trajectories help to explore the various mechanisms associated with the acceleration. Based on the location of the particles, the acceleration mechanisms are found to vary. We highlight the importance of the convective electric field in the inflow as well as the outflow region inside large magnetic islands in the acceleration of particles. The interaction and reflection of the particles with the reconnection exhausts inside the large scale primary magnetic islands is found to have a significant effect on the energization of the particles.