The Enhancement of Ion Heating in Kinetic, Anti-Parallel Reconnection in the Presence of a Flow Shear

TL;DR

This paper uses kinetic simulations to show that flow shear enhances ion heating during magnetic reconnection, modifies the reconnection geometry, and reduces outflow speeds, providing insights into plasma energy dissipation.

Contribution

It introduces a kinetic model demonstrating how flow shear increases ion heating and alters reconnection dynamics, differing from previous MHD studies.

Findings

Ion heating increases by up to 300% with flow shear

Reconnection outflow speeds are reduced due to pressure gradients

A theoretical model accurately predicts exhaust heating and outflow reduction

Abstract

We investigate the kinetic effects of upstream, magnetic field-aligned, flow shear on anti-parallel magnetic reconnection using 2.5D Particle-In-Cell simulations. Our results demonstrate that flow shear significantly alters the reconnection process, leading to enhanced ion heating, reduced outflow speeds, and a modified reconnection geometry. In contrast to previous Hall Magnetohydrodynaic (MHD) studies, we find that reconnection becomes a more efficient plasma heating mechanism in the presence of sub-Alfv\'enic flow shear, with ion heating increasing by as much as 300\%. This enhanced heating is achieved by efficiently converting the incoming flow shear energy into thermal energy through istropization in the exhaust. The enhanced heating leads to a pressure gradient away form the x-line exerting a force that reduces the outflow jet speed and slows down the reconnection process. This conversion is due to beam selection effects, mixing and scattering in the exhaust. A theoretical model is developed which predicts well the exhaust heating and outflow speed reduction. These results offer a potential explanation for recent Parker Solar Probe observations of suppressed reconnection in the presence of flow shear and carry significant implications for energy dissipation in turbulent plasmas.