The effects of plasma beta and anisotropy instabilities on the dynamics of reconnecting magnetic fields in the heliosheath

TL;DR

This study examines how plasma beta influences magnetic reconnection in the heliosheath, revealing that high beta conditions lead to elongated islands and suppressed reconnection due to instabilities.

Contribution

It provides new insights into the role of plasma beta and anisotropy instabilities in magnetic reconnection dynamics within the heliosheath.

Findings

Low beta results in modestly elongated, rounder islands.

High beta causes saturation and elongation of islands due to firehose instability.

Reconnection is suppressed in high beta conditions by kinking instabilities.

Abstract

The plasma {\beta} (the ratio of the plasma pressure to the magnetic pressure) of a system can have a large effect on its dynamics as high {\beta} enhances the effects of pressure anisotropies. We investigate the effects of {\beta} in a system of stacked current sheets that break up into magnetic islands due to magnetic reconnection. We find significant differences between {\beta} < 1 and {\beta} > 1. At low {\beta} growing magnetic islands are modestly elongated and become round as contraction releases magnetic stress and reduces magnetic energy. At high {\beta} the increase of the parallel pressure in contracting islands causes saturation of modestly elongated islands as island cores approach the marginal firehose condition. Only highly elongated islands reach finite size. The kinking associated with the Weibel and firehose instabilities prevents full contraction of these islands, leading to a final state of highly elongated islands in which further reconnection is suppressed. The results are directly relevant to reconnection in the sectored region of the heliosheath and possibly to saturation mechanisms of the magnetorotational instability in accretion flows.