arXiv Analytics

Sign in

arXiv:1810.04135 [astro-ph.HE]AbstractReferencesReviewsResources

Onset of magnetic reconnection in a collisionless, high-beta plasma

Andrew Alt, Matthew W. Kunz

Published 2018-10-09Version 1

In a magnetized, collisionless plasma, the magnetic moment of the constituent particles is an adiabatic invariant. An increase in the magnetic-field strength in such a plasma thus leads to an increase in the thermal pressure perpendicular to the field lines. Above a $\beta$-dependent threshold (where $\beta$ is the ratio of thermal to magnetic pressure), this pressure anisotropy drives the mirror instability, producing strong distortions in the field lines on ion-Larmor scales. The impact of this instability on magnetic reconnection is investigated using a simple analytical model for the formation of a current sheet (CS) and the associated production of pressure anisotropy. The difficulty in maintaining an isotropic, Maxwellian particle distribution during the formation and subsequent thinning of a CS in a collisionless plasma, coupled with the low threshold for the mirror instability in a high-$\beta$ plasma, imply that the geometry of reconnecting magnetic fields can differ radically from the standard Harris-sheet profile often used in kinetic simulations of collisionless reconnection. As a result, depending on the rate of CS formation and the initial CS thickness, tearing modes whose growth rates and wavenumbers are boosted by this difference may disrupt the sheet before standard tearing modes are able to develop. A quantitative theory is developed to illustrate this process, which may find application in the tearing-mediated disruption of kinetic magnetorotational "channel" modes.

Comments: submitted to Journal of Plasma Physics Letters on 26 Sept 2018
Related articles: Most relevant | Search more
arXiv:2006.08940 [astro-ph.HE] (Published 2020-06-16)
Self-sustaining sound in collisionless, high-beta plasma
arXiv:2003.01879 [astro-ph.HE] (Published 2020-03-04)
Kinetic simulations of nonrelativistic perpendicular shocks of young supernova remnants. III. Magnetic reconnection
arXiv:1007.0774 [astro-ph.HE] (Published 2010-07-05)
Magnetic Reconnection with Radiative Cooling. I. Optically-Thin Regime