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Title: Onset of magnetic reconnection in a collisionless, high-β plasma

Abstract

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 hence leads to an increase in the thermal pressure perpendicular to the field lines. Above a $$\unicode[STIX]{x1D6FD}$$-dependent threshold (where $$\unicode[STIX]{x1D6FD}$$ 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 effect 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-$$\unicode[STIX]{x1D6FD}$$plasma, imply that the geometry of reconnecting magnetic fields can differ radically from the standard Harris-sheet profile often used in simulations of collisionless reconnection. Because of this, 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 mirror-infested CS before standard tearing modes can develop. A quantitative theory is developed to illustrate this process, which may find application in the tearing-mediated disruption of kinetic magnetorotational ‘channel’ modes.

Authors:
ORCiD logo [1]; ORCiD logo [1]
  1. Princeton Univ., NJ (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1547059
Grant/Contract Number:  
AC02-09CH11466
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Plasma Physics
Additional Journal Information:
Journal Volume: 85; Journal Issue: 1; Journal ID: ISSN 0022-3778
Publisher:
Cambridge University Press
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; astrophysical plasmas; plasma instabilities; plasma nonlinear phenomena

Citation Formats

Alt, Andrew, and Kunz, Matthew W. Onset of magnetic reconnection in a collisionless, high-β plasma. United States: N. p., 2019. Web. doi:10.1017/S0022377819000084.
Alt, Andrew, & Kunz, Matthew W. Onset of magnetic reconnection in a collisionless, high-β plasma. United States. doi:10.1017/S0022377819000084.
Alt, Andrew, and Kunz, Matthew W. Wed . "Onset of magnetic reconnection in a collisionless, high-β plasma". United States. doi:10.1017/S0022377819000084.
@article{osti_1547059,
title = {Onset of magnetic reconnection in a collisionless, high-β plasma},
author = {Alt, Andrew and Kunz, Matthew W.},
abstractNote = {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 hence leads to an increase in the thermal pressure perpendicular to the field lines. Above a $\unicode[STIX]{x1D6FD}$-dependent threshold (where $\unicode[STIX]{x1D6FD}$ 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 effect 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-$\unicode[STIX]{x1D6FD}$plasma, imply that the geometry of reconnecting magnetic fields can differ radically from the standard Harris-sheet profile often used in simulations of collisionless reconnection. Because of this, 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 mirror-infested CS before standard tearing modes can develop. A quantitative theory is developed to illustrate this process, which may find application in the tearing-mediated disruption of kinetic magnetorotational ‘channel’ modes.},
doi = {10.1017/S0022377819000084},
journal = {Journal of Plasma Physics},
number = 1,
volume = 85,
place = {United States},
year = {2019},
month = {2}
}

Journal Article:
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This content will become publicly available on February 27, 2020
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