Particle acceleration with anomalous pitch angle scattering in 2D magnetohydrodynamic reconnection simulations

Borissov, A., Kontar, E.P. , Threlfall, J. and Neukirch, T. (2017) Particle acceleration with anomalous pitch angle scattering in 2D magnetohydrodynamic reconnection simulations. Astronomy and Astrophysics, 605, A73. (doi:10.1051/0004-6361/201731183)

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Publisher's URL: http://dx.doi.org/10.1051/0004-6361/201731183

Abstract

The conversion of magnetic energy into other forms (such as plasma heating, bulk plasma flows, and non-thermal particles) during solar flares is one of the outstanding open problems in solar physics. It is generally accepted that magnetic reconnection plays a crucial role in these conversion processes. In order to achieve the rapid energy release required in solar flares, an anomalous resistivity, which is orders of magnitude higher than the Spitzer resistivity, is often used in magnetohydrodynamic (MHD) simulations of reconnection in the corona. The origin of Spitzer resistivity is based on Coulomb scattering, which becomes negligible at the high energies achieved by accelerated particles. As a result, simulations of particle acceleration in reconnection events are often performed in the absence of any interaction between accelerated particles and any background plasma. This need not be the case for scattering associated with anomalous resistivity caused by turbulence within solar flares, as the higher resistivity implies an elevated scattering rate. We present results of test particle calculations, with and without pitch angle scattering, subject to fields derived from MHD simulations of two-dimensional (2D) X-point reconnection. Scattering rates proportional to the ratio of the anomalous resistivity to the local Spitzer resistivity, as well as at fixed values, are considered. Pitch angle scattering, which is independent of the anomalous resistivity, causes higher maximum energies in comparison to those obtained without scattering. Scattering rates which are dependent on the local anomalous resistivity tend to produce fewer highly energised particles due to weaker scattering in the separatrices, even though scattering in the current sheet may be stronger when compared to resistivity-independent scattering. Strong scattering also causes an increase in the number of particles exiting the computational box in the reconnection outflow region, as opposed to along the separatrices as is the case in the absence of scattering.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Kontar, Dr Eduard
Authors: Borissov, A., Kontar, E.P., Threlfall, J., and Neukirch, T.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astronomy and Astrophysics
Publisher:EDP Sciences
ISSN:0004-6361
ISSN (Online):1432-0746
Published Online:12 September 2017
Copyright Holders:Copyright © 2017 ESO
First Published:First published in Astronomy and Astrophysics 605:A73
Publisher Policy:Reproduced under a Creative Commons License
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
631581Consolidated grant in solar and astrophysical plasmasLyndsay FletcherScience & Technology Facilities Council (STFC)ST/L000741/1S&E P&A - PHYSICS & ASTRONOMY