Publication Date:
2016-10-15
Description:
Fast magnetic reconnection can occur in different astrophysical sources, producing flare-like emission and particle acceleration. Currently, this process is being studied as an efficient mechanism to accelerate particles via a first-order Fermi process. In this paper, we analyse the acceleration rate and the energy distribution of test particles injected into three-dimensional magnetohydrodynamical (MHD) domains with large-scale current sheets where reconnection is made fast by the presence of turbulence. We study the dependence of the particle acceleration time with the relevant parameters of the embedded turbulence: the Alfvén speed V A , the injection power P inj and scale k inj ( k inj = 1/ l inj ). We find that the acceleration time follows a power-law dependence with the particle kinetic energy: t acc E α , with 0.2 〈 α 〈 0.6 for a vast range of values of c / V A ~ 20–1000. The acceleration time decreases with the Alfvén speed (and therefore with the reconnection velocity) as expected, having an approximate dependence t acc ( V A / c ) – , with ~ 2.1–2.4 for particles reaching kinetic energies between 1 and 100 m p c 2 , respectively. Furthermore, we find that the acceleration time is only weakly dependent on the P inj and l inj parameters of the turbulence. The particle spectrum develops a high-energy tail, which can be fitted by a hard power law already in the early times of the acceleration, consistent with the results of kinetic studies of particle acceleration by magnetic reconnection in collisionless plasmas.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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