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Title: Particle acceleration in relativistic magnetic flux-merging events

Abstract

Using analytical and numerical methods (fluid and particle-in-cell simulations) we study a number of model problems involving merger of magnetic flux tubes in relativistic magnetically dominated plasma. Mergers of current-carrying flux tubes (exemplified by the two-dimensional ‘ABC’ structures) and zero-total-current magnetic flux tubes are considered. In all cases regimes of spontaneous and driven evolution are investigated. We identify two stages of particle acceleration during flux mergers: (i) fast explosive prompt X-point collapse and (ii) ensuing island merger. The fastest acceleration occurs during the initial catastrophic X-point collapse, with the reconnection electric field of the order of the magnetic field. During the X-point collapse, particles are accelerated by charge-starved electric fields, which can reach (and even exceed) values of the local magnetic field. The explosive stage of reconnection produces non-thermal power-law tails with slopes that depend on the average magnetization$$\unicode[STIX]{x1D70E}$$. For plasma magnetization$$\unicode[STIX]{x1D70E}\leqslant 10^{2}$$the spectrum power-law index is$p>2$$; in this case the maximal energy depends linearly on the size of the reconnecting islands. For higher magnetization,$$\unicode[STIX]{x1D70E}\geqslant 10^{2}$$, the spectra are hard,$$p<2$$, yet the maximal energy$$\unicode[STIX]{x1D6FE}_{\text{max}}$$can still exceed the average magnetic energy per particle,$${\sim}\unicode[STIX]{x1D70E}$$, by orders of magnitude (if$$p$is not too close to unity). The X-point collapse stage is followed by magnetic island merger that dissipates a large fraction of the initial magnetic energy in a regime of forced magnetic reconnection, further accelerating the particles, but proceeds at a slower reconnection rate.

Authors:
; ; ;
Publication Date:
Research Org.:
Purdue Univ., West Lafayette, IN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1538924
DOE Contract Number:  
SC0016369
Resource Type:
Journal Article
Journal Name:
Journal of Plasma Physics
Additional Journal Information:
Journal Volume: 83; Journal Issue: 6; Journal ID: ISSN 0022-3778
Publisher:
Cambridge University Press
Country of Publication:
United States
Language:
English
Subject:
Physics

Citation Formats

Lyutikov, Maxim, Sironi, Lorenzo, Komissarov, Serguei S., and Porth, Oliver. Particle acceleration in relativistic magnetic flux-merging events. United States: N. p., 2017. Web. doi:10.1017/s002237781700071x.
Lyutikov, Maxim, Sironi, Lorenzo, Komissarov, Serguei S., & Porth, Oliver. Particle acceleration in relativistic magnetic flux-merging events. United States. doi:10.1017/s002237781700071x.
Lyutikov, Maxim, Sironi, Lorenzo, Komissarov, Serguei S., and Porth, Oliver. Fri . "Particle acceleration in relativistic magnetic flux-merging events". United States. doi:10.1017/s002237781700071x.
@article{osti_1538924,
title = {Particle acceleration in relativistic magnetic flux-merging events},
author = {Lyutikov, Maxim and Sironi, Lorenzo and Komissarov, Serguei S. and Porth, Oliver},
abstractNote = {Using analytical and numerical methods (fluid and particle-in-cell simulations) we study a number of model problems involving merger of magnetic flux tubes in relativistic magnetically dominated plasma. Mergers of current-carrying flux tubes (exemplified by the two-dimensional ‘ABC’ structures) and zero-total-current magnetic flux tubes are considered. In all cases regimes of spontaneous and driven evolution are investigated. We identify two stages of particle acceleration during flux mergers: (i) fast explosive prompt X-point collapse and (ii) ensuing island merger. The fastest acceleration occurs during the initial catastrophic X-point collapse, with the reconnection electric field of the order of the magnetic field. During the X-point collapse, particles are accelerated by charge-starved electric fields, which can reach (and even exceed) values of the local magnetic field. The explosive stage of reconnection produces non-thermal power-law tails with slopes that depend on the average magnetization$\unicode[STIX]{x1D70E}$. For plasma magnetization$\unicode[STIX]{x1D70E}\leqslant 10^{2}$the spectrum power-law index is$p>2$; in this case the maximal energy depends linearly on the size of the reconnecting islands. For higher magnetization,$\unicode[STIX]{x1D70E}\geqslant 10^{2}$, the spectra are hard,$p<2$, yet the maximal energy$\unicode[STIX]{x1D6FE}_{\text{max}}$can still exceed the average magnetic energy per particle,${\sim}\unicode[STIX]{x1D70E}$, by orders of magnitude (if$p$is not too close to unity). The X-point collapse stage is followed by magnetic island merger that dissipates a large fraction of the initial magnetic energy in a regime of forced magnetic reconnection, further accelerating the particles, but proceeds at a slower reconnection rate.},
doi = {10.1017/s002237781700071x},
journal = {Journal of Plasma Physics},
issn = {0022-3778},
number = 6,
volume = 83,
place = {United States},
year = {2017},
month = {12}
}

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