Particle acceleration and plasma dynamics during magnetic reconnection in the magnetically dominated regime

Journal Article · Wed Jun 17 04:00:00 UTC 2015 · The Astrophysical Journal (Online)

DOI: https://doi.org/10.1088/0004-637X/806/2/167 · OSTI ID:1240428

Guo, Fan ^[1]; Liu, Yi -Hsin ^[2]; Daughton, William ^[1]; Li, Hui ^[1]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. NASA Goddard Space Flight Center, Greenbelt, MD (United States)

Magnetic reconnection is thought to be the driver for many explosive phenomena in the universe. The energy release and particle acceleration during reconnection have been proposed as a mechanism for producing high-energy emissions and cosmic rays. We carry out two- and three-dimensional (3D) kinetic simulations to investigate relativistic magnetic reconnection and the associated particle acceleration. The simulations focus on electron–positron plasmas starting with a magnetically dominated, force-free current sheet (σ ≡ B² / (4πn_em_ec²) >> 1). For this limit, we demonstrate that relativistic reconnection is highly efficient at accelerating particles through a first-order Fermi process accomplished by the curvature drift of particles along the electric field induced by the relativistic flows. This mechanism gives rise to the formation of hard power-law spectra f α (γ - 1)^-p and approaches p = 1 for sufficiently large σ and system size. Eventually most of the available magnetic free energy is converted into nonthermal particle kinetic energy. An analytic model is presented to explain the key results and predict a general condition for the formation of power-law distributions. The development of reconnection in these regimes leads to relativistic inflow and outflow speeds and enhanced reconnection rates relative to nonrelativistic regimes. In the 3D simulation, the interplay between secondary kink and tearing instabilities leads to strong magnetic turbulence, but does not significantly change the energy conversion, reconnection rate, or particle acceleration. This paper suggests that relativistic reconnection sites are strong sources of nonthermal particles, which may have important implications for a variety of high-energy astrophysical problems.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: DOE Office of Science; USDOE
• Grant/Contract Number: AC52-06NA25396
• OSTI ID: 1240428
• Report Number(s): LA-UR--14-29249
• Journal Information: The Astrophysical Journal (Online), Journal Name: The Astrophysical Journal (Online) Journal Issue: 2 Vol. 806; ISSN 1538-4357
• Publisher: Institute of Physics (IOP)Copyright Statement
• Country of Publication: United States
• Language: English