Particle Acceleration during Magnetic Reconnection in a Low-beta Plasma

Journal Article · Tue Jun 27 00:00:00 EDT 2017 · The Astrophysical Journal (Online)

DOI:https://doi.org/10.3847/1538-4357/aa745e· OSTI ID:1524226

Li, Xiaocan ^[1]; Guo, Fan ^[2]; Li, Hui ^[2]; Li, Gang ^[3]

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1. Univ. of Alabama, Huntsville, AL (United States). Dept. of Space Science; Univ. of Alabama, Huntsville, AL (United States). Center for Space Plasma and Aeronomic Research; Los Alamos National Lab., Los Alamos, NM (United States)
2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
3. Univ. of Alabama, Huntsville, AL (United States). Dept. of Space Science

Magnetic reconnection is a primary mechanism for particle energization in space and astrophysical plasmas. By carrying out two-dimensional (2D) fully kinetic simulations, we study particle acceleration during magnetic reconnection in plasmas with different plasma β (the ratio between the thermal pressure and the magnetic pressure). For the high-β cases, we do not observe significant particle acceleration. In the low-β regime ($$\beta \lt 0.1$$), we find that reconnection is efficient at energizing both electrons and ions. While the distribution of accelerated particles integrated over the whole simulation box appears highly non-thermal, it is actually the superposition of a series of distributions in different sectors of a 2D magnetic island. Each of those distributions has only a small non-thermal component compared with its thermal core. By tracking a large number of particles, we show that particles get energized in X-line regions, contracting magnetic islands, and magnetic island coalescence regions. We obtain the particle energization rate $${\boldsymbol{j}}\cdot {\boldsymbol{E}}$$ by averaging over particle drift motions and find that it agrees well with the particle kinetic energy change. We quantify the contribution of curvature drift, gradient drift, polarization drift, magnetization, non-gyrotropic effect, and parallel electric field in different acceleration regions. We find that the major energization is due to particle curvature drift along the motional electric field. The other particle motions contribute less but may become important in different acceleration regions. The highly efficient particle energization in low-β plasmas may help us understand the strong particle energization in solar flares and accretion disk coronae.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center
• Sponsoring Organization: USDOE
• OSTI ID: 1524226
• Alternate ID(s): OSTI ID: 22876082
• Journal Information: The Astrophysical Journal (Online), Journal Name: The Astrophysical Journal (Online) Journal Issue: 1 Vol. 843; ISSN 1538-4357
• Publisher: Institute of Physics (IOP)
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
Sun: corona
Sun: flares
acceleration of particles
accretion
accretion disks
magnetic reconnection