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Title: Large-scale Compression Acceleration during Magnetic Reconnection in a Low- β Plasma

Abstract

In solar flares and other astrophysical systems, a major challenge for solving the particle acceleration problem associated with magnetic reconnection is the enormous scale separation between kinetic scales and the observed reconnection scale. Because of this, it has been difficult to draw any definite conclusions by just using kinetic simulations. A particle acceleration model that solves the energetic particle transport equation can capture the main acceleration physics found in kinetic simulations and thus provide a practical way to make observable predictions and directly compare model results with observations. Here we study compression particle acceleration in magnetic reconnection by solving the Parker (diffusion–advection) transport equation using velocity and magnetic fields from two-dimensional magnetohydrodynamics (MHD) simulations of a low-β high-Lundquist-number reconnection layer. We show that the compressible reconnection layer can give significant particle acceleration, leading to the formation of power-law particle energy distributions. We analyze the acceleration rate and find that the acceleration in the reconnection layer is a mixture of first- and second-order Fermi processes. When including a guide field, we find that the spectrum becomes steeper and both the power-law cutoff energy and maximum particle energy decrease as plasma becomes less compressible. This model produces a 2D particle distribution thatmore » one can use to generate a radiation map and directly compare with solar flare observations. This provides a framework to explain particle acceleration at large-scale astrophysical reconnection sites, such as solar flares.« less

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [1]; ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); New Mexico Consortium, Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); National Aeronautic and Space Administration (NASA); National Science Foundation (NSF)
OSTI Identifier:
1489962
Report Number(s):
LA-UR-18-26786
Journal ID: ISSN 1538-4357
Grant/Contract Number:  
89233218CNA000001; SC0018240
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Volume: 866; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS

Citation Formats

Li, Xiaocan, Guo, Fan, Li, Hui, and Li, Shengtai. Large-scale Compression Acceleration during Magnetic Reconnection in a Low- β Plasma. United States: N. p., 2018. Web. doi:10.3847/1538-4357/aae07b.
Li, Xiaocan, Guo, Fan, Li, Hui, & Li, Shengtai. Large-scale Compression Acceleration during Magnetic Reconnection in a Low- β Plasma. United States. doi:10.3847/1538-4357/aae07b.
Li, Xiaocan, Guo, Fan, Li, Hui, and Li, Shengtai. Fri . "Large-scale Compression Acceleration during Magnetic Reconnection in a Low- β Plasma". United States. doi:10.3847/1538-4357/aae07b. https://www.osti.gov/servlets/purl/1489962.
@article{osti_1489962,
title = {Large-scale Compression Acceleration during Magnetic Reconnection in a Low- β Plasma},
author = {Li, Xiaocan and Guo, Fan and Li, Hui and Li, Shengtai},
abstractNote = {In solar flares and other astrophysical systems, a major challenge for solving the particle acceleration problem associated with magnetic reconnection is the enormous scale separation between kinetic scales and the observed reconnection scale. Because of this, it has been difficult to draw any definite conclusions by just using kinetic simulations. A particle acceleration model that solves the energetic particle transport equation can capture the main acceleration physics found in kinetic simulations and thus provide a practical way to make observable predictions and directly compare model results with observations. Here we study compression particle acceleration in magnetic reconnection by solving the Parker (diffusion–advection) transport equation using velocity and magnetic fields from two-dimensional magnetohydrodynamics (MHD) simulations of a low-β high-Lundquist-number reconnection layer. We show that the compressible reconnection layer can give significant particle acceleration, leading to the formation of power-law particle energy distributions. We analyze the acceleration rate and find that the acceleration in the reconnection layer is a mixture of first- and second-order Fermi processes. When including a guide field, we find that the spectrum becomes steeper and both the power-law cutoff energy and maximum particle energy decrease as plasma becomes less compressible. This model produces a 2D particle distribution that one can use to generate a radiation map and directly compare with solar flare observations. This provides a framework to explain particle acceleration at large-scale astrophysical reconnection sites, such as solar flares.},
doi = {10.3847/1538-4357/aae07b},
journal = {The Astrophysical Journal (Online)},
issn = {1538-4357},
number = 1,
volume = 866,
place = {United States},
year = {2018},
month = {10}
}

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Cited by: 1 work
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Figures / Tables:

Figure 1 Figure 1: Out-of-plane current density jz and plasma density ρ at t=2.5τA, 7.5τA, and 10τA for half of the simulation box (x=1.0–2.0), where τA is the Alfvén crossing time Ly/vA. The initial plasma density ≈1.0.

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.