Title: Ion acceleration and heating by kinetic Alfvén waves associated with magnetic reconnection

Abstract

In a previous study on the generation and signatures of kinetic Alfv en waves (KAWs) associated with magnetic reconnection in a current sheet revealed that KAWs are a common feature during reconnection [Liang et al. J. Geophys. Res.: Space Phys. 121, 6526 (2016)]. In this paper, ion acceleration and heating by the KAWs generated during magnetic reconnection are investigated with a three-dimensional (3-D) hybrid model. It is found that in the outflow region, a fraction of inflow ions are accelerated by the KAWs generated in the leading bulge region of reconnection, and their parallel velocities gradually increase up to slightly super-Alfv enic. As a result of waveparticle interactions, an accelerated ion beam forms in the direction of the anti-parallel magnetic field, in addition to the core ion population, leading to the development of non-Maxwellian velocity distributions, which include a trapped population with parallel velocities consistent with the wave speed. We then heat ions in both parallel and perpendicular directions. In the parallel direction, the heating results from nonlinear Landau resonance of trapped ions. In the perpendicular direction, however, evidence of stochastic heating by the KAWs is found during the acceleration stage, with an increase of magnetic moment μ. The coherence in the T_$$\perp$$ ion temperature and the perpendicular electric and magnetic fields of KAWs also provides evidence for perpendicular heating by KAWs. The parallel and perpendicular heating of the accelerated beam occur simultaneously, leading to the development of temperature anisotropy with the perpendicular temperature T_$$\perp$$>T_{$$\parallel$$} temperature. The heating rate agrees with the damping rate of the KAWs, and the heating is dominated by the accelerated ion beam. In the later stage, with the increase of the fraction of the accelerated ions, interaction between the accelerated beam and the core population also contributes to the ion heating, ultimately leading to overlap of the beams and an overall anisotropy with T_$$\perp$$>T_{$$\parallel$$}.

Authors:

Liang, Ji ^[1]; Lin, Yu ^[2]; Johnson, Jay R. ^[3]; Wang, Zheng-Xiong ^[1]; Wang, Xueyi ^[2]

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+ Show Author Affiliations

1. Dalian Univ. of Technology (China). School of Physics
2. Auburn Univ., AL (United States). Physics Dept.
3. Andrews Univ., Berrien Springs, MI (United States). Dept. of Engineering and Computer Science

Publication Date:

Tue Sep 19 00:00:00 EDT 2017

Research Org.:

Auburn Univ., AL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)

OSTI Identifier:

1392930

Alternate Identifier(s):

OSTI ID: 1392712

Grant/Contract Number:  

SC0010486; AGS 1405225

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 24; Journal Issue: 10; Journal ID: ISSN 1070-664X

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; magnetic reconnection; kinetic Alfven waves; ion acceleration; ion heating; nonlinear wave-particle interaction