TY - JOUR

T1 - An Explosive Scaling Law for Nonlinear Magnetic Reconnection and Its Insensitivity to Microscopic Scales’0

AU - Hirota, Makoto

N1 - Funding Information:
This work was supported by JSPS KAKENHI Grant Number 16K05627. Numerical calculations were performed on the UV1000 at the Institute of Fluid Science, Tohoku University.
Publisher Copyright:
© 2017 The Japan Society of Plasma Science and Nuclear Fusion Research. All Rights Reserved.

PY - 2017

Y1 - 2017

N2 - The nonlinear phase of magnetic reconnection is investigated by numerically solving a gyrofluid model. The scaling law for the explosive reconnection rate, which has been recently derived for an ideal two-fluid model [Hi-rota et al., Phys. Plasmas 22, 052114 (2015)], is found to consistently hold when either the ion-sound gyroradius ρS or the ion gyroradius ρi is comparable to the electron skin depth de, even in the presence of finite resistivity η. In this explosive phase, a local X-shaped current layer is spontaneously generated, in which the reconnection speed is closely related to the macroscopic shape of the layer and is almost independent of the layer width. The reconnection speed is therefore insensitive to the size of the microscopic scales, ρS, ρi, de and n. On the other hand, in the cold plasma limit, where ρS = ρi = 0, the intermittent acceleration of the reconnection speed is caused by the plasmoid instability. This also seems to be explosive on average, but the rate always falls below the explosive scaling law. The reconnection time extrapolated from this scaling law is shown to be fast enough to explain the time scale ofsolar flares.

AB - The nonlinear phase of magnetic reconnection is investigated by numerically solving a gyrofluid model. The scaling law for the explosive reconnection rate, which has been recently derived for an ideal two-fluid model [Hi-rota et al., Phys. Plasmas 22, 052114 (2015)], is found to consistently hold when either the ion-sound gyroradius ρS or the ion gyroradius ρi is comparable to the electron skin depth de, even in the presence of finite resistivity η. In this explosive phase, a local X-shaped current layer is spontaneously generated, in which the reconnection speed is closely related to the macroscopic shape of the layer and is almost independent of the layer width. The reconnection speed is therefore insensitive to the size of the microscopic scales, ρS, ρi, de and n. On the other hand, in the cold plasma limit, where ρS = ρi = 0, the intermittent acceleration of the reconnection speed is caused by the plasmoid instability. This also seems to be explosive on average, but the rate always falls below the explosive scaling law. The reconnection time extrapolated from this scaling law is shown to be fast enough to explain the time scale ofsolar flares.

KW - explosive instability

KW - gyrofluid model

KW - magnetic reconnection

KW - plasmoid instability

KW - solar flare

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U2 - 10.1585/pfr.12.1401010

DO - 10.1585/pfr.12.1401010

M3 - Article

AN - SCOPUS:85115635477

VL - 12

SP - 1

EP - 8

JO - Plasma and Fusion Research

JF - Plasma and Fusion Research

SN - 1880-6821

ER -