An Explosive Scaling Law for Nonlinear Magnetic Reconnection and Its Insensitivity to Microscopic Scales

Abstract

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 [Hirota et al., Phys. Plasmas 22, 052114 (2015)], is found to consistently hold when either the ion-sound gyroradius ρ S or the ion gyroradius ρ i is comparable to the electron skin depth d e , 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, ρ S , ρ i , d e and η. On the other hand, in the cold plasma limit, where ρ S = ρ i = 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 of solar flares.

Summary of the fundamental plasma physics session in the first AAPPS-DPP conference

“…Hirota reported the progress on a theory for explosive reconnection based on the gyrofluid energy principle framework 29 . Two-fluid model including the Larmor radius effect is applied, in which the governing equations are the continuty and momentum equations for ions and electrons.…”

“…The plasmoid instability is shown in right panels. Reprinted from[29], with permission from JSPF. the energy principle based on gyro-fluid is applied to the tearing instability, it is found that:(i) only a two-parameter trial function for the inner layer ( i.e.…”