Current disruption and modulation of Electron Current layer by current-driven Electrostatic and Electron Tearing Instabilities.

Abstract:

We study the evolution of an electron current layer (ECL) through its several stages by means of three-dimensional PIC simulations with ion to electron mass ratio M/m =400. ECL evolves through the following sequential stages, culminating in fast isotropic heating of electrons and ions: (i) Electrostatic current-driven instability (CDI) soon after its formation, (ii) current disruption in the central part of the ECL by trapping electrons and generation of anomalous resistivity, (iii) electron tearing instability (ETI) with growth rates larger than that predicted by theories, (iv) the ETI growth rate maximizes at a wave number kw ~ 0.5 where k is the wave number parallel to the ECL magnetic field B and w is its half width, (v) the ECL width and current are modulated by the ETI, (vi) interactions between the induced electric fields of the ETI and the density cavities created by the CDI cause further current disruption and fine-grained modulation of the ECL current associated with highly spiked electric field structures like in double layers and (vii) the spiky electric fields very effectively heat both electrons and ions. The developing ETI generates in-plane currents that support out-of-plane magnetic fields around the X-lines. The ETI and the spiky electrostatic structures are accompanied by fluctuations in the magnetic fields near and above the lower hybrid (ion plasma) frequency, including the whistler frequency range. Fluctuations in the magnetic field are also enhanced above the electron plasma frequency. We will compare our results with satellite observations [1] and laboratory experiments [2].

[1] F. S. Mozer et al., New features of electron diffusion regions observed at subsolar magnetic field reconnection sites, Geophys. Res. Lett., 32, L24102, doi:10.1029/2005GL024092.

[2] S. Dorfman et al. (20013), Three-dimensional, impulsive magnetic reconnection in a laboratory plasma, Geophys. Res. Lett., 40, 233, doi:10.1029/2012GL054574.