Current sheet bifurcation and collapse in electron magnetohydrodynamics

TL;DR

This paper investigates how electron inertia and dissipation affect magnetic reconnection in electron magnetohydrodynamics, revealing nonlinear solutions, collapse phenomena, and the independence of reconnection rates from dissipation parameters.

Contribution

It predicts and confirms new nonlinear solutions for current sheets in EMHD, highlighting the role of electron inertia and viscosity in reconnection dynamics.

Findings

Electron inertia causes current sheet collapse below the inertial length.

Viscosity regularizes small-scale solutions, preventing collapse.

Reconnection rate is independent of electron inertia and dissipation coefficients.

Abstract

Inertial effects in nonlinear magnetic reconnection are studied within the context of 2D electron magnetohydrodynamics (EMHD) with resistive and viscous dissipation. Families of nonlinear solutions for relevant current sheet parameters are predicted and confirmed numerically in all regimes of interest. Electron inertia becomes important for current sheet thicknesses $\delta$ below the inertial length $d_{e}$. In this case, in the absence of electron viscosity, the sheet thickness experiences a nonlinear collapse. Viscosity regularizes solutions at small scales. Transition from resistive to viscous regimes shows a nontrivial dependence on resistivity and viscosity, featuring a hysteresis bifurcation. In all accessible regimes, the nonlinear reconnection rate is found to be explicitly independent of the electron inertia and dissipation coefficients.