The role of Hall currents on incompressible magnetic reconnection

Abstract

Magnetic reconnection is one of the most important energy conversion processes in space plasmas. Theoretical models of magnetic reconnection have been traditionally developed within the framework of magnetohydrodynamics (MHD). However, in low density astrophysical plasmas as those found in the magnetopause and the magnetotail, the current sheet thickness can be comparable to the ion inertial scale and therefore the Hall electric field becomes non-negligible. The role of the Hall current is to increase the reconnection rate with respect to MHD predictions, which therefore poses a promising mechanism for fast reconnection. We present results from parallel simulations of the incompressible Hall MHD equations in 2 1 2 dimensions. We quantitatively evaluate the relevance of the Hall current in the reconnection process by performing a set of simulations with different values of the Hall parameter. We compute the corresponding reconnection rates as a function of time, and explore the spatial structure of the fields in the surroundings of the diffusion region. We quantify the increase of the reconnection rate as a function of the Hall parameter, and confirm the presence of a quadrupolar structure for the out-of-plane magnetic field.