Coalescence of magnetic islands including anomalous resistivity

Abstract

Two-dimensional compressible magnetohydrodynamic simulations of the coalescence instability in a low-beta plasma are presented in which anomalous resistivity is permitted to occur. The instability is considered in a uniform current sheet configuration, initially perturbed by an infinite chain of spots of anomalous resistivity. The two phases of the instability known from simulations based on the Fadeev equilibrium—ideal and resistive—can clearly be distinguished also in this configuration. It is found that the conversion of magnetic energy into kinetic energy dominates Ohmic heating. The main energy release occurs within a few Alfvén transit times. The scaling of several key parameters in the current layer formed between the coalescing islands is compared to the scalings obtained with uniform resistivity. The numerical results indicate that the peak reconnection rate decreases toward large Lundquist numbers (S≫104) as S−α with α=15–13 and that a transition to slow reconnection (α∼12) may occur at S≳107, where S is based on the background resistivity.