Magnetic reconnection and plasmoid formation driven by the two-dimensional resistive kink instability in a current hole configuration

TL;DR

This study explores how the resistive internal kink mode in a 2D current hole configuration leads to magnetic reconnection and plasmoid formation, revealing a transition from Sweet-Parker to plasmoid-dominated regimes at high Lundquist numbers.

Contribution

It demonstrates the nonlinear evolution of the resistive kink mode and identifies the critical Lundquist number for plasmoid formation in a current hole setup.

Findings

Reconnection rate of approximately 0.02 observed.

Plasmoid formation occurs when Lundquist number exceeds ~10^4.

Transition from Sweet-Parker to plasmoid-dominated reconnection regimes.

Abstract

We investigate the nonlinear evolution of the $m = 1$ resistive internal kink mode in a two-dimensional (2D) configuration containing a central region of negative current density, also known as the "current hole" setup. The finite-element code FINMHD is used to solve a reduced set of incompressible Magnetohydrodynamic (MHD) equations with a current-vorticity formulation. First, the kink instability linearly develops in agreement with the general theory of resistive internal kink mode, and it subsequently leads to the formation of a current sheet. At relatively low Lundquist number $S$, a magnetic reconnection process proceeds with a rate predicted by the Sweet-Parker regime. Conversely, when $S$ exceeds a critical value that is $S_c \simeq 10^4$, the current sheet is disrupted by the formation of plasmoids on a slightly sub-Alfv\'enic time scale. In the latter case, a stochastic reconnection regime exhibiting Petshek-type features enriched by plasmoids is reached. A relatively fast normalized reconnection rate value of order $0.02$ is also measured. Finally, we compare our results with those obtained in similar 2D previous studies using ideal MHD instabilities to initiate the process, and discuss their relevance for the general theory of plasmoid chains formation and associated fast reconnection regime.