Formation of Plasmoid Chains in Magnetic Reconnection

TL;DR

This study numerically investigates magnetic reconnection at very high Lundquist numbers, revealing the formation of plasmoid chains that challenge the traditional steady-state reconnection model.

Contribution

It provides the first detailed numerical analysis of plasmoid formation and scaling laws at Lundquist numbers up to 10^8, confirming theoretical predictions.

Findings

Plasmoid number scales as S^{3/8}

Growth rate scales as S^{1/4}

Reconnection becomes inherently time-dependent at high S

Abstract

A detailed numerical study of magnetic reconnection in resistive MHD for very large, previously inaccessible, Lundquist numbers ($10^4\le S\le 10^8$) is reported. Large-aspect-ratio Sweet-Parker current sheets are shown to be unstable to super-Alfv\'enically fast formation of plasmoid (magnetic-island) chains. The plasmoid number scales as $S^{3/8}$ and the instability growth rate in the linear stage as $S^{1/4}$, in agreement with the theory by Loureiro et al. [Phys. Plasmas {\bf 14}, 100703 (2007)]. In the nonlinear regime, plasmoids continue to grow faster than they are ejected and completely disrupt the reconnection layer. These results suggest that high-Lundquist-number reconnection is inherently time-dependent and hence call for a substantial revision of the standard Sweet-Parker quasi-stationary picture for $S>10^4$.