Hall magnetohydrodynamic reconnection in the plasmoid unstable regime

TL;DR

This paper investigates how Hall effects influence the stability and formation of plasmoids in large current sheets, revealing faster growth rates and more plasmoids compared to traditional resistive MHD.

Contribution

It extends resistive MHD analysis by incorporating Hall physics, showing modified growth rates and plasmoid numbers in the plasmoid instability regime.

Findings

Secondary islands grow faster in Hall MHD regime.

Maximum growth rate scales with $(d_i/L)^{6/13} S_L^{7/13}$.

Number of plasmoids scales with $(d_i/L)^{1/13} S_L^{11/26}$.

Abstract

A set of reduced Hall magnetohydrodynamic (MHD) equations are used to evaluate the stability of large aspect ratio current sheets to the formation of plasmoids (secondary islands). Reconnection is driven by resistivity in this analysis, which occurs at the resistive skin depth $d_\eta \equiv S_L^{-1/2} \sqrt{L v_A/\gamma}$, where $S_L$ is the Lundquist number, $L$ the length of the current sheet, $v_A$ the Alfv\'{e}n speed, and $\gamma$ the growth rate. Modifications to a recent resistive MHD analysis [N.\ F.\ Loureiro, A.\ A.\ Schekochihin, and S.\ C. Cowley, Phys.\ Plasmas {\bf 14}, 100703 (2007)] arise when collisions are sufficiently weak that $d_\eta$ is shorter than the ion skin depth $d_i \equiv c/\omega_{pi}$. Secondary islands grow faster in this Hall MHD regime: the maximum growth rate scales as $(d_i/L)^{6/13} S_L^{7/13} v_A/L$ and the number of plasmoids as $(d_i/L)^{1/13} S_L^{11/26}$, compared to $S_L^{1/4} v_A/L$ and $S^{3/8}$, respectively, in resistive MHD.