Three-dimensional plasmoid-mediated reconnection and turbulence in Hall magnetohydrodynamics

TL;DR

This paper investigates how three-dimensional Hall MHD simulations reveal that plasmoid instability can lead to turbulent reconnection, differing from 2D results and providing insights into the transition from collisional to collisionless regimes.

Contribution

It demonstrates that 3D Hall MHD simulations can produce turbulent reconnection states, contrasting with 2D results, and explores the conditions under which turbulence develops.

Findings

3D reconnection less likely to be single-X-line compared to 2D

Hall MHD can realize turbulent reconnection depending on parameters

Energy spectra and eddy anisotropy analyzed in turbulent states

Abstract

Plasmoid instability accelerates reconnection in collisional plasmas by transforming a laminar reconnection layer into numerous plasmoids connected by secondary current sheets in two dimensions (2D) and by fostering self-generated turbulent reconnection in three dimensions (3D). In large-scale astrophysical and space systems, plasmoid instability likely initiates in the collisional regime but may transition into the collisionless regime as the fragmentation of the current sheet progresses toward kinetic scales. Hall MHD models are widely regarded as a simplified yet effective representation of the transition from collisional to collisionless reconnection. However, plasmoid instability in 2D Hall MHD simulations often leads to a single-X-line reconnection configuration, which significantly differs from fully kinetic particle-in-cell simulation results. This study shows that single-X-line reconnection is less likely to occur in 3D compared to 2D. Moreover, depending on the Lundquist number and the ratio between the system size and the kinetic scale, Hall MHD can also realize 3D self-generated turbulent reconnection. We analyze the features of the self-generated turbulent state, including the energy power spectra and the scale dependence of turbulent eddy anisotropy.