Role of the Plasmoid Instability in Magnetohydrodynamic Turbulence

TL;DR

This study uses high-resolution simulations to explore how plasmoid instability influences energy transfer and spectral properties in 2D MHD turbulence, revealing a steepened energy spectrum and scale-dependent alignment effects.

Contribution

It demonstrates the role of plasmoid instability in energy cascade and spectral steepening in 2D MHD turbulence through detailed numerical simulations.

Findings

Plasmoid formation is prolific in high-Reynolds-number turbulence.

Energy spectrum slope is close to -2.2 in the plasmoid-mediated regime.

Scale-dependent dynamic alignment with a slope near 0.25 is observed.

Abstract

The plasmoid instability in evolving current sheets has been widely studied due to its effects on the disruption of current sheets, the formation of plasmoids, and the resultant fast magnetic reconnection. In this Letter, we study the role of the plasmoid instability in two-dimensional magnetohydrodynamic (MHD) turbulence by means of high-resolution direct numerical simulations. At sufficiently large magnetic Reynolds number ($R_m=10^6$), the combined effects of dynamic alignment and turbulent intermittency lead to a copious formation of plasmoids in a multitude of intense current sheets. The disruption of current sheet structures facilitates the energy cascade towards small scales, leading to the breaking and steepening of the energy spectrum. In the plasmoid-mediated regime, the energy spectrum displays a scaling that is close to the spectral index $-2.2$ as proposed by recent analytic theories. We also demonstrate that the scale-dependent dynamic alignment exists in 2D MHD turbulence and the corresponding slope of the alignment angle is close to 0.25.