Magnetohydrodynamic Turbulence in the Plasmoid-Mediated Regime

TL;DR

This paper develops a self-consistent theory of magnetohydrodynamic turbulence that incorporates magnetic reconnection and plasmoid formation, revealing complex interactions that alter the energy cascade and spectral properties in astrophysical plasmas.

Contribution

It introduces a novel theory linking turbulence and reconnection, showing how plasmoid-mediated processes modify the energy spectrum and dissipation scales in MHD turbulence.

Findings

The energy spectrum steepens in the plasmoid-mediated range.

The transition to plasmoid influence occurs at modest magnetic Reynolds numbers.

Dissipation and transition scales do not follow simple power laws.

Abstract

Magnetohydrodynamic turbulence and magnetic reconnection are ubiquitous in astrophysical environments. In most situations, these processes do not occur in isolation, but interact with each other. This renders a comprehensive theory of these processes highly challenging. Here, we propose a theory of magnetohydrodynamic turbulence driven at large scale that self-consistently accounts for the mutual interplay with magnetic reconnection occurring at smaller scales. Magnetic reconnection produces plasmoids that grow from turbulence-generated noise and eventually disrupt the sheet-like structures in which they are born. The disruption of these structures leads to a modification of the turbulent energy cascade, which, in turn, exerts a feedback effect on the plasmoid formation via the turbulence-generated noise. The energy spectrum in this plasmoid-mediated range steepens relative to the standard inertial range and does not follow a simple power law. As a result of the complex interplay between turbulence and reconnection, we also find that the length scale which marks the beginning of the plasmoid-mediated range and the dissipation length scale do not obey true power laws. The transitional magnetic Reynolds number above which the plasmoid formation becomes statistically significant enough to affect the turbulent cascade is fairly modest, implying that plasmoids are expected to modify the turbulent path to dissipation in many astrophysical systems.