Self-generated turbulence in magnetic reconnection

TL;DR

This paper demonstrates through 3D MHD simulations that a self-generated turbulence in magnetic reconnection leads to fast, resistivity-independent reconnection rates, challenging traditional models and highlighting the role of 3D instabilities.

Contribution

The study reveals that three-dimensional MHD instabilities can induce fast reconnection without external turbulence or kinetic effects, expanding understanding of magnetic reconnection mechanisms.

Findings

Reconnection rate becomes independent of Lundquist number in 3D simulations.

3D instabilities occur even at Lundquist numbers where 2D plasmoid instability is absent.

Self-generated turbulence facilitates fast magnetic reconnection in MHD models.

Abstract

Classical Sweet-Parker models of reconnection predict that reconnection rates depend inversely on the resistivity, usually parameterized using the dimensionless Lundquist number ($\Lund$). We describe magnetohydrodynamic (MHD) simulations using a static, nested grid that show the development of a three-dimensional instability in the plane of a current sheet between reversing field lines without a guide field. The instability leads to rapid reconnection of magnetic field lines at a rate independent of $\Lund$ over at least the range $3.2\times 10^3 \lesssim \Lund \lesssim 3.2 \times 10^5$ resolved by the simulations. We find that this instability occurs even for cases with $\Lund \lesssim 10^4$ that in our models appear stable to the recently described, two-dimensional, plasmoid instability. Our results suggest that three-dimensional, MHD processes alone produce fast (resistivity independent) reconnection without recourse to kinetic effects or external turbulence. The unstable reconnection layers provide a self-consistent environment in which the extensively studied turbulent reconnection process can occur.