Non-linear Tearing of 3D Null Point Current Sheets

TL;DR

This paper investigates the non-linear tearing instability in 3D magnetic null point current sheets, revealing how it enhances magnetic reconnection rates and flux mixing in complex topologies.

Contribution

First study of non-linear tearing instability in 3D null point geometries, showing increased reconnection rates and flux mixing compared to 2D models.

Findings

3D null current layers are susceptible to tearing instability.

Tearing creates a boundary layer with hyperbolic flux structure.

Reconnection rate increases due to flux mixing within the envelope.

Abstract

The manner in which the rate of magnetic reconnection scales with the Lundquist number in realistic three-dimensional (3D) geometries is still an unsolved problem. It has been demonstrated that in 2D rapid non-linear tearing allows the reconnection rate to become almost independent of the Lundquist number (the `plasmoid instability'). Here we present the first study of an analogous instability in a fully 3D geometry, defined by a magnetic null point. The 3D null current layer is found to be susceptible to an analogous instability, but is marginally more stable than an equivalent 2D Sweet-Parker-like layer. Tearing of the sheet creates a thin boundary layer around the separatrix surface, contained within a flux envelope with a hyperbolic structure that mimics a spine-fan topology. Efficient mixing of flux between the two topological domains occurs as the flux rope structures created during the tearing process evolve within this envelope. This leads to a substantial increase in the rate of reconnection between the two domains.