Interacting tilt and kink instabilities in repelling current channels

TL;DR

This study uses advanced numerical simulations to explore how tilt and kink instabilities interact in current channels, revealing new mechanisms that could trigger solar eruptions like coronal mass ejections.

Contribution

It extends the understanding of tilt and kink instabilities in 3D resistive MHD simulations, highlighting their combined effects and potential role in solar phenomena.

Findings

Secondary tearing disruptions occur in near singular current sheets.

Both tilt and kink instabilities can be stabilized by tension forces in 3D.

Interacting tilt-kink instabilities offer a new pathway for solar eruptions.

Abstract

We present a numerical study in resistive magnetohydrodynamics where the initial equilibrium configuration contains adjacent, oppositely directed, parallel current channels. Since oppositely directed current channels repel, the equilibrium is liable to an ideal magnetohydrodynamic tilt instability. This tilt evolution, previously studied in planar settings, involves two magnetic islands or fluxropes, which on Alfvenic timescales undergo a combined rotation and separation. This in turn leads to the creation of (near) singular current layers, posing severe challenges to numerical approaches. Using our open-source grid-adaptive MPI-AMRVAC software, we revisit the planar evolution case in compressible MHD, as well as its extension to 2.5D and full 3D scenarios. As long as the third dimension remains ignorable, pure tilt evolutions result which are hardly affected by out of plane magnetic field components. In all 2.5D runs, our simulations do show secondary tearing type disruptions throughout the near singular current sheets in the far nonlinear saturation regime. In full 3D, both current channels can be liable to additional ideal kink deformations. We discuss the effects of having both tilt and kink instabilities acting simultaneously in the violent, reconnection dominated evolution. In 3D, both the tilt and the kink instabilities can be stabilized by tension forces. As a concrete space plasma application, we argue that interacting tilt-kink instabilities in repelling current channels provide a novel route to initiate solar coronal mass ejections, distinctly different from currently favored pure kink or torus instability routes.