Steady state reconnection at a single 3D magnetic null point

TL;DR

This study investigates the formation and evolution of steady or quasi-steady current sheets during magnetic reconnection at a 3D null point, using numerical simulations to explore their scaling relations and dynamics.

Contribution

It demonstrates the possibility of establishing a quasi-steady reconnection process at a 3D null point through continuous shear driving, and identifies stable ratios of key parameters during evolution.

Findings

Quasi-steady reconnection can be achieved at 3D nulls with shear driving.

Current layer growth is limited by domain geometry and driving profile.

Scaling relations are identified but not conclusive for lower resistivity or faster driving.

Abstract

To systematically stress a rotationally symmetric 3D magnetic null point by advecting the opposite footpoints of the spine axis in opposite directions. This stress eventually concentrates in the vicinity of the null point forming a local current sheet through which magnetic reconnection takes place. The aim is to look for a steady state evolution of the current sheet dynamics which may provide scaling relations for various characteristic parameters of the system. The evolution is followed by solving numerically the non-ideal MHD equations in a Cartesian domain. The null point is embedded in an initially constant density and temperature plasma. It is shown that a quasi-steady reconnection process can be set up at a 3D null by continuous shear driving. It appears that a true steady state in unlikely to be realised as the current layer tends to grow until restricted by the geometry of the computational domain and imposed driving profile. However, ratios between characteristic quantities clearly settle after some time to stable values -- so that the evolution is quasi-steady. The experiments show a number of scaling relations, but they do not provide a clear consensus for extending to lower magnetic resistivity or faster driving velocities. More investigations are needed to fully clarify the properties of current sheets at magnetic null points.