Reconnection at 3D Magnetic Null Points: Effect of Current Sheet Asymmetry

TL;DR

This paper develops analytical models to understand how asymmetry in current sheets affects magnetic reconnection at 3D null points, revealing significant impacts on flux transport and reconnection rates.

Contribution

It introduces new kinematic models for asymmetric spine and fan reconnection at 3D nulls, highlighting how asymmetry influences flux transport and reconnection rates.

Findings

Asymmetry causes asymmetric flux reconnection across spine and fan.

Local and global reconnection rates are affected by sheet deformation.

Current sheet asymmetry significantly impacts flux transport in 3D null reconnection.

Abstract

Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a symmetric 3D null with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is inherently equal and opposite in how flux is reconnected across the fan plane. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis it is shown that when the ohmic dissipation in the layer is assumed to be constant, the increase in the local rate bleeds from the global rate as the sheet deformation is increased. Both models suggest that asymmetry in the current sheet dimensions will have a profound effect on the reconnection rate and manner of flux transport in reconnection involving 3D nulls.