Dynamics of braided coronal loops II: Cascade to multiple small-scale reconnection events

TL;DR

This study uses 3D resistive MHD simulations to explore how braided coronal loops undergo a cascade of small-scale reconnection events, leading to a relaxed, force-free magnetic configuration.

Contribution

It demonstrates the cascade process of multiple reconnections in braided loops and characterizes the final equilibrium state, advancing understanding of coronal magnetic relaxation.

Findings

Multiple small-scale reconnection events occur during relaxation.

Higher magnetic Reynolds number prolongs the cascade.

Final state resembles a non-linear force-free field with flux tubes.

Abstract

Aims: Our aim is to investigate the resistive relaxation of a magnetic loop that contains braided magnetic flux but no net current or helicity. The loop is subject to line-tied boundary conditions. We investigate the dynamical processes that occur during this relaxation, in particular the magnetic reconnection that occurs, and discuss the nature of the final equilibrium. Methods: The three-dimensional evolution of a braided magnetic field is followed in a series of resistive MHD simulations. Results: It is found that, following an instability within the loop, a myriad of thin current layers forms, via a cascade-like process. This cascade becomes more developed and continues for a longer period of time for higher magnetic Reynolds number. During the cascade, magnetic flux is reconnected multiple times, with the level of this `multiple reconnection' positively correlated with the magnetic Reynolds number. Eventually the system evolves into a state with no more small-scale current layers. This final state is found to approximate a non-linear force-free field consisting of two flux tubes of oppositely-signed twist embedded in a uniform background field.