Two-fluid and magnetohydrodynamic modelling of magnetic reconnection in the MAST spherical tokamak and the solar corona

TL;DR

This paper investigates magnetic reconnection in spherical tokamaks and the solar corona using resistive MHD, Hall MHD simulations, and relaxation theory models to understand plasma merging, heating, and magnetic field restructuring.

Contribution

It introduces new 2D resistive and Hall MHD simulation results and extends relaxation theory models to tight aspect ratio geometries for predicting merged states and heating.

Findings

Simulations show detailed temperature distributions of ions and electrons during reconnection.

The relaxation model predicts the final merged state and plasma heating.

Implications for solar corona heating are discussed.

Abstract

Twisted magnetic flux ropes are ubiquitous in space and laboratory plasmas, and the merging of such flux ropes through magnetic reconnection is an important mechanism for restructuring magnetic fields and releasing free magnetic energy. The merging-compression scenario is one possible start up scheme for spherical tokamaks, which has been used on the Mega Amp Spherical Tokamak MAST. Two current-carrying plasma rings, or flux ropes, approach each other through the mutual attraction of their like currents, and merge, through magnetic reconnection, into a single plasma torus, with substantial plasma heating. 2D resistive MHD and Hall MHD simulations of this process are reported, and new results for the temperature distribution of ions and electrons are presented. A model of the based on relaxation theory is also described, which is now extended to tight aspect ratio geometry. This model allows prediction of the final merged state and the heating. The implications of the relaxation model for heating of the solar corona are also discussed, and a model of the merger of two or more twisted coronal flux ropes is presented, allowing for different senses of twist.