Relaxation and magnetic reconnection in plasmas

TLDR

Plasma relaxation theory describes how plasmas evolve toward minimum‑energy states, with the resulting relaxed state depending on the container’s topology and boundary conditions. Turbulence with low resistivity drives rapid magnetic reconnection that erases ideal invariants, leaving only total magnetic helicity and producing distinct relaxed states depending on geometry. Experimental data from toroidal pinches, OHTE, multipinch, and spheromaks confirm the theoretical predictions of plasma relaxation.

Abstract

The theory of plasma relaxation is described and developed. Turbulence, allied with a small resistivity, allows the plasma rapid access to a particular minimum-energy state. This process involves reconnection of magnetic field lines in a manner that destroys all the topological invariants of ideal plasma so that only total magnetic helicity survives. Although this mechanism, and the equations describing the relaxed state, are similar in all systems, the properties of the relaxed state depend crucially on the topology---toroidal or spherical---of the container and on the boundary conditions. Consequently there are several different types of relaxed state, each with its own special characteristics, which are derived and discussed. The measurements made on many experiments, including toroidal pinches, OHTE, multipinch, and spheromaks, are reviewed and shown to be in striking agreement with the theoretical predictions.