Relaxation models for Single Helical Reversed Field Pinch plasmas

TL;DR

This paper revisits a relaxation theory for single helical reversed field pinch plasmas, numerically solving eigenvalue problems and proposing a method to predict the dominant helicity based on minimizing the difference from a generalized Taylor relaxation state.

Contribution

It introduces a new approach to determine the dominant helicity by minimizing the distance to a generalized relaxation state, enhancing the predictive capability of the model.

Findings

Solutions reproduce experimental magnetic fields

Method predicts scaling with aspect ratio and reversal parameter

Provides a way to determine the dominant helicity

Abstract

In this paper a relaxation theory, proposed several years ago for plasmas where a single dominant mode is present, is revisited. The solutions of the related eigenvalue problem are numerically calculated and discussed. Although these solutions are very rich and can reproduce well the magnetic fields measured in experiments, there is no manner within the theory to determine the dominant helicity, which is a free parameter in the model. To find the preferred helicity in the system, we propose to minimize the distance of the relaxed state from another state which is constructed as a two region generalization of the Taylor relaxation model allowing current jumps. It is found that this comparison is able to predict the observed scaling with the aspect ratio and reversal parameter for the dominant mode in the Single Helical states.