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Relaxation models for Single Helical Reversed Field Pinch plasmas

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.