Relaxation models for Single Helical reversed field pinch plasmas at low aspect ratio

A recent study [1] about the scaling with the aspect ratio (i.e. the ratio between the major and minor radius of the torus) of the dominant mode in Single Helical (SH) Reverse Field Pinch (RFP) plasmas has shown, at intermediate aspect ratio, that the dominant toroidal mode number in the helical states can be interpreted as the result of a relaxation process. In this work, the theoretical model is compared and validated with the experimental data obtained in the low aspect ratio RELAX device [2]. [1] R. Paccagnella, Phys. of Plasmas 23 (2016) 092512. [2] S. Masamune et al, J. Phys. Soc. Japan 76 ( 2007) 123501.