Detailed toroidal effects on the force free magnetostatic solution for toroidal reversed field pinches

The self-reversal of the toroidal magnetic field during the discharge in RFPs (reverse field pinches) is studied analyzing in detail the effects due to toroidal geometry. In particular force-free solutions for the magnetic field in toroidal geometry are determined using a perturbative expansion appropriate for a torus of large aspect-ratio. It is proved that minimum magnetic energy solutions are necessarily axisymmetric. Finally a possible physical model is proposed for describing the process of self-reversal