MHD STABILITY ANALYSIS OF FORCE-FREE REVERSED FIELD PINCH CONFIGURATIONS

The MHD current driven instabilities of Reversed Field Pinch (RFP) configurations are analyzed for a plasma in contact with a perfectly conducting wall. The equilibrium distributions are obtained on the basis of a model which allows a parametric variation of the value of the safety factor on the axis, q(0), and of the current density distribution. The RFP is found to be stable in a wide range of parameters. However, when the toroidal field reversal becomes too deep, unstable modes, resonant outside the reversal surface, are found in analogy to the stability limit at theta equals 1. 56 for the Taylor's theoretical, fully relaxed states. Nevertheless, it is shown that these modes are not very significant in that they arise in a region of the parameters space which is only rarely approached in experiments.