The non-linear evolution of resistive interchange modes in a reversed-field pinch

A two-dimensional resistive MHD computer code is used to study the non-linear behaviour of resistive interchange modes in finite-β Reversed-Field Pinches (RFP). This model is applied to a specific equilibrium that is known to be stable to both resistive and ideal current-driven modes as well as Suydam modes. It is found that the m = 1 resistive interchange saturates at extremely low amplitude when the singular surface lies outside the field reversal point and is more active non-linearly, but still fairly localized, if the singular surface is inside the field null. In contrast, it is found that, at high β, the m = 0 resistive interchange can lead to significant flux surface distortion and interchange vortices of large radial extent. The effect of temperature-dependent resistivity on this mode is presented. In addition, the possibility of Ohmic heating of the pinch in the presence of the m = 0 resistive interchange mode is discussed. It is found that, if the plasma is initially in a low-β state, significant Ohmic heating can occur.