The computation of resistive MHD instabilities in axisymmetric toroidal plasmas

We describe the linear MHD eigenmode code NOVA-R, which calculates the resistive stability of axisymmetric toroidal equilibria. A formulation has been adopted which accurately resolves the continuum spectrum of the ideal MHD operator. The resistive MHD stability equations are transformed into three coupled second-order equations, one of which recovers the equation solved by the NOVA code in the ideal limit. The eigenfunctions are represented by a Fourier expansion and cubic B-spline finite elements which are packed about the internal boundary layer. Accurate results are presented for dimensionless resistivities as low as 10^-30 in cylindrical geometry. For axisymmetric toroidal plasmas we demonstrate the accuracy of the NOVA-R code by recovering ideal results in the ν → 0 limit, and cylindrical resistive interchange results in the a R → 0 limit. Δ′ analysis performed using the eigenfunctions computed by the NOVA-R code agree with the asymptotic matching results from the resistive PEST code for zero β equilibria.