Studies of 3D resistive MHD stability using the SPECTOR-3D code

A description is given of a 3D resistive magnetohydrodynamic code, SPECTOR-3D. The code is designed to find the linear, incompressible modes for stellarator-like plasmas, with an emphasis on the unstable modes. SPECTOR-3D is structured to receive input from the 3D equilibrium code VMEC followed by a mapping section which reconstructs the metric and Jacobian of the equilibrium in terms of Boozer coordinates. The linearised MHD equations are expressed in terms of the vector potentials for the perturbed magnetic field and the velocity. These equations are then Fourier analysed in both the toroidal and poloidal directions, giving a coupled set of second-order differential equations in terms of the corresponding to the poloidal flux. A staggered difference scheme is used which maintains the divergence of the curl operator to be zero within the numerical scheme. This assists in suppressing any spurious modes.The eigenvalues of the resulting block- tri-diagonal matrix equation, found by either inverse iteration or the Jacobi-Davidson method, correspond to the complex growth rate of both the unstable and stable modes. Copyright (2002) Australian National University- Research School of Physical Sciences and Engineering