A Comparison of VMEC and SPEC Equilibria for Tokamak and Stellarator Configurations

An extensive comparison of the equilibria from VMEC [S. P. Hirshman and O. Betancourt, J. Comput. Phys. 96, 99 (1991)], an Ideal MHD equilibrium code which assumes continuous nested flux surfaces, and SPEC [S. R. Hudson, et al., Phys. Plasmas 19, 112502 (2012)], an Ideal MHD equilibrium code which assumes a multi-region relaxation model (the pressure is flat except at a finite number of flux surfaces), is undertaken. Equilibria with the same boundary, volume-average beta, and rotational transform on the finite number of surfaces assumed in SPEC are developed for comparison. The comparison will include the shapes of the interior surfaces, profiles of pressure, rotational transform, and current density. The comparisons will include axisymmetric configurations and fully 3-D configurations. The axisymmetric configurations include a tokamak with an elliptical cross-section and an ITER configuration. The stellarator configurations include simpler ones such as a CTH configuration and we are attempting to develop a comparison for a strongly shaped configuration such as W7-X. The results of the comparisons will be presented.