Overview of NIMROD modeling at the University of Wisconsin-Madison

The NIMROD code [1] has been applied to investigate macroscropic dynamics in many plasma configurations. Current efforts at UW-Madison include developing an efficient representation for stellarators and applications to RFPs, tokamaks, and spherical-tokamak startup. The stellarator development, NIMSTELL, is a major refactoring to use a 3D representation of the geometry and of the equilibrium/steady-state fields [2]. It also uses H(curl) elements for vector potential so that the magnetic divergence constraint is satisfied to roundoff. The RFP study includes pressure dynamics to investigate the pressure-curvature drive and energy transport in the presence magnetic relaxation, according to the visco-resistive MHD model. Our recent tokamak simulations consider RE confinement [3] and transient-induced disruptions in MST tokamak discharges. We also implemented a reduced model of RE effects on magnetic-field evolution. The Pegasus study restarts our previous investigation of local helicity injection [4], now tailored for conditions in the Pegasus-III upgrade. [1] Sovinec, et al., JCP 195, 355; [2] Sovinec and Cornille, BAPS 66(13); [3] Cornille, et al., PoP 29, 052510; [4] O'Bryan, et al.; PoP 19, 080701.