Progress on Modeling Asymmetric Vertical Displacement Events with NIMROD

Recent nonlinear fluid-based computations of asymmetric vertical displacement events (AVDEs) evolve equilibrium-scale fields self-consistently with MHD perturbations, including rudimentary anisotropic transport evaluated in the time-dependent 3D fields. Implicit computation with the NIMROD code [Sovinec, et al., JCP 195, 355 (2004)] allows large separation of the Alfvenic, resistive-wall, and plasma-resistive temporal scales, which is representative of most large experiments. Results show distinct thermal quench (TQ) and current quench (CQ) phases with the characteristic increase of net plasma current occurring when the current density profile broadens due to the MHD activity that induces the TQ. Asymmetric magnetic fields that penetrate the resistive wall lead to horizontal forcing. NIMROD AVDE computations use the thin-shell model, where the surface current density that leads to force density is tantamount to the discontinuity in tangential field across the wall. Here, it is natural to use the Pustovitov computation of integrated magnetic stress over the outer surface of the shell [NF 55, 113032 (2015)], which assumes that the plasma-wall system is electrically isolated and that plasma inertia is negligible.