Development of non-axisymmetric resistive wall models for MHD simulations of HBT-EP and other tokamaks*

The NIMROD [1] code is used to validate multiphysics models (MHD + resistive wall) for the prediction of mode structures and scrape-off-layer (SOL) currents in tokamaks using high-resolution current, magnetic, and optical diagnostics of HBT-EP [2]. NIMROD’s existing thin resistive wall model is extended to include non-axisymmetric wall resistivity, capturing effects of ports and other wall structures. Simulations with a resistive wall observe non-disruptive, saturated, mode activity, consistent with experimental data on HBT-EP. Effects of varying wall resistivity with toroidal mode number are investigated in the context of a saturated resistive wall mode complete with magnetic islands and disruptions initiated with an artificial thermal quench. Work on improving boundary conditions in the resistive wall model to capture large-scale n=0 equilibrium evolution during disruptions will be discussed. Applications toward better understanding the 3D structure of wall-connected currents and the effects of runaway electron mitigation coil (REMC) fields will be presented. Plans to validate numerical models of wall-connected currents and quantify phase differences between diagnostic signals on HBT-EP, including current-sensing tiles, will be presented with the goal of improving SOL and wall models for ITER and next-step devices.

[1] C. Sovinec et al., J. Comput. Phys. (2004)

[2] J. Levesque et al., Nucl. Fusion (2017)