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 boundary condition is extended to include non-axisymmetric wall resistivity, capturing effects of ports and other wall structures. Simulations of HBT-EP with a resistive wall observe non-disruptive, saturated mode activity consistent with experimental data. Effects of varying thermal transport and varying wall resistivity with toroidal mode number are investigated in the context of a saturated external kink resistive wall mode with magnetic islands. Simulations of sawtoothing activity are established with varied macroscopic transport and current ramping rates for comparison to experiment. Work on improving the resistive wall boundary conditions to capture bulk n=0 equilibrium evolution during disruptions is shown. Applications toward better understanding the 3D structure of wall-connected currents and the effects of runaway electron mitigation coil (REMC) fields will be presented. Initial validation studies of numerical models for SOL currents are conducted by analyzing synthetic and experimental phase differences between diagnostic signals on HBT-EP 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)

[3] Boting Li et al., Nucl. Fusion (2024)