Simulations of Neoclassical Tearing Mode Growth with Realistic Wall Boundary Conditions

Nonlinear MHD simulations study the mechanisms via which neoclassical tearing modes (NTMs) lock and trigger disruptions using reconstructions of DIII-D ITER Baseline Scenario discharges [La Haye R. J., et al., Nucl Fusion 2022]. Simulations build on NIMROD development that enables NTM modeling [Howell E.C., et al., Phys Plasmas 2022]. Previous simulations use a close-fitting conducting wall at the separatrix which has two major impacts on NTM dynamics: 1) The braking torque that arises due to the decay of wall eddy currents is absent. 2) The close proximity of the wall strongly stabilizes the edge tearing modes which alters the mode coupling. Here, simulations use a wall approximating DIII-D's vacuum vessel with both resistive and conducting boundary conditions. An applied perturbation seeds a growing m/n=2/1 NTM. As the NTM grows large it destabilizes higher-n core modes which degrade the core magnetic surfaces. We present analysis of the simulation as it progresses through the thermal quench and report on parameter scans varying the wall resistivity.