Benchmarking RMP Response Models using KSTAR Discharges*

Limited L-mode and diverted H-mode KSTAR discharges are used to benchmark fluid response models uisng the extended MHD codes NIMROD and M3D-C1. Initial comparisons use inner wall limited L-mode discharges where the in-vessel control coils (IVCC) are used to apply a predominantly n=1 magnetic perturbation. The IVCC currents are linearly ramped in time, and ECEI measurements provide experimental measurements of the resulting 2/1 island in both strongly screened and locked states. Early in time (prior to locking) linear and nonlinear models predict a strongly screened response in agreement with experimental observations. Later (after locking) linear models show penetration of the resonant fields; however, M3D-C1 calculations show more reconnected flux at the 2/1 surface, resulting in a larger island than NIMROD. Efforts to reconcile this disagreement are discussed, and comparisons with JOREK and GPEC are planned. Nonlinear NIMROD modeling shows damped oscillations in agreement with resistive MHD models [R. Fitzpatrick, Phys. Plasma 21 (2014)]. NIMROD simulations will explore the impact two-fluid and neoclassical physics. Initial calculations of the RMP response in an ELM suppressed H-mode discharge are presented.