Progress in Understanding Transport across Core Magnetic Islands in KSTAR*

This study presents updated findings from KSTAR experiments, revealing increased turbulence near the X-point of the 2/1 core magnetic island. Through accurate comparisons with KSTAR ECE and ECEI measurements, we analyze the validity of linear and nonlinear MHD simulations and plasma response models (M3D-C1, NIMROD). The results of the plasma response modeling are in good agreement with ECEI measurements for the width of the resulting magnetic island. Nonlinear GTC simulations using the DKE model and incorporating EFIT pressure profiles and M3D-C1 equilibrium with n=1 islands demonstrate the spreading of turbulence across the 2/1 magnetic surface and show the observed fluctuations across the island X-point. The experimental and numerical results are consistent with the previous BES measurements across core and edge RMP islands in DIII-D discharges. BES measurements also show a decrease in fluctuation levels in front of the island O-point compared to the no-RMP case. The observation of localized island transport is consistent with the previously proposed ExB convection mechanism across the island X-point. The results of the simulations give confidence that the understanding of the underlying physics of transport in the presence of 3D fields and magnetic islands can be extrapolated to edge islands, giving us insights into RMP ELM suppression mechanisms.