The use of 3D magnetic fields is one of the promising approaches to control edge localized modes (ELMs), and ITER has plans to utilize a flexible 3D coil set for ELM suppression using 3D fields. This study focuses on optimizing the 3D field spectrum to expand the operational window for n = 1 resonant magnetic perturbation (RMP) ELM suppression in KSTAR. The optimized n = 1 RMP effectively suppresses ELMs throughout the entire H-mode discharge, including the first ELM crash, while avoiding the onset of disruptive locked modes in low-density L-mode plasmas. The predicted suppression window aligns well with experimental data, highlighting the challenges and solutions of using n = 1 RMP at low densities. Moreover, the optimization successfully achieved n = 1 RMP ELM suppression for the first time in ITER-relevant q95 and shaping conditions, including cases with q95 as low as 3.6, as well as other q95 and shape configurations. This highlights the importance and utility of 3D coil optimization while emphasizing the potential of long-wavelength low-n RMP, which will be valuable for ex-vessel coils designed to avoid complications of nuclear degradation.
This study optimizes 3D magnetic fields to expand the operational window for n=1 resonant magnetic perturbation (RMP) edge localized mode (ELM) suppression in KSTAR. The optimized n=1 RMP effectively suppresses ELMs throughout the discharge, including the first ELM, while avoiding disruptive locked modes at low densities. The optimization also achieved n=1 RMP ELM suppression for the first time in ITER-relevant conditions, highlighting the importance of 3D coil optimization and the potential of long-wavelength low-n RMP for ex-vessel coils.