KSTAR Cuts Error Field Compass Scans to One H-Mode Discharge via Island Healing

The experiment deployed new triggering algorithms in the KSTAR plasma control system during long-pulse H-mode plasmas with strong resonant magnetic perturbations. Researchers applied a non-disruptive compass scan that healed magnetic islands while monitoring plasma response, achieving error field identification without the multiple shots or close-in magnetics sensors required in prior DIII-D, JET, and MAST-U work. This approach succeeded because KSTAR combines high RMP coil strength with pulse lengths long enough for real-time correction within one discharge. The data showed consistent n=1 error field detection and healing across repeated single-shot trials, with island width suppression matching multi-discharge benchmarks from earlier devices. The method avoids strong real-time magnetics diagnostics that will be unavailable on ITER and future pilot plants. Results confirm the technique works in the H-mode regime relevant to reactor operation rather than only Ohmic or L-mode conditions. Previous multi-discharge methods imposed cumulative disruption risk and time costs incompatible with disruption-averse devices. By embedding the scan inside normal H-mode operation, KSTAR demonstrates a pathway that preserves plasma performance while mapping error fields. Remaining gaps include scaling the algorithm to ITER's larger size, validating against 3D equilibrium codes, and demonstrating robustness across varying beta and rotation profiles. Next steps require testing on devices with ITER-like diagnostics and integrating the technique into automated control for sustained high-performance operation. Successful closure of these gaps would directly reduce downtime and disruption probability in fusion pilot plants.