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Boron powder injected into KSTAR lower single null, H-mode discharges with a W monoblock divertor reduced impurity influx from the plasma-facing components (PFCs). The wall conditioning effect provided by the B powder injection resulted in a ~40% reduction in radiated power, ~30% reduction in core electron density, and ~20% reduction in $Z_{eff}$. W-I and O-II line emission brightness was also reduced by as much as 50%, both during and after B injection. A dynamic particle balance found that conditioning via B powder injection resulted in lower wall fueling at start-up, by as much as 99%. While these results qualitatively agree with previous results from full-C KSTAR, WEST, DIII-D, AUG, and EAST, there is a key difference: these KSTAR results show a reduction in W-I line emission during and after B injection, while AUG, EAST, and WEST showed a constant or increased emission during injection, associated with B induced sputtering. Ongoing analysis is underway to understand the origin of this discrepancy. The reduced W influx from the wall supports the use of solid boron injection as a risk-mitigation strategy for controlling core impurity content and radiated power to facilitate the achievement of Q = 10 in ITER.
B powder was also injected into Ne-seeded plasmas to evaluate the effects of combined impurity injection. With simultaneous B injection, the Ne-seeded plasmas had a lower divertor W flux compared to Ne-seeding alone. BN powder injection resulted in periods of reduced ELM activity, which correlated with the excitation of edge harmonic modes. New results from the 2025-2026 KSTAR experimental campaign will also be shown, where we will report on the first Li injection experiments in KSTAR.
Reducing the impurity content and radiative losses is crucial for reactor operation, as well as for KSTAR as it prepares for a full-W upgrade of the first wall in 2026. B powder injection offers a promising wall conditioning technique that can be deployed in real-time. Further work will focus on understanding the long-term dynamics of these B layers, including their lifetime and hydrogen retention properties.
This work is supported by the U.S. Dept. of Energy under Contract DE-AC0209CH11466, and by the Korean Ministry of Science and ICT under the KFE R&D Program ‘KSTAR Experimental Collaboration and Fusion Plasma Research (KFE-EN2401-15)’.