Integrated Core-Edge Instability and Transport Control for Long-Pulse Scenarios in KSTAR with a Tungsten Divertor

The multi-institutional team from US and Korea have enhanced integrated core-edge instability and transport control to develop long pulse scenarios in KSTAR compatible with the new tungsten (W) divertor. Adaptive control of 3D fields was optimized with modeling to predict core and edge coupling of the field amplitude and phase incorporating AI/ML to extend ELM suppression for long pulse scenarios while avoiding locked modes and disruptions. Feedback control of the pedestal density and divertor detachment through the location of the edge radiation front has been achieved with fast data processing of multiple diagnostics using ML. Type I ELM suppression was achieved for relatively long pulses up to 32 s with the W divertor. Increased radiation with the W divertor resulted in reduced plasma pressure for a given heating power, requiring higher density operation, which made long pulse ELM suppression more challenging than with the previous carbon divertor. To control the impurity radiation, the addition of boron in real-time with the Impurity Powder Dropper was effective for conditioning the plasma facing components to achieve low enough densities for long pulse ELM suppression with the W divertor. Further integration of these advanced control techniques with multiple diagnostics and actuators together with an improved understanding of tungsten transport will be essential for future long pulse high performance scenarios in KSTAR, ITER and future FPPs.