Demonstration of Real-Time Multi-Actuator Plasma Density Control in KSTAR via Adaptive Fueling

H. Al Khawaldeh, S. T. Paruchuri, V. Graber, T. Rafiq, E. Schuster, A. Pajares, J. W. Juhn, S. H. Park

34th Symposium on Fusion Technology (SOFT)

Aix-en-Provence, France, September 21-25, 2026

Particle fueling is a key component of tokamak plasma operation because it directly affects several critical control objectives, including density regulation and plasma detachment. However, reliably injecting particles for precise control in large-scale devices is challenging due to their size and operational complexity. The injected particles do not affect the plasma immediately, and the resulting changes in plasma conditions are often difficult to accurately predict. These uncertainties can reduce control performance and ultimately compromise the plasma stability. Consequently, next-generation tokamaks require advanced control frameworks capable of overcoming these fueling uncertainties and validated on existing devices under reactor-relevant conditions. To support such efforts, KSTAR has recently been equipped with feedback capabilities for both gas puffing and pellet injection, along with emulation of ITER-like delayed gas actuation via the NERF mode. Leveraging these capabilities, a real-time indirect model-reference adaptive control algorithm has been developed and experimentally validated in KSTAR. The algorithm regulates the line-averaged electron density around desired targets using coordinated gas puffing and pellet injection under reactor-relevant conditions, despite unknown fueling efficiencies and input time delays. Experimental results demonstrate effective plasma density regulation, highlighting a control framework capable of addressing fueling challenges in large-scale tokamaks and applicable to other plasma control objectives.

*Supported by the U.S. DOE under Awards DE-SC0010537, DE-FC02-04ER54698, and the KSTAR Experimental Collaboration and Fusion Plasma Research (EN2401-12) through the Korea Institute of Fusion Energy (KFE).