Adaptive Control of Plasma Density in Tokamaks Using Coordinated Gas Puffing and Pellet Injection

H. Al Khawaldeh, S. T. Paruchuri, V. Graber, T. Rafiq, E. Schuster

31st IEEE Symposium on Fusion Energy (SOFE)

Cambridge, MA, USA, June 23-26, 2025

Regulating plasma density at desired levels is crucial for achieving optimal performance in tokamaks. While gas puffing has proven effective for fueling current devices, its performance is expected to degrade in future reactor-grade tokamaks such as ITER due to increased device sizes and higher plasma densities. This will lead to longer transit times from gas valves to the plasma edge and limit gas penetration into the core. Furthermore, advanced plasma conditions will demand more precise and rapid control to ensure optimal and safe operation. To address these challenges, pellet injection has emerged as a promising solution, capable of delivering fuel directly into the plasma core. However, the practical implementation of pellet injection for density control remains largely unexplored in current tokamaks. The discrete nature of pellet injections, variations in pellet size and injection speed, and the travel time of the pellet in the tubes all pose significant performance challenges. To address these challenges, an adaptive control technique has been developed for the regulation of the line-averaged electron density. The proposed approach coordinates gas puffing and pellet injection while accounting for uncertainties in actuator responses and rapid shifts in plasma conditions. Simulation studies indicate that the adaptive strategy is well suited to regulate density around desired targets for a variety of operating scenarios, offering a robust path toward consistent fueling in next-generation tokamaks.

*Supported by the US DOE (DE-SC0010661, DE-SC0010537).