Advanced Density Regulation for ITER-emulated Scenarios on DIII-D via Adaptive Control Techniques*

In present tokamaks, plasma density regulation is commonly achieved through gas puffing. However, this actuation will not be suitable for future reactor-grade tokamaks like ITER. The large size of these machines introduces significant time delays when actuating the gas valves, and the high plasma densities in the core prevent neutral fueling gas from effectively penetrating the plasma. Hence, pellet injection is expected to be utilized in reactor-grade tokamaks. Despite its potential, pellet injection is largely unexplored as actuator for routine density control in existing tokamaks and presents unique challenges, including the discrete nature of the actuation, the impact of the pellet size on the plasma dynamics, and the possibility of pellet drops. A model reference adaptive control algorithm is proposed in this work for the regulation of the line-averaged electron density in DIII-D for ITER relevant scenarios by combining gas puffing and pellet injection. This controller is based on a multiple-reservoir global particle model tailored to the DIII-D dynamics. The performance of the controller is assessed in both simulations and experiments, where an emulation algorithm in the Plasma Control System enables testing with ITER-like actuators.