Model Predictive Current Profile Control in Tokamaks by Exploiting Spatially Moving Electron Cyclotron Current Drives

S.T. Paruchuri, T. Rafiq and E. Schuster

Symposium on Fusion Technology (SOFT)

September 18-23, Dubrovnik, Croatia, 2022

The plasma control systems in next-generation tokamaks like ITER will balance competing control objectives to achieve the desired level of performance in advanced scenarios while preventing magnetohydrodynamics instabilities and disruptions. During conventional tokamak discharges, the deposition profile of the electron cyclotron current drive (ECCD) is usually fixed in space. However, the deposition profile can be modified in real-time by changing the angles of the mirrors that reflect the electromagnetic waves generated by the ECCD. Altering the deposition profile, in turn, varies the controllability of the system. For instance, changing the ECCD deposition profile may place the power demands necessary to achieve a particular scenario within saturation limits. Therefore, using the ECCD position, which is related to the ECCD mirror angle, as a supplementary controllable variable may facilitate access to a given target scenario. However, active control algorithms have not been designed so far to fully exploit this capability in real time. In this work, a model predictive controller that can handle actuation locations as control inputs is developed. In particular, the controller is designed to regulate both the auxiliary powers and the ECCD positions in a pre-defined optimal sense to achieve the control objective of attaining and sustaining a target current profile. The proposed controller is tested for a DIII-D tokamak scenario in nonlinear simulations using the Control Oriented Transport SIMulator (COTSIM).

*Supported by the US DOE under DE-SC0010661.