Identification of the magneto-thermal plasma response for plasma state control in advanced tokamaks

The paper deals with the basic elements of an integrated model-based control strategy for extrapolating present-day advanced tokamak scenarios to steady state operation. Taking advantage of the large ratio between the time scales involved in the magnetic and thermal diffusion processes, the model identification procedure makes use of a multiple time scale approximation. The methodology is generic and can be applied to any device, with different sets of heating and current drive actuators, controlled variables and/or parameter profiles. It has been applied to experimental data from JET and JT-60U, and satisfactory models have been obtained. A profile controller can then be articulated around two composite feedback loops operating on the resistive and confinement time scales, respectively. The controller aims to use the combination of H&CD systems in an optimal way to regulate the evolution of the magneto-thermal state of the plasma. First experimental results obtained with three H&CD actuators to control the safety factor profile on JET are displayed. Simultaneous real-time control of the q-profile and toroidal velocity profile on JT-60U, using four groups of neutral beam injectors, has been simulated and typical results are presented.