A multiple-time-scale approach to the control of ITBs on JET

The simultaneous real-time control of the current and pressure profiles could lead to the steady state sustainment of an internal transport barrier (ITB), region where heat and particle transport are strongly reduced and so to a stationary optimized plasma regime. Recent experiments in JET have demonstrated significant progress in achieving such a control: different current and temperature gradient target profiles have been reached and sustained for several seconds using a controller based on a static linear model identification. Nevertheless, these experiments have shown that the controller was sensitive to rapid plasma events such as transient ITBs during the safety factor profile evolution or magneto-hydrodynamics (MHD) instabilities which modify the pressure profiles on the confinement time scale. The control technique has been improved by using a multiple-time-scale approximation in order to better respond to these rapid plasma events. The paper describes the theoretical analysis and closed-loop simulations using the controller that will be tested experimentally in JET during the forthcoming campaign