Plasma models for real-time control of advanced tokamak scenarios

Anintegratedplasmaprofilecontrolstrategy,ARTAEMIS,isbeingdevelopedforextrapolatingpresent-dayadvanced tokamak (AT) scenarios to steady-state operation. The approach is based on semi-empirical modelling and was initiallyexploredonJET(Moreauetal2008Nucl.Fusion48106001). Thispaperdealswiththegeneralapplicability of this strategy for simultaneous magnetic and kinetic control on various tokamaks. The determination of thedevicespecific, control-oriented models that are needed to compute optimal controller matrices for a given operation scenario is discussed. The methodology is generic and can be applied to any device, with different sets of heating and current drive actuators, controlled variables and profiles. The system identification algorithms take advantage of the large ratio between the magnetic and thermal diffusion time scales and have been recently applied to both JT-60U and DIII-D data. On JT-60U, an existing series of high bootstrap current (∼70%), 0.9MA non-inductive AT discharges was used. The actuators consisted of four groups of neutral beam injectors aimed at perpendicular injection (on-axis and off-axis), and co-current tangential injection (also on-axis and off-axis). On DIII-D, dedicated system identification experiments were carried out in the loop voltage (Vext) control mode (as opposed to current control) to avoid feedback in the response data from the primary circuit. The reference plasma state was that of a 0.9MA AT scenario which had been optimized to combine non-inductive current fractions near unity with 3.5 <β N < 3.9, bootstrap current fractions larger than 65% and H98(y,2) = 1.5. Actuators other than Vext were co-current,counter-currentandbalancedneutralbeaminjection,andelectroncyclotroncurrentdrive. Powerandloop voltage modulations resulted in dynamic variations of the plasma current between 0.7 and 1.2MA. It is concluded that the response of essential plasma parameter profiles to specific actuators of a given device can be satisfactorily identified from a small set of experiments. This provides, for control purposes, a readily available alternative to first-principles plasma modelling. (Some figures in this article are in colour only in the electronic version)