Real-time control of the safety factor profile diagnosed by magneto-hydrodynamic activity on the Tore Supra tokamak

Real-time control is essential for many aspects of tokamak operation. A key parameter to control is the current profile, since both confinement properties and magneto-hydrodynamic (MHD) activity depend on it in quite a sensitive way. The long pulse capability of the Tore Supra tokamak has allowed a unique type of experiment, where successive stationary states of the safety factor profile, defined by their MHD activity, are established and controlled in real time. Multiple target stationary states could be requested and reached during the main heating phase of a single plasma discharge. Experiments have been carried out featuring (i) control of the presence/absence of sawteeth with varying plasma parameters, (ii) obtaining and sustaining a ‘hot core’ plasma regime without MHD activity and (iii) recovery from a voluntarily triggered deleterious MHD regime. During these experiments, the influence of fast ions on MHD stability could be observed and characterized, as well as indications of an enhanced ‘hot core’ confinement in electron heat transport during quiescent MHD states.