Open loop characterization of an active control system of MHD modes

During the last year different saddle coil set-ups were tested on EXTRAP T2R performing experiments of plasma MHD modes active control. In particular, a series of shots both without and with plasma were aimed at the electromagnetic characterization of the open loop system and to the validation of a model developed for the design of a digital control system. good agreement was observed between model and experiment both in terms of single coil electromagnetic parameters and in terms of harmonic distribution at different frequencies. The quality of the harmonic content as a function of the number of active coils was also analysed. Finally, encouraging results were obtained comparing theoretical and experimental growth rates of unstable modes after applying static perturbations of different toroidal order n.