Development and validation of an electromagnetic model of the active control system of MHD modes in RFX-mod

Dramatic improvements in RFX-mod plasma discharges have been achieved after starting operation of the active control system of MHD modes. In view of the design of more sophisticated controllers fully exploiting the system capability, an electromagnetic model of the active system was developed, which takes into account toroidal geometry and effects of passive structures. The model parameters were estimated by processing available data collected in dedicated measurement campaigns. State space representations were adopted to describe the dynamics of the active saddle coil currents and the fluxes measured by saddle probes. Open and closed loop responses were calculated and compared with experimental data. The building of the model along with the results of the extensive validation tests are described in the paper.