Integrated identification of RFX-mod active control system from experimental data and finite element model

The RFX-mod system for the active control of MHD instabilities has been operating for more than 2 years contributing to improvements of the discharge quality and length. In the past years a dynamic black-box model of the active coils and saddle probes has been developed to analyze and simulate the system electromagnetic behaviour, which is strongly dependent on the frequency due to the presence of passive conductors. Satisfactory results were achieved in reproducing most of experimental responses and the model was used to select and test the gains of operating PID regulators. However, difficulties have emerged in reproducing some flux distributions such as those corresponding to m = 0, low n current patterns. In view of higher current operation a further increase in control system performance and model accuracy is desirable, if not mandatory. To this purpose, new measures have been recently acquired in order to reassess data of critical magnetic couplings and an activity has been started aimed at the verification and integration of data from a white-box model provided by the 3D finite element electromagnetic code Cariddi. The above verification is also a preliminary step for the validation of the CarMa computational tool adaptation to RFX-mod, which has been undertaken to study the plasma resistive wall modes. The paper describes the results of a comparative analysis carried out on experimental and simulation data obtained with the black-box and white-box models.