New real-time RFX-mod feedback control algorithms in the MARTe framework

The RFX-mod experiment is equipped with a sophisticated magnetic feedback system that controls simultaneously different types of MHD instabilities. Thanks to the recent introduction of the MARTe real-time framework [1], the RFX-mod control systemhas gained new potentialities allowing a flexible and efficient implementation of more complex and computation-demanding control schemes. These upgraded capabilities of RFX-mod make possible to study new MHD feedback algorithms relevant to both Reversed Field Pinch (RFP) and tokamak operation and, thus, to contribute to the scientific debate on the optimal feedback control strategies by a systematic experimental investigation on the problem. Recently, two new feedback schemes have been developed in RFX-mod for the radial magnetic field sensors: the Plasma Response and the Improved CleanMode Control (CMC). The Plasma Response algorithm uses as feedback variable the component of the radial magnetic field that is obtained by subtracting the field produced by the active coils from the measurements. Even if this control scheme is considered not very effective with radial sensors at least for the RWM control, as predicted by some models developed at RFX-mod [2-3], the actual radial sensor inefficiency has never been experimentally tested in RFX-mod and, thus, the aimof this new control option will be to validate the model predictions. As regards the second feedback scheme, the capabilities of the new control system have allowed to refine the sidebands computation inthe original CMC algorithm [4], where only the copper shell is considered and a fixed set of sideband harmonics are subtracted. The new model takes into account both the copper shell and the mechanical structure and subtracts a wider set of sideband harmonics in the computation. These new algorithms are planned to be tested in RFX-mod in both RFP and tokamak operation. In the latter configuration,the results will be compared to the ones obtained using the poloidal magnetic field as feedback variable in order to investigate the effectiveness of the different feedback schemes. References [1] Netò A. et al 2010 IEEE Trans. Nucl. Sci. 57 [2] Zanca P. et al 2012 Plasma Phys. Control. Fusion 54 [3] Marchiori G. et al 2012 Nucl. Fusion 52 [4] Zanca P. et al 2007 Nucl. Fusion 47