Conceptual design of the real-time control system of MHD modes in RFX

Real-time control is a key issue in the upgrade of the magnetic boundary of the reverse field experiment (RFX)machine, a toroidal experiment in nuclear fusion research. The upgrade aims at providing RFX with effective instruments for the active plasma control. A new active system has been designed consisting of 48 (toroidal) x 4 (poloidal) saddle coils arranged to cover the toroidal shell surface, a set of insulated gap bipolar transistors (IGBT)-based fast power supply units to feed the coils, an extensive number of magnetic probes to measure the local radial and toroidal field inside the vacuum vessel. By properly driving the currents in the saddle coils, the system can control the radial magnetic field outside the vacuum vessel (active shell), can generate magnetic rotating perturbations to drag the Magneto-hydro dynamic (MHD) modes, and can affect the plasma equilibrium and shape. The paper describes briefly the hardware arrangement of the new shell, focusing on the control operational scenarios. The requirements of the digital systems implementing the control are derived and presented, with particular reference to the required system reaction times and the envisaged data flow. Possible system architectures suitable for the implementation are discussed with emphasis on real-time communication and system distribution.