Control of plasma parameters by the externally applied toroidal field in RFX-mod

The recent modifications brought to the RFX experiment, now RFX-mod, pose a strong focus on the active control of the plasma magnetic configuration. The new machine layout features a thin stabilizing shell which makes active control feasible and necessary at the same time. The new set of actuators includes a complex saddle coils system and a redesigned power supply system driving the toroidal field coils. The new toroidal power supply system allows a great flexibility since each sector, composed by four coils, is driven by an independent d.c./d.c. switching converter, in series with the main power supply providing the bias current. The current control on the load, performed by the four quadrant fast switching converter, allows producing the desired waveforms of toroidal field. To fully exploit the capabilities of such a system two different controllers have been designed enabling to track automatically a selected evolution of either the toroidal field at the plasma edge or the reversal F parameter, respectively. The new control systems allow to perform experiments in specified plasma configurations targeting particular physics issues and improved the overall reproducibility of the RFX-mod discharges. (c) 2007 Elsevier B.V. All rights reserved.