Final Design of SiC-based Power Supply system for Resistive-Wall-Mode control in JT-60SA

Effective control of Resistive-Wall-Modes (RWM) is mandatory in JT-60SA, the satellite tokamak under construction in Naka (Japan), since one of its main objectives is to reach steady-state high-beta plasmas. The RWM control system is based on a set of 18 in-vessel sector coils, placed on the plasma side of a conductive wall and individually fed by a dedicated fast power supply system (RWM-PS). For each coil, the RWM-PS has to produce arbitrary current waveforms following in real time the reference generated by the JT-60SA MHD Controller. The time response shall be fast enough to avoid excessive growing of plasma instability. Previous studies allowed establishing the main RWM-PS requirements, both in terms of output voltage and current ratings (240 V - 300 A) and in terms of dynamics. The latter in particular is very demanding: current bandwidth of 3 kHz in closed loop and latency between reference and output less than 50 ms. Possible technical solutions were explored in the past; the most convenient, based on 18 H-bridges was assumed as reference design once verified the feasibility of the fulfilment of the dynamic requirements. The development of a prototype was launched at this purpose and successful results were achieved thanks to the adoption of new hybrid Silicon-Silicon Carbide (Si-SiC) IGBT, driven by a fast full digital control board. The reference design approach with these switches was confirmed for the procurement of the whole system, presently in progress; the design phase is expected to be completed in summer 2016. This is the first PS system for fast control of plasma instabilities in fusion experiments adopting SiC semiconductors. The paper will give an overview of the whole final design with particular emphasis on the newest features and on the interface issues for an effective integration with the JT-60SA power and control systems.