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Fast Discharge Units (FDU) forming part of the ITER coil power supply systems are intended for protection of superconductive coils by extracting the energy stored in the magnet system in case of a quench or other abnormal events. It will be provided by opening the coil current circuits by normally closed circuit breakers, thus diverting the current into discharge resistors. The interruption of DC currents in the inductive circuits is provided with the help of counter pulse circuits (CPC), the discharge of which in the direction opposite to the coil current direction ensures the arc extinguishing in the circuit breakers. The paper describes the design of two CPC modifications and presents the results of the type tests carried out on CPC full-scale prototypes. The successful results of the tests demonstrated the working efficiency of CPCs, confirmed their compliance with the design requirements and gave green light to the manufacturing of these devices to be delivered to the ITER Site.

When the capacitor cell is discharged in the short-circuit mode, the current pulse amplitude and duration are maximal. Therefore, this mode is the most severe for discharge switches of capacitive energy storage. The characteristics of the transient process of the discharge capacitive energy storage and the current loads acting in the facility discharge circuit have been defined for this mode. The test bench for definition of the LTT (Light Triggered Thyristors) loading capacity is described. The limiting characteristics have been experimentally obtained for LTT, at which there emerges the thermo-generation peak. The process of OFF-ON switching of LTTs has been investigated, the necessity is shown to use the speed-up R-C circuits to ensure fast and stable transition of LTT into the conducting state. The design of the switch unit for the capacitive energy storage comprising LTTs and crowbar diodes is described, and the transient processes of current switching in crowbar diodes are considered. The tests carried out during switching of pu1se current up to 100 kA at a voltage of 6 kV have confirmed the workability of the switch unit. Keywords: Energy storage, Power semiconductor switches, Photothyristors, Pulse power systems

A capacitive energy storage is intended for generating high-power current pulses. The setup consists of two capacitive energy storage modules, a control console, and a cable collector for connecting a load to the setup. Each module is a capacitive energy storage with a 0.5-MJ stored energy and 18-kV voltage, which is based on eight capacitor cells with reverse switch-on dynistors as switches. The module volume is 1.3 m3. The semiconductor switches in the capacitor cells are activated by light pulses, which are transmitted from the control console through fiber-optic cables. The unit is designed for operating in the programmable discharge mode, at which the semiconductor switches in the capacitor cells are switched on nonsimultaneously but in accordance with a specified program. When the discharge of all the cells is switched on simultaneously and the load is short-circuited, the maximal amplitude of the output current pulse is 800 kA. The rise time of the discharge current pulse of the cell is 150 μs.

The capacitor banks are intended for generation of the counter current pulse in vacuum circuit breakers of a two-step powerful contactor (switchgear). This switchgear is part of the power supply system of ITER superconductive coils and provides fast discharge of coil magnetic field energy by breaking the coil current supply loop and connecting in the loop the high energy resistors. The superconductive coils of the ITER facility store considerable energy (several gigajoules) and the counter pulse capacitor bank should generate the pulse current not less than 70 kA during about 600 μs at an initial voltage up to 10 kV. After generation of the current pulse the discharge switch of the capacitor bank is closed and a high voltage exceeding the initial one (10 kV) is applied to the discharge switch. The paper presents the features of the transients during the commutation cycle, design of the capacitor bank and its main components (semiconductor discharge switch, inductor, charger, etc.), as well as the results of the capacitor bank testing.