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JT-60SA is a superconducting tokamak in the framework of the broader approach agreement between Europe and Japan. For this international project among its various procurements, the Italian National Agency for new technology energy and sustainable economic development (ENEA) is providing four ac/dc converters for the central solenoid (CS) superconducting magnets, two ac/dc converters for the equilibrium field (EF) superconducting magnets, and two ac/dc converters for the fast plasma position control coils (FPPCC). Furthermore, ENEA is also providing six converter transformers of which four are of the dry type for FPPCC power supplies (PSs) and two of oil type for CS PSs. CS/EF PSs feed poloidal superconducting magnets of JT-60SA, whose purpose is the generation of strong magnetic fields able to induce and confine the plasma current in a prefixed geometrical configuration. The control system of CS/EF PSs has to be able to reproduce in real-time a reference current or voltage profile, known as “scenario” and these are particularly critical in these systems for the high currents required and for the high magnetic energy stored in the superconducting magnets. All performed type tests, carried out in accordance to the IEC60146 Standards, pointed toward a good dynamic behavior of the control system both for forward and for reverse rectifier bridges, assuring the smooth transitions between different operating modes: single mode, circulating current mode and dual mode. This is the focus of this paper. [ABSTRACT FROM AUTHOR]

JT-60SA, the superconducting tokamak under construction in Japan, will be equipped with a mix of new and reused Power Supply Systems. Most of the new Power Supply Systems are procured by European Voluntary Contributors under the framework of Broader Approach agreement between Europe and Japan. For the toroidal circuit, the 25.7 kA steady state ac/dc converter is procured by CEA. For the poloidal circuits, the procurement of 10 ac/dc converters, almost all rated ±20 kA and about ±1 kV is shared between CEA and ENEA. The two in-vessel coils for fast control of plasma position are supplied with two independent thyristor converters procured by ENEA, each one rated ±5 kA and ±1 kV. The operation of four Switching Network Units procured by ENEA inserts settable resistors in series to each Central Solenoid module, producing up to 5 kV at the nominal current of 20 kA and allowing stable plasma initiation. The protection of toroidal and poloidal superconducting magnets is assured by thirteen Quench Protection Circuits procured by Consorzio RFX, rated ±20 kA and ±3.8 kV for poloidal coils and 25.7 kA and 2.8 kV for toroidal ones, inserting a discharge resistor in the related circuit for fast dissipation of the magnetic energy stored in the coil. Finally, the suppression of Resistive Wall Modes is actively performed by 18 in-vessel coils, independently supplied by a corresponding number of fast inverters procured by Consorzio RFX, each one rated for 300 A and 240 V. The key aspects of the design of the aforementioned Power Supply Systems are described in the paper, informing also about the present status of the procurement: their design was completed and some systems were already manufactured, tested and delivered to Japan. [ABSTRACT FROM AUTHOR]

This paper first recalls the main characteristics, design criteria, and strong points of the ac/dc conversion system of RFX-mod. Then, after having described some innovative experimental scenarios and performance improvements which have been devised, the corresponding impact on the ac/dc conversion system and the compatibility with the present design are discussed. Some possible upgrades are identified and the pros and cons are evaluated, also through dedicated simulations. [ABSTRACT FROM PUBLISHER]

This paper presents the development and testing of the prototype of a hybrid mechanical–static dc circuit breaker (CB) for quench protection of superconducting magnets based on a mechanical switch paralleled to a static CB. In normal operation, the mechanical switch is closed and it handles the continuous flow of dc current, minimizing the on-state losses. In case of intervention, the mechanical switch opens, commutating the current into the static CB that quickly interrupts and transfers the current into a discharge resistor, withstanding the reapplied voltage. This paper was carried out to face and solve some issues of this design solution being not available in the literature examples of similar applications rated for significant power levels. The operation of the hybrid CB has been successfully tested up to a current of 10 kA with a recovery voltage of about 1 kV. Special tests have been dedicated to characterize the reliability and the repeatability of the current commutation from the mechanical switch to the static CB and to characterize the arc voltage under different conditions. [ABSTRACT FROM AUTHOR]

This paper describes the feasibility studies of a hybrid dc circuit breaker (CB) for quench protection of superconducting magnets rated for current up to some tens of kiloamperes (kA) and voltage of several kilovolts (kV). The proposed scheme is based on a mechanical switch paralleled to a fully controlled static CB; integrated gate commutated thyristors (IGCTs) were selected. In normal operation, the mechanical switch handles the continuous flow of dc current minimizing the on-state losses. When protection against quench is requested, the current is diverted into the static breaker that quickly interrupts the current, withstanding the reapplied voltage of several kV. The reliable turn-ON of several IGCTs in parallel with low voltage applied between anode and cathode is an issue to be assessed to confirm the feasibility of this design solution. The paper highlights that the components commonly used as snubber or protection circuit can guarantee the turn-ON of all the devices in parallel and that the IGCTs can be turned-ON with few volts applied; this latter aspect was proved by means of specific tests. Finally, a comparison between a static only and a hybrid CB is performed, highlighting the benefits introduced by the hybrid solution. [ABSTRACT FROM AUTHOR]