Alessandro Lampasi

Advancement on the procurement of Power Supply systems for JT-60SA

JT-60SA will be provided with a set of power supply systems procured by Europe and Japan under the framework of Broader Approach Agreement. The toroidal circuit is supplied by an ac/dc thyristors converter rated for 25.7 kA in steady state, and the toroidal superconducting coils are protected by three Quench Protection Circuits (QPC) assuring fast dissipation of the stored magnetic energy of about 1 GJ in case of fault. The poloidal circuits are supplied by ten ac/dc thyristor converters, almost all rated for ±20 kA and ±1 kV; ten QPC rated for the same nominal current and ±3.8 kV assure the protection of the poloidal superconducting coils. The high voltage required for the plasma breakdown is generated in the poloidal circuits by four Booster ac/dc converters and by six Switching Network Units (SNU). The Booster converters are rated +4/-14.5 kA and ±5 kV for short time, thus are inserted in the circuits only when needed and then bypassed. The SNU are operated in order to insert in the circuits settable resistors, producing up to 5 kV at the nominal current of 20 kA, and then to by-pass them after plasma initiation phase. Two in-vessel coils for fast control of plasma position are supplied by two independent ac/dc thyristor converters, rated ±5 kA and ±1 kV, and the in-vessel coils for Resistive Wall Mode control are supplied by 18 fast inverters rated for 300 A and 240 V. After a preliminary definition of the reference schemes and main requirements of the components, the procurement of the Power Supply systems has been started by means of contracts awarded to industrial suppliers including detailed design, manufacturing and test. Besides highlighting the main characteristics of Power Supply systems of JT-60SA as resulting after the detailed design, the paper describes the present status of their procurement: the QPC units have been already installed in Japan for the final acceptance test; the manufacture and factory tests of some SNU have been successfully completed; the detailed design of ac/dc converters for toroidal and poloidal circuits has been finalized, and the first units have been manufactured and are ready for factory testing.

Detailed Analysis of the Transient Voltage in a JT-60SA PF Coil Circuit

A superconducting coil system is actually complicated by the distributed parameters, e.g. the distributed mutual inductance among turns and the distributed capacitance between adjacent conductors. In this paper, such a complicated system was modeled with a reasonably simplified circuit network with lumped parameters. Then, a detailed circuit analysis was conducted to evaluate the possible voltage transient in the coil circuit. As a result, an appropriate (minimum) snubber capacitance for the Switching Network Unit, which is a fast high voltage generation circuit in JT-60SA, was obtained.

The European DEMO fusion reactor: Design status and challenges from balance of plant point of view

DEMO initial conceptual design studies are being conducted in Europe as part of the European Union Roadmap to Fusion Electricity, which aims to demonstrate the feasibility of electricity produced by nuclear fusion reactors around the middle of this century. The aim of this paper is to provide an overview of the DEMO project, highlighting its main characteristics and challenges in terms of design, integration, and operation. Particular emphasis is given on some important systems of the Balance of Plant (BoP), such as the primary heat transfer systems, the related power conversion systems, and the electrical power plant. The relevance of such systems is due to the need of a continuous reanalysis at any significant design change because of their huge dimensions, technical complexity, and strong impact on design integration, maintenance, and safety.

Commissioning of the plasma central column for the PROTO-SPHERA spherical tokamak

PROTO-SPHERA is the first plasma project with a simply connected configuration, namely not requiring other objects inside the plasma. This is obtained by a hydrogen plasma arc, shaped as a screw pinch, acting as the central column of a spherical torus with minimal aspect ratio. The reduced size and complexity of the configuration can lead to several physical and engineering advantages, providing relevant contributions to the magnetic plasma confinement methods. Moreover, due to the limited costs and requirements, the set-up is attractive for replication and developments also on an industrial scale with many potential applications. This paper describes the initial activities of the PROTO-SPHERA project, with emphasis on the electrical tests and commissioning performed to implement the plasma central column. In particular, an intermediated experiment classified as MULTI-PINCH was designed to investigate the breakdown conditions and the pinch stability.

A new generation of pulsed power supplies for experimental physics based on supercapacitors

Big physics experiments often require high power peaks for a short duration with low duty cycle. Even though the effective energy may be relatively small, the power supplies of these experiments can be critical from the technical, economic, and environmental points of view. This paper shows that the supercapacitor technology can simplify many power supply systems and can extend the scenarios explored by the experiments. Supercapacitors were already proposed and introduced for many applications, but their use is particularly advantageous in big physics experiments, especially when the current is high and the voltage is relatively low. This statement will be supported by some models and case studies based on real experimental devices (operating or that are going to be commissioned) with currents up to 60 kA. The presented designs based on supercapacitors simplify the existing apparatus, reduce the costs, increase the local power availability, and even extend the possible experimental activities. The reported analyses and results are mainly focused on nuclear fusion researches, but can be easily applied to many other fields.

ETHICAL: A modular supercapacitor-based power amplifier for high-current arbitrary generation

ETHICAL (Efficient Time to High-I Converter with Affordable Load) project aims to develop modular systems based on supercapacitors able to “amplify” at their output the power and the current adsorbed at their input. The project is named after the principle to take into account the social, environmental and economic impacts of the power supplies. Using the ETHICAL approach, high currents and high powers with arbitrary waveforms can be obtained from low voltage and low power sources, even in places without invasive structures and high or medium voltage grids. The input power features also a good quality, as the reactive power and harmonic content are negligible. The design of a prototype rated 120 V and 2 kA is presented, but these values can be increased by parallel connection or by part replacing. The extreme modularity and flexibility improve the general reliability and simplify the maintenance, fault detection and replacement activities. Therefore, the ETHICAL approach could be introduced in many fields of engineering.

A novel conceptual design for gyrotron's high voltage power supplies

The scope of this paper is a detailed description for an innovative conceptual design of high voltage power supplies for 110/138 GHz gyrotrons, including both the High Voltage Main Power Supply (HVMPS), that feeds in parallel the two gyrotron cathodes, both the Body Power Supplies (BPS), that establishes a voltage between Body and Collector and regulating the voltage between Body and Cathode; and both the Anode Power Supplies (APS) that controls the voltage between Anode and Cathode in order to keep the beam current and the electron pitch factor of gyrotrons. This conceptual design consists in a complete set of simulations that points out how the dynamic behavior of all ECPSs is compliant technical requirements. It is the result of a collaboration between the National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) and POSEICO SPA. expert in power electronic converters. The advantages include a small amount of power modules and a high level of reliability and redundancy.

Survey of electric power supplies used in nuclear fusion experiments

Nuclear fusion could ensure a large-scale, safe, environment-friendly and virtually inexhaustible source of energy. A nuclear fusion facility can be considered as a complex electrical machine with many power supplies and electrical systems. This paper presents a survey of the main features of the power supplies in nuclear fusion facilities (tokamaks). The main characteristics in terms of nominal ratings, operational parameters and performances are shown and compared for many experiments, as ITER, JT-60SA, EAST, KSTAR, JET, ASDEX, FTU and DTT.

Installation, commissioning and acceptance tests of the Switching Network Units for the central solenoids of JT-60SA

JT-60SA is an international tokamak being built in Naka (Japan) as a joint collaboration between Europe and Japan for the applied researches on the use of nuclear fusion as a new energy source. The procurement of the different systems composing JT-60SA is managed as in-kind contribution shared between European and Japanese institutions. The procurement of the Switching Network Units (SNUs) for the Central Solenoid (CS) is supported by Europe. After a four-year design and manufacturing in Europe, the JT-60SA CS SNUs and the related components were delivered to Japan in October 2016. This paper describes the activities for the on-site installation, commissioning and tests of this procurement.

Switching Network Units for High Currents and Voltages or Plasma Applications

OCEM and ENEA gained a wide experience in the design and experimental characterization of fast and accurate switching systems for high DC currents, as required to control magnets and superconductors. The exploited idea consists in inserting an electronic switch in parallel to a fast electromechanical switch in air, to combine the benefits of both devices. The electronic switch is turned on and off to support the electromechanical commutations, reducing the jitter to tens microseconds and limiting the arcs that would reduce the system lifetime. During the performed tests, DC currents up to 20 kA were diverted in less than 100 μs with good repeatability. In case of emergency, the current can be interrupted in few tens of milliseconds. If necessary, a resistor can be inserted in parallel to the switch to dissipate the energy trapped in inductive loads or to produce desired overvoltages (a voltage up to 5 kV was reached in this configuration). Specific circuits were designed to preserve the components from transient voltage overshoots. This switching system is expected to work for 10000 operations without major maintenance. The developed solutions may be extended to many relevant applications as particle accelerators and HVDC networks.