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The article is focused on the electromagnetic analysis of the toroidal field superconducting coils (TFCs) of the Divertor Tokamak Test facility (DTT) when electrical transients occur in the TFCs system: for example, during the operations of the fast discharge units (FDUs) and considering also, the simultaneous occurrence of a fault condition. During the FDU intervention, a transient voltage excitation lasting few milliseconds occurs at the TFC terminals and it electrically stresses the insulations of TFCs itself. To investigate the voltage distribution across, inside and between different double pancakes (DPs) of each TFC, a lumped parameters circuital model has been developed and implemented in Ansys Simplorer simulation environment. This model includes both the detailed submodel of each TFC and FDU. The transient analyses have been carried out for two different scenarios: a reference one and a failure scenario, considering three different fault resistance values and also two different values of the resistance connecting the TF case to ground. In order to verify the correct sizing of the coil insulation and the TF case-to-ground resistance value inserted in the circuit of each TFC, the voltages of each TFC (terminal-to-terminal, terminal-to-ground, across of adjacent DPs, and between other circuit points) were computed in the time domain (in the range of milliseconds) for both scenarios. An overview of calculations and simulation results is presented and discussed, pointing out a high sensitivity of fault conditions and of overvoltage values and addressing mitigation strategies. [ABSTRACT FROM AUTHOR]

In many relevant cases requiring a net energy comparable with that of a household appliance, the power supplies (PSs) and the electrical systems must be oversized to sustain short peak demands. The same equivalent energy could be achieved by storing and distributing the power over the time. These considerations lead to a new PS concept based on the exploitation of the energy stored between the actual operations. The new compact ($60\,\,\text {cm} \times 120\,\,\text {cm} \times 190$ cm) PS is able to generate arbitrary currents up to 2 kA by an integrated energy storage system based on supercapacitors. The delivered output power (approximately 200 kW) is obtained from a very low and tunable input power (<1 kW). Furthermore, a portion of the injected power can be recovered in the storage system. Even though the system was designed for a specific project (the PROTO-SPHERA spherical tokamak), the presented approach can be applied to general-purpose PSs, and there are encouraging prospects to extend it to large facilities with higher currents and voltages. [ABSTRACT FROM AUTHOR]

The plasma in the tokamak JT-60SA is initiated mainly by operating the four Switching Network Units (SNUs) inserted in the four modules of the Central Solenoid. In the framework of the “Broader Approach” agreement, these four SNUs were procured by the European Union. This paper presents the final assembly of the SNU system and the main tests performed in the last years before shipping it to Japan. The experimental results demonstrated the capabilities of the SNUs to comply with the JT-60SA requirements, even with better performances. [ABSTRACT FROM AUTHOR]

Plasma properties can be useful in a wide spectrum of applications. Experimental projects on controlled nuclear fusion are the most challenging of these applications and, at the same time, the best way to approach plasma science. Since nuclear fusion reactors can ensure a large-scale, safe, environmentally-friendly and virtually inexhaustible source of energy, several fusion-oriented megaprojects and innovative companies are appearing all over the world. PROTO-SPHERA (Spherical Plasma for HElicity Relaxation Assessment) is the first plasma project with a simply connected configuration, namely not requiring additional objects inside the plasma volume. This is obtained by a plasma arc, shaped as a screw pinch, acting as the centerpost of a spherical torus with minimal aspect ratio. Due to its intrinsic physical, engineering and economic advantages, this new approach is attractive also on an industrial scale and with several developments that still needs to be explored. This paper presents the PROTO-SPHERA basic principles, its first encouraging results and its expected and potential evolutions. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the approved detailed design of the four Switching Network Units (SNUs) of the superconducting Central Solenoid of JT-60SA, the satellite tokamak that will be built in Naka, Japan, in the framework of the “Broader Approach” cooperation agreement between Europe and Japan. The SNUs can interrupt a current of 20kA DC in less than 1ms in order to produce a voltage of 5kV. Such performance is obtained by inserting an electronic static circuit breaker in parallel to an electromechanical contactor and by matching and coordinating their operations. Any undesired transient overvoltage is limited by an advanced snubber circuit optimized for this application. The SNU resistance values can be adapted to the specific operation scenario. In particular, after successful plasma breakdown, the SNU resistance can be reduced by a making switch. The design choices of the main SNU elements are justified by showing and discussing the performed calculations and simulations. In most cases, the developed design is expected to exceed the performances required by the JT-60SA project. [Copyright &y& Elsevier]

The Divertor Tokamak Test (DTT) facility, construction starting at Frascati, Italy, is designed to test different solutions for divertor in view of DEMO. A preliminary analysis of the error fields (EFs) assumed a simplified model of rigid and independent displacements and rotations. A methodology based on the first order truncated Taylor expansion has been applied, linking the displacement parameters and the EFs within the required accuracies. A system of in-vessel copper coils has been designed to counteract EFs and the ampere-turns necessary to force them back within the request limits has been calculated. Here, the details of the analysis have been provided. [ABSTRACT FROM AUTHOR]

ECRH&CD systems are extensively used on tokamak plasmas due to their capability of highly tailored power deposition, allowing very localised heating and non-inductive current drive, useful for MHD and profiles control. The high electron temperatures expected in DEMO will require ECRH systems with operating frequency in the 200–300 GHz range, equipped with a reasonable number of high power ( P ≥ 1 MW) CW RF sources, for allowing central RF power deposition. In this frame the ENEA Fusion Department (Frascati) is coordinating a task force aimed at the study and realisation of a suitable high power, high frequency reliable source. [ABSTRACT FROM AUTHOR]