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Pulsed power supply systems are employed in many fusion projects and in other scientific applications. A novel power supply approach and a first prototype unit were specifically developed to feed pulsed loads (low duty cycle), as the resistive or superconducting coils used to produce high magnetic fields for some seconds or longer. Thanks to the integrated energy storage, the high pulsed power required for the load is not drawn directly from the electrical grid. In fact, a huge amount of energy can be stored at low power (even through a single-phase 10 A plug, as normally used for household appliance). A significant fraction of the energy stored in the load can be recovered for successive operations. Without such energy storage, all the power supply devices and the upstream chain must be oversized and installed only in locations provided with adequate power. The first power supply unit (2 kA) was able to replace a previous system with comparable performances, but the old system occupies an extremely larger volume and needs a 20-kV connection at the input. Moreover, a specific solution was implemented to achieve a very fast (600 kW) energization of the magnets. The energy storage capability is intrinsically scalable: the setup can be rearranged and the storable energy can be updated even after the installation (for example, to increase the pulse duration). [ABSTRACT FROM AUTHOR]

The Divertor Tokamak Test (DTT) facility will be the link between ITER and DEMO as regards the study of the power exhaust in the divertor structure. In order to accomplish this goal, the Italian DTT will be a complete superconducting tokamak with 45 MW of additional power coupled to the plasma. According to the last requirements, the DTT coil power supplies are designed to achieve a toroidal field of 6 T and a 5.5 MA plasma in single-null configuration, but also to achieve double-null (with plasma at 5.5 MA), snow-flake (4.5 MA), super-X (3 MA) and other advanced configurations. This paper presents the conceptual design of the DTT power supply and electrical systems, including the site layout, the distribution networks, the expected scenarios and the mechanisms for breakdown and emergency discharge. In particular, the main rationales for the selection of the power supply topology are summarized. The power demand from the grid, presented in the various design options, can reach values above 300 MVA, including the contribution of the additional heating and current drive systems and of the auxiliary services. [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]

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]

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]

This paper presents the main characteristics and test results of the first Switching Network Unit (SNU) of the Central Solenoid for plasma initiation in the international experiment JT-60SA. The SNU can interrupt a direct current up to 20 kA producing at its terminals a voltage up to 5 kV with a rise time shorter than 100 μs. This is obtained by synchronizing the operation of a light electromechanical contactor with a static switch in order to combine the benefits of both devices. Even though the design was based on the JT-60SA specifications, the adopted solutions can be extended to many fusion and industrial applications. Due to the novelty of the developed solutions, an exhaustive set of tests were performed both on relevant single devices and on the complete SNU, even at full current, full voltage and full energy. The most relevant tests were performed using the Frascati Tokamak Upgrade (FTU) facilities reproducing the JT-60SA operating conditions. As the presented tests demonstrated the capabilities of the SNU to comply with the requirements, the manufacturing of the remaining three Central Solenoid SNUs can proceed and is expected to be completed by 2015. [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 nuclear fusion project JT-60SA is presently under construction in Naka (Japan) as a joint collaboration between Europe and Japan, within the framework of the Broader Approach Agreement. According to such agreement, the various JT-60SA systems are supplied by European and Japanese institutions. In particular, the Italian Agency ENEA was in charge for the procurement of the four Switching Network Units (SNUs) for the JT-60SA Central Solenoid (CS). The main SNU function is to interrupt a DC current up to 20 kA in a short time (less than 1 ms) in order to produce an overvoltage of up to 5 kV, crucial to generate and sustain the fusion plasma. The SNU design, manufacturing and factory test activities have been completed in 2016. After the delivery in Naka, the four SNUs have been installed and successfully commissioned in 2017. After an overview on the main technical characteristics of the SNUs and the key aspects of their design, this paper describes the activities performed on-site, highlighting the results obtained during the final acceptance tests and comparing them with the design simulation and the factory test results. [ABSTRACT FROM AUTHOR]

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]

Due to the high electron temperature during the plasma burning, both a higher power (>1 MW) and a higher frequency (up to 300 GHz) are required for plasma heating in future fusion experiments like DEMO. For this task, ENEA started a project to develop a cyclotron auto-resonance maser (CARM) able to produce an electron radiation in synchronism with the electromagnetic field and to transfer the electron beam kinetic energy to the plasma. This facility requires an advanced pulsed high voltage power supply (HVPS) with the following technical characteristics: variable output voltage up to 700 kV; variable pulse length in the range 5–50 μs; overshoot < 2%; rise time < 1 μs; voltage accuracy (including drop, ripple and stability) <0.1%. This paper describes the conceptual design and the technical solutions adopted to achieve the performance requested for the CARM HVPS. [ABSTRACT FROM AUTHOR]

Towards the middle of the current century, the DEMOnstration power plant, DEMO, will start operating as the first nuclear fusion reactor capable of supplying its own loads and of providing electrical power to the European electrical grid. The presence of such a unique and peculiar facility in the European transmission system involves many issues that have to be faced in the project phase. This work represents the first study linking the operation of the nuclear fusion power plant DEMO to the actual requirements for its correct functioning as a facility connected to the power systems. In order to build this link, the present work reports the analysis of the requirements that this unconventional power-generating facility should fulfill for the proper connection and operation in the European electrical grid. Through this analysis, the study reaches its main objectives, which are the definition of the limitations of the current design choices in terms of power-generating capability and the preliminary evaluation of advantages and disadvantages that the possible configurations for the connection of the facility to the European electrical grid can have. In reference to the second objective, the work makes possible a first attempt at defining the features of the point of connection to the European grid, whose knowledge will be useful in the future, for the choice of the real construction site. [ABSTRACT FROM AUTHOR]

Supervisory control system for superconducting magnet power supplies in JT-60SA is designed and developed. This system is in charge of many kinds of control; discharge sequence control, real-time magnet current control, data acquisition, machine protection and human safety. In the design, communication interface has to be optimized according to all requirements. The most important feature is real-time control with 4 kHz which is required for equilibrium control of plasma. In order to satisfy this requirement, reflective memory (RFM) network is applied for high speed data sharing with multiple controllers. This paper describes the architecture of the control system and the operation of the power supply system under the supervision. [ABSTRACT FROM AUTHOR]

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]

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]

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]

• DTT is a facility under construction in ENEA research centre and its part of European nuclear fusion research. • Fast Discharge Unit is a safety key component for the protection of the Superconducting Toroidal Field Coils through a discharge on Dump Resistors. • A new study with a switched Dump Resistor has been carried out with a result of a linear discharge and better performances. • A Fault Analysis has been carried out in order to evaluate the behaviour of the system with multiple faults. The paper is focused on the optimal design of Fast Discharge Unit (FDU) for the quench protection of the Toroidal Field (TF) magnets of the Divertor Tokamak Test facility (DTT), an experimental facility under construction in ENEA Frascati Research Centre (Rome, Italy). The FDU is a safety key component that protects the superconducting magnets when a quench is detected through the fast extraction of the energy stored in the magnets by adding a discharge dump resistor (DR) in the TF magnets circuit. A comparison between a fixed DR and a switched variable DR has been implemented by changing resistor parameters and by using multiple current control of the power electronics components (IGCTs). The new configuration allows to reduce the maximum voltage and the thermal stresses both for superconducting magnets and for FDUs (Fast Discharge Units), so reducing the insulation level of all TF (Toroidal Field) coil circuits, including also the power supply, reducing the hotspot temperature on the TF coils and the specific energy through them. Another advantage of the proposed configuration is the reduction of the size of all electrical devices of TF coil circuits so achieving a more effective and reliable design, also decreasing the overall costs. [ABSTRACT FROM AUTHOR]

The most relevant electrolytes used in commercial electrical double layer capacitors (EDLCs) are based on non-aqueous solvents as acetonitrile (ACN) and propylene carbonate (PC). However, these solvents are synthesized from non-renewable fossil feedstocks, making it desirable to develop more sustainable alternatives. To address this issue, in this work lactic acid was used to synthesize a panel of substances with small structural variation. The investigated products belong to the chemical family of ketals, and among them the 5-methyl-1,3-dioxolan-4-one (LA-H,H) was found to be the most suitable to prepare electrolytic solutions. Therefore, LA-H,H was combined with triethylmethylammonium tetrafluoroborate (TEMABF4), and analyzed in symmetrical EDLC. This electrolyte was thoroughly characterized by cyclic voltammetry, galvanostatic cycles and electrochemical impedance spectroscopy (EIS), disclosing competitive performances compared to PC-based electrolyte. The EDLC with LA-H,H/TEMABF4 displayed a specific energy and power of 13.4 Whkg−1 and 22.5 kWkg−1 respectively, with an optimal cycling stability over 5000 cycles at different current densities. [ABSTRACT FROM AUTHOR]

EU-DEMO is a European project, having the ambitious goal to be the first demonstrative power plant based on nuclear fusion. The electrical power that is expected to be produced is in the order of 700–800 MW, to be delivered via a connection to the European High Voltage electrical grid. The initiation and control of fusion processes, besides the problems related to the nuclear physics, need very complex electrical systems. Moreover, also the conversion of the output power is not trivial, especially because of the inherent discontinuity in the EU-DEMO operations. The present article concerns preliminary studies for the feasibility and realization of the nuclear fusion power plant EU-DEMO, with a special focus on the power electrical systems. In particular, the first stage of the study deals with the survey and analysis of the electrical loads, starting from the steady-state loads. Their impact is so relevant that could jeopardy the efficiency and the convenience of the plant itself. Afterwards, the loads are inserted into a preliminary internal distribution grid, sizing the main electrical components to carry out the power flow analysis, which is based on simulation models implemented in the DIgSILENT PowerFactory software. [ABSTRACT FROM AUTHOR]