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SPIDER is the full-scale prototype of the ion source of the ITER Heating Neutral Beam Injector, where negative ions of Hydrogen or Deuterium are produced by a RF generated plasma and accelerated with a set of grids up to ~100 keV. The Power Supply System is composed of high voltage dc power supplies capable of handling frequent grid breakdowns, high current dc generators for the magnetic filter field and RF generators for the plasma generation. During the first 3 years of SPIDER operation different electrical issues were discovered, understood and addressed thanks to deep analyses of the experimental results supported by modelling activities. The paper gives an overview on the observed phenomena and relevant analyses to understand them, on the effectiveness of the short-term modifications provided to SPIDER to face the encountered issues and on the design principle of long-term solutions to be introduced during the currently ongoing long shutdown., 8 pages, 12 figures. Presented at SOFT 2022

The Acceleration Grid Power Supply of the MITICA test facility in Padova (Italy) is currently under commissioning. The power conversion system, the DC generator, and the High Voltage equipment have been individually commissioned, whereas the integration tests are ongoing. It is a challenging process due to the unconventional application, to the variety of different electrical technologies involved and to the complexity of the interfaces. During the integrated tests of the power supplies the achievement of 700kV stable operation has been demonstrated for the first time in a Neutral Beam Injector, but an unexpected event occurred, most likely a breakdown in the HV part, which resulted in a fault of the DC generator. A subsequent test using an auxiliary power supply was performed to check the voltage withstanding capability of the HV plant, but another breakdown occurred at around 1MV. This paper describes the activity performed to identify the location of the breakdowns affecting the integrated tests. A test campaign has been devised with increased diagnostic capabilities and specific strategy conceived to trigger intentional breakdowns in specific locations and collect measurement patterns for different cases. The results of the campaign will be presented and the current understanding of the issue will be described, with a view on future tests and further improvements of diagnostics.

This paper presents the design criteria and the preliminary characteristics of the power supply and electrical systems of the Divertor Tokamak Test (DTT) facility. The power supply system has to feed: 6 superconducting modules of the central solenoid, 6 poloidal field superconducting coils, 18 toroidal field superconducting coils designed for a current up to 50 kA, some coils for plasma fast control and vertical stabilization, the electron (ECRH) and ion (ICRH) cyclotron additional heating systems designed to deliver about 25 MW to the plasma, further 20 MW to the plasma generated by a neutral beam injector (NBI) and all the auxiliary systems and services. The analysis was carried out on a reference scenario with a plasma current of 6 MA, mainly to estimate the electrical power needed to operate the facility, but also to identify some design choices and component ratings.

SPIDER is the full scale prototype of the ITER Heating Neutral Beam Injector ion source and the most powerful RF driven negative ion source currently in operation. In SPIDER the negative ions are extracted from a plasma generated by a 4x2 array of drivers, relatively small highly engineered antennas, each designed to be supplied with up to 100 kW at the frequency of 1 MHz. The drivers are fed in pairs by 4 independent RF oscillators in the push-pull configuration through 4 RF rigid lines and 4 "normal" L-type matching networks on board of the ion source. The basic concepts, previously developed and tested on smaller scale ion sources, were further improved and combined in a single facility considering all the constraint and restrictions relevant for ITER. The RF generators interact through their loads and the effects observed during the experimentation are frequency and output power modulations, which affect the plasma parameters and the ion beam performances. Furthermore, during the experimental campaign a common mode stray RF current was observed in the power supplies and in the ion source diagnostics system, causing faults and making the measurements unreliable. These issues have different root causes located both on the power supplies side and on the ion source side: the RF stray currents are mainly due to the transducers for the oscillators output voltage measurement, which provides low impedance path for them; the interactions among the oscillators are influenced by the layout of the RF circuit on board on the ion source that introduces large loops, thus magnetic coupling. The paper describes the original RF circuit and system, presents the understanding of the issues identified during the experimental campaigns and discusses the effectiveness of the provisions introduced to improve the performance.

The paper describes a proposal for the new power supply of the RFX toroidal field system based on IGCT semiconductors used in d.c./d.c. converters and in d.c. current interrupters. The analyses carried out asseses its capability to validate the performance of the previous scheme and to satisfy the new requirements. The design criteria of the main devices will be also reported.