Search

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 SPIDER ion source has been designed to generate a current of H- ions up to 60 A and accelerate them up to 100 keV. In addition, the ratio between the co-extracted electrons and negative ions has to be below 1, and a beam inhomogeneity within 10 % has to be attained. A magnetic filter field is produced by a current flowing through the plasma electrode in the vertical direction with the aim of reducing electron temperature and density in the extraction region, so as to enhance the survival probability of H- ions while reducing the co-extracted electrons. Another strategy to reduce the co-extracted electrons is to apply a small bias voltage to the plasma grid with respect to the ion source body. In addition to this, a so-called bias plate is installed in the vicinity of the plasma grid, which can also be biased with respect to source body. However, the application of a bias voltage affects the beam inhomogeneity by modifying the ExB plasma drift within the ion source. Recently, the filter field configuration of SPIDER was modified so as to improve the plasma diffusion towards the extraction region. In addition, the voltage ratings of the bias power supplies were increased. Both these modifications permit to efficiently lower the electron co-extracted current. The present contribution describes such improvements while focusing on the effects they have on the beam inhomogeneity.

The aim of this work is the manufacture of high heat flux mock-ups with Be armour tiles on a CuCrZr heat sink for fabricating the beryllium section of the divertor vertical target (DVT) in the ITER reactor. Diffusion bonding between the CuCrZr bar and the beryllium tiles was obtained by inserting an aluminium interlayer to accommodate surface irregularities as well as to provide a compliant layer for accommodating thermal mismatches during both manufacturing and operation and cycles.

The European divertor outboard channel provides the use of adjustable keys for the attachment system of the ITER divertor components, in particular vertical target and wing. Mechanical and electrical tests will be used to characterise the vertical attachment system. Mechanical tests are aimed to the verification of reaction moment due to friction in different conditions, air or vacuum, while electrical tests will be performed feeding the joint with a DC or AC current. The mechanical test results show that the sliding of the keys occurs correspondingly to an applied torque about 10 times less than the one originated by the halo current and dead weight loads. This implies that the vertical target cannot be held by the friction only but one dumbell key must be fixed. The electrical tests show no damage occurs up to the reference conditions, in spite of a reduction of the unscrewing torque. In the final analysis it can be stated that the dumbell keys are capable to carry safely the expected halo current fraction.

To reach fusion conditions and control plasma configuration in ITER, a suitable combination of additional heating and current drive systems is necessary. Among them, two Neutral Beam Injectors (NBI) will provide 33 MW hydrogen/deuterium particles electrostatically accelerated to 1 MeV; efficient gas-cell neutralisation at such beam energy requires negative ions, obtained by caesium-catalysed surface conversion of atoms inside the ion source. As ITER NBI requirements have never been simultaneously attained, a Neutral Beam Test Facility (NBTF) was set up at Consorzio RFX (Italy), including two experiments. MITICA is the full-scale NBI prototype with 1 MeV particle energy. SPIDER, with 100 keV particle energy, aims at testing and optimising the full-scale ion source: extracted beam uniformity, negative ion current density (for one hour) and beam optics (beam divergence