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SPIDER is the 100 keV full-size Negative Ion Source prototype of the ITER Neutral Beam Injector, operating at Consorzio RFX in Padova, Italy. The largest Negative Ion Source in the world, SPIDER generates an RF driven plasma from which Deuterium or Hydrogen negative ions are produced and extracted. At the end of 2021, a scheduled long-term shutdown started to introduce major modifications and improvements aiming to solve issues and drawbacks identified during the first three years of SPIDER operations. The first action of the shutdown period was the disassembly and characterization of the SPIDER beam source after removal from the vacuum vessel and its placement inside the clean room. Each component was carefully assessed and catalogued, following a documented procedure. Some source components, i.e., the Plasma Grid, Extraction Grid and Bias Plate, revealed the presence of different and non-uniform red, white and green coatings that might be correlated to back-streaming positive ions impinging on grid surfaces, electrical discharges and caesium evaporation. Thus, several analyses have been carried out to understand the nature of such coatings, with the study still ongoing. The evidence of caesium evaporation and deposition on molybdenum-coated SPIDER components, such as the formation of oxides and hydroxides, is demonstrated through surface characterization analyses with the use of the Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). [ABSTRACT FROM AUTHOR]

The ITER Neutral Beam Test Facility (NBTF) is hosted in Padua and includes two experiments: MITICA, the 1 MeV full-scale prototype of the ITER HNB injector, and SPIDER, the 100 keV full-size ITER Radio Frequency (RF) negative ion source. SPIDER and MITICA experiments are actively cooled by Ultrapure Water (UPW) to electrically insulate in-vessel components that are biased to high voltage levels. Water conductivity is an important monitored parameter to ensure components' insulation by limiting the leakage current of active cooled equipment. A very low conductivity water is especially important in MITICA, where components need to operate up to 1 MVdc, an insulation level beyond the actual industrial standard. Careful selection of suitable materials for any in-vessel (vacuum insulation) and out-vessel component (air insulation) is of utmost importance, as their interaction with water and different environment may affect their chemical and mechanical properties. Additionally, materials selection can severely influence water chemical characteristics: cooling circuits are made of metals (copper, aluminium, steel) and insulating materials (plastic, rubber) when connecting parts at different electric potentials. During the first years of cooling plant exploitation, it was shown that water degrades more quickly than estimated by design. The Primary Circuits (PCs) that showed the most severe water degradation during operation are SPIDER and MITICA power supply ones, respectively called PC01 and PC08. This paper describes the results of specific experimental tests performed on MITICA PC08 to evaluate possible causes of water degradation and detect sources of contaminants that might compromise future experimental campaigns. The cooling circuit was subdivided in different sections and water circulation tests were performed at constant temperature and flowrate. Water samples were collected and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analyses were performed to quantify the type and amount of metals released. Moreover, components samples collected along their cooling circuits were characterized by Scanning Electron Microscope (SEM) technique to detect undesired contaminants and immersed in UPW to study their corrosion behaviour using metal release tests. [ABSTRACT FROM AUTHOR]

The Source for Production of Ions of Deuterium Extracted from a Radiofrequency plasma (SPIDER) is the 100 keV full-size Ion Source prototype of the International Thermonuclear Experimental Reactor (ITER) Neutral Beam Injectors (NBI), currently in operation at Consorzio RFX in Padova, Italy. The SPIDER vacuum pumping system is designed to operate at a nominal gas pressure of 0.3 Pa inside the Beam Source (BS), and it consists of two primary pumping groups, four turbo-molecular pumps, and eight cryogenic pumps. However, during the first three years of SPIDER operations, it was found that increasing the BS pressure to 0.6 Pa was necessary to achieve nominal performance. Additionally, a specific experimental study conducted in 2019 revealed the existence of a pressure limit in the SPIDER Vacuum Vessel (VV) that must be respected to reduce the probability of Radio Frequency breakdown. These two factors have necessitated an upgrade to the current vacuum pumping system. To address the issue of limited space for installing new pumps, a Vacuum Enhancement Module (VEM) will be added to the existing SPIDER Vacuum Vessel (VV). The VEM will house up to 512 Non-Evaporable Getter (NEG) pump cartridges in 16 × 32 modules. The pumps will need to be regenerated at temperatures up to 600 °C for up to 72 h to extract the hydrogen isotopes absorbed during operation. To prevent the heating of surrounding parts, such as the SPIDER Beam Source (BS) and electrical connections, a dedicated cooling system is required to cool down the VEM components during the NEG regeneration process. This paper presents a thermal-hydraulic study, design, and analysis of the cooling system for the VEM using Computational Fluid Dynamics (CFD) analyses. [ABSTRACT FROM AUTHOR]