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Investigations on Caesium Dispersion and Molybdenum Coating on SPIDER Components

Candela V.; Cavallini C.; Gasparrini C.; Armelao L.; Candeloro V.; Dalla Palma M.; Fadone M.; Marcuzzi D.; Pavei M.; Pepato A.; Pouradier Duteil B.; Rancan M.; Rizzolo A.; Sartori E.; Segalini B.; Serianni G.; Spolaore M.; Zorzi F.; Sonato P.

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).

ID 475736
DOI 10.3390/ma16010206
PRODUCT TYPE Journal Article
LAST UPDATE 2023-07-23T16:06:55Z
TITLE Implementation of activities described in the Roadmap to Fusion during Horizon 2020 through a Joint programme of the members of the EUROfusion consortium