[en] Deuterium retention and release behavior were investigated in this study, for beryllium, tungsten and mixed beryllium/tungsten thin layers which are of concern for next-generation thermonuclear fusion devices like International Thermonuclear Experimental Reactor. The layers prepared with thermionic vacuum arc technology by using two different ion acceleration voltages 0 V and −700 V respectively were subsequently implanted by exposure to a steady-state deuterium plasma with ion energies of 240 eV/D for D₃ and 360 eV/D for D₂ at a specific fluency of 2.85 × 10²⁰ m⁻² s. Morphology is strongly influenced by layer composition and by the ion acceleration voltage applied in-situ during layer deposition. Crystalline structure analysis shows the presence of a polycrystalline W metallic phase and also highlights a dependence between tungsten crystallite size and Be/W atomic ratio. The amount of deuterium in mixed layers is lower than in pure beryllium layers indicating that W is mitigating D binding states. Results extrapolated for a ‘cold chamber and divertor scenario’ indicate a limited desorption efficiency (∼20%), if the wall baking scenario, for tritium removal procedure in ITER, is to be applied to the investigated layers. (paper)

[en] Cleaning techniques for metallic first mirrors are needed in more than 20 optical diagnostic systems from ITER to avoid reflectivity losses. Plasma sputtering is considered as one of the most promising techniques to remove deposits coming from the main wall (mainly beryllium and tungsten). Previous plasma cleaning studies were conducted on mirrors contaminated with beryllium and tungsten where argon and/or helium were employed as process gas, demonstrating removal of contamination and recovery of optical properties. Still, both above-mentioned process gases have a non-negligible sputtering yield on mirrors. In this work, we explored the possibility to use a sputter gas having a small impact on mirrors while being efficient on Be deposits, e.g. deuterium. Two sputtering regimes were studied, on laboratory deposits as well as on mirrors exposed in JET-ILW, namely physical sputtering (220 eV ion energy) and chemically assisted physical sputtering (60 eV ion energy) using capacitively coupled plasma with radio frequency. The removal of Be and mixed Be/W contaminants, as well as the recovery of reflectivity, was achieved when deuterium was employed at 220 eV while cleaning at 60 eV was only fully efficient on laboratory beryllium deposits. On mirrors exposed in JET-ILW, the situation is more complex due to the presence of tungsten in the contaminant film, leading to the formation of a tungsten enriched surface that is not easily sputtered, especially at 60 eV. (paper)