Diamond coatings exposure to fusion-relevant plasma conditions

Several types of diamond layers have been deposited on molybdenum tiles by chemical vapour deposition techniques, and exposed under erosion-dominated conditions in the SOL of TEXTOR in order to assess them as a suitable candidate for plasma-facing material. Post-exposure characterisation of physical properties and surface modification induced by the plasma was performed by SEM imaging, investigation of diamond surface by micro-Raman spectroscopy and deuterium retention measurements by NRA. The analyses evidenced that lightly boron-doped micro-crystalline diamond is performing better than undoped and heavily doped samples, and nano-crystalline diamond and diamond-like carbon, as it showed lower surface modification, lower presence of arcing traces at the surface and lower deuterium retention. High concentration of boron in the layers led to higher retention of deuterium, whereas undoped (insulating) diamond showed increased arcing activity. Nano-crystalline diamond and diamond-like carbon layers generally showed poorer mechanical properties.