Effects in CVD diamond exposed to fusion plasmas

Micro and nanocrystalline diamond layers have been deposited on molybdenum substrates by hot‐filament CVD, and tested in the Mega Amp Spherical Tokamak as a protective coating of fusion plasma‐facing materials. The modification of surface properties induced by high density plasma was investigated by SEM, X‐ray photoelectron spectroscopy and Raman spectroscopy. Although some modifications of the coating, amorphization and some traces of arcing, diamond proved to be a viable protection as most of the samples were still coated after the plasma exposure. Fuel retention measurements, evaluated by nuclear reaction analysis, showed that a small amount of deuterium was trapped in the surface of the coatings. The chemical erosion of the layers was 50% lower than graphite, as evaluated by dedicated experiments in Pilot‐PSI, a linear plasma simulator device.