Hydrogen permeability of beryllium films prepared by the thermionic vacuum arc method

Beryllium films will be applied in fusion reactors as the first wall tile coating in the near future. The morphology, adhesion and thermal stability of these thin films deposited by the thermionic vacuum arc (TVA) method have been confirmed to be compatible with extremely high demands. Actual Be films used in the future plasma experiments may contain voids or channels causing unwanted porosity which may change the tritium interaction kinetics with the tiles. Permeation through such films is thus the only method to verify film integrity and its capability for hydrogen isotopes migration. In this paper, we present results of hydrogen permeation through 8 μm thick Be films deposited by the TVA method on Eurofer membranes having the geometric area exposed to hydrogen of 8.4 cm2. The permeation flux was determined on five samples at 400 °C and 1 bar hydrogen pressure. It varied from 5.1 × 1012 to 3.1 × 1013 H2/(cm2 s) which means that the permeation reduction factor (PRF) was between 83 and 15, respectively, compared to the uncoated Eurofer membrane. Permeability of Be is reconstructed from these data and compared to published data for bulk Be. The reason for data scatter in our experiments and for even greater scatter of published data is discussed.