Testing of molybdenum film mirrors under bombardment by deuterium plasma ions

Results are presented on the behaviour of molybdenum coatings on substrates from TZM alloy and single-crystal molybdenum when bombarded by deuterium plasma ions with a wide energy distribution. Blisters were found to appear in the near-surface layer of the substrate in the case of TZM alloy and on the film–substrate interface in the case of single-crystal molybdenum. By improving the vacuum conditions during film deposition, we managed to suppress the blistering process and to produce films which are able to retain their optical properties for the whole time of operation of the International Thermonuclear Experimental Reactor, provided that the flux of charge exchange atoms to their surface is weakened by not less than an order of magnitude in comparison with the flux to the first wall.