Accumulation of Deuterium and Helium in Co-Deposited W Layers Formed in He-Seeded Deuterium Plasma

The effect He in plasma has on the co-deposition of D–W films is investigated for the room–800 K range of substrate temperatures and two He/D 2 ratios of 5 and 20%. He can both raise and lower the content of D in a film, and a mechanism is proposed for this effect. The ratio of He/D in the film is higher than in gas, due to the stronger diffusivity and bonding energy of He. A similarity is observed between the dependences of D and He content on temperature, and it is suggested that the low temperature release of D and He during TDS could be due to annealing-induced relaxation of stresses in the film structure. It is expected that the desorption of He above 1300 K could lead to underestimates of the He content.