Damage to N-NBI systems due to positive ion back-streaming

Sputtering yields of molybdenum (Mo) are computed for deuterium, oxygen and carbon as impurity ions from the residual gas vacuum system, well Mo Cs using Yamamura formula. The incident ion energy ranges 10 keV to 1 MeV, back-streaming beam extraction voltage up ITER full acceleration potential. sputtering yield against reached ten atoms per was largest among investigated species. effect due retention deuterons in studied case grazing angle incidence D+ at D- confirm small onto yield; result obtained 10% D increased only by 2%. MeV should make a layer high concentration deuterium 6 µm depth surface. Possible failure mode associated with particle implantation is discussed.