DESORPTION OF TID2 FILMS FORMED DURING SIMULATED TOKAMAK GETTERING CYCLES

The desorptions of titanium deutero-tritide films formed during TFTR (Tokamak Fusion Test Reactor) operation were simulated by the decompositions of essentially clean titanium deuteride films at 523K. A simulated desorption cycle consisted of the deposition of a 0.09 μm film followed by deuteriding and isothermal desorption. This thickness film would correspond to that anticipated after ~30 discharge/gettering cycles in TFTR. Two series of experiments were run: In one, the deposition/desorption cycle was repeated four times with fully deuterided films, resulting in the formation and desorption of films between 0.09 μm to 0.36 μm thick. In the second series, partially deuterided films between 0.09 μm to Q.72 μm thick were deposited and desorbed. All the observed data were in agreement with a simple model which predicted the desorption rates to be determined solely by the average film D Ti ratios: These results showed that rapid decomposition occurred between D Ti ratios of 2→1.5 followed by a constant, lower desorption rate between D Ti ratios of 1.5 to 0.1. This rate, which was independent of film thickness, was ~2.2 × 1012D2 molecules mm-2 s-1. At D Ti ratios <.1, the rate decreased to near zero at D Ti ~0. The data indicate that desorption of essentially clean, radiation damage-free films as thick as 1.2 μm could occur in ≲4 × 104s at 523K. © 1979.