Exposure of stainless steel mirrors in T-10 tokamak

Stainless steel (SS) mirrors were exposed in the upper port of T-10 in front of the graphite limiter during the experimental campaign. Three mirrors were located at different distances from the plasma (22 cm, 45 cm, 66 cm), and three more were placed at 22 cm from the plasma inside a box that was opened at working discharges only. Deposits were found on all the mirrors as a result of the exposure. The deposited films not only reduced the intensity of the reflected radiation, but also strongly changed its spectra. The deposits had a layered structure and consisted of complex CnDm compounds with a D/C ratio of about 0.3. The film thickness was about 12 µm on the mirror located without protection 22 cm from the plasma – that is, about 100 times larger than that on the samples placed inside the box. The deposition rate for the protected mirrors was about 0.2 nm/s. The ablation of deposits under pulsed excimer laser radiation was demonstrated by a complete recovery of the initial reflectance of the mirrors.