Surface composition of the Be limiters and the stainless-steel torus wall after operation in UNITOR

The surfaces of two Be limiters and of a test sample from the stainless-steel torus wall used in UNITOR were analyzed by RBS, PIXE, AES, and SEM/EIXE. The main foreign atoms found on the limiters are 0 (2x1017 to 2x1018/cm2), Fe, Ni, Cr and Sn (2x1015 to 2x1016/cm2). There are no large differences in the foreign atom coverage on the different surface areas of the limiters. Generally, the front surfaces of the limiters show slightly lower coverage than the sides. On limiter 2, the Sn coverage is about a factor of 4 larger than on limiter 1, indicating that the Sn source was close to this limiter. The stainless-steel test sample from the torus wall shows islands of BeO, which can be attributed to splashes or droplets eroded from the limiters during disruptions. Major erosion of the limiters occurrd only during the first 100 shots, when many discharges were terminated by disruptions. Redeposited wall material is found on the wall sample which partly covers the BeO deposits. The surface modifications of limiters and wall samples were discussed by taking into account the particle fluxes from and to the walls and limiters. (orig.)