Formation of carbon containing layers on tungsten test limiters

Tungsten test limiters of mushroom shape and a plasma facing area of approximately 100 cm(2) were exposed at the TEXTOR-94 tokamak to a number of deuterium fuelled discharges performed under various operation conditions. Two types of limiters were tested: a sole tungsten limiter and a twin limiter consisting of two halves, one made of tungsten and another of graphite. The exposed surfaces were examined with ion beam analysis methods and laser profilometry. The formation of some deposition zones was observed near the edges of the limiters. The deuterium-to-carbon concentration ratio was in the range from 0.04 to 0.11 and around 0.2 for the sole tungsten and the twin limiter, respectively. Significant amounts of the co-deposited tungsten and silicon atoms were found on the graphite part of the twin limiter indicating the formation of mixed W-C-Si compounds.