Graphite-tungsten twin limiters in studies of material mixing processes onhigh heat flux components

Graphite-tungsten twin limiters have been used at the TEXTOR tokamak for te sting of high-Z metals as plasma facing materials and, in particular, for s tudies of the local and global transport of tungsten. The emphasis was on t he change in surface morphology of limiters: the formation and properties o f multicomponent co-deposits and the trapping characteristics of fuel on ca rbon and high-Z substrates exposed to the plasma under various operation co nditions, i.e., heating scenarios, configuration of limiters, etc. Vast qua ntities of tungsten have been found to be locally transported to the adjace nt graphite surfaces. Ion beam analysis also indicated strong intermixing o f carbon, tungsten and boron on the hottest parts of the limiters. The resu lts are discussed in terms of various mechanisms involving the transport of tungsten-containing species, possibilities of oxide production and formati on of mixed (W-C-B) compounds. (C) 2000 Elsevier Science B.V. All rights re served.