Investigation of erosion and deposition on wall components of TEXTOR-94

The paper describes in the first part the formation of carbon flakes up to 10-20 mu m thickness (average growth rate 2 nm/s) on the graphite tiles of the toroidal belt limiter. This occurred as a consequence of a slight chang e of the geometry and turned parts of the surface area from net erosion int o net deposition zones. The possible influence of the morphology on this be haviour is discussed in the second part by means of an erosion experiment w here the gradual disappearance of a boron substrate could be discriminated from the simultaneous carbon deposition on the surface. The two counter-act ing processes co-exist within 10-30 mu m distance and lead to an extremely non-uniform carbon deposition even in net erosion zones. The carbon agglome ration coincides with surface imperfections, e.g. grooves, but agglomeratio n by temperature enhanced mobility is not excluded. The changeover from net deposition to net erosion averaged over larger distances can still be obse rved and is due to the hydrogen and carbon fluxes in the SOL. This is confi rmed by Monte-Carlo code calculations.