The structure of the plasma boundary and its influence on impurity release in the limiter tokamak textor

The edge parameters and the corresponding particle fluxes and impurity-sources have been studied for two different cases: the limiter and wall material comprise a) only metals and b) only carbon. Radial density profiles in the plasma boundary are measured at different locations along the plasma flow directed towards the limiter. Large toroidal variations of the scrape-off layer thickness by factors 3-5 are discussed using a simple model. It is shown that with increasing edge cooling by radiation due to enhanced C-contamination a strongly contracted, but thermally stable plasma column is formed. The release of the wall/limiter-materials carbon and metal is studied. The importance of the residual oxygen-contamination, the influence of edge-temperatures on metal sputtering, the formation of molecular states and the relation between ion-fluxes and low-Z impurities is discussed