Spectroscopic studies of plasma-wall interaction and impurity behaviour in tokamaks

The impurity contamination of tokamak plasmas is determined by the impurity influxes from surrounding surfaces, and by the impurity confinement in the plasma, both in relation to the respective hydrogen behaviour. Models and measurements of impurity confinement times are presented. The influx behaviour of oxygen, carbon and metals in JET, both during OH and additional heating, is described and implications for the plasma contamination are discussed. The processes of impurity production are well explained in the case of metals in JET and other tokamaks, questions are still unanswered for light impurities, in particular concerning the chemical processes and molecular compounds. Migration, deposition and erosion of chromium in JET has been observed and analysed. In many cases, a consistent picture of impurity production, shielding and impurity densities in the plasma has emerged. (orig.)