THE SPUTTERING YIELDS AND IMPURITY SPATIAL DISTRIBUTIONS AT THE BERYLLIUM BELT LIMITERS IN JET

The sputtering yields for deuterium on carbon and beryllium at the belt limiters in JET are determined with an OMA spectrometer and/or photomultiplier detectors with optical interference filters. The apparent sputter yield for carbon in the absence of oxygen varies from 4-10%, and for beryllium the yield varies from 6-30%. A CCD camera with optical interference filters has been used to record the 2-D spatial distributions of the BeI (825.4 nm) line radiation at the belt limiters. Clearly resolved individual tile images are observed, and the dependence of the toroidal and poloidal impurity distributions on plasma density and input power has been investigated. Transport of the Be neutrals has been modelled with the LIM impurity code over the plasma density range (0.35-2.50) X 10(19) m-3 for 3 MA ohmic discharges, and good agreement with the experimental data has been obtained.