SURFACE-LAYER COMPOSITION OF THE JET VESSEL WALLS

After the 1990/91 discharge period several samples have been cut from the JET vessel walls, the carbon and the beryllium limiters, and the carbon and the beryllium X-point divertor tiles. The surface layers of these samples have been analysed in detail by ion beam techniques, such as PIXE, HIERDA, RBS, SIMS and Sputter-Auger for the absolute amounts as well as for the depth distributions of the different deposits. The major deposits are H, D, Be, C and O, as well as other impurities, such as Ni, Cr, Fe, and C. From the measurements on the carbon samples it was found that the oxygen deposits correlate with the Be deposits, while the measurements on the Be samples show that the C deposits correlate with the D deposits, indicating a codeposition of these elements. In addition H concentrations mostly larger than the D concentrations are measured. These may partly originate also from adsorption during the exposure to air.