Performance of tungsten coatings as plasma facing components used in ASDEXUpgrade

Tungsten coated graphite tiles were mounted in the divertor of the ASDEX Up grade tokamak and exposed to approximately 800 plasma discharges with varyi ng average heat fluxes of up to 6 MW/m(2). After the experimental campaign, cracks were detected on almost all tiles in accordance with results of ele ctron beam tests. The W-coated tiles in the inner divertor were found to be covered by deposited layers of low-Z material with thicknesses in the mu m range and only a few percent tungsten remaining on the surface. In contras t the outer divertor is dominated by erosion. Here, the tungsten concentrat ion at the surface was found to be close to the initial level. The global W -migration pattern was determined by analyzing the deposition of tungsten o n a complete poloidal set of plasma facing wall components. Both divertor r egions display broad deposition peaks with deposited layers at least one or der of magnitude thicker than the main chamber values. (C) 1998 Elsevier Sc ience B.V. All rights reserved.