Tungsten redistribution patterns in ASDEX Upgrade

In ASDEX Upgrade tungsten is used as a high-Z plasma facing material. Its erosion, migration and subsequent deposition have been studied by analysis of a set of customised marker tiles, which was installed in the divertor and at the central column for one experimental campaign. Erosion rates were determined at the central column, which was the main tungsten source in that campaign. Deposition rates were determined at the central column and in the divertor region. The W-deposition in the divertor is strongly correlated to the local strike point exposure time. In contrast to low-Z wall materials, where deposition occurs mainly in the inner divertor, tungsten is found in similar quantities also in the outer divertor. The total amount of tungsten deposited outside the central column is about 40% of the gross W-source at the central column. One possible explanation for the 60% undetected tungsten might be the prompt local redeposition of eroded W atoms.