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P: Plasmaphysik

P 12: Plasma Wall Interaction, Diagnostic and Low Temperature Discharges (Poster Session)

P 12.2: Poster

Freitag, 6. April 2001, 12:30–15:00, AT2

Tungsten erosion and deposition of plasma-facing surfaces at the central column of ASDEX Upgrade — •Wolfgang Schneider¹, Dieter Hildebrandt¹, Rudolf Neu², Volker Rohde², and ASDEX Upgrade team² — ¹Max-Planck-Institut für Plasmaphysik, Euratom Association, D 10117 Berlin, Germany — ²Max-Planck-Institut für Plasmaphysik, Euratom Association, D 85478 Garching, Germany

Carbon erosion and the subsequent deposition of thick gas-containing carbon layers as a consequence of plasma transport is considered as a serious problem in fusion devices with long pulse operation.

In the tokamak ASDEX Upgrade about 10 % of the graphite tiles of the inner heat shield were covered with a 400 nm thick tungsten layer in order to reduce the removal and migration of carbon. After 6 months of operation the surfaces of these tungsten-covered graphite tiles as well as other divertor tiles were investigated by Auger Electron Spectrometry and Secondary Ion Mass Spectroscopy. The plasma impact caused a modification of the original tungsten surface by erosion and deposition phenomena. The local distribution of the erosion and deposition dominated areas indicates that the erosion of the tungsten layer is mainly caused by plasma ions. The eroded tungsten is found on the entrance plate of the inner divertor indicating direct transport of tungsten via the scrape-off plasma. No effect on plasma performance caused by tungsten was observed. In particular no impurity contamination of the main plasma was found.