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P: Plasmaphysik

P 1: Plasma Wall Interaction

P 1.1: Vortrag

Montag, 17. März 2003, 15:45–16:05, FO1

Erosion and redeposition of tungsten in the tokamak ASDEX Upgrade — •K. Krieger, A. Geier, H. Maier, R. Neu, R. Pugno, V. Rohde, and ASDEX Upgrade Team — Max-Planck-Institut für Plasmaphysik, EURATOM Association, Boltzmannstr. 2, D-85748 Garching

In the tokamak experiment ASDEX Upgrade, tungsten coated wall components are used in the plasma main chamber as an alternative to carbon based materials. Incident plasma particles lead to continous erosion of plasma facing surfaces. Respective tungsten erosion rates at the inner wall of the plasma main chamber were determined spectroscopically. It turned out that W erosion occurs mainly during discharge phases with direct plasma contact to the wall. The spatial distribution of the W erosion, integrated over a full experimental campaign, was determined by measuring the change of the thickness of W layers using ion beam methods. The resulting distribution can be explained by the local magnetic field line geometry, which shows that the erosion is, as already suggested by the spectroscopic results, mainly due to impact of ions.

From the amount and the spatial distribution of redeposited W atoms, which were determined by ion beam analysis of wall components removed after an experimental campaign, one can obtain informations on the respective transport channels. It turned out that only approximately 10% of the eroded W atoms end up in the divertor particle exhaust region. In agreement with transport simulations one can infer that eroded W atoms are mainly redeposited locally, which leads to a significant reduction of the tungsten net erosion rate.