Further insight into the mechanism of hydrocarbon layer formation below the divertor of ASDEX Upgrade

M Mayer, V Rohde, the ASDEX Upgrade Team
2006 Nuclear Fusion  
The surface loss probability of hydrocarbon radicals was measured below the roof baffle of the ASDEX Upgrade divertor using the cavity technique. Hydrocarbon layers are mainly formed by sticking of hydrocarbon radicals with high surface loss probabilities of about 0.2 and close to unity. In addition to sticking re-erosion by atomic hydrogen plays an important role in layer formation. The temperature dependence of layer formation was measured with heated and cooled long term samples from 77 K to
more » ... amples from 77 K to 475 K. The layer growth rate is larger by a factor of about 40 at 77 K compared to room temperature, while it is lower by a factor of about 70 at 475 K than at room temperature due to enhanced re-erosion. Implications of the results for predictions of tritium retention in future fusion devices and hydrocarbon layer formation on mirror surfaces are discussed.
doi:10.1088/0029-5515/46/11/005 fatcat:xtpec7qnqbgbphbhjbudgfdj5a