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Interaction of Beryllium Oxide with Hydrogen Plasma

Proceedings article published in 2007 by C. Tomastik, W. S. M. Werner, H. Störi
This paper is available in a repository.
This paper is available in a repository.

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Abstract

Beryllium is considered a candidate material for the first wall of nuclear fusion plasma devices. For this application, the interaction of beryllium oxide with a D/T plasma is important with respect to beryllium as oxygen getter. Since it is not yet fully clear if and how much oxide will develop during operation, we investigated the interaction of beryllium samples with hydrogen plasma. Oxide layer thicknesses were measured by sputter depth profiling, using a high resolution Auger electron microscope. Exposure of beryllium samples with native oxide layers and pre-oxidized samples to hydrogen plasma resulted in oxide layers of similar thickness, suggesting the development of an equilibrium state during exposure. In order to determine the relation between equilibrium oxide layer thickness and oxygen concentration in the plasma, the samples were exposed to hydrogen plasma with various additions of water vapour. The experiments so far suggest that higher water vapour concentration results in a higher oxide layer thickness, as would be expected, and that oxide layer formation takes place down to a water vapour fraction in hydrogen of at least 3·10 -6 . Water vapour fractions above 10 -2 seem to lead to erosion of the samples. An operation of beryllium liners as a non-evaporable getter is therefore not to be expected. Getter activity linked to the transport of beryllium from the liner to some deposition areas is however possible.