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P: Fachverband Plasmaphysik

P 14: Plasma Wall Interaction II / HEPP III

P 14.4: Talk

Wednesday, March 30, 2022, 16:45–17:10, P-H12

Effects of thin surface oxide films on deuterium uptake and release from ion-damaged tungsten — •Kristof Kremer, Maximilian Brucker, Thomas Schwarz-Selinger, and Wolfgang Jacob — MPI for Plasma Physics, Garching, Germany

In a fusion reactor, the uptake of deuterium (D) and tritium fuel into the plasma-facing tungsten (W) components is a critical issue with respect to fuel loss and radioactive inventory. However, the possible influence of natural surface oxides on the D uptake in W is not fully understood yet.

Therefore, we investigated the D uptake into W through 33 to 55 nm thick oxide films in dependence of D fluence, D ion energy and sample temperature. To trace the D, we created a 2 micron thick layer of self-ion-damaged W underneath the oxide. It acts as a getter layer and traps any D that permeates the oxide film. We measured the depth-resolved concentration of D and oxygen with ion beam analysis and the surface modifications of the oxide film with scanning electron microscopy. To study D release through the oxide we filled the self-damaged layer with D prior to oxidation and measured the D release with thermal desorption spectroscopy.

We observed a strong influence of surface oxide films on D uptake and release. Uptake: The oxide films block D uptake into metallic W. We explain this by the different heat of solution of D in W oxide and metallic W. At high ion energies, however, D partly reduces the oxide film and enters the metallic W. Release: The oxide film delays the D release until it is chemically reduced under formation of heavy water.