B:D layer preparation, characterization and hydrogen isotope permeability for fusion application

With the change of the first wall material from Be to W in the fusion device ITER, which was decided in 2024, a boronization procedure has to be implemented in the wall conditioning phase. These thin boron coatings, applied by glow discharge boronization, are necessary for gettering impurities, especially O, in order to ensure a reliable start-up phase and an efficient plasma operation. In order to study the influence of the boron coatings on the hydrogen retention and permeation, well-defined laboratory B and mixed B coatings are produced by magnetron sputter deposition and characterized. In the first step, pure boron coatings were prepared with an Ar plasma and a pure B target on W and steel substrates and investigated. As a second step, B:D coatings are prepared with the same technic using D 2 gas for co-deposition. With this technique, a deposition rate of around 32 nm/h is reached and thin (160 nm) and thick layers (320 nm) on W and steel are produced. The Ar to D 2 gas ratio is varied and the D/B ratio is around 10%, which is obtained by ion beam analysis. Furthermore, in order to study the D binding in B, thermal desorption spectroscopy is used and it is shown that the D release starts around 220 ∘ C , reaches the maximum at around 370 ∘ C and is linearly decreasing until 830 ∘ C . Further characterizations show, that the coatings are homogeneous and temperature stable up to 1000 ∘ C on a W substrate. No oxidation of the boron layer is detected when exposed to air, but an uptake of humidity is very likely. The hydrogen isotope permeability is studied and compared to a non-coated steel substrate. No measurable influence on the permeation flux is observed. Due to this finding the conclusion is, that a B:D layer does not have any influence on the hydrogen isotope permeation behaviour of first wall materials.