Boron layer preparation, characterization and hydrogen isotope permeability for fusion application

Due to the re-baseline of the fusion device ITER and the strategical decision to change from Be to W as first wall material, a boronization procedure has to be implemented into the wall conditioning phase. Since the functionality of boron layers in carbon free fusion devices is not understand in detail so far, this study aims to be a starting point of the investigation of boron layers for fusion applications. In the first step, pure boron coatings are prepared in a magnetron sputter deposition device on W and steel substrates. The homogeneity, crystal phase and composition is studied and it is proved that an amorphous, stable boron layer is obtained with this deposition procedure. No impurities, e.g. O, N, C, are detected and a deposition rate of 20 nm/h is reached. The coatings are temperature stable up to 1000 ∘ C . No oxidation of the boron layer is detected when exposed to air, but a uptake of humidity is possible. Therefore, the samples should be stored in vacuum after deposition. The hydrogen isotope permeability is studied and a low layer permeability, which is four orders of magnitude lower as steel is found. In the future, the investigation will be broadened to mixed boron layers, e.g. B:D and B:W, which are more alike as boron layers in fusion devices, and these mixed layers will be compared to the pure boron layers as a next step. • Pure B layers are prepared by magnetron sputter deposition on W and steel substrates. • The layers are analyzed regarding the composition and microstructure. • The layers are temperature stable up to 1000 °C and no boron oxide is detected. • The hydrogen isotope permeability of these B layer is measured and is four orders of magnitude lower compared to steel. • This study serves as a starting point for the investigation of mixed B layers, such as B:D, which are applied in fusion reactors for gettering impurities.