Speaker
Description
Due to the change of first wall material in ITER from Be to W, a glow discharge boronization (GDB) system is included in the re-baseline in order to guarantee efficient plasma operation (https://doi.org/10.1016/j.nme.2024.101854). Even though the GDB is used in many fusion devices for decades, its conditioning effect and possibility for recovering fuel from the B layers was not studied in detail so far. Furthermore, ITER is expected to have a lower carbon inventory compared to the majority of today’s fusion devices. The presences of C has an influence on the B layer characteristics, which might change the boronization mechanism as well.
The study focuses on plasma exposure conditions relevant to Ion Cyclotron (IC) Wall Conditioning and Glow Discharge (GD) Conditioning in ITER. With this study, the efficacy of these tritium removal techniques for ITER can be assessed and further insight into the boronization mechanism will be gained.
W substrates are coated with B:D layers (160-320 nm) by magnetron sputter deposition. Two kind of samples with different D content (D/B ratio between 0.1 and 0.2) are produced and pre-characterized (e.g. microstructure, composition, morphology and crystal phase). For the study of isotope exchange, samples are exposed to different hydrogen plasmas at the toroidal plasma device TOMAS and the linear plasma device PSI-2 at different sample temperatures. The hydrogen isotope content is measured before and after exposure by thermal desorption spectroscopy and nuclear reaction analysis.
The deuterium content in the layer of a GD plasma exposed sample is significantly reduced by about 35% compared to a non-exposed sample. In opposite to this observation, a first IC plasma exposure of a B:D layer results in a much smaller reduction of the D content in the layer. Further exposures with different plasma conditions are performed and the analysis will show, if it is possible to efficiently clean the B:D layers by isotope exchange and which plasma condition is suitable for the tritium removal.