Deuterium plasma effects on porous boron and boron-tungsten layers in the GyM linear device

Boron (B) films play a key role in various technological applications due to their unique chemical, physical, and nuclear properties. In magnetic confinement nuclear fusion, thin boron layers are applied to tokamak plasma-facing components to control the concentration of low-Z impurities, such as water and oxygen, thereby mitigating radiative losses and improving plasma performance. This work investigates micrometre-thick porous B and boron–tungsten (B-W) layers exposed to deuterium plasma under ITER tokamak first wall-relevant conditions. Model B coatings with 5%–50% of bulk density (ρBjavax.xml.bind.JAXBElement@2872df8) and B-W coatings containing ≈5 at.% W were produced using femtosecond pulsed-laser deposition. Plasma exposures were performed in the linear device GyM to study layer erosion, morphological evolution, and W enrichment. Scanning electron microscopy reveals that B films with 30%–50% of ρBjavax.xml.bind.JAXBElement@7b76e819 evolved from nanoparticle-aggregates to cone-like structures, attributed to molybdenum deposition from the sample holder and the formation of sputter-resistant localised phases of B, oxygen, carbon, and deuterium. Nanocones did not develop in B films with 5% of ρBjavax.xml.bind.JAXBElement@6dd599e7, as their highly porous, tree-like structure prevented the formation of regions with a low erosion rate. Mass loss measurements indicated that boron erosion is consistent with physical sputtering at ion energies >70 eV, while enhanced erosion at lower values is likely driven by ion-assisted chemical processes at the exposure temperature of 550 K. In B-W layers, preferential B sputtering led to W enrichment, with W reaching up to 10 at.% according to energy-dispersive X-ray spectroscopy.