Ab initio study of the stability of H-He clusters at lattice defects in tungsten

The interaction of a H-He pair embedded in various types of lattice defects in the bcc tungsten, such as vacancies, tilt grain boundaries, a core of screw and edge dislocations has been studied using ab initio calculations. It is shown that H-vacancy and He-vacancy clusters are weaker traps for He and H single atoms, respectively, as compared to a single vacancy. H or He atom, solely, is strongly attracted to the studied grain boundary interfaces, while the mutual H-He interaction is negligible (close to the interaction in vacuum) if both atoms are placed in the adjacent trapping sites located on the grain boundary. The H-He pair placed in the core of the screw or edge dislocation exhibits the binding energy of ~0.2–0.3 eV, which is close to the H-He attraction in the bulk W. The ground-state configurations for H-He dimers located in various lattice defects in W were rationalized on the basis of atomic structure visualizations, bond analysis and charge density distributions. The obtained data are discussed in the frame of the thermal desorption spectroscopy results offering a better understanding of the detrapping stages of He and H isotopes under mixed plasma exposure conditions.