Helium-vacancy interaction in tungsten

First temperature stage evolution of irradiation-induced defects in tungsten studied by positron annihilation spectroscopy

“…What appears less clear are the temperature boundaries of these stages, especially those of step one, which concerns the monovacancy migration. Indeed, despite that the energy [8][9][10][11] and temperature [6,7,12] migration of the monovacancy in tungsten have been the scope of many studies, there is not actually an agreement on these values; for example, the monovacancy temperature migration is found to vary from 553 K to 873 K. This value must be specified since it is a fundamental and basic data necessary for a complete understanding of the vacancy like defects creation and evolution in temperature. Consequently, the present paper deals with the determination of the monovacancy migration temperature in tungsten; the resultant defects evolution is also examined.…”

“…The study by PAS of defects created in tungsten, either by ion implantation or irradiation, has already been the scope of several research works [2][3][4][5]; besides, the defects evolution upon subsequent thermal treatment has also been investigated [2,4,6,7]. From the obtained results, the following four steps scheme can be drawn: (i) stage zero (0), from room temperature (RT) to $573 K: a possible dissociation of small vacancy-impurity (V-Im) complexes can arise, leading to an increase of the concentration of small vacancies, principally monovacancies; (ii) stage one (I), from $573 K to $773 K: monovacancies migrate through the crystal lattice and either agglomerate with other vacancy like defects to form larger defects or annihilate at defects sinks such as grain boundaries; (iii) stage two (II), from $773 K to $1723 K: this stage is equivalent to stage one but for larger vacancy like clusters, which can migrate and annihilate at defects sinks or agglomerate to form small cavities; (iv) stage three (III), from $1723 K to $2773 K (the usual $0.7 T f reference for complete recovery): anneal out of most of the vacancy like defects (large clusters and cavities).…”

Ab initio simulations of the structure, energetics and mobility of radiation-induced point defects in bcc Nb

“…On the second case, for high enough temperatures the vacancies will be able to move and join other n-vacancies to create larger vacancy clusters. A final mechanism is the trap mutation process [43] produced when the accumulation of He atoms inside a monovacancy (or more generally an n-vacancy) displaces a metallic atom from its position creating a dumbbell 〈111〉 that easily migrates to a surface or interface. Our calculations support the second mechanism due to the relatively low migration energy of the vacancies (see Section 3.3.3).…”

Accommodation of prompt alpha-particle loss in a compact stellarator power plant

“…As interstitials, they are very mobile, but they will be trapped at lattice vacancies, impurities, and vacancy-impurity complexes. The following activation energies are associated with the different He processes in tungsten [10]: …”