“…In the latter situation, the system gains more than 6 eV, showing the great repulsion established between the He and the metallic atoms in the bulk as suggested before [33]. Wang et al [39] show the formation energy for He with respect to the position in the W-cell and the depth at which this cell is located. In the plane just below the surface, the He atom is not stable and so they have only shown an unrelaxed value of the energy.…”
A rst principles analysis of the behaviour of point defects, namely, selfinterstitial atoms, a single vacancy and light impurity atoms such as H and He in tungsten is reported. These defects can be produced in the rst wall of the future nuclear fusion reactors due to the high radiation uxes present. The evolution of defects that appear in the bulk and end up reaching the surface has been followed. An energetic study has been combined with a detailed charge density analysis of the system by means of the SIESTA code. The resulting data have been validated by confronting them with those obtained with a more precise plane wave code, namely VASP. Meanwhile, the structural and the mechanical properties of the system have been positively compared with experimental measurements. Such comparisons have led us to present a new SIESTA basis for tungsten. This complete analysis establishes a nanoscopic view of the phenomena involving the presence of light atoms at native defects in tungsten, paying special attention to the vicinity of surfaces.
“…In the latter situation, the system gains more than 6 eV, showing the great repulsion established between the He and the metallic atoms in the bulk as suggested before [33]. Wang et al [39] show the formation energy for He with respect to the position in the W-cell and the depth at which this cell is located. In the plane just below the surface, the He atom is not stable and so they have only shown an unrelaxed value of the energy.…”
A rst principles analysis of the behaviour of point defects, namely, selfinterstitial atoms, a single vacancy and light impurity atoms such as H and He in tungsten is reported. These defects can be produced in the rst wall of the future nuclear fusion reactors due to the high radiation uxes present. The evolution of defects that appear in the bulk and end up reaching the surface has been followed. An energetic study has been combined with a detailed charge density analysis of the system by means of the SIESTA code. The resulting data have been validated by confronting them with those obtained with a more precise plane wave code, namely VASP. Meanwhile, the structural and the mechanical properties of the system have been positively compared with experimental measurements. Such comparisons have led us to present a new SIESTA basis for tungsten. This complete analysis establishes a nanoscopic view of the phenomena involving the presence of light atoms at native defects in tungsten, paying special attention to the vicinity of surfaces.
“…12), which is consistent with the results reported in Refs. [48][49][50] using other simulation methods. Thus, the nanochannels not only shorten the diffusion distance of He atoms, but also promote the accumulation of He atoms at the nanochannel surfaces.…”
Tungsten (W) as plasma facing material (PFM) needs to face an unprecedented harsh environment in the fusion reactor, which puts forward high requirements for its radiation tolerance. Among the many challenges, the rapid accumulation of helium (He) atoms to form numerous bubbles or even "fuzzy" nanostructure leads to swelling and embrittlement of W matrix and seriously shorten its service life, which is one of the most serious problems faced by PFM-W at present. In this review, we summarize the recent works on the nanochannel W films with high surface-to-volume ratio deposited by magnetron sputtering, and the behaviors of He in the nanochannel W films at different fusion-related irradiation environment. Experimental and simulation results showed that the nanochannel W films have better radiation tolerance performance in managing He behaviors than that of commercial bulk W.
“…According to previous Refs. [7,8], vacancies in tungsten will play a role of trapper for helium ions because the high binding energy with helium ions. Nucleation will prefer to happen in vacancies then bubbles will be formed.…”
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