First principle calculations of energy of agglomerated helium in the period 6 elements

Omori, K.; Itô, Akira; Mun, I.; Yamashita, N.; Ibano, Kenzo; Lee, H.T.; Ueda, Y.

doi:10.1016/j.nme.2018.07.003

Cited by 6 publications

(4 citation statements)

References 24 publications

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“…Therefore, from the perspective of atomic structure, the aggregation of He atoms in the adjacent tetrahedral sites can be converted into aggregation in the vacancy as the number of He atoms in the tetrahedral sites increases. Similar phenomena have also been observed from DFT calculations [66]. Undoubtedly, by further adding He atoms close to the He cluster, some of the newly added He atoms can gather at the new vacancy created above.…”

Section: Resultssupporting

confidence: 82%

Microscopic mechanism of nucleation and growth of helium bubbles in monovacancy in tungsten: helium regulates the charged states of tungsten atoms

Wang

Pan

2023

Nucl. Fusion

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In fusion reactor, tungsten (W) has been selected as a candidate for plasma-facing materials (PFMs) due to its excellent properties. However, W-PFMs suffer from helium (He) bubbles where He atoms are produced during deuterium tritium fusion in fusion reactors. To date, there have been few contributions to uncovering the formation of He bubbles from the perspective of the microscopic electronic structure of He-mediated tungsten. In this work, we develop a tight-binding potential model for the W-He interaction to study He atom aggregation and nucleation in the electronic ground state as well as in different electronic excited states. The most important finding of this paper is that caused by the He atoms in the vacancy, some d-orbital electrons of the W atoms at the inner wall of the vacancy are transferred to the W atoms farther away from the vacancy, leading to the feature of positively charged W ions at the inner wall of the vacancy. As the number of He atoms in the vacancy increases, these W ions become more cationic. Under the repulsion between these adjacent cationic ions, the volume of vacancies increases, and more He atoms tend to gather and nucleate there. At the same time, the enhancement of the electronic excitation can also promote the abovementioned electron transfer between W atoms and further increase the vacancy volume, which increases the self-aggregation of the He atoms in the vacancy. Our results shed new light on understanding He self-aggregation in many different metal materials.

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Section: Resultssupporting

confidence: 82%

Microscopic mechanism of nucleation and growth of helium bubbles in monovacancy in tungsten: helium regulates the charged states of tungsten atoms

Wang

Pan

2023

Nucl. Fusion

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“…Therefore, normal stresses near the He bubbles in the material could become higher. This difference was clearly seen by DFT calculation on Hevacancy interaction [588,589]. The formation mechanism of nano-fibers has been studied using several simulation techniques such as DFT for interatomic potential calculations, MD (Molecular Dynamics) for the dynamics of He atoms and defects, and KMC (Kinetic Monte Carlo) for He bubble dynamics [316,586,[590][591][592].…”

Section: Surface Modification Of Tungsten By High Flux He Irradiationmentioning

confidence: 99%

Behavior of tungsten under irradiation and plasma interaction

Rieth

Doerner

Hasegawa

et al. 2019

Journal of Nuclear Materials

151

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“…While He diffusion and coalescence plays an important role in bubble growth, it cannot explain the larger bubble diameters observed for increasing Mo concentration. The He atom diffusivity is ∼2.5x higher in Mo than W at these temperatures [51], but the binding energies for He clusters and He-vacancy complexes is larger in W than Mo [51][52][53][54][55] (indicating that He more easily agglomerates in W than Mo with or without a vacancy). Furthermore, niobium forms fuzz with larger fiber diameters (and hence likely larger bubbles) than Mo [53] despite larger He atom diffusivity [51,56,57] and larger He cluster binding energy in Mo [52,53]; the larger fiber diameters in niobium can be explained by the lower shear modulus for niobium compared to Mo [58,59].…”

Section: Film Thickness Dependence (Mo Film On W)mentioning

confidence: 92%

Material migration in W and Mo during bubble growth and fuzz formation

Patino¹,

Nishijima²,

Tokitani³

et al. 2021

Nucl. Fusion

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Growth of helium (He) induced bubbles and fuzz in tungsten (W) and molybdenum (Mo) is investigated using samples of W films on Mo substrates and Mo films on W substrates exposed to He-containing plasma in the temperature range of 340 to 1075 K, fluence range of 1.0–14 × 1025 He·m−2, and incident ion energy of <50 eV. No fuzz (only up to 2 nm diameter bubbles) and no material transport occur in W films at ⩽750 K, while precursors-of or fully-developed fuzz and material mixing occur in W and Mo films at ⩾800 K. This suggests that fuzz forms in multi-material systems as long as one material meets the conditions for fuzz formation, namely T s/T m ∼ 0.27–0.5 where T s and T m are the sample exposure and material melting temperatures, respectively. Larger He bubbles, more material mixing, and further-developed fuzz occur at higher temperature due to increased mobility of He atoms and small He clusters. Accumulation of substrate material at the surface of fuzzy W and Mo thin-film (<80 nm) samples suggests fuzz growth by material transport from the bubble layer in the bulk up to the fiber tip, likely by a two-step process: (i) diffusion of punched dislocation loops in the bulk toward the fuzz base and (ii) diffusion of adatoms along the fuzz base and fiber surface (with effective transport of adatoms upwards due to trapping of adatoms at curved surfaces of fiber tips and/or due to the continuous generation of adatoms at the fuzz base). While the bubble size and fuzz thickness increase with reduced W concentration in Mo thin-film samples at 838 K likely due to an increase in trap mutation and dislocation loop punching in Mo compared to W, the fuzz thickness decreases with reduced W concentration at 1075 K despite an increase in the bubble size likely due to slower diffusion of interstitial loops in Mo.

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First principle calculations of energy of agglomerated helium in the period 6 elements

Cited by 6 publications

References 24 publications

Microscopic mechanism of nucleation and growth of helium bubbles in monovacancy in tungsten: helium regulates the charged states of tungsten atoms

Microscopic mechanism of nucleation and growth of helium bubbles in monovacancy in tungsten: helium regulates the charged states of tungsten atoms

Behavior of tungsten under irradiation and plasma interaction

Material migration in W and Mo during bubble growth and fuzz formation

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