A Molecular Dynamics Study of Subsurface Hydrogen-Helium Bubbles in Tungsten

Bergstrom, Z.J.; Cusentino, Mary Alice; Wirth, Brian D.

doi:10.13182/fst16-121

Cited by 39 publications

(13 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For annealing above the He irradiation temperature, small He bubbles diffuse and disappear in the first few nanometer layer below the surface leaving a pristine W decorated with larger He bubbles where D can diffuse and bind to the bubbles periphery, thus increasing the D retention. Indeed, DFT and MD studies [25,26,27] have shown that deuterium atoms bind around He-vacancy clusters complexes and ∼2 nm He bubbles with a large binding energy range of 0.8-2.0 eV consistent with our broad D desorption peak. Our interpretation is also consistent with the following observation: a higher He release for the LF sample but a higher D retention for the HF sample.…”

Section: Thermodesorption Analysissupporting

confidence: 83%

Hydrogen trapping in tungsten: impact of helium irradiation and thermal cycling

et al. 2020

View full text Add to dashboard Cite

The impact of helium (He) plasma exposure with He fluxes relevant for ITER and WEST on the near-surface microstructure of polycrystalline tungsten (W) is investigated by coupling transmission electron microscopy (TEM) analysis and thermal desorption spectrometry (TDS) measurements. The samples were exposed in the PSI-2 linear plasma device to 75 eV He ions up to the fluence of 3 × 10 23 He m −2 with the surface temperature in the range 1053-1073 K. The obtained He bubbles-enriched W samples are subsequently probed with sequences of low flux and low fluence 250 eV deuterium (D) ion implantations and TDS measurements in an ultra-high-vacuum setup to study the effects of the near-surface morphology changes due to the helium irradiation on fundamental mechanisms of deuterium retention. The results obtained for two different nearsurface layer He bubbles morphologies revealed that the effects of He irradiation on D retention in W strongly depend on its subsequent thermal cycling. For annealing below 900 K, deuterium retention is similar to the one measured in pristine W. In contrast, for annealing above 1150 K, deuterium retention in the He bubbles enriched W is increased 3 to 8-fold as compared to non-damaged W. Additionally, the deuterium desorption peak shifts from 540 to 450 K. This increase of D trapping in the He bubbles enriched W annealed above 1150 K is presumably associated with a modification of the near-surface microstructure concurrent with an outgassing of He.

show abstract

Section: Thermodesorption Analysissupporting

confidence: 83%

Hydrogen trapping in tungsten: impact of helium irradiation and thermal cycling

et al. 2020

View full text Add to dashboard Cite

show abstract

“…Recent modelling effort has looked at the influence of H on the formation of He bubbles, where experimental data has so far proved inconclusive (although it generally suggests that H plays a role) [360] . Atomistic simulations (MD and ab-initio) appear to be consistent with the idea that H is trapped within He bubbles [329][330][331] . Helium is strongly trapped at grain boundaries and can dramatically change material performance.…”

Section: Discussionsupporting

confidence: 70%

“…As well, there are numerous indications that atomic H that is trapped at the interface of high pressure He bubbles, as was identified in work on He implanted bcc Fe by Meyers and co-workers [327] and in the nickel base alloy X-750 irradiated in CANDU reactors with very large He production by Judge and coworkers [328] . The experimental assessments indicating the segregation and trapping of atomic H at high pressure He bubbles is consistent with atomic-scale modelling using MD [329] and DFT calculations in both bcc Fe [330] and W [331] . The modelling predicts that the segregation and trapping of atomic H to the interface of noble gas bubbles is relatively insensitive to gas densities of over-pressurized bubbles.…”

Section: Bubble Formationsupporting

confidence: 80%

Perspectives on multiscale modelling and experiments to accelerate materials development for fusion

Gilbert

Arakawa²,

Bergstrom

et al. 2021

Journal of Nuclear Materials

View full text Add to dashboard Cite

“…Density functional theory (DFT) calculations show strong attraction between He and HIs [9,15], indicating preferential trapping of H around He clusters. Molecular dynamics (MD) simulations show that a large amount of H can be accommodated around He bubbles [16,10,17]. Increased D retention was observed experimentally in a recent study after thermal cycling of He irradiated W samples where visible bubbles were observed [18].…”

Section: Introductionmentioning

confidence: 86%

Deuterium transport and retention in the bulk of tungsten containing helium: the effect of helium concentration and microstructure

Markelj¹,

Schwarz-Selinger

Pečovnik³

et al. 2020

Nucl. Fusion

View full text Add to dashboard Cite

The effect of helium (He) on deuterium (D) retention and transport in the bulk of tungsten (W) was investigated. For this purpose samples were irradiated by 500 keV He ions at 300 K to different fluences in order to obtain He maximum concentrations of 1 at.%, 3.4 at.%, and 6.8 at.% in 0.84 µm depth. In order to discern the effect of irradiation damage caused by He implantation from the effect of the pure He presence on D retention, the W samples were irradiated at 300 K by 20 MeV tungsten ions in advance to create displacement damage in the crystal lattice to a damage dose of 0.23 dpa. The samples were exposed to a D atom beam at 600 K with a flux of 3.5 ×10 18 D/m 2 s to populate all the created defects. The D depth profiles were measured in situ during and at the end of exposure by nuclear reaction analysis to follow the dynamics of the D uptake. Thermal desorption spectra were collected ex situ at the end of the exposure. We show that D retention increases with implanted He fluence linearly following a D/He ratio of 0.29. We obtained peaking of D concentration at the position of maximum He concentration, reaching for the 6.8 at.% He sample three times higher D concentration (1.1 at. %) than obtained on high dpa W ion irradiated samples (0.37 at. %) for the same loading conditions. D retention and transport was also studied on He containing samples that were annealed to 1700 K. There was no reduction of D retention in the He zone but 80 % reduction in the only W irradiated zone was observed, meaning displacement damage was almost completely removed. In the He zone the D concentration increased to 1.35 at.% and this we attribute to trapping of D around He bubbles of 1.5 nm size created at the He peak maximum as obtained by transmission electron microscopy. Neither in the as He implanted nor the 1700 K annealed sample He did act as diffusion barrier. From this study one can conclude that in the main wall of a future fusion device the effect of He will not dominate D retention in tungsten but at high heat flux areas where displacement damage possibly anneals out He could accumulate in the material that it could eventually dominate over the effect of displacement damage.

show abstract

A Molecular Dynamics Study of Subsurface Hydrogen-Helium Bubbles in Tungsten

Cited by 39 publications

References 41 publications

Hydrogen trapping in tungsten: impact of helium irradiation and thermal cycling

Hydrogen trapping in tungsten: impact of helium irradiation and thermal cycling

Perspectives on multiscale modelling and experiments to accelerate materials development for fusion

Deuterium transport and retention in the bulk of tungsten containing helium: the effect of helium concentration and microstructure

Contact Info

Product

Resources

About