Theoretical Model of Helium Bubble Growth and Density in Plasma-Facing Metals

Hammond, Karl D.; Maroudas, Dimitrios; Wirth, Brian D.

doi:10.1038/s41598-020-58581-8

Cited by 36 publications

(16 citation statements)

References 61 publications

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“…This model however has a few caveats, some of which have already been discussed by Faney et al 30 . First, the He-to-vacancy ratio of 4:1 in this work differs from MD studies 35 , 46 . The dilute limit approximation may also not be valid as soon a the volume fraction occupied by He becomes comparable to unity.…”

Section: Discussionmentioning

confidence: 63%

“…This assumption is motivated by MD computations showing that trap mutation events occur for every four additional helium in large vacancy-helium clusters. Moreover, theoretical models for He bubbles growth in metal suggest a similar trend 35 . Dissociation of large clusters is neglected (i.e.…”

Section: Methodsmentioning

confidence: 80%

“…In future work, this model will be used to estimate bubble production induced by indirect He production (tritium decay and W transmutation). The use of more accurate correlations for He bubbles growth 35 , 46 would tend to reduce the overall He content. Additional bubble models such as bursting or coalescence will also be investigated.…”

Section: Discussionmentioning

confidence: 99%

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Influence of exposure conditions on helium transport and bubble growth in tungsten

Ialovega

Hodille

Mougenot

et al. 2021

Sci Rep

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Helium diffusion, clustering and bubble nucleation and growth is modelled using the finite element method. The existing model from Faney et al. (Model Simul Mater Sci Eng 22:065010, 2018; Nucl Fusion 55:013014, 2015) is implemented with FEniCS and simplified in order to greatly reduce the number of equations. A parametric study is performed to investigate the influence of exposure conditions on helium inventory, bubbles density and size. Temperature is varied from 120 K to 1200 K and the implanted flux of 100 eV He is varied from $$10^{17}\,{\text{m}^{-2}\, \text{s}^{-1}}$$ 10 17 m - 2 s - 1 to $$5 \times 10^{21}\, {\text{m}^{-2}\, \text{s}^{-1}}$$ 5 × 10 21 m - 2 s - 1 . Bubble mean size increases as a power law of time whereas the bubble density reaches a maximum. The maximum He content in bubbles was approximately $$4 \times 10^{8}$$ 4 × 10 8 He at $$5 \times 10^{21}\,{\text{m}^{-2}\, \text{s}^{-1}}$$ 5 × 10 21 m - 2 s - 1 . After 1 h of exposure, the helium inventory varies from $$5 \times 10^{16} \,{\text{m}^{-2}}$$ 5 × 10 16 m - 2 at low flux and high temperature to $$10^{25} \,{\text{m}^{-2}}$$ 10 25 m - 2 at high flux and low temperature. The bubbles inventory varies from $$5 \times 10^{12}$$ 5 × 10 12 bubbles m$$^{-2}$$ - 2 to $$2 \times 10^{19}$$ 2 × 10 19 bubbles m$$^{-2}$$ - 2 . Comparison with experimental measurements is performed. The bubble density simulated by the model is in quantitative agreement with experiments.

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Section: Discussionmentioning

confidence: 63%

Section: Methodsmentioning

confidence: 80%

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Influence of exposure conditions on helium transport and bubble growth in tungsten

Ialovega

Hodille

Mougenot

et al. 2021

Sci Rep

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“…Among those potentials, the most reliable parametrization is the Juslin–Wirth (JW) potential parametrization, which is based on the embedded-atom method (EAM) potential of Finnis and Sinclair with subsequent short-range modifications by Ackland and Thetford and further extreme-short-range modifications by Juslin and Wirth . This potential parametrization has been used successfully in plasma-exposed tungsten models under various plasma exposure conditions and has been employed in large-scale MD simulations to investigate the evolution of the near-surface region of PFC tungsten under He irradiation conditions that approach typical fusion reactor operating conditions. ,,, Also, we have used the JW parametrization in our recent study of the elastic properties of PFC tungsten; hence, predictions of tungsten elastic properties by the SNAP and JW parametrizations merit a proper comprehensive comparison before setting out to explore mechanical behavior beyond the elastic regime. In addition, we have compared these interatomic potential results with predictions from first-principles density functional theory (DFT) calculations within the quasi-harmonic approximation (DFT-QHA).…”

Section: Methodsmentioning

confidence: 99%

Molecular-Dynamics Analysis of the Mechanical Behavior of Plasma-Facing Tungsten

Weerasinghe

Martínez

Wirth

et al. 2023

ACS Appl. Mater. Interfaces

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We report a systematic computational analysis of the mechanical behavior of plasma-facing component (PFC) tungsten focusing on the impact of void and helium (He) bubble defects on the mechanical response beyond the elastic regime. Specifically, we explore the effects of porosity and He atomic fraction on the mechanical properties and structural response of PFC tungsten, at varying temperature and bubble size. We find that the Young modulus of defective tungsten undergoes substantial softening that follows an exponential scaling relation as a function of matrix porosity and He atomic content. Beyond the elastic regime, our high strain rate simulations reveal that the presence of nanoscale spherical defects (empty voids and He bubbles) reduces the yield strength of tungsten in a monotonically decreasing fashion, obeying an exponential scaling relation as a function of tungsten matrix porosity and He concentration. Our detailed analysis of the structural response of PFC tungsten near the yield point reveals that yielding is initiated by emission of dislocation loops from bubble/matrix interfaces, mainly 1/2⟨111⟩ shear loops, followed by gliding and growth of these loops and reactions to form ⟨100⟩ dislocations. Furthermore, dislocation gliding on the ⟨111⟩{211} twin systems nucleates 1/6⟨111⟩ twin regions in the tungsten matrix. These dynamical processes reduce the stress in the matrix substantially. Subsequent dislocation interactions and depletion of the twin phases via nucleation and propagation of detwinning partials lead the tungsten matrix to a next deformation stage characterized by stress increase during applied straining. Our structural analysis reveals that the depletion of twin boundaries (areal defects) is strongly impacted by the density of He bubbles at higher porosities. After the initial stress relief upon yielding, increase in the dislocation density in conjunction with decrease in the areal defect density facilitates the initiation of dislocation-driven deformation mechanisms in the PFC crystal.

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“…Such bubbles are technologically significant because they occur during ion implantation in Si [24,27], in nuclear waste disposal [28] and readily form in the metallic cladding of nuclear reactors [22,29,30] where these helium bubbles can exert such pressures that the structural integrity of the host material is put at risk. The problem of helium bubble growth in plasma-facing materials is fast becoming a major issue in nuclear fusion materials research [31].…”

Section: Introductionmentioning

confidence: 99%

Confined helium, density dependence of the inelastic electron and photon scattering cross-sections and the optical oscillator strength

Pyper

Whelan

2022

Proc. R. Soc. A.

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The electron and photon excitation of confined and compressed atoms is discussed. It is shown that the optical oscillator strength, the inelastic X-ray and electron impact cross-sections are all density-dependent. Ab-initio electronic structure calculations are presented for the 1 s 2 → 1 s 2 p ( 1 P ) transition in helium, which predict that the amplitudes for the inelastic scattering of electrons, optical absorption and the excitation energy are all significantly increased in bulk condensed phases of pure helium compared to those of an isolated atom. The enhancements increase with atomic density but are very similar for bcc and fcc structured bulk phases of the same density. These enhancements need to be incorporated into the analysis of scanning transmission electron microscope studies of helium nano bubbles embedded in different materials. The excitation energy and cross-section enhancements with increasing density arise from the contraction of the 2 p orbital on entering a condensed phase. For the bulk phases, but not the bubbles, the close agreement between the experimental and computed values of the energy shifts can be well described by a simple relationship.

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Theoretical Model of Helium Bubble Growth and Density in Plasma-Facing Metals

Cited by 36 publications

References 61 publications

Influence of exposure conditions on helium transport and bubble growth in tungsten

Influence of exposure conditions on helium transport and bubble growth in tungsten

Molecular-Dynamics Analysis of the Mechanical Behavior of Plasma-Facing Tungsten

Confined helium, density dependence of the inelastic electron and photon scattering cross-sections and the optical oscillator strength

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