3D modelling of tungsten fuzz growth under the bombardment of helium plasma

Shi, Quan; Dai, Shuyu; Wang, Dezhen

doi:10.1016/j.fusengdes.2018.03.019

Cited by 16 publications

(7 citation statements)

References 14 publications

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“…However, under low-energy helium plasma exposure, with incident ion energies higher than a threshold value of 35 eV [5][6][7], and a temperature range very similar to the conditions expected at the divertor wall of ITER, a fragile nanofiber-like crystalline structure grows on the tungsten surface [5][6][7][8][9][10][11]; this nanostructure, known as 'fuzz', poses a major operational challenge in ITER [8][9][10][11]. Over the past two decades, several theoretical [12][13][14] and simulation [15][16][17][18][19][20][21][22] studies have attempted to decipher and elucidate the mechanism of fuzz formation. In our previous studies, we identified stress-driven surface diffusion as the primary driving force for nanotendril growth at the early stage of plasma exposure, where the stress is developed in the nearsurface layer of plasma-facing component (PFC) tungsten due to over-pressurized nanometer-size bubbles formed by the implanted helium ions in the PFC material.…”

Section: Introductionmentioning

confidence: 99%

Effects of surface vacancy-adatom pair formation on PFC tungsten surface morphological response

et al. 2023

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We report a simulation study of the effect of He-irradiation-induced surface vacancy-adatom pair formation on the surface morphological evolution of plasma-facing component (PFC) tungsten and examine a number of factors that impact such evolution. Our analysis is based on self-consistent dynamical simulations according to an atomistically-informed, continuum-scale surface evolution model that has been developed following a hierarchical multiscale modeling strategy and can access the spatiotemporal scales of relevance to fuzz formation. The model accounts for the flux of surface adatoms generated as a result of the surface vacancy-adatom pair formation effect upon He implantation, which contributes to the anisotropic growth of surface nanostructural features due to the different rates of adatom diffusion along and across step edges of islands on the tungsten surface. We have carried out atomic-scale computations of optimal diffusion pathways along and across island step edges on the W(110) surface and calculated Ehrlich-Schwoebel (ES) barriers in adatom diffusion along and across such step edges. This aspect of surface adatom diffusion contributes to anisotropic surface atomic fluxes, terrace and step diffusive currents, and has been incorporated into our PFC surface evolution model, which predicts the formation of preferentially aligned nanoridge stripe patterns on the PFC surface. We establish that these anisotropic diffusive currents accelerate nanotendril growth on the PFC surface and the onset of surface nanostructure pattern formation. We also explore systematically the dependence of the PFC surface morphological response on the surface temperature and He ion incident flux, characterize in detail the resulting surface topographies and growth kinetics, and compare the predicted surface morphologies with experimental observations. Our simulation predictions for the emerging surface nanostructure patterns under certain plasma exposure conditions are consistent with experimental findings in the literature.

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Section: Introductionmentioning

confidence: 99%

Effects of surface vacancy-adatom pair formation on PFC tungsten surface morphological response

et al. 2023

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“…The SURO-FUZZ program was originally developed to simulate the formation of tungsten fuzz under helium ion bombardment [31]. However, physical processes such as helium migration and agglomeration, helium bubble growth and rupture and so on during tungsten fuzz growth are very time-consuming to simulate [40,41].…”

Section: Suro-fuzzmentioning

confidence: 99%

“…In this work, modelling of the hydrogen reflection coefficient on the tungsten fuzzy surface has been performed by SURO-FUZZ [31]. SURO-FUZZ was developed based on the 3D rough surface code SURO, which was originally developed to study the influence of surface roughness on impurity erosion and deposition characteristics in fusion experiments [32][33][34].…”

Section: Introductionmentioning

confidence: 99%

Modelling of hydrogen reflection on tungsten fuzzy surface in an erosive hydrogen plasma

et al. 2020

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Modelling of the reflection of energetic hydrogen atoms from tungsten fuzz under hydrogen plasma exposure has been performed using the three-dimensional kinetic Monte Carlo program SURO-FUZZ. The simulation results show that the hydrogen reflection coefficient on a porous tungsten fuzzy surface is 50% lower in comparison with a smooth tungsten surface, which shows good agreement with the measurements. The time evolution of the tungsten fuzzy structure has been investigated under energetic hydrogen bombardment. A sustained removal of the porous tungsten fuzzy structure is obtained, which results in a reduced height of tungsten fuzz with exposure time and finally a smoothing of the tungsten fuzz. The erosion-induced degradation of the tungsten fuzzy structure leads to a high hydrogen reflection coefficient with exposure time. The simulated temporal evolution of the hydrogen reflection coefficient is in reasonable agreement with the experimental data. The simulation results show that the reflection coefficient of hydrogen atoms on fuzzy surfaces is decreased with increasing porosity. Parametric studies with varying porous structures have been performed to gain insights into hydrogen reflection characteristics on tungsten fuzzy surfaces.

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“…Under such conditions, tungsten readily forms a fragile crystalline nanotendril-like structure, commonly called 'fuzz' [6][7][8][9][10][11][12]; formation of nanotendrils emanating from the PFC surface constitutes a precursor to the growth of fuzz, a surface layer consisting of such interconnected nanotendrils with complex morphological features. Over the last two decades, a number of theoretical [13][14][15], simulation [16][17][18][19][20][21][22][23], and experimental [6,10,24,25] studies have been conducted to decipher the intriguing physics/mechanism of fuzz formation because, if it remains unmitigated, the fragile fuzz of the high-Z tungsten (W) can be exfoliated and released into the plasma and, thus, severely compromise the performance of the reactor [9][10][11][12]. Helium has a very low solubility in tungsten; as a result, upon implantation, He atoms readily self-cluster and nucleate helium bubbles, which subsequently grow by absorbing helium and emitting tungsten Frenkel pairs, a process known as the 'trap-mutation' reaction [24,26].…”

Section: Introductionmentioning

confidence: 99%

Helium bubble size effects on the surface morphological response of plasma-facing tungsten

Patel

Dasgupta

Wirth

et al. 2023

Mater. Res. Express

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We report a simulation study on the effects of helium (He) bubble size on the morphological evolution and pattern formation on the surface of tungsten used as a plasma-facing component (PFC) in nuclear fusion devices. We have carried out a systematic investigation based on self-consistent dynamical simulations of surface morphological evolution according to an atomistically-informed, 3D continuum-scale model that captures well the relevant length and time scales of surface nanostructure formation in PFC tungsten. The model accounts for PFC surface diffusion, driven by the biaxial compressive stress originating from the over-pressurized He bubbles in the near-surface region of PFC tungsten as a result of He plasma exposure, combined with the formation of self-interstitial atoms in tungsten that diffuse toward the PFC surface and the flux of surface adatoms generated as a result of surface vacancy-adatom pair formation upon He implantation; this transport of surface adatoms contributes to the anisotropic growth of surface nanostructural features due to the different rates of adatom diffusion along and across step edges of islands on the tungsten surface. Our detailed analysis reveals that varying the average He bubble size plays an important role in the PFC surface growth kinetics as well as the resulting surface topography. Specifically, we find that an increase in the He bubble size leads to a deceleration in the growth rate of the tungsten nanotendrils that emanate from the PFC surface. We also find that the separation distance between the resulting surface features increases with increasing He bubble size, as well as over time. This coarsening effect is a thermally activated process resulting in an accurate description of the temperature dependence of the average surface feature separation by an Arrhenius relation.

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3D modelling of tungsten fuzz growth under the bombardment of helium plasma

Cited by 16 publications

References 14 publications

Effects of surface vacancy-adatom pair formation on PFC tungsten surface morphological response

Effects of surface vacancy-adatom pair formation on PFC tungsten surface morphological response

Modelling of hydrogen reflection on tungsten fuzzy surface in an erosive hydrogen plasma

Helium bubble size effects on the surface morphological response of plasma-facing tungsten

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