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Suche nach „[A.] [Hamid]“ hat 3 Publikationen gefunden
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    NachhaltigF: Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    A. Hamid, J. Sun, H. Zhang, Thomas Stirner

    Molecular dynamics simulation analysis of helium cluster growth conditions under tungsten surfaces

    Computational Materials Science, vol. 186, no. January

    2021

    DOI: 10.1016/j.commatsci.2020.109994

    Abstract anzeigen

    Molecular dynamics simulations have been performed to study the effects of helium fluxes on helium cluster size underneath tungsten surfaces under bombardment of helium atoms with incident energy 30 100 eV at temperature 300 2100 K. The simulation results show that the helium cluster size depends on the magnitude of the helium flux: at a higher flux, the helium clusters on average form in smaller size in tungsten but with larger number; while the clusters form further away from the surface at a lower flux. The coalescence of He atoms and helium bubbles depends on the tungsten temperature: at elevated temperatures around 2000 K, the incident He atoms in tungsten slow down more rapidly than at 1000 K but the number of vacancies per He cluster is smaller. The incident energy has a strong effect on the retention of helium atoms: The helium retention rate increases with the incident energy, and the helium retention depends weakly on temperature in the low energy range of interest. It is also found that the surface orientation plays an important role not only in determining the depth distribution but also in determining the helium retention and cluster size: at the surface {1 1 0}, the retention rate of helium atoms is the lowest, and at the surface {1 1 1}, the clusters grow easily in the lateral direction. The present simulation results suggest that the {0 0 1} surface is favorable for fuzz growth. The results obtained in the present work provide insight to the reasons why the fuzz only grows within a certain parameter range at the atomic level.

    NachhaltigF: Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    H. Zhang, J. Sun, Y. Wang, Thomas Stirner, A. Hamid, C. Sang

    Study of lattice thermal conductivity of tungsten containing bubbles by molecular dynamics simulation

    Fusion Engineering and Design, vol. 161, no. December

    2020

    DOI: 10.1016/j.fusengdes.2020.112004

    Abstract anzeigen

    Exposed to high fluxes of helium/hydrogen isotope particles and heat, tungsten divertor plates will suffer damage thus degrading its performance such as its thermal conductivity. This paper presents a study on the effect of bubbles on the lattice thermal conductivity of tungsten at the atomic level using molecular dynamics simulations. The present study finds that empty bubbles in tungsten lead to a decrease in the lattice thermal conductivity of tungsten. Furthermore, He/D filled bubbles aggravate this decrease. The physical origin of this behavior is discussed. It is also found that the decrease in lattice thermal conductivity depends strongly on both the impurity density in the bubbles and the bubble size.

    NachhaltigF: Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    Thomas Stirner, Ali Hamid, J. Sun, H. Zhang, A. Jadon

    Molecular dynamics simulations of helium clustering and bubble growth under tungsten surfaces

    Computational Materials Science, vol. 163, no. June, pp. 141-147

    2019

    DOI: 10.1016/j.commatsci.2019.03.008

    Abstract anzeigen

    We study the surface response of W to helium bombardment using molecular dynamics simulations. Simulations have been performed for incident helium of energy 80 eV and surface temperature 2100 K. The saturation of He retention has been observed to be high, a result of the bubbles trapping helium atoms and preventing them from diffusing to the surface and further back into the plasma. On the other hand, we have observe near-surface “cluster rupture” leading to the expulsion of helium atoms towards the vacuum. We have found that bubbles typically grow in a relatively narrow band of He/V ratios (1–3). Besides, it was observed that tungsten atoms migrated from the top surface into the bulk. The coalescence of helium bubbles has also been observed.