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Title: Crystal orientation effects on helium ion depth distributions and adatom formation processes in plasma-facing tungsten

Abstract

We present atomistic simulations that show the effect of surface orientation on helium depth distributions and surface feature formation as a result of low-energy helium plasma exposure. We find a pronounced effect of surface orientation on the initial depth of implanted helium ions, as well as a difference in reflection and helium retention across different surface orientations. Our results indicate that single helium interstitials are sufficient to induce the formation of adatom/substitutional helium pairs under certain highly corrugated tungsten surfaces, such as (1 1 1)-orientations, leading to the formation of a relatively concentrated layer of immobile helium immediately below the surface. The energies involved for helium-induced adatom formation on (1 1 1) and (2 1 1) surfaces are exoergic for even a single adatom very close to the surface, while (0 0 1) and (0 1 1) surfaces require two or even three helium atoms in a cluster before a substitutional helium cluster and adatom will form with reasonable probability. This phenomenon results in much higher initial helium retention during helium plasma exposure to (1 1 1) and (2 1 1) tungsten surfaces than is observed for (0 0 1) or (0 1 1) surfaces and is much higher thanmore » can be attributed to differences in the initial depth distributions alone. The layer thus formed may serve as nucleation sites for further bubble formation and growth or as a source of material embrittlement or fatigue, which may have implications for the formation of tungsten “fuzz” in plasma-facing divertors for magnetic-confinement nuclear fusion reactors and/or the lifetime of such divertors.« less

Authors:
 [1]
  1. Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996–2300 (United States)
Publication Date:
OSTI Identifier:
22305777
Resource Type:
Journal Article
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 116; Journal Issue: 14; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-8979
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ATOMS; CRYSTAL GROWTH; CRYSTALS; DEPTH; HELIUM IONS; LIFETIME; MAGNETIC CONFINEMENT; ORIENTATION; PLASMA; PROBABILITY; REFLECTION; SIMULATION; SPATIAL DISTRIBUTION; SURFACES; TUNGSTEN

Citation Formats

Hammond, Karl D., Wirth, Brian D., E-mail: bdwirth@utk.edu, and P.O. Box 2008, MS-6003, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831–6003. Crystal orientation effects on helium ion depth distributions and adatom formation processes in plasma-facing tungsten. United States: N. p., 2014. Web. doi:10.1063/1.4897419.
Hammond, Karl D., Wirth, Brian D., E-mail: bdwirth@utk.edu, & P.O. Box 2008, MS-6003, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831–6003. Crystal orientation effects on helium ion depth distributions and adatom formation processes in plasma-facing tungsten. United States. https://doi.org/10.1063/1.4897419
Hammond, Karl D., Wirth, Brian D., E-mail: bdwirth@utk.edu, and P.O. Box 2008, MS-6003, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831–6003. 2014. "Crystal orientation effects on helium ion depth distributions and adatom formation processes in plasma-facing tungsten". United States. https://doi.org/10.1063/1.4897419.
@article{osti_22305777,
title = {Crystal orientation effects on helium ion depth distributions and adatom formation processes in plasma-facing tungsten},
author = {Hammond, Karl D. and Wirth, Brian D., E-mail: bdwirth@utk.edu and P.O. Box 2008, MS-6003, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831–6003},
abstractNote = {We present atomistic simulations that show the effect of surface orientation on helium depth distributions and surface feature formation as a result of low-energy helium plasma exposure. We find a pronounced effect of surface orientation on the initial depth of implanted helium ions, as well as a difference in reflection and helium retention across different surface orientations. Our results indicate that single helium interstitials are sufficient to induce the formation of adatom/substitutional helium pairs under certain highly corrugated tungsten surfaces, such as (1 1 1)-orientations, leading to the formation of a relatively concentrated layer of immobile helium immediately below the surface. The energies involved for helium-induced adatom formation on (1 1 1) and (2 1 1) surfaces are exoergic for even a single adatom very close to the surface, while (0 0 1) and (0 1 1) surfaces require two or even three helium atoms in a cluster before a substitutional helium cluster and adatom will form with reasonable probability. This phenomenon results in much higher initial helium retention during helium plasma exposure to (1 1 1) and (2 1 1) tungsten surfaces than is observed for (0 0 1) or (0 1 1) surfaces and is much higher than can be attributed to differences in the initial depth distributions alone. The layer thus formed may serve as nucleation sites for further bubble formation and growth or as a source of material embrittlement or fatigue, which may have implications for the formation of tungsten “fuzz” in plasma-facing divertors for magnetic-confinement nuclear fusion reactors and/or the lifetime of such divertors.},
doi = {10.1063/1.4897419},
url = {https://www.osti.gov/biblio/22305777}, journal = {Journal of Applied Physics},
issn = {0021-8979},
number = 14,
volume = 116,
place = {United States},
year = {Tue Oct 14 00:00:00 EDT 2014},
month = {Tue Oct 14 00:00:00 EDT 2014}
}

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Works referencing / citing this record:

Molecular-dynamics analysis of mobile helium cluster reactions near surfaces of plasma-exposed tungsten
journal, October 2015


Helium segregation and transport behavior near ⟨100⟩ and ⟨110⟩ symmetric tilt grain boundaries in tungsten
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He-ion induced surface morphology change and nanofuzz growth on hot tungsten surfaces
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Helium in-plane migration behavior on 〈1 0 0〉 symmetric tilt grain boundaries in tungsten
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Recent advances in modeling and simulation of the exposure and response of tungsten to fusion energy conditions
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Continuum-scale modeling of helium bubble bursting under plasma-exposed tungsten surfaces
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Helium flux effects on bubble growth and surface morphology in plasma-facing tungsten from large-scale molecular dynamics simulations
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On the origin of ‘fuzz’ formation in plasma-facing materials
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Dynamics of Small Mobile Helium Clusters Near a Symmetric Tilt Grain Boundary of Plasma-Exposed Tungsten
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