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

Abstract

Here, 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 highermore » than can be attributed to differences in the initial depth distributions alone. Lastly, 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:

Hammond, Karl D. ^[1]; Wirth, Brian D. ^[2]

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+ Show Author Affiliations

1. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Nuclear Engineering
2. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Nuclear Engineering; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Publication Date:

Thu Oct 09 00:00:00 EDT 2014

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR); USDOE Office of Science (SC), Fusion Energy Sciences (FES)

OSTI Identifier:

1348314

Grant/Contract Number:  

AC05-00OR22725; SC0008875; SC0002060; AC02-06CH11231; AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Applied Physics

Additional Journal Information:

Journal Volume: 116; Journal Issue: 14; Journal ID: ISSN 0021-8979

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

74 ATOMIC AND MOLECULAR PHYSICS; Tungsten; Interatomic potential energy surfaces; Atom surface collisions; Surface tension; Bubble formation