A multi-technique analysis of deuterium trapping and near-surface precipitate growth in plasma-exposed tungsten

Journal Article · Mon Aug 17 00:00:00 EDT 2015 · Journal of Applied Physics

DOI: https://doi.org/10.1063/1.4928184 · OSTI ID:1235305

Kolasinski, Robert ^[1]; Shimada, Masashi ^[2]; Oya, Yasuhisa ^[3]; Buchenauer, Dean A. ^[1]; Chikada, Takumi ^[3]; Cowgill, Donald F. ^[1]; Donovan, David ^[1]; Friddle, Raymond William ^[1]; Michibayashi, Katsu ^[3]; Sato, Misaki ^[3]

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1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
2. Idaho National Lab. (INL), Idaho Falls, ID (United States)
3. Shizuoka Univ., Shizuoka (Japan)

We examine how deuterium becomes trapped in plasma-exposed tungsten and forms near-surface platelet-shaped precipitates. How these bubbles nucleate and grow, as well as the amount of deuterium trapped within, is crucial for interpreting the experimental database. Here, we use a combined experimental/theoretical approach to provide further insight into the underlying physics. With the Tritium Plasma Experiment, we exposed a series of ITER-gradetungsten samples to high flux D plasmas (up to 1.5 × 10²² m^-2 s^-1) at temperatures ranging between 103 and 554 °C. Retention of deuterium trapped in the bulk, assessed through thermal desorption spectrometry, reached a maximum at 230 °C and diminished rapidly thereafter for T > 300 °C. Post-mortem examination of the surfaces revealed non-uniform growth of bubbles ranging in diameter between 1 and 10 μm over the surface with a clear correlation with grain boundaries. Electron back-scattering diffraction maps over a large area of the surface confirmed this dependence; grains containing bubbles were aligned with a preferred slip vector along the <111> directions. Focused ion beam profiles suggest that these bubbles nucleated as platelets at depths of 200 nm–1 μm beneath the surface and grew as a result of expansion of sub-surface cracks. Furthermore, to estimate the amount of deuterium trapped in these defects relative to other sites within the material, we applied a continuum-scale treatment of hydrogen isotope precipitation. Additionally, we propose a straightforward model of near-surface platelet expansion that reproduces bubble sizes consistent with our measurements. For the tungsten microstructure considered here, we find that bubbles would only weakly affect migration of D into the material, perhaps explaining why deep trapping was observed in prior studies with plasma-exposed neutron-irradiated specimens. We foresee no insurmountable issues that would prevent the theoretical framework developed here from being extended to a broader range of systems where precipitation of insoluble gases in ion beam or plasma-exposed metals is of interest.

• Research Organization: Sandia National Laboratories (SNL-CA), Livermore, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-4); USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000; AC07-05ID14517
• OSTI ID: 1235305
• Report Number(s): SAND--2015-6826J; 598917
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 07 Vol. 118; ISSN 0021-8979
• Publisher: American Institute of Physics (AIP)Copyright Statement
• Country of Publication: United States
• Language: English