A multi-technique analysis of deuterium trapping and near-surface precipitate growth in plasma-exposed tungsten
- Sandia National Laboratories, Hydrogen and Combustion Technology Department, Livermore, California 94551 (United States)
- Fusion Safety Program, Idaho National Laboratory, Idaho Falls, Idaho 83415 (United States)
- Department of Chemistry, Graduate School of Science, Shizuoka University, Shizuoka 422-8529 (Japan)
- Sandia National Laboratories, Energy Nanomaterials Department, Livermore, California 94551 (United States)
- Institute of Geosciences, Shizuoka University, Shizuoka 422-8529 (Japan)
In this work, 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-grade tungsten samples to high flux D plasmas (up to 1.5 × 10{sup 22 }m{sup −2} s{sup −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. 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. In addition, 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.
- OSTI ID:
- 22494757
- Journal Information:
- Journal of Applied Physics, Vol. 118, Issue 7; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
$\langle 0\,0\,{\rm 1}\rangle $ edge dislocation nucleation mechanism of surface blistering in tungsten exposed to deuterium plasma
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journal | December 2018 |
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