| Autor: |
Kolasinski, R. D., Shimada, M., Oya, Y., Buchenauer, D. A., Chikada, T., Cowgill, D. F., Donovan, D. C., Friddle, R. W., Michibayashi, K., Sato, M. |
| Předmět: |
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| Zdroj: |
Journal of Applied Physics; 8/21/2015, Vol. 118 Issue 7, p073301-1-073301-13, 13p, 1 Black and White Photograph, 1 Diagram, 2 Charts, 9 Graphs |
| Abstrakt: |
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 1.5×1022m-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 lm over the surface with a clear correlation with grain boundaries. Electron backscattering 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 lm 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. [ABSTRACT FROM AUTHOR] |
| Databáze: |
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