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

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 thesemore » 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.« less
Authors:
; ; ;  [1] ;  [2] ; ; ;  [3] ;  [4] ;  [5]
  1. Sandia National Laboratories, Hydrogen and Combustion Technology Department, Livermore, California 94551 (United States)
  2. Fusion Safety Program, Idaho National Laboratory, Idaho Falls, Idaho 83415 (United States)
  3. Department of Chemistry, Graduate School of Science, Shizuoka University, Shizuoka 422-8529 (Japan)
  4. Sandia National Laboratories, Energy Nanomaterials Department, Livermore, California 94551 (United States)
  5. Institute of Geosciences, Shizuoka University, Shizuoka 422-8529 (Japan)
Publication Date:
OSTI Identifier:
22494757
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 7; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; BACKSCATTERING; BUBBLE GROWTH; BUBBLES; CRACKS; DEFECTS; DESORPTION; DEUTERIUM; DIFFRACTION; GRAIN BOUNDARIES; ION BEAMS; ITER TOKAMAK; NEUTRONS; PLASMA; SPECTROSCOPY; SURFACES; TRITIUM; TUNGSTEN