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Title: Direct depth distribution measurement of deuterium in bulk tungsten exposed to high-flux plasma

Abstract

Understanding tritium retention and permeation in plasma-facing components is critical for fusion safety and fuel cycle control. Glow discharge optical emission spectroscopy (GD-OES) is shown to be an effective tool to reveal the depth profile of deuterium in tungsten. Results confirm the detection of deuterium. Furthermore, a ~46 µm depth profile revealed that the deuterium content decreased precipitously in the first 7 µm, and detectable amounts were observed to depths in excess of 20 µm. The large probing depth of GD-OES (up to 100s of µm) enables studies not previously accessible to the more conventional techniques for investigating deuterium retention. Of particular applicability is the use of GD-OES to measure the depth profile for experiments where high diffusion is expected: deuterium retention in neutron irradiated materials, and ultra-high deuterium fluences in burning plasma environment.

Authors:
ORCiD logo [1];  [1]
  1. Idaho National Lab. (INL), Idaho Falls, ID (United States)
Publication Date:
Research Org.:
Idaho National Lab. (INL), Idaho Falls, ID (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1372955
Alternate Identifier(s):
OSTI ID: 1360916; OSTI ID: 1421267
Report Number(s):
INL/JOU-17-41539
Journal ID: ISSN 2158-3226
Grant/Contract Number:
AC07-05ID14517
Resource Type:
Journal Article: Published Article
Journal Name:
AIP Advances
Additional Journal Information:
Journal Volume: 7; Journal Issue: 5; Journal ID: ISSN 2158-3226
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; depth profile; deuterium; glow discharge optical emission spectroscopy; tungsten

Citation Formats

Taylor, Chase N., and Shimada, M.. Direct depth distribution measurement of deuterium in bulk tungsten exposed to high-flux plasma. United States: N. p., 2017. Web. doi:10.1063/1.4983384.
Taylor, Chase N., & Shimada, M.. Direct depth distribution measurement of deuterium in bulk tungsten exposed to high-flux plasma. United States. doi:10.1063/1.4983384.
Taylor, Chase N., and Shimada, M.. Mon . "Direct depth distribution measurement of deuterium in bulk tungsten exposed to high-flux plasma". United States. doi:10.1063/1.4983384.
@article{osti_1372955,
title = {Direct depth distribution measurement of deuterium in bulk tungsten exposed to high-flux plasma},
author = {Taylor, Chase N. and Shimada, M.},
abstractNote = {Understanding tritium retention and permeation in plasma-facing components is critical for fusion safety and fuel cycle control. Glow discharge optical emission spectroscopy (GD-OES) is shown to be an effective tool to reveal the depth profile of deuterium in tungsten. Results confirm the detection of deuterium. Furthermore, a ~46 µm depth profile revealed that the deuterium content decreased precipitously in the first 7 µm, and detectable amounts were observed to depths in excess of 20 µm. The large probing depth of GD-OES (up to 100s of µm) enables studies not previously accessible to the more conventional techniques for investigating deuterium retention. Of particular applicability is the use of GD-OES to measure the depth profile for experiments where high diffusion is expected: deuterium retention in neutron irradiated materials, and ultra-high deuterium fluences in burning plasma environment.},
doi = {10.1063/1.4983384},
journal = {AIP Advances},
number = 5,
volume = 7,
place = {United States},
year = {Mon May 08 00:00:00 EDT 2017},
month = {Mon May 08 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1063/1.4983384

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  • Understanding tritium retention and permeation in plasma-facing components is critical for fusion safety and fuel cycle control. Glow discharge optical emission spectroscopy (GD-OES) is shown to be an effective tool to reveal the depth profile of deuterium in tungsten. Results confirm the detection of deuterium. Furthermore, a ~46 µm depth profile revealed that the deuterium content decreased precipitously in the first 7 µm, and detectable amounts were observed to depths in excess of 20 µm. The large probing depth of GD-OES (up to 100s of µm) enables studies not previously accessible to the more conventional techniques for investigating deuterium retention.more » Of particular applicability is the use of GD-OES to measure the depth profile for experiments where high diffusion is expected: deuterium retention in neutron irradiated materials, and ultra-high deuterium fluences in burning plasma environment.« less
  • An effect of enhanced trapping of deuterium in tungsten at high flux was discovered. It was shown analytically and confirmed experimentally that the deuterium trapping in a presence of high density of defects in tungsten (W) depends on the ion energy and ion flux. Newly developed analytical model explains experimentally observed discrepancy of deuterium trapping at radiation-induced defects in tungsten at different ion fluxes that significantly improves a prediction of hydrogen isotope accumulation in different plasma devices, including ITER and DEMO. The developed model can be used for many system of hydrogen in a metal in both normal and extrememore » environments (high fluxes, elevated temperatures, neutron irradiation, etc.). This new model allows, for the first time, to validate density function theory (DFT) predictions of multiple occupation of a defect with deuterium against experimental data that bridge the gap in length and time scale between DFT calculations and experiments. By comparing first-principle calculations based on DFT and semi-empirical “adsorption model,” it was proved that the mechanism of hydrogen isotope trapping in a vacancy cluster is similar to a chemisorption on a surface. Binding energies of deuterium with different types of defects in W were defined. Moreover, the surface barrier of deuterium to be chemisorbed on a clean W surface was found to be less than 1 eV and kinetics of deuterium release is limited by de-trapping from defects rather than to be limited by surface effects.« less
  • 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 maximummore » 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.« less
  • Cited by 6