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High-flux plasma exposure of ultra-fine grain tungsten

Journal Article · · International Journal of Refractory and Hard Metals
 [1];  [1];  [2];  [3];  [3];  [4];  [4];  [1];  [1]
  1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  2. Univ. of California, San Diego, La Jolla, CA (United States)
  3. Univ. of Utah, Salt Lake City, UT (United States)
  4. Shizuoka Univ., Shizuoka (Japan)
+ Show Author Affiliations

Here we examine the response of an ultra-fine grained (UFG) tungsten material to high-flux deuterium plasma exposure. UFG tungsten has received considerable interest as a possible plasma-facing material in magnetic confinement fusion devices, in large part because of its improved resistance to neutron damage. However, optimization of the material in this manner may lead to trade-offs in other properties. Moreover, we address two aspects of the problem in this work: (a) how high-flux plasmas modify the structure of the exposed surface, and (b) how hydrogen isotopes become trapped within the material. The specific UFG tungsten considered here contains 100 nm-width Ti dispersoids (1 wt%) that limit the growth of the W grains to a median size of 960 nm. Metal impurities (Fe, Cr) as well as O were identified within the dispersoids; these species were absent from the W matrix. To simulate relevant particle bombardment conditions, we exposed specimens of the W-Ti material to low energy (100 eV), high-flux (> 1022 m-2 s-1) deuterium plasmas in the PISCES-A facility at the University of California, San Diego. To explore different temperature-dependent trapping mechanisms, we considered a range of exposure temperatures between 200 °C and 500 °C. For comparison, we also exposed reference specimens of conventional powder metallurgy warm-rolled and ITER-grade tungsten at 300 °C. Post-mortem focused ion beam profiling and atomic force microscopy of the UFG tungsten revealed no evidence of near-surface bubbles containing high pressure D2 gas, a common surface degradation mechanism associated with plasma exposure. Thermal desorption spectrometry indicated moderately higher trapping of D in the material compared with the reference specimens, though still within the spread of values for different tungsten grades found in the literature database. Finally, for the criteria considered here, these results do not indicate any significant obstacles to the potential use of UFG tungsten as a plasma-facing material, although further experimental work is needed to assess material response to transient events and high plasma fluence.

Research Organization:
Sandia National Laboratories (SNL-CA), Livermore, CA (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
AC04-94AL85000
OSTI ID:
1257802
Alternate ID(s):
OSTI ID: 1359210
Report Number(s):
SAND--2016-2776J; PII: S0263436815303334
Journal Information:
International Journal of Refractory and Hard Metals, Journal Name: International Journal of Refractory and Hard Metals; ISSN 0263-4368
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (2)

Helium segregation and transport behavior near ⟨100⟩ and ⟨110⟩ symmetric tilt grain boundaries in tungsten journal June 2018
Helium in-plane migration behavior on 〈1 0 0〉 symmetric tilt grain boundaries in tungsten journal July 2018

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70 PLASMA PHYSICS AND FUSION TECHNOLOGY