DEUTERIUM RETENTION STUDIES AT THE INEEL FOR C-BeAND C-W MIXED PLASMA-FACING MATERIALS
R.A. ANDERL, G.R. LONGHURST, R.J. PAWELKO Idaho National Engineering and Environmental Laboratory, Idaho Falls, Idaho, United States of America
Abstract
This paper presents a summary of the results of experiments to investigate hydrogen isotope retention in mixed plasma-facing component materials. The results are based on thermal desorption spectroscopy measurements of deuterium retained in ion implanted samples of C-Be and C-W mixed materials.
1. INTRODUCTION
Mixed-materials research at the Idaho National Engineering and Environmental Laboratory (INEEL) has focused on the C-Be and C-W systems. The primary purpose of this work was to investigate hydrogen isotope retention in these systems. For this purpose, we simulated plasma-mixed-material layers by using carbon-coated Be and carbon-coated W specimens that were heat-treated and tungsten carbide specimens prepared by chemical vapor deposition (CVD). Sample preparation and characterization activities are summarized in another contribution to this issue. This contribution summarizes the results of our hydrogen isotope retention studies based on thermal desorption spectroscopy (TDS) measurements for deuterium-implanted samples, with an emphasis on experiments for the C-W system.
Detailed results of this work on C-Be were published in refs. [1-3]. References [4-6]
document the results of our studies on the C-W system and compare deuterium retention data to results derived from previous permeation experiments for tungsten foil [7].
2. DEUTERIUM RETENTION STUDIES
weight), a reduction-rolled, powder-metallurgy product. This material was from the same lot as that used for earlier permeation studies [7]. These foils were implanted “as-received” and after annealing at 1200oC. Samples of 0.5-mm W1%La discs were polished to a mirror finish and in some cases were annealed at 1000oC or coated with a carbon surface layer. Tungsten and tungsten carbide samples were made using proprietary CVD processes.
Test samples were implanted with a 1.5-keV D3+ ion beam (500 eV/D, flux density of
~3×1019 D/m2-s) to fluences from 1 to 3×1023 D/m2. Sample temperatures were set at values between 27oC and 400oC during implantation. Retained quantities of deuterium were measured using TDS (23 to 1000oC, 30oC/min). Figures 1-5 show representative TDS spectra for un-annealed W foil (Figure 1), annealed W foil (Figure 2), W disc (Figure 3), CVD-W2C disc (Figure 4) and C-coated W1%La disc (Figure 5). Figure 6 shows a comparison of deuterium retention data that were derived from the various TDS experiments and from previous permeation experiments [7] for 25-µm W foil that was annealed at temperatures from 450 to 1400°C.
Principal findings of this work included the following:
(1) TDS retention data for the 25-µm W foil are consistent with retention values derived from the permeation experiments for material from the same batch.
(2) Annealing of 25-µm W foil to 1200oC results in a retention reduction by a factor of 4 for deuterium implanted at 200oC, with similar retention reductions observed for other W types that were annealed.
(3) Retention in CVD-W and W1%La is below that in W foil for implantation temperatures
<200oC, indicating that different fabrication processes for disc and foil materials and the resulting intrinsic defect structures influence the retained quantities.
(4) Above 200oC, TDS results indicate the opposite trend, possibly due to higher bulk retention in thicker CVD-W and W1%La samples, resulting from diffusive transport into the bulk.
(5) Retention in CVD-W2C was somewhat higher than that in CVD-W for temperatures below 300oC, most likely because of trapping at trace C impurities in the bulk, at impurities and porosities in micro-structural defects or at beam-induced damaged sites produced by recoil C.
(6) Desorption peaks (D2 + HD) were observed at similar temperatures (130, 300, 400 and 530oC) for these W and W2C materials, with the relative magnitudes varying from material to material.
(7) Implantation into C-coated tungsten specimens results in retention that is orders of magnitude greater than that in a pure tungsten surface. Implanted deuterium was released primarily as D2 and CD4 with TDS peaks at 750°C and 525°C, respectively.
Annealing studies for C-coated W indicated little inter-diffusion of C and W for temperatures less than 800oC.
0 15 30 45 60 75 Elapsed time (min)
0.00 0.30 0.60 0.90 1.20 1.50
(E15)Gas release (D/min)
0 200 400 600 800 1000
Temperature (o C)
Temperature W1NOANC-100 W1NOANB-200 W1NOANA-300
Figure 1. TDS spectra for un-annealed 25-µm W foils implanted at 100°C, 200°C and 300°C.
0 15 30 45 60 75
Elapsed time (min) 0
1 2 3 4 5 6 7 8
(E15)
Gas release (D/min)
0 200 400 600 800 1000
Temperature (o C)
Temperature W11200D-100 W11200E-200 W11200B-300
Figure 2. TDS spectra for 25-µm W foils annealed at 1200°C and implanted at 100°C, 200°C and 300°C.
0 15 30 45 60 75 Elapsed time (min)
0.00 0.20 0.40 0.60 0.80 1.00
(E15)Gas release (D/min)
0 200 400 600 800 1000
Temperature (o C)
Temperature CVDW3-4-100 CVDW3-2-200 CVDW3-3-300 CVDW3-6-400
Figure 3. TDS spectra for CVD-W sample implanted at 100°C, 200°C, 300°C and 400°C.
0 15 30 45 60 75
Elapsed time (min) 0
1 2 3 4 5 6
(E15)Gas release (D/min)
0 200 400 600 800 1000
Temperature (o C)
Temperature CVDW2C2-2-27 CVDW2C2-3-100 CVDW2C2-4-200 CVDW2C2-7-300
Figure 4. TDS spectra for CVD-W2C sample implanted at 27°C, 100°C, 200°C, and 300°C.
0 10 20 30 40 50 60 Elapsed time (min)
0.00 0.20 0.40 0.60 0.80 1.00
(E-8)QMS signal (relative)
0 100 200 300 400 500 600 700 800 900 1000
Temperature (o C)
QMS mass-4 QMS mass-20 Temperature
Figure 5. TDS spectra (Mass-4 is D2 and Mass-20 is CD4) for C-coated W1%La sample, implanted at 200°C with 500 eV/D ions to a fluence of 1.1x1023 D/m2.
0 100 200 300 400 500
Implantation exposure temperature (oC) 10 18
10 19 10 20 10 21
Retained deuterium (D/m2 )
Unannealed W foil
C-coated W1La W foil (1200OC ann.)
CVD-W2C disc CVD-W disc
W1La disc (1000OC ann.)
W perm foil (450OC ann.)
W perm foil (1000OC ann.) W perm foil (1400OC ann.)
Figure 6. Deuterium retention data from implantation/TDS experiments for un-annealed and annealed W foil, W1%La discs, C-coated W1%La discs, CVD-W discs and CVD-W2C discs.
Results of this work [4-6] demonstrated that retention of deuterium implanted into tungsten and tungsten carbide samples is highly dependent on the material type and structure, anneal condition and the presence of free carbon. Consequently, retention in W-C mixed material layers and carbon-covered tungsten PFC components may be dominated by uptake in the carbon.
This work was performed within an IAEA Co-ordinated Research Project (CRP) on
“Plasma-Material Interaction (PMI) Data for Mixed Plasma Facing Materials in Fusion Reactors” and supported by the US Department of Energy, Office of Sciences, under DOE Idaho Operations Contract Number DE-AC07-99ID13727.
REFERENCES
[1] ANDERL, R. A., CAUSEY R. A., DAVIS, J. W., DOERNER, R. P., FEDERICI, G., HAASZ, A. A., LONGHURST, G. R., WAMPLER, W. R., WILSON, K. L., J. Nucl.
Materials273 (1999) 1–26.
[2] ANDERL, R. A., LONGHURST, G. R., PAWELKO, R. J., OATES, M. A., J. Fusion Energy 16 (1997) 95–100.
[3] ANDERL, R. A., “Initial Deuterium implantation thermal desorption experiments for Be and C-coated Be,” Engineering Design File, EDF No: ITER/US/96/TE/SA-13, August 7, 1996, INEEL, Idaho Falls, ID.
[4] ANDERL, R. A., PAWELKO, R. J., SCHUETZ, S. T., J. Nucl. Materials 290-293 (2001) 38–41.
[5] ANDERL, R. A., PAWELKO, R. J., SCHUETZ, S. T., “Deuterium retention in W foil, CVD-W and CVD-W2C,” INEEL External Report INEEL/EXT-2000-00702, June, 2000.
[6] ANDERL, R. A., “Deuterium implantation and mobilization behavior in carbon-coated tungsten,” Engineering Design File, EDF No: ITER/US/98/TE/SA-14, July 17, 1998, INEEL, Idaho Falls, ID.
[7] ANDERL, R. A., HOLLAND, D. F., LONGHURST, G. R., PAWELKO, R. J., TRYBUS, C. L., SELLERS, C. H., Fusion Technol. 21 (1992) 745–752.
MIXED-MATERIAL HYDROGEN INVENTORY AND REMOVAL TECHNIQUES IN PISCES
R.P. DOERNER and the PISCES Team
Center for Energy Research, University of California – San Diego, La Jolla, California, United States of America
Abstract
The deuterium inventory in mixed-material surface layers formed during plasma bombardment of beryllium and tungsten samples has been investigated. The temperature of the sample during the formation of the layer plays a dominant role in determining the deuterium content of the layers. For carbon containing mixed-material films, the retention properties of the films are similar to that of pure graphite and can easily dominate the retention expected in the underlying substrate material. Cathodic transfer arc cleaning has been investigated as a mechanism to remove mixed-material films after they have formed on plasma-facing materials. The arc cleaning technique has been demonstrated to reduce the amount of deuterium in the coated samples to levels below our detection limit.