24P078-P
Deuterium Permeation in Tungsten under Simultaneous
Deuterium and Carbon Irradiation
重水素・炭素同時照射下でのタングステン中の重水素透過特性
Han Yee Peng1, Heun Tae Lee1, Yusuke Ohtsuka1 and Yoshio Ueda1, Masakatsu Fukumoto2
Peng Han Yee1, Lee Heun Tae1，大塚 裕介1，上田 良夫1，福本 正勝2
1

Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
2
Japan Atomic Energy Agency, 801-1 Mukoyama, Naka, Ibaraki 311-0193, Japan1
大阪大学大学院工学研究科 〒565-0871 大阪府吹田市山田丘2-1
2
日本原子力研究開発機構 〒311-0193 茨城県那珂市向山801-1

Ion driven permeation of D through W under simultaneous D+C irradiation at 1 keV ion energy and 1020
m-2s-1 irradiation flux was studied as a function of specimen temperature (550 K < Tw < 1050 K) and C
fraction in the incident flux (0.1% < fC < 3%). A prominent feature of the D permeation under simultaneous
D+C irradiation is the temperature dependent increase in steady state D permeation flux with a maximum
at 700-800 K. W/C mixed surface layer was observed from XPS analysis. This W/C mixed layer formation
was interpreted to reduce the recombination coefficient or/and diffusivity, resulting in the observed
increase in permeation flux.

1. General
Tungsten (W) is a leading candidate for plasma
facing material in future fusion reactors and will
be used in divertor region of ITER. Although W
has lower hydrogen retention under hydrogenisotopes (H, D, T) irradiation, there still remain
important issues under fusion environment suchas release and diffusion processes of H isotopes
in W. At present, a tungsten divertor withcarbon-fibre composite as the strike plate isplanned for the initial stages of ITER. Carbon (C)impurities resulting from erosion, transport, anddeposition processes will result in simultaneous
irradiation of W by H and C species. The
resulting interaction will modify the tungsten
material forming a W-C “mixed-material” withproperties different from a pure W material. Thischange will affect both H release and diffusion
processes in W, with corresponding impact onfuel recycling and retention. Therefore, a clear
understanding of the impact of C on H diffusion
in W is desirable.
The diffusion behavior of hydrogen isotopes inW can be evaluated by studying the permeation ofdeuterium (D) in W. Previous studies of H
retention in mixed W-C materials indicate that thepresence of C on the W surface increases theinward transport of H into W bulk [1]. However,the data on the effect C on hydrogen ion driven
permeation in tungsten is very limited with only
one previous study having examined single D ion
driven permeation in carbon film coated W [2]. In
this study, we present experimental results of ion
driven permeation of D through W undersimultaneous D+C irradiation, and show theeffect of C on D transport in W.
2. Experimental
Permeation experiments were performed using ahigh flux ion beam test device (HiFIT) [3], wherethe incident energy of the ions was 1 keV at a flux of1020 m-2s-1. The specimens used were stress-relieved
99.99% pure polycrystalline W with diameter of
34.8 mm and thickness of 30 μm [4]. The W
specimen was isolated from the permeation side bysealing it between two standard conflat flanges anda copper gasket [4]. The specimen was irradiated atincident angle of 15o through an 8 mm diameter
aperture. The D permeation flux was measured byusingahighresolution
quadrupole
mass-spectrometer (MKS microvision plus) with amass range of 1-6 amu. The main experimental
parameters varied were the specimen temperature(550 K < Tw < 1050 K) and the C fraction in theincident flux (0.1% < fC < 3%). Following D+C
permeation experiments, the irradiated specimen
surfaces were observed under an optical microscope
and a scanning electron microscopy (SEM). Also,
the surface atomic compositions and the depth
profiles of the implanted C at the front surface
following irradiation were analyzed by X-ray
photoelectron spectroscopy (XPS) at Osaka
University and Japan Atomic Energy Agency(JAEA).
3. Results and Discussion
Temperature dependent increase in the Dpermeation flux under simultaneous D+C

irradiation was observed in comparison to D-only
irradiation case, with a value of 200 times larger at
700-800 K, as shown in Fig. 2. XPS analysis
showed that the surface was a mixed compositionof C and W. Hence, the increase in D permeation
flux can be interpreted as a reduction inrecombination coefficient or/and diffusivity due totungsten carbide formation at the incident surface.
In addition, temperature dependent increase inblister size on W surface was observed. This
indicates that the enhanced D diffusion by the C/Wlayer causes blistering on the W surface, since thediffusion of D into the W bulk is necessary forblistering [5]. However, the measured C/W surface
composition
wastemperature
independent,indicating that the C on the W surface was notdirectly correlated to the temperature dependent
increase in D permeation flux.

Permeation Flux (1017 D m-2s-1)

6.0

Tw = 620K

D+C(fC~1.4%)

5.0
4.0
3.0

D-only (x10)

2.0
1.0
0.0

020

40

60

80

100

Elapsed Time (min)Fig.1. Comparison of beam-on transient curves during
D-only and simultaneous D+C irradiation. The origin
corresponds to beam on time, and the D-only curve isscaled up by a factor of 10 for comparison. (Taken fromRef. [6])Permeation Flux (D m-2s-1)

1E19
D+C simulteneous
fc ~ 3%fc ~ 1.4%
fc ~ 0.9%
D-only (base line)
fc ~ 0.1%

1E18

1E17

1E16500

600

700

800

900

10001100Irradiation Temperature (K)Figure 2: Steady state D permeation flux plotted as afunction of temperature at different C fractions in theincident flux (0.1% < fC < 3%). (Taken from Ref. [6])We present permeation flux data under various
experimental conditions to discuss the temperaturedependency and C fraction dependency of D
permeation in W. Furthermore, we discuss themodification of the W surface and correlate themodified surface with changes in the permeation
flux data. Finally, we compare our result to thesimple diffusion theory of Doyle and Brice [7]which describes the steady state H transport in W tounderstand the C effect on D diffusion.
References[1] V. Kh. Alimov et. al.: J. Nucl. Mater. 375 (2008)
192.
[2] Yu. Gasparyan et. al.: Modeling of deuterium
permeation through tungsten coated with a carbon
film (2010) 19th PSI Conference, San Diego, U.S.,
P2-33H.
[3] Y. Ueda, H. Kikuchi, T. Shimada, et al.: Fusion Eng.
Design 61/62 (2002) 255-261.
[4] H.T. Lee, H. Tanaka, Y. Ohtsuka, Y. Ueda: J. Nucl.
Mater. 415 (2011) S696–S700.
[5] Y. Ueda et. al.: J. Nucl. Mater. 337-339 (2005) 1010.
[6] H.Y. Peng, H.T. Lee, Y. Ohtsuka, Y. Ueda:Ion-driven permeation of deuterium in tungsten bydeuterium and carbon-mixed ion irradiation, Phys.
Scr. T144 (2011), accepted.
[7] B.L. Doyle, B.K. Brice. Radiat Eff. 89 (1985) 21.