24P058-P
Gas retention in Tungsten exposed to Noble gas plasmas
希ガスプラズマ照射を受けたタングステンのガス吸蔵特性
Miyuki Yajima1 , Masato Yamagiwa1, Shin Kajita2, Noriyasu Ohno1,Masayuki Tokitani3, Naoaki Yoshida4
矢嶋美幸1 , 山際 正人1, 梶田 信2, 大野 哲靖1,
時谷 政行3, 吉田 直亮4

1

Department of Energy Engineering and Science, Graduate School of Engineering, Nagoya University, Furo-cho,Chikusa-ku, Nagoya, Aichi, 464-8603, Japan
2
EcoTopia Science Institute, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8603, Japan
3
National Institute for Fusion Science, Oroshi 322-6, Toki, 509-5292, Japan
4
Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen Kasuga, Fukuoka,816-8580, Japan
名古屋大学工学研究科エネルギー理工学専攻 〒464-8603 名古屋市千種区不老町2
名古屋大学エコトピア科学研究所 〒464-8603 名古屋市千種区不老町
3
核融合科学研究所 〒509-5292 土岐市下石町322-6
4
九州大学応用力学研究所 〒816-8580 春日市春日公園6-1

1

Tungsten specimens were exposed to pure Ar or Ne plasmas at 1000-2000 K and several incident ion
energies. Even under the irradiation condition under which the tungsten nanostructures were formed by He
plasma irradiation, holes/bubbles and fiberform nanostructure were not formed on the surface by exposing
to Ar or Ne plasmas. In addition, EDX results supported the results that Ar and Ne did not remain in thesample.

1. Introduction
Tungsten (W) has a high melting point, lowneutron activation cross-sections and low tritium
retention, so that it is a candidate of plasma-facing
materials. In spite of these advantages, it is known
that helium holes/bubbles [1,2] and fibreform
nanostructure [3,4] are formed on tungsten surface
by exposing to He plasma. In addition to He, Neand Ar are introduced to fusion plasma for radiative
cooling. Those noble gases have potential to form
irradiation damages like bubbles and nanostructures.
However, those irradiation effects have not been
fully understood yet. Thus, this study aims toinvestigate the interaction between noble gas
plasmas and tungsten.
2. Experimental
Specimens were powder metallurgy W disks(Nilaco.Co.) 5 mm in diameter. The polishedspecimens were irradiated by noble gas plasmas in
the linear divertor plasma simulator (NAGDIS-II[5]). Irradiation condition is 1000-2000 K in thesurface temperature and higher than 20 eV inincident ion energy. Those conditions are the one inwhich the tungsten nanostructure is easily formed
by He plasma irradiation [6]. After the irradiation,

the irradiated surface was analyzed by scanningelectron microscopy (SEM), transmission electron
microscopy (TEM), and energy dispersive X-ray
analysis (EDX).
3. Results and discussion
3.1 Analysis of irradiation area and cross-sectional
Figure 1(a) shows a cross-sectional TEM imageof the Ar irradiated surface. The incident ion energy,
surface temperature, and ion fluence were 100 eV,1650 K and 2.8×1025 m-2, respectively. Those
irradiation conditions are the one in which thetungsten nanostructure is easily formed by Heplasma irradiation. For example, figure 1(b) showsa cross-sectional TEM image of the He irradiatedsurface [6]. The incident ion energy, surface
temperature and ion fluence were 50 eV, 1400 K
and 5.5×1025 m-2, respectively. Figure 2(b) shows adramatic change in the surface morphology.
However, on the sample irradiated with Ar plasma(Figure 1(a)), holes/bubbles and fibreform
nanostructure were not observed on the surface.
Also, for the case of Ne ion irradiation,
holes/bubbles and fibreform nanostructure were notobserved.

3.2 Analysis of EDX
Figure 2 shows the cross-sectional SEM
micrograph of specimen, which were exposed topure Ar plasma at 1650 K and 100 eV with the Ar
fluence of 2.8 × 1025 m-2. Figure 3 shows thecompositional analysis of the cross-section in figure
2. EDX spectra taken from the rine area regions ofmarked 'A' and 'B' in figure 2. Near the plasma
irradiated surface is 'A'. Meanwhile, 'B' is the bulk
tungsten.
EDX spectra shows Ar, Mo, C, and W peak. The
presence of Mo is likely due to the sample holder ofEDX, which is made of Mo. O are likely due tosurface oxide passivation and C adhered to tungsten
surface on contact with atomosphere when targets areremoved from NAGDIS-II after cooling to ambient
temperature. The Ar peak of 'A' and 'B' is small
compared with W peak. The Ar peak level is aboutnoise level. Therefore, EDX result shows thatsufficient amounts of Ar did not remain in thesample. Also, for the case of Ne ion irradiation,
recognizable Ne peak was not observed. EDX
results supported the results that sufficient amountsof Ar and Ne did not remain in the sample.

Figure 3. EDX spectra taken from the rine area regionsof marked 'A' and 'B' in figure 2.

4. Conclusion
In the present work, Tungsten exposed to pure
Ar or Ne plasma at 1000-2000 K and several
incident ion energy, even under the irradiation
condition that the tungsten nanostructure is formed
by He plasma irradiation. However, holes/bubbles
and fiberform nanostructure were not formed ontungsten surface by exposing to Ar or Ne plasmas.
In addition, EDX results supported the results thatsufficient amounts of Ar and Ne did not remain in
the sample. It is likely that holes/bubbles andfiberform nanostructure cannot be easily formed ontungsten surface by the exposure to Ar or Ne
plasmas, even under the irradiation condition underwhen the tungsten nanostructure is formed by He
plasma irradiation.

Figure 1. TEM images are Ar (a) and He ( b [6] ).

Acknowledgments
The authors thank Dr. Tokitani at National
Institute for Fusion Science and Professor Yoshida
at Kyusyu University for useful discussion andcomments in this work.

Figure 2. Cross-sectional SEM micrograph of W target
that was exposed at exposed to pure Ar plasma.

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J. Nucl. Mater. 283-287 (2000)1134.
[2] D. Nishijima, M.Y. Ye, N. Ohno, S. Takamura,
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[4] M.J. Baldwin and R.P. Doerner, Nucl. Fusion 48(2008) 035001 (5pp).
[5] S. Takamura, N. Ohno, D. Nishijima, Y. Uesugi,
Plasma Sources Sci. Technol.11 (2002)A42[6] S. Kajita, W. Sakaguchi, N. Ohno, N. Yoshida andT. Saeki, Nucl. Fusion 49 (2009) 095005 (6pp).

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