24P057-P
Evaluation of deuterium dynamics in materials with device of Plasma Surface
dynamics with Ion Beam Analysis (PS-DIBA)
イオンビーム解析を用いたその場計測装置PS-DIBAによる材料中での重水素動的挙動の評価
Masato Yamagiwa1, Yuki Nakamura1, Noriaki Matsunami2, Makoto Takagi1, Noriyasu Ohno1,Shin Kajita2, Masayuki Tokitani3, Suguru Masuzaki3 and Akio Sagara3
山際 正人, 中村 祐貴, 松波 紀明, 高木 誠, 大野 哲靖, 梶田 信,
時谷 政行, 増崎 貴, 相良 明男
1

Department of Energy Engineering and Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
名古屋大学大学院工学研究科 〒464-8603 名古屋市千種区不老町
2Ecotopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
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3National Institute for Fusion Science, Oroshi-cho 322-6, Toki, Gifu 509-5292, Japan
核融合科学研究所 〒509-5292 土岐市下石町322-6
We developed a new compact divertor plasma simulator PS-DIBA (Plasma Surface Dynamics with Ion
Beam Analysis), a device which makes it possible to carry out in-situ ion beam analysis of deuterium
retention under high density plasma irradiation, relevant to divertor plasma conditions. Dynamic behavior
of deuterium retention in tungsten was investigated during and after plasma exposure by using Nuclear
Reaction Analysis (NRA) in PS-DIBA. Decay time of deuterium retention of ITER grade W after
plasma disappearance was about 5 hours, which was much shorter than that of powder metallurgy
tungsten (40 hours). The result indicateed that the decay time could be different depending on
manufacturing methods for W.

1. Introduction
Control of hydrogen isotope retention inplasma-facing components (PFC) is essential toestablish steady-state operation. In particular,
tritium retention inside the vacuum vessel poses
serious problem in the operation of the ITER togive a limit of the number of plasma discharges.
Therefore, the prediction of dynamic behavior ofhydrogen isotope retention behavior in PFC isconsiderable for practical purpose. The dynamic
retention leads to several effects, such as hydrogen
recycling and net erosion of plasma-facing surfaces.
Especially, important issues related to dynamic
retention are Optimization of the timing of fuelingand Flux dependence of chemical sputtering.
However, these phenomena remain relativelypoorly understood, primarily due to the lack ofproper plasma-surface analyses except for a few
devices [1-3].
Hence, we have developed a device called'Plasma Surface Dynamics with Ion Beam Analysis'(PS-DIBA) including nuclear reaction analysis(NRA), elastic recoil deflection (ERD) toinvestigate the dynamic retention property indivertor plasma environments. By using thePS-DIBA, the temporal evolution of deuterium
retention on tungsten was investigated during andafter plasma irradiation.

2. Experiments
Figure 1 shows a schematic of the PS-DIBA
device. The steady state plasma was produced witha DC arc discharge using a zigzag-shaped LaB6cathode, which was heated up to 1500 K by
direct-current Joule heating. Anode is made of acopper tube cooled by water. Discharge gases are
introduced between the two cathodes, contributing
to an efficient usage of the neutral gas for thedischarge.

Fig.1 Schematic top view of PS-DIBA device.

Figure 2 shows the discharge power dependencesof electron density, ne, and temperature, Te, at thecenter for a plasma column. In helium plasma, nereaches 1.1x1019 m-3 at the discharge power of 2.7
kW. The incident ion energy can be controlled byelectrically biasing the sample.

(a)Fig.2 Discharge power dependence of the electron
density ne and electron temperature Te.

The deuterium retention in sample were analyzed
by NRA of 1.0 MeV D(3He,p)α using a Van deGraaff accelerator. The solid-state detectors for
NRA is sealed by mylar film to maintain highvacuum state and Al film is also used to repel
plasma photons. A rotating gold plate was equipped
between the sample and the beam exit and used fora beam chopper, where the beam current wasmonitored by using RBS.
3. Experimental Results
ITER grade tungsten was used for specimens.
Figure 3 shows the irradiation sequence with an
initially fresh tungsten sample. The plasma
parameters were gradually changed in Fig. 3(b).
The retention was determined by integrating themeasured D concentration over the entire detection
depth. The measurement result in the present study[4] also represents a similar tendency, indicating theretention amount is dependent primarily on thesurface temperature. Therefore, precise control ofsurface temperature is required independently fromthe plasma condition in future study. After plasma
termination, D retention gradually decreased. The
desorption time constant was evaluated to be 5.0(+1.7/-1.1) hours. We have conducted same
experiment by using powder metallurgy tungsten(PM-W). The preliminary result of time evolutionof D retention for PM-W shows that the desorption
time constant is about 40 hours, which is much
longer than that in ITER R&D tungsten.
4. Summary
Plasma surface dynamics with ion beam analysis(PS-DIBA) device has been set up on the line at theVan de Graaff accelerator. The dynamic behaviourof deuterium retention on tungsten was investigatedFig.3 (a) Deuterium retention in ITER grade W measured
with NRA. (b) is enlargement of (a) and deuterium
plasma exposure conditions.

by using PS-DIBA.The deuterium retention ofITER grade tungsten was mainly determined bysample temperature. The decay time of ITER grade
tungsten was shorter than that of PM-W, whichsuggested that the decay time depends on
manufacturing method of tungsten. In this study,
because of the lack thermal control, plasma flux
was selected to keep the sample temperature low.
Acknowledgments
This work is performed with the support andunder the auspices of the NIFS Collaboration
Researchprograms(NIFS08KOBP010,NIFS11KLEF003).
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