Deuterium concentration of co-deposited carbon layer by deuterium arc discharge
重水素アーク放電で作成した同時堆積炭素膜の重水素濃度
Jun Kanazawa, Yuji Nobuta, Yuji Yamauchi, Tomoaki Hino, Kenji Yokoyama, Satoshi, Suzuki,
Koichiro Ezato, Mikio Enoeda, Masato Akiba
1
2
金澤潤 、信太祐二 、山内有二 2、日野友明 2、横山堅二 3、鈴木哲 3、江里幸一郎 3、榎枝幹男 3、秋場真人 3
1.

Graduate School of Engineering Hokkaido University
kita13, nishi8, Sapporo, Hokkaido 060-8628, Japan
2. Faculty of Engineering Hokkaido University
kita13, nishi8, Sapporo, Hokkaido 060-8628, Japan
3. Japan Atomic Energy Agency
4-49 Muramatsu, Tokai-mura, Naka-gun, Ibaraki 319-1184, Japan
1.北海道大学大学院工学院 〒060-8628 北海道札幌市北区北 13 条西 8 丁目
2.北海道大学大学院工学研究院 〒060-8628 北海道札幌市北区北 13 条西 8 丁目
3.日本原子力研究開発機構 〒319-1184 茨城県那珂郡東海村村松 4 番地 49
Tritium retention of a carbon film deposited on the gap side surface of plasma facing
materials is a primary issue for fusion reactor because carbon layer in the gap is hardly toremove. In this study, deuterium concentration and retention profile in a gap were investigatedfor carbon films prepared by using deuterium arc discharge with carbon electrodes. Deuterium
retained in the carbon layer desorbed mainly in the form of D2, HD, CD4 and C2D4. The
amount of deposited carbon and retained deuterium in the gap decreased exponentially with theincrease of the depth and more rapidly decreased with decreasing gap width. The atomic ratiosof D/C of the carbon had almost no dependence on the distance from gap entrance and slightly
increased with increase in the gap width.

1. Introduction
Carbon material has been widely used asplasma-facing materials in present fusion devices
and is a candidate for the divertor target plate of
ITER. Divertor target is exposed to high particle
flux and heat load, and eroded. The sputteredcarbon atom is re-deposited in vacuum vessel
incorporating fuel hydrogen. Therefore, it isimportant to investigate the hydrogen retention on
co-deposited carbon layer. In particular, the tritium
retention in the side surface of gaps between
plasma-facing tiles is important because carbon
films in the gap could retain a lot of fuel hydrogenand it is difficult to remove [1]. In this study, weinvestigated the deuterium concentration ofco-deposited carbon layer in gap prepared bydeuterium arc discharge with carbon electrodes.
2. Experimental
Co-deposited carbon layers used in this study wereprepared using a D2 arc discharge. Fig.1 shows
schematic diagram of arc discharge device. The
sample stage had a gap with a depth of 100 mm,
and 10 molybdenum substrates (52×6×0.05 mm)
were set on the side surface of the gap. During thearc discharge, the carbon electrode was heated up
and sublimation of carbon occurred.

Ｄ 2gasGas flow controller

DG

Ｄ 2 arc discharge
Carbon electrode8 、 15、15 、 50mm
Mo

T.M.P+R.P.
OrificeFig.1 Schematic diagram of arc discharge device.

The emitted carbon atoms deposited on Mo
substrates in the gap incorporating deuterium atoms.
The voltage and current of the discharge were 10-20
V and 50 A, respectively. Discharge pressure waskept at 5-10 Pa and Substrate temp was: 673K. The
distances of the gap were varied from 8 to 50 mm.
After the arc discharge, the carbon layers depositedon Mo substrate were analyzed. The amount ofdeposited carbon was estimated from weight gain of
the substrates after the discharge by a microbalance.
The amount of retained deuterium in the carbon

layer was measured with thermal desorption
spectroscopy (TDS). Based on the measurements,
the deuterium concentration in the carbon layer wasestimated.
3. Results and discussion
Deuterium retained in the carbon layer desorbed
mainly in the form of D2, HD, CD4 and C2D4. Fig.2
shows typical thermal desorption spectra of
D-containing molecule for the carbon layer
prepared with at gap width of 50 mm. The D2 andCD4 desorption rate had a main peak around 1100 K
and 750 K, respectively. These desorption spectra
are similar to those of the isotropic graphite
irradiated energetic deuterium ions [2].

Fig.4 shows deuterium concentration of carbon
films against distance from gap entrance. The
deuterium concentration (D/C) had almost nodependence on the gap depth. The deuterium
concentration tended to increase with increase in
the gap width. The D/C for the gap width of 8, 15
and 50 mm were 0.15 - 0.25, 0.10 - 0.25 and 0.05 0.17, respectively.

Fig.4 Dueterium concentraition of carbon films vs distncefrom gap entrance.

Fig.2 Thermal desorption spectra of D2, HD and CD4for the carbon layer prepared at 50mm gap.

Fig.3 shows deuterium retention and weight gainof Mo substrate as a function of distance from gap
entrance. The amount of carbon deposition anddeuterium retention decreased exponentially withincrease of the gap depth, and decayed more rapidly
with decreasing gap width.

Fig.3 Deuterium retention and Weight gain of Mo
substrate vs distance from gap entrance.

4. References[1] T. Hino et al, Fusion Engineering and Design,61-62 (2002) 605-609[2] Y. Yamauchi et al., J. Nucl. Mater. 241–243(1997) 1016–1021.