反射率測定によるLHD第一壁ヘリウム燃料粒子吸蔵分布

反射率測定によるLHD第一壁
ヘリウム燃料粒子吸蔵分布評価の試み
G. Motojima1, M. Yajima1, S. Masuzaki1, M. Tokitani1, N. Yoshida2,
Y. Ueda3, M. Oya3, H. Yamada1, R. Sakamoto1, H. Tanaka1,
T. Morisaki1, M. Sakamoto4, H. Kasahara1 and LHD experiment
group1
1National
Institute for Fusion Science,
322-6 Oroshi-cho, Toki, Gifu 509-5292, Japan
National
Institutes
of
Natural
Sciences,
2Research
Institute for Applied Mechanics, Kyushu University, 6-1, Kasuga, Fukuoka 812-8580, Japan
3Graduate
School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan
4Plasma
Research Center, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan
This work is performed with the support and under the auspices of the NIFS Collaboration
Research program (NIFSUMPP003-1 and NIFSULPP037).
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
Outline
Global particle balance analysis and its relationship with the plasma
wall interaction (PWI) emerging for the first time in long pulse
helium discharges over 40 min. on the Large Helical Device (LHD).
(i) Global particle balance in long pulse helium
discharges
the wall retention has a phased characteristics and a possible
explanation of the characteristics is discussed.
(ii) Its relationship with PWI
G. Motojima

Retention property of helium in the deposition layer on the first wall
the mixed-material deposition layer which plays an important role of the
wall retention is successfully quantified by the reflection measurement.

Retention property of helium in the divertor plate
helium retention of the graphite is observed in the sample analyses by
the ion beam and plasma exposure experiments
第12回QUEST研究会プログラム、九州大学、20160920
1/17
Inside the LHD vacuum vessel
First wall
(SUS316)
 Plasma facing components
 Total area of PFCs: 700 m2
 First wall panels: SUS316L (~650 m2)
 Divertor plates: Graphite (~50 m2)
G. Motojima
First wall
(SUS316)
17 April 2013, S. Masuzaki
第12回QUEST研究会プログラム、九州大学、20160920
NBI
armor
(C)
2/17
long-pulse helium discharge
• Heated by ICH + ECH (1.2 MW × 48 min = 3.4×103 MJ).
• The heating energy injected into plasma is a new world record in toroidal plasmas.
• A line-averaged electron density is 1.2 × 1019 m-3, and electron and ion
temperatures of 2 keV are obtained.
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
Phased wall retention is observed for
the first time in long pulse discharge
2min. discharge
28min. discharge
G. Motojima et al., J. Nucl. Mat. 463 (2015) 1080.
48min. discharge
He sink
@Phase1
He source
@phase2
He sink@phase3
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
3/17
70
60
50
40
30
20
-200
300
800
1300 1800 2300 2800
Time [s]
He amount in wall
Temperature [oC]
Simple hypothesis:
two kinds of helium reservoir
Time, Temperature
To understand the mechanism of dynamic helium retention, characteristics of the
retention of the PFCs on parameters such as time and temperature is crucial. =>
4/17
9/20
Discussion with specimen analysis
第12回QUEST研究会プログラム、九州大学、20160920
G. Motojima
Outline
Global particle balance analysis and its relationship with the plasma
wall interaction (PWI) emerging for the first time in long pulse
helium discharges over 40 min. on the Large Helical Device (LHD).
(i) Global particle balance in long pulse helium
discharges
the wall retention has a phased characteristics and a possible
explanation of the characteristics is discussed.
(ii) Its relationship with PWI

Retention property of helium in the deposition layer on the first wall
the mixed-material deposition layer which plays an important role of the
wall retention is successfully quantified by the reflection measurement.

Retention property of helium in the divertor plate
helium retention of the graphite is observed in the sample analyses by the
ion beam and plasma exposure experiments
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
First wall
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
Retained He increases proportional to the
thickness of the deposition layer
M. Tokitani et al., J. Nucl. Mat. 463 (2015) 91 .
 Relationship of total retention of He desorbed at 300-600K and thickness of the deposition
layer as a function of an exposure time
 Amount of He retention is linearly proportional to the thickness of the deposition layers.
 Saturation of a He retention was not observed even at around 10,000 s exposure.
The contribution of the deposition layer on the first wall to helium retention can be deduced
if the distribution of the deposition layer distribution is evaluated.
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
5/17
Reflection coefficient measurement
using compact color analyzer
Portable Color Meter with Integrating Sphere DM-1
（Hitachi Kinzoku, 2014）
integrating sphere
monitor
grip
measurement
window
switch
Measurement：RGB（Red, Green, Blue）, HSV（Hue, Saturation, Value）
Measurement window diameter：Φ 8.1 mm
Internal diameter of integrating sphere：Φ 47 mm
Light source： white LED
RGB range：0~1023
Weight： ~160 g
Measurement time： 3 seconds
Simple and in-situ measurement is possible in compact color analyzer.
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
6/17
QUESTにおける反射率測定
プラズマ対向壁の膜厚は上下非対称性を示した
下地、修士論文（2015年）
GAMMA-10においても、壁面の変色情報から壁材料の損耗・輸送・再堆積の過程について
評価することを目的として、反射率測定が行なわれている。肉眼での観察では、真空容器内
構造物の周辺には指向性を持った変色が起きていることが確認されており、カラーアナライ
10におけるプラズマ対向壁面の変色評価」
ザーにより壁面の反射率測定 を行い変色を定量的に測定した。 「GAMMA
伊能、プラ核第３３回年会2016、東北大学、 30aP76
11/
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
7/17
Location of
long-term exposed samples
Inner Board
Outer Board
10
9
4
8
7
6
5
In this study, the averaged RGB value is regarded as the reflection
coefficient because the red, green, and blue intensities showed the same
tendency for each object measured.
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
8/17
Cross sectional TEM images of long-term
exposed samples
 In some samples, the boundary of the deposition layer is difficult to identify. In
such a case, tungsten is deposited on the surface (the Nagata method).
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
9/17
Binarization method for the thickness evaluation of
the deposition layer
Example of cross-sectional TEM images
before/after binarization method
Thickness vs. RGB
thickness
 The RGB value and thickness are shown to have an exponential relationship.
 The RGB value identifies the thickness up to several hundred nm.
 The sample with the thickness over 1000 nm is excluded from the fitting due to
the evaluation limitation.
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
10/17
Result of reflection coefficient
measurement
G. Motojima et al., Plasma. Fus. Res. 10 (2015) 1202074.
divertor
10
Saddle portion Inner
outer
9
plasma
(Rax = 3.60m)
inner
divertor
4,
5
6,7,8
Outer
 In outer torus side: almost all stainless plates are close to black.
In inner torus side: the RGB value is close to white except for the area near the divertor plates.
These results suggest that the outer torus side is a deposition dominant area and the inner torus side is mainly
an erosion dominant area.
 The RGB value is close to white in the case where the stainless plates are located near the plasma and close to
black if they are located far from the plasma. This suggests the relation between the RGB value and the distance
of the stainless plates to the plasma.
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
11/17
Distribution of the thickness
of deposition layer
 The outer torus side is deposition-dominant, while the inner torus side is primarily erosiondominant except for the area near the divertor plates.
 Reflection coefficient measurements indicate that approximately 60% of the area on the
measured coil can, which is a part of the first wall, is coated with a deposition layer over 10 nm
thick, suggesting that this area plays a role of the wall retention.
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
12/17
Order estimation of the contribution of
the first wall to helium retention
If we assume that the coated area over 10 nm retains helium constantly, the total
average retention amount for the long pulse discharge can be calculated as 1.6 × 1016
He/m2 s × 110 m2 × 2880 s = 5.1 × 1021 He. Since the total wall retention is
estimated at 2.2 × 1022 He as shown in Table I, the contribution of the wall retention
on the helical coil can is evaluated at about 25%.
Helical coil can
torus
Upper and
Lower Port
Outer and Inner
Port
200 m2
100 m2
200 m2
150 m2
60% coated
almost area
coated
almost area
coated
unknown
It is confirmed that almost areas are covered with the
deposition layer. Therefore, the surface area of 410 m2 is at
least coated by the deposition layer. The total average
retention amount for the long pulse discharge can be
estimated as 1.6 × 1016 He/m2 s × 410 m2 × 2880 s = 1.8
× 1022 He, which is close to the total retention amount by
the global particle balance.
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
13/17
Divertor plates
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
Fluence dependence is compared between with
LHD and Lab. experiments.
M. Oya et al., to be submitted to JNM.
 Laboratory experiments show that the retention ratio (= Retention/Fluence)
were 0.1 ~ 0.5 %
 In LHD, typical divertor flux is ~8x1021/m2s -> totally ~2.4x1024 He for 300 s of
Phase 1 (assuming wetted area as ~1 m2).
Retention ratio is calculated at
Lab. experiments have shown the similar characteristics with the LHD experiments
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
14/17
TDS result shows the peak desorption rate is the
same order as the desorption rate (~1018 He/s) in
the phase 2
100 s discharge condition
As temp. increasing up to 500 K, He retention in graphite decreases.
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
15/17
Qualitative understanding of the dynamic
wall behavior has been obtained
He amount in wall
Divertor
plates
20
40
1.5x1020
30
1.0x1020
20
19
5.0x10
0.0
0
10
2000 4000 6000 8000 10000
0
Thickness of depo. layer [nm]
He desorbed at 300-600K [He/m2]
The experimental results suggest that the first wall contributes a constant retention by the
formation of the deposition layer during the discharge. On the other hand, the divertor
contributes the retention only at the first phase of the discharge and then decrease the
retention due to the increase of the surface temperature of the divertor.
TDS results First wall
TDS results
50
2.0x10
Graphite
Exposure time [s]
First wall with
deposition
layer
Time, Temperature
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
16/17
Summary
This study reports the global particle balance analysis and its relationship with the plasma wall
interaction emerging for the first time in long pulse helium discharges reaching 48 min on the
Large Helical Device (LHD).
Experimental observations show that
(i) the wall retention has phased characteristics.
(ii) the mixed-material deposition layer which plays an important role in the wall retention is
quantified by the reflection coefficient measurement, suggesting that the depositiondominant area such as the outer side and near the divertor on the helical coil can, which is a
part of the first wall, in the measured toroidal section is a possible sink of the wall retention.
(iii) helium retention of the graphite is observed in the sample analyses by the ion beam and
plasma exposure experiments.
The order estimation of the wall retention is discussed by the experimental results between the
global particle balance and the plasma exposed samples analyses, resulting that the differences
of the plasma facing material, which are composed of the first wall with stainless steel and the
divertor with graphite, is a possible candidate to explain the wall retention qualitatively.
G. Motojima
第12回QUEST研究会プログラム、九州大学、20160920
17/17