S-R5-2
Surface analysis techniques and in-situ measurements of dust particles infusion devices
核融合プラズマ装置で発生したダストに対する表面分析評価およびその場計測法について
Naoko Ashikawa1), Nobuyuki Asakura2), Kazunori Koga3), Makoto Tabata4), Ichiro Adachi5),
Takao Hayashi6), Masakatsu Fukumoto6), Katsushi Nishiyama3), Masaharu Shiratani3), Takeo
Muroga1) and the LHD experimental group1)
1)

2)

3)

4)

5)

6)

6)

3)

芦川直子 ，朝倉伸幸 ，古閑一憲 ，田端誠 ，足立一郎 ，林孝夫 ，福本正勝 ，西山雄士 ，
3)
1)
1)
白谷正治 ，室賀健夫 ，LHD 実験グループ
1)

National Institute for Fusion Science, 322-6, Oroshi-cho, Toki, Gifu 509-5292,Japan
核融合科学研究所 〒509-5292 岐阜県土岐市下石町 322-62)
Japan Atomic Energy Agency, 2-166 Omotedate, Obuchi, Rokkasho, Aomori 039-3212 Japan
日本原子力研究開発機構，〒039-3212, 青森県上北郡六ケ所村大字尾駮字表舘 2 番 1663)
Kyushu University, 744, Moto-oka, Nishi-ku, Fukuoka, Fukuoka, 819-0395, Japan
九州大学大学院システム情報科学府 〒819-0395 福岡県福岡市西区元岡 7444)
Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, 252-5210, Japan
宇宙航空研究開発機構，〒252-5210 神奈川県相模原市中央区由野台 3-1-15)
High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaragi, 305-0801, Japan高エネルギー加速器研究機構，〒305-0801 茨城県つくば市大穂 1-16)
Japan Atomic Energy Agency, Mukoyama 801-1 Naka 311-0193, Japan
日本原子力研究開発機構，〒311-0193 那珂市向山801-1
Investigation of dust particles in the fusion device is potential problems for impurity accumulations
and tritium retentions. In this talk, two kinds of topics are presented. The first is the surface analysis
method using collected dust particles after vacuum vent. The second is the in-situ measurement of
dust counting and trapping. As one example of experimental data, a dust detection using silica aerogelin LHD is shown.

1. Introduction
Dust generation in the fusion device and its ejection
to the confined plasma are potential problems for
impurity accumulations and tritium retentions.
Movements and characteristics of the dust particles havebeen measured by different diagnostics such as fastvisible and IR TV cameras, laser scattering, andelectrostatics detector (developed by C. Skinner inPPPL) in stellarator/heliotrons and tokamaks. Surface
analysis on the first wall can provide properties andcompositions of dust particles, but information of thedust dynamics at the implantation or deposition is lost.
In this talk, two kinds of topics are presented. The
first is the surface analysis method using collected dust
particles after vacuum vent in Fusion devices. An
estimation of remained dust particles and locations in
vessel in ITER are important, and then many groups infusion devices have been done these researching works.
In Japan, LHD in NIFS, JT-60U in JAEA andTRIAM-1M in Kyushu Univ. were collected. Major
method of surface analysis is scanning microscope(SEM) with energy dispersive spectroscopy (EDX), an
optical microscope and microbalance. In the limited case,transmission electron spectroscopy (TEM), X-ray
photoelectron spectroscopy (XPS), thermal desorption
spectroscopy (TDS), laser Raman spectrum are used.
Diameters of dust particles are reported from the order of
1 nm to a few 100 microns and then an observation of
those small particles is needed additional technicalmethod. For example, if small particles have to install invacuum area of analyzer, such as SEM, TEM and XPS,
dust particles have to be connected or coated on the otherbase material.
The second is the in-situ measurements of dust
counting and trapping. For example, a laser scattering
method counts passing dusts on the optical axis and anelectrostatics detector counts dust particles attached
between vias grids applied voltage. These in-situ data areimportant to discuss a relation between operationalparameter of plasmas and produced dust particles.
Some of analytical method is the same in theresearching fields of space plasmas and industries. As

one example, a dust detection using silica aerogel isshown in this abstract.

increases the surface temperature. At present, thermal
effect is considered as the main reason.

2. Experimental result
Silica (SiO2) aerogel has been used as a dust collectorin space plasma research: an aerogel (a silicon-basedsolid with porous) has sponge-like structure in which
99 % of the volume is empty space. In fusion devices,
the same type of silica aerogel has been tested to detectaccelerated dust particles and their trajectories, i.e.
incident dust particles are trapped into the aerogel, andthey are remained after vacuum vent. Information of
the dust transport such as trapped angle and velocity
as well as the particle properties such as size, shape andmorphology can be evaluated by surface analysis. Fourkinds of Silica aerogels with different densities,
0.020-0.061g/cc, were provided by KEK/JAXA. In thisexperiment, the highest surface density (0.0061g/cc) waschosen.
Two kinds of materials, i.e. Silica aerogel (15 mmx15 mm, t = 15 mm) and Si samples (10 mm x20 mm, t= 0.6 mm), are installed on the same holder. This holder
is set on the movable probe system at the 4.5 lower port
and the top of this holder was kept at the first wall level
during LHD experiments. The total exposure time duringhydrogen plasma discharges is about 300 seconds and asurface temperature is about room temperature. After thisexperiment, Silica aerogels were extracted from highvacuum level, 10-6 Pa to atmosphere of 104 Pa. Surface
morphologies on the surface of aerogel were measured
by digital microscope (THX-1000, KEYENCE). One ofthese images are shown in Fig.1. The dust size of 10 x 20
micron is observed and the dust surface is the same levelof the aerogel surface. Thus, it is considered the dust
particle itself is trapped into the base aerogel.
Number density of dust particles trapped on theaerogel is two times larger than that on the Si target. Thismethod is applicable for analysis of the dust deposition
process without disturbance at changing pressure from ahigh vacuum area to atmosphere.
For comparison of the aerogel exposed to the plasma,
image of as-reserved aerogel surface is shown in Fig.2. It
is found that only the aerogel exposed to plasma have
many small wrinkles on the surface and small dots arebroken pieces of aerogel itself. At the last campaign in2009FY, the same type aerogel was exposed to glow
discharges in LHD. From the comparison of surface
morphologies on the side and the top surfaces on theaerogel, only the top surface have wrinkles, while theside surface looks flat surface similar to the as-received
aerogel. These results show that these wrinkles areproduced by the plasma exposure. Following two reasonsare considered. One is due to deposition of particle flux
such as plasma ions, neutrals and impurities during
plasma experiments or glow discharges. Second is due tothe thermal effect, i.e. heat load caused by plasma andradiation. Since aerogel material is low thermal
conductivity, even small heat load on the surface

Trapped dust
AerogelFig.1 Surface morphology of trapped dust
particle into silica aerogel. Magnification of thescope is 2000.

Fig.2 Surface morpholory of as-reserved
silica aerogel. White background is aerogel
surface.