05pE40P
水素プラズマとグラファイト壁の相互作用により発生するダスト粒子の輸送
Transport of dust particles generated due to interaction
between H2 plasmas and graphite wall
○立石 瑞樹1，古閑 一憲1，山下 大輔1，鎌滝 晋礼2，徐 鉉雄1，板垣 奈穂1,3，白谷 正治1，芦川 直子4，増崎 貴4，西村 清彦4，相良 明男4，LHD 実験グループ4○Mizuki Tateishi1, Morita Yasuhiko1, Daisuke Yamashita1, Kunihiro Kamataki1, Hyunwoong Seo1,Naho Itagaki1, Kazunori Koga1,Masaharu Shiratani1, Naoko Ashikawa2, Suguru Masuzaki2,Kiyohiko Nishimura2, Akio Sagara2, the LHD Experimental Group2
1
九州大学システム情報科学府, 2九州大学所基幹教育院, 3さきがけ, 4核融合科学研究所
1Faculty of Information Science and Electrical Engineering, Kyushu University, 2Fuculty of Artsand Science, Kyushu University, 3PRESTO Japan Science and Technology Agency, 4National
Institute for Fusion Science

H2 plasmaport

H2 plasma

port

ratio of dust flux towards back side
-2 -1
to target side (arb. units)
dust flux (m s )In fusion devices, dust particles produced due to plasma wall interaction may become safety hazard due
to tritium retention and their chemical reactivity. Dust particles also may cause deterioration of plasma
confinement [1]. Therefore, the maximum quantity of carbon dust particles in International Thermonuclear
Experimental Reactor is limited below 6 kg [2]. So far, we have developed a divertor simulator using helicondischarges to study generation and transport mechanisms of dust particles. Using the discharges, we havefound generation of dust particles in nm size due to interaction between plasmas and graphite target, which isa divertor material in Large Helical Device in National Institute Fusion Science, Japan [3,4]. Here wecollected dust particles in the divertor simulator to discuss mechanisms of dust transport from dust
generation region toward the reactor wall.
Experiments were carried out with the divertor simulator [4]. H2
face the target : spherical
810
face the target : flakegas was supplied at a pressure of 5mTorr. The discharging period was(a)back side : spherical0.25 s, and the interval was 1.0 s. Dust particles were produced dueback side : flake7
to interactions between a graphite target and H2 plasmas. Dust
10
particles were collected on c-Si substrates set in the radial direction
on a Ti holder placed at z=25 mm from the target and r =60, 80, 100,
610120, and 140 mm from the center of plasma column. The surface ofsubstrates faces the graphite target (target side) and discharge tube
510(back side). The inner radius of the reactor is 133 mm and substrates
at r =140 mm were set in the port. The size and shape of the dust
4particles collected on the substrates were measured with a scanning
1010electron microscope.
spherical(b)flakeCollected dust particles can be classified into two kinds: sphericalparticles and flakes. We have obtained the dust flux Γd of spherical
1particles and flakes toward the substrate, which is obtained by ns/ttotal,
where ns and ttotal are the area density of dust particles with size range
between 50 nm and 1 μm and the total discharging period (581 s),-110respectively. Fig. 1(a) shows distance dependence of dust flux. No
spherical particles are observed at r = 120 and 140 mm on back side.
As shown in Fig. 1(b), the ratio of dust flux towards back side to-2
10target side decreases with increasing r =60 to 100 mm. The flux ratio
04080120 160of flake dust drastically decreases by 1.5 order of magnitude withr (mm)increasing r=100 to 120 mm. It suggests that transport mechanisms Fig. 1. (a) Distance dependence ofof dust particles near the vessel wall differ from in the middle of the dust flux, (b) Distance dependencevessel.
of ratio of dust flux towards backside to target side.
[1] S. I. Krasheninnikov, et al., Plasma Phys. Control. Fusion 50(2008) 124054.
[2] S. Rosanvallon, et al., J. Nucl. Mater. 390 (2009) 57.
[3] K. Koga, et al., Plasma Fusion Res. 4 (2009) 34.
[4] S. Iwashita, et al., J. Plasma Fusion Res. SERIES 8 (2009) 308.