27E46P
ダイバータシミュレータで発生したカーボンダストの生成と輸送の放電電力の効果	 

Effects of Discharge Power on Formation and Transport of Carbon Dust Particles
Generated in a Divertor Simulator○西 山 雄 士 1， 森 田 1 康 彦 1， 山 下 1 大 輔 1， 鎌 滝 2 晋 礼 1， 内 田
儀 一 郎 1， 徐
鉉 雄 1， 板 垣奈 穂 1，22
2
古閑 一憲 ，白谷 正治 ，芦川 直
子 ， 増 崎 貴 3， 西 村 清 彦 ，3 相 良 明 男 ，LHD 実 験 グ1ル ー プ 2, Sven Bornholdt, Holger Kersten
2九州大学，
核融合科学研究所，
キール大学 3○1111
1
Katsushi Nishiyama ,1 Morita Yasuhiko, Daisuke Yamashita, Kunihiro Kamataki, Giichiro Uchida,1112
Hyunwoong Seo , Naho
Itagaki,KazunoriKoga,
Masaharu
Shiratani,Naoko
Ashikawa,
Suguru Masuzaki2, Kiyohiko Nishimura23, Akio Sagara2, the LHD
Experimental Group2,3
Sven Bornholdt , and Holger Kersten
Kyushu Univ. 1, National Institute for Fusion Science 2, University of Kiel 3
E-mail: k.nishiyama@plasma.ed.kyushu-u.ac.jp

In fusion devices, dust particles pose safety issues related to its chemical activity, tritium retention, andradioactive content. They are also known for causing operational issues such as deterioration of plasma
confinement [1]. Due to these reasons, the maximum quantity of dust particles in the ITER vessel is limited below
6 kg of carbon. So far we have found that large amount of dust particles in nanometer size are generated both in theLarge Helical Device (LHD) and in a helicon discharge reactor [2, 3]. Here we discuss formation and transportmechanisms of dust particles based on results of the power dependence of energy fluxes from plasmas towards atarget wall and dust flux towards a substrate for dust collection in the helicon discharge reactor.
Experiments were carried out using the helicon H2 discharge reactor [2]. The magnetic field of 150 Gauss wasapplied uniformly along the center axis of the discharge tube with the four magnetic coils. H2 gas was supplied witha pressure of 5mTorr. H2 plasmas were generated by applying 13.56 MHz pulsed RF voltage to a helicon antennausing an RF power supply. The discharging period was 0.25 s, and the interval was 1.0 s. Dust particles wereproduced due to interactions between a graphite target and H2 plasmas. Dust particles were collected by DC biased
Si substrates of 15x10 mm2 which were set at 110 mm below the graphite target and on the reactor wall. The area
density of dust particles was obtained from the number of dust particles and the observation with a scanningelectron microscope (SEM) measurements. Energy influxes from plasmas toward the graphite target were measured
using with a calorimetric probe [4].
The collected dust particles can be classified into three kinds: spherical particles, agglomerates, and flakes. The
discharge power dependence of the dust flux toward the substrate was obtained with the dust collection on thesubstrate which was biased at +50 V. The dust flux toward the substrate decreases with increasing the discharge
power, whereas the energy influx increases with increasing
the discharge power. From these results, the energy influx
dependence of the dust flux is deduced as shown in Fig. 1.
This figure shows that the dust flux toward the dust
collecting substrate decreases with increasing the energy
influx toward the target. This result shows a possibility thatfor the higher discharge power, the more number of dust
particles tend to redeposit onto the target due to the higher
ion drag force. Therefore dust inventory depends strongly onenergy influx to graphite divertor plates in fusion devices.
[1] S. I. Krasheninnikov, et al., Plasma Phys. Control. Fusion
50 (2008) 124054.
[2] S. Iwashita, et al., J. Plasma Fusion Res. SERIES 8(2009) 308.
Fig. 1 Energy influx dependence of dust flux
[3] K. Koga, et al., Plasma Fusion Res. 4 (2009) 34.
[4] S. Bornholdt, et al, Surf. Coat. Technol. 205 (2011) 388.