24P053-P
Generation of Detached Plasmas by using Simple Closed Divertor Module
簡易閉ダイバータモジュールを用いた非接触プラズマ生成
Takashi Tomiyama1, Noriyasu Ohno1, Shin Kajita2, Makoto Takagi1, Mizuki Sakamoto3 andYousuke Nakashima3
冨山貴史, 大野哲靖, 梶田 信, 高木 誠, 坂本瑞樹, 中嶋洋輔
1

Graduate School of Engineering, Nagoya University,Fro-cho, Chikusa-ku, Nagoya 464-8603, Japan
名古屋大学工学研究科, 〒464-8603 名古屋市千種区不老町
2
EcoTopia Science Institute, Nagoya University,Fro-cho, Chikusa-ku, Nagoya 464-8603, Japan
名古屋大学エコトピア科学研究所, 〒464-8603 名古屋市千種区不老町
3Plasma Research Center, Tsukuba University, Tennoudai1-1-1, Tsukuba, Ibaraki, 305-8577, Japan筑波大学プラズマ研究センター, 〒305-8577 茨城県つくば市天王台1-1-1

To establish detached plasmas as methods to reduce particle and thermal loads, it is necessary to clarify the influence
to core plasma confinement properties and stability of detached plasmas. Now a closed divertor module on theaxisymmetrized tandem mirror GAMMA10 is planed to introduce to promote systematical research of detachedplasmas. In this study, we develop the simple closed divertor module as a prototype. We conduct its performance test ina liner divertor plasma simulator.

1. Introduction
Generation of detached plasmas by plasma-gas
interaction is thought to be effective methods toreduce particle and thermal loads on divertor plates
in magnetic confinement fusion reactors.
Mechanism of generation of detached plasmas has
been investigated in terms of atomic molecule
processes by using the liner divertor plasma
simulator. However, to establish detached plasmas
to reduce particle loads and thermal loads, it isnecessary to clarify the influence to core plasma
confinement properties and stability of detachedplasma.
Now a closed divertor module on theaxisymmetrized tandem mirror GAMMA10 isplaned to be installed to promote systematicalresearch of detached plasmas. In the mirror end of
the GAMMA10, a cryopump is equipped. Therefor,
if we puff the large amount of gas in the end,
neutral particles are evacuated. To suppress theevacuation to increase the neutral pressure, a closed
divertor module is essential [1].
In this study, we developed the simple closed
divertor module as a prototype. We investigate its
performance test in the liner divertor plasma
simulator NAGDIS-Ⅱ.
2. Experiments
Figure. 1 shows the design of the simple closed
divertor module. This module consists of silica tube
and target plate which is made of the boron
nitride(BN) and the gas pipe. The inner diameterand length of the silica tube are 48 mm and 400 mm,respectively. The diameter of the plasma is 20 mm[2]. In the silica tube, ten electrostatic probes aremounted. At the BN target, seven electrostatic
probes are mounted. The gas pipe is equipped tomeasure neutrality gas pressure in the silica tube.

Fig.1 Design of the closed divertor module.

The recycling process increases the neutrality gaspressure in the tube. The increase in the neutralpressure may contribute to enhance therecombination process, which is essential for a
detached plasma.
3. Results and discussion
Figure. 2 shows the neutrality gas pressure insideand outside of the tube on increasing the electron
density outside the tube. The pressure inside thetube increases with increasing the electron density.
The outside pressure decreases with increasing theelectron density. The result indicates that theneutrality pressure increases by the recyclingprocess. However, detached plasmas was notformed in this experiment. The plasma in front of

the target is shown in Fig. 3. It might be attributed
to the fact that the neutral pressure in front of thetarget was not sufficiently increased by the module.
4.5

inside pressure
outside pressurepressure [mTorr]

43.5
3
2.5
24

6

8

10

12

14
18

16

18-3

electron density [×10 m ]Fig.2 The neutral
outside(cross) the tube.

pressure

inside(circle)

andFig.3 A picture of plasma in front of the target.

To generate detached plasmas, the neutralitypressure inside the tube needs to be increased more.
It is planned to improved the module to increase theneutral pressure inside the tube more efficiently.
References[1] Y. Nakashima, Y. Higasizono, et al., J. Nucl. Mater.
390 (2009) 511.
[2] N. Ohno, D. Nishijima, et al., J. Nucl. Mater. 41(2001) 1055.