24P033-P
Development of Noble DC Plasma Source for Divertor Simulation Study
ダイバータ模擬研究のための高性能直流プラズマ源の開発
Makoto Takagi1, Masato Yamagiwa1, Yuki Nakamura1, Tetsuya Utiyama1,Masahiro Teraoka1, Shin Kajita2 and Noriyasu Ohno1
髙木 誠, 山際正人，中村祐貴，内山徹也，寺岡正広，梶田 信，大野哲靖
1Graduate school of Engineering, Nagoya University, 2 Ecotopia Science Institute, Nagoya University
Furo-chou, Chikusa-ku, Nagoya 464-8603, Japan
名古屋大学 工学研究科・エコトピア科学研究所 〒464-8603 名古屋市千種区不老町

Divertor simulation study is important to understand plasma wall interaction and edge plasma physics. Forthat purpose, development of DC plasma source of high density and steady state plasma is an important
issue. Lately, we developed a compact and noble DC plasma source that used directly heated LaB6 cathode.
One of the plasma sources can be attached to a CF114 vacuum flange and can generate a plasma with theelectron density of ~1019 m-3. For the other one, the heating efficiency was improved and a high-density
plasma was produced. The detailed structure and the characteristic of the generated plasma are reported.

1. Introduction
LaB6 is remarkable thermionic electron emission
material for cathodes to generate plasmas. LaB6 has
a property of efficient thermionic electron emission
and lower work function than any refractory metals.
And LaB6 has an advantage that the necessary
power can be reduced, because the operating
temperature is lower than the other cathodematerials [1].
We have been using LaB6 as the cathode material
for DC plasma sources [2]. Especially, the input
power of directly heated cathode is lower thanindirectly heated cathode, and the size of thedirectly heated cathode can be more compact. In
this study, we report the detailed structures of twodifferent cathodes plasma sources that we lately
developed and the characteristic of the generatedplasmas.

connected in series.

2. Structure and Heating Efficiency of the DC
Plasma Source
The DC plasma sources that we will show consistof two directly heated LaB6 cathodes. The crosssection is 2mm×4mm. These cathodes are placedalmost parallel, so that they can be heated due toeach other’s radiation heat more efficiently. Plasma
is generated toward the side of the LaB6 cathodes.

The connection method is different from usualway. The LaB6 cathode tapered with V
configuration is fixed by being pushed to amolybdenum terminal with a V-shaped groove.
This method was used to reduce the thermal stressof the connection of thermally fragile LaB6. Gas issupplied from the hole of the boron nitride basis
center behind the laB6 cathodes. The generated
plasma is focused and come out from a orifice in 13
diameters of a boron nitride circular disc. And theLaB6 cathodes are covered with a tantalum cylinder.
This cover improves the heat-retaining property andcan efficiently supply the gas for discharge. As aresult, flat temperature distribution of the LaB6
cathode surface was realized, as shown in Fig.2.
Temperature distribution of the LaB6 cathodesurface is shown in Fig. 2. The temperature of the

2.1 DC Plasma Source for the Device PS-DIBA
The plasma source was newly developed for thedevice PS-DIBA. The plasma source assembly isshown in Fig. 1.
The plasma source is very compact and can be
attached to a CF114 vacuum flange. Two directly
heated LaB6 cathodes are angled to 6 degrees(toward the direction of the generated plasma) andFig. 1. Plasma source assembly for the device
PS-DIBA.

connection of the LaB6 cathode (triangle mark inFig. 2) is a little lower.
A H2 plasma that was generated with a toroidal
magnetic field intensity of 20 mT, gas pressure of
2.0 Pa and discharge power of 2.0 kW had theelectron density of 1.1×1019 m-3 and electron
temperature of 4.0 eV.

The LaB6 cathodes are also covered with fiveboron nitride thin boards except the side of thegenerated plasma. Therefore flat temperature
distribution of the LaB6 cathode surface wasrealized, as shown in Fig.4.
The cross-section shape of the generated plasma
is sheet. A deuterium detached plasma that wasgenerated with the magnetic field intensity (Bt: 13mT, Bv: 0.9 mT), gas pressure of 1.2~1.5 Pa anddischarge power of 6.0 kW had the electron densityof 3.8×1018 m-3 and electron temperature of about
0.1 eV.

Fig. 2. Temperature distribution of LaB6 cathodesurface.

2.2 DC Plasma Source for the Device NAGDIS-T
Another plasma source was developed toimprove the heating efficiency and producehigher-density plasma for the device NAGDIS-T.
The plasma source assembly is shown in Fig. 3.
Two directly heated LaB6 cathodes are angled 7
degrees (toward the direction of the generated
plasma, left side in Fig. 3) and connected in series.
Gas is supplied from the hole of a boron nitride
basis right-and-left center and further into the cell.

Fig. 4. Temperature distribution of LaB6 cathodesurface.

3. Summary
The structure of two DC plasma sources andtemperature distribution of the LaB6 cathodesurface were reported in detail. It was shown thathigh-density hydrogen and deuterium plasmas on
the order of 1018~1019 m-3 were produced by using
the compact plasma sources.
References[1] D.M. Goebel, Y. Hirooka, and T.A. Sketchley: Rev.
Sci. Instrum. 56, (1985) 1717.
[2] S. Masuzaki, N. Ohno, M. Takagi and S. Takamura:Tans. IEE of Japan, 112-A, No.11 (1992) 913.

Fig. 3. Plasma source assembly for the device
NAGDIS-T.