23P113-P
Change in parameters of a CT passing through a neutralization cell,and its relation to production of a neutral particle flow
中性粒子化セル中におけるCTパラメータの変化と中性粒子フロー生成との関係
N. Fukumoto1, J. Miyazawa2, M. Goto2, T. Takahashi3, Y. Kikuchi1,
M. Nagata1, T. Asai4, S. Masamune5, H. Yamada2
福本直之1，宮澤順一2，後藤基志2,高橋俊樹3，菊池祐介1，
永田正義1，浅井朋彦4，政宗貞男5，山田弘司2
1

Graduate school of Engineering, University of Hyogo, 2167 Shosya, Himeji, Hyogo 671-2280, Japan2
National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan
3
Graduate school of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan
4
College of Science and Technology, Nihon University, 7-24-1 Narashinodai, Funabashi, Chiba 274-8501, Japan
5
Graduate school of Science and Engineering, Kyoto Institute of Technology, Sakyo-ku, Kyoto, 606-8585, Japan1
兵庫県立大学大学院工学研究科 〒671-2280 兵庫県姫路市書写2167
2
自然科学研究機構 核融合科学研究所 〒509-5292 岐阜県土岐市下石町322-6
3
群馬大学大学院工学研究科 〒376-8515 群馬県桐生市天神町1-5-1
4
日本大学理工学部 〒274-8501 千葉県船橋市習志野台7-24-1
5
京都工芸繊維大学大学院工芸科学研究科 〒606-8585 京都府京都市左京区松ヶ崎御所海道町Recently, in order to apply Compact toroid (CT) injection technique to more effective fueling, production
and injection of super-high speed neutral particle flow have been studied. The neutral particle flow
injection has a performance advantage over supersonic gas jet and can play a specific role beyond neutralbeam injection. We have then proposed a fueling system of CT-based neutral particle flow by using a CT
injector. The system may allow us to make various plasma controls.

1. Introduction
We have developed the Compact toroid (CT)injector of SPICA (SPheromak Injector using
Conical Accelerator) for furling LHD at NIFS [1].
The CT formation and acceleration performance
was investigated on the single-stage SPICA withconnecting only the acceleration bank unit to bothelectrodes as shown in fig.1. SPICA achieved aCT speed of 76 km/s and a density of 1×1022 m-3
at the muzzle [2]. The kinetic energy density of
the hydrogen CT was calculated at 34 kJ/m3,
which was an energy density to penetrate into aLHD plasma at a low magnetic field of 0.3 T. Theenergy density is rather low. However, thedensity is remarkably high. If the CT plasmoid iscompletely neutralized, the particle inventory ofthe neutral particle flow (NPF) is estimated at be
5×1020 from the full-width at the base. The
inventory corresponds to a density increment of2×1019 m-3 in an LHD plasma at the volume of 30
m3. Here, for the same fueling efficiency of 40%
as CT injection on JFT-2M, the particle inventory
is calculated at 2×1020. In the penetration process,while a kinetic energy of the NPF is 100 eV, athermal energy would be less than 1 eV. Thus theradial diffusion is two orders smaller than theNPF penetration. The speed of NPF is two orders
larger than that of supersonic gas jet with a laval

Fig.1. Schematic draw of the SPICA CT injector and the neutralizer cell.

nozzle. The NPF injector by using CT injection
technique can be useful as a new fueling device.
2. Experimental Setup
SPICA injector has a single-stage coaxial
electrode with connecting only the accelerationbank unit to both inner electrodes (for formation
and acceleration) as shown in fig. 1. By using thesimple SPICA injector, we started the research onproduction of super-high speed NPF. The
experimental scenario is considered as follows; thesingle-stage SPICA accelerates a CT plasmoid andinjects it into the neutralizer cell filled withhydrogen gas, then super-high speed NPF is
produced owing to CX reaction between the CT
plasma and the neutral gas on the back ground.
A piezoelectric valve was mounted at the upper
port of P8 to puff hydrogen gas into t the neutralizer
cell (a length of 1.8 m, a volume of 5.5×10-2 m3).
The characteristics were tested, and the trigger
timing and the pulse width for driving apiezoelectric valve were optimized in considerationof neutral gas diffusion. The pressure in theneutralizer cell is up to 10-2 Torr. We also arranged
measurement
systems
toinvestigate
theperformance of the simple SPICA and theproduction of NPF. PIN diodes (L1-4) weremounted at P1, P4, P7 and P10/P11 for theobservation of a CT moving, and a He-Ne laserinterferometer was at P6 for CT plasma density at
the injector muzzle. Then the interferometer wasmoved to be set at the side port of P9 for that in theend region of the neutralizer. Recently, aSchultz-Phelps type ion gauge with a PIN diodewas also installed at P11 to detect a fast increase inpressure in the flux conserver (FC). The PIN diodemonitored emission from a filament of the gauge.
In the operation of SPICA, the charging voltageof the acceleration bank was set at 25 kV for theperformance test of the single-stage SPICA and 15kV for the production test of NPF.
3. Experimental Results
By using the simple SPICA injector, a CT plasma
was injected into the neutralizer cell filled withhydrogen gas. Figure 2 shows the typical evolutionof PIN diode signals and the CT density. The
vertical offsets are proportional to the axial locationof each measurement. Although the electron density
at the end region of the neutralizer cell decreasedmuch less than that at the muzzle, the electron
density of about 5×1020 m-3 remained. Both plasma
and NPF reached the FC. The complete
neutralization was not experimentally obtained yet.
The other result also showed that CT plasma wasdecelerated in the cell filled with hydrogen gas. The
partially NPF would separated from the plasma, andthen reach the FC earlier than that.

Fig. 2. Typical evolution of PIN diode signals andthe CT density along CT’s path.

4. Summary
We have conducted the experiment to produce
NPF by using the single-stage SPICA. Fromestimating NPF parameters based on the obtained
CT parameter, the performance advantage of NPF
injection over supersonic gas jet and neutral beam
injection was indicated. However, in the experiment,
the complete neutralization was not achieved yet.
Thus, in order to understand the neutralization
process and investigate the conditions for highneutralization efficiency, we have mademeasurement of the partially NPF by using
Schultz-Phelps type ion gauge with a PIN diode. Inaddition, Gunma Univ. group has made a
Monte-Carlo simulation on the neutralization of CT
plasma [3].
Acknowledgments
This work was performed with the partial supportof Grant-in-Aid for Scientific Research (B)(21360453) and with the support and under theauspices of the NIFS Collaboration Research
Program (NIFS09KCPP006, NIFS11KLEF006).
References[1] D. Liu, N. Fukumoto, Y. Kikuchi, M. Nagata, J.
Miyazawa: J. Plasma Fusion Res. SERIES 8 (2009)999.
[2] N. Fukumoto, J. Miyazawa, T. Takahashi, M. Nagata,M. Goto, T. Asai, S. Masamune, Y. Kikuchi, H.
Yamada: 23rd IAEA FEC, Daejon, Korea, Oct. 10-16,FTP/P1-05 (2010) .
[3] S. Fujii, T. Ohshima, T. Takahashi, N. Fukumoto, M.
Nagata: IEEE Trans. Plasma Science 38 (2010) 1473.