22P054-P
Plasma Source in an Ion Beam Systemwith Low Energy and High Current Density
低エネルギー高電流密度イオンビームシステムにおけるプラズマ源の開発
Haruhisa Koguchi, Manabu Kiyama, Hajime Sakakita,SATO Yasuhiro, Toshio Shimada, and Yoichi Hirano
小口治久、木山 學、榊田 創、佐藤康宏、島田壽男、平野洋一
Innovative Plasma Technologies Group, Energy Technology Research Institute, National Institute of Advanced
Industrial Science and Technology (AIST), Tsukuba Central 2, Umezono 1-1-1, Tsukuba 305-8568, Japan

産業技術総合研究所エネルギー技術研究部門先進プラズマ技術グループ〒305-8568 つくば市梅園1-1-1、つくば中央２
The coaxial shunting arch plasma gun has been developed as a plasma source for the ion source of the ion
beam injector. Carbon plasma has been successfully generated from solid material without methane gas by
the plasma gun. The duration of the plasma gun discharge is 5 msec. We installed a RF generator and anantenna to sustain the plasma generated by the plasma gun. A long time plasma generation is achieved by
the plasma gun and by the RF discharge.

1. Plasma gun
The ion beam source has been developed for a
new type of the deposition system for diamondand other carbon materials in AIST. Pure carbon
plasma source is required for the plasma sourceof the ion beam. Gun type plasma source cangenerate a plasma without any carrier gas and isadopted as the pure carbon plasma source of theion beam. The access port of the ion chamber islimited to size of the ICF-34 flange port to makethe cusped magnetic field in side of the ionchamber. The coaxial shunting arch plasma gun
has been designed as a plasma source [1]. The
surface of the plasma gun except the insulation
between the inner and outer electrode is made by
the graphite in order to avoid the influx ofimpurities into the ion beam. The shunting bar,
the conductor bridging between the inner and theouter electrodes, is made by a Plastic Formed
Carbon (PFC) in order to make it's the impedance
higher than the impedance of the discharge
current pass. A certain amount of input energy isconsumed in the shunting bar. Figure 1 a) shows
the discharge voltage and the current of theplasma gun for 600 V charging voltage of thepulse forming network (PFN). The pulse durationand the typical impedance of the PFN are
designed 2.4 ms and 0.039 Ohm respectively. Thewaveform of the gun current shows the flat top
phase is same with the designed pulse duration.
Figure 1 b) shows the discharge impedance
estimated from the gun voltage and the guncurrent and the CI line (247.8 nm) emission fromthe plasma gun. The designed impedance of thePFN is same order with the plasma discharge
impedance. The CI line emission shows thecarbon plasma is generated during the plasma gun
discharge.
2. RF source installed on the cusp field chamber
The RF generator (2.45 GHz, 1 kW, IDX Inc.,
MHA-10AHSB) is installed on the ion chamber.

Fig 1 a). The discharge voltage (red line) and thedischarge current (blue line).

Fig 1 b). The discharge impedance (red line) and theline intensity of CI (247.8 nm).

Figure 2 shows the experimental setup. The size ofthe access port is limited, and the tapered coaxial
waveguide is designed to downsize the coaxial
waveguide to ICF-34 from ICF-70. Hydrogen gas is
not used for the ion beam source, and the hydrogen
embrittlement of copper can be avoided. The
coaxial waveguide and the antenna can be made bycopper. The tapered coaxial waveguide is installedinside of the access port in order to insulate heat
flux to the access port from the waveguide. The
cylindrical copper conductor of the waveguide isconnected to the water cooler at the bottom of thetapered coaxial waveguide. The 1/2 or 1/4
wavelength antenna is installed on the coaxial
waveguide. We used the copper antenna in thispaper. The carbon antenna is also prepared. The
plasma can be generated by the microwave andelectron cyclotron resonance (ECR) in the cusped
magnetic field. We usually apply 200 W of the RFpower to sustain the plasma.

chamber. The plasma discharge is short, and thesignal of the gun discharge is indicated as a spikesignal within the green ellipse. Figure 3 b) shows
the probe signal for a 6th single discharge of theplasma gun. The single discharge is limited within 5
ms. The effect of the microwave discharge is shown
before the gun discharge and after a few
milli-second from the gun discharge. After the RF
turn-off, the plasma is also terminated. This
indicates the plasma discharge can be sustained
longer time. At the last, we note that the carbon isdetected in the mass spectrum measured at anotherside of the vacuum pump from the ion chamber.
Acknowledgments
This study was financially supported by theBudget for Nuclear Research of the Ministry ofEducation, Culture, Sports, Science and Technologyof Japan, based on the screening and counseling of theAtomic Energy Commission, and in part by the Japan
Society for the Promotion of Science Core-to-Core
Program 22001.
References[1] H.Koguchi, H. Sakakita, S. Kiyama, T. Shimada, Y. Satoand Y. Hirano, 'Shunting arc plasma source for purecarbon ion beam', Proc. of ICIS2011, is submitted to Rev.
of Scientific Instruments.

Fig 2. Experimental setup.

3. Combination discharge the plasma gun andRF discharge
The plasma gun can generate the carbon plasma
without any hydrocarbon gas as shown in section 1.
However, the pulse width is limited within thedesigned pulse width of the PFN. We apply themicrowave to sustain the plasma generated by theplasma gun during the cycle of the gun discharge.
The cycle of the plasma gun discharge is selectable.
10 seconds of the cycle is selected in this paper.
The number of the cycles is limited to be 8 by thedata acquisition. However, the purpose of theexperiment is to optimize the plasma gun discharge,
and the plasma cycle is enough for this purpose of
the experiment. The microwave source is adjusted
for the case that the ion chamber is filled with thesteady Helium plasma, and the reflection of themicrowave is reduced after discharging the plasmagun. The microwave is applied before the plasma
gun trigger and is terminated after 8 cycles of theplasma discharges. Figure 3 a) shows the probe
signal from double probe installed in the ion

Fig. 3 a). The double probe signal.

Fig. 3 b). The double probe signal for a single gun
discharge.