23D04
Discharge Characteristics of Multi-Phase AC Arc for In-Flight Processing
インフライト処理に用いる多相交流アークの放電特性
Manabu Tanaka, Yaping Liu, Yosuke Tsuruoka, Tomoki Ikeba and Takayuki Watanabe
田中 学, 劉 雅萍，鶴岡洋佑，池場友樹，渡辺隆行
Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology4259, Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8502, Japan
東工大院総理工 〒226-8502 神奈川県横浜市緑区長津田町4259
Multi-phase AC arc is suitable for the in-flight melting treatment of the granulated glass raw materials
because of its large plasma volume, low gas velocity and high energy efficiency. The discharge mechanismof the multi-phase AC arc plasma was investigated by a high-speed video camera observations
synchronized with voltage measurements and an image analyses of high temperature distributions werecarried out. Uniform high temperature distributions are broadened with increasing the number of the phase.

1. Introduction
The concept of controlled generation of an arc
by rotated magnetic field or by multiple
electrodes has already been studied [1]. These
power sources for arc generation areaccomplished by DC power supply, although ittakes more cost in the apparatus for converting
AC to DC. The conventional single-phase andthree-phase AC power supplies have acharacteristic of intermittent discharge which
limits the application of arc systems [2]. To
obtain a more effective arc reactor, a multi-phase
AC power supply has been developed [3]. The
important advantage of this system is larger
number of discharging paths among theelectrodes. Therefore, discharges among theelectrodes always exist to realize smooth arc
re-ignition. Consequently, the multi-phase AC arc
have been attracted to be applied to waste
treatment, synthesis of nano-sized materials, andin-flight glass melting processes [4].
Only few researches about the characterizationof the discharge mechanism of the multi-phase
AC arc, however, have been reported. In order toenhance the performance of the in-flighttreatment, the discharge mechanism of themulti-phase AC arc should be understood. The
objective of this study is to investigate thedischarge mechanism of the multi-phase AC arc.
2. Experimental
Figure 1 shows the schematic diagram of theexperimental setup of the multi-phase AC arc. It
consisted of twelve electrodes, reaction chamber
and AC power supply. Twelve electrodes weresymmetrically arranged by the angle of 30 degree
and were divided into two layers, upper six
electrodes and lower six electrodes. The details

about the experimental setup can be shown in ourprevious work [4]. In this study, a high-speed video
camera was installed on the top of the reactor toobserve the behavior of the multi-phase AC arc.
Voltage measurements were also conducted withsynchronizing the camera observations. Three typesof the electrode configuration, clockwise (CW),flip-flop (FF), knight connection (KC), wereapplied to control the arc region, which corresponds
to the high-temperature region.
3. Results and Discussion
Figure 2 shows the representative of thehigh-speed video images of the multi-phase AC arc
for different types of the electrode configurations.
The sinusoidal waves of voltages were applied asindicated in the expression in Fig. 2.
The luminance area is cyclically distributed withfluctuation caused by phase shifting in themulti-phase AC arc. Then the fluctuation of theFig.1. Schematic of multi-phase AC arc reactor.

4. Conclusion
Multi-phase AC arcs were characterized byhigh-speed video observations and its image
analysis. Obtained results indicated that thecontrollability of the high temperature region bychanging the electrode configuration, which would
be useful for various plasma processes.

Fig.2. Representatives of the high-speed video
images of the multi-phase AC arcs;(a) CW, (b) FF, (c) KC pattern.
2000

Luminance Area [mm 2]

12 Phase Arc (FF)
1500

100050002 1052 1051 1055 104050100150200

Time [ ms ]12 Phase Arc (FF)Luminance Area [mm 2]

luminance area was evaluated from high-speed
video images. Figure 3 shows the fluctuation of theluminance area of the FF patterned 12-phase arc,and its result of fast Fourier transfer (FFT) analysis.
Here, the strongest peak of 100 Hz is observed.
This is originated from the power source.
The behavior of the multi-phase AC arc iscomplicated and fluctuated as indicated in previous
section because of its complex effects of rotating
electro-magnetic fields and the Lorentz forces
between the arcs. In order to evaluate thehigh-temperature region near the electrodes tip as
well as the area among the electrodes, thehigh-speed video images were analyzed by theimage processing. The analyzed images byaccumulating the high-temperature region during acycle (20 ms) are shown in Fig. 4. As indicated inFig. 4, the high-temperature regions for three typesof the electrode configurations are compared. The
results indicate that the more uniform
high-temperature region can be obtained in CW
pattern than others. This is because the opposite
side of voltages (For example, V1 and V7) areapplied to the opposite side of the electrodes,
resulting in the longer arc passing through thecenter of the electrode region. In contrast, thehigh-temperature region of the arc in FF patternshows the doughnut-shaped. This is because thearcs exist only near the electrodes. These results
indicated the controllability of the multi-phase AC
arc

00200

400600800

1000Frequency [Hz]Fig.3. (a) Fluctuation of luminance area and (b) FFTanalysis of the luminance area for multi-phase AC
arc in FF pattern.

Acknowledgments
The financial support provided by the Strategic
Development of Energy Conservation Technology
Project of NEDO (New Energy and Industry
Technology Development Organization, Japan) isgratefully acknowledged.
References[1] J. Harry and J. Knight: Appl. Phys. 17 (1984) 343.
[2] L. Fulchri: Carbon. 38 (2000) 797.
[3] T. Matsuura, K. Taniguchi, and T. Watanabe: Thin
Solid Films. 515 (2007) 4240.
[4] T. Watanabe, K. Yatsuda, Y. Yao, T. Yano, and T.
Matsuura: Pure Appl. Chem. 82 (2010) 1337.

Fig.4. Contour maps of the arc existence frequencyof the multi-phase AC arcs;(a) CW, (b) FF, (c) KC pattern.