st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Analysis of atmospheric serpentine plasma phenomenon using a high-speed
camera
Shin-ichi Aoqui1, Fumiaki Mitsugi2, Hiroharu Kawasaki3, Shigeru Kinouchi4, Tetsuro Baba5 Tomoaki Ikegami2
1
Department of Computer and Information Sciences, Sojo University,4-22-1 Ikeda, Kumamoto, 860-0082, Japan
Graduate school of science and technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555, Japan
3
Department of Electrical & Electronics Engineering, Sasebo National College of Tech., 1-1 Okishin, Sasebo, 857-1171,
Japan
4
DITECT Corporation,1-8, Nanpeidai-cho, Shibuya-ku, Tokyo 150-0036, Japan
5
VIC International, Inc., Nishitama-gun Mizuho city, Tokyo 190-1232, Japan
2
Abstract: Because simple constitution is possible as for atmospheric pressure plasma, it is
expected in bio-application, agriculture and medical field. However, a low power electric
discharge forma such as dielectric barrier electric discharge and surface discharge does not
become always effective when we think about an application such as fields of agriculture. We
continued investigating a gliding arc (GA) discharge. GAD can spend large consumption
power, but an unexplained point remains in the electric discharge system. In this study a
high-speed camera was used, and it was investigated the details of electric discharge.
Keywords: atmospheric pressure plasma, gliding arc discharge, serpentine plasma
1. Introduction
A development of a sanitization and sterilization
technology in a medical, agriculture, biotech field using
atmospheric pressure plasma is remarkable now. [1-8] In
an atmospheric pressure electric discharge, we paid
attention to gliding arc (GA) discharge. GA discharge has
a word to express "arc" in a part of the name but it is a
discharge type that is considerably different from
so-called DC arc and AC arc. Furthermore it is hard to say
that the discharge mechanism of GAD is understood well.
As for a GA plasma production is possible with the power
consumption that is smaller than an arc discharge that is
generally used under atmospheric pressure environment.
With electric power lower than an arc, generation of
atmospheric pressure plasma is possible for a GA. We
continue researching a discharge mechanism explication
of a GA using an ultra high-speed camera (DITECT:
HAS-D3) and IV characteristic. [9,10] However, our
previous study on simultaneous observation of the
dynamic behavior of the plasma path via a high-speed
camera and the corresponding electrical properties
revealed that the plasma path was very complicated due to
gas flow rate and reconnections were repeated especially
in high gas flow to maintain plasma. Moreover, the
plasma impedance was not as low as that of normal arc
discharge because plasma length increased with gliding.
Therefore, we call this plasma as serpentine plasma. A
serpentine plasma discharge was nonequilibrium, a kind
of the non-steady discharge, and a large number of
applied research works has been performed as a gliding
arc discharge. We carried out the observation using a
high-speed camera about the discharge mechanism of the
serpentine plasma. It was confirmed by using the
high-speed camera where paths of discharge between
electrodes existed temporally. This measurement had
been performed in the serpentine plasma discharge system
of 2, 3 and 6 electrodes type.
2. Experimental
In this study, we used 2, 3 and 6 phases alternating
current as a power supply system to supply 2, 3 and 6
electrodes. Fig.1 shows 6 electrodes type serpentine
plasma equipment including power supply. (Three pieces
of electrodes were removed by the setup of 3 electrodes
device and 2 electrodes type was different system but
discharge and measurement system was almost same as 6
electrodes type.) Pure iron was used for the electrode
material. The distance between countered electrodes was
adjusted at 3-10 mm. Argon gas was introduced from the
electrode lower part. Ar gas flow rate was adjusted 5-65
litter/min. The voltage was regulated 0-3000 V. The
electrode was surrounded with optics glass tube (6
electrodes: diameter of 248 mm, IWAKI, TE-32 Glass, 2
electrodes: plane substrate of a rectangular by TE-32),
and the upper part edge was thrown open by the
atmosphere. Electric discharge images were taken in 3
and 6 electrodes type from the upper part and in 2
electrodes type by the front of the electrodes. Current
probe(s) (Tektronix TCP2020) and voltage probe
(Tektronix P6015A) were connected to a high-speed
oscilloscope (LeCroy WaveRunner 204Xi-A), and it was
measured with a high-speed camera control PC in
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
synchronization by a synchronization signal of a pulse
generator (Hamamatsu C10149).
Fig.1
Experimental setup
Fig.3 High-speed images
(Ar: 5 L/min, image interval: 20/10,000 sec)
4. Results and discussion
Discharge image of 6 electrodes type is shown in Fig. 2.
Serpentine plasma looks to man's eyes like a ‘flame’.
However, it depends on an afterimage phenomenon, and
the appearance is constituted by only one or two
discharge path which moves at high speed.
Fig.4 High-speed images
(Ar: 10 L/min, image interval: 6/10,000 sec)
Fig.2 Discharge image of 6 electrodes type
3.1 Single-phase AC discharge experiment
Fig.3 to 6 shows high-speed camera images of
serpentine plasma by a rate of Ar gas flow (5, 10, 20, 35
65 L/min, respectively). All images were taken in 10,000
fps. The left to the right of an image is the direction of a
time-axis. However, the interval of a next image is
different. That is to say it is every 20 frames, 6 frames, 3
frames, 1 frame, respectively.
Fig.5 High-speed images
(Ar: 35 L/min, image interval: 3/10,000 sec)
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Fig. 7(b). Synchronization measurement of high-speed
images (Ar: 35 L/min) (See Fig. 7(a))
Fig.6 High-speed images
(Ar: 65 L/min, image interval: 1/10,000 sec)
In the case of 5 L/min, path of discharge rose over from
the electrodes bottom to top then return to bottom every
360/10,000 second. In the case of 10 L/min, it was
84/10,000 seconds, 35 L/min, it was 45/10,000 seconds
and in the case of 65 L/min, frame speed was insufficient
in 1/10,000 fps. With the rise of the Ar gas flow rate, a
rise speed of paths of discharge increased. In other words,
it was confirmed that discharge strongly depended on Ar
gas flow rate. However this reason was not clear now
because the time for gas flow scale is different from a
time for electric discharge scale widely. In addition, when
gas flow rate rose, the rise speed of discharge rose, but the
time for electric discharge not to exist became longer. It
means the time for discharge current not to exist between
electrodes is long on higher gas flow rate. Furthermore,
consumption electrical power decreased by increase of Ar
gas flow rate. A synchronization measurement result of
current, voltage and high-speed images in case of 35
L/min was shown in Fig. 7(a), (b). A discharge current
flowed only in a half cycle and a voltage waveform was
close to sin waveform in another half cycle. A current is 0
A sections, paths of electric discharge did not exist on
high-speed images.
A current waveform was approximately symmetric in
case Ar gas flow rate was lower than 30L/min. With the
rise of the gas flow rate, absolute value of discharge
current decreased, too. (It is not listed in figure). In
addition, a strange phenomenon that paths of discharge
recombined dynamically was confirmed.
3.2 Multi-phase AC discharge experiment
Fig.8 shows high-speed camera image of multi-electrode
type from top view. In this case, 3 electrodes with taking
speed of 1000 fps and Ar flow rate of 20 L/min were used.
The time interval between each image was 20/1000. A
path of discharge moved to the top from the bottom with
image No. 8 to 16. This time corresponded for 180/1000
seconds, and it was slower more than 10 times than the
case of a single-phase discharge experiment.
Fig. 8 High-speed camera image of 3 electrodes type from
top view. (1000 fps, Ar flow rate of 20 L/min)
Fig. 7(a) Synchronization measurement t of I-V
(Ar: 35 L/min) (See Fig. 7(b))
Next Fig.9 shows high-speed images of 6 electrodes type
from top view. In case of this experiment, taking speed of
5000 fps and Ar gas flow rate of 20 L/min was used. The
time interval between each image was 60/5,000. From
image information of Fig. 8, it seemed that phenomenon
with 3 electrodes type equally on Fig.9.
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Fig. 9 High-speed camera image of 6 electrodes type from
top view. (5,000 fps, Ar flow rate of 20 L/min)
A path of discharge moved to the top from the bottom
with image No. 5 to 23. This time corresponded for
1,200/5,000 seconds, it became a value equivalent to 3
electrodes type. A single-phase power supply and a
multi-phase power supply need to consider what is
different. In single phase, AC voltage of peak to peak is
supplied to electrodes. On the other hand multi-phases, a
voltage from which 120 degrees or 60 degrees of phases
shifted is supplied to electrodes. That is, in 6 phases, as
for line voltage, there is little difference and electric
discharge seems to be hard to occur. However, an electric
discharge starting voltage did not have a large difference,
and what there were paths of electric discharges more
than two parts was always confirmed in multi-phases by
experiment results.
4. Conclusions
Measurement of serpentine plasma using the high-speed
camera which was synchronized with I-V measurement
was carried out.
The important results are as follows.
1. It was confirmed that a behavior of discharge strongly
depended on Ar gas flow rate in the single-phase AC.
2. If Ar flow rate becomes higher, a motion of a path of
discharge will become intense, but electric power
becomes small.
3. The reason of 2. was for discharge only a half-phase, if
a flow rate goes up (about 35 L/min).
4. In multi-electrode type discharge, the rising speed of a
path of discharge was more than 10 times slower
compared with single phase.
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