22E06
Dynamics of Atmospheric Pressure Microwave Plasma Torch
大気圧マイクロ波プラズマトーチの動的挙動	 
Naomichi Ezumi1, Takahiro Koide1, Yuki Hayashi1, Kazuhiko Akahane1, Shinya Shiozawa1,Keiji Sawada2 and Noriyasu Ohno3
江角直道1, 小出嵩大1, 林祐貴1, 赤羽和彦1, 塩沢慎也1, 澤田圭司2, 大野哲靖3
1

Nagano National College of Technology, 716 Tokuma, Nagano 381-8550, Japan
Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan3
Graduated School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Naogya 464-8603
1
長野工業高等専門学校 〒381-8550	  長野市徳間7162
信州大学工学部	  〒380-8553	  長野市若里4-17-1
3
名古屋大学大学院工学研究科	  〒464-8603	  名古屋市千種区不老町
2

Dynamical behaviors of a plasma torch generated by microwave in atmospheric pressure have been
investigated. Changes of the plasma structure and its dynamics for gas flow and discharge power have been
observed by using a high-speed camera. With respect to probe measurements, we have found the strong
influence of a probe electrode on the plasma torch. A probe with metal electrode has drastically disturbed
the plasma structure.

1. Introduction
Many application studies using atmosphericpressure plasmas have been tackled in the fields
such as surface treatment, environment, medical,
light source and so on, because of the easy
productivity and inexpensive facility comparedwith the conventional low-pressure plasmas.
So far, we have studied an atmosphericpressure plasma torch generated by 2.45 GHz
microwave with a monopole antenna in order toclarify the property. In this paper, changes ofplasma structure and its dynamics observed byusing a high-speed camera have been shown.
Furthermore, influences of probe electrode onprobe measurements have been discussed.
2. Experimental Setup
Figure 1 shows a schematic diagram of theexperimental apparatus for investigating theatmospheric pressure microwave plasma using ahigh-speed camera and an electrical probe. A
solid-state microwave power supply with 2.45 GHz
in frequency (Nagano Japan Radio Co. Ltd.
NJZ-2450A) is connected to a plasma source
through an automatic matching box. The source
consists of a aluminum chassis, an aluminum
antenna, a coaxial connector and a cylindrical glass
tube. The inside diameter of the glass tube is 10 mm.
The tube covered the surface of the aluminumchassis in the discharge region, thus a generated
plasma does not interact with the metal surface
except for the antenna. Argon gas is fed into theplasma discharge region through the sidewall of theplasma source. When gas flow rate is 2~4 L/min, aflame-like plasma torch with about 10 mm in length
has been generated.

Fig. 1. Experimental setup for observing an
atmospheric pressure microwave plasma
torch using a high-speed camera and anelectrical probe.
3. Experimental Results and Discussion
3.1 Turbulent and Fragmental Structures [1,2]
Increasing the gas flow rate of Ar, the structureof the plasma torch is changed. In the case of 2.0
L/min, the structure is almost stable. However,increase the gas flow rate to 4.0 L/min, the structure
become an unstable state. Figure 2 shows thepropagation of the unstable flame structure
observed by a high-speed camera in 50000 fps. The
velocity of the flame propagation is evaluated to
1.2m/s. The velocity is almost same as gas flow

velocity, and then the global turbulent structure ofplasma flame depends on the gas flow velocity.
The high-speed camera measurements also
clarify the detail structure of the tip of the plasma
torch as shown in Fig. 3. Oscillating fragmentations
have been clearly observed at the tip of the torch.
Each distance between fragmented elements isabout 0.55 mm. In this experimental condition(4L/min, 100W), the elements moved to back withsame velocity. According to the detailmeasurements, the oscillations have had properties
for propagation velocity is proportional to themicrowave power with keeping same distancebetween the fragments.

a)b)Fig. 4. Comparison of the influence of probe
electrodes on the structure of plasma; (a)insulator, (b) metal electrode (single probe)
In addition, fast repetition of transition of theplasma torch which attaches and detaches to a metalprobe electrode has been observed. In order toinvestigate the phenomena during repetition,
simultaneous measurements with high-speed
camera and an electrical probe have been done. The
details are shown in our presentation.

Fig. 2. Propagation of a flame structure of theplasma torch (Ar: 4 L/min, Microwave
power: 100W).

Fig. 3. Observation of a fragmental structure at thetip of the plasma torch (Ar: 4 L/min,Microwave power: 100W).
3.2 Influence of a probe electrode [3]Figure 4 shows the behavior of the plasma torchwhen an insulator rod or a floating metal electrodeput near the plasma. In the case of the insulator rod(Al2O3) without metal electrode, the plasma torch isbended like as avoiding the rod. In contrast, themetal electrode pulls the plasma even though it iselectrically floating, and then the plasma torch
completely attaches to the electrode. Thisphenomena suggest us a metal probe electrodebecome an antenna for microwave even if it iselectrically floating.

4. Summary
Dynamics of the atmospheric microwave plasma
torch have been investigated by using a high-speed
camera. It is clarified that propagation of theflame-like structure is related to gas dynamics.
Moreover, we have found oscillations of the tip of
the plasma torch along the axis-direction. The
phenomena would be related to the propagation ofmicrowave as surface wave. With respect to probe
measurements, simultaneous measurements withhigh-speed camera and probe current have been
done. Fast repetition of attachment and detachmentof the plasma torch to the probe electrode has been
observed. These results suggest us an insulated
probe method would be effective in avoiding thedisturbance.
Acknowledgments
This work was supported by Research
Foundation for the Electrotechnology of Chubu,
Nagano JRC Co.Ltd. and Shinano-Kenshi Co.Ltd.
References[1] N. Ezumi, S. Yamada, T. Kobayashi, K. Todoroki etal.: 25th JSPF Annual Meeting, Utsunomiya, Japan,
2- 5 Dec. (2008), 4aB35P, in Japanese.
[2] K. Yanagisawa, S. Iio, N. Ezumi and T. Ikeda:
International Conference on Jets, Wakes andSeparated Flows, Cincinnati, Ohio USA, Sep. 27-30(2010)[3] N. Ezumi, N. Kodama, K. Akahane, S. Shiozawa etal.: 9th International Workshop on Electrical Probes
in Magnetized Plasmas, Iasi, Romania.21-23 Sep.
(2011).