25pB01

Initial Ignition Dynamics of Radio Frequency
Induction Thermal Plasma in Atmospheric Pressure

M. Abdur RAZZAK1), Shuichi TAKAMURA1), Yoshihiko UESUGI2) and Noriyasu OHNO3)
1)
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
2)
Faculty of Engineering, Kanazawa University, Ishikawa 920-8667, Japan
3)
EcoTopia Science Institute, Nagoya University, Nagoya 464-8603, Japan
Thermal plasmas generated by inductively coupled plasma (ICP) technique have been drawn a considerable
attention in a diversity of researches over the last few decades due to its wide range of operating conditions, andvarious industrial and commercial applications [1-3]. So far, however, attention has been drawn on heating, andstabilization of induction plasmas. But, when operated at high-pressures (around 1 atm or more), initial start-up is
one of the important issues to ignite the discharge of induction plasmas, as the starting of high-pressure rf plasma
torches are hard, and a high-voltage initiation is usually required. So far several techniques, such as, dc arc jet [1]and dc-rf hybrid plasma torch [2] are used to initiate the high-pressure rf inductive discharges. But, these hybrid
plasma torches characteristically operate at power levels of 50 to 100 kW or even more, where the dimensions of
the second-stage, high-power unit make it difficult to initiate and operate in a stable manner [3]. But to promoteinduction plasmas into industrial and commercial fields, it is mandatory to make it cost effective with as low
power as possible. Therefore, it is necessary to understand the physical mechanisms of the formation of highpressure induction plasmas, which is quite different with that of the low-pressure plasma dynamics. With those inmind, we have studied the dynamics of atmospheric pressure argon induction thermal plasma (ITP) at the ignition
stage experimentally to find a simple and easy ingnition method of atmospheric pressure ITP. High-speed imaging(13500 f/s) is performed to investigate the dynamics of physical processes and initial formation of rf discharge. A
very interesting result is observed from the experiment, which clarify the dynamics of high-pressure inductivedischarges. The experimental observations reveal that (1) firstly, multiple streamer-like discharge paths, which iscalled the electrostatic discharge or E discharge [Fig. 1(a) & (b)], are developed due to strong electrostatic field(100-200 kV/m), (2) secondly, the discharge paths connect among the streamers due to the induced azimuthal
electric field thereby forming the electrically conducting ring-shaped azimuthal discharge, which is called theelectromagnetic discharge or H discharge [Fig. 1(c) & (d)], and (3) finally, volumetric induction plasmas [Fig.
1(e)] are formed due to the Joule heating with the azimuthal current flowing through the electrically conducting
ring. The transition between electrostatic and electromagnetic discharge is called the E-H mode transition. The EH mode transition time, which corresponds to the duration of H-discharge, is estimated from high-speed imaging
as well as by observing the time behavior of high-frequency plasma loading impedance at the E-H mode transition
stage.
Side view

E discharge(a) 0.9 ms, 0.2 kW(b) 1.0 ms, 0.3 kW

E-H transition(c) 1.4 ms, 0.5 kW
Top view

H discharge(d) 1.7 ms, 2.0 kW(e) 2.0 ms, 4.0 kW

Fig.1 High-speed imaging to understand the initial formation of high-pressure induction thermal plasma[1] Takashi Uesugi, Osamu Nakamura, Toyonobu Yoshida, and Kazuo Akashi, J. Appl. Phys. 64, 3874 (1988).
[2] Toyonobu Yoshida, Toshihiko Tani, Hirobumi Nishimura and Kazuo Akashi, J. Appl. Phys. 54, 640 (1983).
[3] J Reece Roth, Industrial Plasma Engineering-Volume 1 (Institute of Physics Publishing, Bristol, 1995).