24G02
Discharge characteristic of atmospheric plasma generated using
water-dielectric multi-layer electrode
水‐誘電体多層電極を用いた大気圧プラズマの放電特性
Tatsuya Misawa, Keiichi Yamamoto, Yuusuke Akiyoshi and Nobuya Hayashi
三沢達也，山本恵一，秋吉雄介，林信哉
Department of Electrical and Electronic Engineering, Saga University
1 Honjyo-machi, Saga 840-8502, Japan
佐賀大学大学院工学系研究科電気電子工学専攻 〒840-8502 佐賀市本庄町1番地
For generation of atmospheric glow discharge plasma, deveropment of discharge method using coaxial
water-dielectric multi-layer electrode were carried out. In the case of coaxial electrode, the stable Ar
glow plasma was generated. The increase of temperature and decrease of dielectric constant of internal
fluid affects the improvement of plasma density and stability of atmospheric discharge. And stability
mechanism of internal fluid is spatially effective on surface of inner glass tube.

1. Introduction
In general, Atmospheric plasma is generatedusing discharge electrodes which are stuck or
coated the insulator in the metal electrode in orderto suppress the arc discharge and localization ofelectric discharge. And electric property ofelectrode and insulator and condition of junctionseems to influence the discharge characteristic.
In this study, in order to improve the discharge
property and stability of atmospheric glow
discharge plasma, development of f discharge method
using coaxial water-dielectric multi-layer electrodewere carried out.

2. Experimental Setup
Experiments were carried out using coaxial
water-dielectric multi-layer electrode shown infigure 1. The inner glass tube was inserted center ofthe outer glass tube which is 90mm in length, andouter glass tube was being sealed by silicon rubbercork. The inner and outer glass tube was made ofborosilicate glass. The diameter of inner and outer
glass tube were 6mm and 18mm respectively, andthickness of glass tube is 1mm. Between inner andouter glass tube, the internal fluid was beingenclosed. The inner electrode covered with alumina
tube was inserted center of glass tube. The outercylindrical electrode (width is 10mm) was placed
over the outside of outer glass tube.

The high voltage ac power supply (10kHz,9kVp-p) was connected with inner electrode andouter cylindrical electrode, and the potential ofouter cylindrical electrode was equal to the ofground and external electrode which was placed inorder to draws the plasma outside of discharge
region. The discharge gas is supplied from the gas
inlet connected with glass tube. Argon and oxygengas was used, pressure of gas is 1 atm and flow rate
is 3 L/min. By applying discharge voltage to innerand outer electrode, the atmospheric plasma wasgenerated and extracted from inside of the inner
glass tube.
In this investigation, water, ethanol and toluene
were used as internal fluid. Ethanol and toluene issuperior insulating material, and water and ethanol
have high dielectric constant εr and high electric
dipole moment p (Table I). In addition, it is notedthat the dielectric constant εr of water and ethanol
remarkably decreases with the increase in theTable I. Electric property of internal fluid(D=3.36×10−30 C·m)

tap water
methanoltolueneσ (S/m)~10-2
3.0×10-5
1.4×10-5

εr
80
33
2.4p
1.85D
1.69D
0.36D

Fig.1 Experimental setup

temperature.
In addition to previous setup, glass bulb
condenser (Allihn condenser) with H2O as internal
fluid, which has the length of 300 mm, was used inorder to generate the large volume atmosphericplasma.
3. Experimental result
Typical image of atmospheric plasma generated
by coaxial water-dielectric multi-layer electrodeand glass bulb condenser were shown in Fig.2. In
the case of coaxial electrode (Fig.2(a)), the stable
Ar glow plasma was generated and reach external
electrode, and length of glow plasma run into
30mm. The conductivity of internal fluid is not
required for this discharge (Fig.3). During
discharge, temperature of internal fluid andemission intensity increase with the dischargetime, and H2O and methanol are remarkable. On
the other hand, in the case of toluene,temperature and emission intensity hardlychange. It is considered that the fluid heating isdependent on the electric dipole moment of fluid(Table I), and dielectric constant of fluid decreasein the increase of temperature. This result
indicates that the increase of temperature anddecrease of dielectric constant of internal fluid
affects the improvement of plasma density andstability of atmospheric discharge.
In the case of glass bulb condenser (Fig.2(b)),
large volume Ar plasma stably generated in inner
glass tube. Especially, in spite of the change of thediameter of the inner glass tube, the plasma wasuniformly generated. This result suggests thatstability mechanism of internal fluid is spatiallyeffective on surface of inner glass tube.

Acknowledgments
This work was supported by the Programme for
Promotion of Basic and Applied Researches forInnovations in Bio-oriented Industry .

Fig.2 Typical image of atmospheric dischargeusing water-dielectric multi-layer electrode.
(a): straight inner grass tube(Fig.1), (b): using
glass bulb condenser (Allihn condenser).

Fig.3 Time evolution of temperature ofinternal fluid and emitted light intensity fromAr plasma using water-dielectric multi-layerelectrode. (a): Temperature of fluid, (b):lightintensity measured by multi channel
spectrometer. In the case of methanol,
temperature of fluid exceeded the boiling point
after 5 minutes from the start, and experiment
was stopped.