22P038-P
Generation of Microwave Plasma Jet and Analysis on Launcher Nozzle
at Atmospheric Pressure in Airtight Chamber
気密容器内での大気圧マイクロ波プラズマ・ジェット生成とそのためのランチャー解析
Yuki Uchiyama, Shuichi Takamura
内山 雄貴, 高村秀一
Faculty of Engineering, Aichi Institute of Technology
Toyota 470-0392, Japan
愛知工業大学 〒470-0392 豊田市
Launcher nozzle for microwave plasma jet at atmospheric pressure has been developing by improving
TIAGO nozzle which has no air-tight configuration. Electromagnetic analysis code, PHOTON Series-‘Wave jω’ gives field distribution around the nozzle which helps the optimization of launcher nozzle.
Generation of microwave plasma jet at atmospheric pressure in airtight chamber would make the PWI
experiment possible. Generation of microwave plasma jet at atmospheric pressure in airtight chamber andPWI experiment have been done under the electromagnetic analysis.

1. Introduction
Atmospheric-pressure plasmas have attracted
much interest recently for applications inmaterials synthesis, surface treatment, etching,film deposition, medical treatment, environmental
application and many more. They may also havegreat potentiality for the very high heat-flux
plasma beam intended for fundamental researchon plasma-wall interactions (PWI) in next-fusion
devices,suchasITER(InternationalThermonuclear Experimental Reactor).
In recent years, the production of microwave
plasma jets at atmospheric pressure using therecently developed TIAGO nozzle[1, 2] become
very popular due to its simplicity, easy ignition,
unnecessity of airtight chamber and sustainmentof discharge at the open air having a gas flow
function.
But TIAGO system has no air-tight structure foratmospheric-pressure. Recently, launcher nozzle[3] for PWI experiment using airtight chamber has
been developed. Launcher nozzle has a structure
which connects the waveguide with the airtightchamber.
Here, we use an electromagnetic analysis codefor the launcher nozzle. The evaluation andoptimization have been made. We also tried togenerate high heat flux plasma jet in the airtightchamber for PWI studies.

top of nozzle which has a tapered conicalstructure. Also, standing wave peak generated
with a short plunger along the waveguide isadjusted in position so that the loop of standing
electric field is located at the nozzle.
Electromagnetic configuration in the waveguide
is TE10mode. Launcher nozzle is developed bychanging the TIAGO nozzle by adding a airtightfunction as shown in Fig.1. The chamber is set
perpendicular to the waveguide.
Details of Launcher nozzle and microwave
circuit are shown in Fig.1.

2. Experimental Set-up
Generation system of microwave plasma jet atatmospheric-pressure with TIAGO nozzle
strengthens the microwave electric field on theFig.1.Microwave circuit and launcher nozzle

3. Numerical Analysis
PHOTO Series–‘Wave jω’ of PHOTON Co hasbeen used for the electromagnetic analysis. The
programme employed is three-dimensionalfrequency response code by finite element method.
It gives electric field distribution over the free spaceby taking account of boundary conditions.
As boundary conditions, we have either asymmetric or nonreflective boundary conditions
depending on the boundary property. The
wavelength in free space is λ = 122.4mm so that themesh size is set < λ/6 = 20.40mm. Wavelength in
the waveguide (TE10 mode) is λg/4 =36.94mm. The
field at the waveguide entrance is put Ey = 1V/m,corresponding to a reference electric field.
Deployment models and the mesh are shown in
Fig.2.

the suppression of WO3 formation since it has ayellow color.
Reading of crystal gauge is increased when the
microwave power turns off. We thought that the
air comes into the airtight chamber when the
microwave power turns off. Because He gas isexpanded by the plasma heat, it shrinks by the
microwave turn off, and the air comes into theairtight chamber at this instance.

Fig.2.Model configuration with meshfor numerical analysis

4. Summary4-1.Analysis on Launcher nozzle
The numerical analysis gives the electric field
distribution along the nozzle height. Basic nozzle
length is 66mm (H=66mm).
The distance d between the nozzle tip and thefirst node of electric field distribution is less thanλ/4. It means that the terminal load in the sense of
distributed transmission line would be capacitive
due to the radiative electric field. The distance
between the neighboring loops or node isapproximately a half of free space wavelengths.
4-2 PWI Experiment
PWI experiment has been done in the airtightchamber, where the working gas is He. Before
generating a plasma, we will put to inject gas inturn He → N2 → He in order to purge the oxygenfor preventing the formation of tungsten trioxide.
The W surface temperature, its floating potential
and the gas pressure in airtight chamber havebeen followed for 5 min. Temperature has beenmeasured by radiation thermometer. Emissivity ofradiation thermometer is set 0.43 at thewavelength of 0.9μm. The time traces of thesequantities are shown in Fig.4.
The temperature approaches to near 1800K.
Even such a high surface temperature of tungsten
material does not give any color change, meaningFig.3. (a) Launcher nozzle set on the waveguide(b) Electric field distribution along the nozzle

Fig.4. Temporal evolutions of W surface temperature,
the floating potential and the gas pressure in the chamber.
He gas flow rate is 1.5L/min, and microwave power is390W. Irradiation time is about 5 minutes.
References[1] M. Moisan, Z. Zakrzewski and J.C. Rostang :Plasma Sources Sci. Technol. 10, 387 (2001).
[2] S. Takamura, M. Kando, N. Ohno : Plasma Fusion
Res. 8, 910 (2009).
[3] M. A. Razzak, S. Takamura, T. Tsujikawa, H.
Shibata and Y. Hatakeyama : Plasma Fusion Res. 4,047 (2009).