24P116-P
Investigation of Hydrogen Isotope Combustion Processes
in Atmospheric Pressure Plasma
大気圧プラズマによる水素燃焼反応過程の解明	 
Kazuhiko Akahane1, Naomichi Ezumi1, Keiji Sawada2, Yasunori Tanaka3, Masahiro Tanaka4,Tatsuhiko Uda4 and Kiyohiko Nishimura4
赤羽和彦1, 江角直道1，澤田圭司2，田中康規3，田中将裕4，宇田達彦4，西村清彦4
1

Nagano National College of Technology, 716, Tokuma, Nagano-city, Nagano 381-8550, Japan
2
Shinsyu University, 4-17-1, Wakasato, Nagano-city, Nagano 380-8553, Japan
3
Kanazawa University, Kakuma-cho, Kanazawa-city, Ishikawa 920-1192, Japan
4
National Institute for Fusion Science, 322-6, Oroshi-cho, Toki-city, Gifu 509-5292, Japan1
長野高専 〒381-8550	  長野県長野市徳間716
2
信州大学 〒380-8553	  長野県長野市若里4-17-1
3
金沢大学 〒920-1192	  石川県金沢市角間町4
核融合科学研究所	 〒509-5292	  岐阜県土岐市下石町322-6	 

Atmospheric pressure plasmas have many advantages for widespread applications since no necessary touse vacuum equipments. In this study, preliminary experiments of hydrogen oxidation using an
atmospheric pressure plasma have been done with a small amount of hydrogen and oxygen in an argon
plasma. As a result of mass spectrometric measurement, we have confirmed that hydrogen could beoxidized during the atmospheric pressure plasma discharge. The hydrogen conversion rates depend on theinput power for discharge. Moreover, optical emission spectra measurements indicate that OH radical andO radical would be important role for the oxidation process.

1. Introduction
Recovery of tritium in a nuclear fusion reactor
building is one of the important issues. So far, thetritium removal system removes tritium from agasbycracking
thetritium-containingcomponents on a heated precious metal catalyst.
The tritium combines with oxygen in the airstream to form tritiated water. Then the tritiatedwater contained in the air stream is removed by amolecular sieve bed [1]. Although this system hassuitable performance efficiency, there are someproblems for such as high pressure drop, theutilization of a large amount of precious metals
and heating efficiency etc, when the processing
throughput is quite huge.
On the other hands, atmospheric pressureplasmas are widely applied in a variety of fields
such as chemical processing, medical andmaterial engineering in the recent years [2].
These plasmas have advantages with respect tothe cost effect and the low energy consumption
since those can be produced without vacuum
equipments. Also, hydrogen and oxygen radicals
are easily generated by high energy electron andion impact in the plasma. These radicals play animportant role in hydrogen oxidation in the gas
phase reactions [3-6]. Therefore, it is expectedthat a highly effective oxidation process without
precious metals can be constructed by using theatmospheric pressure plasma.
The purpose of this study is to investigate thefeasibility of new hydrogen isotope oxidation
processing using atmospheric pressure plasma
generated by microwave discharge.
2. Experimental Setup
A schematic diagram of the experimental
apparatus for hydrogen oxidation using a
microwave discharge in atmospheric pressure isshown in Fig. 1. A 2.45 GHz microwave power
supply is connected to a plasma source through an
automatic matching box. The maximum output
power is 150W. Notice that the effective
microwave power reached at antenna in a plasma
source is less than 50% of the output of the power
supply. A glass vessel is connected to the plasma
source with a NW flange.

Fig. 1. Experimental setup for hydrogen oxidation using
an atmospheric pressure microwave discharge.

A moisture absorbent is put at upstream of aquadrupole mass spectrometer (QMS) to remove
the background moisture and generated watermolecule during the discharge. H2, O2 and Ar wereused as the sample combustion gas. The mixture
gas of H2, O2 and Ar was fed into the plasma source
through a buffer tank. Each gaseous flow wascontrolled by mass flow controllers. The QMS
mainly measures the time evolution of hydrogen,oxygen and argon gas. Simultaneously, visible lightemissions from the plasma are observed by aspectrometer through a biconvex lens and an opticalfiber. In this experiment, the flow rates of H2, O2and Ar are set 0.04 SLM, 0.40 SLM and 1.56 SLM,respectively. Thus, the concentrations of hydrogenand oxygen are corresponding to 2.0 vol% and 20.0
vol%, respectively. The microwave power fordischarge are changed from 20 W to 100 W as theoutput power of the power supply.

oxidation is possible under the atmosphericpressure plasma condition. Increasing of thehydrogen conversion rate with increasing thedischarge power has been clarified. These results
indicate that the rate can be controlled by thedischarge power which is related to plasma density
and temperature.

Fig. 2. Dependence of hydrogen conversion rate on
the input microwave power.

3. Results and Discussion
In order to evaluate the performance of thehydrogen oxidation, we introduce the hydrogen
conversion rate Xh , defined as follows [3],X h (%) =[H 2 ]i − [H 2 ]o× 100[H 2 ]i(1)where [H2]i and [H2]o are the hydrogen molecule
densities
which correspond to ion current of the€QMS before and after oxidation reaction,respectively.
Figure 2 shows the dependence of conversion
rate Xh on the microwave power. Xh increase withincreasing the power. Furthermore, the Xh seems tosaturate in high power region. The saturations
would be due to the characteristics of the plasma
source because the plasma density could also
saturate with increasing the discharge power in ourexperimental condition. Maximum hydrogen
conversion rate has been reached to 85.5% in thisexperimental condition.
Figure 3 shows emission spectra during thedischarge with a mixture of H2, O2 and Ar. The
optical emission spectra from OH radical and O
radical are observed. It is found that the emission
intensities of OH radical and O radical for 100W
are higher than 20W. These results indicate OH
radical would be key role to oxide hydrogen gas.
4. Summary
A feasibility of hydrogen oxidation process andthe fundamental characteristic during atmosphericpressure microwave discharge have beeninvestigated. It has been confirmed that theFig. 3. Optical emission spectra from the atmosphericpressure microwave argon plasma withhydrogen and oxygen.

Acknowledgments	  This work was supported by NIFS Collaborative
ResearchProgram(NIFS09KFSS015
andNIFS11KESA005).
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