22P017-O
OH radical measurement in a short-pulsed discharge plasma
短パルス放電プラズマ中におけるＯＨラジカルの計測
Masato Watanabe, Naozo Saimaru, Jia Li, Eiki Hotta and Naohiro Shimizu*
渡辺正人，西丸直蔵，李 鉀，堀田栄喜，清水尚博*
Department of Energy Sciences, Tokyo Institute of Technology
Nagatsuta 4259, Midori-ku, Yokohama 226-8502, Japan
東京工業大学 〒226-8502 横浜市緑区長津田町4259* NGK INSULATORS, LTD.
2-56, Suda-cho, Mizuho, Nagoya 467-8530, Japan日本ガイシ株式会社 〒467-8530 名古屋市瑞穂区須田町2-56
Dielectric barrier discharge (DBD) is developed for application of the plasma sterilization technology.
Lifetimes for OH radicals were measured with two kinds of electrode configuration, needle-plate andcrossed electrode using laser-induced fluorescence method for understanding the plasma sterilization
process.

electrode with the metal prate covered by a plastic
film. The other consists of two crossed electrodes
with both covered by ceramic pipes as shown in201010500-10-5-20-10-2

2. Experiment
In our experiment, two kinds of electrodeconfigurations were prepared. One is a needle-plate-1

012t (μsec)

Fig. 2 Voltage and current waveform

I (A)Fig. 1 Photograph of crossed electrodeV (kV)

1. Introduction
As one of the promising technology forbiologicalandbiomedicalapplications,sterilization using non-thermal plasma hasrecently been receiving much attention[1].
Especially, due to its ability to avoid glow-to-arctransition, dielectric barrier discharge (DBD)
plasma provides an excellent alternative toconventional sterilization technique such as heat,chemical and radiation.
Although the exact mechanism for plasma
sterilization is still unclear, it is widely acceptedthat radicals, i.e. active chemical species like OH,
are playing the important role. In plasma, radicals
from atoms or molecules are usually generated byhigh-energy electron impact and have very highreactivity. Once the radicals interact with thebacteria, chemical reaction like oxidation will
occur immediately causing the death of bacteria.
Understanding this process will be helpful toclarify the mechanism for plasma sterilization.
However, because this reaction mechanism is still
not clarified, it is necessary to observe both thegeneration and reaction process of radicals.
Moreover, it is necessary to investigate the spatial
distribution of radical in detail.
In this paper, in order to investigate thecharacteristic and distribution of OH radical in
DBD plasma driven by nanosecond short pulses,
the laser-induced fluorescence (LIF) experiments
were carried out.

electrode spreads with cone shape. Average
lifetimes of OH radicals for both electrodes weresimilar, that is 74 μsec for cross electrodes and is 75
μsec for needle-plate electrodes.
2000
LIF signal (a.u.)

Fig. 1. The gap distance (d) is taken from theshortest distance between two crossed ceramic
pipes. The applied voltage has a duration of ~ 400
ns with a repetition rate of 1 kHz. The typicalvoltage and current waveforms are shown in Fig. 2.
For the electric discharge at atmospheric pressure,voltage and the peak value of current were 13.0 kV
and 5.5 A, respectively.
For the OH radical observation, LIF method[2][3]was employed. The experimental setup is shown inFig. 3. The excitation wavelength of around 283 nm
was generated by a dye laser (Quanta System
D-100, Rhodamine 590) pumped with afrequency-doubled Nd:YAG-laser (Quanta System
HY-710). Fluorescence light at around 310 nm wasdetected perpendicular to the laser propagation
direction using a bandpass filter (Asahi Spectra,MZ0310) and a photomultiplier tube (HamamatsuPhotonics, R2256-2).

100000100t (μsec)

200(a) Crossed electrode

LIF signal (a.u.)

500

25000Fig. 3 Experimental setup of LIF measurement

3. Results and discussion
Figures 4 show the time dependence of the OH
LIF signal for both electrode configurations. Zeroon the horizontal axis indicates the beginning of thelight emission from the each discharge. Solid line isthe curve fitted by using following equation.

ln(LIF signal) = -1/τ・t + CHere, τ is average life time and C is a constant.
Moreover, in order to eliminate the influence ofozone interference[4], average value of OH LIF
signal between 200 μsec and 900 μsec after
discharge was subtracted from the observed value
until 200 μsec.
It was observed that more OH radicals weregenerated by the cross electrode than by theneedle-plate electrodes. The reason that OH radicals
generated by cross electrodes did not diffuse sincedischarge plasma is having column shape, while thedischarge plasma generated by needle-plate100t (μsec)

200(b) Needle-plate electrodeFig. 4 Time dependence of OH LIF signal

4. Conclusion
Lifetimes for OH radicals were measured for
DBD plasma with two kinds of electrodeconfiguration, needle-plate and crossed electrode,by using LIF method. We will measure thetemporal distribution of OH radicals for bothelectrodes in near future.
References[1] M. Laroussi: IEEE Trans. Plasma Sci. 20 (2002)
1409.
[2] J. Luque and D.R. Crosley: J. Chem. Phys. 109(1998) 439.
[3] A. Ershov and J. Borysow: J. Phys. D: Appl. Phys.
28 (1995) 68.
[4] G.P. Smith and D.R. Crosley: J. Geophys. Res. 95(1990) 16427.