23E03
Measurement of Electric Field in Pulsed Corona Discharge
パルスコロナ放電進展時の電界計測
Ippei Yagi, Ryo Ono, Tetsuji Oda and Koichi Takaki
八木一平，小野 亮，小田哲治，高木浩一
Department of Advanced Energy, The University of Tokyo
5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8561, Japan東京大学 〒277-8561 千葉県柏市柏の葉 5-1-5Electric field of streamer is estimated using spectroscopic method. The streamer discharge inatmospheric pressure is ignited by the pulsed high voltage generator supplying ten nanoseconds ofpulse rise time. In synthetic air, the intensity and the length of secondary streamer are increased by theapplied voltage. The emission intensity of N2(C3u) and N2+(B2u+) are measured using
monochromator and photomultiplier tube in order to estimate the electric field of streamer.

1. Introduction
Non-thermal plasma driven by pulsed streamer
discharge in atmospheric pressure is a promisingtechnology for the decomposition of environmental
pollutants and in medical treatment [1-2]. For
industrial use, evaluation of the electric fieldstrength in the plasma has been expected. Someworkers have evaluated the electric field of thestreamer in experiment [3-4]. However, the electricfield estimation of streamer is not well understood
yet due to the measurement is hard to carry out due
to the high spatio-temporal resolution in several
hundreds of micrometer and a sub-nanosecond.
In this paper, we observe the monochromic light ofnitrogen emission to estimate the electric field ofstreamer using photomultiplier tube and digital
camera with image intensifier. We particularly pay
attention to the influence of the voltage waveformwith or without generating secondary streamer on
the electric field.
2. Methodology
Fig. 1 shows the sketch of experimental set up fortime resolved measurements of nitrogen emission in
streamer discharge. The needle-to-plate electrodes
having gap of 7 mm are employed to generate thedischarge in particular location. The electrodes areplaced in a cylindrical reactor filled with synthetic
air. The applied voltage of 18.5 kV, generated by thepulse power generator, has pulse width (FWHM) of
98.8 ns and pulse rise time (10-90% of maximumvoltage) of 10.2 ns.
The emission from the discharge is focused on theinput slit of a monochromator (Nikon, P250) withboth the slits width of 0.1 mm. A photomultiplierFig. 1. Sketch of the experimental setup.

tube PMT1 (0.57 ns in rise time) for detection of
monochromatic light as the main signal and PMT2
for the down edge trigger of the oscilloscope as thesynchronizing signal are used, since the derivative of
this signal is actually used to define the zero-point of
the relative time scale. The discharge propagatedbetween the electrodes is observed with digital
camera with image intensifier unit.
The data procedure of electric field estimation isthat the intensity ratio of nitrogen emission fromequation (1) and (2), considered with quenching by
neutral particles of oxygen and nitrogen, finds theratio of rate constant and calculates the electric fieldusing BOLSIG+ software package [5]
∏→

∏(1)

∑→

∑(2)

3. Results
Fig. 2 shows the image of streamer observed
between electrodes by digital camera with image
intensifier unit. The streamer exhibits branching inboth cases. The length of the secondary streamer
increases with applied voltage, being and 3mm at
18.5 kV.
Fig. 3 shows that both emissions of IB and IC,
being IB and IC of monochromatic light in thereaction (1) and (2) respectively, begin at 0 ns withapplied voltage of approximately 8.6 kV. The
maximum intensity of IB is approximately 100 times
smaller than peak intensity of IC. The emission
intensity of IB decays slower than IB and has thesecond peak of emission from secondary streamer(see Fig. 2).
The reduced electric field has the first peak of 800
Td at 3.9 ns after emission beginning and decreases
to 372 Td at 9.1 ns. It is considered that thetransition from primary to secondary streamer isoccurred at the time of approximately 9.1 ns and thesecondary streamer maintains the relatively low
electric field between 350 to 575 Td for 25.6 ns. It isalso considered that the sharp decline of the reduced
electric field at 5.1 ns is caused by the electricalreflection in PMT1’s circuit. The peak value ofelectric field on primary streamer seems suitable forthe numerical calculations [6]. On the other hand,the value of electric field on secondary streamerafter the time at 9.1 ns is 3-5 times higher than thenumerical calculation [7]. It is considered that theemission of IB (equation (2)) is relatively strong at
the tip of the needle electrode due to the higher
electric field.
4. Conclusion
As a conclusion, the emission intensity ofprimary streamer and the length of secondary
streamer increased with applied voltage.
The reduced electric field sharply dropped to thevalue between 350 and 575 Td after sustaining thepeak of 800 Td driven by primary streamer until 9.1
ns. It was shown that the transition from primary to
secondary streamer.
Acknowledgment
The authors would like to acknowledge that thisresearch work is partially supported by JSPS Research
Fellowships for Young Scientists.

NeedlePlateFig. 2. Streamer channels for applied voltages of18.5 kVFig. 3. Waveforms of applied voltage, emission
intensity of IB and IC, and electric field of streamer.
[2]

[3]
[4]
[5]
[6]

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