S3-5
パルスパワーを用いたプラズマの生成と液相応用
Pulsed Power Generated Streamer Discharges and Its Application on Liquids
王 斗艶，浪平 隆男，秋山 秀典
Douyan Wang, Takao Namihira, and Hidenori Akiyama
熊本大学 パルスパワー科学研究所
Institute of Pulsed Power Science, Kumamoto University
1. Introduction
Pulsed power generated discharge plasma
enables a large volume, various reactive species, alarge amount of high energy electrons, and has
sufficient energy efficiency of gas and liquid
treatments. This manuscript briefly introduces its
characteristics and examples of applications.
2. Pulsed Discharges Generated by Pulsed PowerTechnology
To generate discharges by pulsed power, thesimplest power supply is the capacitor bank, which
consist of a DC power source, a capacitor and aswitch. The advantages of this system are thesimple circuit structure and available with any kindsof load connection. The disadvantage is that time
duration of output voltage varies with time constantbased on the circuit and load combination. In
general, one of the most important issues of pulsed
power technology for non-thermal plasma
application is to form a square pulse and theimpedance matching between power supply andload. Thus, making a flat top of voltage waveformmeans it is able to transfer high voltage to load
constantly which produces large amount of reactivespecies. In this point, the advanced pulsed power
supply shall be the pulse forming network, PFN.
PFN consists with a DC source, a series of LC
ladder modulators, and a switch. This also can besubstituted by using a coaxial cable, namely pulse
forming line, PFL [1].
Fig. 1 shows a framing image and a streak imageof a 100 ns pulsed discharge in a coaxial electrodegenerated by a three-stage Blumlein line generator:
a kind of PFL [2]. From Fig. 1, two stages of thedischarge can be clearly defined during the pulseddischarge. The first one is the “streamer discharge,”
which means the phase of streamer headpropagation between electrodes. The other one is
the “glow discharge” that follows the streamerdischarge. The averaged propagation velocity of thestreamers was 1.2 mm/ns for 60 kV applied voltage.
It was also observed that the gas temperature

increased by about 150 K during the glow discharge
phase. The temperature rise indicates thermal loss
during the plasma reaction process that would lower
treatment efficiency in applications.
3. Nanosecond Pulsed Streamer Discharge
In order to make plasma reactions with higher
energy efficiency, a pulsed discharge aimed toreduce the glow discharge phase has invested:
namely the “nanosecond pulsed streamer discharge”.
Fig. 2 shows the images taken with the same
method using a nanosecond pulsed power generator
which theoretically has 5 ns of pulse duration [2].
From Fig. 2, it is clearly observed that the time
duration of the streamer discharge was within 6 ns.
At around 5 ns, emission from the central rod
electrode was observed, which attributed to thestrong electric field at the rod, but finallydisappeared at around 7 ns. In this case, the glow
discharge phase was not observed. The averaged
Brightness

Glow discharge

Central rod
electrodeCentral rod(a) Framing image(b) Streak image
Fig.1. Images of a 100 ns pulsed discharge in a coaxial
electrode taking from axial direction [2].
Brightness

Central rod
electrodeCentral rod(a) Framing image(b) Streak image
Fig.2. Images of a 5 ns pulsed discharge in a coaxial
electrode taking from axial direction [2].

NO removal eficiency, mol/kWh

propagation velocity of the streamers was 6.1
mm/ns for 67 kV applied voltage, which is about 5times faster than 100 ns one. Using nanosecond
pulsed discharge, its energy efficiency in gas
treatment applications shows the better performance
than other non-thermal plasma methods. Fig. 3
gives the examples in case of nitric monoxide
treatment and ozone generation [3].
0.8Nanosecond
Pulsed Discharge

was fixed at same experimental conditions, and thefeeding gas was O2 to generate discharge plasma.
Treatment time was 3 hours. The results shows that
TOC are reduced with all samples.
5. Conclusion
Nanosecond pulsed discharge plasma generated
by pulsed power has sufficient energy efficiency forplasma processing application, due to its unique
physical properties of discharge phenomenon.

0.6

0.4

0.2
DBD
00

Pulse CoronaDischarge

20406080
NO removal raio, %100(a) NO treatment
Nanosecond
Pulsed Discharge

500DBD narrowgap(0.05-0.8mm)

DBD

400

Superimposed
Discharge

300

Pulsed Corona
Discharge

DC Corona(Pos.&Neg.)

CommercialOzonizer

200 Surface
Discharge
100
00.001 0.01

Fig.4 Schematic diagram of water treatment systemusing nanoseconds pulsed discharges.

1000.1

1

10

100

1000

Ozone concentration, g/m3(b) Ozone generation
Fig.3. Characteristics map of nitrogen monoxide (NO)treatment (a) and oxygen-fed ozone generation (b) basedon different discharge methods [3].

4. Treatment of Liquids Using Nanosecond
Pulsed Streamer DischargeTo achieve the higher surface-area-to-volume
ratio of plasma-liquid reaction, wastewater wassprayed into the discharge reactor where gas phaseplasma was generated. Fig. 4 shows the schematic
diagram of water treatment system using
nanoseconds pulsed discharge. The spray unit wasmounted in the upper inlet of the discharge reactor,
and treatment water was circulated at a certain flowrate. Fig. 5 shows the treatment results withdifferent persistent organic pollutants (POPs) that
all has different chemical structures. The treatment

TOC removal ratio, %Ozone yield, g/kWh600

Acetic acid80

Phenol60

SDBS401,4‐dioxanePFOS

200Fig.5 Treatment of different persistent organic pollutants
in water using nanoseconds pulsed discharges.
References[1] D. Wang, T. Namihria and H. Akiyama: J. Inst.
Electrostat. Jpn. 39(6), 230-236 (2015) in Japanese.
[2] D. Wang, S. Okada, T. Matsumoto, T. Namihira, H.
Akiyama: IEEE Trans. Plas. Sci. 38(10) 2746-2751(2010).
[3] D. Wang, T. Namihira, H. Akiyama: J. Adv. Oxi.
Tech. 14(1) 131-137 (2011).