SPATIAL DISTRIBUTION OF MICROPLASMAIN SMALL DISCHARGE GAPS
Marius Blajan and Kazuo Shimizu
Organization for Innovation and Social Collaboration, Shizuoka University,
3-5-1 Jyouhoku, Hamamatsu, 432-8561, JAPAN; E-mail：blajanmarius@yahoo.com
Emission Spectroscopy

Introduction

The fundamental phenomena of microplasma
discharge are not fully understood. The
development and optimization of microplasma
technologies depend on the clarification ofmicroplasma physics. Our microplasma is adielectric barrier discharge at atmosphericpressure.

Emission spectrum was measured
camera shutter opened for 1 µs.

withThe observation of microdischarge by ICCD
camera shows the streamer formation
phenomena and the correlation of themicrodischarge evolution with the discharge
current.

18000

(a)

16000
14000

Intensity (a.u.)

Microplasma
canbefoundinmany
applications. In the last years, the technology
was used in applications such as NOx removal,
surfacetreatment
andsterilization
orinactivation of bacteria.

Ar I

Ar I

12000
10000

Ar I

8000
6000

Ar I

Spatial and Temporal Evolution ofMicroplasma

Ar I

4000
2000
0410

Experimental Setup

415

420

425

430

435440

Wavelength (nm)18000(1)Microplasma Electrodes

214000Intensity (a.u.)

The electrodes consist in perforated metallic
plates covered with a dielectric layer.

Ar
0.5% N2 in Ar(b) N SPS
2N SPS

16000
12000

N2 SPS

10000
8000

N2 SPS

6000
4000

1) Streamer reaches cathode up to 1 ns

N2 SPS

OH0 ns

2000

1 ns

2 ns

0280 300 320 340 360 380 400 420 440 460 480 500
Wavelength (nm)16000

Fig. 1 Microplasma electrodes.

Emission spectrum was measured by aspectrometer, an ICCD camera and aphotomultiplier
tube.
Photosof
microdischarges
weretakenusinga
microscope and a digital camera.
A fast ICCD camera was used for taking
photos at specific moments during discharge.
Gas flow rate: Ar, N2/Ar and O2/Ar at 10L/min.

12000
10000
8000
6000
4000
2000

Anode(2) Experimental setup

0.5% O2 in Ar
1% O2 in ArAr(c)CathodeElectrode size was 20 mm versus 40 mm foremission spectroscopy analysis. Discharge gap
was set from 30 μm to 100 μm in this study.
A Marx Generator with MOSFET switches aspulse power supply:•Output Voltage: -2 kV negative•Rise time: 100 ns•Pulse width: 1 µsIntensity (a.u.)

14000

100 µm

0300 302 304 306 308 310 312 314 316 318 320
Wavelength (nm)2) Cathode layer formation up to 30 ns

10 ns

15 ns

30 ns

Fig. 6 Emission spectrum of microplasma in: (a) Ar;(b) N2/Ar; (c) O2/Ar at -1.2 kV.
N2 molecules excited argon neutrals andreaction in argon plasma with N2 addition:
Ar*+ N2(X1Σg+)v=0 → N2(C3πu)v’=0 + Ar
Spontaneous radiation of formed excitedstate of nitrogen:N2(C3πu)v’=0 → N2(B3πg)v’’=0 + hνSpatial distribution outside of electrodes
shows a distribution of about 1 mm for theOH peak at 309 nm and 500 µm for the Ar I
peak at 696.5 nm respectively.

Relative intensity (a.u.)1.23) Cathode layer enhancement up to 70 ns

OH peak 309 nm

1Ar I peak 696.54 nm

40 ns

50 ns

60 ns

0.8
0.6
0.4
0.2

Grounded electrode0Fig. 2 Experimental setup.

0200

400

600

800

1000

Distance (um)LeftelectrodeactiveMeasuredarea(a)Gas flowLeftelectrodeactiveMeasured area(b)Gas flow

Fig. 3 Measured area of emission spectra: (a)outside the electrode; (b) in discharge gap.
(3) Electrical Characteristics
Very small discharge gaps and relatively low
discharge voltages (about 1 kV)

Fig. 7 Spatial distribution of OH radical and Ar I
at the outside of grounded electrode forelectrode arrangement shown in Fig. 3 (a).
Spatial and temporal distribution of Ar I peakat 696.5 nm and N2 SPS peak at 337.1 nm
shows higher intensity towards anode up to20 ns and after that shifted to cathode.
The experiment were carried out with theside part of electrodes towards open air thus
effect of oxygen should be considered.

Cathode4) Cathode layer decay up to 270 ns

70 ns

100 ns270 nsAnodeFig. 10 Spatial and temporal evolution ofmicroplasma discharge in 3% N2 in Ar at 1 kV .
ICCD camera shutter was opened for 2 ns.
Microdischarges
phenomenawaswellcorrelated with the discharge current value.

Fig. 4 Waveforms of the discharge voltage,corresponding discharge current and gate signal for
ICCD camera.
A high intensity electric field (107-108 V/m)assures the formation of microplasma and acorresponding discharge current.

Negativeelectrode Negative glow(high voltage)

Fig. 8 Spatial and temporal evolution of therelative intensity of Ar I peak at 696.5 nmfor microplasma discharge in Ar at 1 kV.
CathodeAnodeDiameterØ~10 µm•Emission spectrum of microplasma shown
intensity peaks of N2 SPS, OH and ArI.
•Spatial distribution of ArI peak at 696.54
nm and OH peak at 309 nm outside thegrounded electrode was measured up to 500µm for ArI peak and 1 mm for OH peak
respectively.
•Spatial and temporal evolution of therelative intensities of ArI peak at 696.54 nm
and N2 SPS peak at 337.1 nm showed higher
intensity towards anode up to 20 ns andafter it shifted towards cathode.

60 µm•ICCD camera images showed the evolutionof microdischarges from the phase when
streamer reaches anode to cathode layer
formation, cathode layer enhancement anf
finally cathode layer decay.

Grounded Positive Faraday dark
spaceelectrode column
Fig. 5 Phenomena of microdischarges.

Conclusions

Fig. 9 Spatial and temporal evolution of the relative
intensity of N2 SPS peak at 337.1 nm formicroplasma discharge in 1% N2 in Ar at 1 kV.