Dielectric barrier discharge microplasma
in 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
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.

Experimental Setup(1)Microplasma Electrodes
The electrodes consist in perforated metallic
plates covered with a dielectric layer.

Emission Spectroscopy
Emission spectrum was measured
camera shutter opened for 1 µs.

with

18000
16000

Ar
0.5% N2 in Ar

N2 SPS N SPS
214000Intensity (a.u.)

Microplasma can be found in many applications.
In the last years, the technology was used inapplications such as NOx removal, surface
treatment and sterilization or inactivation ofbacteria.

Discharge voltage andcorresponding discharge current

12000

N2 SPS

10000
8000
6000
4000

N2 SPSOH

N2 SPS

0 ns

2000

1 ns

2 ns

0280 300 320 340 360 380 400 420 440 460 480 500
Wavelength (nm)Fig. 5 Emission spectrum of microplasma in N2/Ar
at -1.2 kV.

AnodeCathodeCathodeN2 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 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.

Fig. 1 Microplasma electrodes

1) Streamer reaches cathode up to 1 ns

100 µm2) Cathode layer formation up to 30 ns

10 ns

15 ns

30 ns

AnodeElectrode size was 20 mm versus 40 mm foremission spectroscopy analysis. Discharge gap
was set at 100 μm in this study.
A Marx Generator with MOSFET switches aspulse power supply:•Output Voltage: -2 kV negative•Rise time: 40 ns•Pulse width: 1 µs(2) Experimental setup
Emission spectrum was measured by aspectrometer,anICCDcameraanda
photomultiplier
tube.
Photosofmicrodischarges
weretaken
usingamicroscope and a digital camera.
Gas flow rate: Ar and N2/Ar at 10 L/min.

3) Cathode layer enhancement up to 70 ns

40 ns

50 ns

60 ns

Fig. 6 Spatial and temporal evolution of therelative intensity of Ar I peak at 696.5 nm
for microplasma discharge in Ar at 1 kV.
CathodeAnode4) Cathode layer decay up to 270 ns

70 ns

100 ns270 nsFig. 2 Experimental setup.

LeftelectrodeactiveMeasured area

Gas flow

Fig. 3 Measured area of emission spectra.

Fig. 7 Spatial and temporal evolution of the relative
intensity of N2 SPS peak at 337.1 nm for
microplasma discharge in 1% N2 in Ar at 1 kV.

(3) Microdischarges
Very small discharge gaps and relatively low
discharge voltages (about 1 kV). A highintensity electric field (107-108 V/m) assures
the formation of microplasma.

Negative
electrode Negative glow
(high voltage)

Diameter
Ø~10 µm

Spatial and Temporal Evolution ofMicroplasma
The observation of microdischarge by ICCD
camera shows the streamer formation
phenomena and the correlation of themicrodischarge evolution with the discharge
current.
Microdischarges
phenomena
waswellcorrelated with the discharge current value.

60 µm
Grounded Positive Faraday dark
spaceelectrode column
Fig. 4 Phenomena of microdischarges.

J=5.2 A/cm2 for Ø30 µm microdischarge
ne=J/(Eµee) – electron density
vd - electron drift velocity = 2x105 m/s
E – intensity of electric field=1kV/100 µmµe=vd/E – electron mobility=200cm2/(V s)ne = 1.6 x 1012 cm-3

Fig. 8 Spatial and temporal evolution ofmicroplasma discharge in 3% N2 in Ar at 1 kV .
ICCD camera shutter was opened for 2 ns.

Conclusions•Emission spectrum of microplasma shown
intensity peaks of N2 SPS, OH and ArI.
•Spatial and temporal evolution of therelative intensities of ArI peak at 696.5 nm
and N2 SPS peak at 337.1 nm showed higher
intensity towards anode up to 20 ns and after
it shifted towards cathode.
•ICCD camera images showed the evolutionof microdischarges from the phase when
streamer reaches anode to cathode layer
formation, cathode layer enhancement andfinally cathode layer decay.