Characteristics of Atmospheric 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

Stark Broadening

Microplasma
canbefoundin
manyapplications. In the last years, the technology
was used in applications such as NOx removal,
surfacetreatment
andsterilization
orinactivation of bacteria. The fundamental
phenomena of microplasma are not fully
understood. Emission spectroscopy, imaging
and Stark broadening techniques were used toclarify the characteristics of microplasma. Dueto the small discharge gaps our microplasma
could be analyzed only using these noninvasive methods.

A pseudo Voigt function was used todetermine Lorentzian FWHM of the Ar I peakat 696.5 nm.
LW2V( )  V0  S(mu22 4(   0 )  L W

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

(1  mu )Discharge voltage andcorresponding discharge current

4 ln 24 ln 2exp( 2 (   0 )2 )
G W
GW

Gw is Gaussian FWHM, Lw is Lorentzian
FWHM, λ is the wavelength, λ0 is the centroid
wavelength. Calculated Lw=0.0042564 nm
and considering van der Waals broadening
Ww=0.003
nm→
Starkwidth
Sw=0.0012564 nm.

1) Streamer reaches cathode up to 1 ns

0 ns

1 ns

2 ns

S W  2(1  1.75* 104 * 4 Ne *  *(1  0.0068* 6 Ne1)) * 1016 * w * Ne
TeFor electron temperature Te=10000
electron density Ne=1.338*1015 /cm3.

→

AnodeCathode100 µm2) Cathode layer formation up to 30 ns

10 ns

15 ns30 nsFig. 1 Microplasma electrodes
Electrode 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, and an ICCD camera. Photos ofmicrodischarges
weretakenusingamicroscope and a digital camera.
Gas flow rate: Ar and N2/Ar at 10 L/min.

Fig. 5 Measured and fitted spectra of Ar I peak at
696.5 nm .
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.

CathodeAnode3) Cathode layer enhancement up to 70 ns

40 ns

50 ns

60 ns4) Cathode layer decay up to 270 ns

70 ns
Fig. 2 An experimental setup.

270 nsFig. 6 Spatial and temporal evolution of therelative intensity of Ar I peak at 696.5 nm
for microplasma discharge in Ar at 1 kV。
CathodeLeft
electrodeactive

100 nsAnode

Measured area

Gas flow

Fig. 3 Measured area of emission spectra.
(3) Microdischarges

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

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.

Negativeelectrode Negative glow
(high voltage)

Conclusions

Diameter
Ø~10 µm

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

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。

Spatial and Temporal Evolution ofMicroplasma
The observation of microdischarge by ICCD
camera shows the streamer formation andthecorrelationofthe
microdischarge
evolution with the discharge current.

•Stark broadening was used for calculating
electron density and estimated to be
Ne=1.338*1015 /cm3.
•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 andafter 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.