Spatial Distribution of Microplasma Light Emission
Marius Blajan, and Kazuo Shimizu
Innovation and Joint Research Center, Shizuoka University,
3-5-1 Jyouhoku, Hamamatsu, 432-8561, JAPAN ; E-mail：blajanmarius@yahoo.com

Introduction
Microplasma
canbefoundinmany
applications. In the last years, the technology
was used in applications such as NOx removal,surface
treatment
andsterilization
orinactivation of bacteria.
The fundamental phenomena of microplasma
discharge are not fully understood. The
development and optimization of microplasma
technologies depend on the clarification ofmicroplasma physics. Emission spectroscopy
is one of the methods for plasma analysis.
Moreover due to the particularities of
microplasma such as small discharge gap, theanalysis can be performed only by this noninvasive technique. 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.

(4) Electrical Characteristics
Very small discharge gaps and relatively low
discharge voltages (about 1 kV)⇨A high intensity electric field (107-108 V/m)assures the formation of microplasma and acorresponding discharge current.

High voltage

Grounded

electrodeelectrode(negative)

100 µmFig. 5 Waveforms of the discharge voltage,corresponding discharge current and gate signal
for ICCD camera.

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

withHigh voltage

Grounded

18000

(a)

Intensity (a.u.)

16000
14000

Ar I

electrode

Ar I

12000
10000

(negative)
Ar I

8000
6000

Ar I

30 µm

Ar I

4000
2000

Fig. 1 Microplasma electrodes.

0Electrode size was 20 mm versus 40 mm foremission spectroscopy analysis. Discharge gap
was set at 30 μm, 100 μm and 200 μm in thisstudy.

410

420

425

430

435440

18000
16000

Ar
0.5% N2 in Ar(b) N SPS
2N SPS
2The streamer diameter was proportionallywith the discharge gap and thinner thanpreviously reported. It has a wider area
towards negative electrode and a smaller
towards the grounded or positive one.

12000

N2 SPS

10000
8000
6000
4000

N2 SPSN2 SPS

OH

2000

1.02

01+V

280 300 320 340 360 380 400 420 440 460 480 500
Wavelength (nm)Fig. 6 Emission spectrum of microplasma in:(a) Ar; (b) N2/Ar at -1.2 kV.

Trigger
Vout
Fig. 2 Photo of negative pulse Marx Generator.

(3) Experimental setup
Emission spectrum was measured by aspectrometer, an ICCD camera and aphotomultiplier
tube.
Photosofmicrodischarges
weretakenusingamicroscope and a digital camera.
Gas flow rate: Ar and N2/Ar at 10 L/min.

Emission spectrum in Ar and Ar/N2 shows:•N2 second positive band system peaks at315.9, 337.1, 357.7, 380.4, 400 and 405 nm.
•OH peaks at 306.4, 307.8 and 308.9 nm.
•Ar I peaks were measured at 415.8, 419.1,419.8, 420.1, 426.6, 427.2, 425.9, 433.3,696.5, 706.7, 727.3, 738.3, 703.2, 750.4 and772.4 nm.
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 696.54 nm respectively.

Relative intensity (a.u.)

OH peak 309 nm

1Ar I peak 696.54 nm
0.8

Measuredarea

Gas flow(a)LeftelectrodeactiveMeasured area

Gas flow

Gas flow

RightelectrodeactiveFig. 4 Measured area of emission spectra:(a) outside the electrode; (b) in discharge gap.

(b)

Negative pulse

0.98
0.96
0.94
0.92

Right electrode active
Left electrode active

0.9
0102030405060708090100X axis (um)Fig. 9 Spatial distribution of N2 SPS peak at 337.1nm in the discharge gap for electrode arrangement
shown in Fig. 4 (b).
Spatial distribution inside the discharge gap
shows a higher intensity towards thenegative electrode as also shown in thestreamer photos.
Vibrational temperature was Tvib=3160 K.
Electron temperature was Te = 23000 K.
Rotational temperature Tgas = Trot = 300 K.
⇨Microplasma=Nonthermal plasma

0.4

Grounded electrode00200400•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.

0.6

0.2

Left
electrodeactiveNegative pulse

Conclusions

1.2

Fig. 3 Experimental setup.

Fig. 8 Photo of a streamer from microplasma
discharge.

Intensity (arb. units)

Intensity (a.u.)Marx Generator with MOSFET switches:•Output Voltage: -2 kV negative•Rise time: 100 ns•Pulse width: 1 µs
•Frequency: 1-24 kHz

415

Wavelength (nm)14000(2) Power Supply

electrode

600

800

1000

Distance (um)Fig. 7 Spatial distribution of OH radical and Ar Iat the outside of grounded electrode forelectrode arrangement shown in Fig. 4 (a).

•Streamer diameter was proportionally withthe discharge gap.
•Spatial distribution of N2 SPS peak at 337.1
nm in the discharge gap shown a higher
intensity near the negative electrode.