22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Comparison of plasma jets generated by a dielectric barrier discharge (DBD)
and discharge with bare electrodes (DBE) by double probe measurements
E.R. Ionita1, M. Bazavan2, M. Teodorescu1 and G. Dinescu1
1
National Institute for Laser, Plasma and Radiation Physics, 077125 Bucharest-Magurele, Romania
2
Physics Department, University of Bucharest, 077125 Bucharest-Magurele, Romania
Abstract: In the present work we present estimated values of electron densities and
temperatures using double probe measurements technique for two planar atmospheric
pressure plasma jets. The plasma jets are generated in argon by a Dielectric Barrier
Discharge (DBD) and Discharge with Bare Electrodes (DBE) plasma sources, powered by
radiofrequency.
Keywords: DBD, DBE, plasma jet, double probe
1. Introduction
Recently, we have developed two atmospheric pressure
plasma jet sources based on different discharge types but
working in similar conditions. One of these two is
Dielectric Barrier Discharge (DBD), uses a dielectric
barrier at both electrodes, while the other one, Discharge
with Bare Electrodes (DBE), has both electrodes in
contact with the discharge. Both sources (Fig. 1) have the
same geometry, the same discharge space respectively
and have the same operating range in respect with the
radiofrequency (RF) power and gas (argon) flow rate.
Investigation of atmospheric pressure plasma with
electrical probes is a difficult problem, due the collisional
regime. Still, there are a few reports on this problem [1,
2]. Herewith we attempted to obtain and compare data on
DBD
DBE
Fig. 1. Image with atmospheric pressure plasma jets
DBD and DBE (Pfwd = 12 W, 5000 sccm argon flow)
electron densities and temperature in the two plasma jets
using double probe measurements.
2. Experimental Set-up
Fig. 2 presents the experimental set-up designed for
double probe measurements on both DBD and DBD
plasma sources. The radiofrequency (RF) power supply
used to generate the discharge in DBD and DBE sources,
was a RF generator type Advanced Energy 136 CESAR
C3 (13.56 MHz). The matching of the discharge
impedance to the generator output impedance (50 Ω) was
achieved through an automatic matching network type
Advanced Energy Match Network. The RF forward
P-I-2-15
power value investigated was 12 W (the reflected RF
power value was 0 W). The DBD and DBE jet plasma
sources were fed with gas (argon) by a mass flow
controller type Bronkhorst High-Tech series EL FLOW.
The double probe was inserted perpendicular to the
plasma jet plane with equal distance from electrodes to
the nozzle line. The probe consisted of two electrodes that
penetrate the plasma jet. The electrodes are cylindrical,
made of copper coated with gold, with a diameter of 0.45
Fig. 2. The experimental set-up used for double probe
measurements on both DBD and DBE plasma sources.
mm and a length of 15 mm. The distance between the
electrodes is 2.54 mm. The electrodes were connected to a
Source Measure Unit (SMU) Keithley 2410. The SMU
was programed to sweep with 1000 steps the voltage
range -175...175 V.
3. Results and Discussion
To determine the temperature and the electron density
were acquired current-voltage curves corresponding to the
simple Langmuir probe and double probe with
experimental system described above. In Fig. 3(a) are
shown graphically, two current-voltage curves
corresponding for the simple probe, in the DBD and DBE
discharge, obtained at a flow rate of 2500 sccm of argon
1
2 ⋅ I1+ ⋅ I 2 +
I1+ + I 2 +
Ne ≈
k BTe
T λ
p 
A⋅ ⋅e⋅
⋅ e ⋅ +
M
Tg R p
2
and 1.5 mm distance from the nozzle. Since both
electrodes are isolated in DBD discharge, they are not
being in electric contact with the plasma, simple probe
characteristic cannot be evaluated similarly to the case of
DBE discharge, where there is reference electrode.
Consequently, in the present study were analysed only
curves obtained with the double probe (Fig.3 (b)).
300.0µ
800.0n
DBD, 12 W, 1.5 mm, Ar 2500 sccm
DBE, 12 W, 1.5 mm, Ar 2500 sccm
600.0n
DBD, 12 W, 1.5 mm, Ar 2500 sccm
DBE, 12 W, 1.5 mm, Ar 2500 sccm
1.0µ
400.0n
200.0µ
200.0n
150.0µ
0.0
100.0µ
50.0µ
-400.0n
0.0
Ip (A)
Ip (A)
Ip (A)
500.0n
-200.0n
0.0
-500.0n
-600.0n
(a)
-1.0µ
-50.0µ
(b)
-100.0µ
-800.0n
-200
-150
-100
-50
0
50
100
150
-1.5µ
-200
200
-150
-100
-50
0
50
100
150
200
Up (V)
Up (V)
 T
⋅ 1 + g
 Te
 1
 ⋅
 Λ
where: A is the probe area in contact with plasma, M
is the mass of an argon ion, Tg is the temperature of gas
1.5µ
250.0µ
(2)
Fig.3 Simple Langmuir probe curves (a) and double
probe curves (b) for DBD and DBE discharge,
obtained at 1.5 mm from nozzle and with 2500 sccm
(400 K), R p is the radius of the electrode, λ+ is the mean
free path of ions due to elastic collisions. Λ is a
dimensionless parameter that takes into account the
influence of the ionic current plasma cooling [4]; Λ ≈ 1 in
the centre of the plasma and Λ ≈ 2 at the edge of plasma.
In the present case we have Tg ≈ Tambient , and it was
considered Λ = 1 .
For the calculation of electronic temperature ( Te ) we
used the relationship (1) [1, 2]:
1.40E+017
1.20E+017


0
⋅ FD
(1)
1.00E+017
Ne (m-3)
1
e I ⋅I
Te = ⋅ 1+ 2 + ⋅
k B I1+ + I 2 +  dI S

 dU S
DBD, 12 W, 1.5 mm
DBE, 12 W, 1.5 mm
8.00E+016
6.00E+016
where: e is the elementary charge, k B is the
Boltzmann's constant, I1+ and I 2+ are ion saturation
currents, I S current probe, U S the voltage applied to the
probe and FD is electronic correction factor
corresponding to Knudsen number; this factor expresses
the influence of particle collisions in space charge layer
around the probe [3].
4.00E+016
2.00E+016
0
4000
6000
8000
10000
Flow Rate (sccm)
Fig. 5 Electron density depending on the flow of
argon, the double probe was placed at 1.5 mm
nozzle.
The obtained dependences of electron temperature upon
the flow of argon obtained by applying relation (1) are
shown graphically in Fig. 4. In the case of DBE discharge
68000
64000
Te increases
DBD, 12 W, 1.5 mm
DBE, 12 W, 1.5 mm
60000
Te (K)
2000
with gas flow, but having smaller values in
the case of DBD discharge.
The dependences of electron density (from (2)) upon
the flow rate of argon, are shown graphically in Fig. 5. In
both cases, DBD and DBE discharge, we have almost a
linear increase of N e with gas flow increase. The N e
56000
52000
values for DBD discharge are lower than for the DBE
discharge.
48000
0
2000
4000
6000
8000
10000
Flow Rate (sccm)
Fig. 4. Electron temperature depending on the
flow of argon, the double probe was placed at 1.5
mm nozzle.
Electron
density
( Ne )
was
determinated
For a DBD-DBE comparative representation of
electronic temperatures, in Fig. 6 are presented the ratios
of DBD and DBE and as well the ratio curves for electron
densities.
with
relation (2):
2
P-I-2-15
22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Previous OES measurements of excitation temperatures
(T exc ), based on Ar lines in a axial DBE source,
performed on other atmospheric pressure jet plasma
sources [5] indicated a result of T exc ≈1.5 eV The results
obtained with the double probe in the present study
indicated 3<T e <6.5, therefore systematically greater.
[3] S. Klagge and M. Tichý, Czech Journal of Physics B,
35, 9 (1985).
[4] X. M. Zhu, Y. K. Pu, N. Balcon and R. Boswell,
Journal of Physics D: Applied Physics, 42, 14 (2009).
[5] M. Teodorescu, M. Bazavan, E. R. Ionita and G.
Dinescu, Plasma Sources Sci. Technol. 21, 055010
(2012).
TDBD
/TDBE
, NeDBD/NeDBE
e
e
1.4
1.2
, 12 W, 1.5 mm
/TDBE
TDBD
e
e
1.0
NeDBD/NeDBE, 12 W, 1.5 mm
0.8
0.6
0
2000
4000
6000
8000
10000
Flow Rate (sccm)
Fig. 6 DBD and DBE Ratio of electron density
and temperatures for upon gas flow rate.
In addition, when comparing the electron densities
determined with the double probe (1016-1017 m-3) with
those obtained from OES measurements (1020-5x1021 m-3)
we noticed that the first are values systematically lower.
A possible explanation could be given by a non-Maxwell
distribution. Electron temperature and electron density
obtained by double probe in such a case would be
appropriate only for fast electrons group from plasma
(higher temperature and lower density).
4. Conclusions
We tentatively applied probe methods to investigate by
probe methods DBD and DBE plasma jets. A comparison
of results by single probe was not possible, the single
probe measurements in DBE jets being inadequate.
Instead, double probe measurements produced
characteristics suitable for interpretation. However, the
obtained values for electron densities and temperatures
are different from the results produced by OES, difference
which is
assigned to the fact that in double probe
techniques the tail of the distribution function is
investigate.
5. Acknowledgements
The financial support of the Romanian Ministry of
National Education, UEFISCDI-CNCS, in the frame of
the contract: PN-II-RU-PD-2012-3-0583 is gratefully
acknowledged.
6. References
[1] M. Čada, Z. Hubička, M. Šı́cha, Churpita, L. Jastrabı́k,
L. Soukup and M. Tichý, Surface and Coatings
Technology, 174–175, 530–534, (2003).
[2] L. Prevosto, H. Kelly and B. R. Mancinelli, Review of
Scientific Instruments 85, 053507 (2014).
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