Jianjun Shi, Fangchuan Zhong, Jing Zhang and Jianjun Shi, Fangchuan Zhong, Jing Zhang and Michael KongMichael Kong
College of Science, Donghua University, Shanghai, 201620 ChinaDept of Electronic and Electrical Eng, Loughborough University, Loughborough, UK
Control of operation modes in radio Control of operation modes in radio frequency Atmospheric pressure frequency Atmospheric pressure
glow Discharges by excitation glow Discharges by excitation frequencyfrequency
Towards stable & cold atmospheric plasmas
OutlinesOutlines Introductions
Operation modes in RF APGDs• Numerical characteristics;• Experimental studies;
Excitation frequency on RF APGDs• Mode expansion studied by simulation• Experimental studies on excitation
frequency;
Conclusions
Chengdou- 2007: page-2
Towards stable & cold atmospheric plasmas
Introductions
Widely applied low pressure radio frequency plasmasWidely applied low pressure radio frequency plasmas
Atmospheric pressure radio frequency plasmasAtmospheric pressure radio frequency plasmas
Chengdou- 2007: page-3
Towards stable & cold atmospheric plasmas
Operation modes in RF APGDs
0 20 40 60 80 100 120200
250
300
350
400
RM
S A
pplie
d vo
ltage
(V
)
RMS current density (mA/cm2)
region
region
-
-
0.0 0.2 0.4 0.6 0.8 1.00.0
0.4
0.8
1.2
1.6
2.0
2.4
Time normalized to cycle period
Inte
rele
ctro
de
po
sitio
n (
mm
)
0.0 0.2 0.4 0.6 0.8 1.00.0
0.4
0.8
1.2
1.6
2.0
2.4
Time normalized to cycle period
Inte
rele
ctro
de
po
sitio
n (
mm
)
Mode: VolumetricMode: Volumetric
Differential conductivity: Differential conductivity: PositivePositive
Mode: dominated in sheath regionMode: dominated in sheath region
Differential conductivity: Differential conductivity: NegativeNegative
Modes in RF APGDs-NumericalModes in RF APGDs-Numerical
Ref: J. J.Shi and M. G. Kong, J. Appl. Phys., 97, 023306 (2005).
Chengdou- 2007: page-4
Towards stable & cold atmospheric plasmas
Modes characterization
0 20 40 60 80 100 120100
200
300
400
500
600
700
RMS current density (mA/cm2)
Sh
ea
th t
hic
kne
ss (
m)
50
100
150
200
250
300
350
Sh
ea
th vo
ltag
e (V
)
Modes in RF APGDs-NumericalModes in RF APGDs-Numerical
Ref: Jianjun Shi and Michael G. Kong, IEEE Transaction on Plasma Science, 33, 624 (2005)
100 200 300 400 500 6000.1
1
10
n e,m
ax (
101
1 c
m-3
)
RF voltage amplitude (V)
=0.3 =0.1 =0.03 Mode transition dependent on Mode transition dependent on
secondary emission coefficient. secondary emission coefficient.
Sheath thickness:Sheath thickness:
Change of slopeChange of slope
Sheath voltage:Sheath voltage:
Change of differential conductivityChange of differential conductivity
Chengdou- 2007: page-5
Towards stable & cold atmospheric plasmas
Operation modes in RF APGDsModes in RF APGDs-ExperimentalModes in RF APGDs-Experimental
0.0 0.2 0.4 0.6 0.8 1.00
100
200
300
400
500
600
(H)
(G)(F)
(E)
(D)
(C)
(B)
(A)
RM
S V
olta
ge (
V)
RMS Current (A)
Ref: J. J. Shi, X. T. Deng, R. Hall, J. D. Punnett and M. G. Kong, J. Appl. Phys., 94, 6303-6310 (2003)Ref: J.J. Shi, D. W. Liu and M. G. Kong, Applied Phys. Lett., 90, 031505 (2007)
Mode: Volumetric across the discharge gapMode: Volumetric across the discharge gap
Mode: Constricted single columnMode: Constricted single column
Chengdou- 2007: page-6
Towards stable & cold atmospheric plasmas
Evolution of RF APGDModes in RF APGDs-ExperimentalModes in RF APGDs-Experimental
Chengdou- 2007: page-7
Towards stable & cold atmospheric plasmas
Taken by nano-second ICCD.Taken by nano-second ICCD.
Sheath region formed above twoSheath region formed above two
electrodes alternatively.electrodes alternatively.
Excitation frequency on modes
1 10 100 1000250
300
350
400
450 f =6.78 MHz f =13.56 MHz f =27.12 MHz
RM
S A
pp
lied
vo
ltag
e (
V)
RMS current density (mA/cm2)
0 5 10 15 20 25 30 350
50
100
150
200
250
RM
S c
urre
nt d
ensi
ty (
mA
/cm
2 )
Frequency (MHz)
300
330
360
390
420
450
RM
S a
pplie
d vo
ltage
(V
)
Frequency on modes-NumericalFrequency on modes-Numerical
Ref: J.J. Shi and M. G. Kong, Applied Phys. Lett., 87, 201501 (2005)
FrequencyFrequency 6.78 MHz6.78 MHz 13.56 MHz13.56 MHz 27.12 MHz27.12 MHz
Voltage (V)Voltage (V) 420.2420.2 356.6356.6 339.4339.4
Current density (mA)Current density (mA) 17.6817.68 49.549.5 176.8176.8
Chengdou- 2007: page-8
Towards stable & cold atmospheric plasmas
Excitation frequency on modesFrequency on modes-NumericalFrequency on modes-Numerical
Ref: J.J. Shi and M. G. Kong, Applied Phys. Lett., 87, 201501 (2005)
Chengdou- 2007: page-9
5 10 15 20 25 30 356
8
10
12
14
Frequency (MHz)
Max
imum
ele
ctro
n en
ergy
(eV
)
0
4
8
12
16
20
Max
imum
ele
ctro
n de
nsity
(10
11cm
-3)
1 10 100 1000100
200
300
400
500
600
700
0
100
200
300
400
500
RMS current density (mA/cm2)
Sh
ea
th th
ickn
ess
(m
)
f =6.78 MHz f =13.56 MHz f =27.12 MHz
Sh
ea
th v
olta
ge
(V
)
Towards stable & cold atmospheric plasmas
Plasma reactivity:Plasma reactivity: Mean electron energy increases;Mean electron energy increases; Electron density increases.Electron density increases.Sheath structure:Sheath structure:
Sheath voltage: similar to applied voltage;Sheath voltage: similar to applied voltage; Sheath thickness: sustain in Sheath thickness: sustain in mode and collapse in mode and collapse in mode. mode.
Excitation frequency on modesFrequency on modes-ExperimentalFrequency on modes-Experimental
Excitation frequency: double & tripleExcitation frequency: double & triple Discharge current range expanded;Discharge current range expanded; Applied voltage reduced.Applied voltage reduced.
With increasing excitation frequency:With increasing excitation frequency: Stable operation Stable operation region expanded. region expanded.
Chengdou- 2007: page-10
0 50 100 150 200 250 3000
100
200
300
400
500
RM
S v
olta
ge
(V
)
RMS current (mA)
6.78 MHz 13.56 MHz 20.34 MHz
0 5 10 15 20 25 300
20
40
60
80
100
120
RM
S c
urr
en
t de
nsi
ty (
mA
/cm
2 )
Excitation frequency (MHz)
Before gas breakdown
region
region
Towards stable & cold atmospheric plasmas
Voltage regime in modesFrequency on modes-ExperimentalFrequency on modes-Experimental
Breakdown voltage:Breakdown voltage: Decreases with excitation frequency;Decreases with excitation frequency; maintain in higher frequencies.maintain in higher frequencies.
With increasing excitation frequency:With increasing excitation frequency: Voltage regime is constricted.Voltage regime is constricted.
Chengdou- 2007: page-11
0 5 10 15 20 25 30200
300
400
500
600
RM
S v
olta
ge (
V)
Excitation frequency (MHz)
Minimum sustain voltage - transition voltage
0 5 10 15 20 25 30200
300
400
500
600
RM
S b
rea
kdo
wn
volta
ge
(V)
Excitation frequency (MHz)
Towards stable & cold atmospheric plasmas
Excitation frequency on modesFrequency on modes-ExperimentalFrequency on modes-Experimental
With increasing excitation frequency:With increasing excitation frequency: More reactive species are obtained in RF APGDs.More reactive species are obtained in RF APGDs.
Chengdou- 2007: page-12
0 50 100 150 200 250 300
0
5
10
15
20
OE
I @ 7
06
nm
(a
.u.)
RMS current (mA)
6.78 MHz 13.56 MHz 20.34 MHz
Using optical emission intensity to indicate the energetic electron density.Using optical emission intensity to indicate the energetic electron density.
Towards stable & cold atmospheric plasmas
ConclusionsConclusions
• Different operation modes (- and -mode) are found in RF APGDs in numerical simulation and experiments;
• The mode in RF APGDs is suggested to be expanded by higher excitation frequencies in simulation results.
• The expansion of mode in RF APGDs by higher excitation frequency is also found in experimental studies.
Chengdou- 2007: page-13
Towards stable & cold atmospheric plasmas
Thank you!Thank you!
Chengdou- 2007: page-14
Towards stable & cold atmospheric plasmas