35
OPOLE Opole University Institute of Physics, Plasma Spectroscopy Group
OPOLE Opole University
Institute of Physics,Plasma Spectroscopy Group
1
Symmetry
of
the plasma
produced in
a wall-stabilized d.c. arc
2
Wall-stabilized arc (Maecker)
3
Wall-stabilized arc (Shumaker)
4
Main advantages of the wall-stabilized arc
5
•very stable (as well spatially as temporally)
•long time of stable work (hours)
•cylindrical symmetry of the plasma
•uniformity of the plasma along the arc axis(neglecting infinitesimally small area near electrodes)
•the plasma is at least close to theLocal Thermal Equilibrium
Usually the discharge is conducted in an inert gas atmosphere with small
admixtures of the element under study.
6
•Argon
•Helium
temperature: 8 000 – 15 000 (K)
pressure: 1 atmosphere
electron densities: 1015 – 1017 (cm–3 )
Typical parameters of plasma produced in a wall-stabilized arc
7
Wall-stabilized arc (this work)
8
Gas inlet-outlet
9
Ca
thod
e
A rH e
Flo
wm
ete
rs
s ide w indow
Ano
de
Gas flow 10
Experiment parametersEstimated Ar
concentration
(per vol.)
Discharge
current
(A)
30 10.0 % 45
60 25.7% 4.5%
45
11
Optical set-up :A – top view,B – side view;
1a – wall-stabilized arc, 1b – tungsten strip lamp (standard source),
2 – flat mirror,3 – spherical mirror,4 – filter, 5 – spectrograph, 6 – CCD camera, 7 – PC computer, 8 – flat mirror.
12
Detector tracks 13
Spectra registered in 6545–6685Å range 14
6540 6560 6580 6600 6620 6640 6660 6680
Wavelength (Å)
C athode
A node
ArI
I 664
3.69
7 Å
HeI
667
8.15
2 Å
ArI
I 668
4.78
8 Å
H
6562
.8 Å
Spectra registered in 6945–7095Å range 15
6960 6980 7000 7020 7040 7060 7080
Wavelength (Å)
C athode
A node
HeI
706
5.17
9 Å
HeI
706
5.21
7 Å
HeI
706
5.71
0 Å
ArI
706
7.21
7 Å
ArI
703
0.25
1 Å
ArI
696
5.40
9 Å
What can cause the differences in line intensities?
Changes of plasma parameters (enhancement of the excitation)
Changes in chemical plasma composition(partial pressure or concentration of the species)
16
Methods
ne = f (FWHM(H))
T = f (ne,Ar I, Ar II)
natoms Ar,H = fBoltzmann(T, )
nions Ar,H = fSaha(T, ne,natoms)
natoms He = patm– k·T · ni
aHe = nHe/nHe( HeI)
nions He = fSaha(T, ne,natoms, aHe)
Method (B){system of LTE equation}
natoms He,Ar,H = fBoltzmann(T, )
nions He,Ar,H = fSaha(T, ne,natoms)
T = p/(k· n)
ne = z· niz
Method (A){partial LTE}
17
Axial distribution of the temperature at different discharge currents (values on the arc axis). 18
Method (A)
-4 -3 -2 -1 0 1 2 3 410000
11000
12000
13000
14000
15000
16000
17000
18000
19000
i = 30 A i = 45 A i = 60 A
T (
K)
Distance from the arc center (cm)
Method (B)
-4 -3 -2 -1 0 1 2 3 410000
11000
12000
13000
14000
15000
16000
17000
18000
19000
i = 30 A i = 45 A i = 60 A
T (
K)
Distance from the arc center (cm)
Axial distribution of the electron density at different discharge currents
(values on the arc axis). 19
Method (A)
-4 -3 -2 -1 0 1 2 3 4
0.0
5.0x1015
1.0x1016
1.5x1016
i = 30 A i = 45 A i = 60 A
n e (c
m-3 )
Distance from the arc center (cm)
Method (B)
-4 -3 -2 -1 0 1 2 3 4
0.0
5.0x1015
1.0x1016
1.5x1016
i = 30 A i = 45 A i = 60 A
n e (c
m-3 )
Distance from the arc center (cm)
Axial distribution of the temperature at different plasma compositions (values on the arc axis). 20
Method (A)
-4 -3 -2 -1 0 1 2 3 410000
11000
12000
13000
14000
15000
16000
17000
18000
19000
large amount of Ar small amount of Ar
T (
K)
Distance from the arc center (cm)
Method (B)
-4 -3 -2 -1 0 1 2 3 410000
11000
12000
13000
14000
15000
16000
17000
18000
19000
large amount of Ar small amount of Ar
T (
K)
Distance from the arc center (cm)
Axial distribution of the electron density at different plasma compositions
(values on the arc axis). 21
Method (A)
-4 -3 -2 -1 0 1 2 3 4
0.0
5.0x1015
1.0x1016
1.5x1016
large amount of Ar small amount of Ar
n e (c
m-3 )
Distance from the arc center (cm)
Method (B)
-4 -3 -2 -1 0 1 2 3 4
0.0
5.0x1015
1.0x1016
1.5x1016
large amount of Ar small amount of Ar
n e (c
m-3 )
Distance from the arc center (cm)
Spatial distribution of plasma parameters
(method A, i = 60 A)
-2-1
01
2
-0.2
-0.1
0.0
0.1
0.2
10000
12000
14000
16000
18000
T (
K)
Distance from the arc center (cm)
cathode
anode
-2-1
01
2
0.0
5.0x1015
1.0x1016
1.5x1016
-0.2
-0.1
0.0
0.1
0.2
n e (c
m -3
)
r (cm
)
Distance from the arc center (cm)
cathode anode
22
Spatial distribution of Argon mass fraction (method A , i = 60 A)
-2-1
01
2
0.0
0.1
0.2
0.3
0.4
0.5
-0.2
-0.1
0.0
0.1
0.2
Ar
mas
s fr
actio
n
r (cm
)
Distance from the arc center (cm)
cathode anode 23
Spatial distribution of Hydrogen mass fraction (method A , i = 60 A)
-2-1
01
2
0.0000
0.0002
0.0004
0.0006
0.0008
0.0010
0.0012
-0.2
-0.1
0.0
0.1
0.2
H m
ass
frac
tion
r (cm
)
Distance from the arc center (cm)
cathode anode 24
Spatial distribution of Helium mass fraction (method A , i = 60 A)
-2-1
01
2
-0.2
-0.1
0.0
0.1
0.2
0.4
0.5
0.6
0.7
0.8
0.9
He
mas
s fr
actio
n
Distance from the arc center (cm)
cathode
anode
25
End-on spectra – how to interpret it?
Cathode
Anode
6560 6580 6600 6620 6640 6660 6680
W avelength (Å )
ArII
6643
.697
Å
HeI
6678
.152
Å
ArII
6684
.788
Å
H
6562
.8Å
26
Demixing effect
27
Murphy has shown that in a mixture of two homonuclear gases that do not react with each other the treatment of diffusion can be greatly simplified if local chemical equilibrium is assumed.
In this case, instead of considering the diffusion of individual species separately, one can consider the diffusion of gases.
Here a gas, for example nitrogen, is defined to consist of all the species that can be derived from that gas, for example N2, N2
+, N, N+, N++, and the electrons derived from the ionization of nitrogen molecules and atoms.
A. B. MurphyPhys. Rev. E 55
7473 (1997)
28
Temperature dependence of the mole fractions of the species present in a mixture of argon and helium if no demixing occurs.
Demixing effect
• mole fraction (or partial pressure) gradient,
Demixing can be caused by:
• frictional forces,
• thermal diffusion,
• external forces (e.g. electric field).
29
A. B. Murphy, Phys. Rev. Lett. 73,
1797 (1994)
30
Combined diffusion coefficients for different mixtures of argon and nitrogen.
(a) Mole fraction diffusion coefficient; (b) temperature diffusion coefficient; (c) thermal diffusion coefficient.
Radial distributions of Argon mass fraction (7 different gas mixtures). 31
0.00 0.05 0.10 0.15
0.87
0.78
0.00 0.05 0.10 0.15
0.78
0.79
0.00 0.05 0.10 0.150.69
0.70
0.71
0.72
0.73
0.74
0.00 0.05 0.10 0.150.52
0.53
0.54
0.55
0.56
0.57
0.58
0.59
0.60
0.61
0.00 0.05 0.10 0.150.32
0.33
0.34
0.35
0.36
0.37
0.38
0.39
0.40
0.41
0.42
0.43
0.44
0.45
0.46
0.47
0.48
0.49
0.50
0.00 0.05 0.10 0.150.24
0.25
0.26
0.27
0.28
0.29
0.30
0.31
0.32
0.33
0.34
0.35
0.36
0.37
0.38
0.39
0.40
0.41
0.42
0.00 0.05 0.10 0.15
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
0.28
0.30
0.89A
r m
ass
frac
tion
r (cm) r (cm)
0.70
r (cm)
0.54
r (cm)
0.37
r (cm)
0.28
r (cm)
Ar mass fraction in gas mixture
0.14
r (cm)
Radial distributions of Argon mass fraction (2 different gas mixtures).
0.00 0.05 0.10 0.15 0.200.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
Ar mass fraction (0.89 in gas mixture)
r(cm)
mas
s fr
actio
n A
r in
arc
pla
sma
{in c
old
gas
0.89
}
Ar mass fraction in gas mixture
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40 Ar mass fraction
(0.14 in gas mixture)
Ar m
ass fraction in arc plasma {in cold gas 0.14}
32
Radial distributions of temperature (7 different gas mixtures). 33
0.00 0.05 0.10 0.15 0.20
8000
9000
10000
11000
12000
Ar mass fractionin gas mixture
0.89 0.78
0.700.540.370.280.14
T (
K)
r (cm)
Effective temperaturesDdetermined based on intensities of •Ar I 6965.43Å •Ar I 7030.25 Å (E1.5 eV)
34 34
Eff
ect
ive
te
mp
era
ture
(K
)
-4 -3 -2 -1 0 1 2 3 40
2000
4000
6000
8000
10000
12000
14000
16000
between stabilizing pla tes within stabilizing plates
Distance from the arc center (cm)
CATHODE
ANODE
0.00 0.05 0.10 0.15 0.20 0.25 0.300
2000
4000
6000
8000
10000
12000
14000
16000
r (cm)
Te
mp
era
ture
(K
)
CATHODE
ANODE
0.00 0.05 0.10 0.15 0.20 0.25 0.30-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
r (cm)
Em
mis
sion
coe
ffici
ent (
a.u.
)
Ar I 7030.25 Å 0.0
0.5
1.0
1.5
2.0
2.5
3.0
Em
mission coefficient (a.u.)
The End
THANK YOUTHANK YOUfor your attentionfor your attention
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