I am from..

1
I am from..
OPOLE
Opole University
Institute of Physics, Plasma Spectroscopy Group
1
2
Symmetry of
the plasma
produced ina wall-stabilized d.c. arc
2
3
Wall-stabilized arc (Maecker)
3
4
Wall-stabilized arc (Shumaker)
4
5
Main advantages of the wall-stabilized arc

• very stable (as well spatially as temporally)

• long time of stable work (hours)

• the plasma is at least close to theLocal Thermal
  Equilibrium

• cylindrical symmetry of the plasma

• uniformity of the plasma along the arc
  axis(neglecting infinitesimally small area near
  electrodes)

5
6
Usually the discharge is conducted in an inert
gas atmosphere with small admixtures of the
element under study.

• Argon

• Helium

6
7
Typical parameters of plasma produced in a
wall-stabilized arc
temperature 8 000 15 000 (K)
electron densities 1015 1017 (cm3 )
pressure 1 atmosphere
7
8
Wall-stabilized arc (this work)
8
9
Gas inlet-outlet
9
10
Gas flow
10
11
Experiment parameters
11
12
Optical set-up A  top view,B  side
view1a  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
13
Detector tracks
13
14
Spectra registered in 65456685Å range
14
15
Spectra registered in 69457095Å range
15
16
What can cause the differences in line
intensities?
Changes in chemical plasma composition (partial
pressure or concentration of the species)
Changes of plasma parameters (enhancement of the
excitation)
16
17
Methods
Method (B)
Method (A)
system of LTE equation
partial LTE
ne f (FWHM(H?))
ne ? z niz
T f (ne,?Ar I, ?Ar II)
T p/(k? n)
natoms Ar,H fBoltzmann(T, ?)
natoms He,Ar,H fBoltzmann(T, ?)
nions Ar,H fSaha(T, ne,natoms)
nions He,Ar,H fSaha(T, ne,natoms)
natoms He patm kT ? ni
aHe nHe/nHe(? HeI)
nions He fSaha(T, ne,natoms, aHe)
17
18
Axial distribution of the temperature at
different discharge currents (values on the arc
axis).
18
19
Axial distribution of the electron density at
different discharge currents (values on the arc
axis).
19
20
Axial distribution of the temperature at
different plasma compositions (values on the arc
axis).
20
21
Axial distribution of the electron density at
different plasma compositions (values on the
arc axis).
21
22
Spatial distribution of plasma parameters (method
A, i 60 A)
22
23
Spatial distribution of Argon mass fraction
(method A , i 60 A)
23
24
Spatial distribution of Hydrogen mass fraction
(method A , i 60 A)
24
25
Spatial distribution of Helium mass fraction
(method A , i 60 A)
25
26
End-on spectra how to interpret it?
26
27
Demixing effect

• 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.

27
28
A. B. MurphyPhys. Rev. E 55 7473 (1997)

• Temperature dependence of the mole fractions of
  the species present in a mixture of argon and
  helium if no demixing occurs.

28
29
Demixing effect
Demixing can be caused by

• mole fraction (or partial pressure) gradient,

• frictional forces,

• thermal diffusion,

• external forces (e.g. electric field).

29
30
A. B. Murphy, Phys. Rev. Lett. 73, 1797 (1994)

• Combined diffusion coefficients for different
  mixtures of argon and nitrogen.
• (a) Mole fraction diffusion coefficient (b)
  temperature diffusion coefficient (c) thermal
  diffusion coefficient.

30
31
Radial distributions of Argon mass fraction (7
different gas mixtures).
31
32
Radial distributions of Argon mass fraction (2
different gas mixtures).
32
33
Radial distributions of temperature (7 different
gas mixtures).
33
34
Effective temperatuers

• Effective temperatures
• Ddetermined based on intensities of
• Ar I 6965.43Å
• Ar I 7030.25 Å
• (?E?1.5 eV)

34
34
35
The End

• THANK YOU
• for your attention

35