Environmental Engineering Reference
In-Depth Information
Ta b l e 5 . 1
The electric potential (
) on one striation for three types of striations in inert gas-
es [86]. The atomic excitation energy
Δ
E
V
is given along with the atomic ionization potential in
the ground
J
and metastable
J
states.
Types of striation
P
R
S
Δ
E
,eV
J
,eV
J
,eV
He
14.2
-
30.05
19.8
24.6
4.8
Ne
9.2
12.7
19.5
16.62
21.5
4.9
Ar
6.7
9.5
12.0
11.55
15.76
4.2
atoms exceeds the striation length significantly. Under these conditions, the varia-
tion of the electron energy as a result of the electron displacement from coordinate
x
1
to coordinate
x
2
along the field is [114, 115]
ε
(
x
1
)
C '
(
x
1
)
D
ε
(
x
2
)
C '
(
x
2
),
where
is the plasma electric
potential at this point. Hence, in the first approximation each electron acquires a
certain energy after passage of one striation.
Let us combine this with the Novak rule [116], according to which the energy
acquired by an electron after passage of one striation period is constant for a given
striation type, that is, it is independent of the gas pressure and discharge current.
One can conclude from this that a certain energy is given to an individual elec-
tron on each striation. On this basis one can construct a certain physical picture of
plasma processes with formation of striations. Indeed, if a group of electrons lose
ε
is the electron energy at an indicated point and
'
Figure 5.16
Distributions of the number density of electrons (a) and the electric field strength
(b) along a gas discharge tube of small radius under the formation of striations.
