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The impedance of the discharge positive columnat medium pressures under different metastable level decay schemes
Published online by Cambridge University Press: 11 March 2005
Abstract
The impedance of a positive column has been calculated
at medium pressures i.e. at the regime of step
ionization-ambipolar diffusion. Calculations were carried out for
two cases:
(a) metastable level decay by electron impact;
(b) metastable level decay on the walls as a result of
diffusion.
In both cases the impedance has generally an inductive character. In
the case of metastable level decay by electron impact, the
impedance curve starts from the coordinate origin at $\omega =0 $.
At low frequencies the PC has a negatron property, while the
static volt-ampere characteristics of the stationary PC becomes
parallel to the current axis. The module |Z| reaches its
maximum value at frequencies of about the order of $\sqrt{
\tau_a^{-1}\alpha _{m}n_{0}}$
. At very high frequencies $\omega
\longrightarrow \infty $
, the impedance reaches the real value of
$Z=R_{0}$
.
In the case when metastable
levels decay as a result of diffusion, the impedance curve starts
from the negative real values at $\omega=0$
. The volt-ampere
characteristics of the stationary PC drops. The module |Z|
reaches its maximum value at frequencies of about the order of
$\sqrt{\tau_a^{-1} \tau^{-1}_{m}}$
. At very high frequencies
$\omega \longrightarrow \infty $
, the impedance reaches the real
value of $Z=R_{0}$
. In both cases, impedance curves have single
structured shapes in spite of existence of several characteristic
time scales of different order.
- Type
- Research Article
- Information
- Copyright
- © EDP Sciences, 2005