Speaker
Gianpiero Colonna
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.302.pdf
Self–consistent modeling of Discharge: the role of superelastic collisions
G. Colonna
PLASMI Lab NANOTEC CNR Bari (Italy)
To determine the rate coefficients of electron-induced processes the Boltzmann equation for
free electrons must be solved to calculate the electron energy distribution function (eedf). Inte-
grating the cross sections over the eedf, the rates of electron induced processes are calculated.
The most advanced approach consists in coupling self–consistently the Boltzmann equation,
with the state-to-state kinetics, determining at the same time the eedf and the level distribu-
tion, accounting for their mutual interaction. To simplify the calculation, under the assump-
tion that eedf relaxes much faster than the gas composition, the rate coefficients can be related
only to the local electric field (local field approximation, LFA). However, LFA cannot consider
the contribution of the superelastic collisions in the electron kinetics. In participating to the
Round Robin [1] activity for the verification of different plasma kinetic codes, strong effects of
superelastic collisions on the plasma prop-
!2
erties have been observed, when a self– 1014 P
=
t
e t/t0
P0 t0
Ar*
consistent coupling of free electron and level 1011 P0 = 10
W
particle density [cm-3]
cm3
kinetics has been considered. It is well known t0 = 10 3
s
108
e-
that superelastic collisions are very important
105
in the post-discharge. In the present work we
Ar* e-
102
have observed that they are effective also in
10–1
the presence of high electric field, as shown in 10–10 10–8 10–6 10–4 10–2 100
time [s]
the figure, where the density of free electrons
and argon metastable are reported when su- Figure 1: Electron and argon metastable densities
perelastic collisions are neglected or included with (continuous lines) and without (dashed lines)
superelastic collisions in the Boltzmann equation.
in the Boltzmann equation. When superelas-
tic collisions are considered in the electron ki-
netics, some plateaux appear in the eedf [2, 3], which completely change the rates of electron
induced processes. These rates depends not only on the electric field, but also on the level pop-
ulation and on the plasma composition, affecting the time evolution of species densities.
References
[1] L. Pitchford et al.: Plasma chemistry round robin, GT1.00063, 70th Annual GEC, 2017.
[2] G. Colonna, A. D’Angola (Ed), Plasma Modeling: Methods and Applications, IOP (2017)
[3] M: Capitelli et. al, Fundamental Aspects of Plasma Chemical-Physics: Kinetics (2016)
