by N A Almeida, M S Benilov, R N Franklin and G V Naidis
Abstract:
The ionization layer (presheath) separating a fully ionized low-temperature thermal plasma from the space-charge sheath adjacent to a solid surface is described by means of a (multi)fluid model. The character of the solution is governed by &agr;, the ratio of the ionization length to the mean free path for ion–atom collisions. If &agr; ⩾ 1, the solution is determined by physically transparent boundary conditions, namely, by the Bohm criterion at the sheath edge and the condition of full ionization on the plasma side of the ionization layer. If &agr; $<$ 1, the latter condition becomes ineffective. An alternative boundary condition is found for a certain range of &agr; below unity, &agr;$_{cr}$ ⩽ &agr; $<$ 1. An approximate approach which spans the whole range of &agr; is suggested. While being incomplete theoretically, this approach is sufficient for practical purposes and gives results that are in agreement with experiment. On the other hand, the question of what is the lacking boundary condition in the range 0 $<$ &agr; $<$ &agr;$_{cr}$ remains open and challenging.
Reference:
N A Almeida, M S Benilov, R N Franklin and G V Naidis, "Transition from a fully ionized plasma to an absorbing surface", J. Phys. D: Appl. Phys., vol. 37, no. 22, pp. 3107-3116, 2004.
Bibtex Entry:
@ARTICLE{2004b,
author = {N A Almeida and M S Benilov and R N Franklin and G V Naidis},
title = {Transition from a fully ionized plasma to an absorbing surface},
journal = {J. Phys. D: Appl. Phys.},
year = {2004},
volume = {37},
pages = {3107-3116},
number = {22},
abstract = {The ionization layer (presheath) separating a fully ionized low-temperature
thermal plasma from the space-charge sheath adjacent to a solid surface
is described by means of a (multi)fluid model. The character of the
solution is governed by \&agr;, the ratio of the ionization length
to the mean free path for ion\–atom collisions. If \&agr; \⩾
1, the solution is determined by physically transparent boundary
conditions, namely, by the Bohm criterion at the sheath edge and
the condition of full ionization on the plasma side of the ionization
layer. If \&agr; $<$ 1, the latter condition becomes ineffective.
An alternative boundary condition is found for a certain range of
\&agr; below unity, \&agr;$_{cr}$ \⩽ \&agr; $<$ 1. An approximate
approach which spans the whole range of \&agr; is suggested. While
being incomplete theoretically, this approach is sufficient for practical
purposes and gives results that are in agreement with experiment.
On the other hand, the question of what is the lacking boundary condition
in the range 0 $<$ \&agr; $<$ \&agr;$_{cr}$ remains open and challenging.},
file = {2004b.pdf:2004b.pdf:PDF},
url = {http://stacks.iop.org/JPhysD/37/3107}
}