M. Jugroot et al., Self-consistent modelling of charged and neutral particle dynamics in short-gap helium and hydrogen discharges, J PHYS D, 32(2), 1999, pp. 106-120
A self-consistent model of charged and neutral particle dynamics is develop
ed for the case of high pressure short-gap discharges in helium (0.48 mm x
760 Torr) and hydrogen (0.48 mm x 760 Torr and 1.8 mm x 500 Torr). Boundary
wail effects on the electron swarm parameters are first investigated by a
Monte Carlo method in order to verify the validity of the classical local h
eld approximation in short-gap discharges. The hydrodynamic transport equat
ions of the self-consistent model are then described with an emphasis on th
e different terms involved in the close coupling between charged and neutra
l particles and the electric field. These equations are solved by powerful
two-dimensional numerical schemes for both transport and electrical field e
quations. The discharges are studied from an initial electronic cloud to th
e first stages of breakdown. Cathode emission is discussed in terms of its
prime importance in the spatio-temporal evolution of the short-gap discharg
es and it is shown that the principal difference between helium and hydroge
n discharges is due to the mode of cathode emission. The particular observa
tions in the luminosity in hydrogen are discussed in terms of ionization of
the gas and secondary emission processes at the surface. A detailed analys
is reveals a complex distribution of charged particles due to the superposi
tion of ionization and transport effects. Furthermore, Joule heating of the
neutral medium is evaluated in the entire time scale of the discharge and
its influence on the discharge evolution is discussed.