Non-equilibrium Ionization Of Cesium-seeded Helium Using A Two-electron Group Model

Here we consider the plasma electrons to consist of two Maxwellian groups, a bulk electron group described by a temperature T
_b
and having kinetic energies (½ m v
²
= e V) from 0 to e V
₀₁
= 1.3856 ev, and a tail electron group described by a temperature T
_t
< T
_b
and having kinetic energies e V > e V
₀₁
. Energy flows between the bulk and tail electron groups through electron-electron interactions and through inelastic and superelastic collisions with the cesium seed atoms. The rate coefficients for the various plasma processes are determined by integrating the cross section for each process using the Maxwellian distribution and observing that at the discontinuity in the distribution, at e V = e V
₀₁
, the electron temperature drops from T
_b
to T
_t
. We also describe the cesium-seeded noble gas mixture of atoms by a three-energy level model. We assume that, for the electron temperature range of interest in Closed-Cycle MPD Energy Conversion applications, only the cesium seed atoms are excited or ionized, with the helium atoms serving only as elastic collision targets. The three energy levels of the model consist of the ground state level of cesium (the 6
²
S
_½
level), V
₀
= 0 volt, an excited state level with an excitation potential, V
₀₁
= 1.3856 volt, representing the first two resonance excited state doublet of cesium (the 6
²
P
_½
& 6
²
P
_3/2
doublet with threshold potentials of 1.3856 & 1.4543 volt), and with the third level being the ground level of the positive ion of cesium with a threshold ionization potential V
_0p
= V
_i
= 3.893 volts.