A 0-D model of
the plasma parameters within the orifice of orificed Hollow Cathodes (HC)
developed by Mandell and Katz (M&K) is analyzed. The model is explained in
detail and its predictions are studied under different hollow cathode operation
conditions. The M&K model is solved for the case when the ions have the
plasma electron temperature and also when the ions are in thermal equilibrium
with the neutral gas at lower temperature than the plasma electrons. A new
model based on different assumptions is also developed, and its predictions are
analyzed and compared with those of the M&K model. In the new model the
plasma ions and neutral atoms are at the same temperature while the plasma
electrons have a higher temperature. It is found that the two models predict a
similar qualitative behavior for the plasma density, plasma electron
temperature and ion output. The two models predict also a similar response of
the plasma parameters under rescaling of the electron discharge current, total
flow rate and orifice dimensions. The quantitative predictions of the two
models can differ by a factor of more than two. In the new model the
qualitative behavior of the plasma potential drop along the orifice depends on
the radius of the orifice, while in the M&K model such dependence does not
exist. In the new model, the plasma ions at the input of the orifice can be
dragged into the orifice by the gas flow, while in the M&K model the ions at
that location are always driven by the electric field to the insert region.
A 0-D model of
the plasma parameters inside the insert region is also studied. The model is
solved for two HC with different dimensions in order to illustrate the possible
self heating mechanisms of the insert and the possible plasma heating
mechanisms. The limitations of the model are carefully analyzed.
