A critical review of orificed hollow cathode modeling

A critical review of zero-dimensional orificed hollow cathode modeling is presented, with a focus on the validity of model assumptions, the reproducibility of model results, and the general scaling behaviors observed. Most require substantial input in the form of experimental data or free parameters in order to achieve agreement with experimental results. The purpose of this work is to address the deficiencies of existing models and to offer constructive criticism on improved handling of the underlying physics. The models that offered sufficient detail for re-implementation were capable of recreating the original results of their authors, but were generally unable to produce agreement with experimental data when applied to different cathode geometries and operating conditions. The assumption that the plasma and sheath potentials are equal is common to most models, inating the contribution of ion bombardment of the emitter and the power deposition in the insert plasma by sheath electrons while essentially neglecting the electron ux that returns to the emitter. Only one of the models reviewed makes any attempt to resolve the potential structure of the emitter sheath beyond the inclusion of the plasma density decay in the pre-sheath. Neutral flow models used in orificed hollow cathodes often neglect plasma contributions to the cathode pressure, and assume conditions incompatible with cathode environments. The importance of stepwise processes and their variation with plasma parameters also needs to be addressed in order to justify the assumption that they can be safely neglected. The use of inconsistent property data and the inappropriate evaluation of convective and particle uxes between control volumes are pervasive, and change the relative contributions of plasma processes.