Plasma behavior of a low current orificed hollow cathode using krypton propellant for electric thruster applications

As a fundamental component, hollow cathodes have been widely used in electric thruster applications. Krypton has become one of the ideal alternative propellants for hollow cathode due to its economy, thus it is vital to understand the basic physical process of the discharge of krypton-fed hollow cathode. This study sets out to establish a two-dimensional fluid model coupled with the equations for gas flow and heat transfer allowing to obtain a self-consistent description of the cathode discharge. The anomalous collision term based on the formulations of Sagdeev and Galeev is considered in this model. The model is validated by comparing the simulated and measured plasma characteristic parameters and reasonable agreement is reached. The findings show that the discharge of the krypton-fed hollow cathode is characterized by the lower plasma density, higher electron temperature, and higher spatial electric potential compared to that of the xenon-fed hollow cathode and tends to present a higher plasma density in the cathode plume region when it is operating with the diode configuration. The double layer formed at the keeper orifice is an important factor for the low electron temperature distribution, which is greatly affected by the keeper current. These findings add to our understanding of plasma behavior in the discharge of a low current krypton-fed hollow cathode and support further development of credible krypton-fed hollow cathode.