• low-current
• orificed hollow cathodes
• reduced-order model

Thermionic hollow cathodes are currently used in a wide variety of applications, including electric thrusters and plasma contactors. Since the cathode geometry strongly impacts their performance and the plasma diagnostic is difficult to perform, simple numerical tools are needed to determine the optimal geometry and operating conditions for a given mission profile. A reduced-order numerical model has been developed to guide the design of low-current orificed hollow cathodes. The suggested model is self-consistent, since it does not require experimental data as input. It considers volume-averaged plasma properties, as well as steady-state conditions. A system of particle and energy balance equations is numerically solved to evaluate the plasma parameters in the cathode assembly without the assumption of the LTE hypothesis, thus avoiding the use of the Saha equation. A simplified thermal model is combined with the plasma model to determine the cathode temperature profile along its longitudinal axis. The power distribution and heat transfer mechanisms are investigated together with the effect of the emitter thermal shielding. The plasma penetration depth is evaluated on the basis of the computed internal pressure introducing a method based on empirical data found in the literature. A preliminary validation of the model showed good agreement between theoretical and experimental results, in both magnitude and trends of the relevant parameters. The theoretical results were then used to draw some scaling guidelines for the cathode design.