• comsol multiphysics
• electric propulsion
• heater
• hollow cathodes
• plasma
• redundancy
• thermal analysis

Hollow cathodes are electron-emitting devices mainly used in Hall and Ion thrusters to ionize the propellant and neutralize the outgoing ion beam.This component, during its operating life, is subjected to thousands of high temperature ignition cycles and it is therefore exposed to high risks of breakage. Melting of the heater and short circuits can occur during its operation. The work herein tries to describe, from a thermal point of view, the two main phases of a cathode ignition cycle: the preheating phase and the self-heating phase. A thermal model is developed, within the Comsol Multyphysics environment, to describe the thermal behaviour of the cathode during the preheating phase, when the heat comes entirely from the heater. The model is applied to HC3, a low-current cathode developed at SITAEL, in order to compare different configurations, in terms of materials and geometry, and to see which of them improve its efficiency. Moreover, the model is also preliminarily validated, by comparison with a thermal test performed on the same cathode. Subsequently the thermal model is applied to HC60, a high-current cathode developed at SITAEL, to analyse how the introduction of a redundancy in the heater, with the aim of increasing its reliability, affects its thermal behaviour. Then, a plasma model is developed to describe the self-heating phase of the cathode. It is able to estimate the heat flows coming from the plasma and to use them to determine the temperature of the cathode during this phase, through the coupling with the previously developed thermal model.