Investigation on plasma ionization process of a micro-cathode arc thruster

Micro-cathode arc thrusters (μCATs) are space propulsion options suitable for microspacecraft, and have recently attracted much attention because of their low electrical power requirements and simple, compact propellant systems. The plasma ionization process, however, is not currently well understood. In this study, a μCAT prototype was designed with the use of different specific materials for each component, enabling the study of the ionization process from the emissive light of excited and ionized states from different elements. ICCD emission spectroscopy and scanning monochromator measurements are conducted inside the electrode channel of a μCAT with a coaxial configuration. The excited state atomic spectral results and ionization state spectral results give us a comprehensive understanding of the behavior of neutral particles and ions during the discharge process of the μCAT. The ionization sequence follows in the order of C⁺, Al⁺, Ti⁺, Cu^+, and Ti²⁺. From the duration of the spectral lines, C I has the shortest duration (16.9 μs), which shows that the ablation of the conductive film is mainly concentrated during the first half of the discharge, while anode and cathode ionization occur over the entire discharge duration. Additionally, Al⁺ ionization is observed during the discharge process, showing that part of the discharge energy is expended in ionizing the thruster outer shell, resulting in efficiency loss. An ionization ratio of k is proposed in this work to represent the relative ionization of the conductive film and cathode material, aiding us in determining the optimal operation conditions for lifetime extension.