Investigation on the ion evolution in different ionization states inside the electrode channel of the micro-cathode arc thruster by time-resolved optical image and emission spectroscopy

Micro-cathode arc thrusters (μ-CAT) hold critical applications in the national economy, serving as primary propulsion systems for orbit maintenance and formation flying missions of small satellites. Compared to steady-state thrusters (e.g., Hall thrusters or ion thrusters), the performance and lifetime of the μ-CAT depend on the ablation state of the cathode. However, it is challenging to characterize ablation-driven plasma properties due to the lack of a method to determine the time-resolved metal ion densities from cathode ablation during single-pulse discharge. In this work, we present an OES method to determine the Ti⁺ and Ti²⁺ ion densities based on ionic lines from different ionization states, and observe the “three-stage evolution” of the plasma inside the electrode channel of the micro-cathode arc thruster with capacitive discharge mode based on the high-speed imaging subsystem. The time-resolved Ti⁺ and Ti²⁺ ion densities during the interelectrode plasma and the early stage of the anode spot period are determined by synchronously triggering the power processing unit of the μ-CAT and optical emission spectroscopy subsystem. Besides, the impulse bit during a single pulse is obtained, supported by the determined ion densities and time-of-flight ion velocity monitoring method. Our method will help improve the engineering test efficiency and accelerate the design and development of the μ-CAT.