Investigation and optimization of performance degradation in a microwave cusped field thruster for micro-Newton propulsion

Microwave cusped field thrusters (MCFTs) are promising candidates for micro-Newton propulsion required in high-precision space missions such as space-borne gravitational wave detection. However, the long-term operational stability of miniature plasma thrusters remains a key challenge. In this work, the performance degradation of a xenon-fed micro-Newton MCFT during long-duration operation is experimentally investigated. A 100-h endurance test shows that the anode current decreases by 5.5%–59.2% under different operating conditions. The deposited layer modifies the wall properties and increases electron loss, thereby reducing the plasma density in the discharge channel. To mitigate this effect, a localized magnetic-mirror configuration is designed to reduce the sensitivity of the plasma to deposition-induced wall-property variations. For the optimized prototype, the anode current remains at 96.8% of its initial value after 16 h of operation, whereas that of the original prototype decreases to approximately 50% within 5 h. A further 500-h operation test verifies the effectiveness of the optimized design. The proposed magnetic-field-based strategy improves the tolerance of MCFTs to metallic deposition and provides a practical approach for enhancing the lifetime of miniature plasma thrusters.