Preliminary Experimental Characterization of a Microwave Discharge Cusped Field Thruster

The cusped field thruster has become a candidate thruster in next-generation space science missions due to its low complexity and potential long life over a wide range of thrust conditions. However, the reduction of propellant utilization and, as a result, the total performance degradation has emerged in works on cusped field thruster downscaling. In this work, a coaxial resonator is utilized to feed the microwave (MW) into the near-anode region of the cusped field thruster, which contributes to ionization at a relatively low mass flow rate. With a LaB6 thermionic emission cathode, the thruster can operate in two modes: MW excited mode and the MW-DC mixed mode. The results show that the thruster can operate with a minimum mass flow rate minimum of 0.004 mg/s and achieves a continuously adjustable thrust from 1.9 μN to 30.8 μN. The performance variation characteristics over the three control parameters (anode voltage, mass flow rate, and MW power) are considered. Additionally, a plume plasma diagnosis is performed with a Faraday probe and a retarding potential analyzer to analyze the discharge performance and plasma characteristics with different operating conditions.