Effects of propellant pressure distribution in the discharge channel on an air-breathing microwave cusped field thruster

This study investigates the combined effects of pressure magnitude and spatial pressure distribution within the discharge channel of a cusped field thruster with microwave-DC hybrid ionization on thruster performance, with a particular focus on the coaxial supply conditions of the passive collection device in air-breathing electric propulsion. A gas buffer chamber and high-transparency anode were developed, with internal pressure characterized via a ZJ-27 ionization gauge probe and simulations. The buffer chamber effectively reduces the numerical density in the primary ionization zone compared to direct pipeline supply. The homogenized propellant produces a more uniform plasma distribution, reducing the maximum plume divergence angle from 48° to 39°. At a numerical density of 5.55×10¹⁸ m⁻³ (0.022 Pa), the system, coupled with a microwave cathode, achieved a specific impulse exceeding 1100 s and an ionization rate exceeding 25%. The results demonstrate that, for a cusped field thruster, a direct gas supply via a gas pipeline commonly used in ground testing can lead to an overestimation of thruster performance by 3.6% to 26.4% compared to coaxial supply conditions provided by passive collection devices. By preliminarily demonstrating the significant impact of pressure distribution within the discharge channel on thruster performance, this work establishes a foundation for transitioning from ground testing to integrated end-to-end testing.