MPD thruster with a strong applied field up to 0.5 T using cryogenic fluid-cooled magnetic coil

To achieve an electric thruster with both high efficiency and high thrust density, we propose an applied-field magnetoplasmadynamic thruster that utilizes liquid hydrogen both as a propellant and as a coolant for high-temperature superconducting magnets. In this study, as an initial step toward this goal, we developed an applied filed magnetoplasmadynamic thruster with a strong magnetic field applied by a conventional normal-conducting copper coil cooled with cryogenic liquid nitrogen. This paper primarily focuses on the engineering aspects of integrating a novel thruster system with a cryogenic fluid-cooled coil. Additionally, it provides initial insights into the thruster’s operating modes under a strong magnetic field. The cryogenic coil successfully achieved a magnetic field of 0.5 T by cooling the coil with liquid nitrogen, thanks to the appropriate thermal and sealing designs. The developed cryogenic cooling system can also be applied to high-temperature superconductors. Discharge experiments using argon as a propellant revealed that the thruster operated in an electrothermal mode, exhibiting both high-voltage and low-voltage modes akin to arcjet thrusters. The specific impulse in this mode was limited to around 340 s. However, when the cathode position was shifted downstream, a mode with strong blue emission along the central axis, resembling electromagnetic acceleration, was occasionally observed. The current-voltage characteristics also appeared to indicate characteristics of electromagnetic acceleration. Further investigation into the transition to electromagnetic acceleration mode is necessary for future work.