Investigation of Hall and combined mode operations in a multimode acceleration coaxial (MAC) thruster under chamber background pressure

The Multimode Acceleration Coaxial (MAC) thruster is a multimode propulsion concept based on Hall thruster technology, incorporating an internally mounted cathode/gasjet that integrates Hall discharge, magnetoplasmadynamic arcjet discharge, and gasjet operations. Each of these modes has distinct characteristics and can be useful for various missions; however, the most noteworthy feature is their ability to operate in combination. In this study, we investigate the characteristics of the combined mode, in which both the Hall mode and cold gasjet mode are activated simultaneously. Since the combined mode operation inevitably experiences background pressure effects due to the high flow rate, the background pressure dependence of the Hall mode was first investigated and then applied to the evaluation of the combined mode results. A significant synergistic enhancement in thrust performance was observed in the combined mode with Ar and Kr propellants, exceeding the theoretical linear sum of the two individual modes. Possible mechanisms underlying this phenomenon are discussed based on the ion beam measurement results.