Advancing the Performance of Water Vapor Propellants in an ECR Plasma Cathode*

Electron cyclotron resonance (ECR) plasma cathodes are microwave-driven electron sources that can be utilized in a variety of applications, including space propulsion and plasma etching. Due to their use of microwaves to generate the seed plasma, a wide range of gases may be used in the system, including complicated molecular species such as water vapor and carbon dioxide. Operating plasma thrusters on molecular species, especially water vapor, is an attractive proposition due to its availability and storability for long missions; however, previous experiments have shown discharge losses too large for practical applications. In this work, we investigate the capacity for improvement of a wave-heated ECR plasma source operating on water vapor propellant for plasma cathode applications, with the overarching goal of achieving discharge losses sub-100 W/A. We present findings that depict both the efficacy and the efficiency of the plasma cathode at operating on water vapor in the form of macroscopic parameters such as discharge losses [W/A] and extraction current [A]. The plasma composition and characteristics are assessed using electrostatic probes and optical emission spectroscopy.