Comparative study of electron temperature and ion energy in two different magnetic nozzle thruster designs

Conventional ion thruster technologies face challenges such as electrode and grid erosion and the need for additional neutralizer devices. In this article, we discuss two thruster concepts that achieve plasma acceleration by means of a magnetic nozzle, and thus avoid the need of a neutralizer device. The concept of a magnetic nozzle converting the thermal energy available in the electrons movement to ion kinetic energy is a well accepted model in the community. We discuss a novel thruster concept based on electrode-less electron cyclotron resonance plasma generation via a slot antenna design. The geometry of this thruster concept results in a converging-diverging character of the magnetic field topology along the plume direction. To this date it is not known in which way this new thruster design influences the electron dynamics and thus the ion energy. To understand the correlation between ion energy and electron temperature of this thruster system, it is compared with a well-known thruster prototype operating on similar principles, however, realizing microwave coupling and magnetic field topology in a different way. Both thruster designs operate within comparable power, frequency, and volume flow ranges. The ion energy with maximum probability is measured for both thrusters using a retarding potential analyzer in the same vacuum environment. Additionally, the electron temperature is measured with a Langmuir probe for various operation points of the thrusters, differing in input power level, volume flow, set excitation frequency, and argon or xenon as propellant.