Comparative Study of Electron Temperature and Ion Energy in Two Different Magnetic Nozzle Thruster Designs

Abstract 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 to ion kinetic energy is a well accepted model in the community. We discuss a 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 electrode-less coupling of the microwave 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 in a different way. Both thruster designs operate within comparable power, frequency, and volume flow ranges. Maximum ion energy is measured for both thrusters using a retarding potential analyzer under the same surrounding conditions. Additionally, the electron temperature is measured with a Langmuir probe for various operation points, such as variable input power, volume flow, set frequency, and argon and xenon as propellant.