Magnetic nozzle radiofrequency plasma thruster approaching twenty percent thruster efficiency

Kazunori Takahashi

doi:10.1038/s41598-021-82471-2

Abstract

Development of a magnetic nozzle radiofrequency (rf) plasma thruster has been one of challenging topics in space electric propulsion technologies. The thruster typically consists of an rf plasma source and a magnetic nozzle, where the plasma produced inside the source is transported along the magnetic field and expands in the magnetic nozzle. An imparted thrust is significantly affected by the rf power coupling for the plasma production, the plasma transport, the plasma loss to the wall, and the plasma acceleration process in the magnetic nozzle. The rf power transfer efficiency and the imparted thrust are assessed for two types of rf antennas exciting azimuthal mode number of m=+1 and m=0, where propellant argon gas is introduced from the upstream of the thruster source tube. The rf power transfer efficiency and the density measured at the radial center for the m=+1 mode antenna are higher than those for the m=0 mode antenna, while a larger thrust is obtained for the m=0 mode antenna. Two-dimensional plume characterization suggests that the lowered performance for the m=+1 mode case is due to the plasma production at the radial center, where contribution on a thrust exerted to the magnetic nozzle is weak due to the absence of the radial magnetic field. Subsequently, the configuration is modified so as to introduce the propellant gas near the thruster exit for the m=0 mode configuration and the thruster efficiency approaching twenty percent is successfully obtained, being highest to date in the kW-class magnetic nozzle rf plasma thrusters.

Highlights

Development of a magnetic nozzle radiofrequency plasma thruster has been one of challenging topics in space electric propulsion technologies
The rf power is mainly coupled with electrons and utilized for the plasma production in the helicon double layer thruster (HDLT), the HPT, and the electron cyclotron resonance plasma thruster (ECRT), which are operated at rf power levels ranging from several
Several experiments have been performed to improve the performance of the magnetic nozzle rf plasma thruster, where the first direct thrust measurement showed the thruster efficiency less than a p ercent[54,55]

Summary

Introduction

Development of a magnetic nozzle radiofrequency (rf) plasma thruster has been one of challenging topics in space electric propulsion technologies. Tens of W to several kW; the electron thermal energy is often converted into the directed ion energy via electrostatic ion accelerations in a current-free double layer and an ambipolar electric field[17], where the accelerated ions are neutralized by electrons overcoming the potential d rop[18] Fundamental studies on such an electronheated magnetic nozzle plasma thruster have shown that an internal azimuthal plasma current induces an axial Lorentz force in the magnetic nozzle, resulting in an increase in the thrust[19,20,21]. Testing different antennas in the unchanged source geometry will provide an insight on the antenna optimization for the thruster performance

Methods

Results

Conclusion