A circular waveguide electron cyclotron resonance plasma thruster prototype driven by microwaves at 5.8 GHz (80–300 W) is characterized. The magnetic field is generated by a combination of Sm-CoYXG32 magnets and an electromagnet, which enables the tuning of the resonance position and magnetic nozzle shape. The main plasma plume properties are analyzed by using electrostatic probes when the mass flow rate (Xenon), microwave power, electromagnet current, and propellant injector design are varied. An estimation of the propulsive performance of the device is also presented. Results show that a single radial injector hole is not sufficient for a symmetric ion current profile and that magnetic nozzle shape and strength tuning can significantly affect the divergence angle and thruster floating potential. A utilization efficiency of up to 70% and electron temperatures of up to 16 eV have been measured.

Xenon ion velocity is mapped in the magnetic nozzle of a circular waveguide electron cyclotron resonance thruster operating at 5.8 GHz by means of laser-induced fluorescence spectroscopy in the near-infrared spectral range. An array of thruster operational parameters are explored to investigate the influence on the acceleration profile and terminal ion velocity. Owing to several mechanisms which broaden the measured spectra, e.g. Paschen-Back/Zeeman effect, inference of the most probable velocity along with the axial kinetic temperature requires full lineshape modeling, especially in the near-field plume and inside the source. Ions are effectively accelerated along the magnetic nozzle, reaching up to 12000 m/s for the lowest neutral pressure tested. A relatively large axial kinetic temperature is observed, typically in the order of 5000 K, which can be attributed to an extended ionization region that overlaps with the acceleration region.