Ion dynamics in the magnetic nozzle of a waveguide ECR thruster via laser-induced fluorescence spectroscopy

Abstract

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.

Thrust measurements of a waveguide electron cyclotron resonance thruster

“…Results in agreement with these were obtained through LIF measurements performed on this thruster in Ref. 23, where the spread in ion energies was referred to as axial kinetic temperature. In the present study, ion temperatures in the order of 4000-10 000 K were found for most of the cases.…”

“…Indeed, the LIF measurements in Ref. 23, revealed a mean ion velocity of À500 m/s directed toward the backplate at z ¼ À10 mm (middle of the discharge chamber) for the same thruster design as in this study.…”

“…In order to further investigate the physics of waveguide ECRTs and identify the limitations of this technology, in this work we report thrust and plasma plume measurements of a newly designed waveguide ECRT. [20][21][22][23] The MW frequency used is 5.8 GHz, allowing for smaller waveguide dimensions (D ¼ 36 mm) with respect to the usual 2.45 GHz frequency (D % 80 mm), and consequently lowering the size of the device, its mass flow rate and power requirements. Thanks to this design choice, no dielectric filling of the waveguide is needed as in Ref.…”