Transport-Property Measurements in the Plume of an SPT-100 Hall Thruster

Abstract

To understand the interaction between the SPT-100 thruster and the spacecraft, accurate knowledge of exhaust plume properties must be obtained. This investigation utilized a suite of interrelated diagnostic probes in an effort to provide detailed knowledge of the exhaust plume on a molecular kinetic level. Probes used for the investigation included a retarding potential analyzer, a planar Faraday probe, an emissive probe, both total-and radiant-heat-ux probes, as well as a newly developed neutral particle ux probe. Combining the knowledge gained from these probes it was possible to quantify the transport of mass, energy, and charge within the plume at 0.5-and 1.0-m radius from the thruster exit. Among the phenomena uncovered were a high-energy ionic annulus surrounding a narrow low-energy core within the plume at 0.5-m radius from the thruster exit. This core structure was lled in at 1.0-m radius. Additionally, a population of energetic charge-exchange neutrals was found within 25 deg of the thruster centerline along with the corresponding low-energy charge-exchange ions attributed to plume/background gas interactions.

Conditions and growth rate of Rayleigh instability in a Hall thruster under the effect of ion temperature

“…(26) and (27), it is inferred that the oscillations will grow into the Rayleigh instability only when their frequency remains within a frequency band described by the following inequalities:…”

Laser-induced fluorescence measurements of velocity within a Hall discharge

“…Furthermore, a time-averaged broadening of the fluorescence excitation spectra can arise due to oscillations in the zone of ionization. King has shown by mass and resolved energy analysis that the axial velocity of the ions has an energy distribution of approximately 10 eV (in the far field) due in part to the plasma oscillations within the Hall thruster [23]. The issue of the distribution of ion velocities due to the axial location where they were born is minimized by examining the fluorescence spectra in the radial direction.…”

Evaluation of a Magnetically Filtered Faraday Probe for Measuring the Ion Current Density Profile of a Hall Thruster

“…de Grys, et al, suggest that CEX ions due primarily to facility effects are below a typical material threshold and have energies less than 20 eV. 14 Previous methods for obtaining the true ion current density profile have had varying degrees of success and have included using a second Faraday cup pointed away from the thruster, 15 a retarding potential analyzer (RPA) to screen out CEX ions, 16 a gridded Faraday probe, and a biased collimator to filter CEX ions before they reach a Faraday probe. 10,14 Each of these techniques has its own advantages, but there is still another possible approach to obtaining the true ion current density profile.…”