Near- and Far-Field Characterization of Stationary Plasma Thruster Plumes

Abstract

A comprehensive investigation of Hall thruster plume plasma ion energy distribution functions and ion charge state has been made on both ight-and laboratory-model engines. An energy analyzer, mass spectrometer, and E £ B probe were used to characterize Hall thruster plume ions. The results of this investigation show that the distribution function of the ion beam exhibits both Maxwellian and Druyvesteyn traits and that the Hall thruster plume contains a nontrivial amount of energetic, multiply charged particles that must be accounted for in modeling the erosion rate of solar array cover glass and interconnect material. Detection of these multiply charged ions by energy analyzers has been hampered in the past by charge exchange and elastic collisions. The high-energy tail seen in numerous energy analyzer data is thought to result from charge exchange and elastic collisions between singly and multiply charged ions and neutrals. The role of facility pressure was also investigated and was found to have an in uence mainly on the width of the ion energy distribution function. This pressure broadening is caused by elastic collisions between beam ions and background chamber gas particles. Nomenclaturecollector current, A n i = ion number density, m ¡3 q = elementary charge, C q I = charge state of ion r = position vector, m t = time, s u i = ion speed, m/s V i = beam ion acceleration potential, V v = ion velocity vector, m/s

Ion-Energy Plume Diagnostics on the BHT-600 Hall Thruster Cluster

“…In a similar fashion, TOPAZ was rotated vertically with respect to the ion beam, and the optimum guiding plate voltage V G , which maximized the counts at a particular elevation angle , was determined. Equations (2) and (3) display these relationships, with the units in brackets.…”

“…measured ions remains unknown; however, previous measurements on anode layer type Hall thruster plumes reveal a majority of plume ions are singularly charged [2].…”

Computation of Neutral Gas Flow From a Hall Thruster Into a Vacuum Chamber

“…At elevated background pressures, residual gas particles can be entrained into the thruster discharge region artificially increasing engine thrust. Elevated facility pressure has also been found to increase the width of the ion energy distribution function through elastic collisions between beam ions and neutral background particles [4]. Due to these effects, the validity of comparisons made between data taken in facilities with different background pressures, especially at 10" 4 Torr and higher, is questionable.…”

Evaluation of a 4.5 kW Commercial Hall Thruster System for NASA Science Missions

“…The main areas of concern include sputtering of spacecraft surfaces due to high-energy particles in the plume, the forces imparted on spacecraft surfaces due to the momentum flux in the plume, and the deposition on the spacecraft of contaminant efflux from the thruster. Many experimental and modeling studies have been performed for Hall thruster plumes 43,44,45,46 and also for EP missions beyond GEO. 47,48 The plume of the BPT-4000 thruster has been characterized through detailed diagnostic experiments, 49 materials sputter testing and modeling, 50 and spacecraft-level plume effects modeling.…”