Near- and far-field characterization of stationary plasma thruster plumes

A comprehensive investigation of Hall thruster plume plasma ion energy distribution functions and ion charge state has been made on both fight- and laboratory-model engines. An energy analyzer, mass spectrometer, and E x 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 influence 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.