Miniature ion thrusters are well suited for future space missions that
require high efficiency, precision thrust, and low contamination in the mN to
sub-mN range. JPL's miniature xenon Ion (MiXI) thruster has demonstrated an
efficient discharge and ion extraction grid assembly using filament cathodes
and the internal conduction (IC) cathode. JPL is currently preparing to incorporate a miniature
hollow cathode for the MiXI discharge. Computational analyses anticipate that an axially
upstream hollow cathode location provides the most favorable performance and beam
profile; however, the hot surfaces of the hollow cathode must be sufficiently downstream
to avoid demagnetization of the cathode magnet at the back of the chamber, which can
significantly reduce discharge performance. MiXI's ion extraction grids are
designed to provide >3 mN of thrust; however, previous to this effort, the low-thrust
characteristics had not been investigated. Experimental results obtained with the
MiXI-II thruster (a near replica or the original MiXI thruster) show that sparse average
discharge plasma densities of ∼5×1015–5×1016 m-3 allow the use of very low
beamlet focusing extraction voltages of only ∼250–500 V, thus providing thrust levels
as low as 0.03 mN for focused beamlet conditions. Consequently, the thrust range
thus far demonstrated by MiXI in this and other tests is 0.03–1.54 mN.
Implementation of a ¼ Inch Hollow Cathode into a Miniature Xenon Ion Thruster (MiXI)