Plume characteristics of a multiple ion source thruster

Citation

Tierney, C. Michael (1995) Plume characteristics of a multiple ion source thruster. Engineer's thesis, California Institute of Technology. doi:10.7907/mj8f-q926. https://resolver.caltech.edu/CaltechETD:etd-07112007-133241

Abstract

This report describes ion plume characteristics of a multiple ion source thruster that are important to propulsion subsystem, spacecraft system, and mission design engineers with respect to incorporation of the segmented ion thruster (SIT) within a space mission. These characteristics will address issues related to operational performance, lifetime, thruster interaction with a host spacecraft, multiple ion beam interaction, and repeatability of construction and operation. Information contained within this report can be helpful in evaluating subsystem / mission performance, and resolve possible thruster / spacecraft integration issues.

Characteristics of the exhausted ion beam(s) were evaluated through two sets of experiments. The first involved measuring the two-dimensional ion current density distribution at several downstream locations from the thruster with concurrent operation of up to three ion sources. Assessments were made of plume symmetry, plume development as a function of downstream position, interactions between multiple ion beams, and beam divergence angles were calculated for individually operated ion sources. Ion beam asymmetries about the ion source centerline were observed. Construction of multiple ion source current density profiles through superposition of data obtained from operation of individual ions sources was attempted. Charge exchange effects appear to have impacted the analyses and some discrepancies between 'real' and 'constructed' results were observed. Beam divergence angles for R = 0.893 cases ranged from 10° to 18° and from 16° to 22° for R = 0.643 cases.

The second set of experiments involved collection of ion charge state data with the use of an ExB mass spectrometer placed downstream of the thruster. Charge state data was collected along the ion source centerline for 3 fixed propellant flow rates and varible beam currents. Data was also collected for a fixed flow rate and beam current at positions located along the horizontal and vertical axes passing through the ion source centerline. Correction factors for thrust and propellant utilization based upon doubly charged ion production, as well as propellant backflow into the discharge chamber were determined. Asymmetries in the radial profiles, as well as inconsistencies between the profiles of singly and doubly charged ions and charge state ratio, were observed.

Thesis Files