Plasma properties in the far-field plume of a radiofrequency plasma thruster

A radiofrequency plasma source was previously developed at the University of Michigan to study the behavior of ions downstream of a diverging magnetic field.^1,2 A follow-up experiment investigates the performance of the plasma source operating as a thruster. During this experiment, simultaneous thruster performance and far-field plume measurements of the rf plasma source are taken in the Large Vacuum Test Facility (LVTF) at the University of Michigan. Thruster performance is measured using an inverted-pendulum thrust stand, and plume properties are investigated using a nude Faraday probe, a retarding potential analyzer, and a commercial rf-compensated Langmuir probe. The pressure in the LVTF is held below 5.5×10^-6 torr during operation of the thruster in order to reduce facility effects on probe measurements. The work presented here focuses on the results of the probe analysis.