Investigation of the Impact of Plasma Instabilities on Electron Detachment in Low Temperature Magnetic Nozzles

Proposed here is an analysis of facility effects on a small helicon plasma source with a magnetic nozzle. Backpressure effects will first be recorded and analyzed. Electrical effects of a conducting vacuum chamber will then be determined. While a small amount of research has so far been done on these thrusters, this will be the first on a plasma source several centimeters in diameter. Furthermore, no research has explored effects at pressures as low, and none has determined electrical effects of the chamber wall. The plasma source used in this research is the Small Propulsive Ionic Nozzle eXperiment (SPHINX), a plasma source several centimeters in diameter developed at the University of Michigan. The experiments performed on SPHINX will take place in the Nanosatellite Engine Operation Vacuum Chamber (NEOVac) and the Large Vacuum Test Facility (LVTF). NEOVac is a small chamber designed specifically for testing thrusters of SPHINX's size. LVTF is much larger and has the ability to reach lower pressures, representing a more space-like environment in which to test SPHINX. First, a baseline will be established with tests in NEOVac, iterating across all possible operating pressures. Ion velocity distribution functions (IVDF) and ion density will be recorded by Laser Induced Fluorescence (LIF) and Langmuir probes, respectively. SPHINX will then be moved to LVTF, where pressure will be iterated across the same values. Pressure will then be lowered incrementally to the lowest possible operating pressure with IVDF and density measurements taken at each step. Finally, a conducting plate will be introduced into the chamber. LVTF will run at high vacuum, and the conducting plate will be repositioned parallel to SPHINX under operation. Electric potential will be taken on the plate, and the magnetic field at the plate will be measured at each step using an Inductive Magnetic Field Probe. This process will then be repeated with the plate grounded, and current through the plate will be recorded. Data will be analyzed to determine what effects background pressure and conducting chambers have on magnetic nozzle plasma operation. With data on backpressure effects, the influence of neutral ingestion, charge exchange collisions, and momentum exchange collisions will be analyzed to determine where primary influences lie and the significance of those influences. If the theory behind these three mechanisms is insufficient to explain results, the theory will be modified. The existence of a Current Free Double Layer (CFDL) will be determined in each step by LIF measurements. The influence of facilities on CFDL's will thus be determined. Small magnetic nozzle thrusters are of potential use for CubeSat propulsion. However, little research has been done examining how these thrusters perform in space, and how this performance will vary from ground tests. Developing the theory behind facility effects of these thrusters will allow a more reliable prediction of space performance, yielding a broader mission applicability. According to NASA, further enabling of CubeSat propulsion is an important step in the furthering of our space program, and this research aims to increase the usability of small EP devices on CubeSats. Furthermore, detection of CFDL's in these situations will yield a better understanding of the source of these phenomena. As an ion acceleration mechanism, they are relatively poorly understood and have been theorized to be simply a result of facility interference. As a potential source of thrust for these thrusters, their formation mechanism needs to be more fully understood before further research can be conducted.