Gatsonis, Nikolaos A.
This project is part of an effort to characterize the plasma properties of pulsed plasma thruster plumes. Knowledge of plume properties is important in plume/spacecraft interaction studies as well as in thruster performance optimization studies. In this project electron temperature and density were measured in the plume of a NASA Lewis laboratory model pulsed plasma thruster (PPT) using triple Langmuir probes. Experiments were performed in a vacuum facility at NASA Lewis Research Center's Electric Propulsion Laboratory. A movable probe support was designed and attached to a linear translation table allowing the probes to be moved to various positions downstream of the thruster exit plane without having to vent the vacuum tank. A probe positioning procedure was developed including the construction of a position location plate that provided the reference point used to determine probe position. A glow cleaning procedure was established in order to remove accumulated contaminants on the probes. Proper grounding procedures were also established. Measurements were taken on planes perpendicular and parallel to the thruster electrodes, for radial positions between 6 cm and 20 cm downstream the Teflon propellant surface and angular positions of 0, 10, 20, and 30 degrees from the centerline. The thruster was operating at discharge energy levels of 5, 20, and 40 Joules. Analysis of data taken along the centerline shows the time evolution of electron temperature and density. The maximum values of electron temperature range from 3 to 6 eV and the maximum values of electron density range from 3.5 x 10? m? to 4.5 x 10?? m?. Results show that the maximum electron density decreases as a function of downstream distance while the maximum temperature remains almost constant. It is also found that electron density increases significantly with increasing discharge energy level while electron temperature remains almost unaffected.
Worcester Polytechnic Institute
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