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Title:Development and Testing of a Gallium Electromagnetic (GEM) Thruster
Author(s):Thomas, Robert E., II
Director of Research:Burton, Rodney L.
Doctoral Committee Chair(s):Burton, Rodney L.
Doctoral Committee Member(s):Miley, George H.; Glumac, Nick G.; Elliott, Gregory S.; Polzin, Kurt
Department / Program:Aerospace Engineering
Discipline:Aerospace Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Electric Propulsion: Plasma Diagnostics: Space Propulsion: Pulsed Power
Abstract:An ablative, quasi-steady electromagnetic plasma accelerator is tested to quantify various characteristics of its operation. An array of diagnostics are used to characterize a gallium plasma produced by an arc discharge with current levels in the range of 5.6 - 22.6 kA. Discharge current and arc voltage measurements yield arc impedance values in the range of 6 - 7 milliohms at peak current. The absence of high-frequency oscillations in the arc voltage trace indicates lack of the ``onset" condition often seen in MPD arcs, suggesting that a sufficient number of charge carriers are present for current conduction. It is found that the mass bit varies quadratically with the discharge current which yields a calculated exhaust velocity of 20 km/s. A perpendicular probe and time-of-flight method yield on-axis exhaust velocities in the range of 15-22 km/s that is found to be invariant with the discharge current. Macroparticle ejection is unavoidable when testing with a central anode; this is possibly due to the presence of high-current density anode spots present on the gallium surface. A spatially and temporally broad spectroscopic survey in the 220-520 nm range is used to determine which species are present in the plasma. The spectra show that neutral, singly, and doubly ionized gallium atomic and ionic species are present in the discharge. Axial triple Langmuir probe measurements yield electron temperatures in the range of 0.8 - 3.6 eV and electron densities in the range of 8e20 - 2e22 electrons per meter cubed. The plasma expands isentropically with divergence half-angles in the range of 16 - 20 degrees. Spatially resolved magnetic field probe data reveals a symmetric arc discharge with no evidence of the current spoking instability. A power balance model is coupled with a sheath model to yield values of the electric field, temperature, and current density at the surface of the cathode.
Issue Date:2011-01-21
Rights Information:Copyright 2010 Robert E. Thomas
Date Available in IDEALS:2011-01-21
Date Deposited:2010-12

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