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Influence of tailored applied magnetic fields on high-power MPD thruster current transport and onset-related phenomena

Show simple item record Moeller, Robert C. Polk, James E. 2014-02-26T23:38:08Z 2014-02-26T23:38:08Z 2013-10-07
dc.identifier.citation 33rd International Electric Propulsion Conference (IEPC2013), Washington, D.C., October 6-10, 2013 en_US
dc.identifier.clearanceno CL#13-4474
dc.description.abstract This work investigated the effects of tailored, externally-applied magnetic fields on current transport and near-anode processes in the plasma discharge of a magnetoplasmadynamic thruster (MPDT). Electrical and plasma diagnostics were used to investigate how localized applied magnetic fields could mitigate the effects of the “onset” phenomena, including large-amplitude terminal voltage fluctuations and high anode fall voltages associated with unstable operation and anode erosion. An MPDT with a multi-channel hollow cathode was developed and tested with quasi-steady pulses of 1 ms duration at power levels of 36 kW (20 V, 1800 A) to 3.3MW(255 V, 13.1 kA) with argon propellant in three different magnetic configurations: self-field, applied B field tangential to the anode lip near the exit plane, and applied cusp B field. The current pattern and current densities redistributed to follow the applied poloidal magnetic field lines, which created increased conduction paths to the anode. Also, the anode fall voltage was substantially reduced with both applied B field topologies over a large range of currents. For example, at 10.7 kA, the cusp applied magnetic field decreased anode fall voltages from 45–83 V down to 15 V or lower along much of the anode. The amplitude and frequency of the voltage fluctuations were also reduced over a broad range of currents with the applied fields. E.g., the standard deviations of the fluctuations were lowered by 37–49% at 8–9 kA. In addition, decreases in the mean terminal voltages as large as 31% were measured with the applied magnetic fields. These effects are shown to be associated with the increased current conduction along the applied magnetic field lines in the near-anode region. These results also suggest a reduction in frequency and intensity of current-concentrating filaments and anode spots, which contribute to erosion. Overall, both applied magnetic field configurations enabled significant reductions in onset-related behaviors relative to self-field operation. These improvements should lead to reduced anode erosion, i.e., improved thruster lifetime, and increased thruster efficiency with the applied fields. The applied fields used in this study differ from both the topologies and relative field strengths typically used in the vast majority of conventional, so-called “applied-field MPD thrusters” (AF-MPDTs). These results suggest a distinctive and more effective approach to influencing the near-anode phenomena and mitigating the deleterious effects of onset with appropriately designed applied magnetic fields. en_US
dc.description.sponsorship NASA/JPL en_US
dc.language.iso en_US en_US
dc.publisher Pasadena, CA : Jet Propulsion Laboratory, National Aeronautics and Space Administration, 2013 en_US
dc.subject spacecraft propulsion technologies en_US
dc.subject delta-V en_US
dc.subject Electric propulsion (EP) en_US
dc.subject magnetoplasmadynamic thruster (MPDT) en_US
dc.title Influence of tailored applied magnetic fields on high-power MPD thruster current transport and onset-related phenomena en_US
dc.type Preprint en_US

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