Low-Voltage Hall Thruster Mode Transitions

Past investigations of the 6kW-class H6 Hall thruster during low-voltage operation revealed two operating modes, corresponding to the presence or absence of azimuthal propagating plasma spokes. The modes exhibited differences in thruster performance and plume properties, including electron current t...

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Bibliographic Details
Main Authors: Brown, Daniel L, Lobbia, Robert B, Blakely, Joseph M
Format: Report
Language:English
Subjects:
CATHODES
Electric and Ion Propulsion
HALL THRUSTERS
LOW VOLTAGE
MAGNETIC FIELDS
STABILITY
WUQ18A
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Summary:Past investigations of the 6kW-class H6 Hall thruster during low-voltage operation revealed two operating modes, corresponding to the presence or absence of azimuthal propagating plasma spokes. The modes exhibited differences in thruster performance and plume properties, including electron current to the anode that varied by up to 10% of the discharge current between operating modes. New evidence is presented that provides insight into the transition between operating modes, including hysteresis and the impact of cathode location. Global maps of thruster stability were examined, including maps of thruster current-voltage-magnetic field (I-V-B) and variation in cathode to ground potential for the IV-B surface. These I-V-B topologies were characterized for the H6 Hall thruster from 100V to 200V discharge, with variation in cathode flow fraction, cathode position inside and outside the magnetic field seperatrix, asymmetric magnetic field, and anode flow rate. Results indicate different plasma processes may trigger the transition to a highly oscillatory, global operational mode at reduced discharge voltage and low magnetic field strength. The transition at low magnetic field is insensitive to variation in cathode flow and cathode configuration, and occurs at a constant magnetic field for discharge voltage greater than 130V. The transition at low voltage is influenced by cathode flow fraction, cathode configuration, and anode flow rate. Possible mechanisms are considered, including the electron gyroradius and electron mobility. Technical paper presented at 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Cleveland, OH, 28-30 July, 2014. The original document contains color images.