Azimuthal Spoke Propagation in Hall Effect Thrusters

Spokes are azimuthally propagating perturbations in the plasma discharge of Hall Effect Thrusters (HETs) that travel in the E B direction. The mechanisms for spoke formation are unknown, but their presence has been associated with improved thruster performance motivating a detailed investigation. Th...

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Bibliographic Details
Main Authors: Sekerak, Michael J, Longmier, Benjamin W, Gallimore, Alec D, Brown, Daniel L, Hofer, Richard R, Polk, James E
Format: Report
Language:English
Subjects:
ACOUSTIC VELOCITY
AZIMUTH
DISPERSION RELATIONS
Electric and Ion Propulsion
Electricity and Magnetism
FIELD CONDITIONS
FIELD INTENSITY
HALL EFFECT
HALL THRUSTERS
IMAGE PROCESSING
MOTIVATION
NEAR FIELD
OSCILLATION
PERFORMANCE(ENGINEERING)
PERTURBATIONS
PLASMA JETS
PLUMES
PROBES
PROPAGATION
SATURATION
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Summary:Spokes are azimuthally propagating perturbations in the plasma discharge of Hall Effect Thrusters (HETs) that travel in the E B direction. The mechanisms for spoke formation are unknown, but their presence has been associated with improved thruster performance motivating a detailed investigation. The propagation of azimuthal spokes are investigated in a 6 kW HET using high-speed imaging and azimuthally spaced probes. The spoke velocity is determined from high-speed image analysis using three methods with similar results. The spoke velocity for three discharge voltages (300, 400 and 450 V) and three anode mass flow rates (14.7, 19.5 and 25.2 mg/s) are between 1500 and 2200 m/s across a range of magnetic field settings. The spoke velocity is inversely dependent on magnetic field strength for lower B-fields and asymptotes at higher B-fields where a different oscillatory mode is noted in the thruster. An empirically approximated dispersion relation of = v chk ch where 1 yields a characteristic velocity that matches the ion acoustic speed for 5 eV electrons which exist in the near-anode and near-field plume regions of the discharge. Dispersion plots from ion saturation reference probes in the plume 1.5 mean discharge channel radii downstream are qualitatively similar to high-speed imaging dispersion plots of the discharge channel. Spoke velocities calculated from the probes are consistently higher by 30 % or more. The 33rd International Electric Propulsion Conference, The George Washington University, USA October 6 10, 2013. Sponsored in part by AFRL.