(Color online) A series of frames displaying the visible light emission from the rotating spoke instability in the 2.6 cm cylindrical Hall thruster. The 15–35 kHz spoke can be seen to rotate in the counter-clockwise direction, which corresponds to the E × B direction. Operating parameters include 250 V discharge bias, 4 sccm Xe mass flow, −2.0 A in the front magnet coils and +2.5 A in the rear coils. Color is artificial.
(Color online) Cross-section view of a cylindrical Hall thruster. Electrons are magnetized and are confined by a combination of the mirror force and the electric field. Ions are not magnetized and are accelerated by the electric field. Segmented anode shown.
(Color online) Simulation of the magnetic field in the cusp configuration, with +2.5 A in the back coils and −2.0 A in the front coils. The enhanced cusp shape forms a stronger mirror field. Image is shown about the axis of symmetry. The maximum magnetic field is 875 Gauss and occurs 6 mm from the anode.
(Color online) CAD model of the segmented anode assembly. Boron nitride houses the four stainless steel segments. Threaded rods extrude radially to affix the segments and connect the current path. The 8 internal and 16 external semi-circle holes allow gas distribution.
(Color online) Probe holes in the ceramic channel are visible in this figure. Only those nearest the anode were used in this experiment and may be seen by the circular grooves in the face of the channel and blue highlights. Numbers refer to approximate positions on a clock. Emissive probes were placed at positions 2 and 11 while Langmuir probes were placed at 5 and 8.
Characteristic waveform of the current through the rotating spoke to a single segment of the anode. The current rises and falls as the spoke becomes centered over the segment, then passes onto the next. The trace was determined by averaging over several hundred spoke cycles. The time axis is normalized to the spoke period, which ranges from 30 μs to 80 μs. The maximum is 0.57 with a standard deviation of 0.13.
(Color online) (a) Normalized electron density, temperature, and potential fluctuations relative to the rotating spoke-induced current. The density has a maximum of 3.1 ± 0.6 × 1012 cm−3, the temperature a maximum of 7.1 ± 0.5 eV, and the potential a maximum of 230 ± 2 V. (b) Azimuthal electric field deduced from the plasma potential and fluctuation-induced drift current relative to the segmented anode-measured current.
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