Feedback control of an azimuthal oscillation in the E × B discharge of Hall thrusters.

Feedback control of a low-frequency azimuthal wave known as a 'rotating spoke' in the E × B discharge of a cylindrical Hall thruster was demonstrated. The rotating spoke is an m = 1 azimuthal variation in density, electron temperature, and potential that rotates at about 10% of the local E × B electron rotation speed. It causes increased electron transport across the magnetic field and is suspected to be an ionization wave. Feedback control of this wave required special consideration because, although it causes a rotating azimuthal variation in the current density to the anode, it does not show up as a signal in the total thruster discharge current. Therefore, an extra source of information was needed to track the oscillation, which was addressed by using a special anode that was split azimuthally into four segments. The current to each segment oscillates as the rotating spoke passes over it, and feedback is accomplished by resistors connected in series with each anode segment which causes the voltage on a segment to decrease in proportion to the current through that segment. The feedback resulted in the disappearance of a coherent azimuthal wave and a decrease in the time-averaged total discharge current by up to 13.2%. [ABSTRACT FROM AUTHOR]