Feedback Control of Azimuthal Oscillations in Hall Thrusters: Enhanced Thruster Efficiency and Performance

Web Published:

Princeton Docket # 12-2808


Researchers at Princeton Plasma Physics Laboratory have developed a novel method to achieve feedback control of low-frequency azimuthal waves (rotating spoke oscillation) in the ExB discharge of a Hall thruster.  This technology will enhance thruster efficiency and performance.


The Hall thruster is a plasma-based propulsion system for satellites and in the future, space vehicles.  The field traps electrons in azimuthal ExB orbits inside the thruster channel, neutralizing the ion space charge and allowing the Hall thruster to produce a high thrust density.  With a typical propellant velocity around 20 km/s, and thrust from 10-1000 mN, Hall thrusters are attractive for orbit station-keeping, orbit insertion, and inner-planetary missions.  However, the efficiency of the thruster is degraded by azimuthal oscillations that increase electron transport to the anode.  Further, electromagnetic interference from plasma oscillations in the thruster can interfere with satellite electronics.  Thus, there is an urgent need for controlling the azimuthal oscillations in the Hall thrusters.


Princeton researchers have designed a special anode that is split azimuthally into a number of segments. The current to each segment oscillates as the rotating spoke passes over it, and feedback is accomplished by either by resistors connected in series with each anode segment or more complex passive feedback circuitry comprising resistor, inductor and/or capacitor and or active feedback, which causes the voltage on a segment to decrease in proportion to the current through that segment.  A laboratory prototype of this system with feedback based on resistors has been fabricated and demonstrates that this new method can suppress a coherent azimuthal wave in a Hall thruster and decrease the time-averaged total discharge current by up to 13.2%.



·        To suppress azimuthal oscillations in Hall thrusters and other ExB devices

·        To excite and control azimuthal oscillations



·        Enhanced Hall thruster performance by reducing electron cross-field transport

·        Improved Hall thruster efficiency by allowing the production of more thrust for a given power input

·        More stable operation of the Hall thruster


Intellectual Property status

Patent protection is pending.

Patent Information:
For Information, Contact:
William Gowen
Licensing Associate
Princeton University
Martin Griswold
C. Leland Ellison
Yevgeny Raitses
Nathaniel Fisch