A low-power, linear-geometry Hall plasma source with an open electron-drift

This paper presents a discussion of the physics of modem Hall plasma thrust ers and its impact on the design of new plasma thrusters of varying geometr y and power. A particular emphasis is placed on the design and development of a linear-geometry (noncoaxial) source with an open electron-drift curren t. The operating characteristics of a linear-geometry Hall discharge scaled to operate in the 50 to 100 W power range are presented. Two thruster acce leration channels were fabricated--one of alumina and one of boron nitride. Differences in operation with the two channel materials are attributable t o differences in the secondary electron emission properties. In either case , however, operation is achieved despite the lack of a closed electron curr ent drift in the Hall direction, suggesting that there is an anomalous axia l electron mobility, due to either plasma fluctuations or collisions with t he channel wall. Strong low-frequency oscillations in the discharge current , associated with the depletion of propellant within the discharge, are see n to appear and vary with changes in the applied magnetic field strength. T he frequency of this oscillatory mode is higher than that seen in larger (a nd higher power) discharges, due to the decreased residence time of the pro pellant within the channel.