Performance of a Linear Hall Discharge with an Open Electron Drift

This paper presents a recent characterization of the thrust efficiency and specific impulse of a low power, linear-geometry (non-coaxial) Hall thruster with an open electron-drift current. The thruster was constructed with a boron-nitride insulating channel surrounded by a magnetic circuit served by four electromagnet coils, and was designed to operate in the 100-Watt power class. A survey of the thruster operation demonstrated promising performance (7= 2.1 mN, rj = 14.6%, I sp = 1070 sec) in the very low power range (< SOW). The thruster showed poor long-term stability at these operating conditions that demanded extremely high magnetic fields (~1.6kG). Operation at lower magnetic field strengths (-300-400G) and therefore lower discharge power (<50W), allowed for continuous operation for extended durations, and permitted laser-induced fluorescence measurements of the ion velocities across and downstream of the linear exit channel. Velocities in excess of 3 km/s were measured at the discharge exit, and 8 km/s approximately 1.5 cm downstream of the discharge exit plane, consistent with measurements reported on for a similar co-axial discharge. The near exit-plane velocities were found to be somewhat sensitive to the xenon mass flow servicing the oversized hollow cathode, confirming the possible interferences that the cathode flow may have on the ion beam development in the near exit region as a result of possible charge-exchange collisions.