Langmuir Probe Measurements in the Discharge Channel of a 6-kW Hall Thruster

Abstract

In an effort to understand the role of neutral flow dynamics in the operation of Hall thrusters, a cylindrical Langmuir probe was used to measure the electron temperature, floating potential, and ion number density in the discharge channel of a 6-kW Hall thruster operating at 300 V and anode flow rates of 10, 20, and 30 mg/s. To isolate the effect of propellant flow rate, the cathode flow fraction and magnetic field topology were held constant while varying magnetic field strength to minimize discharge current while maximizing thrust. The probe was inserted and removed from the discharge channel by a high-speed positioning system at nine radial locations. The peak ion density calculated by the thin sheath analysis technique was typically upstream of the peak electron temperature location by 3-5% of the channel length. The peak ion density calculated by the orbitalmotion limited analysis technique coincided with the peak electron temperature location. The peak electron temperature dropped by approximately 5 eV and moved downstream by 3-5% of the channel length for each addition of 10 mg/s. The electron cooling was attributed to increased electron-neutral collisions. The results indicate a strong dependence between neutral flow rate and the peak plasma property magnitude and location.