Anomalous Electron Transport in Hall Thrusters: Electric Field Fluctuation Measurement

Abstract

Anomalous transport of electrons has considerable impact on the overall performance of Hall thrusters. Numerous studies have shown that high-frequency (on the order of MHz) fluctuations in both the electric field and plasma density are one of the causes of the anomalous transport. This phenomenon has yet to be measured in detail, however, because it is difficult to evaluate the density distribution of neutral particles and the dispersion relation of plasma oscillation in the several MHz range. It was therefore necessary to develop a device to measure the fluctuations in order to elucidate the cause of the anomalous transport. Here we focus on electric field fluctuations in the azimuthal direction inside a Hall thruster, and measure floating potential difference between two Langmuir probes. When a discharge current increases under a strong magnetic field, the azimuthal fluctuation in the frequency of 1-5 MHz is enhanced and fluctuations at ~100 kHz appear. These results suggest that azimuthal fluctuations in the electric field play an important role in the anomalous transport of electrons in the Hall thruster.