Microwave Plume Measurements of a Closed Drift Hall Thruster

Abstract

The plasma plume from a closed drift hall thruster has been characterized using a 17-GHz microwave diagnostic system. Electron number density profiles are obtained throughout the thruster plume via differential phase measurements. A functional model of plasma density has been developed combining a near-field Gaussian beam term and a far-field point source expansion term. An outcome of this work is a mapping of the transition region between the nearand far-field plume. An indication of slight plume asymmetry is obtained by evaluating total integrated density measurements along rays emanating from the thruster. Additional evaluations have determined the plasma plume effect on attenuation and spectral characteristics of a wave transmitted through the plume. The attenuation was small, with slightly over 2 dB loss at 0.09 m along the thruster axis. However, ray-tracing attenuation modeling based on plasma density profiles indicates a greater effect for lower-frequency operation. The spectral data of the signal transmitted through the plume exhibited clear 26-kHz harmonic sidebands and added broadband noise. Estimates of potential impact to communication and other electromagnetic satellite systems can be obtained directly from the measurements and from the electron number density distribution models derived from the measurements.