MICROWAVE PLUME MEASUREMENTS OF A CLOSED DRIFT HALL THRUSTER

The plasma plume from a closed drift hall thruster has been characteri zed using a 17-GHz microwave diagnostic system. Electron number densit y profiles are obtained throughout the thruster plume via differential phase measurements. A functional model of plasma density has been dev eloped 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 tr ansition region between the near- and far-field plume. An indication o f slight plume asymmetry is obtained by evaluating total integrated de nsity 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 t he thruster axis. However, ray-tracing attenuation modeling based on p lasma density profiles indicates a greater effect for lower-frequency operation. The spectral data of the signal transmitted through the plu me exhibited clear 26-kHz harmonic sidebands and added broadband noise . Estimates of potential impact to communication and other electromagn etic satellite systems can be obtained directly from the measurements and from the electron number density distribution models derived from the measurements.