Density and spectral measurements using a 34 GHz interferometry system
Interferometry was used to investigate the impact of the plasma plume of the University of Michigan P5 thruster on microwave signals. Measurements were made at 34 GHz using a newly built Ka-band interferometer and also at 17 GHz similar to other measurements made on Hall thrusters [2, 4], Very close to the thruster’s exit plane (.05 m) a peak phase shift of 32 and 60 degrees at 34 and 17 GHz, respectively, was measured. At 0.5 m from the P5 exit plane, the peak phase shift measured was 16 degrees at 34 GHz and 9 degrees at 17 GHz. Signal attenuation measurements showed at. 05 m from the thruster’s exit plane around 1.2 dB of signal attenuation for 17 GHz and about 0.5 dB of attenuation for 34 GHz on centerline of the thruster. Electron densities profiles were calculated using Abel inversion on the phase shift measurements. At a discharge voltage of 300 V and a discharge current of 10 A, a peak electron density of about 4el0 cm-3 was found. 05 m from the exit plane. At 300 V, 5 A, and. 05 m from the exit plane, a peak density of 2.2el0 cm-3 was found. Spectral measurements of a signal propagating through the plasma plume were also made showing that the presence of specific harmonics is strongly dependent on operating conditions.
