Experimental characterization of azimuthal and axial oscillations in a microwave discharge neutralizer

Abstract

This study presents the first successful experimental observation of azimuthal oscillations in a microwave discharge neutralizer across a wide range of operating conditions. The neutralizer was operated with water vapor as the propellant and in the diode mode, which utilizes a positively biased collector plate to extract electrons from the neutralizer. By segmenting the collector plate into 43 sections in the azimuthal direction, azimuthal current measurements were achieved without introducing perturbations to the neutralizer. Azimuthal oscillations in the frequency range of 1–2 MHz were observed under all tested conditions. Furthermore, the axial current also exhibited oscillatory behavior. This axial oscillation would be explained by a combination of azimuthal oscillations and non-uniform electron emission from orifices. The amplitude of the axial current oscillations implies that the oscillation mode changes from incoherent to coherent as the mass flow rate increases. This mode transition is expected to influence the performance of the microwave discharge neutralizer utilizing water vapor propellant.