A Time-resolved Investigation of the Hall Thruster Breathing Mode.

Abstract

The existence of plasma oscillations in the near and far field discharge of a Hall effect thruster alters the conventionally held view of their operation as steady electrostatic propulsion devices. Indeed, the consequences from fluctuations in ionized propellant density, temperature, and potential may include increased thrust, exacerbated engine erosion, and spacecraft interference. In this work, the unsteady nature of a Hall effect thruster discharge is investigated via two-dimensional, time-resolved plasma measurements. A novel dual Langmuir probe diagnostic is developed to enable an unprecedented temporal resolution for electrostatically acquired plasma properties near the upper theoretical limits of this probe. Observations of large amplitude transient oscillations caused by the Hall thruster breathing mode are seen for all thruster conditions at all spatial locations and in all measured plasma properties including: discharge current, electron density, electron temperature, and plasma potential. A unique method of spatiotemporal data fusion facilitates visualization of two-dimensional time-resolved planar plasma density contour maps is also developed where discrete turbulent bursts of plasma are tracked as the thruster exhales breaths of ionized propellant at velocities in excess of 12 km/s. This time-resolved investigation of the plasma downstream from a Hall thruster unveils an environment rich in oscillatory behavior dominated by the Hall thruster breathing mode. These insights emphasize the importance of time-resolved plasma measurements and, through enhanced understanding of the discharge process, may ultimately lead to improved thruster designs that work in concert with plasma fluctuations to achieve enhanced performance.