Non-Intrusive, Time-Resolved Hall Thruster Near-Field Electron Temperature Measurements

Abstract

Abstract : With the growing interest in Hall thruster technology, comes the need to fully characterize the plasma dynamics that determine performance. Of particular interest is the existence of a periodic low frequency oscillation, commonly referred to as the breathing mode. Although there has been a significant effort to quantify plasma properties, this has been primarily limited to time-averaged measurements. In order to fully understand the periodic instabilities characteristic of Hall thruster behavior, time resolved techniques must be developed. This study presents a non-intrusive method of determining time-resolved electron temperature fluctuations during the breathing mode cycle. A triggering system was developed to synchronize measurements to thruster discharge current oscillations. Emission in the NIR is measured near the thruster exit plane using an optical fiber coupled to a 1.25 m focal length spectrometer and intensified CCD (ICCD) detector. ICCD gating is controlled using the output of the triggering system and a user controlled gate delay. This allows emission sampling only from the desired portion of the breathing mode cycle. Emission is integrated over several periods to allow for improved signal to noise ratio (SNR). Electron temperature is determined using the intensity of Xe I emission lines in the context of a collisional-radiative model. The resulting measured electron temperature fluctuations during a nominal breathing mode cycle are presented for a 600 W Hall effect thruster at a single nominal operating condition.