Examination of plasma-wall interactions in Hall effect thrusters by means of calibrated thermal imaging

A semiempirical time-dependent thermal model of Hall effect thrusters was developed to compute evolution of the thruster channel wall temperature during a transient regime. The model accounts for heat conduction through dielectric walls and radiative transfer as the channel is considered as a thermal enclosure. The graybody view factors are experimentally determined during the cooling period that follows a power shutdown. The model permits the assessment of the amount of power delivered to walls by fitting calculated temperature profiles to experimental profiles obtained by means of calibrated infrared imaging. Plasma-surface interactions are examined in this contribution for three types of thrusters, namely, SPT100-ML, PPS (R) 1350-G, and the 5-kW-class PPSX000-ML. The electrical input power range that is probed stretches out from 500 W to 5 kW. The energy flux passed to the discharge chamber dielectric walls varies between 0.1 and 2 W/cm(2). The overall amount of power delivered to the external and internal walls is found to vary linearly with the applied power. It is in favor of an energy loss mechanism driven by ion bombardment. A departure from the linear trend is observed at high discharge voltage. Production of multiply charged ion species could be an explanation. The impact of thruster design and wall material on power losses inside the thruster channel is also investigated from both a technological and a physics standpoint. (c) 2007 American Institute of Physics.