Atomic boron speed distribution measurements in the plume of a hall thruster using laser-induced fluorescence

Summary form only given. Hall thrusters are a type of electric propulsion device which are increasingly used for satellite station keeping and deep-space propulsion applications. Despite the widespread use and maturity of Hall thruster technology, much of the plasma physics which governs their operation remains unknown. Of particular interest is the sputter erosion process which slowly erodes the insulating channel walls. A cavity ring-down spectroscopy (CRDS) sensor has been developed for real-time in-situ measurements of the eroded atomic boron density^1,2, which, when coupled with the boron speed distribution, yields an absolute channel erosion rate. While the speed distributions of sputtered boron are fairly well known from a simple planar geometry and with controlled plasma conditions³, a Hall thruster is more complicated.We present measurement of sputtered atomic boron speed distributions within the plume of an operating SPT-70 Hall thruster. To the best of our knowledge, these measurements are the first LIF measurements of sputtered products within the plume of a Hall thruster. When high-energy xenon atoms impact the thruster wall, boron atoms are ejected into the thruster plume. Laser-induced fluorescence near 250 nm was used to measure the Doppler shift of the boron atoms and therefore the speed of these atoms along the thruster axis. A hollow-cathode lamp provided an unshifted-frequency reference (i.e. a zero-speed reference point). The measured boron velocity distributions closely follow a Sigmund-Thompson distribution. The first moment of the velocity distribution was found to be 3836 ± 183 m/s, and did not change significantly at two channel locations. Such distributions will allow absolute channel erosion measurements using the aforementioned CRDS sensor, as well as help validate high-fidelity thruster erosion models.