Langmuir Probe Measurement Approach for Capturing the Electron Drift Velocity in a Hall-effect Thruster

Langmuir probes (LP) are used to obtain electron temperature, density, and electron velocity distribution function (EVDF) in the plumes of Hall-effect Thrusters (HETs). Confounding straightforward implementation of the EVDF measurement and subsequent analysis of IV traces from cylindrical probes is the flowing plasma. The usual simplifying assumption is that the EVDF is Maxwellian, which requires the probes to be aligned with the flow. There is evidence to suggest that the electrons are actually non-Maxwellian. In this regard, it’s critical to measure EVDF without simplifying assumptions.  The true energetics of the electrons may yield a great deal of insight into the so-called anomalous electron diffusion problem in Hall thrusters. Here, we present an approach to obtaining the EVDF where the probe’s axis is oriented perpendicular to the plasma flow. The resulting characterization of the EVDF revealed that the distribution is best described by a drifting Maxwellian. The implications of the drift velocity value are discussed.