Quadruple Langmuir Probe Measurements of a Hall Effect Thruster Plume

Abstract

Measuring time-dependent plasma parameters requires a diagnostic capable of making instantaneous measurements. A quadruple Langmuir probe measures the instantaneous electron temperature, electron density, and ion velocity. In this thesis, a quadruple Langmuir probe was designed, manufactured, and utilized to characterize the breathing mode of a HallEffect Thruster. This quadruple Langmuir probe has a probe radius of 0.117 cm and collects current with graphite electrodes. An applied potential of approximately 27 V was applied to the ion saturation current collecting parallel and perpendicular probes. A measurement of the breathing mode was successfully taken for a Hall thruster operating with a discharge voltage of 250 V. The frequency of the breathing mode was estimated to be 28.4 kHz. The electron temperature varied between 1 and 3.4 eV for one breathing mode cycle. The electron density was measured on the order of 10^{17} m^{−3}. Thin-sheath Langmuir probe theory was applied, but results indicated that transitional sheath theory should be applied. Using the collected data, the average Mach number and ion velocity was calculated at 10.9 and 20 km/s, respectively. The plasma potential was calculated to have a mean value of 15.3 V, estimated from the electron temperature. Trends of time averaged plasma parameters were also compared with the Hall thruster’s discharge voltage. Quadruple Langmuir probe measurements of a Hall thruster breathing mode have been presented.