Hot Flow Pressure Map of a Vacuum Facility as a Function of Flow Rate to Study Facility Effects*†

A neutral background pressure map of the Large Vacuum Test Facility (LVTF) at the University of Michigan is presented. The LVTF was mapped at hot anode (i.e., discharge on) flow rates of 5.25 and 10.46 mg/s, corresponding to P5 Hall thruster operating conditions of 1.5 and 3.0 kW. The chamber pressure was mapped at nominal xenon pumping speeds of 140,000 and 240,000 l/s, corresponding to base pressures of 1.3x10 Torr and 7.3x10 Torr, respectively. The pressure map was performed with a rake consisting of five calibrated Bayard-Alpert (BA) hot-cathode ionization gauges. Analysis of axial pressure profiles on the LVTF’s centerline shows that the plume pressure decreases from a maximum at the thruster exit plane down to the facility background pressure at approximately 2 m downstream of the exit plane. In addition, a neutral gas background pressure map of Vacuum Facility 12 (VF-12) at the NASA Glenn Research Center is presented. VF-12 was mapped at a series of cold anode flow rates corresponding to P5 Hall thruster operating conditions of 1.5, 3.0 and 9.0 kW. The chamber pressure was mapped at a nominal xenon pumping speed of 282,000 l/s with a rake consisting of the same five BA hot-cathode ionization gauges used in the LVTF. The cold flow pressure in VF-12 rapidly decreases out to approximately 2 m downstream of the thruster exit plane. From this point, the pressure slowly, but continually drops as the cryosurfaces are approached. Cryopump location affects the neutral density gradients within a vacuum facility and should be carefully considered when analyzing plume and performance data or designing a new Hall thruster facility. The hot flow neutral density profiles of each facility will be used to help correct performance and plume measurements for facility effects.