Triple Langmuir probe measurements in the plume of a pulsed plasma thruster

An experimental apparatus using triple langmuir probes was designed to obta in electron temperature and density in the plume of a laboratory-model puls ed plasma thruster (PPT) operating at discharge energy levels of 5, 20, and 40 J. Electron temperature and density were obtained on two planes paralle l and perpendicular to the thruster electrodes passing through the thruster 's centerline, Measurements were obtained fur radial distances of 6, 10, 12 , 14, 16, 18, and 20 cm and for polar angles of 10, 20, 30, and 45 deg with respect to the center of the Teflon (R) propellant face. Plume properties show large angular variation on the perpendicular to the electrodes plane h ut small variation on the parallel plane confirming the asymmetry of the PP T plume, Electron density and temperature decrease with increasing radial d istance from the Teflon surface. The average maximum temperature is between 2 and 4 eV for all discharge energy levels considered. The average maximum electron density is 1.6 x 10(20), 1.6 x 10(21), and 1.8 x 10(21) m(-3) for the 5-, 20-, and 40-J discharge, The time average electron density increas es with increasing discharge energy and is in the range between 10(19) and 2 x 10(20) m(-3) for 5 J, 3 x 10(19) and 10(21) m(-3) for 20 J, and 5 x 10( 19) and 1,4 x 10(21) m(-3) for 40 J.