MAGNETO-PLASMA-DYNAMIC THRUSTERS FOR SPACE APPLICATIONS

The paper describes the first results of an experimental investigation on the critical regimes of a gas-fed, applied field Magneto-Plasma-Dynamic thruster (also said Hybrid Plasma Thruster, HPT). A hollow cathode with a 20 mm diameter is placed in the center of a cylinder with an inner diameter of 200 mm, which acts as anode. Eight straps divide the region inside the cylinder into a central chamber and a peripheral chamber. The thruster is powered by a pulse with an electrical current up to 8 kA for 2.5 ms. Tests were performed using argon with a mass flow rate of 660 mg/s, both with and without an externally applied magnetic field. Values of the field on the thruster axis were of 40 and 80 mT. Time and space behavior of electron temperature, density and floating potential have been measured by means of a system of 7 aligned electrical probes, inserted into the thruster plume. The balanced triple probe configuration has been utilized. It is shown that the external magnetic field flattens the density profile and increases the fluctuation levels of electron temperature and density. The radiation emitted by the discharge plume, has been observed by means of an optical multi-channel analyzer. The observations refers to a time interval of 0.5 ms. In the spectrum, lines of neutral argon and of singly ionized argoh ions, are present. The lines of the metals of the electrodes are not observed. The intensity of the ion lines increases both with the enhancement of the applied voltage of the pulse and with the use of the external magnetic field. The average value of the electron temperature derived from the line intensity, is in accordance with the average value measured by the probe method.