Optical investigations on a magneto-plasma-dynamic thruster

This paper describes the results of an optical investigation of a gas-fed, applied field Magneto-Plasma- Dynamic thruster. The investigation is performed to obtain a better knowledge of the basic phenomena which occur in the plasma of the MPD during the regime and to determine possible relations with the thruster performance. The radiation emitted by the plasma plume has been observed by utilizing an optical multi-channel analyzer (OMA) in the range of 300 - 900 nm. The optical detector of the OMA was placed outside the vacuum chamber and inside of it. The insertion of the detector into the plasma avoids the absorption of the radiation that occur between 300 nm and 500 nm. An optical probe containing the detector has been placed in different positions inside the plasma plume. By means of the Boltzmann plot obtained from the measured line intensities, the excitation temperature of several levels has been derived. The low level excitation temperature is 0.5 - 1 eV. The high level temperature ranges between 3 and 9 eV and is of the range of the electron temperature. The electron density ne has been estimated from the Ha and Hβ lines. ne is evaluated to be between 1018 m-3 and 1019 m-3. In order to see whether structures are present in the plasma, an imaging technique has been utilized. A fast shutter CCD camera has been placed outside the plasma plume. A plasma clot travelling with a velocity about ten times lower than the gas velocity has been observed during the discharge onset. © 2003 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.