Self-field MPD thruster with atomic and molecular propellants

Abstract

This study is devoted to the design, the operational characteristics and optimization of a self-field magnetoplasmadynamic (MPD) arc in view of its applications as a thruster and as a plasma source for recombination lasers. Its principal characteristics, i.e. its terminal voltageVE1and the exhaust speedueas functions of the square of the discharge currentI divided by the mass flow ratem are determined experimentally for atomic propellants. On the basis of measured diagramsVE1versus (I2/m) our discharge configuration is found to be well comparable to those applied by other laboratories. However, in order to further increase the specific impulse, these devices should make use of propellants of low molecular weight. Therefore, we also show that these thrusters can be operated in a quasi-steady mode for atomic as well as for molecular propellants, e.g. H2, N2, O2. Existing theories and interpretations of observations on atomic propellants are reviewed and, if possible, extended to explain the experimental results obtained with molecular propellants. In the framework of these extended theories the high-power limit of a stable operation is well understood.