Simple thrust formula for an MPD thruster with applied-magnetic field from magnetic stress tensor

Abstract

It has been previously shown that the application of an axial magnetic field to an MPD thruster increases the thrust and focuses the plasma jet. The goal of this paper is to obtain a simple and ready-to-use theory to predict the thrust generated by an applied-field MPD. To derive a simple thrust formula some assumptions have been made: the applied field is assumed to be purely axial inside the thruster and the total current, plasma temperature, mass flow rate and axial velocity at the exit section of anode to be not sensibly influenced by the application of the magnetic field. Using the magnetic stress tensor the forces acting on the plasma inside the thruster can be derived. Assuming that the detachment from the magnetic nozzle outside the MPD happens when the charged particle motions violate the adiabatic condition the thrust expression can be finally derived. Comparison with experimental data confirms these hypotheses and gives good agreement with theory.

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