Energy loss in pulsed coaxial plasma guns

Abstract

The one-dimensional flow of a current-carry ing plasma, driven into neutral gas by its selfmagnetic field, is considered for the case where both the neutral gas and the current have arbitrary distributions in the direction of flow. The conservation laws are used to derive a simple expression for the amount of input power that goes into all forms of internal energy. It is shown that this power depends mainly on the rate at which the current sheet sweeps up neutral gas. In principle, internal energy can be converted into directed energy by expansion; however, it is argued that, in the coaxial plasma accelerators currently used in propulsion studies, most of the internal energy will be lost by excitation and subsequent radiation or ionization before expansion occurs.