INSTABILITIES IN MPD THRUSTER FLOWS - 1 - SPACE-CHARGE INSTABILITIES IN UNBOUNDED AND INHOMOGENEOUS PLASMAS

For a few years, the study of magnetoplasmadynamic instabilities has r eceived increased attention because they may explain the so-called 'on set' phenomena which limit the efficiency and, thus, the use of coaxia l plasma accelerators in space propulsion and other applications. A sy stematic investigation of instabilities in magnetoplasmadynamic flows was initiated at the Institut fur Raumfahrtsysteme in 1987. Among othe r instabilities, a particular one with the characteristics of the spac e charge instability was found. This instability had until then been k nown to occur only in finite gas discharge geometries. It will be show n in this paper that, in the presence of gradients of the flow variabl es, space charge instabilities can also appear in unbounded plasmas. T he conditions for their development and growth are determined and disc ussed.