Diocotron Instability in Plasmas and Gas Discharges

The wave interaction underlying the diocotron effect is re-examined and a physical model of the instability presented. A wave analysis is then given for circular, wall-enclosed charge layers with finite length in the axial direction. Circular layers are of particular interest, since they apply to various plasma, discharge, and electron device geometries. Their instability behavior is found to be similar in many respects to the behavior of linear charge sheets, described in earlier work by R. W. Gould. In contrast to linear sheets, however, circular layers are unstable only when their thickness is sufficiently small. This effect is associated with the inability of charge perturbations to have a wavelength which exceeds the layer circumference. Data are presented for the magnitude of growth in various configurations and for the critical layer width at which growth terminates.