Results of an experimental study of the properties of ion-beam modes found in a double plasma device containing a hemispherical separating screen

Abstract

Ion-beam modes have been generated in a double plasma device containing argon in which the driver and target plasmas were separated by a hemispherical screen biased negatively with respect to both plasmas. Making the driver plasma positive with respect to the target plasma resulted in the formation of an ion beam flowing from the driver plasma to the target plasma and causing the formation of a focal region in the target plasma. Both single pulses and pulse trains were excited in the target plasma by application of positive voltage pulses and/or sine waves to the hemispherical grid. Detection of these modes was accomplished using a positively biased spherical probe capable of axial and rotational movement. The wave amplitude and the phase velocity along the axis of the target plasma were measured over a distance of more than two hemispherical grid radii. Since no theoretical treatments have as yet been published for the hemispherical case, the measured values have been compared with theoretical values for a spherical separating screen.