RESULTS OF AN EXPERIMENTAL-STUDY OF THE PROPERTIES OF ION-BEAM MODES FOUND IN A DOUBLE PLASMA-DEVICE CONTAINING A HEMISPHERICAL SEPARATING SCREEN

Ion-beam modes have been generated in a double plasma device containin g argon in which the driver and target plasmas were separated by a hem ispherical screen biased negatively with respect to both plasmas. Maki ng the driver plasma positive with respect to the target plasma result ed in the formation of an ion beam flowing from the driver plasma to t he target plasma and causing the formation of a focal region in the ta rget plasma. Both single pulses and pulse trains were excited in the t arget plasma by application of positive voltage pulses and/or sine wav es to the hemispherical grid. Detection of these modes was accomplishe d using a positively biased spherical probe capable of axial and rotat ional movement. The wave amplitude and the phase velocity along the ax is 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 b een compared with theoretical values for a spherical separating screen .