Space charge layers in a double plasma machine

Experimental and numerical studies on the behaviour of space charge layers (SPLs) and related sheath-like phenomena generated in a double plasma machine (DPM) are reported. A detailed evaluation of the performance of the multidipole source used in this device indicated that, under the conditions best suited for the investigation of these structures, the emitted electron species used to form the sheath structures could contain significant quantities of electrons with a temperature approximately twice that normally assumed for such plasma sources. It is also suggested that a trapped ion population on the low-potential side of the layer region could cause inflection-like distortions as observed in the sheath potential profiles reported here and in the literature. This hypothesis was investigated using a simple one-dimensional Vlasov - Poisson kinetic model and it was found that such anomalies could also be generated with the trapped ion population absent if a high-temperature electron population was present in the plasma on the high-potential side of the layers.