SPACE-CHARGE LAYERS IN A DOUBLE PLASMA MACHINE

Experimental and numerical studies on the behaviour of space charge la yers (SPLs) and related sheath-like phenomena generated in a double pl asma machine (DPM) are reported, A detailed evaluation of the performa nce of the multidipole source used in this device indicated that, unde r the conditions best suited for the investigation of these structures , the emitted electron species used to form the sheath structures coul d contain significant quantities of electrons with a temperature appro ximately twice that normally assumed for such plasma sources. It is al so suggested that a trapped ion population on the low-potential side o f 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 Vlaso v-Poisson kinetic model and it was found that such anomalies could als o be generated with the trapped ion population absent if a high-temper ature electron population was present in the plasma on the high-potent ial side of the layers.