Filamentary double layers

The properties of double layers produced in current filaments have been studied. The experiments were performed in a magnetized triple plasma device in which the diameter of the central plasma column could be varied. The scaling of the double layer potential drop Vdl with the parameter jd2, where j is the current density in the double layer and d is the double layer thickness, was determined for several values of the current filament radius R0. For relatively large values of R0, the one-dimensional (Langmuir) scaling was obeyed, Vdl∼(jd2)2/3. When R0 was decreased, a departure from the strictly one-dimensional scaling was observed, with Vdl becoming less and less dependent on the parameter jd2.