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 V_dl 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, V_dl∼(jd²)^2/3. When R₀ was decreased, a departure from the strictly one-dimensional scaling was observed, with V_dl becoming less and less dependent on the parameter jd².