Plasma Boundaries

Abstract

A plasma separates itself from metallic or dielectric surfaces by forming a boundary layer, which appears darker than the bulk plasma itself. This is a first hint that the boundary layer is depleted of electrons that are needed to excite the neutral atoms producing the glow of an electric discharge. It was Langmuir who identified these dark spaces as regions that are not electrically neutral but are governed by a net (positive) space charge. The particle motion is determined by physical mechanisms that are different from those discussed for the quasineutral part of the plasma. The interaction of an ion with the electric field from the space charge of all the other ions is a new type of many-body interaction that is characteristic for the collective behavior of a plasma.