Transition from plasma to space-charge sheath near the electrode in electrical discharges

The transition between a quasi-neutral plasma (presheath) and a space charge sheath is considered and a model of patching between these two regions is proposed. In most cases the presheath and the sheath regions have very different scale lengths. Therefore separate calculation of these two regions is performed and a model that allows smooth patching procedure is formulated. It is shown that two solutions can be joined together if proper boundary conditions are formulated for the sheath problem, determined by ion velocity and electric field. The dependence of the ion velocity and the electric field at the space-charge sheath region edge on the Debye length to the collision mean free path ratio is considered.