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

Joined solutions of quasi-neutral collisional plasma (presheath) and space-charge collisionless sheath is obtained in a hydrodynamic approximation taking into account nonzero electric field at the sheath edge. Separate calculation of these two regions is performed and the procedure for obtaining smooth solution is formulated. The procedure is based on proper selection of boundary conditions which are the ion velocity and the electric field at the plasma-sheath interface. The dependencies of the ion velocity and electric field at the interface on the Debye length to the collision mean free path ratio are calculated.