Consistent analysis of the boundary layer of a Saha plasma

The non-equilibrium boundary layer of a Saha plasma contacting material walls or electrodes is analysed in the parameter regime lambda (D) less than or equal to lambda (CX) less than or equal to lambda (i), where lambda (D) is the Debye length, lambda (CX) is the mean free path for charge exchange collisions and lambda (i) is the ionization length. According to this scaling, the boundary layer is split up into the separate model zones of: (i) a space-charge zone (scale lambda (D)); (ii) a Knudsen layer (scale lambda (CX)); (iii) a transition layer (scale lambda (i)). The collision dominated transition layer is analysed in the mobility-diffusion approximation. The Knudsen layer, which is characterized by strong inhomogeneities and by strong deviations from an equilibrium distribution, is treated kinetically. The model zones are related to each other by a consistent matching procedure. Handy formulae for overall quantities are supplied for convenient applications.