Partially ionized plasmas corresponding to different ionization degrees are derived and connected one with each other by the diffusion approximation methodology. These plasmas are the following electrical discharges: a thermal arc discharge, glow discharges in local thermodynamic equilibrium -LTEand in non-LTE, and a non-LTE glow discharge interacting with an electron beam (or flow).

This is a tutorial article. An introductory discussion of direct current gas discharges is presented. Beginning with basic ideas from kinetic theory, gas discharge plasmas are described in terms of phenomena observed in the laboratory. Various models are introduced to account for electrical breakdown, plasma boundaries and the longitudinal and transverse structure of discharges.