Modeling of low-pressure microwave discharges in Ar, He, and O2: similarity laws for the maintenance field and mean power transfer

A kinetic study of low-pressure microwave discharges in Ar, He, and O₂ is carried out using electron-transport parameters and rate coefficients derived from solutions to the Boltzmann equation, together with the continuity and transport equations for the charged particles, taking into account stepwise-ionization processes. The Boltzmann equation is solved over a wide range of the applied frequency, ω/2π, but assuming that the angular frequency ω>τ _e^-1, with τ_e, denoting the characteristic time for electron-energy relaxation by collisions. The formulation provides discharge characteristics for the maintenance field and for mean absorbed power per electron in the three gases, which are shown to agree satisfactorily with experimental data obtained from surface-wave discharges. It is shown that such an agreement would not always be obtained without consideration of the role played by stepwise-ionization processes in sustaining the discharge