On the self-consistent modeling of a traveling wave sustained nitrogen discharge

Abstract

We present a self-consistent formulation to study low-pressure traveling wave (azimuthally symmetric surface transverse magnetic mode) driven discharges in nitrogen. The theoretical model is based on a self-consistent treatment of the electron and heavy particle kinetics, wave electrodynamics, gas thermal balance, and plasma–wall interactions. The solution provides the axial variation (as a result of nonlinear wave power dissipation along the wave path) of all discharge quantities and properties of interest, such as the electron energy distribution function and its moments, population densities of all relevant excited and charged species [N2(X 1Σg+,ν),N2(A 3Σu+,a′ 1Σu−,B 3Πg,C 3Πu,a 1Πg,w 1Δu), N2+, N4+, e], gas temperature, degree of dissociation [N(4S)]/N, mean absorbed power per electron, and wave attenuation. A detailed analysis of the energy exchange channels among the degrees of freedom of the heavy particles is presented. Particular attention is paid to the axial variation of the gas and wall temperatures, which affect in a complex way the discharge operation. For the high electron densities and reduced electric fields achieved at 2.45 GHz, it is shown that the contribution of exothermic reactions involving excited molecules in metastable states to the total gas heating can be significant. The role of the triplet N2(A 3Σu+) metastable state as an energy “reservoir” that pumps translational modes of gas particles is pointed out. A strong correlation between the degree of dissociation, the concentration of metastable N2(A 3Σu+), N(2D,2P) particles, and surface kinetics is shown to exist. Spatially resolved measurements of the gas and wall temperatures, electron density, and wave propagation characteristics provide a validation of the model’s predictions.