Self-consistent kinetic model of a surface-wave-sustained discharge in nitrogen

A self-consistent kinetic model based on a set of coupled equations consisting of the local electron Boltzmann equation and the rate balance equations for the most important excited species (vibrationally and electronically excited molecular states) and charged particles in a nitrogen discharge has been developed. The system under analysis is a plasma column produced by a travelling, azimuthally symmetric surface wave. Electron collisions of first and second kind with nitrogen molecules and electron-electron collisions are accounted for in the Boltzmann equation. Therefore, this equation is coupled to the set of equations for electronic and vibrational populations through both inelastic and superelastic collisions. The field strength necessary for the discharge steady-state operation is obtained from the balance between the total rate of ionization (including associative, direct and step-wise ionization) and the total rate of electronic losses (due to diffusion to the wall and bulk recombination). The model determines, as a function of the discharge operating parameters (pressure, tube radius, wave frequency, degree of ionization), the electron energy distribution, the populations of the vibrational levels of the electronic ground state and the most important electronic states N-2(A (3) Sigma(u)(+), a' (1) Sigma(u)(-), B (3) Pi(g), a (1) Pi(g), C (3) Pi(u)) as well as the concentrations of N-2(+) and N-4(+) ions, consistently with the discharge maintaining electric field. Theoretical results for the electron energy distribution function and some of its moments are compared with experimental ones obtained in a low-pressure surface-wave-sustained discharge at a wave frequency of 500 MHz.