SELF-CONSISTENT KINETIC-MODEL OF A SURFACE-WAVE-SUSTAINED DISCHARGE IN NITROGEN

A self-consistent kinetic model based on a set of coupled equations co nsisting of the local electron Boltzmann equation and the rate balance equations for the most important excited species (vibrationally and e lectronically excited molecular states) and charged particles in a nit rogen discharge has been developed. The system under analysis is a pla sma column produced by a travelling, azimuthally symmetric surface wav e. Electron collisions of first and second kind with nitrogen molecule s 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 discharg e steady-state operation is obtained from the balance between the tota l rate of ionization (including associative, direct and step-wise ioni zation) and the total rate of electronic losses (due to diffusion to t he wall and bulk recombination). The model determines, as a function o f the discharge operating parameters (pressure, tube radius, wave freq uency, degree of ionization), the electron energy distribution, the po pulations of the vibrational levels of the electronic ground state and the most important electronic states N-2(A (3) Sigma(u)(+), a' (1) Si gma(u)(-), B (3) Pi(g), a (1) Pi(g), C (3) Pi(u)) as well as the conce ntrations of N-2(+) and N-4(+) ions, consistently with the discharge m aintaining electric field. Theoretical results for the electron energy distribution function and some of its moments are compared with exper imental ones obtained in a low-pressure surface-wave-sustained dischar ge at a wave frequency of 500 MHz.