LANGMUIR PROBE DIAGNOSTICS AND SPECTROSCOPIC MEASUREMENTS IN THE POSTDISCHARGE OF A DINITROGEN METHANE MICROWAVE PLASMA

Measurements of electron temperature (T-e) and ion density (n(+)) are reported for mixtures of dinitrogen with methane in the afterglow of a high frequency discharge (2450 MHz). Methane is added upstream or downstream the discharge. Ion density is derived by means of the Su and Kiel theory (continuum theory based on Poisson's equation and continuity equations). Results are compared with values obtained by means of the theory of Sicha et al. (collisional theory). Both theories give results of the same order of magnitude in our experimental conditions. The influence of the location of the methane introduction, of the ratio of methane in the mixture and of the microwave power is studied. A decay of ion density is observed when methane is added to the plasma. Spectroscopic emission measurements of N-2(+) (first negative) and CN (violet system) show simultaneous ion density decrease and new chemical species formation.