Mechanism of a nitrogen abnormal glow discharge. Computation and measurements of the spatial light distribution

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Abstract
In order to understand better the mechanisms of an abnormal glow discharge in nitrogen, the results of spectroscopic measurements have been compared to those of Monte Carlo simulation. Measurements were performed on the space distribution of the 1 S- and 2 S+ bands of the nitrogen molecule. With a model which does not take into account any current dependent alteration produced within the gas by the discharge, large differences appear between experiment and modelling. An improved model has been solved based on additional measurements of the discharge in its build-up phase and discharge change due to cathode cooling. Evidence is obtained that the local change in the distribution of the neutral molecules density induced by the variations of the gas temperature seems to be the most important factor explaining the difference between computed and experimental results for the space distribution of the emitted light. Investigation is required of the angular scattering cross section associated with collisions between electrons and vibrationally excited nitrogen, because of production of a high concentration of vibrational species within the discharge. Also, the density of nitrogen in the metastable A3 Sigma u+ level seems to give a non-negligible contribution to the creation of nitrogen in the C3 Pi u state. In any case, the gas modification induced by the discharge must be taken into account in modelling the abnormal glow discharge.