Theoretical study of the role of ultraviolet radiation of the non-equilibrium plasma in the dynamics of the microwave discharge in molecular nitrogen

Abstract

A self-consistent plasmachemical model describing the dynamics of the non-equilibrium microwave discharge in molecular nitrogen with consideration for kinetic, photochemical and electrodynamic phenomena is proposed. The photochemical block of the model accounts for the processes of photoexcitation and photoionization of nitrogen molecules in the ground and excited electronic states. Radiative emittance of the discharge plasma is conditioned by the processes of photorecombination of electrons and positive ions as well as by the processes of spontaneous radiation of electronically excited molecules. Solution of radiation transfer equations and calculation of photochemical constants were made with allowance for the vibrational-rotational structure of the corresponding radiative transitions. The calculations performed have shown that the velocities of the ionization front propagation in the microwave discharge that were observed experimentally may be explained without invoking considerations concerning the existence of easily ionizable admixtures in nitrogen. The phenomenon of electron generation in the photohalo region of the discharge is mainly conditioned by the processes of stepwise photoionization of nitrogen molecules. The mechanisms leading to the development of kinetic instabilities in the discharge region are analysed, and a satisfactory agreement between calculation and experimental results is noted.