Study of the microwave streamer evolution using a new semi-analytical model

A microwave (MW) plasma channel (filament, plasmoid, and plasma dipole) shows promise for its applications for off-body non-electrode modification of a gas flow (plasma aerodynamics) and in the plasma assisted combustion process. A full-scale study of the plasma channel evolution requires a self-consistent solution of Maxwell's equations, plasma chemical kinetics equations, and gasdynamics equations. An attempt is made to develop a simple electrodynamic (based on the solution of Maxwell's equations) "fast" model for studying the evolution of the plasma channel in conjunction with a fairly complete system of plasma chemical reactions. The model is based on a simplifying assumption about the shape of the channel, which converts a 3D problem into a 1D one. The results of numerical calculations in air within the pressure range P=20-150Torr are presented. An experimental study of plasmoid development was carried out to verify the predictions of the model. The calculated results agree well with all available experimental data within the pressure range P=20-150Torr. The proposed electrodynamic approach made it possible to reveal (i) the mechanism of self-organization during the development of a MW streamer and (ii) the reason for a sharp decrease in the velocity of its elongation, as well as to obtain relations connecting the main characteristics of the streamer (the amplitude of the electric field in the channel and on its heads, the velocity of ionization waves, and the characteristic scale of their fronts). The proposed model will be useful both for estimating the channel parameters and for deciphering the dynamics of radiation scattered by the plasma dipole. The development of such an approach will allow one to study the evolution of multiplasmoid structures of a high-pressure MW discharge.