Location of the Front of a Subthreshold Microwave Discharge and Some Specificities of Its Propagation

It is proposed to determine the propagation velocity of a self-sustained subthreshold microwave (SSM) discharge by measuring the beatings between the reflected radiation and the reference signal. It is shown that the velocity of the head part of the SSM discharge determined from the fundamental frequency harmonic of the beating signal coincides with the velocity of the front of UV discharge radiation. The proposed method allows one to measure the velocity of the head part of the discharge along the microwave beam path, variations in this velocity caused by changes in the microwave beam power, the reduction in the gas density along the beam path, and the time delay in the initiation of the burning wave in methane–air mixtures.