The Possibility of Measuring Electron Density of Plasma at Atmospheric Pressure by a Microwave Cavity Resonance Spectroscopy

The electron density of the nonstationary atmospheric pressure discharge in a helium flow is estimated using microwave cavity resonance spectroscopy. For this, a measurement scheme was developed based on a spectrum analyzer and a cylindrical resonator with the first three transverse electric (TE) eigenmodes in the range of 1-1.5 GHz. The main working mode was the TE TE112 mode, which made it possible to place the high-frequency measuring and discharge power supply circuits in the most optimal geometry. By measuring the eigenfrequency shift of this mode and its Q factor, gas-discharge plasma parameters were calculated using the well-known perturbation theory. The results are in good agreement with the known data from the literature. This method was additionally tested on a glass rod and a thin low-pressure gas discharge tube.