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.