Diagnostics of Atmospheric Plasma Jets of Helium and Argon Barrier Discharge in a Cylindrical Microwave Cavity Resonator

Abstract

Introduction. Technologies related to the use of low-temperature atmospheric plasmas are developing at a rapid pace. Creation of new low-temperature plasma sources for specific applications requires monitoring of dynamic processes in such discharges with a high time resolution. Electron concentration is one the most important plasma characteristics, which can be very low for a low-temperature atmospheric pressure plasma. However, the methods currently available for diagnostics of gas-discharge plasmas are either characterized by insufficient sensitivity or unable to monitor dynamic processes in non-stationary discharges. In this regard, the development of new diagnostic approaches to low-temperature atmospheric plasma seems to be a relevant research direction.Aim. To develop a diagnostic method for an atmospheric plasma with a low gas temperature and a low electron concentration in a cylindrical microwave resonator.Materials and methods. The proposed diagnostic method is based on the well-known principle of measuring the frequency shift and the Q-factor of the eigenmodes of the microwave resonator, inside which the plasma under study is located.Results. Measurements of the atmospheric barrier discharge plasma jets in a helium and argon stream in a cylindrical microwave resonator were performed. The proposed geometry made it possible to significantly increase the sensitivity of measurements. It became possible to exclude the effect of polarization degeneracy in a round cylindrical resonator. The developed system was also tested on test objects with a known value of permittivity.Conclusion. A method for microwave diagnostics of stationary and non-stationary cold atmospheric plasma jets in a cylindrical resonator, inside which transmitting and receiving antennas are installed, as well as an orthogonal thin conductor preventing the excitation of undesirable modes, was developed.

Keywords

• microwave cavity resonator
• plasma jet
• barrier discharge
• electron collision frequency
• q-factor
• transverse electric (te) modes