Spectroscopic characterization of nitrogen plasma generated by waveguide-supplied coaxial-line-based nozzleless microwave source

Abstract

In this paper, results of spectroscopic study of microwave (2.45 GHz) plasma at atmospheric pressure and high flow rate are presented. The plasma is generated by waveguide-supplied coaxial-line-based microwave plasma source (MPS). Pure nitrogen was used as working gas. An additional nitrogen flow rate of 50 l/min was introduced to the plasma by four gas ducts which formed a swirl flow inside the quartz tube. The swirl concentrated near the quartz cylinder wall, stabilized plasma generation and protects the quartz tube wall from overheating. Working gas flow rate and microwave absorbed power varied from 50 up to 200 l/min and from 600 up to 5500 W, respectively. The emission spectra in the range of 300 – 600 nm were recorded. The rotational and vibrational temperatures of N2+ ions and N2 molecules, as well as the rotational temperature of OH radicals were determined by comparing the measured and simulated spectra. The plasma gas temperature inferred from rotational temperature of heavy species ranged 4000 to 6200 K. It depended on location in plasma, microwave absorbed power and working gas flow rate. The MPS can be used in various gas processing applications.