Fred Valk will defend his doctoral thesis titled "Nitrogen emission spectrum as a measure of electric field strength in low-temperature gas discharges" on 25. January 2017 at 14.15 at W. Ostwaldi 1, room B103.
Märt Aints, Institute of Physics, University of Tartu
Peeter Paris, Institute of Physics, University of Tartu
dr Ronny Brandenburg, Leibniz Institute for Plasma Sciences and Technology, Germany
Optical emission spectrum of molecular nitrogen is an important tool for investigating electric discharge phenomena in ambient atmosphere, and it is also often used for diagnostics of low-temperature gas discharge plasmas. The study is focused on a development of a spectroscopic method for determination of electric field strength in low-temperature gas discharge plasmas in atmospheric air. Measuring electric field strength by using probes or other contact methods is possible only in limited cases. In particular, the intensity ratio of spectral bands with bandhead wavelengths at 391.4 nm and 337.1 nm (or 394.3 nm), corresponding to FNS 0–0 and SPS 0–0 (or 2–5) transitions, is often used for electric field strength determination in nitrogen-containing gas discharges. The excitation threshold energies for the upper states of these bands differ considerably and, therefore, the ratio of emission intensities is sensitive to comparatively small changes in the mean electron energy. This dependence can be used for electric field strength estimation in low-temperature gas discharges, if the excitation of nitrogen molecules from the ground state by electron impact is the dominant process. Despite a rather wide use of the above-mentioned intensity ratio for estimating electric field strength in gas discharge plasmas, the relation between the intensity ratio, electric field strength and gas number density was estimated by earlier authors only theoretically. Moreover, theoretical intensity ratios of different authors differ considerably. According to our knowledge, no experimental verification of these theoretical curves had yet been made. The aim of the present work was to experimentally determine the relationship between radiation intensity and electric field strength in air discharges for the above-mentioned transitions, and clear up physical processes that are significant for development of this relationship.