Generation of atmospheric pressure air diffuse discharge plasma in oxygen enriched working gas with floating electrode

In this work, a floating electrode is employed to generate a stable large-area diffuse discharge plasma under an open oxygen-rich environment. The discharge image and the optical emission spectra of the N₂(C-B), ${\mathrm{N}}_2^{+}$(B-X), N₂(B-A), and O(3p–3s, 777 nm) are measured to analyze the morphological and optical characteristics of the discharge. The effects of applied voltage, gas flow rate, and electrode gap on the reactive species, vibrational temperature and rotational temperature are investigated, and the discharge mode is discussed by simulating the electrostatic field before the breakdown. It is found that the changes of applied voltage and electrode gap causes the transition of the discharge modes among corona mode, diffuse discharge mode and spark mode. It is shown that the floating electrode can inhibit the transition from discharge to spark mode to a certain extent, which is conducive to maintaining the stability of discharge. As is vividly illustrated in this study, the increase of applied voltage or the decrease of electrode gap contributes to the generation of more active particles, such as N₂(C) and ${\mathrm{N}}_2^{+}$(B). Furthermore, the Joule heating effect becomes more evident with the increased applied voltage when the electrode gap is 15 and 20 mm. Moreover, as the applied voltage increases, the vibrational temperature increases at the electrode gap of 25 mm.