The dielectric barrier discharge (DBD) is one of the main ways for generating non-equilibrium plasmas, which is suitable for various industrial applications. Reactive species play a key role in DBD plasma treatment process, and adding a certain amount of O to the carrier gas may promote the yielding of a high concentration of reactive species. For better control of the DBD treatment processes, it is importance to study on the influence of O contents on the properties of DBD. In this paper, the influences of O addition on discharge characteristics of DBD in Ar are studied by electrical and optical diagnostics. The voltage current waveforms, light-emission pictures and emission spectroscopy are measured, and then the discharge parameters such as discharge power, transported charge, electron excitation temperature as well as vibrational temperature and rotational temperature are calculated to study their changing tendencies with water vapor content. Results show that with the increase of the water vapor content, the lighting emission intensity becomes weak and the discharge filaments become more and more dense, the uniformity of discharge improves; the discharge power and transported charge decreases, but the rotational temperature and vibrational temperature increases. The intensity of the main active particles such as O and OH reaches their maximum value at O content of 0.3%, and it has higher activity at this O content.
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