Three modes in the array of surface microdischarge in atmospheric pressure He+N2 mixture

Summary form only given. As an atmospheric pressure cold plasma source capable of producing large-scale and macro-uniform plasma, the surface microdischarge (SMD) has attracted many researchers´ interests. Despite of its widespread usage in medicine, aerodynamic control, and environmental remediation, it remains unknown whether SMD possess different discharge modes in the gas mixture of helium and nitrogen. The discharge process is a function of nitrogen concentration. In this study, the spatial and temporal evolution of the discharge in different gas mixture are investigated by an intensified charge coupled device (ICCD) camera and an optical emission Spectrometer (OES). The device configuration and experimental setup of SMD have been reported in detail in our previous work¹.With increasing the impurity of nitrogen, the plasma surface confined by one hexagon-shaped rim electrode is seen to evolve from a glow discharge to self-organized pattern discharge and filamentary discharge. In the gas mixture of He+N2 (0.2%), it has all the specific structure of a glow discharge with Aston dark space, negative glow, Faraday dark space and positive column in the discharge areas. In the negative cycle of the glow discharge, the plasma is ignited near the middle of the side electrode and moves away from the electrode to the center of each hexagon. It is also important that the high energy electrons are seen to distribute in the front of moving plasma and contribute to this cathode directed movement of plasma. In contrast, the self-organized pattern discharge is observed in the N2 impurity of 2%. The pattern discharge is a result of globally adaptive response to the drop of the electron density. Two kinds of pattern switch each other in each half cycle of the discharge. Additionally, the plasma generates randomly in the filamentary discharge, when the impurity of N2 rises to 20%. There is no obvious emission intensity at 709nm of helium excited state which can indica- e the high temperature electrons in He+N2 (20%). Therefore, the discharge modes affect the electrons energy and as such the reaction chemistry which influences the density of reactive species and intensity of UV radiation in the discharge.