Dynamic characteristics of discharge particles are described within the framework of a two-dimensional photoionization-hydrodynamic numerical model for the discharge process of SF6-N2-CO2gas mixtures at atmospheric pressure,under a uniform DC applied field.The finite difference–flux corrected transport(FD-FCT)algorithm is used in the numerical implementation for improving the accuracy and efficiency.Then the tempo-spatial distributions of the gap–space electric field and electron velocity are calculated from the microscopic mechanism,and the dynamic behaviors of charged particles are obtained in detail.Meanwhile,the tempo–spatial critical point of the avalanche-to-streamer in this model is discovered,and several microscopic parameters are also investigated.The results showed that the entire gap discharge process can be divided into two phases of avalanche and streamer according to Raether-Meek criterion;the electron density within the discharge channel is lower compared to that of positive and negative ions;space charge effect is a dominant factor for the distortion of spatial electric field,making the discharge channel expand toward both electrodes faster;photoionization provides seed electrons for a secondary electron avalanche,promoting the formation and development speed of the streamer.
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