## 4 Simulation Results and Discussion  
### Microscopic Process of Corona Discharge  
Under the given model's geometry and gas conditions, the microscopic process of particles' motion and reaction during gas discharge at the tip defect of a wire is obtained by simulation. When the conductor's radius is 5 mm, the curvature radius and the height of tip defect are 0.1 mm and 6 mm and the background pressure is 1013 hpa. The distribution diagram of the electric field near the tip defect at different moments is shown in Figure 8.  
From Figure 8a, it can be seen that when a positive voltage of 48.5 kV is applied to the wire and the tip, a strong electric field is first formed near the tip with the smallest curvature radius, and the field strength reaches 92.1 kV/cm within 1.2798 ns. In Figure 8b, after applying a positive voltage for 3.1131 ns, the electric field decreases in the area closest to the tip of the wire. In contrast, the area slightly farther away from the tip of the wire has a larger electric field [34]. The reason for the analysis is that at the initial moment, there are a large number of electrons distributed near the positive electrode. Under the strong electric field, the electrons move towards the positive electrode at high speed, which generates new ions and electrons through a series of collision reactions on the way. The mass of positive ions is much larger than that of electrons, but their moving speed is much slower than that of electrons, so when the electrons reach the anode, a large number of positive ions are still on the way, which weakens the electric field near the anode. As can be seen from Figure 8c, near the anode, there is an almost electrically neutral region, which shows an almost zero-value charge density and is called the plasma region [35]. The reason for the analysis is that there are a large number of positive ions gathered near the anode, and their density is very high; when the electrons approach this region, the recombination reaction occurs in front of it, and the attachment reaction occurs inside it to  
Figure 8: Distribution of electric field (kV/cm). (**a**) 1.2798 ns; (**b**) 3.1131 ns; (**c**) 6.2033 ns; (**d**) 15.992 ns. produce more negative ions. In the region where a large number of positive and negative ions are concentrated, it is easy to form plasma. With the continuous development of the discharge, a small number of electrons continue to converge to the plasma region, which is extended. As shown in Figure 8d, the length of plasma is obviously longer, and its distribution in width is relatively uniform, and it is extending to the cathode at a faster speed. Above, Figure 8 shows the process of corona initiation and discharge development [34; 35]. By simulation, the distribution diagram of electron density near the tip at different moments is obtained, as shown in Figure 9.  
From the analysis of Figure 9, it is shown that after 5.0944 ns, electrons appear in the region slightly farther away from the positive electrode, and with the development of time, the region where electrons are distributed becomes larger and larger, and the place with the highest electron density always appears in the streamer head farthest from the positive electrode. The reason for this phenomenon is that the photoionization effect always occurs in the high-electric-field-strength area of the streamer head; further, new electrons are continuously generated through collision ionization, making the electron density of the streamer head the largest, about 1 \(\times\) 10\({}^{20}\) m\({}^{-3}\). In addition to the above density distribution of electrons, another 12 particles in the reaction group and their microscopic density distribution and variation can also be obtained by the hybrid numerical model. As shown in Figures 10 and 11, during the development of discharge, the density of N\({}_{2}\) decreases continuously due to collision and ionization reactions; meanwhile, the density of the newly reaction-generated particle N\({}_{2}\)\({}^{+}\) increases continuously.