## 1 Introduction
At present, there has been extensive discussion and simulation studies on the microscopic processes and discharge mechanisms of coronas, based on plasma chemical reactions. The models used in the simulations can be roughly divided into the global model and the fluid model. The former considers as many chemical reactions as possible to simulate an accurate corona discharge process [15; 16; 17; 18; 19], whereas the latter only uses a small number of important chemical reactions to investigate the temporal and spatial evolution of the corona discharge [20; 21; 22; 23; 24; 25; 26]. In contrast, the latter model is considerably less complex. For its application, as in reference [20; 21], a numerical model based on plasma chemistry and hydrodynamics, which takes into account 35 collision reactions between 12 particles in dry air, was proposed. Using this hybrid model, electric field distribution, electron temperature distribution, and space charge distribution in the process of DC positive corona discharge were studied. The results obtained can help in understanding air discharge microscopically. Indeed, the macroscopic and microscopic characteristics of corona discharge are always inextricably linked. In [22], a numerical simulation was carried out to obtain voltage-current characteristics of gas discharge, which corresponds to the entire discharge evolution from normal glow discharge to arc discharge. Therefore, according to different discharge stages, voltage-current characteristics can be segmented to obtain the results of plasma parameters for each segment. Furthermore, in reference [23], a hybrid model for investigating the negative corona discharge in an air gap was presented. Researchers analyzed in detail variations in corona discharge current as well as the distribution morphology of particles and the reaction rates of plasma chemistry at certain typical moments. Results indicate that the effects of various chemical reactions vary at different discharge stages, which correspondingly affect the number density changes of particles. To summarize, the studies mentioned above reveal that current simulations of gas discharge mainly focus on the corona discharge of rod-plate electrodes or needle-plate electrodes. Moreover, there are many studies on the microscopic plasma chemistry of coronas, but there are few studies on corona discharge characteristics. In response to existing problems, in this study, the tip structure of a DC conductor in a two-dimensional plane was established and a hybrid numerical model based on fluid-chemical reactions was used to simulate the discharge process of a defective conductor. During positive corona discharge, the process of the motion and reaction of electrons and heavy particles was studied, and the variation of the characteristic parameters such as corona voltage and discharge current under different defect states and pressure conditions were analyzed. Additionally, relevant experiments were carried out to verify the rationality of the model. In the experimentation, a cavity with a corona cage was designed and built, and the obtained discharge current and corona inception voltage were compared with the results obtained in simulation.