| Solid-vacuum insulation structure is common in pulsed power devices, and is also a weak point of them. Drive by various application in pulsed power technology, there is a rapid development of large pulsed power devices, and also higher demand for insulation techniques has been raised. From1950s and1960s, the research on surface flashover in vacuum has been carried on the study of theory model, simulation method and advanced experiment techniques. The knowledge of physics mechanism of surface flashover is getting more and more clear, and different types of theories and models for surface breakdown have been established. Theories and factors influencing surface flashover were studied a lot. Based on existing theories, models and experiment data, ways to improve the insulation strength of materials was proved to be effective. Among efforts in seeking for high efficiency insulators and insulator design techniques, the High Gradient Insulator (HGI) is a very good invention, which was driven by the application in dielectric wall accelerator. It was fabricated and tested to be effective in improving electrical strength in the experiment. In order to decrease difficulties in fabricating techniques of these insulators and to broaden its use in different insulation structure, a novel type of insulator——High gradient surface micro-strip insulator (SMSI), which features a similar structure as HGI, is introduced; in this paper. The main content of this paper is about theory study of high gradient surface micro-strip insulator using the commonly accepted model of secondary electron emission avalanche (SEEA), and numerical simulation method and method for design of parameter of micro-strip.The SEEA model of surface flashover theory is described in this paper. And the physics process of three stages of flashover, based on this model, including primary electron emission, secondary emission and gas desorption from insulator surface is described in detail. On the basis of this, the study on mechanism of surface flashover of SMSI is carried out. Firstly the relationship of delay time of flashover and flashover electric strength is analyzed theoretically, and the influence of pulse shape on surface flashover of SMSI is analyzed, and the maximum gap of micro-strip is deduced theoretically; Secondly the electric field distribution of SMSI has been calculated using finite element method; the influence of micro-strip structure on processes in flashover and the interaction of micro-strip and electrons in the SEEA was analyzed, including the effect of micro-strip on holding up SEEA, influencing the secondary emission and surface charging, the capacitor effect of micro-strip and charge transferring from one metal strip to another, the feedback mechanism of micro-strip on electron emission from cathode triple junction, and equilibrium between electrons and micro-strip charging.In the next chapter, numerical simulation method on surface flashover of SMSI was studied. In this chapter, the physics model, program design method, and the core arithmetic adopted in the program was introduced. The numerical simulation program in this paper involved finite element method, Particle In Cell method, Monte Carlo method, and ideas of simulating the flashover process was proposed. The physics model of SMSI under finger shape electrodes was established, and the ways to deal with difficulties in calculation using simplified method using finite element method, PIC and MC method was discussed. It is possible to do the electro-magnetic calculation and particle kinetic calculation, and simulate the whole surface charging process.Lastly, the fundamental principles of parameter design was discussed, and the influence of micro-strip parameter on surface electric field and flashover performance was studied. |
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