氮气火花开关击穿机制的理论和数值研究

三电极气体火花开关带有触发极,相比两电极开关,其开关导通的可控性较高,工作电压较低且抖动小,所以气体火花开关中三电极开关的应用较为广泛.本文针对大气压氮气环境下的两电极开关和三电极开关的击穿机制进行了理论与数值模拟研究.通过理论和数值计算发现,对于平板-平板的两电极开关来说,低电压下(小于6.3 kV)无法产生流注击穿,高电压下(大于6.3 kV)会先形成由阴极到阳极的负流注,然后再形成由阳极向阴极的正流注.而在三电极开关的击穿过程中,首先会在触发极和绝缘体之间发生击穿,然后这个通道不断向阴阳极扩展,最终形成阴阳极之间的电弧通道.在本文的计算工况下,如果需要阴极-触发极、阳极-触发极同时击穿的话,其阴极-触发极之间的外加电压需要大于1.18 kV,而阳极-触发极之间的外加电压需要大于3 kV.当考虑触发极的场致发射后,该击穿阈值可以显著降低.

Theoretical and numerical study on breakdown mechanism of nitrogen spark switch

Compared with the two-electrode gas spark switch,the three-electrode gas spark switch has high controllability,low working voltage and small jitter,so the three-electrode gas spark switch is widely used in pulse power technology.The discharge of gas spark switch is high pressure gas discharge,which is characterized by high electron collision frequency(1012 Hz),small mean free path(10–6 m),short breakdown time(10–9 s),and complex physical process(including the secondary electron emission,the generation of seed electrons,the space charge effect and various collision processes between electrons and nitrogen molecules,etc).At present,it is difficult to quantitatively describe the breakdown process of the three-electrode gas switch,and the detailed theoretical research is lacking.Therefore,the breakdown mechanism of atmospheric pressure nitrogen spark switch,including two-electrode and three-electrode,is studied theoretically and numerically in this paper.The purpose of this study is to compare the simulation results of the two different gas spark switches,and obtain the characteristics of stream breakdown in different gas spark switches.Firstly,the numerical simulation and theoretical analysis of two-electrode gas spark switch are carried out.According to theoretical and numerical calculation,it can be found that for the plate-plate two-electrode switch,the stream breakdown cannot be generated under low voltage(less than 6.3 kV),while under high voltage(more than 6.3 kV),first the anodedirected streamer is formed,and then the cathode-directed streamer is created.In addition,the simulation results show that the plasma generated by the trigger can effectively reduce the breakdown voltage.Finally,the three-electrode gas spark switch is studied theoretically and numerically.It can be seen that in the breakdown process of the three-electrode gas spark switch,the breakdown first occurs between the trigger and the insulator,and then this plasma channel expands to the anode and cathode,finally forming the arc channel between the anode and the cathode.Under the calculation conditions in this paper,if the cathode-trigger and the anode-trigger are required to break down simultaneously,the applied voltage between the cathode-trigger should be greater than 1.18 kV,while the applied voltage between the anode-trigger should be greater than 3 KV.When the field emission of the trigger is considered,the breakdown threshold can be significantly reduced.