| Research on the high power pulsed power switches with shorter delay time and higher switching precision has great significance for the developments of pulsed power technology in China.Two types of high voltage laser triggered series-connected vacuum gaps(LTSVG)for different fields are proposed in the thesis utilizing the advantages of laser triggered vacuum switch(LTVS),including the multi-gap LTVS and laser triggered multi-stage vacuum switch(LTMVS).Based on the theoretical analysis on closing process of LTVS and the improvements for its trigger performances,time-delay characteristics of double-gap LTVS and LTMVS are separately investigated in this paper.Trigger mechanisms and trigger performances of LTSVG can be revealed according to the results,benefiting to the research on high voltage LTSVG with better performances,and promoting the development of pulsed power technology in China.Different periods during the closing process of LTVS are theoretical studied at first.With analysis about the generation,development and diffusion processes of initial plasma in LTVS,influences different factors on the trigger delay time are discussed.Calculation formulas for the trigger delay time of LTVS are given.Based on above analysis,test platform for LTVS are built with detachable vacuum chamber.Trigger performances of LTVS are improved by optimizing its target configurations and electrode structures.Trigger delay time of LTVS is mainly affected by the melting and evaporation time of target materials,and the diffusion time of initial plasma.Under 30 m J laser energy and 12 k V operating voltage,the calculated trigger delay time of 4mm positive polarity LTVS is 28.1ns.And trigger delay time of negative polarity LTVS is 44.8ns.There are slightly differences between calculation results and experimental results.The LTVS with 90°conical target and proper target depth obtains better trigger performances.Besides,Trigger delay time of the developed 30 k V LTVS reaches 25±1ns.The designed optical fiber trigger system can transfer 16 m J laser energy,triggering the LTVS reliably.Then,closing delay time of the propoed double-gap LTVS(DLTVS)are investigated with adjusted detachable chamber.Combining analysis on the closing processes of DLTVS under different conditions,mechanisms of the dynamic charge transfers between gaps are discussed.Closing delay time of DLTVS with different parameters are studied later.And the differences of closing delay time between DLTVS and LTVS are compared.The results indicate that,the imbalanced developed plasma between gaps leads to the charge transfer process,affecting the closing performances of DLTVS.The DLTVS with 1: 1 laser split ratio and two positive gaps obtains shortest closing delay time.With the increase of laser energy,closing delay time of DLTVS gradually decreased.There are no evidently effects by increasing operating voltage.Under 90 m J laser energy,closing delay time of the DLTVS with two positive gaps can be controlled within 103±1.5ns,but still about 10 ns longer than LTVS.It’s suggested to uniformly distribute the parameters in multi-gap LTVS,benefiting to improving its closing performances.Besides,for the applications with changed voltage directions,the switch is recommended to be with positive and negative gaps in series to promise its reliability.Trigger performances of LTMVS are studied finally.With analysis on the trigger process of LTMVS,related influence factors on its trigger delay time are discussed.By equivalently simplifying test prototype,trigger delay time of double-gap LTMVS are compared.To reveal the influences of different factors on trigger performances,time-delay characteristics of laser trigger gap and the breakdown gap are separately studied.Trigger delay time of LTMVS mianly depends on the delay time of laser triggered gap and the first breakdown vacuum gap.Trigger delay time of LTMVS gradually reduces with the increase of laser energy,and exponentially declines with the rise of operating voltage.Steeper impulse voltage can be formed to breakdown gap by increasing of laser energy and operating voltage on laser triggered gap,accelerating the breakdown process of short vacuum gap.Under 30 m J laser energy and 35 k V operating voltage,trigger delay time of double-gap LTMVS with 4: 1 voltage ratio reaches 113±2.6ns.And delay time of the 0.8mm breakdown gap can be controlled within 74±3.7ns.It’s suggested to set the gap distances and gap amounts in LTMVS properly.Each gap in the switch should maintain higher operating voltage.Laser triggered gap ought to form higher voltage ratio to breakdown gap,promising the hold-off voltage and trigger performance of the switch.Based on theoretical analysis on closing process of LTVS and improvements for its trigger performances,time-delay characteristics of proposed two types of LTSVG are studied in the thesis.Combining the research results,design suggestions for multi-gap LTVS and LTMVS are given,providing research basis for the developments and application of high voltage,high power LTSVG with better performances. |
