Breakdown Characteristics Of Gas Switch And Its Influence On The Output Parameters Of Fast Linear Transformer Driver

Fast linear transformer driver (FLTD) is a developing technology for constructing high current high voltage pulse generator. The main feature of FLTD is inductively adding the relatively low voltage straight out of the capacitors. Its output pulse can be directly applied to the load without any pulse compressing and forming unit. Also, FLTD can be connected conveniently in series or parallel with different output parameters. Therefore, FLTD technology makes pulsed power devices more compact and less expensive to produce one hundred nanosecond pulse with high efficiency of energy transformation. It has wide application prospect in the fields of flash photography, high power microwave, excimer laser, Z-pinch and future inertial fusion energy, etc. As one of the critical elements, huge amounts of gas switches directly influence the output parameters, the stability and reliability of FLTD. In recent few years, gas switch and its breakdown characteristics are becoming focus and hot issues. As a result, the studies on the breakdown characteristics of multi gap gas switch and its influence on the single module FLTD and multi modules FLTD in series are important and urgent for the development of FLTD technology both in theory and application.In this dissertation, a gas switch with six gaps in series has been designed and improved for FLTD. A research platform was established for the breakdown characteristics of gas switch, which mainly included the basic discharging loop similar to a single brick of FLTD that consisted of six-gap gas switch, capacitors, load resistor and strip lines. Rogowski coil and resistance voltage divider were also developed for monitoring the pulse current and load voltage, respectively.The working ratio with different charge voltage and gas pressure were calculated according to the self breakdown voltage curve derived from the self break experiment data of six-gap gas switch. A new trigger access method with inductance isolation was proposed in this dissertation. The comparative experiment with both inductance isolation and resistance isolation indicates that the former method not only has benefit in reducing the switch jitter, but also effectively protects the adjacent switches and trigger generator if one of the switches in FLTD module prefires. The experimental results with different charge voltages, gas pressures and working ratios show that when it was used in FLTD, the working ratio of the six-gap gas switch should limited between 60%~65% to reduce the switch jitter and the prefire probability. The breakdown delay time can be calculated by using T.H. Martin formula with the constant term revised.By using three parameters Weibull probability distribution model, the prefire probability of six-gap gas switch was calculated according to the self breakdown data of three hundreds shots. A rule was proposed and proved based on the repetitive operation of six-gap gas switch with two thousands triggered breakdown shots, which indicates that the delay time distribution of the switch approximately obeys the normal probability distribution. The self breakdown voltages, triggered breakdown delay times and switch jitters of sixteen switches for FLTD module were studied. The difference of the average delay times of sixteen switches was also derived from the experiment results. The trigger access structure will cause trigger pulse of each switch different in the FLTD module. Therefore, equivalent switch jitter was put forward to simulate the difference of the trigger pulse parameters of each switch.A FLTD experimental system with fourteen bricks was established. Two models built by using PSPICE and MATLAB were proved by the experimental result of the FLTD system with short circuit load. The models were used to simulate the influence of switch jitter and faults on the output of FLTD module, respectively. The simulation indicates that switch jitter affects the pulse front more obviously than the pulse amplitude. The switch faults, however, has little effect in the single FLTD module.The principle of FLTD with sixty stages in series was analyzed. The parameters of equivalent circuit were derived and the model of sixty stages in series has been established. The simulated results indicate that the influence of switch jitter on the output pulse decreases when the FLTD system in series includes a large amount switches. Stage prefire as well as switch prefire in the first stage more likely cause prefires in the following stages. However, switch faults in the middle stages and end stage has little effect in the FLTD system. Even if the middle stages and end stage can not be triggered, they will breakdown slightly later than the normal trigger sequence because of the induced voltage.