Influence mechanisms and optimization of pulsed breakdown characteristics of a megavolt class cascade self-triggered switch
WANG Tianchi1,2, XIE Linshen2, LI Junna3, YANG Youheng1,2, HUANG Tao2, CHEN Zhiqiang2, GUO Fan2, DU Yingchao1, CHEN Wei2
1. Key Laboratory of Particle & Radiation Imaging (Tsinghua University), Ministry of Education, Beijing 100084, China; 2. State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi'an 710024, China; 3. State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an 710049, China
Abstract：Megavolt switches in large pulses typically use a cascade configuration to increase operating voltage and ensure electric field uniformity. We must reduce their jitter when we need multipulse superposition to obtain a higher voltage pulse. Moreover, in the high-altitude electromagnetic pulse simulator, the megavolt pulsed switch needs to adopt the self-triggering technique to simplify the structure and reduce weight for good mobility and hoisting requirements. However, it is difficult to carry out a large number of experiments and completely reveal the influence mechanisms of the characteristics of megavolt switches via experiments. Therefore, this paper derives a breakdown probability distribution model of a cascade switch based on the characteristic parameters of a single-stage switch, which can be obtained easier from experiments. The experiment of the cascade switch is then carried out to validate the model analysis. In the model, we assume that the rising rate of the pulse voltage is a constant and that the breakdown probability of a single-stage switch follows the Weibull distribution. It is common in cascade switches to allow one stage to break down in triggered mode while others are in self-breakdown mode due to overvoltage. When the cascade switch has n stages, and one stage is triggered, it is seen as three equivalent switches based on their breakdown sequence. This paper assumes that x self-breakdown stages first close, the triggered stage closes next, and finally, (n-x-1) self-breakdown stages close. The range of x is [0, n-1]. Then the breakdown probability distribution model of each equivalent switch can be derived using the existing calculation method. The influence mechanisms of the breakdown characteristics of a three-stage cascade switch are semiquantitatively analyzed based on the model. If the uniformity of breakdown characteristics of each triggered switch can be guaranteed and three stages are all triggered, the switch jitter is approximately equal to the jitter of a single-stage triggered switch because the latter two stages break down under high overvoltage. The mean breakdown voltage of each stage is lower than a single-stage triggered switch. When only one stage is triggered, most probably, the triggered stage will close first, followed by two self-breakdown stages under high overvoltage. The switch jitter is significantly lower than that under the self-breakdown mode, and the mean breakdown voltage of each stage is higher than that when all three stages are triggered. However, the possibility that one self-breakdown stage closes first results in the switch jitter being approximately twice when all three stages are triggered. The improvement path of the switch jitter characteristics can be inferred using the model analysis. The jitter of the triggered single-stage switch should be reduced, and it is preferable to trigger all stages if the uniformity of the breakdown characteristic of each single-stage switch can be guaranteed. In the experiment, the three-stage cascade switch operates on a pulsed voltage with a rise time of 300 ns and an operating voltage range of 0.8—2.0 MV. Self-triggered continuous preionization is adapted to eliminate the influence of trigger gap jitter on the switch jitter, ensuring the uniformity of breakdown characteristics of each single-stage switch. When one stage is triggered, the time delay jitter is 2.9—7.7 ns, and the breakdown voltage jitter is 0.51%—2.21%. When three stages are triggered, the time delay jitter is 2.3—3.6 ns, and the breakdown voltage jitter is 0.59%—0.91%. The preceding analysis is verified, and the switch characteristics are improved compared to the original one. Moreover, the self-breakdown characteristic is more stable when the gas pressure exceeds 0.3 MPa; thus, the switch jitter is approximately the same when we trigger one or three stages.
[1] GILMAN C, LAM S K, NAFF J T, et al. Design and performance of the FEMP-2000: A fast risetime, 2 MV EMP pulser [C]//Digest of Technical Papers. 12th IEEE International Pulsed Power Conference. Monterey, USA: IEEE, 1999: 1437-1440. [2] BAILEY V, CARBONI V, EICHENBERGER C, et al. A 6-MV pulser to drive horizontally polarized EMP simulators [J]. IEEE Transactions on Plasma Science, 2010, 38(10): 2554-2558. [3] SU J C, ZENG B, GAO P C, et al. A voltage-division-type low-jitter self-triggered repetition-rate switch [J]. Review of Scientific Instruments, 2016, 87(10): 105118. [4] NAFF J T. Spark gaps for EMP and SREMP pulsers [C]//Proceedings of the 17th IEEE Pulsed Power Conference. Washington, USA: IEEE, 2009: 322-331. [5] HEGELER F, MYERS M C, WOLFORD M F, et al. Low jitter, high voltage, repetitive laser triggered gas switches [J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2013, 20(4): 1168-1188. [6] YIN J H, SUN F J, QIU A C, et al. 2.8-MV low-inductance low-jitter electrical-triggered gas switch [J]. IEEE Transactions on Plasma Science, 2016, 44(10): 2045-2052. [7] WARNE L K, VAN DEN A J A, LEHR J M, et al. Fundamental science investigations to develop a 6-MV laser triggered gas switch for ZR: First annual report [R]. Albuquerque, NM, Livermore: Sandia National Laboratories, 2007. [8] LECHIEN K R, SAVAGE M E, ANAYA V, et al. Development of a 5.4 MV laser triggered gas switch for multimodule, multimegampere pulsed power drivers [J]. Physical Review Special Topics-Accelerators and Beams, 2008, 11(6): 060402. [9] WAKELAND P E, WEMPLE N R, SAVAGE M E. 6+ MV laser triggered gas switch used on Z [C]// Proceedings of the 2017 IEEE 21st International Conference on Pulsed Power. Brighton, UK: IEEE, 2017: 1-6. [10] LI J N, JIA W, TANG J P, et al. A 3-MV low-jitter UV-illumination switch [J]. IEEE Transactions on Plasma Science, 2013, 41(2): 360-364. [11] LI J N, XIE L S, WU W, et al. Design and experiment of a 4-MV self-triggered switch [J]. IEEE Transactions on Plasma Science, 2022, 50(1): 97-102. [12] 李俊娜. 百纳秒紫外预电离放电对MV级开关击穿特性的影响[D]. 西安: 西北核技术研究所, 2015. LI J N. Influences of UV illumination discharge on breakdown characteristic of switch under hundred- nanosecond MV pulsed voltage [D]. Xi'an: Northwest Institute of Nuclear Technology, 2015. (in Chinese) [13] STYGAR W A, IVES H C, WAGONER T C, et al. Flashover of a vacuum-insulator interface: A statistical model [J]. Physical Review Special Topics-Accelerators and Beams, 2004, 7(7): 070401. [14] 陈志强. 电磁脉冲模拟装置用同轴薄膜电容器关键技术研究[D]. 西安: 西安交通大学, 2020. CHEN Z Q. Study on key technologies of coaxial film capacitor for electromagnetic pulse simulator [D]. Xi'an: Xi'an Jiaotong University, 2020. (in Chinese) [15] WANG T C, HUANG T, WANG H Y, et al. Using self-triggered sustaining pre-ionization to obtain nanosecond jitter in a MV pulsed gas switch [J]. IEEE Transactions on Plasma Science, 2021, 49(12): 4034-4037. [16] WANG T C, LI J N, WANG H Y, et al. Optical diagnosis of preionization mechanisms and breakdown characteristics in a nanosecond switch [J]. IEEE Transactions on Plasma Science, 2022, 50(6): 1912-1926.
2023, Vol. 63 
