Study of laser target triggering for spark gap switches

The use of laser targets as a method to decrease the required laser energy to trigger a laser triggered gas switch has been investigated at the University of Missouri. Target materials were identified based on durability, melting point, reactivity and reflection coefficient. Laser targets were placed into a cathode of a laser triggered gas switch. The switch was pulse charged by the Tiger pulsed power machine to between 185 kV and 330 kV. The switch was triggered by directing a 1064 nm or 266 nm wavelength laser pulse from an Nd:YAG laser onto a laser target to ablate material and create plasma, closing the switch. The goal of the project was to trigger a high voltage gas switch with less than 1 mJ of laser energy while maintaining a switch jitter comparable to present electrically triggered switches for LTD based systems. The study successfully demonstrated that triggering the switch using a 1 mJ infrared pulse and a graphite target resulted in a jitter less than 5 ns. Findings will be used in the design of switches for LTD based systems.     

激光触发多级开关触发延迟及其抖动的研究

实验研究了激光触发多级多通道开关触发延迟时间及其抖动与激光脉冲能量等实验光学参量之间的关系。建立了基于Boltzmann方程的激光触发间隙零维数值模拟模型,并与基于T H Martin经验公式的过压自击穿间隙击穿时延计算程序相结合,对实验现象进行了初步的理论解释。     

场畸变气体开关寿命预测

气体开关是脉冲功率装置的关键元件之一,快速准确地预测开关的工作寿命,对于确定开关乃至脉冲功率装置的维修周期、预防事故的发生等具有重要的作用。选取自击穿电压和触发抖动表征开关性能,定义开关失效率,建立开关寿命计算模型,预估气体开关寿命。进行不同放电电荷量和电流峰值时的触发放电验证实验,结果表明,开关工作寿命可以分为稳定和失效2个阶段,所建模型能够有效地预测开关最大放电次数,即开关工作寿命。     

An ultra compact back-lighted thyratron for nanosecond switching applications

An ultra-compact back-lighted thyratron (BLT), which is also named as mini-BLT, with effective volume of 15 cm^{3 was developed to serve as a high voltage switch in compact transient plasma ignition systems. The mini-BLT can hold off 40 kV and was used to conduct a peak current up to 4.5 kA. A 30 ns switching delay with 2 ns jitter was achieved when triggered by a 70 mJ, 355 nm laser pulse. Delay and jitter increase as the photon energy of the trigger pulse decreases. The plasma density in the switch measured at a peak current of 3.2 kA is 9×1014 cm-3. The mini-BLT was successfully used as the switch in a 100 ns, 60 kV pulse generator for generation of streamers in a plasma ignition system.}     

Switching characteristics of vacuum gap switch employing UV‐laser triggering

The switching time and arc‐ignition probability of a sustained main discharge in a laser trigger vacuum gap were measured. The third harmonic beam of an Nd:YAG pulse laser (wavelength 355 nm, energy 5 mJ/pulse, power density 4 × 10⁷ W/cm²) was used to trigger the gap. The main electrodes 85 mm in diameter were made of oxygen‐free copper. The gap length was 1.6 mm and the experimental chamber was evacuated to about 1.3 × 10⁴ Pa by a turbomolecular pump. The UV beam from the laser was focused at normal incidence onto the grounded cathode. The switching time decreased and the arc‐ignition probability increased with increasing applied voltage. The switching time was 326 ns at 15 kV with a circuit inductance of 107 μH. Its jitter was 24.8 ns. The advantageous results obtained with the UV beam are compared to the previously reported data on triggered vacuum gaps. © 2000 Scripta Technica, Electr Eng Jpn, 132(3): 8–13, 2000     

激光触发真空开关触发稳定性及时延特性

为了研究影响激光触发真空开关(LTVS)导通时延及抖动特性的关键因素,搭建LTVS高电压大电流实验平台,分别改变触发激光能量、工作电压、触发极性以及触头间距等参数,考察其对LTVS导通时延和抖动特性的影响,并对LTVS的导通机制及触发稳定性进行理论分析。实验结果表明:在一定范围内,增加触发激光能量、增加主间隙电压、采用阴极触发方式或者缩短触头间距均可减少开关的导通时延及时延抖动;LTVS的导通是激光轰击触发极产生初始等离子体的热过程与主间隙两端电场加速初始等离子体扩散过程共同作用的结果,实验中所得到的结论对LTVS的优化具有重要意义。     

场畸变触发开关新型触发电极的设计与实验

气体触发开关是脉冲功率电路的重要组成器件。针对工程中对低抖动、长寿命气体触发开关的需求,结合三电极场畸变型触发开关,设计一种拥有较多孔隙的多环型触发极结构。对三种主电极-触发极分别为平板-多环、平板-圆盘、球冠-圆盘的开关进行击穿特性实验研究,结合电场仿真对比分析实验结果。实验结果表明:在22.4k V/40ns的触发脉冲和5.0~7.5k V的工作电压下,平板-多环结构的开关时延及抖动比较稳定,开关时延基本在81.0~84.5ns之间,抖动为0.8~1.1ns。平板-多环电极结构开关时延、抖动均明显优于平板-圆盘结构,其开关时延、抖动与球冠-圆盘结构基本相同但使用寿命优于球冠-圆盘结构。     

高介碳酸钡陶瓷沿面闪络伪火花开关的研究

为了满足脉冲功率技术和脉冲电流试验技术对放电开关的要求,笔者设计了BaTiO3高介电常数的电介质沿面闪络伪火花开关的触发装置。通过对表面放电触发器的实验发现:在伪火花开关的工作气压范围内,高介沿面闪络触发器显示出很强的电荷发射能力和快速的电荷注入能力,在气压为7 Pa时,触发器能够在30 ns内释放1.5μC,触发电流的上升陡度为1.2×1011A/s,发射的电子数达到9.4×1012。对自放电电压为28 kV的伪火花开关,可靠工作的最低电压可降低到130 V,放电时延为35～100 ns,最小抖动为6～25 ns。     

Control of SF6 discharge gap switch by XeCl excimer laser

Experimental studies have been carried out on triggering characteristics of the SF₆ discharge gap switch by use of XeCl excimer laser (wavelength = 308 nm). First, laser irradiation characteristics are studied on a pure SF₆ in the pressure range of p = 160 ～ 3,800 torr. Using a lens of f (focal length) = 133 mm, the laser is irradiated into the gas, where the energy absorption is studied. If the laser is injected into the gas with the energy above a certain threshold for the breakdown, the rate of energy absorption is found to be ～ 17 percent of the incident energy at p > 760 torr. Injecting the laser into the SF₆-filled gap switch (gap length = 7 mm, p = 760 torr), we have studied the triggering characteristics. Excellent triggering characteristics were obtained; delay time for the discharge ～ 20 ns, and the jitter ～ 260 ps when the gap voltage is operated at 99 percent of the self-breakdown voltage. In addition, the triggering characteristics are studied by changing the focusing point axially. It is found that both the delay time and the jitter decrease when the focusing point tends to approach the high-voltage electrodes.     

平板电极型激光触发真空开关的导通特性研究

强激光触发方式的真空开关由于触发精度高、可靠性好、并能有效避免触发装置的电磁干扰,在快速关合开关、电磁发射、串联补偿电容保护等领域具有非常广阔的应用前景。设计了一种平板电极型激光触发真空开关。为了提高其触发寿命,针对触发电极进行优化。触发电极耐烧蚀,靶材选取TiH_2,其能为开关导通提供丰富的初始等离子体,开关的触发性能得到加强,开关的最短时延可达650 ns。详细讨论激光参数、聚焦镜位置、主电压值等对开关的触发阈值、最低工作电压和时延特性的影响,提出触发阈值理论和电弧形成机制,为此类开关的性能优化提供理论依据。实验表明:开关稳定的触发阈值达4.5×10~7W/cm~2,最低工作电压为30 V;采用正常聚焦模式能大幅度降低开关的时延;电弧电流的开始阶段存在强烈振荡过程,电流值大于5 A后,如果外加电压足够高,振荡现象消失,真空电弧稳定燃烧。     

激光触发变压器型脉冲调制器的实验研究

本文设计了一台激光触发变压器型脉冲调制器并开展了单次及1Hz重频实验研究。该调制器由水介质同轴脉冲形成线、激光触发开关、脉冲变压器、假负载等组成。在调制器主开关导通电压为-795k V时,激光到达开关25ns后调制器主开关导通,在负载上得到了电压-402k V、电流26k A、脉冲宽度128ns的准方波高功率电脉冲。当调制器主开关分别为氮气、六氟化硫时对调制器激光触发气体开关的延时、抖动特性进行了实验研究,266nm激光触发时,氮气具有较小的延时和抖动;同时对自击穿和激光触发两种情况下负载电压的前沿特性进行了对比,最后对实验结果进行了分析。     

多棒极型触发真空开关触发特性

主要研究多棒极型触发真空开关(TVS)的触发特性及其影响因素.研究表明,真空开关的触发时延主要由导通时延决定,增加触发电流的幅值和陡度(di/dt)可减小TVS的导通时延及其分散性.脉冲变压器直接触发TVS,可通过减小变压器漏感、提高触发电容的充电电压或增加触发电容电容量来降低导通时延及其分散性,但触发电容增加到一定值后对增加触发能量无帮助,没有必要继续增加.变压器直接触发方式可使导通时延减小至4ms左右,但分散性较大,且存在较小的触发回路电流导致的触发极熄弧现象.在脉冲变压器直接触发回路的基础上设计并研究了两种改进的触发回路:一种为脉冲变压器匹配续流回路,TVS导通时,通过续流回路的充电电容续流可使触发电流达kA级,导通时延减小至2～4μs,由于回路结构复杂,受到杂散参数影响,触发电流的幅值和陡度受到限制;一种为改进的触发回路,在触发极和阴极两端直接并接电容,导通时延可保持在1μs之内.最后研究并确定了并接电容选取依据和取值区间;对触发电压较小的TVS可在并接电容和触发极之间串联间隙,增大电容的充电电压和触发极能量,达到TVS可靠、精确触发的目的.     

快放电直线变压器型驱动源用场畸变型低电感气体火花开关

快放电直线变压器型驱动源（FLTD）是组建大型脉冲功率源的新技术,作为其中的关键器件,气体火花开关的动态工作特性对FLTD驱动的负载电流参数有重要影响。为了减小开关电感,简化开关结构,设计了一种三电极场畸变气体火花开关。根据开关内部充电过程和触发过程电场分布的数值计算结果,优化了开关结构,并对开关的静态充电特性和动态触...     

铁电体触发开关的实验研究

利用铁电体作为脉冲开关的触发源,是当前脉冲功率技术发展的一个重要研究方向,为掌握铁电体作为触发极的工作性能,阐述了铁电体触发开关在真空条件下的工作原理和实验结果,给出了铁电体触发开关的设计思路及电极结构图并进行了真空条件下铁电体触发开关的实验研究,在开关间距0.3mm、真空压力度8cPa的条件下测得开关的抖动<800ps。实验结果表明:触发电压的高低对开关抖动的影响很大,随着触发电压的升高开关的抖动越来越小,但触发电压超过某一值时开关的抖动又会增加;开关阴阳极之间的间距对开关抖动基本无影响,对于不同的铁电体触发极,其触发电压的最佳值不同。     

Optimization of a low jitter, 50 kV, 100 Hz triggered spark gap with high pressure gas mixtures

Recent research efforts at Texas Tech University on impulse antenna phased array has needed to develop a reliable high voltage, high repetition rate switch that will operate with ultra low jitter. An ideal jitter of a small fraction of the risetime is required to accurately synchronize the array to steer and preserve the risetime of the radiated pulse. In [1], we showed the initial test system with sub-ns results for operations in different gases and gas mixtures. This paper discusses in detail 50 kV, 100 Hz switch operations with different gases. The effects of gases and gas mixtures have on switch performance which includes recovery rate and in particular jitter will be investigated. Gases tested include, dry air, H², N², and SF₆, as well as H₂-N₂, and N₂-SF₆ gas mixtures. Switch jitter as a result of triggering conditions is discussed, also including a comprehensive evaluation of jitter as a function of formative delay in the various gases. The temperature of gas and its effects on switch jitter is also documented in this paper. A 50 Ω, 1 nF pulse forming line is charged to 50 kV and provides the low inductance voltage source to test the different gases. Triggering is provided by a solid state opening switch voltage source that supplies ~150 kV, 10 ns risetime pulses at a rep rate up to 100 Hz in burst mode. A hermetically sealed spark gap with a Kel-F - PCTFE (PolyChloroTriFluoroEthylene) lining is used to house the switch and high pressure gas.     

铁心式脉冲变压器的谐振充电特性

基于脉冲变压器的陡脉冲发生器是神光III能源模块主放电开关的触发方案之一。该类型触发器利用脉冲变压器对高压电容谐振充电,并通过陡化开关输出陡脉冲触发气体开关。分析杂散电阻和激磁电感对谐振充电变比和效率的影响,理论推导了环形铁心脉冲变压器的铁心体积最小值,并在实际工程中验证。设计了带载电容为1.08 nF,输出电压峰值为130 kV,绕组变比为65的干式铁心式脉冲变压器。研制了基于脉冲变压器谐振充电的气体开关触发器,其输出脉冲峰值大于120 kV,上升时间小于30 ns,能够稳定可靠地触发两电极气体开关。     

铁电体触发赝火花开关实验研究

本文阐述了铁电体触发开关的工作原理,进行了铁电体触发开关的实验研究。得出了气压与开关导通时间和延时的关系,并对此实验结果进行了分析。在开关间距为3mm、真空度为2.5Pa、阴极腔的深度为19mm、小孔直径为4mm的条件下测得开关的抖动小于3ns。实验结果表明触发电压的高低对开关抖动的影响很大,随着触发电压的升高开关的抖动越来越小。当触发电压达到6kV左右时,开关的抖动小于1ns。     

A TEA‐CO2 laser oscillation by an inductive energy storage pulsed‐power generator using a wire‐fuse opening switch

We have carried out experiments on TEA‐CO₂ laser oscillation using the inductive energy storage pulsed‐power generator, which has a copper wire fuse as an opening switch. Maximum laser output energy of about 1 J/pulse was obtained in the case of a fuse length of 5 cm and energy storage inductance of 8 μH. The laser output energy depends on the energy storage inductance and the parameters of the fuse. In this paper, the dependencies of laser output energy on inductance and fuse length, and a comparison between the inductive and capacitive system were described. Furthermore the laser efficiency was discussed by calculating the electron energy distribution of laser main discharge region. © 2000 Scripta Technica, Electr Eng Jpn, 132(1): 15–21, 2000     

基于真空触发开关的合成关合试验回路及其控制策略

概括了断路器关合短路电流时由预燃弧阶段开始的物理过程,对比了触发火花间隙和真空触发开关用作快速关合装置时的触发特性,提出了一种在全电压条件下进行合成关合的试验回路。对全电压条件下进行合成关合试验时,外施电压相位控制、外施电压与关合电流相位差要求进行了分析,并提出了相应的控制策略和解决方法:对影响控制准确度的主要因素进行了分析。     

触发真空开关的导通特性

介绍触发真空开关导通特性的实验研究结果,研究了不同的电极极性,电极距离,电极形状,不同的触发方式和触发能量以及主电路负载性质对开关导通特性,特别是最小导通电压的影响,实验结果表明,触发真空开关的最小导通电压比火花隙开关小两个数量级,因而具有工作电压范围很宽的优点。