Transition of a diffuse discharge to a spark at nanosecond breakdown of high-pressure nitrogen and air in a nonuniform electric field

The transition of a runaway-electron-induced diffuse discharge initiated in a nonuniform electric field under a high pressure of air and nitrogen to a spark is studied. High-voltage pulses with a rise time of 0.5 ns are applied to a discharge gap with a tubular cathode having a small radius of curvature. It is shown that the leader of the spark discharge propagates toward the tubular cathode along preproduced tracks and may pass from one track to another. For a pulse rise time of about 0.5 ns and a gap length of 12 mm or more, it is found that spark leaders originating at the cathode (which has a small radius of curvature) do not reach the anode and accordingly, do not cause the spark breakdown of the gap. It is confirmed that the spark breakdown of the gap is associated with a spark leader that moves away from the plane electrode after the appearance of a bright spot on it.     

大气压空气中重复频率纳秒脉冲气体放电模式研究

利用上升沿100ns、脉宽150ns的单级磁压缩纳秒脉冲电源,通过电压电流测量和放电图像拍摄实验,研究了大气压空气中极不均匀电场结构重复频率纳秒脉冲气体放电的放电模式。结果表明纳秒脉冲气体放电存在三种典型的放电模式:电晕放电、弥散放电和火花放电。施加的脉冲电压幅值对放电模式影响显著,随着电压幅值的增加,放电依次经历电晕、弥散和火花放电。固定电压幅值时,放电可能同时存在两种模式。重复频率加强了放电强度,弥散放电的激发电压随重复频率的增加变化不大,但火花放电的激发电压随着重复频率的增加而降低。因此降低重复频率有利于在较大电压范围获得大气压空气弥散放电。     

Formation of a small ‘bead lightning’ in a half-microsecond discharge in air

The formation of periodic plasma clots which form a discharge channel similar to bead lightning has been studied with a four-channel intensified charge-coupled device (ICCD) camera simultaneously with the recording of voltage and current waveforms. It was found that a diffuse discharge was formed at the initial stage due to the development of a wide streamer. Runaway electrons were registered. Beads were formed as a result of the development of the spark leader after the diffuse stage. It was assumed that the diameter of the spark leader periodically changes in accordance with the change in the electric field strength in the spark leader head. As a result, narrow sections of the channel heat up more and glow brighter.     

气体火花开关放电的数值模拟

 基于Rompe-Weizel火花动态电阻公式,数值计算了电容器经火花开关放电时负载电阻上的输出电压。在相同电参数条件下,计算所得的峰值电压为54 kV,前沿为2.0 ns,与实验所得的55 kV和2.3 ns基本吻合。基于Braginskii火花动态电阻公式,在假定火花开关电导率恒定与电导率渐变的条件下,利用传输线放电电路数值计算了气体火花开关的非线性动态电阻。与已有实验测量结果(0.7～0.9 Ω)对比,发现电导率渐变模型(0.5～0.8 Ω)更适合用于反映火花开关的动态电阻变化过程。进而在此模型中引入了负载电阻项,通过计算负载端的透射电流,数值计算得单脉冲形成线对负载放电时的电压脉冲前沿为7～9 ns,而利用单线经高压氢气自击穿火花开关放电得到初步实验结果为8 ns。     

氮气介质高气压开关特性

从理论分析、软件模拟、实验研究等方面研究了氮气介质高气压开关的工作特性。根据强度理论计算所设计并加工的开关的理论压强可达10 MPa。对氮气介质高气压开关进行实验,得到在气压范围2,4,6 MPa、电极间隙0.1,0.5,1.0 mm时,气隙的击穿延时小于14 ns,抖动小于1 ns;在气压2 MPa、电极间隙0.1 mm时50%击穿电压约为34 kV。与常压空气开关相比较,该开关具有很好的稳定性和绝缘特性。     

多组多路输出100 kV快前沿电脉冲触发系统

 在多路并联运行的电容储能型脉冲功率源中,为实现初级储能气体开关和脉冲形成主开关的同步,需要多组延时可调、每组多路输出的快前沿高电压脉冲来分别触发,为此研制了一套快响应低抖动100 kV快前沿电脉冲触发系统。该系统由同步机DG535和多组电脉冲放大单元组成,各组放大单元输出脉冲的延迟时间可调,延时步长由DG535设定,每组最短延时时间约为305 ns,抖动2 ns,可同时输出多路触发脉冲,在高阻负载上幅值可达180 kV,当输出信号为4路时,上升时间10 ns,当输出信号为8路时,上升时间15 ns。     

大电流两电极气体开关研究

 由于引燃管难以满足现在能源系统对放电开关承受大电流的要求,因此研制了大电荷转移量两电极气体开关。这种新型气体开关电极间距可调,无触发极,采用同轴结构,并将主电极置于金属腔体内,减少了放电对绝缘支撑的污染。主电极为铜钨合金材料,设计为平顶圆柱状,以提高烧蚀均匀度和热传导效率,减少电极材料喷溅,延长其寿命。绝缘支撑采用碗状结构,提高了机械强度,增加了沿面击穿距离。该开关工作电压达25 kV,放电电流超过100 kA（脉冲宽度600 μs）,单次脉冲电荷转移量达50 C。实验结果显示该气体开关触发性能稳定,电极表面烧蚀均匀,多次大电流实验后电极表面保持完好,可应用于强激光能源系统。     

调制器型加速器的波形整形

提出用火花隙开关法对调制器型加速器的输出波形前后沿进行锐化的方案,给出了锐化电路中的电容器电容值的确定和火花隙开关的设计.在已研制的脉冲调制器型加速器上进行了实验研究,实验中得到输出电压500kV、脉宽900ns、前沿时间80ns、后沿时间100ns的近似矩形的脉冲波形,并进行了1Hz重复运行实验.     

气流对微秒脉冲滑动放电特性的影响

脉冲电源驱动的滑动放电能够在大气压下产生高能量、高功率密度的低温等离子体. 为了研究微秒脉冲电源在针-针电极结构中产生滑动放电的特征, 本文采用电压幅值为0–30 kV, 脉冲宽度约8 μs, 脉冲重复频率为1–3000 Hz的微秒脉冲电源, 通过测量电压、电流波形和拍摄放电图像, 研究了微秒脉冲滑动放电的电特性. 实验结果表明, 随着施加电压的增加微秒脉冲滑动放电存在三种典型的放电模式: 电晕放电、弥散放电和类滑动放电. 不同放电模式的电压、电流波形和放电图像之间差异显著. 脉冲重复频率对微秒脉冲滑动放电特性有影响, 表现为当气体流量较小(2 L/min)时, 类滑动放电的放电通道随着脉冲重复频率的增大逐渐集中, 而当气体流量较大(16 L/min)时, 类滑动放电的放电通道随着脉冲重复频率的增大逐渐分散. 不同气流下重复频率对滑动放电特性的影响与放电中粒子的记忆效应和气流的状态有关.     

Minimum ignition energy of hydrogen–air mixture: Effects of humidity and spark duration

The minimum ignition energy (MIE) of hydrogen–air mixture is measured using capacitive spark discharge. First, the effect of humidity on MIE is studied. It is shown that the MIE is approximately constant when the relative humidity increases from 0% to 90% at room temperature. This indicates that humidity has no significant influence on MIE. Next, the effect of spark duration on MIE is studied. The spark duration is increased by connecting a series resistor to the spark circuit. It is shown that the MIE is approximately constant when the spark duration is varied from 5 ns to 1 ms.     

平面火花隙三电极开关研制及性能测试

 研制了一种适用于平行板传输连接的平面火花隙三电极开关，开关正负电极为半圆形状，触发电极为细条状。将之替代立体式（半球形电极）火花隙三电极开关并应用于爆炸箔起爆装置中，装置回路参数将得以优化。实验测试了空气间隙为4.12， 3.14和2.2 mm的平面火花隙三电极开关的性能。结果表明，在开关间隙间距一定的情况下，随着电压的升高，开关间隙的放电时延和分散时间呈指数降低，开关电感小于15 nH；对于不同范围内的应用电压，使用不同间隙间距的开关，其分散时间不大于10 ns。该开关应用于较低充电电压（小于10 kV）的脉冲功率装置中，与立体式火花隙三电极开关相比，回路电感降低了约50 nH，放电周期缩短近1/3，峰值电流增加约1/3。     

Laser Interferometric Measurements of a Laser-Preionization-Triggered Spark Column

A KrF laser (248 nm) is used to volume preionization trigger a 40-100-kV, > 10-kA, 100-ns spark gap switch. This method of triggering creates reproducible and axisymmetric spark columns having low temporal and spatial jitter. A short pulse (< 5 ns) tunable dye laser and a Mach-Zehnder interferometer are used to obtain spatial and temporal measurements of the spark column. The spatial resolution of the interferograms is better than 5 ?m. The fringe shifts of the interferograms are used to calculate the electron and heavy particle density distributions within the spark column as a function of time during the spark. Results are presented for sparks in 5-percent SF6/ 20-percent N2/75-percent He and 1-percent Xe/99-percent H2 gas mixtures. Dc and pulsed self-breakdown voltages are also measured in order to provide a reference for the laser-triggered results. Data on laser-triggering reliability and spark breakdown delay time are also presented.     

Air breakdown times of two-stage spark gaps and their applications

The air breakdown times of second spark formation, geometrically in series with trigatron switching, are studied and compared to that of a triggered spark gap. Despite a large breakdown jitter of ⩾1 μs in the trigatron, the latter is not observed to affect the electrical closure times of the series-connected second spark gap, which is triggered largely as a result of their direct electrical and optical coupling. While most of the multistage spark gaps are designed for fast and precision switching of high voltages, the air breakdown times of the second spark formation find a number of useful applications, particularly in achieving uniform glow discharge in pulsed gas lasers     

Microstructure of the current channel of an atmospheric-pressure diffuse discharge in a rod-plane air gap

The multichannel structure of the current channel of an atmospheric-pressure diffuse discharge excited in a 10-cm rod-plane air gap was investigated using the imprint technique. A voltage pulse with an amplitude of 240 kV, a duration of 180 ns, and a rise time of 14 ns was applied to a 1-cm-diameter bullet-shaped cathode with a tip curvature radius of 0.2 mm; the discharge current reached 350 A. It is found that the diameter of the discharge channel in the anode plane varies in the range 2.5–9.7 mm from shot to shot. The overall imprint of the current channel is formed of 170–9500 imprints of microchannels with an average diameter of 5–20 μm. The parameters of the observed microstructure do not correlate with variations in the main electric characteristics of the discharge and the parameters of the generated X-ray pulse. It is shown that the formation of the microstructure is related to the onset of cathode-directed plasma structures developing from the anode. It is suggested that the same mechanism is responsible for both the formation of the current channels structure and the anode microstructure of diffuse nanosecond discharges developing in atmospheric-pressure air gaps with a highly nonuniform electric field.     

气体火花开关电阻特性

利用二极管输出电压约1 MV、脉宽约40 ns的重复频率Tesla型脉冲功率驱动源,对大间隙、高气压的重复频率氮气火花开关进行了实验研究。通过将开关等效为RLC电路,利用测量得到的形成线电压与锥形段电压来计算氮气火花开关电阻。电阻的变化情况是放电开始时刻比较大,随着放电通道的形成,电阻迅速变小,最终达到级的阻值。通过计算值与理论公式推算值比较,检验Barannik,Rompe-Weizel,Demenik,Toeple,Vlastos公式适用性,并尝试对Rompe-Weizel公式常数项进行了修正。     

Marx发生器建立时间及抖动实验研究

 Marx发生器建立时间及抖动与Marx发生器中球隙开关的工作状态有关，同时与开关的触发电压幅值及极性有关。通过实验获得了Marx发生器建立时间及抖动最小时最佳工作状态的相关参数。天光一号电子束加速器从同步机发出指令信号至主Marx输出，总的延时及抖动为（1629±8.4）ns，满足MOPA系统建立时间抖动小于20ns的要求。     

火花通道长度对激光触发开关特性的影响

利用超高速相机,在曝光时间100 ns时,对不同能量下激光在氮气气体开关中形成的火花通道进行拍照,得到了不同焦距下激光波长266 nm时激光火花通道长度与激光能量的关系。开展了激光触发气体火花开关的实验研究,激光触发开关延时、抖动随激光能量的增加而减小。将火花通道长度与激光触发开关的特性进行了分析,气体开关的抖动随着激光火花通道长度的增加而减小,当火花通道沿电极间轴向长度达到开关电极间距40%时,开关的抖动为亚ns量级。     

High-power nanosecond bipolar voltage pulses

This paper presents the design and testing results for a generator of bipolar voltage pulses of amplitude ±200 kV, duration ∼3.5 ns, and repetition rate up to 100 Hz across a 12.5-Ω matched load. The mode of multichannel switching of spark gaps with subnanosecond time delays between the operation of the channels has been realized. A numerical simulation of the generator operation has been performed with its design represented by homogeneous lines and with the parameters of spark gaps described in terms of the Felsenthal-Praud criterion for the breakdown delay and by the Rompe-Weitzel spark model. It has been demonstrated that mixtures of ordinary and inert gases as well as hydrogen show promise as fill gases for spark gaps to reduce losses. The generator is intended to excite wideband transmitting antennas. Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 41–46, December, 1999.     

预电离触发管气体开关特性

利用脉冲火花预电离方式,设计了一种脉冲火花预电离触发的触发管气体开关。开关工作电压等级为100 kV,工作介质采用干燥空气,开关主间隙10 mm,电极材料采用304不锈钢,触发结构设计成盘环嵌套结构。实验结果表明:预电离能够显著减小低工作系数下触发管气体开关的触发时延和抖动。对于ns级快脉冲触发,预电离时刻越早,开关击穿时延和抖动越低。在30 kV/8 ns触发脉冲作用下,脉冲预电离触发的触发管开关在80%工作系数时,平均时延约为40 ns,抖动小于1 ns。     

低抖动三电极火花开关的研制

对影响三电极火花开关分散性的诸因素进行了分析。研制的低抖动三电极火花开关选用了Ｎ２气体,主电极形状为球冠形,触发电极形状为棱形,电极材料为黄铜,对结构进行了优化。并测试了不同气压及电压条件下开关的分散性,获得了开关抖动小于２ｎｓ的结果。