Gas spark switches with increased operating life for Marx generator of lightning test complex

A new design of gas spark switches with an increased operating life and stable dynamic characteristics for the Marx generator of the lightning test complex has been developed. The switches are characterized by the following parameters in the mode of operation: voltage up to 80 kV, discharge current up to 50 kA, flowing charge up to 3.5 C/pulse. An increased operating life is achieved by using torus-shaped electrodes with increased working surface area and a trigger electrode in the form of a thick disk with a hole located between them. Low breakdown delay time and high stability of breakdown voltage under dynamic conditions are provided by gas preionization in the spark gap using UV radiation of an additional corona discharge in the axial region.     

Modeling and optimization of the multichannel spark discharge

This paper reports a novel analytic model of this multichannel spark discharge, considering the delay time in the breakdown process, the electric transforming of the discharge channel from a capacitor to a resistor induced by the air breakdown, and the varying plasma resistance in the discharge process. The good agreement between the experimental and the simulated results validated the accuracy of this model. Based on this model, the influence of the circuit parameters on the maximum discharge channel number(MDCN) is investigated. Both the input voltage amplitude and the breakdown voltage threshold of each discharge channel play a critical role. With the increase of the input voltage and the decrease of the breakdown voltage, the MCDN increases almost linearly. With the increase of the discharge capacitance, the MDCN first rises and then remains almost constant. With the increase of the circuit inductance, the MDCN increases slowly but decreases quickly when the inductance increases over a certain value. There is an optimal value of the capacitor connected to the discharge channel corresponding to the MDCN. Finally, based on these results, to shorten the discharge time, a modified multichannel discharge circuit is developed and validated by the experiment. With only 6-kV input voltage, 31-channels discharge is achieved. The breakdown voltage of each electrode gap is larger than 3 kV. The modified discharge circuit is certain to be widely used in the PSJA flow control field.     

等离子体喷射触发气体开关多通道放电特性

为了能够形成稳定的多通道放电,研制了一种等离子体喷射触发气体开关。在触发电极的内部嵌入多个微型激励腔以形成多通道等离子体喷射,从而在主间隙中诱导多通道放电。研究了触发电路连接方式、触发能量和极性对多通道等离子体喷射的影响,比较了开关在两种工作模式下各间隙放电通道数量随工作系数的变化规律。实验结果表明:采用触发电路II连接方式,触发电极的多通道放电效果更好;高触发能量、负极性和低气压条件有利于形成多通道等离子体喷射;当开关运行在工作模式Ⅱ,且在较高工作系数时,具有更好的多通道放电特性。     

小型场畸变气体开关的击穿抖动特性

基于高功率重复频率脉冲功率源的应用需求,研制了一种三电极场畸变结构气体火花间隙开关,并开展了重复频率条件下的触发特性研究。实验研究了场畸变火花间隙开关的触发特性随重复频率、气体成分、工作压强和工作系数的变化关系,计算了气体开关的触发击穿时延和抖动参数,分析了影响开关触发特性的主要因素。实验结果表明:气体开关触发击穿的抖动随着重复频率增加而增大;填充气体中SF₆和N₂体积比1∶1时,混合气体的综合性能较好;工作系数主要影响开关第二放电火花间隙(间隙2)的击穿抖动。     

A new method for generation of synchronised capacitive sparks of low energy

Conventional tests for investigating the minimum ignition energy (MIE) of dust clouds are restricted to energies above a few mJ, due to the challenges of producing sparks of very low energies that can be synchronised with a transient dust cloud. In this paper, a new circuit for generating capacitive sparks of significantly lower energies than 1 mJ is presented. A measurement system for capturing voltage and current waveforms has been integrated in the circuit, offering the energy delivered to the spark by integration of the power-versus-time curve. When working with such low energy discharges, which are highly transient phenomena, attention must be paid to the measurement technique and methods of noise reduction in the measurement instruments.The measured spark energies range from 0.03 to 7 mJ, and they were found to constitute between 60 and 90 per cent of the energy stored on the discharge capacitors prior to breakdown. Losses to the measurement resistors are increasingly significant at higher energies and larger electrode gaps, due to the relatively large currents, and correspondingly small spark resistances.A simple circuit simulation, in which the spark conductivity is assumed proportional to the spark energy, offers voltage and current waveforms in good agreement with the measured ones, indicating that the spark is mainly resistive. In addition, the discharge channel's ability to carry current depends strongly on the supplied energy. The proportionality factor is found to depend on the breakdown voltage.     

氮气火花开关击穿机制的理论和数值研究

三电极气体火花开关带有触发极,相比两电极开关,其开关导通的可控性较高,工作电压较低且抖动小,所以气体火花开关中三电极开关的应用较为广泛.本文针对大气压氮气环境下的两电极开关和三电极开关的击穿机制进行了理论与数值模拟研究.通过理论和数值计算发现,对于平板-平板的两电极开关来说,低电压下(小于6.3 kV)无法产生流注击穿,高电压下(大于6.3 kV)会先形成由阴极到阳极的负流注,然后再形成由阳极向阴极的正流注.而在三电极开关的击穿过程中,首先会在触发极和绝缘体之间发生击穿,然后这个通道不断向阴阳极扩展,最终形成阴阳极之间的电弧通道.在本文的计算工况下,如果需要阴极-触发极、阳极-触发极同时击穿的话,其阴极-触发极之间的外加电压需要大于1.18 kV,而阳极-触发极之间的外加电压需要大于3 kV.当考虑触发极的场致发射后,该击穿阈值可以显著降低.     

Over recovery in low pressure spark gaps-confirmation of pressurereduction in over recovery

The over recovery in sparkgaps (Nagesh, 1997, Nagesh et al., 1999) operating along the left-hand side of Paschens' characteristics is due to pressure reduction in the gap after the first pulse discharge. This pressure reduction leading to over recovery in low pressure spark gaps has been verified using a low pressure spark gap with two spark gaps placed one above the other in the same chamber. The breakdown voltage strength characteristics of the second gap has been determined for gap spacings of 3.5 mm to 10 mm, diffusion of plasma in the direction of vacuum pumping and opposite, at a pressure of 2.1 Pa for hydrogen gas. The vacuum pumping direction has a great influence on the breakdown strength characteristics of second gap after the first gap discharge. The breakdown voltage of the second gap can exceed its self breakdown voltage only 1) when the diffusion of plasma and vacuum pumping direction are same and 2) when the second gap spacing is greater than or equal to first gap spacing. Shorter gaps can always have breakdown voltage lower than or equal to their self breakdown voltage. The experimental setups, behavior of self breakdown voltages of second gap due to breakdown in the first gap, over recovery characteristics of spark gaps, the results, and discussions are presented here     

用激光点火辅助火花诱导击穿光谱技术实现铝合金的高灵敏元素分析

报道了采用激光点火辅助火花诱导击穿光谱技术分析铝合金中痕量元素时的分析行为。用低能量激光脉冲聚焦于样品表面并在放电电极之间产生等离子体来触发高压火花放电以改善火花诱导击穿光谱技术的分析行为。在当前空间几何配置下,研究得到了最佳的放电电压和储能电容等参数并在最佳实验条件下分析了样品中的铜元素,其检出限达到0.7 ppm。激光点火的辅助手段改善了火花诱导击穿光谱技术在元素分析时信号的稳定性、提高了分析精度。同时它还能够有效地降低放电电压,改善其空间分辨本领。研究表明激光点火辅助火花诱导击穿光谱技术具有灵敏度高、稳定性好以及具有较好的空间分辨本领的特点,非常适合于各种合金中的痕量元素分析。     

不同电极结构下介质阻挡放电电离特征的试验研究

由于具有工作气压高、放电均匀等特点,大气压介质阻挡放电成为近年来非平衡等离子体领域研究的主要技术。电极结构是电离特性的主要影响因素之一,因此,通过电极结构优化来改善电离特性,对等离子体放电设备的应用领域拓展及性能优化至关重要。为改善大气压介质阻挡放电的电离特性,产生高活性、高均匀性的低温等离子体,基于自主设计的同轴介质阻挡放电装置进行了不同电极结构的电离试验及参数诊断;在一个标准大气压、放电频率11.4 kHz、放电峰值电压5.4～13.4 kV条件下进行了氩气电离试验;采用原子发射光谱法（AES）对氩等离子体谱线的激发、分光进行了检测分析;研究了螺纹电极、齿状电极、圆柱电极放电的特征光谱参数及外施电压对介质阻挡放电特征参数的影响。结果表明,齿状电极放电所形成等离子体的放电强度更大且放电效果显著,电子平均能量利用率低,电子激励温度弱于圆柱电极;圆柱电极放电强度较弱,但易形成大面积均匀性等离子体;大气压环境下电子激励温度不因外源电压的升高而单调递加,这表明通道内微放电的主要特征并不依赖于外施电压的供给,而是取决于电极结构、气体组份、气体压强;增大外施电压仅能增加单位时间内微放电的数量,经整合电子激励温度可达3 500 K,符合典型的低温等离子体特征。     

Theory of gas breakdown in an inhomogeneous field

Consideration is given to an independent electrical gas discharge in an inhomogeneous field, with photoionization of the gas as secondary mechanism. The condition for an independent discharge to exist is derived; this condition enables the breakdown voltage to be calculated, and also explains the short times required to form the discharge and the fact that the breakdown voltage is independent of the cathode material. The same condition may be considered as a criterion for the ignition of a self-sustaining corona in a long spark gap with nonuniform geometry.     

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。     

喷射等离子体触发气体开关导通特性

利用内嵌微孔火花放电产生喷射等离子体、作用于两电极开关,研究了间隙距离、气压、气体种类、开关工作系数和电压极性配合等因素对等离子体喷射控制开关导通特性的影响。实验结果表明,等离子体喷射触发开关可在工作系数为10%的条件下可靠快速导通,当开关采用0.5 MPa_N₂作为绝缘介质、间隙距离5 mm时,触发导通时延为11.7 μs,抖动为1.42 μs;当间隙距离增大到18 mm时,触发导通时延增大至19.7 μs,触发可靠性降低;当工作系数由10%增大到60%时,触发导通时延由11.7 μs降低至1.1 μs。在确保开关自击穿电压一致的前提下,短间隙、高气压、负触发脉冲电压、正工作电压更有利于减小开关触发导通时延。     

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.     

�����н�����-�����ѹ�Թ�ŵ�

空气中的大气压辉光放电通常因放电易过渡到火花状态而难以产生。在静态大气压空气针-板等离子体发生器中，采用阻容耦合负反馈方法控制等离子体放电发展过程，成功地抑制了辉光放电向火花放电的过渡，产生了稳定的交流辉光放电。研究了电压、电极间距等参数变化对放电的影响。     

直流场畸变开关中混合气体击穿特性

氩气中一般含有大量亚稳态原子,在强外电场作用下容易产生自由电子,能够促进放电通道快速形成。采用场畸变型气体开关,在直流电压下设计了实验平台来探究气体开关中采用SF6-Ar或N2-Ar混合气体后放电时延及抖动的变化情况。改变多种气体状态进行一系列实验,并得出场畸变气体火花开关中SF6-Ar及N2-Ar的击穿特性,根据工程需要对气体种类及混合比例进行最优化设计。实验表明SF6-Ar中Ar质量分数达到20%及以上时,开关放电时延及抖动明显减小。     

Geometrical study of spark ignition in two dimensions

Spark ignition, as the first step during the combustion in Otto engines, has a profound impact on the further development of the flame kernel. Over the last ten years growing concern for environment protection, including low emission of pollutants has increased the interest in the numerical simulation of ignition phenomena to guarantee successful flame kernel development even for lean mixtures.

However, the process of spark ignition in a combustible mixture is not yet fully understood. The use of detailed reaction mechanisms, combined with electrodynamical modelling of the spark, is necessary to optimize ignition of lean mixtures.

This work presents simulations of the coupling of flow, chemical reactions and transport with discharge processes in order to investigate the development of a stable flame kernel initiated by an electrical spark. A two-dimensional code to simulate the early stages of flame kernel formation, shortly after the breakdown discharge, has been developed. The model includes Joule heating. The spark plasma channel formed as a consequence of the breakdown is incorporated into the initial conditions. The computations include the initial phase (1–5 µs), which is governed by pressure wave formation, but also the transition to flame propagation. A thorough study of the influence of the electrodes' geometry, i.e. shape and size, and gap width, has been performed for air and a lean H₂–air mixture. Also a detailed methane-air mechanism was chosen as another example including combustion.

Due to the fast expansion of the plasma channel, together with the geometrical complexity of the electrodes, a complicated flow field develops after the emission of a pressure wave by the expanding channel. Special numerical methods, including artificial viscosity, are required to resolve the complicated flow field during these first 1–5 µs. The heat release through chemical reactions and transport processes is almost negligible during this short phase. The second phase, i.e. the development of a propagating flame and the flame kernel expansion, can last up to several milliseconds and is dominated by diffusive processes and chemical reactions. It has been found that the geometry greatly influences the developing flame kernel and the flow field. As soon as chemical reactions begin to contribute significantly to the heat release, the effect becomes smaller.     

Electrostatic analysis for designing of efficient discharge cell structures in AC plasma displays

The high luminous efficacy of plasma display demands high luminance at reduced discharge power. The discharge power can be reduced by several steps, one of them being reduction of gas breakdown voltage. In this paper, improved discharge cell structures are introduced that favor reduction of the gas breakdown voltage. The simulated electric field profiles for these structures indicate the low voltage requirement with increased electric field concentration in the discharge gap. The experimental measurements of breakdown voltage and discharge delay time in the test panels also support the simulation results. The important features of these discharge cell structures are discussed.     

Experimental study of pulsed corona discharge in air

We report on the results of experimental investigation of a pulsed corona discharge in electric fields with different degrees of nonuniformity under the action of a standard thunderstorm pulse in a wide range of voltages from the origination threshold to the breakdown. A high-sensitivity video camera makes it possible to record microdischarge and streamer processes in air long before the spark breakdown. It is known that the size of the corona discharge sheath increases with the supplied voltage, and the shape of the corona sheath depends on the polarity of the active electrode [1, 2]. It was demonstrated for the first time by Peek [3] that the range of voltages from the initiation of a corona discharge to the spark breakdown increases with the degree of nonuniformity of the electric field. We show that an analogous pattern is observed for a pulsed corona also. Our results show that the form of a pulsed corona discharge considerably depends on the pulse polarity, and a spark breakdown becomes possible when most branches in the streamer corona cover the electrode gap.     

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.     

Electric strength of the accelerating gap of a plasma electron source at rough vacuum

Conditions for the electric breakdown of the accelerating gap of a plasma electron source are determined. It is shown that, depending on the gas pressure and the size of openings in the emission electrode, two types of breakdown can occur. One of them is due to the ignition of a low-voltage discharge between the electrodes of the accelerating system, and the other one is caused by switching of the main discharge from the anode to the accelerating electrode.