人工触发闪电电流波形特征参数分析

通过分析在夏季强雷暴活动频繁的山东滨州地区连续4年人工触发闪电实验中所获得的闪电回击通道底部电流资料,结果表明人工触发闪电回击峰值电流几何平均值为14.6kA,电流波形10％—90%上升时间和30％—90%上升时间的几何平均值分别为2.3μs和1.8μs,相应上升陡度分别为4.7kA/μs和4.4kA/μs.波形半峰值宽度的几何平均值为17μs,回击1ms内转移电荷量的几何平均值为1.2C,回击电流作用积分的几何平均值为6.1×10³A²s.对比研究表明回击峰值电流与接地状况、回击电流波形的上升时间以及半峰值宽度之间没有明显相关性,但与电流波形上升陡度以及回击1ms之内转移电荷量之间存在相关性,回击峰值电流（I_p）与回击1ms内转移电荷量（Q）之间满足关系式：I_p=14.1Q^0.69.通过与自然闪电放电参数的对比分析表明,人工触发闪电回击过程与自然地闪放电的继后回击过程相似. 关键词： 人工触发闪电 地闪 闪电电流 回击     

人工引发闪电上行负先导的发展传输特征

在地面大气电场为正极性的条件下,成功实现12次人工引发闪电,对其放电特征、初始阶段上行负先导的传输特征与机理进行了研究.引发闪电时地面大气电场强度均值约5 kV/m,最高超过13 kV/m.除一次个例的放电发生了正、极性反转并产生多次负回击以外,其他11次引发闪电均未产生继后回击过程,闪电放电电流总体上在几百安培量级.引发闪电起始后,其向上传输的负梯级先导平均二维速度为1.85 × 10~5 m/s,获得132次梯级的长度范围为0.8—8.7 m,平均3.9 m.先导起始阶段的电流和电磁场呈现显著的脉冲特征,其脉冲间隔、电流峰值、转移电荷量、半峰值宽度、电流上升时间T~(10%—90%)平均值分别为17.9 μs,81 A,364 μC,3.1 μs和0.9 μs,单次梯级的等效线电荷密度为118.5 μC/m.先导通道的分叉一般伴随梯级过程发生,存在两种方式:1)先导头部前方成簇的空间茎/空间先导在同一梯级周期内先后与先导头部发生连接,对应的电流脉冲表现为多峰结构,峰值点时间间隔约2—3 μs,最长6—7 μs;2)曾熄灭的空间茎/空间先导重燃后侧向连接至先导通道.     

闪电过程中电磁辐射功率的变化特征

利用无狭缝摄谱仪获得的地闪回击光谱,结合同步电场资料,计算了一次闪电放电过程中的通道温度、电导率、回击电流峰值、通道光亮度和电磁功率峰值等参数,均在文献报道的合理范围内。并由此讨论了回击前截止时间、回击通道光亮度及电磁功率峰值之间的相关性,研究了放电通道的电导率、电流和电磁功率之间的变化关系。结果表明：回击前截止时间越长,回击过程中所中和的电荷越多,形成的电流越大,辐射出的电磁能量越大。当通道电导率变大,同时电场变化峰值也增大时,通道内电流变大,回击过程中辐射出的电磁功率也变大。这方面的工作为计算闪电放电过程中产生的光学能量和电磁能量提供一定的参考依据。     

闪电过程中电磁辐射功率的变化特征（英文）

利用无狭缝摄谱仪获得的地闪回击光谱,结合同步电场资料,计算了一次闪电放电过程中的通道温度、电导率、回击电流峰值、通道光亮度和电磁功率峰值等参数,均在文献报道的合理范围内。并由此讨论了回击前截止时间、回击通道光亮度及电磁功率峰值之间的相关性,研究了放电通道的电导率、电流和电磁功率之间的变化关系。结果表明:回击前截止时间越长,回击过程中所中和的电荷越多,形成的电流越大,辐射出的电磁能量越大。当通道电导率变大,同时电场变化峰值也增大时,通道内电流变大,回击过程中辐射出的电磁功率也变大。这方面的工作为计算闪电放电过程中产生的光学能量和电磁能量提供一定的参考依据。     

依据光谱研究闪电回击通道核心的特征参数

闪电回击通道核心中的大电流及其强电磁辐射是引发多种雷电灾害的主要根源。随着现代科技的飞速发展,闪电防护工作显得越为重要。为了完善闪电防护系统,需要从描述闪电回击通道核心的特征参数入手深入研究闪电通道形成和发展过程的微观物理机制。截至目前,光谱观测是获取闪电通道核心特征参数的最佳手段。2015年夏天在青海高原地区的野外试验中,利用由高速摄像机作为记录系统组装的无狭缝光栅摄谱仪,结合快天线地面电场测量仪,记录到一次包括四个回击的云地闪电放电过程的光谱以及与之同步的快电场变化信息。依据光谱,结合等离子体理论计算得到闪电回击通道核心的电导率。在此基础上,应用闪电电动力学模型计算了闪电回击速度、峰值电流、贯穿通道核心的电磁场以及通道核心单位长度的峰值功率等特征参数。结果表明,回击速度在(1.2～2.3)×108 m·s-1的范围内;贯穿回击通道核心的轴向电场、径向电场和磁感应强度的最大值分别在(1.42～1.74)×105 V·m-1,(8.22～9.99)×108 V·m-1和(1.51～2.83) T的范围内。当闪电回击的峰值电流在(7.52～24.05) kA的范围内时,回击通道核心的峰值功率在(0.63～1.92)×109 W·m-1的范围内。另外,分析了电导率、起始电场峰值、回击速度和峰值电流与峰值功率之间的相关性,结果发现峰值电流和峰值功率具有良好的线性关系。研究结果可为探索闪电回击通道形成和发展过程的微观物理机制提供参考依据。     

光谱法研究闪电回击放电通道的电阻及电流的热效应

闪电放电通道的电阻及电流产生的热效应对雷电灾害研究以及防护设计都具有重要意义,放电通道的热力学特性与其等离子体辐射光谱密切相关。利用无狭缝摄谱仪获得的两次云对地多回击闪电放电的等离子体辐射光谱,依据谱线波长、强度等信息,结合同步地面电场变化资料,应用空气等离子体传输理论,计算了闪电回击放电通道的电导率、峰值电流、核心通道半径,进而得到了闪电回击等离子体通道单位长度的电阻、峰值电流时的热功率及在回击初始前5 μs内通道储存的热能。并与常规金属导体进行比较,分析了闪电回击放电在峰值电流时等离子体通道的热功率与电阻、电流平方之间的相关性关系。结果表明：利用光谱研究得到的闪电放电通道的电阻为0.04～8.41 Ω·m-1、峰值电流时的热功率为0.88×108～2.20×108 W·m-1、回击初始前5 μs内通道储存的热能为1.47×102～3.66×102 J·m-1,以上结果与文献报道的利用其他方法得到的结果相比,在合理的范围内;与常规金属导体相比,闪电回击放电等离子体通道在峰值电流时的热功率与电阻成正比,但与电流的平方呈指数减小的关系;由于闪电等离子体通道的电阻与温度的3/2次方成反比,通常回击放电通道中峰值电流越大,通道温度越高,而电阻会迅速降低,因此热功率也会急剧减小。此结论进一步验证了采用欧姆加热方法加热等离子体的致命缺点。     

光谱法研究闪电通道的导电特性

依据无狭缝光栅摄谱仪在青海获得的云对地闪电回击光谱信息,结合空气等离子体传输理论,用四种不同方法计算了同一闪电放电通道的电导率。结果表明：各种方法所得闪电核心通道的电导率数量级均为104 S·m-1;且同一通道内的电导率随通道高度的增加有减小的趋势;通道内电子与一次、二次电离离子的碰撞以及它们各自的碰撞对通道电导率的贡献不可忽略;用碰撞积分的方法计算闪电核心通道的电导率结果更为合理。在通道电导率的基础上估算了回击通道的放电电流,与辐射峰值电场实验资料所得的相应峰值电流相比,其结果在合理的范围内, 并进一步探讨了温度与电流放电特性的相关性, 为研究闪电放电电流提供了一条可行的途径。     

一次对地转移电荷极性两次反转的人工引发雷电特征及反转机制分析

利用闪电甚高频干涉仪动态成像结果,并结合通道底部电流、电场和光学观测资料对一次罕见的、对地转移电荷极性反转两次的双极性人工引发雷电放电特征进行了详细研究,首次观测到直接导致极性反转的云内击穿放电过程,探讨了对地转移电荷极性两次反转的物理机理.结果发现,此次闪电无回击过程、初始连续电流阶段对地转移电荷极性经历了负-正-负的两次反转,转移电荷量分别约–40.0 C,+13.3 C和–1.0 C.负极性初始连续电流衰减过程中,一支击穿空气的负先导起始于已电离的正先导分支通道上并形成悬浮通道,水平发展28.816 ms后,接地主通道上发生负极性击穿连接到了悬浮通道末端正电荷聚集处或双向发展的悬浮通道的正极性端,随后对地转移电荷极性快速反转为正.负先导熄灭后,对地转移电荷极性缓慢反转为负.击穿空气的负先导连接到接地主通道和持续发展的正先导是此次双极性闪电对地转移电荷极性发生两次反转的重要原因.而负先导的起始,与正先导多分支同时发展引起的先导通道和环境电势分布差异密切相关.     

闪电首次回击过程中通道温度与电导率的演化特征

利用以高速摄像机为记录系统组装的无狭缝摄谱仪,在青海地区获得了多次云对地闪电首次回击过程400-900 nm波长范围的时间分辨光谱,分别计算了闪电电流核心通道和外围发光通道的温度;结合空气等离子体的传输理论,获得了闪电通道的电导率,探讨了回击过程中通道温度及电导率的演化特征.结果表明,闪电电流核心通道的温度比外围通道高约5000-7000 K,并且,与以往关于通道峰值温度持续时间的观点不同,回击过程中,通道保持高温的时间远远大于峰值放电电流存在的时间,在回击电流缓慢减小的数百微秒内,核心电流通道维持20000 K以上高温,这一特性是热效应导致雷电灾害的主要根源.     

闪电首次回击过程中通道温度与电导率的演化特征

利用以高速摄像机为记录系统组装的无狭缝摄谱仪,在青海地区获得了多次云对地闪电首次回击过程400-900 nm波长范围的时间分辨光谱,分别计算了闪电电流核心通道和外围发光通道的温度;结合空气等离子体的传输理论,获得了闪电通道的电导率,探讨了回击过程中通道温度及电导率的演化特征.结果表明,闪电电流核心通道的温度比外围通道高约5000-7000K,并且,与以往关于通道峰值温度持续时间的观点不同,回击过程中,通道保持高温的时间远远大于峰值放电电流存在的时间,在回击电流缓慢减小的数百微秒内,核心电流通道维持20000K以上高温,这一特性是热效应导致雷电灾害的主要根源.     

Coaxial Discharge and Transverse Magnetic Field

The study deals with the effect of an applied transverse magnetic field on the dynamics and parameters of the focused and expanded plasma in a coaxial discharge. The experimental results were found with a 3 kJ Plasma focus device of a Mather geometry. The discharge takes place in hydrogen gas with base pressure of 0.5 Torr. The experiments are conducted with a 10 kV bank voltage, which corresponds to 100 kA peak discharge current with rise time 8 μs. Helmholtz magnetic coils are placed outside the expansions chamber to produce a transverse magnetic field with intensity 280 G perpendicular to the plasma expanded from the coaxial electrodes. The investigations have shown that the plasma flow along the expansion chamber axis is restricted when applying the externally transverse magnetic field and the maximum axial velocity of the expanded plasma is decreased by 33%. X-ray probe has been used to measure the focused plasma electron temperature (T_e). The experimental results and the calculations showed that T_e is decreased from 2.2 keV to 800 eV with the application of a transverse magnetic field. The expanded plasma electron temperature and density have been measured by an electric double probe, the results cleared that the expanded plasma electron temperature is decreased by 2.6 times while its density is increased by 9 times, when a transverse magnetic field is applied.     

On the Role of Capacitance Determination Accuracy for the Electrical Characterization of Pulsed Driven Dielectric Barrier Discharges

A dielectric barrier discharge (DBD) of coaxial geometry has been investigated. The discharge cell was filled by 100 mbar of argon and driven by positive square voltage pulses with a rise time of 20 ns and 75 ns. The internal discharge characteristics such as the discharge current, the gas gap voltage, the instantaneous power and energy have been determined from measured current and voltage waveforms. The peculiarities of the experimental evaluation of the discharge parameters are discussed in detail. Special attention is paid to the accurate experimental determination of the key capacitance values of the DBD, namely the capacitance of the reactor cell C_cell and the capacitance of the dielectric barriers C_d. The influence of the capacitance value accuracy on precision of electrical characterization is demonstrated and it is shown that a small uncertainty in the C_d value leads to large errors in the evaluation of the gas gap voltage. Nevertheless, the obtained accuracy of the capacitance values allows the reliable comparison of the electrical DBD parameters. These are sensitive to the mode of discharge excitation. The shortening of the voltage rise time leads to the increase of the total and instantaneous energy as well as the peak power dissipated into the discharge. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study on the Relation Between Discharge Voltage and Magnetic Field Topography in a Hall Thruster Discharge Channel

The relation between magnetic field topography and operating voltage is investigated in a 1kW Hall thruster discharge channel in order to focus the ion beam effectively and optimize the performance. The curvature of magnetic field line (α) is introduced to characterize the differences of topologies. The optimized magnetic field distribution under each operating voltage is obtained by experiment. Through the curvature transformation, we find that the area of (α > 1) in the channel gradually decreases with the increase of the operating voltage. In response to the results above, two dimensional plasma flows are simulated employing Particle‐in‐Cell method. The distributions of the electric potential, ion density and ion radial velocity are calculated to understand the important influence of the relation above on ion beam focusing. The numerical results indicate that magnetic field curvature and thermal electric field control the ion beam in the ionization and acceleration zone, respectively. The magnetic field topography and discharge voltage interact with each other and together form the focusing electric field. The ion radial mobility is suppressed effectively and the ion beam is focused to the channel centerline. In addition, for a given voltages, when the area of (α > 1) is larger than the optimal scope, the electric potential lines excessively bend to the anode causing ion over focus; contrarily, the electric potential lines will bend to the exit and defocus ions. All these results suggest the relation between magnetic field topography and discharge voltage is important to the ion radial flow control and performance optimization of the Hall thruster (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theory of positive corona in SF6 due to a voltageimpulse

A theoretical examination is made of the mechanism of corona formation for a positive point-plane gap in SF₆ at 100 kPa. The impulse voltage applied has a rise time of 15 ns and peak value of 200 kV. Seed electrons are released 1 ns after the start of the voltage rise. For a 0.5-cm diameter positive sphere located 6.5 cm from a negative plane, the calculated circuit current initially consists of subnanosecond corona onset pulses, and then the current steadily rises to a maximum, as the voltage reaches a maximum, followed by a rapid fall in current. During the current rise a streamer moves out into the gap along a 100-μm channel, with the electric field in the streamer trail E>E*, where E* is the critical field where ionization equals attachment. The light output during the discharge is predicted to be a maximum at the anode with only a minor pulse of light at the streamer head, making it hard to detect. After the current maximum, recombination rapidly reduces the numbers of positive ions, negative ions, and electrons, but the net charge density remains constant and thus so does the electric field. The electric field is E~E* in the streamer trail, but has a sharp maximum, E≫E* at the head of the streamer trail. The origin of mid-gap precursors, observed when the streamer channel reilluminates after some 100 ns, is attributed to this field maximum in the remnant electric field. The evolution of positive ions, negative ions, and electrons is described by one-dimensional continuity equations, with the space-charge electric fields determined by the disk method. The effects of ionization, attachment, recombination, electron diffusion, and photoionization are all included. New numerical methods allow resolution of the streamer head and the anode fall region to be obtained with a 1-μm mesh, while following the streamer propagation for ~2 cm     

高压双扩散漏端MOS晶体管双峰衬底电流的形成机理及其影响

利用0.15μm标准CMOS工艺制造出了工作电压为30V的双扩散漏端MOS晶体管(double diffused drain MOS, DDDMOS).观察到DDDMOS的衬底电流-栅压曲线(I_b-V_g曲线)有两个峰.通过实验和TCAD模拟揭示了DDDMOS衬底电流的形成机理,发现衬底电流第一个峰的成因与传统MOS器件相同;第二个峰来自于发生在漂移区远离沟道一侧高场区的碰撞离化电流.通过求解泊松方程和电流连续性方程,分析了器件的物理和几何参数对导致衬底电流重新上升的漂移区电场的影响.在分析了DDDMOS衬底电流的第二个峰形成机理的基础上,考察了其对器件的可靠性的影响. 关键词： 高压器件 衬底电流 可靠性     

The first Trichel pulse of negative corona discharge in N2 with a small admixture of SF6

Current growth waveforms of transient negative point-to-plane discharge in N₂ and in N₂ with 0·025-0·1% admixture of SF₆ at a pressure of 40 kPa have been measured and compared. The transient glow discharge regime in pure N₂ was found to be preceded by a peaked current signal of conspicuous similarity to the first Trichel pulse rise and its initial decay in N₂+SF₆ mixture. The results are in a basic agreement with a hypothesis on streamer mechanism for Trichel pulse and indicate occurrence of field emission during the rise of Trichel pulse current.     

The impulse dielectric behavior of N2 gas in sphere-plane gap

The focus of this work has been on the pre-breakdown phenomena and the breakdown characteristics of N₂ gas in a sphere-plane gap under various impulse voltages. Both electrical and optical experimental investigation methods were used. Following parameters were considered: gas pressure range from 0.2 to 0.6 MPa, electric field utilization factor of the electrode configuration 71%, positive and negative impulse waveforms with the rise time of 500 ns, 1.2 μs and 180 μs. The observed discharge processes before the breakdown through the light emission images by the ICCD camera are in good agreement with the streamer mechanism. Under both polarity stresses, discharges are initially concentrated around the tip of the sphere and later pointing towards the earth electrode. However, negative streamers are thinner and more diffuse. As expected, the breakdown voltages for negative polarity are lower than those for positive polarity regardless of the gas pressure and shape of the applied impulse voltage. The breakdown voltage is increased with shortening the rise time of pulse waveforms. As a substitute for SF₆, N₂ gas under pressures above 0.3 MPa can reach the standard rated withstand voltage for 24 kV C-GIS.     

The lightning striking distance—Revisited

First return stroke current waveforms measured by Berger [Methods and results of lightning records at Monte San Salvatore from 1963–1971 (in German), Bull. Schweiz. Elektrotech. ver. 63 (1972) 21403—21422] and Berger and Vogelsanger [Measurement and results of lightning records at Monte San Salvatore from 1955–1963 (in German), Bull. Schweiz. Elektrotech. ver. 56 (1965) 2–22] are used to estimate the charge stored in the lightning stepped leader channel. As opposed to previous charge estimates based on the entire current waveform, only the initial portion of measured current waveforms (100 μs in duration) was used in order to avoid the inclusion of any charges not involved in the effective neutralization of charges originally stored on the leader channel. The charge brought to ground by the return stroke within the first 100 μs, Q_f,100 μs (in C) is related to the first return stroke peak current, I_pf (in kA), as Q_f,100 μs=0.61 I_pf. From this equation the charge distribution of the stepped leader as a function of the corresponding peak return stroke current is estimated. This distribution (along with the assumed average electric field of 500 kV/m in the final gap) is used to estimate the lightning striking distance S (in meters) to a flat ground as a function of the prospective return stroke peak current I (in kA): S=1.9 I_pf^0.90. For the median first stroke peak current of 30 kA one obtains S=41 m, while the traditional equation, S=10 I_pf^0.65, gives S=91 m. In our view, the new equation for striking distance provides a more physically realistic basis for the electro-geometric approach widely used in estimating lightning incidence to power lines and other structures.