气体脉冲放电等离子体阻抗的参量研究

在纯净氦气条件下，对高频纵向脉冲放电的等离子体动态阻抗进行了实验研究.测量了放电等离子体阻抗随放电电压、频率以及气体压强之间的变化关系，表明等离子体阻抗随频率和电压的增加而下降，随气压的升高而增大.定性分析了这些宏观参量与等离子体阻抗变化之间的关系，拟合出等离子体阻抗随电压、频率、气压变化的经验公式，并对数值模拟与实验结果进行了比较研究. 关键词： 等离子体阻抗 气体脉冲放电     

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.     

纳秒脉冲电压下同轴场畸变开关多通道放电特性

使气体开关形成多通道放电是减小开关电感、通道电阻、电极熔蚀,提高开关寿命和稳定性的有效措施。设计了一种同轴场畸变气体火花开关,研究了开关在纳秒脉冲电压下的多通道放电现象。研究了脉冲电压上升速率与多通道放电特性的关系,比较了两种体积比的SF6/Ar混合气体多通道放电特性。实验结果表明:一定气压下,平均通道数随着脉冲电压上升率增加而增多,电流分布趋向均匀;相同脉冲峰值与气压比值,不同气压下,高气压下的通道数较多;SF6/Ar混合气体中,氩气含量较高情况下多通道放电特性较好。最后,结合J.C.Martin的多通道放电理论对实验结果作出了初步解释。     

120 kV下常压空气纳秒脉冲电晕放电特性

使用上升沿15 ns、脉宽30~40 ns的重复频率纳秒脉冲电源对120 kV下大气压空气中管-板电极结构电晕放电进行了实验研究,通过电压电流测量、放电图像拍摄和X射线探测分析了纳秒脉冲电晕放电特性。结果表明:纳秒脉冲电晕放电中存在X射线辐射,但辐射强度较弱,X射线辐射计数随着气隙距离的增大而减少,随着脉冲重复频率的增大而增多;放电空间的残余电荷加强了下一个脉冲到来时的局部电场,从而导致高重复频率下易于出现分散的电晕通道。     

Experimental study on characteristics of nanosecond-pulse surface dielectric barrier discharge

在常规大气环境条件下,基于单极性纳秒脉冲电源对表面介质阻挡放电特性进行了实验研究.结果表明:纳秒脉冲表而介质阻挡放电的本质是丝状放电,放电集中在电压脉冲的上升沿;激励电压和脉冲重复频率越大,放电越强烈,越接近均匀放电,但电压的作用更侧重于均匀性,而频率的作用则侧重于放电的强度;电极间隙的优化可以使表面介质阻挡放电特性最好;玻璃作为阻挡介质时容易发生沿面闪络.     

大气压空气纳秒脉冲板-板放电中逃逸电子产生机理

经典放电理论(Townsend和流注理论)解释纳秒脉冲气体放电存在局限性,近年来基于高能电子逃逸的纳秒脉冲气体放电理论研究受到广泛关注.但是目前对大气压空气纳秒脉冲板-板放电中逃逸电子产生机理研究仍较少,严重阻碍了纳秒脉冲放电等离子体的应用发展.本文利用一维粒子模型,对幅值为20 kV的纳秒脉冲电压驱动下,间隙长为1 mm的板-板电极之间的大气压空气放电中逃逸电子的产生机理进行了数值模拟研究..结果表明,在空间电荷动力学行为的影响下,板-板电极之间出现了增强电场区域,使得电子可以满足电子逃逸判据而进入逃逸模式.此外,还观察到放电通道前逃逸电子的预电离效应导致了二次电子崩的产生,随着二次电子崩与放电通道不断汇聚,引导并加速了放电通道的发展,最终导致气隙击穿.本研究进一步揭示了纳秒脉冲板-板放电机理,拓展了纳秒脉冲气体放电基础理论,为纳秒脉冲放电等离子体的应用和发展开辟了新的机会.     

大气压空气针-水结构脉冲气-液放电特性研究

利用纳秒脉冲电源激励大气压空气中针-水结构气液放电,研究了不同脉冲参数下的放电特性、等离子体特性和活化水中活性粒子浓度的变化规律。结果表明,在一个脉冲周期内放电分为3个阶段,其中发生在脉冲持续时间内和下降沿的两次放电较强,上升沿的放电较弱。当脉冲电压增大时,放电电流、平均功率、发光强度和发射光谱强度均逐渐增大;当频率增大时,放电电流几乎不变,但是功率显著增大,放电发光强度和发射光谱强度均增大。电压上升沿时间的增大则会减弱放电强度,相应的放电发光强度和发射光谱强度均减弱。而电压下降沿的增大则会增强放电,发光强度和发射光谱强度增大。当脉冲电压、频率和下降沿时间增大,H_2O_2,NO_2~-和NO_3~-浓度逐渐增大;而电压上升沿时间增大会导致3种活性粒子浓度逐渐降低。     

脉冲驱动氩气真空介质阻挡放电的光谱特性研究

通过自主设计正极性Marx纳秒脉冲电源,在不同放电频率、不同电源电压幅值下,采用发射光谱在真空环境下对氩气放电时的电子激发温度和电子密度进行测量计算。通过双谱线法选取合适的Ar原子谱线,求得电子激发温度在1 550～3 400 K之间,在正极性脉冲电源做电压源,且电源电压一定时,电子激发温度随着电源频率的升高而呈现上升趋势,在电源频率一定时,电子激发温度也随着电源电压的增加而升高。依据Stark展宽原理对真空体积介质阻挡放电时的电子密度进行了测量计算。电子密度的数量级可达10¹³ m^-3,当电源电压不变时,电子密度随电源频率的增加呈现上升趋势,当电源频率不变,电子密度随着电源电压的升高也逐渐提升。     

纳秒脉冲表面介质阻挡放电特性实验研究

在常规大气环境条件下,基于单极性纳秒脉冲电源对表面介质阻挡放电特性进行了实验研究。结果表明:纳秒脉冲表面介质阻挡放电的本质是丝状放电,放电集中在电压脉冲的上升沿;激励电压和脉冲重复频率越大,放电越强烈,越接近均匀放电,但电压的作用更侧重于均匀性,而频率的作用则侧重于放电的强度;电极间隙的优化可以使表面介质阻挡放电特性最好;玻璃作为阻挡介质时容易发生沿面闪络。     

全固态双极性纳秒脉冲电源研制及应用

研制了一种双极性交替的纳秒高压脉冲电源,进行了双极性纳秒脉冲放电产生等离子体研究。该电源先通过固态开关IGBT将直流电压截断成电压脉冲,通过可饱和脉冲变压器拓扑,实现升压并缩短脉冲上升沿。该电源可在一个周期内输出极性相反的2个脉冲,且时序可以灵活控制。通过优化调整器件参数,研制了两种不同输出性能参数的双极性纳秒脉冲电源:①峰值电压10 kV、爆发模式脉冲重复频率500 kHz（正负脉冲间隔2 μs）、连续重复频率1 kHz;②峰值电压25 kV、爆发重频200 kHz、连续重频600 Hz。测试电源的运行性能,发现电源存在温度升高的情况,但长时间（＞0.5 h）运行温度趋于稳定。10 kV电源连续运行在1 kHz时最高温度点50.5 ℃;25 kV电源连续运行在600 Hz时最高温度点60 ℃。利用该电源驱动线板电极阵列和表面介质阻挡放电结构,证实了该电源可以用于常压空气条件下产生大面积等离子体。     

Electron beam formation in a gas diode at high pressures

Electron beam formation in krypton, neon, helium, and nitrogen at elevated pressures are experimentally investigated. It is shown that, when the krypton, neon, and helium pressures are varied, respectively, from 70 to 760 Torr, from 150 to 760 Torr, and from 300 to 4560 Torr, runaway electrons are beamed at the instant the plasma in the discharge gap approaches the anode and the nonlocal criterion for electron runaway is fulfilled. The fast-electron simulation of discharge gap preionization is performed. The simulation data demonstrate that preionization in the discharge gap is provided if the voltage pulse rise time is shorter than a nanosecond under atmospheric pressure.     

Ultrashort electron beam and volume high-current discharge in air under the atmospheric pressure

Conditions are studied under which an electron beam and a volume discharge with a subnanosecond rise time of a voltage pulse are produced in air under atmospheric pressure. It is shown that the electron beam appears in a gas-filled diode at the front of the voltage pulse in ∼0.5 ns, has a half-intensity duration of ≤0.4 ns and an average electron energy of ∼0.6 of the voltage across the gas-filled diode, and terminates when the voltage across the gap reaches its maximum value. The electron beam with an average electron energy of 60 to 80 keV and a current amplitude of ≥70 A is obtained. It is assumed that the electron beam is formed from electrons produced in the gap due to gas ionization by fast electrons when the intensity of the field between the front of the expanding plasma cloud and the anode reaches its critical value. A nanosecond volume discharge with a specific power input of ≥400 MW/cm³, a density of the discharge current at the anode of up to 3 kA/cm², and specific energy deposition of ∼1 J/cm³ over 3 to 5 ns is created.     

X-ray radiation from the volume discharge in atmospheric-pressure air

X-ray radiation from the volume discharge in atmospheric-pressure air is studied under the conditions when the voltage pulse rise time varies from 0.5 to 100 ns and the open-circuit voltage amplitude of the generator varies from 20 to 750 kV. It is shown that a volume discharge from a needle-like cathode forms at a relatively wide voltage pulse (to ≈60 ns in this work). The volume character of the discharge is due to preionization by fast electrons, which arise when the electric field concentrates at the cathode and in the discharge gap. As the voltage pulse rise time grows, X-ray radiation comes largely from the discharge gap in accordance with previous experiments. Propagation of fast avalanche electrons in nitrogen subjected to a nonuniform unsteady electric field is simulated. It is demonstrated that the amount of hard X-ray photons grows not only with increasing voltage amplitude but also with shortening pulse rise time.     

Characterization of the single nanosecond pulsed surface dielectric barrier plasma actuator: Geometric and electric effects

The influence of the electrode length and the voltage pulses on the discharge characteristics of the surface dielectric barrier discharge actuators were investigated numerically by using the plasma kinetic model. The governing equations including the coupled continuity plasma discharge equation, drift-diffusion equation, electron energy equation, Poisson's equation, and Navier–Stokes equation were solved in quiescent air at atmospheric pressure. The results show that the shorter pulse rising time results in higher discharge characteristics, more intense discharge, and bigger discharge region. Differently, the compared discharge characteristics for the electrodes with different lengths prove that the length of the powered and ground electrodes has little effect on the surface dielectric barrier discharge driven by nanosecond pulsed voltage.     

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.     

平行板电极边缘滑闪引起加载电压的“双峰”现象

平板电容器是电磁脉冲(EMP)模拟装置中常用的脉冲压缩器件,在平行板电极的SF₆沿面闪络实验中发现,原本前沿光滑的纳秒脉冲电压加载在平行板电极上,会在脉冲电压前沿上测得一尖峰,使加载的脉冲电压出现“双峰”现象。为探索该现象的原因,首先通过理论分析,认为该现象可能是由于平行板电极边缘发生了滑闪放电,增大了电极等效正对面积,使平行板电极的等效容值发生突变所致,容值变化越大,尖峰越明显。之后开展了不同气压下平行板电极的沿面闪络实验,并对放电过程的图像进行了拍摄,结果表明:平行板电极边缘产生的树枝状放电在低气压时主干明亮粗大,分枝较多,气压升高后,主干亮度和直径逐渐变小,分枝也越来越少;随着气压的增加,由于平行板电极边缘的滑闪放电受到抑制,平行板的等效面积变化率越来越小,尖峰出现时对应的电压幅值越来越高,且尖峰越来越不明显,与理论分析一致。     

High-pressure runaway-electron-preionized diffuse discharges in a nonuniform electric field

High-pressure nanosecond diffuse (volume) discharges in a nonuniform electric field are studied experimentally using a recording system with a ?100-ps time resolution. As the voltage pulse shrinks to a width of ≈100 ps, the initiation of a diffuse discharge without a source of additional ionization is facilitated; specifically, a runaway-electron-preionized diffuse discharge is ignited in atmospheric-pressure air in the case of short interelectrode gaps. It is found that a major energy deposit into the plasma of this discharge is from an abnormal glow discharge following a maximum of the gap voltage.     

On the initiation of a spark discharge upon the breakdown of nitrogen and air in a nonuniform electric field

Switchover from a runaway-electromnduced volume discharge to a spark is studied when a nanosecond discharge is initiated in high-pressure nitrogen an d air at a voltage of 50–250 kV. In the case of a cathode with a small radius of curvature and a flat anode and in the presence of cathode spots, the leader of the spark channel may propagate from the flat cathode. When the rate of rise of the voltage across centimeterwide gaps is high (dU/dt ∼ 10¹⁵ V/s or higher), cathode spots in the case of a corona discharge emerge within 200 ps.     

SF6中氧化铝环氧复合材料的纳秒脉冲闪络特性

氧化铝掺杂环氧树脂复合材料在电力绝缘设备中应用广泛,然而人们对其在纳秒脉冲下的绝缘性能研究较少,这限制了它在指导脉冲功率装置中的应用。为探究其在纳秒脉冲下的沿面绝缘性能,对氧化铝掺杂环氧树脂复合材料在前沿数十ns快脉冲电压下的闪络特性进行了研究,结果显示,其闪络电场较纯环氧有较大提高,闪络电压符合韦伯分布。实验表明,闪络电压随电压上升率的增加而显著增加,从5.8 kV/ns时的108 kV上升到20.5 kV/ns时的226 kV,增幅超过1倍。闪络时延随电压上升率的上升呈现“先快速下降、后趋于平缓”的趋势。在试样闪络通道表面观测到明显的碳化现象,说明实验中的闪络放电对复合材料有破坏性影响。     

正极性纳秒脉冲电压下变压器油中流注放电仿真研究

建立了二维轴对称流体模型, 仿真研究了正极性纳秒脉冲电压下变压器油中针-板电极流注放电的起始与发展过程, 得到了不同的外施电压幅值、脉冲上升沿时间与电极间隙距离下油中流注放电的形貌、 电场强度与空间电荷密度分布等. 仿真结果表明: 空间电荷加强了流注头部前方电场, 使流注通道更易于向前推进, 形成"电离波"; 随着外施电压幅值升高, 流注发展的平均速度显著变大; 较陡的脉冲上升沿形成的放电半径较大, 对应的最大电场强度值变小; 随着电极间隙距离的增加, 流注发展平均速度变快. 仿真显示纳秒脉冲下放电中油温无明显升高, 表明此类放电过程没有明显的油气化现象. 我们认为, 场致电离是油中带电粒子产生的主导机制; 空间电荷效应增强流注前方电场使得电离进一步发展, 最终导致击穿. 本研究有助于加深对变压器油中放电起始、发展直至击穿过程的认识以及对液体电介质中电离机制的理解. 关键词： 变压器油 流体模型 流注放电 空间电荷效应