Stochastic and Relaxation Processes in Argon by Measurements of Dynamic Breakdown Voltages

Statistically based measurements of breakdown voltages U _b and breakdown delay times td and their variations in transient regimes of establishment and relaxation of discharges are a convenient method to study stochastic processes of electrical breakdown of gases, as well as relaxation kinetics in afterglow. In this paper the measurements and statistical analysis of the dynamic breakdown voltages U _b for linearly rising (ramp) pulses in argon at 1.33 mbar and the rates of voltage rise k up to 800 V s ^–1 are presented. It was found that electrical breakdowns by linearly rising (ramp) pulses is an inhomogeneous Poisson process caused by primary and secondary ionization coefficients α , γ and electron yield Y variations on the voltage (time). The experimental breakdown voltage distributions were fitted by theoretical distributions by applying approximate analytical and numerical models. The afterglow kinetics in argon was studied based on the dependence of the initial electron yield on the relaxation time Y ₀ (τ ) derived from fitting of distributions. The space charge decay was explained by the surface recombination of nitrogen atoms present as impurities. The afterglow kinetics and the surface recombination coefficients on the gas tube and cathode were determined from a gas‐phase model. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

μs前沿百kV激光触发水开关的实验研究

开展了百kVμs前沿脉冲作用下激光触发水开关的研究。水开关采用球板电极结构,球头轴向开激光通孔,高压极为平板电极。开关自击穿电压133kV,抖动263ns。实验研究了激光击穿弧长占据间隙不同比例、不同触发能量和不同触发时刻等因素对触发抖动的影响。结果表明激光触发可将抖动有效减小到30ns以内。触发能量高于19mJ时触发抖动与能量大小关系不大。     

RF breakdown by toroidal helicons

Bounded whistlers are well-known for their efficient plasma production capabilities in thin cylindrical tubes. In this paper we shall present their radio frequency (RF) breakdown and discharge sustaining capabilities in toroidal systems. Pulsed RF power in the electronmagnetohydrodynamic (EMHD) frequency regime is fed to the neutral background medium. After the breakdown stage, discharge is sustained by toroidal bounded whistlers. In these pulsed experiments the behaviour of the time evolution of the discharge could be studied in four distinct phases of RF breakdown, steady state attainment, decay and afterglow. In the steady state average electron density of ≈10¹² per cc and average electron temperature of ≈20 eV are obtained at 10⁻³ mbar of argon filling pressure. Experimental results on toroidal mode structure, background effects and time evolution of the electron distribution function will be presented and their implications in understanding the breakdown mechanism are discussed.     

Influence of Electrode Material on Time Delay of Electrical Breakdown in Gases

A significant correlation between the work function of electrode material and the statistical time delay of electrical breakdown in nitrogen-filled diodes has been established. The results obtained confirm that time delay of electrical breakdown increases with increasing of electrode material work function.     

Electron density decay measurements using the 447.1 nm line of neutral helium

The 447.1 nm line of neutral helium has been used to measure the time-dependent decay of the electron density in the afterglow of a pulsed, atmospheric pressure helium discharge. The technique involves using a shutter which consists of a Pockels cell combined with crossed polarizers to gate the light pulse, allowing observation of the spectrum during various time windows in the discharge.     

Conversion of an atomic to a molecular argon ion and low pressure argon relaxation

The dominant process in relaxation of DC glow discharge between two plane parallel electrodes in argon at pressure200 Pa is analyzed by measuring the breakdown time delay and by analytical and numerical models. By using the approximate analytical model it is found that the relaxation in a range from 20 to 60 ms in afterglow is dominated by Ar+2ions,produced by atomic-to-molecular conversion of Ar+ions in the first several milliseconds after the cessation of the discharge.This conversion is confirmed by the presence of double-Gaussian distribution for the formative time delay, as well as conversion maxima in a set of memory curves measured in different conditions. Finally, the numerical one-dimensional(1D)model for determining the number densities of dominant particles in stationary DC glow discharge and two-dimensional(2D) model for the relaxation are used to confirm the previous assumptions and to determine the corresponding collision and transport coefficients of dominant species and processes.     

Initiation of explosive electron emission in microwave fields

The microwave breakdown has been studied for the case in which it is caused by the heating and subsequent thermal destruction of the micropoints present on the cathode surface subjected to the action of a rapidly varying electric field. The heating of a micropoint by the emission current induced by a microwave field has been numerically simulated using the two-temperature model. The delay time to breakdown has been calculated as a function of the frequency of the electric field oscillation for different micropoint geometries     

Measurements of microwave transmission through a decaying plasmacolumn

We have studied the width and the amplitude of the transmitted radio frequency (RF) pulse, as a function of the afterglow time for argon and nitrogen plasmas. In our study, the neutral gas pressure for the case of argon was 2 torr and that for nitrogen was 0.5 torr. The RF energy of the transmitted pulse was found to reach half of its maximum value for afterglow times of about 0.1 s for argon and about 375 μs for nitrogen     

Analysis of statistical nature of electrical breakdown time delay in nitrogen at 6.6 mbar pressure in presence of positive ions and N(4S) atoms

On the basis of the mean value of electrical breakdown time delay and the standard deviation of electrical breakdown time delay σ dependence on the afterglow period τ, the mechanisms which dominantly influence to breakdown initiation in nitrogen were separated. It was shown that the positive ions formed in mutual collision of long‐lived metastable molecules have a dominant role in breakdown initiation for τ values up to 70 ms. The metastable molecules were derived from previous breakdown and discharge. In this case σ ≪ t_d and the total time delay t_d is approximately equal to formative time t_f which decreases in value with the increase of overvoltage. When positive ions have a dominant role in the breakdown initiation the Gaussian distribution describes data of t_d ≈ t_f very well. For τ > 1 s, N (⁴S) atoms formed in previous breakdown and discharge, have a dominant role in the breakdown initiation. Then, σ ≈ and Laue's distribution, which is valid for statistical time delay t_s, describes t_d data very well (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Leakage currents in thin ferroelectric films

The basic mechanisms of leakage current components of thin lead zirconate titanate (PZT) ferroelectric films grown by the sol-gel method have been studied. Characteristic regions of current-voltage characteristics with different charge transport mechanisms have been determined. It has been shown that there is an intermediate region which separates such regions. In one of them, the leakage current depends on properties of the contact of electrodes with PZT film at low voltages; in the other, the leakage current is controlled by intrinsic properties of the PZT film bulk, and the basic mechanism of charge transport is Poole-Frenkel emission. In the intermediate region, a stepwise change in the current has been observed, which is caused by relaxing breakdown of the Schottky barrier. Time dependences of the leakage currents have been determined. It has been shown that the leakage current decreases with increasing delay time before the Schottky barrier breakdown, and the dependence becomes opposite in character after the breakdown.     

LIBS装置检测赣南脐橙中Cu元素时的参数范围分析

为了提高激光诱导击穿光谱(laser induced breakdown spectroscopy,LIBS)实验装置检测赣南脐橙中重金属元素的检测灵敏度和稳定性,可对检测参数进行范围设定。在初次选定延迟时间参数值后,再在包含初定延迟时间的1.10～1.30 μs范围内细分进行实验。实验得出：在该范围内,延迟时间与信背比和被测元素特征谱线强度的关系曲线上出现了多个峰值,并且这些峰值都比初次的要大,用统计学中的区间估计间接求出延迟时间的置信区间为[1.13,1.25],在置信区间内延迟时间由初定的1.20 μs调至1.14 μs时,相对标准偏差(RSD)由0.103降到0.025。由此表明：设定一个LIBS实验装置的参数范围,在对待测元素检测时可以在这一范围内进行自由调节来提高其检测的精度和灵敏度。     

Influence of voltage pulse shape on the delay time for vacuum breakdown

In this paper expressions are derived for the delay time of vacuum breakdown with voltage pulses of ramp and trapezoidal shape. It is shown that the voltage pulse shape has a considerable influence on the delay time. The results obtained may be useful in experimental investigations of vacuum breakdown.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 105–110, September, 1976.     

快脉冲下有机玻璃击穿特性实验

基于CKP1000脉冲源建立了实验平台,实验获得了单次脉冲、不同脉宽、均匀电场下有机玻璃的击穿场强和击穿时延,对有机玻璃的击穿过程进行了分析。实验脉冲的幅值约为230 kV,前沿760~960 ps,脉宽2.3~4.0 ns（FWHM）,试样的平均厚度为1.1 mm。实验结果表明,随着脉冲宽度从2.3 ns增加至4.0 ns,有机玻璃的平均击穿场强从301 kV/mm降至276 kV/mm,平均击穿时延则基本保持不变,其中前沿760 ps,脉宽约2.3 ns时对应击穿时延的分散性增大。     

Generation of dual pulses of the runaway electron beam current during the subnanosecond breakdown of atomic and molecular gases

With a diaphragm placed behind the anode foil, dual runaway electron beams have been provided in helium, hydrogen, nitrogen, and air under a pressure of several torrs to several dozen torrs and a high-voltage pulse amplitude of about 250 kV. These beams consist of two pulses with commensurable amplitudes with a time interval between them of several dozen picoseconds to several hundred picoseconds. It has been shown that the breakdown of the interelectrode gap at pressures from several torrs to several dozen torrs may occur in different regimes and dual pulses of the electron beam current are registered when the initial current through the gap is below 1 kA. It has been found that a supershort avalanche electron beam that consists of one pulse is generated when the delay of breakdown equals several hundred picoseconds. It has been shown that, when the gas pressure reaches several hundred Torr, including atmospheric pressure, the runaway electrons are detected behind the foil after the termination of the supershort avalanche electron beam pulse.     

百kV/cm场强下SF6气体开关纳秒脉冲击穿场强和时延经验公式

百kV/cm高场强纳秒脉冲条件下,采用J. C. Martin经验公式估算SF₆气体击穿场强时,估算值与实验结果差异显著。为了进一步指导高场强脉冲气体开关设计,为开关工作状态调节提供依据,借鉴经典击穿场强经验公式形式建立了百kV/cm场强下SF₆气体开关纳秒脉冲击穿场强和时延与实验参数之间的关系,基于实验数据拟合形成了修正系数的击穿场强和时延经验公式。研究表明,百kV/cm场强和纳秒脉冲条件下脉冲电压斜率对开关击穿特性有重要影响,击穿场强与击穿时延相互关联。百ns至μs脉冲与几十ns脉冲气体放电机理的区别引起放电过程中击穿时延组成发生变化,导致了经典击穿场强经验公式估算值与实验结果的显著差异。修正系数的击穿经验公式可为电磁脉冲模拟器输出开关提供更为精确的工程设计依据。     

Development of afterglow time test system for nanosecond fluorescent screen of low-level-light image intensifier北大核心CSCD

The time characteristics of fluorescent screen is one of the important parameters to evaluate the performance of image intensifier. At present, there is no measurement method for the afterglow time of nanosecond fluorescent screen of low-level-light image intensifier. Based on the traditional test scheme of image intensifier afterglow time, a afterglow time test system for nanosecond fluorescent screen was developed. This system used a high-speed signal generator with the sampling rate of 250 MHz to complete the excitation of the laser diode light pulse, and a photomultiplier tube was used with the descending time of 0.57 ns to complete the photoelectric conversion of the fluorescent screen light signal. The weak photocurrent signal of μA magnitude was amplified and converted to a single-terminal differential circuit to complete the AD conversion in AD9684. Then the digital luminance information of the fluorescent screen was stored in the double data rate SDRAM (DDR) unit after field programmable gate array (FPGA), and the host computer sent instructions to read the DDR memory. The USB3.0 high-speed transmission protocol was used to transmit data to the host computer. In the data processing, the Kalman filtering and fast finding falling edge algorithm were used to realize the accurate measurement of noise filtering from collected data and afterglow time. The test results show that the proposed afterglow time test system for nanosecond fluorescent screen can effectively test the image intensifier with ultrafast optical characteristics. The afterglow test results of P47 phosphor reaches 118.094 4 ns, and the repeatability reaches 2.08%. © 2022 Editorial office of Journal of Applied Optics. All rights reserved.     

Methane Conversion in the Flowing Afterglow of a Dinitrogen Microwave Plasma: Initiation of the Reaction

The reaction of methane in the nitrogen afterglow is studied by combination of direct measurements and computer experiment. The experimental data were obtained by optical emission spectroscopy of the discharge, by gas chromatography of resulting stable products and by probe diagnostics of charged species in afterglow plasma. The simulation was based on a macroscopic kinetic approach covering 24 species and 61 reactions with input data given by the afterglow experiment. In the present stage of the modelling the initiation of methane conversion was studied. It was found that, contrary to active discharge, in the afterglow plasma the active neutral species (mainly excited dinitrogen molecules) are most important for the dissociation of methane into CH_x and H radicals.     

共线双脉冲激光诱导击穿光谱技术检测铝合金中的Cr和Mn

采用两台波长1064 nm的调Q脉冲Nd ∶YAG激光器和多通道小型光纤光栅光谱仪,建立了一套共线双脉冲激光诱导击穿光谱分析装置。与单脉冲激光诱导技术相比,在最佳双脉冲时间延时8 μs时,Mn I 403.07 nm和Cr I 425.43 nm的光谱强度分别增加了14.3倍和17.2倍,以这两条谱线为分析线,铝合金中Mn和Cr的检测限分别由单脉冲时的73和94.5 μg/g降低至双脉冲时的3.76和4.26 μg/g,检测灵敏度提高了约20倍。     

Investigation of the Influence of Overvoltage,Auxiliary Glow Current and Relaxation Time on the Electrical Breakdown Time Delay Distributions in Neon

Results of the statistical analysis of the electrical breakdown time delay for neon‐filled tube at 13.3 mbar are presented in this paper. Experimental distributions of the breakdown time delay were established on the basis of 200 successive and independent measurements, for different overvoltages, relaxation times and auxiliary glows. Obtained experimental distributions deviate from usual exponential distribution. Breakdown time delay distributions are numerically generated, usingMonte‐Carlo method, as the compositions of the two independent random variables with an exponential and a Gaussian distribution. Theoretical breakdown time delay distribution is obtained from the convolution of the exponential and Gaussian distribution. Performed analysis shows that the crucial parameter that determines the complex structure of time delay is the overvoltage and if it is of the order of few percentage, then distribution of time delay must be treated as an convolution of two random variables. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Pressing to the extremes

In the last decade the study of ion-neutral reactions has been dramatically advanced by the development and energetic exploitation of the steady-state flowing afterglow method by Eldon Ferguson and his colleagues at the National Oceanic and Atmospheric Administration (NOAA), Boulder, Colorado. This new technique has provided a very large number of ion–molecule rate coefficients for reactions at thermal energy.

In this method a fast flow of carrier gas (usually helium) is established in a long flow tube, the reactant ions (A⁺) are generated near the gas input end of the tube (the excitation region) and these ions are carried along the tube in the carrier gas flow. The neutral reactant (B) is introduced into the flowing gas stream near the mid-point of the flow tube so that the reaction A⁺+ B →products, takes place along the remainder of the tube length (the reaction region). The reactant ion A⁺ and any ions produced in the reaction are monitored by a mass spectrometer located at the gas exit end of the tube. The variation of the A⁺ mass spectrometer signal as a function of neutral reactant injection rate B yields the rate coefficient k for the reaction if gas flow rates and tube dimensions are known.

The great advantage and versatility of the steady-state flowing afterglow system lies primarily in the separate control that can be exercised over the ions and the neutrals prior to the reaction and also to the fact that the atomic processes occurring in the afterglow are susceptible to many diverse forms of investigation such as emission and absorption spectroscopy, laser spectroscopy, microwave interferometry and Langmuir probes, as well as mass spectrometry. Furthermore, chemically unstable neutral particles can be readily studied in these systems.