Ferrite-induced breakdown. Mechanism of induction by thermal surface explosion

The conditions are investigated for gas breakdown above an Ni–Zn (M4OONN) ferrite surface. The assumption that the discharge is initiated by a thermal explosion of a surface layer of the ferrite modified by current flowing through it is verified experimentally and theoretically. The electric and thermophysical properties of the (ferrite+annealed layer) system are determined. The experimentally observed temporal characteristics of the prebreakdown phase of the discharge and the dependences of the breakdown voltage on the discharge-circuit parameters are described within the framework of a single model.Translated from FIAN Preprint No. 120, Lebedev Physics Institute, Moscow, 1990.     

Variations in the electron energy distribution function in discharge plasma of a unipolar gas breakdown

It is experimentally demonstrated that the electron energy distribution function (EEDF) and electron density in plasma of a little-studied pulse discharge of a unipolar gas breakdown (UGB) significantly vary in time. The revealed behavior of its plasma parameters is explained based on the proposed physical model of a UGB discharge.     

Investigation of a single dielectric barrier discharge in submillimeter air gaps: Uniform field

The characteristics of a single discharge in 0.01–0.2-cm air gaps are investigated under atmospheric pressure between the metal electrodes and in the presence of a polymer barrier on one of the electrodes. The experimentally determined surface charge density distributions are satisfactorily described by a 2D Gaussian function with the proposed parameters. In the uniform field, the breakdown voltage weakly depends on the presence of a dielectric barrier. At the same time, the change from the positive to negative polarity of the metal electrode leads to a manifold increase in the discharge current and in the surface charge. The breakdown occurs under considerable overvoltage; the estimates indicate the streamer mechanism of the breakdown.     

Dynamics of an RF Discharge in a Magnetic Field under Strong Initial Preionization

We demonstrate experimentally the possibility to create and sustain a strongly ionized plasma at low gas pressures by the electromagnetic radiation of the intensity which is below the conventional breakdown level. The conditions of ignition and sustaining the plasma are found, and the plasma parameters are measured. The necessary condition for the discharge formation is strong preliminary ionization of an initial gas. Significant electron heating in the RF field, which ensures the effective gas ionization takes place due to Coulomb collisions with protoplasma ions. Such collisions are much more frequent than the electron-neutral collisions. We propose a qualitative analytical model of the discharge evolution, which describes the effects observed.     

横向表面放电光泵浦源特性研究

 介绍了一种用以泵浦XeF(C-A)激光的横向表面放电辐射源,比较详细地研究了这种泵浦源的放电击穿特性、放电电流与充电电压及不同气体介质的关系、表面放电均匀性以及不同气体成分对表面放电辐射特性的影响。得到了放电击穿时间、放电峰值电流随充电电压、不同气体介质变化的曲线;分析了提高放电均匀性的途径,在电极长50cm、间距6cm、充电电压25kV条件下获得了均匀放电。获得了各种实验条件下放电辐射的光谱曲线;通过对辐射光谱的分析,研究了有利于光解离XeF₂的最佳实验条件,当p_Ar:p_N2=1:1时,放电在远紫外波段产生的辐射最强。     

Breakdown in air in a rising microwave field

Results are presented from studies of a high-pressure electrodeless breakdown in air at the focus of a standing wave in a high-Q quasi-optical two-mirror resonator pumped by single microwave pulses. In the experiment, the breakdown occurred at the front of the pulse of the resonator field. The breakdown field substantially exceeded the critical level and, under fixed conditions, showed a scatter from pulse to pulse. It is shown that the experimentally found excess in the threshold breakdown field over the critical level is due to the fact that the resonator field increases as a discharge plasmoid forms during breakdown and that the appearance of an electron initiating breakdown in a gas is a random event.     

Analysis of time-dependent characteristics for a pseudosparkdischarge in air

The time-dependent resistive voltage and resistance of a pseudospark discharge in air are obtained by solving the equivalent circuit equation using the measured values of the discharge current and breakdown voltage. Pulsed, underdamped discharge currents ranging from about 30 to 100 A are investigated experimentally. The gas pressures range from 0.005-0.1 torr. The discharges can be characterized by three phases: initial, quasi-stationary, and relaxation. The quasi-stationary phase occurs near the time of the current maximum. The variations of the resistive pseudospark voltage are similar to those observed in a spark discharge, which can explain the sparklike behavior of a pseudospark discharge. Details of the current-voltage characteristics and resistance are presented     

A modified Paschen law for the initiation of a dc glow discharge in inert gases

Breakdown of inert gases in a homogeneous dc electric field is studied experimentally and theoretically at various distances L between the electrodes and radii R of the discharge tubes. It is shown that, for arbitrary geometric dimensions of the discharge chamber and cathode materials, the ratio of the breakdown electric field strength to the gas pressure holds constant at the breakdown curve minimum. A modified Paschen law is obtained, according to which the breakdown voltage is a function of both the product of the gas pressure by the distance L and the ratio L/R.     

托卡马克装置的击穿条件

在CT-6B托卡马克实验装置上研究了充气气压、环向磁场、杂散磁场、环电压等放电条件对击穿的影响。发现垂直方向和水平方向的杂散磁场对击穿影响不同。指出实验结果与汤生放电模型的偏离。用Monte-Carlo方法解出击穿阶段电子分布函数,对汤生模型公式作出修正。 关键词：     

The existence of two forms of unipolar gas-breakdown discharge

The existence of two forms of unipolar gas-breakdown discharge that depend on the pulse-repetition frequency and the polarity of high-voltage pulses is experimentally revealed. These two forms differ in their intensities, the distribution of luminescence on the discharge length, and their volt-ampere characteristics. The transition from one discharge form to another proceeds in a narrow frequency range and is caused by the breakdown of the near-electrode layer in some critical field under the inclusion of ion-electron emission process. The transition frequency increases with the growth of the gas pressure and a decrease of the pulse amplitude. The development of discharge instability and the hysteresis of its parameters are observed in the transition area.     

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.     

Electromagnetic radiation sources based on a low-inductive extended z-discharge

Model sources of electromagnetic radiation based on a low-inductive extended z-discharge are studied experimentally and numerically. The discharge is initiated by a high-voltage pulse generator through a long transmission line. It is shown that using a sliding discharge traveling wave, one can provide electrical breakdown of long discharge gaps in a wide range of initial gas pressure and produce a plasma pinch at moderate voltages of the generator. A new nonpinch mechanism of radiation generation is discovered in the soft X-ray range of the spectra. This mechanism offers a higher efficiency of conversion of electrical energy to the energy of an inverted medium.     

Mass transport in a gas discharge

The effect of different parameters on the nature of the axial distribution of atoms evaporated from an electrode in a gas discharge is investigated. Theoretical calculations employing an analytical relation proposed earlier for the atomic concentration have been checked experimentally by changing the transport parameters and the (radial) dimensions of the atomic source. In the first case an arc discharge between graphite electrodes is used, and in the second case a pulsed discharge between metal electrodes, making it possible to localize and vary the dimensions of the source on the surface of the electrode. On the basis of these investigations, the experimentally observed breakdown of proportionality of the atomic concentrations and also the nonlinearity of the calibration graphs used in spectral analysis are explained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 77–80, November, 1973.     

Relation between the distribution of initiation sites of a discharge and the field nonuniformity at an electrode

The connection between the field nonuniformity at an electrode and the distribution of discharge initiation sites over its surface is described. The results of experiments on the breakdown of transformer oil in the cone-plane system of electrodes is analyzed within the framework of a multifractal model of the charge distribution [1]. The conclusion given in [1] that the regions with the maximum local field strength are not always the most probable sites for initiation of a discharge was experimentally confirmed. We observed the theoretically predicted transition of the discharge initiation sites at sharp points on the surface of a cone. For electrodes of stainless steel and transformer oil a value of the index relates the probability of initiation of a discharge to the local field strength was determined.Scientific — Research Institute of High Voltages at Tomsk Polytechnic Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 32–35, April, 1995.     

开放空间重复频率微波脉冲击穿概率理论与实验研究

综合考虑有效初始电子产生理论、雪崩电子击穿理论等过程中的击穿延迟时间,探讨了开放空间微波脉冲的击穿延时概率分布,提出了重复频率微波脉冲击穿概率模型,定义了基于概率模型的微波脉冲击穿阈值。利用S波段微波准光学反射聚焦系统对一定气压大气击穿过程进行了模拟,监测击穿放电发光时刻作为击穿时间,分别在铯137放射源存在与否情况下开展了系列实验。研究结果表明,提高种子电子产生率相较于提高电离率是增大脉冲击穿概率更有效的方法;重复频率过程中,若存在累积效应,击穿延时概率分布曲线将左移并趋于稳定,击穿后的气体在短时间内容易再次击穿。     

纳秒脉冲气体放电机理探讨

 经典Townsend机理和流注理论是气体放电研究的基础,但在解释纳秒脉冲气体放电时均存在一定缺陷。基于经典气体放电理论,探讨纳秒脉冲气体放电机理,分析流注理论判据在纳秒脉冲气体放电中的有效性,解释纳秒脉冲下电子逃逸现象和基于电子逃逸的快速电离波击穿理论,仿真计算高能快电子的逃逸过程。结果认为基于高能量快电子的逃逸击穿将是可能解释纳秒脉冲下气体放电现象的依据。     

Triggering and guiding of high voltage discharge by using femtosecond laser filaments with different parameters

This paper demonstrates the triggering and guiding of the stationary high voltage (HV) discharges at 5--40 kV by using plasma filaments generated by femtosecond laser pulses in air. A significant reduction of the breakdown voltage threshold due to the pre-ionization of the air gap by laser filamentation is observed. The discharge experiments are performed by using laser pulses with different energy from 15--60 mJ. The electron density of filaments is detected by sonography method. The influence of the electron density of laser filaments on the triggering and guiding HV discharge is experimentally investigated. The results have shown that the behaviour of plasma filaments can strongly affect the efficiency of triggering and guiding HV discharge.     

Modeling of pulsed spark discharge in water and its application to well cleaning

This paper presents a simulation model for the generation of strong pressure wave by means of pulsed spark discharge in water and its application to well cleaning. In the simulation model, one-dimensional time-dependent magnetohydrodynamic equations are coupled to a capacitive discharge circuit equation. A cylindrical conducting spark channel formed by electrical breakdown of water gap between a pair of electrodes is treated as a load of which resistance and inductance are allowed to change with time. For describing the spark channel properties accurately, precise calculations on thermodynamic properties and electrical conductivity are included in the simulation model. The simulation results show an excellent agreement with the experimentally measured shock pressure as well as the current and voltage waveforms. The simulation reveals that Joule heating of the spark channel during the very early phase of electrical discharge plays a key role in the formation of shock wave in water. The voltage on a capacitor at breakdown, the circuit inductance, and the resistance of the spark channel are found to be the most important parameters for the shock wave formation. With this technique, a pilot test for the cleaning of a clogged well has been performed in a water well which was constructed as a test-bed for riverbank filtration near the Anseong-cheon (river) in Korea. Well treatments have been carried out with an electrical energy of 510 J stored on a pulsed power system, at which the maximum shock pressure is measured to be around 7 MPa at the position of the well screen, i.e. 0.1 m away from the spark gap. A slug test shows 2.9 times improvement in the hydraulic conductivity of the well, which, combined with a visual inspection inside the well using an underwater camera, clearly demonstrates that the strong pressure wave generated by underwater spark discharge can effectively remove almost all incrustations formed in the well screen and thus improve well performance. Operating parameters for controlling the strength of shock pressure are discussed using the simulation model for extensive applications of the present technique to various types of water wells.     

The influence of electron density on the formation of streamers inelectrical discharges triggered with ultrashort laser pulses

In an ongoing program using ultrashort laser pulses to provoke discharges in air over considerable distances at electric fields below breakdown threshold, we have studied the conditions for the onset of streamers in such laser-produced plasmas, both experimentally and through numerical simulations. The results demonstrate the importance of the electron density and of its gradient on the generation of streamers. Also, a significant reduction of the breakdown voltage for a 30 cm plane-plane gap in air was observed with a laser pulse energy of 15 mJ. Finally, a direct comparison of laser-induced breakdown in air and in nitrogen shows the influence of electron attachment to oxygen on the discharge process     

气体放电击穿过程的物理和数值研究

本文对低气压（１０＾－２Ｐａ）热阴极气体放电的击穿过程给出了物理描述和相应的双流体数学型，并发展了一种选择和调整未知初始条件的有效算法，可以通过伴随试射法得到对初始条件十分敏感的非线性两点边值常微分方程组的数值解，从而给出这类气体放电中击穿过程的定量描述。