Average current per vacuum-arc cathode spot and spot velocity in a magnetic field on a CuCr50/50 nanocomposite

It has been shown that such cathode spot characteristics as the average current per spot and its dependence on tangential magnetic-field induction B _t and the spot velocity and its dependence on B _t for two CuCr50/50 specimens with very different structures (nanocomposite and “solid-state sintered” composite) almost coincide if the surface of contacts has been totally remelted before measurements with the use of moderate arc currents in the process of conditioning.     

Dynamics studies of cathode spots in a vacuum-arc discharge with ring electrodes

The effect of an external pulse magnetic field with axial and radial components on electric characteristics of the discharge and the configuration of cathode spots of a vacuum arc discharge with ring electrodes is studied experimentally. For arc currents within the range of 0.05–2 kA, shots of the cathode spots at different instants of time are obtained. The dependences of the number of the spots on the discharge current and the mean current per spot are determined. It was found that the expansion rate of the cathode spots area depends significantly on the instant value of the discharge current. It is shown that, when the pulse magnetic field is applied, the discharge voltage increases and the discharge current and number of the cathode spots decreases. It was found that the current interruption is a probability process. The probabilities of the current interruption depending on the maximal value of the external pulse magnetic field induction are determined.     

The effect of pulsed vacuum-arc discharge on the surface of elements of a discharger

Regularities of erosion and transport of the material of discharger elements have been studied by the methods of surface structure visualization and X-ray fluorescence elemental microanalysis. Microrelief and oxide film on the surface of cathode material are found to affect the development of arc discharge in a commutator.     

An experimental study of the dynamics of formation of plasma in a vacuum-arc discharge

An experimental study is made of the dynamics of formation of plasma in a vacuum-arc discharge (VAD) at different currents and different transverse dimensions of CuCr50 electrodes. High-speed multipleframe photography is used to obtain the time dependence of the current channel diameter and determine the rate of plasma expansion. It is demonstrated that the rate of expansion under the experimental conditions is independent of the discharge current, as well as of the presence or absence of external axial magnetic field. Two modes are identified, which differ from one another by the rate of expansion. Experiments are performed with anodes and cathodes of different diameters in the range of currents from 2 to 15 kA. It is demonstrated that, with electrodes of different sizes, a discharge initiated at the cathode center expands with time to the size of the smaller electrode while retaining the cylindrical shape. The anode temperature is calculated for two modes in view of the variation of the source power and of the transverse dimension of the zone of heating. It is demonstrated that the anode spot in the mode of rapid expansion is formed under insignificant heating of the anode. In the case of slow expansion, a strong heating of the anode is possible, under which its intense evaporation occurs. The anode temperature is calculated in view of the evaporation losses for modes with different numbers of jumpers arising as a result of the breaking of vacuum switch contacts.     

An experimental study of the effect of nonuniform axisymmetric magnetic field on the breaking of the current of a vacuum-arc discharge

An experimental investigation is made of the effect of breaking of current in a vacuum-arc discharge as a result of superposition of a pulsed axisymmetric magnetic field with longitudinal and transverse components. A study is made of the dependences of the probability of breaking of current on the current magnitude, the pulse amplitude of the magnetic field, and the value of emf of the electric circuit in the current range of 100 to 600 A. The main factors affecting the probability of breaking of current are analyzed.Translated from Teplofizika Vysokikh Temperatur, Vol. 42, No. 6, 2004, pp. 850–855.Original Russian Text Copyright © 2004 by E. F. Prozorov, K. N. Ulyanov, and V. A. Fedorov.     

The effect of axisymmetric two-dimensional magnetic field on the configuration of vacuum-arc plasma

An experimental investigation is made of the effect of axisymmetric two-dimensional magnetic field on the forming of plasma and on the configuration of cathode spots in a vacuum-arc discharge. It is demonstrated that a magnetic field with a transverse (relative to the discharge axis) component has a significant effect on the shape of plasma column and on the rate of expansion of the cathode spot region. In a magnetic field, arc plasma has the form of truncated cone expanding toward the anode. The cathode spots take up a part of the cathode area which decreases with increasing magnetic field. Arguments are given in support of the assumption that the arrangement of cathode spots and the form of arc plasma are defined by the minimum principle similar to the Steinbeck principle. In so doing, the displacement of spots is caused by their emergence in a new region corresponding to a lower arc voltage. Also discussed is the mechanism associated with retrograde motion of cathode spot in view of the effect of azimuthal magnetic field on the axial component of current and of the effect of axial magnetic field on the azimuthal component of current.     

The effect of VAR process parameters on white spot formation in INCONEL1 718

A 20 inch diameter VAR ingot of Inconel 718 was produced at Special Metals Wiggin Limited (Hereford) under conditions of abnormally long arc gap. It was sectioned and analyzed in the as-cast state. White spots were found, along with unusual macrostructural features at the ingot surface. The experimental results are presented and discussed in relation to possible formation mechanisms, and it is shown that the level of niobium found in these white spots was too low to be explained by conventional mechanisms of formation.     

影响铝阳极在NaCl溶液中放电性能因素的研究

为了减缓铝空气电池中铝阳极的自腐蚀及Cl-的腐蚀,在电解液中添加CeCl3可有效控制铝阳极的腐蚀.采用电化学阻抗谱(EIS),结合铝阳极双层模型,研究了缓蚀剂CeCl3浓度、含有CeCl3电解液的温度、pH值对铝阳极放电性能的影响,确定了铝阳极最佳放电条件:缓蚀剂CeCl3的浓度为500 mg/L,含有CeCl3电解液的温度为30℃,pH值在5～6之间.组装模拟电池进行放电性能测试,放电曲线表明,铝阳极在含有缓蚀剂CeCl3的3.5%NaCl溶液中的放电性能远好于在空白溶液中的性能.     

Minimum voltage principle in the theory of a high-current vacuum-arc discharge

The effect of an inhomogeneous magnetic field with axial and radial components on the structure of a high-current vacuum-arc discharge (VAD) has been theoretically studied. The characteristic features of current passage in a short VAD are considered using analytical expressions for the slope of the total current lines (TCLs) relative to the discharge axis, the axial components of the electric and magnetic fields, and the effective conductivity of discharge plasma. A two-dimensional mathematical model has been used to calculate the TCL shapes and the discharge voltage for various dimensions of the region of cathode spots. Calculations showed that the voltage drop on the discharge gap as a function of the arc discharge radius on the cathode has a minimum. The shape of TCLs and the arc radius on the cathode at this minimum agree with the available experimental data.     

The hydrodynamic theory of a positive discharge column in an axial magnetic field

The influence of an axial magnetic field on the performance of a low-pressure cylindrical positive discharge column is studied from the hydrodynamic point of view. It is shown that the magnetic field affects the distribution of the plasma density, its speed, and the energy of electrons. The energy of electrons, the concentration and the speed of plasma, and the azimuth speed of electrons and ions as functions of the radius have been found for a helium atom in a magnetic field of varying intensity. It has been noticed that the electron and ion azimuth movement equations should account for inertia. The obtained hydrodynamic results significantly deviate from the ones obtained in the wide-spread diffusion model of a positive column. It is shown that the distribution of plasma concentration and the radial speed in the positive column are generally close to the results using the diffusion approach, if the axial inductance of the magnetic field and the gas density are increased. However, major differences are found near the walls.     

A theoretical study of the impact of magnetic field of Hall current on the parameters of a high-current vacuum-arc discharge

It is demonstrated that the magnetic field of Hall current in a short high-current vacuum-arc discharge significantly distorts the external axial magnetic field and affects the distribution of current density in the discharge gap. This effect decreases with increasing external magnetic field, with decreasing arc current, and with decreasing ratio of the length of discharge gap to its transverse dimension. A 2D magnetohydrodynamic mathematical model is used to calculate the discharge parameters for different values of induction of external magnetic field. The calculation results are compared with similar results obtained using a 1.5D model in which the impact made by magnetic field of Hall current is ignored. It is inferred that the simpler 1.5D model may be employed in calculations of parameters of vacuum arc in a wide range of variation of arc current and of induction of external magnetic field.     

The effect of a magnetic field on the resistance between electrodes in a current-conducting channel with an anisotropic medium

An electrical network is used to model the function of the resistance between electrodes of various shapes in a current-conducting channel with an anisotropic medium.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 15, No. 5, pp. 918–921, November, 1968.     

The volt-ampere characteristics of a DC arc plasmatron with a distributed anode spot

A new DC plasmatron with a hot rod cathode and cold nozzle anode was proposed and tested at atmospheric pressure, generating nearly spectrally clean plasmas of air, air/diesel fuel mixture, oxygen, and CF₄. The arc Volt-Ampere characteristic (VAC) is an integral indicator reflecting the general behavior of all the arc parts, among which the most important are the by-electrode layers and positive column. The sensitivity of the VAC to the gas flow velocity in the technologic channel confirmed the external vortex nature of the anode arc spot, which does not hide inside the anode orifice, but exits it and interacts with the gas flow.     

The two-dimensional structure of the Penning discharge in a cylindrical chamber with axial magnetic field at a pressure of about 1 Torr

The stationary Penning discharge has been numerically simulated using the diffusion–drift model in the pressure range p = 0.5–5 Torr at emf E of 100 and 200 V. The two-dimensional electrodynamic-discharge structure has been investigated in the calculation region between a cylindrical anode and two flat disk cathodes. Configurations of the discharge plasma and averaged azimuthal motion rates of electrons and ions have been obtained. The evolution of the plasma configuration at a change in pressure, emf, and magneticfield induction is discussed.     

The effect of cathode deuteration on the parameters of vacuum-arc plasma

We propose a model for determining the influence of the relative content of deuterium in a zirconium cathode on the properties of vacuum-arc plasma. It is shown that the occlusion of deuterium in the cathode leads to an additional energy consumption for its ionization and to the related decrease in the average charge of cathode material ions in the discharge plasma. Deuterium in the cathode spot is fully ionized, and the drift velocity of deuterium ions almost coincides with that of ions of the cathode material.     

The mechanism of liquid metal jet formation in the cathode spot of vacuum arc discharge

We have theoretically studied the dynamics of molten metal during crater formation in the cathode spot of vacuum arc discharge. At the initial stage, a liquid-metal ridge is formed around the crater. This process has been numerically simulated in the framework of the two-dimensional axisymmetric heat and mass transfer problem in the approximation of viscous incompressible liquid. At a more developed stage, the motion of liquid metal loses axial symmetry, which corresponds to a tendency toward jet formation. The development of azimuthal instabilities of the ridge is analyzed in terms of dispersion relations for surface waves. It is shown that maximum increments correspond to instability of the Rayleigh–Plateau type. Estimations of the time of formation of liquid metal jets and their probable number are obtained.

     

Visualization of the process of metal heating and melting in the anode zone in an arc discharge with a tungsten electrode

Pictures of an electric arc burning in argon, obtained by means of a digital camera, within the different domains of wavelengths of the visible spectrum are presented. Maps of the thermal fields of the heating spot are plotted, and the plasma temperature in the anode arc zone is calculated. The application potential of the digital image technology in the visible wavelength domain for analysis of the processes directly in the anode arc zone and for estimation of the arc column parameters is shown.     

Electron kinetics in the anode region of glow discharge in crossed electric and magnetic fields

The anode region of dc glow discharge in a coaxial structure has been studied upon the application of a magnetic field, which is crossed with the electric field at the anode. The radial potential profiles (anode fall) and electron distribution functions (EDFs) have been determined. The magnetic field application changes the sign of the anode fall and leads to modification of the potential profile and the EDF.     

The formation of accelerated electrons and their effect on the structure of nanosecond discharge with slot cathode

Experimental investigations are performed of the current-voltage characteristics and spatial distribution of optical radiation of plasma within the cathode cavity and in the discharge gap under conditions of transverse nanosecond electric discharge with a slot cathode. The investigations are performed in helium in the gas pressure range from 1 to 100 torr. It is demonstrated that the cathode layer is formed at the initial stage of discharge and that the electrons accelerated in the narrow cathode region pick up energy of the order of 1 keV. The efficiency of electron beam generation is estimated, and the mechanisms of generation of fast electrons are identified. The free paths of accelerated electrons in plasma under different initial conditions are determined, and the mechanisms of relaxation of energy of this group of electrons are analyzed. The correlation is established between the special features of relaxation of energy of fast electrons and the formation of the structure of beam-plasma discharge with a slot cathode.     

Formation of dense electron beams in a gun with a plasma anode based on a reflecting discharge

A method of obtaining low-energy, high-current electron beams in a gun with a plasma anode based on a reflecting discharge is proposed and implemented for the first time. Pis’ma Zh. Tekh. Fiz. 23, 42–46 (May 26, 1997)