Formation of a cathode crater in a low-voltage cold-cathode vacuum arc

The cathode crater in a low-voltage cold-cathode vacuum arc is planar. The area of the crater and the density of the current flowing through it depend on the thermal and electrical properties of the cathode metal. Pis’ma Zh. Tekh. Fiz. 24, 14–19 (July 12, 1998)     

Singularities of interaction between a cathode stream and anode vapors in a vacuum arc: Numerical simulation results

Numerical simulation is performed of the process of interaction of cathode and anode ions in a highcurrent vacuum arc with evaporating anode. The presence of the friction force between ion flows, as well as of the friction work, leads to heating and acceleration of slow anode ions and deceleration of fast cathode ions. The boundaries of stable passage of current are determined, associated with the presence of the limiting value of density of anode vapors     

The formation and structure of current cells in a vacuum arc cathode spot

A physical model describing the structurization and localization of electric current in the surface layer of a cathode in the initial stage of a vacuum arc discharge is proposed. According to this model, each current cell on the cathode surface represents a dislocation cell containing a ring electron vortex with the axis perpendicular to the electrode surface. It is shown that localization of the electric current at the vortex center leads to the formation of a spatial structure of hot spots acting as precursors of the explosive emission centers, the dynamics of which determines operation of the vacuum discharge.     

Thermionic valve effect and cathode crater rhythm in a low-voltage cold-cathode vacuum arc

A vacuum arc with a cold cathode burns rhythmically. The period of the rhythm is determined by a thermionic valve effect which occurs between the hot crater and the cold cathode as a result of the brief retention of the heat in the crater by the oppositely propagating electron flux. Pis’ma Zh. Tekh. Fiz. 24, 67–72 (July 26, 1998)     

Grain structure in cathode spot trail of low vacuum arc discharge

Low vacuum arc discharge treatment in 10 Pa is applied to cleaning of a stainless steel plate, the surface of which is covered with an oxide layer. During the discharge, several luminous cathode spots move continuously in random directions on the surface of the stainless steel plate. They remove the oxide layer owing to their high energy density and leave their trail on the sample surface. Microscopic observation reveals a chain structure of metallic grains along the center of the cathode spot trail. Some chemical agents put on the oxide layer before cleaning affect on the size and the number density of the grain, which leads to the different surface roughness after treatment.     

Change in cathode spot behavior in vacuum arc cleaning with application of polyethylene glycol

The authors investigated the effect of polyethylene glycol (PEG) application on the oxide removal action of cathode spots. Experimental observations revealed that the cathode spots formed on the oxide layer on the metal surface can be classified into two different sub-types, slow cathode spot (SCS) and fast cathode spot (FCS). Two different sub-types of cathode spots could exist in a same test piece at a same time. The removal rate of oxide depends on the mixture ratio between FCS and SCS. The more the cathode spots belonged to FCS, the faster the oxide layer is removed. The application of PEG enhances the probability of the presence of FCS.     

Influence of the nonideality of near-cathode plasma on the current density in the cathode spot of a vacuum arc

The conductivity of a nonideal plasma is estimated at concentrations of the order of 10²¹ cm⁻³ and temperature of (1.12–3.48)·10⁴ K (1–3 eV). The influence of correlation effects is considered. The conductivity calculated from the Spitzer formula is shown to be higher over the range of temperatures indicated than that of nonideal plasma for the same values of the pertinent parameters. Translated from Izmeritel'naya Tekhnika, No. 5, pp. 46–48, May, 1995.     

A vacuum arc plasma source with extended design

A vacuum‐arc plasma source having an extended design, operating in pulse regime and generating directed conveyer‐type flow was created and investigated. The identified regularity of development of arc discharge allowed controlling generation modes of the plasma source, providing the secure fixation of the cathode spots on the working surface and accelerated conversion of the cathode in the working mode. In this case each stage of development of arc discharge is determined by the conditions of existence of the cathode spots on the working surface of the cathode.     

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.

     

A scanning electron microscope study of the role of copper oxide layers on arc cathode erosion rates

The results are described of scanning electron microscopy of copper surfaces covered initially with oxide films of thickness from 2.5 to 340 nm, which have been the cathodes of electric arcs. The objective of the work has been to learn more about the mechanisms of electrical conduction through oxide films on non-refractory arc cathodes, electron emission into the arc and the erosion of the cathode. It is the latter aspect upon which this paper concentrates. Cathode erosion is a major problem when arcs rotate over electrode surfaces for very long times in certain industrial processes. Erosion rates are calculated here using SEMs, both for stationary 4.5 A arcs of duration 1ec, and for higher current arcs which were magnetically driven once over the cathode surface. Making allowance for the effect of current, these erosion rates are shown to be similar in magnitude and in their variation with oxide thickness, and reasons for this are given. Comparison is then made with erosion rates measured by weight loss for long-duration rotating arcs. In the light of the new data given here, it is now possible to understand better the remarkable changes which have occurred for long-duration arcs when varying arc velocity, water-cooling flow rate and arcing duration.     

Effect of tangential magnetic field on ecton processes in cathode spot of vacuum arc

Emission and erosion processes involved in the final stage of the cathode spot cell operation in vacuum arc in the presence of an external magnetic field have been numerically simulated. It is established that the application of a magnetic field leads to asymmetry in the distributions of current density and heat flux, so that their maxima shift in the “anti-Ampere” direction. For more detailed analysis of the phenomenon of retrograde motion of the cathode spot in a magnetic field, it is necessary to study the behavior of a liquid metal phase in the spot.     

Deposition of cathode carbon films in the plasma of a low-current gas discharge at atmospheric pressure

Plasma-chemical deposition of carbon films is carried out under the conditions of an atmospheric-pressure dc discharge from a mixture of hydrocarbons (methane and butane–propane) with helium on substrates (Ni and Cu) that serve as the cathode in the process of discharge. The formation of predominantly disordered films from graphite crystallites is observed at small deposition times. An array of carbon nanotubes coated with structured carbon is formed, as the duration of deposition increases; layers of graphitized scales are formed along the film’s edges.     

Dynamics of cathode spots in an axial magnetic field on the fall of a current pulse in a high-current vacuum arc

The cathode attachment of a high-current vacuum arc on the fall of a current pulse was studied. Contacts generating an axial magnetic field were used. The revealed transformation of the attachment shape near zero current was explained quantitatively in a way that was in satisfactory agreement with experimental results.     

The preparation and blood compatibility of pure iron thin film using filter cathode vacuum arc

用磁过滤阴极真空弧源法在单晶硅基片上制备纯铁薄膜,分析了薄膜表面的组成、元素价态和薄膜的物相结构,研究了薄膜的腐蚀降解行为和抗凝血性能. 结果表明:具有纳米晶粒的纯铁薄膜其腐蚀速率低于普通晶粒的纯铁,在纯铁薄膜表面粘附的血小板数量少于316L不锈钢, 且激活和团聚比较轻微,增生的伪足数量比较少;纯铁薄膜表面对血浆中的凝血因子激活比较轻微,具有较好的抗腐蚀性和血液相容性.     

Investigation of the parameters of a nonstationary arc spot on a copper cathode by the thermospectroscopic method. I. Current density

A new procedure of determination of the effective density of the current in a nonstationary arc spot with the use of thermophysical and spectroscopic measurements has been proposed and tested. The procedure is based on recording of the critical cathode temperature corresponding to the instant of sharp increase in the intensity of the CuI = 5218 Å atomic spectral line, which coincides with the beginning of intense emission of a copper vapor from the spot, according the hypothesis proposed. New results are compared to those obtained earlier by purely thermophysical methods.__________Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 1, pp. 159–166, January–February, 2005.     

Continuous calibration of a vacuum ultraviolet system from 65 to 125 nm by a cascade arc and comparison with the calibrated line radiation of a hollow cathode

A high-power stationary helium cascade arc has been developed as a standard source for continuum radiation in the VUV spectral range from 65 to 125 nm. The calibration of the VUV system response was based on the calculated and measured continuum radiation of a 2-mmphi pure He arc. Diagnostics of the arc plasma in partial thermal equilibrium yielded the electron density and the temperature that were inserted in the calculations of the continuous radiation. The results were compared with the helium, argon, and krypton radiation lines of a high-current hollow cathode lamp. This lamp was built according to the construction drawings of a hollow cathode, which was calibrated by means of the electron synchrotron radiation at the Physikalisch Technische Bundesanstalt Berlin.     

TC4合金空心阴极真空焊接熔池动态行为的数值模拟

建立了空心阴极真空电弧焊(Hollow Cathode Vacuum Arc Welding, HCVAW)焊接TC4钛合金板(5mm厚)熔池中流体流动和传热过程动态行为的物理、数学模型,并对焊接过程进行了数值模拟计算和工艺试验、通过计算,找出了焊接速度和焊接电流等工艺参数对焊缝成型的影响规律,并计算出焊接过程中工件上的温度场分布和熔池中的流场分布,计算结果与实验结果基本相符.