Erosion of a Copper Cathode in a Nonstationary Arc Spot. III. Generalization of Experimental Results and Modeling of the Influence of Velocity on Erosion

An extensive amount of experimental material on investigation of the dependence of the erosion of a copper cathode on the main operating parameters — the current, the electrode temperature, and the magnetic field — has been generalized with the use of the thermal macroscopic erosion model proposed earlier. It has been shown that the basic regularities of the erosion, modeled in such a manner, are confirmed experimentally with a satisfactory correlation.     

Erosion of a Copper Cathode in a Nonstationary Arc Spot. II. Determination of the Energy Parameters of the Arc Spot by the Thermophysical Method

The results of investigation of the energy parameters of a nonstationary electricarc spot on a copper cathode in an air atmosphere have been presented. The data published earlier on the thermal voltequivalent of the cathode arc spot have been generalized. A nonlinear dependence of the current density on the magnetic field has been obtained. A comparison of the new results and those obtained earlier on other setups and their generalization have been made.     

Droplet Erosion of a Cathode in a High-Current Vacuum Arc

Technical Physics Letters - It is shown that high-current vacuum arcs accompanied by partial melting of the cathode surface and its droplet erosion can generate, in addition to the well-known...     

真空阴极弧离子镀阴极斑点的移动研究

建立了真空阴极弧离子镀圆形平面靶侧面引弧时 ,阴极斑点的受力模型 ,分析了影响电弧运动的因素 ,改进了圆形平面靶侧面形状 ,大大提高了石墨靶阴极斑点从侧面到靶平面的过渡速度     

Structure of the Welding Arc Cathode Spot with a Nonconsumable Electrode

The cathode spot autographs on a glass surface are investigated through an electron microscope, with a magnification up to 100000. We discover that the welding arc cathode spot consists of separate cells with the substructure, current channels, 10–60 nm in diameter. We acquire color photographs of the welding arc cathode spot with the cathode torch. Photograph processing through different filters reveals the shape of the cathode spot and the cathode torch. We perform the estimate calculations of the current density in the welding arc cathode spot substructure.     

A Stationary Vacuum Arc with a Diffuse Spot on a Nonemitting Chrome Cathode

The results are given of experimental investigations of a stationary vacuum arc with a diffuse spot on a hot cathode of solid chrome in the current range from 20 to 220 A. The characteristics of the discharge are compared to those of a similar discharge on a thermionic gadolinium cathode. It is demonstrated that, in the case of a chrome cathode, mechanisms such as the thermionic emission, ion-electron emission, and photoemission are incapable of ensuring the charge transport on the cathode surface. Our results complement the experimental data obtained by other authors in investigations of arcs of this type and thereby contribute to clarifying the mechanism of charge transport on the surface of a chrome cathode.     

微阴极电弧推力器放电特性研究

相对于大型卫星, 微纳卫星具有模块化、发射灵活、可编队飞行等特点。微阴极电弧推力器 (μ-CAT) 是一种适用于微纳卫星的推进装置, 具有体积小、质量轻、功耗小等特点。本文分析了μ-CAT的工作原理, 对推力器结构进行了设计, 并利用高真空电推进实验平台, 完成了对推力器放电特性实验装置的搭建。在高真空条件下对μ-CAT进行了点火试验, 测试了推力器放电时的伏安特性曲线, 分析了单脉冲周期的电压电流变化规律。随后分别在有无外加磁场的条件下, 采用法拉第探针测量了μ-CAT等离子体离子电流空间分布情况, 实验结果表明磁场具有减小等离子体羽流发散角的作用。研究工作可为后续推力器放电参数优化设计和羽流测量工作提供理论指导。     

Mechanism of Formation of a Cathode Coating in a Carbon Arc

The structure and properties of carbon materials formed in an arc between graphite electrodes in the case of decreased pressure of a buffer gas are considered. A mechanism of formation of a cathode coating by positively charged carbon macroparticles is proposed. The particles melt upon collision with the cathode surface and then the stage of growth of a coating from a liquid phase occurs.     

Structure and Features of the Motion of a Cathode Spot on a Continuous Titanium Cathode

High-speed video filming by the VS-FAST-NG CCD-array-based video camera from the firm of Videoskan with speeds of 1000 and 5000 frames per second and exposure time of 1·10⁻³ and 2·10⁻⁴ sec, respectively, is conducted. It is established that the arc burns from two or three cathode spots for (1–1.2)·10⁻³ sec. The mean and local speeds of the group of cathode spots are determined. If there is no external magnetic field present, the mean speed is equal to 5–6 m/sec. If there is a magnetic field B = 0.005 T present, the mean speed is equal to 15–16 m/sec. __________ Translated from Izmeritel'naya Tekhnika, No. 10, pp. 42–44, October, 2005.     

Determination of Thermal Diffusivity by Nonstationary Spot Heating

Technical Physics Letters - A thermographic express method for determining the coefficient of thermal diffusivity (a) of platelike objects is presented. It may be regarded as a modification of, and...     

Cathode Spots of Vacuum Arc Discharges

Vacuum arc discharge is used for formation of pure metal and complex combined coatings, and also for the impact of the discharge on a surface to remove superficial contaminants. Physical processes observed in an arc discharge are mostly determined by the behavior of cathode spots, which are fundamentally unstable plasma formations and are characterized by a certain value of average lifetime. Reliable stabilization of the cathode spots and controlling their movements on the working surface grants the technology a grater importance in application.     

Conditions of Burning of an Arc with a Recoverable Carbon Cathode

A system of equations of integral balances are solved simultaneously with a heat problem in order to determine the parameters of the cathode region of an arc with a recoverable carbon cathode formed from a plasma-generating medium. The solution corresponding to the conditions of recovery is identified in the set of solutions of this system of equations, obtained by varying the input parameters. It is demonstrated that only one solution out of this set corresponds to the mode of carbon cathode recovery, which is indicative of the sensitivity of the recivery mode to the arc parameters in actual practice.     

Cathode Drop of the Potential of a Vacuum Arc of Metals

The basic mechanisms of ionization in the cathode spot of a vacuum arc are considered. It is shown that the singly charged positive ions formed here are a result of the collision ionization of the evaporated atoms of a metal by electrons. On this basis the assumption is made that the cathode drop of the potential of the vacuum arc of metals is determined by the energy of ionizing electrons at which the ionization section attains its maximum.     

一种精确的光点测试系统

介绍了一种精密光点测试系统。它采用脉冲方法刷新光点,并且刷新频率和电源频率保持同步,从而避免了扫描及视频方法引起的测量误差,同时避免了散逸电磁场的影响;并克服了采用扫描光栅、通过信号发生器或者测试软件产生测试信号来进行测试的系统存在的问题。该测试系统尤其适合电子枪和偏转线圈设计人员进行精密的光点测试分析。     

Numerical Investigation of the Effect of the Cathode Geometry on the Characteristics of an Electric Arc

The effect of the cathode geometry on the characteristics of an electric arc is treated. It is found that the characteristics of plasma in discharges with cathodes of different geometry (cone, sphere, cylinder) are almost the same on condition of equality of the areas of current-conducting surfaces. It is assumed that a ring-shaped arc discharge may be realized in the case of axisymmetric arc spot on the external side surface of a cylindrical cathode.__________Translated from Teplofizika Vysokikh Temperatur, Vol. 43, No. 3, 2005, pp. 359–366.Original Russian Text Copyright © 2005 by R. M. Urusov and T. E. Urusova.     

Investigation of CTARA wood-burning stove. Part I. Experimental investigation

This paper describes experimental investigation of a single pot wood-burning stove developed atCtara. The stove incorporates features such as a converging combustion space, a grate, preheated secondary air and a swirling-device. Using chipped wood and a large diameter vessel (30 cm), efficiencies in excess of 40% have been measured. An electric stove, having a geometry similar to that of the woodburning stove, has also been experimented with to obtain magnitudes of heat transfer coefficient at the vessel bottom, to estimate relative contributions of convection and radiation heat transfer to the vessel bottom, to study the effect of flame to grate heat release ratios and to study the effect of depth of insertion of the vessel into the stove. Finally, a 3-pot mud stove used in the Konkan region is investigated and it is shown that provision of a grate improves the efficiency of the stove.     

Laser Spot Welding of Thermoplastic and Ceramic: An Experimental Investigation

Laser welding of dissimilar materials classes has vast potential in a variety of applications due to the non-contact nature of the process. This study investigates the effects of CO₂ laser process parameters on the characteristics of spot welded joint between ceramic and thermoplastic. Using a full-factorial design an experimental investigation is carried out studying the effect of welding parameters (laser exposure, number of spots, stand-off distance) on the tensile strength and the diameter of spot weld. The study reveals an increase of joint tensile strength with the increase in the number of spots and the duration of exposure. However at low laser power, the effect of stand-off distance on the spot weld diameter is found to be inconclusive. Optimal process parameters are estimated using the multi-objective optimization on the basis of ratio analysis. The analysis shows that the higher number of spots and the longest duration of laser exposure result in optimal weld characteristics. Alongside these conditions, a larger stand-off distance is seen to have beneficial impact on the weld characteristics.     

Experimental Investigation of Wire Arrangements for Narrow-Gap Triple-Wire Gas Indirect Arc Welding

A new narrow-gap welding process is proposed by applying triple-wire gas indirect arc (TW-GIA). There are double power supplies and triple wires in this system. Power supplies are only connected between electrode wires and base materials are not linked to power supplies. Since there are different wire arrangements with TW-GIA, this article studies these wire arrangements and their effects on sidewall fusion for narrow-gap welding. Results show that different wire arrangements lead to variant arc behaviors and metal transfer, and consequently they lead to different situation of sidewall fusion. The heat to melt sidewalls is mainly from the indirect arc column and metal transfer with narrow-gap TW-GIA. When side wires deviate from the main wire to opposite directions, heat from arc columns and metal transfer can concentrate toward groove sidewalls. When the whole weld torch is lowered, heat from the indirect arc column and metal transfer increases at the weld bead root.