磁控电弧离子镀阴极斑点特性的高速摄影研究

利用高速摄影技术，对磁控电弧离子镀中阴极斑点大小、寿命及运动轨迹进行了观测，获得了阴极斑点电流密度、运动速度随磁场、电弧电流及背景气体压力改变而变化的关系曲线。     

Study on cathode spot motion and macroparticles reduction in axisymmetric magnetic field-enhanced vacuum arc deposition

Cathode spot motion and macroparticles (MPs) reduction on related films are the two main issues in the application of the vacuum arc deposition (VAD). In the present work, an axisymmetric magnetic field (AMF) was applied to the cathode surface to investigate the influence of the AMF on the cathode spot motion and the MPs reduction on TiN films. The results show that the AMF affected the cathode spot motion by redistributing the dense plasma connected with the initiation of the new spot. With increasing AMF, there is an increasing tendency for the cathode spot to rotate and drift toward the cathode target edge. Based on the results of FEM simulation and the physical mechanism of the cathode spot discharge, the mechanism of the cathode spot motion in the AMF was discussed. The morphology, detailed size distribution, and roughness of the resultant TiN films were systematically investigated. Fewer and smaller MPs ejection is observed with an increase in the transverse component of AMF. The effect of the AMF on the MPs reduction on TiN films was discussed, and the results were compared with the theoretical predictions.     

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.     

Retrograde motion of cathode spots of the first type in a tangential magnetic field

We consider the dynamics of dense plasma of an explosive-electron-emission center—a cell of cathode spot of a vacuum arc in an applied magnetic field. It is established that the explosive expansion of plasma in a transverse magnetic field induces an electric field and an associated current. It is shown that this current initiates the cells of cathode spots of the first type in the direction opposite to the Ampere force action. In this case, the ignition time of a new spot does not exceed a few nanoseconds at a magnetic field of a few kilogauss.     

Singularity in the current density distribution at the boundary of emitting region on a flat cathode surface

The process of electron emission from the boundary of regions with infinite and zero emissivity on a flat cathode surface of a vacuum diode in the space-charge-limited current regime has been theoretically studied. The space charge density, electric field, and velocity field distributions in the interelectrode gap are determined using self-similar solutions of the equations of motion of charged particles. It is established that a singularity, where the emission current density tends to infinity according to a power law, appears at the boundary. From this special point, electrons are emitted at an angle of 103° relative to the electrode surface.     

The effect of axial magnetic filed on the process of anode spot formation in a vacuum-arc discharge with CuCr50 electrodes

An experimental study is made of the effect of an external axial magnetic field on the process of anode spot formation in a pulsed vacuum-arc discharge in the range of currents from 5 to 12 kA in a discharge gap with CuCr50 electrodes. The times and currents, at which an anode spot is formed, are determined for each amplitude value of current depending on the magnitude of magnetic field. The minimal value of magnetic field preventing the anode spot formation is determined for each current. The measured values of diameters of the current channel are used to calculate the anode temperature. It is demonstrated that, under experimental conditions, the heating of anode is insufficient for marked evaporation, and the anode spot formation is associated with the critical flow of fast cathode ions.     

Electron emission in a flat cathode-curved anode system in the space-charge-limited current regime

The process of electron emission in a vacuum diode with curved cathode in the space-charge-limited current regime has been theoretically studied. The space charge density, electric field, and velocity field distributions in the interelectrode gap are determined by means of expansion with respect to a small parameter representing the ratio of the characteristic transverse and longitudinal scales. Based on these results, the current density distribution over the cathode surface is analytically described. The analytical results are compared to the data of numerical calculations available in the literature.     

Cathode spot movement on a continuous carbon fiber reinforced Cu matrix composite in vacuum

The cathode spot movements on a carbon fiber reinforced copper matrix composite (C_f/Cu) were investigated by a scanning electron microscope and a digital high-speed video camera. The composite was prepared by infiltrating a Cu alloy doped with Ti and Cr into a porous carbon/carbon composite in vacuum. It is found that the carbon fibers have a higher ability to withstand the vacuum arc erosion than the Cu matrix. The cathode spot walks randomly on the matrix, rather than on the carbon fibers. The cathode spots are restricted on the Cu matrix in C_f/Cu. The directional movement in the high-speed images is caused by the restricted random walk of the cathode spots. A gradient distribution in the size and density of the cathode spot is present on the Cu matrix. The average arc spreading velocity is estimated to be about 0.36 m/s and the transient arc spreading velocity is in the range of 0.12–0.7 m/s.     

Vacuum Arc Discharge on Integrally Cold Cathode

Initial researches of the existence of a cathode spot on the working surface were conducted in vacuum arc plasma sources of the coaxial design. The moving of the cathode spots on the limited sizes working surface does not give full picture of the development of the arc discharge. This article describes the vacuum arc plasma source of extended design generating the directed belt plasma stream and operating in pulse mode. The researches carried out give additional information about development of the cathode spots of the vacuum arc discharge. It is found that the speed of the cathode spots' motion depends on the cathode temperature.     

Spontaneous arc quenching in the ecton model

It is shown that the phenomenon of spontaneous quenching of a vacuum arc is determined by a finite ecton lifetime and the related cyclic character of processes occurring in a cathode spot of the arc. The main experimental results are explained within the framework of a statistical model based on the ecton model of the cathode spot operation.     

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     

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.     

Coefficient of Ion Erosion of the Vacuum Arc of Metals and Alloys

Consideration has been given to the basic processes in the cathode spot of the vacuum arc of metals and alloys. Based on the analysis of a simplified equation of heat balance of the vacuum-arc cathode spot, formulas for evaluating the values of the coefficient of ion erosion of metals and alloys have been obtained. The calculated and experimentally measured values of the coefficients of ion erosion of certain metals have been compared and their satisfactory agreement has been shown.     

Field emission current and vacuum breakdown by a pointed cathode

Vacuum breakdown of very small gap in the range of 30 nm to 2 μm, between a pointed cathode of thin tungsten wire and a plane anode of stainless steel, was experimentally investigated. The experimental setup, which consists of both electrodes and precise positioning mechanisms actuated by piezoelectric devices, was installed in scanning electron microscope (SEM). Breakdown voltage decreases with decrease of gap length and/or radius of curvature at the tip of cathode. Theoretical consideration shows that the evaporation from the anode surface heated by field emission current is a dominant factor of triggering vacuum breakdown.     

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.     

A model of electron emission from a wedge in the space-charge-limited current regime

The process of electron emission from a wedge-shaped cathode in the space-charge-limited current regime has been theoretically studied. The field distribution in the interelectrode gap is described using a simple analytical model, which is based on the matching of self-similar solutions for electron flows at the vertex region and at the periphery. The dependence of the perveance on the wedge angle in the wedge cathode-flat anode system is determined.     

A simple model for the interaction of a low-current vacuum arc with a copper cathode

Experimental and theoretical studies of the arc-cathode region have been made for several decades, but the task is not yet complete, despite many efforts and much progress. In this work, a numerical model describing the arc-cathode region is developed. The arc is treated as a steady-state phenomenon. The model is then applied to a vacuum arc discharge interacting with a Cu cathode at low current of 4–50 A. The model yields the temperature and electric field strength at the cathode surface, density of the current of the electrons emitted, total current density, cathode spot radius, different kinds of power densities in heating and cooling the cathode, and the plasma electron density. The comparison with experimental results shows good agreement. Published in Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 6, pp. 63–72, November–December, 2007.     

圆锥形阴极真空微三极管的计算机模拟

利用有限元法对圆锥形场致发射阴极的真空微三极管进行了计算机模拟。改变真空微三极管的各项结构参数及阳极和栅极电压 ,得到一系列模拟数据。然后对模拟结果进行分析讨论 ,总结出圆锥形阴极有效发射、阳极电流与真空微三极管的结构尺寸、阳极电压和栅极电压之间的关系 ,对于真空微三极管的实际设计和制作有一定的参考价值     

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.