Analysis of the Cathode Spot of Metal Vapor Arcs

This paper presents an analysis on the statics and dynamics of a current carrying plasma channel under the influence of an applied magnetic field and under very general flow conditions. Based on this analysis a stability criterion for a discharge channel which emanates from a crater of a low-pressure arc cathode attachment wil be derived. As a consequence of this stability theory one may explain arc spot motion by a kink instability of the discharge channel causing the channel to bend more and more and eventually contacting the cathode surface at a nearby site thereby creating a new emitting spot. By means of this criterion, the dissipation mechanisms during a spot lifetime are determined for pure copper and molybdenum cathodes under the assumption of least possible voltage requirement.     

A sensitive arc detection technique for reliable operation of high repetition rate TEA CO2 laser

A simple and sensitive technique, which utilizes the sensing of both the discharge current and the visible light emission from the discharge, has been developed to detect the arc formation during the operation of a high repetition rate TEA CO₂ laser. It is shown that the optical detection in the visible spectral region is more sensitive than that it is in the UV region and hence can be used more effectively to monitor the onset of arc formation, while the current signal is useful in the strong arc formation regime. We demonstrate that the trigger signals generated by both the methods can be employed for reliable protection of the laser system from catastrophic damage due to deleterious arc formation.     

Method for producing nanomaterials in the plasma of a low-pressure pulsed arc discharge

A new method for the production of nanomaterials in the plasma of a low-pressure arc discharge is developed and experimentally studied. This method can be used to synthesize nanoparticles 5–10 nm in size with a narrow size distribution. In this method, a low-pressure arc discharge is used to melt a material, to disperse the molten material, to deliver liquid material droplets to the plasma, to cool the liquid nanoparticles forming in the plasma up to their solidification, and to deposit the solidified nanoparticles onto a substrate.     

Time-of-flight mass spectrometry studies of an ion beam generated by the titan source

The TITAN source generates wide-aperture beams of gas and metal ions of different materials. This is achieved because of two types of cold-cathode arc discharges, which operate simultaneously in the discharge system of the source. For metal ions to be obtained, use is made of the vacuum arc initiated between an ion-forming cathode and a hollow anode. To produce gas ions, a constricted low-pressure arc discharge is initiated with the same hollow anode. The constitution of ion beams generated by the TITAN source has been investigated using a homemade time-of-flight spectrometer. This paper describes the design of the latter and the principle of its operation, and discusses the physical peculiarities of the spectrometer operation, which affect the ion beam constitution. Institute of High Current Electronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 21–28, February, 2000.     

Effect of cathode surface state on the characteristics of pulsed hollow-cathode glow discharges

A study is made of the effect of pulse repetition rate (0.1−10³ s⁻¹) and average discharge current (0–1 A) on the breakdown delay time and burning voltage of low-pressure glow discharges (p<0.1 Pa) in an electrode system of the reverse magnetron type with a large cathode surface area (≈10³ cm²). It is shown that increasing the repetition rate leads to a many-fold reduction in the statistical spread in the delay time and in the discharge formation time, while the average discharge current has a significant effect on the burning voltage. The mechanism for the observed phenomena is interpreted qualitatively in terms of the presence of thin dielectric films on the cathode surface. Zh. Tekh. Fiz. 69, 20–24 (May 1999)     

Formation of the structure and physicomechanical properties of a quasicrystalline Al–Cu–Fe alloy upon plasma spraying

Quasicrystalline coatings prepared under various thermal conditions of spraying have been studied. Initial quasicrystalline powders with dispersion of 10–50 μm were prepared in a low-pressure arc discharge plasma. The coatings have been sprayed on copper rings using a swinging plasmatron. It is found that the increase in the quenching rate of melt droplets increases the chemical homogeneity and leads to formation of nanostructured formations. The precipitation of nanostructured grains (d < 100 nm) in the sprayed alloy leads to an increase in the mechanical characteristics (hardness, deformation, and ductility) and can be considered as an additional factor of hardening of the material.     

The Studies of a Vacuum Gap Breakdown after High-Current Arc Interruption with Increasing the Voltage

Vacuum-gap breakdown has been studied after high-current arc interruption with a subsequent increase in the transient recovery voltage across a gap. The effects of factors, such as the rate of the rise in the transient voltage, the potential of the shield that surrounds a discharge gap, and the arc burning time, have been determined. It has been revealed that opening the contacts earlier leads to the formation of an anode spot, which is the source of electrode material vapors into the discharge gap after current zero moment. Under the conditions of increasing voltage, this fact results in the breakdown. Too late opening leads to the breakdown of a short gap due to the high electric fields.     

Device for Increasing the Magnetic Flux Pinning in Granular Nanocomposites Based on the High-Temperature Superconducting Ceramic

A device for modifying the granular high-temperature superconducting ceramics in the plasma of a low-pressure arc discharge has been considered. The particular features of the design and operational principle of this device have been described. The device made it possible to combine the synthesis of that play a role of additional pinning centers and simultaneous deposition of these nanoparticles on microgranules in a single processing cycle. The experimental results on the effect of additional pinning centers on an increase in the critical current thanks to the formation of self-assembled structures in the form of whiskers have been considered.     

用于真空弧等离子体放电阴极温度场测量的多光谱高温计

阴极表面温度是真空弧等离子体放电过程中一个重要参数,对真空弧等离子体的形成、电极腐蚀预测、热传导以及离子源的寿命都有重要影响。真空弧离子源的阴极具有目标小,放电过程快等特点,其温度的测量,对于时间分辨率和空间分辨率要求都很高,阴极表面温度的测量技术的欠缺,使得仅靠理论解析获得的结果难以得到验证。并且等离子体放电过程中测量仪器极易受到弧光的影响,如何避免放电过程中等离子体的辐射也是采用辐射法测量阴极表面温度要考虑的问题。这无疑给其温度场的测试研究带来困难。针对脉冲真空弧等离子体开展阴极表面温度测试实验有着重要意义,在分析了真空弧等离子体放电特性以及背景辐射特性和等离子体放电阴极测温的实际需求,本文基于高速CCD相机研制了一种新型的多光谱高温计。该高温计采用单色高速CCD相机,主要避免RGB彩色相机不能完全滤除背景辐射的弧光。为使用单色CCD相机实现多光谱辐射测温,设计了高温计的光学系统,该系统采用4孔径分光系统。将4种不同波长的滤光片嵌入到1个滤光片中。该研究设计的高温计可用于2 000~6 000 K的等离子体温度测量。并在中国工程物理研究院电子工程研究所进行现场测试,测试过程中将研制的高温计,通过外部触发形式对等离子体放电过程进行跟踪拍摄,高温计完全拍摄到等离子体放电过程。利用真空弧等离子体金属电极阴极放电的实测数据对高温计进行了验证。实验结果表明,设计的新型多光谱高温计能够用于测量真空弧等离子体放电时阴极温度场信息,测量的温度值低于放电电极的沸点温度,与等离子体放电过程中出现气化现象相符,说明高温计测的是等离子体放电阴极的温度。     

Plasma-chemical reactor based on a low-pressure pulsed arc discharge for synthesis of nanopowders

A reactor for producing nanopowders in the plasma of a low-pressure arc discharge has been developed. As a plasma source, a pulsed cold-cathode arc evaporator has been applied. The design and operating principle of the reactor have been described. Experimental data on how the movement of a gaseous mixture in the reactor influences the properties of nanopowders have been presented.

     

Charge-state distribution of ions in a vacuum arc discharge plasma in a high magnetic field

It is shown that the fraction of multiply charged metal ions generated in a vacuum arc discharge plasma grows substantially in a high magnetic field. This effect was observed for more than 30 different cathode materials. A relation is established between growth of the mean charge of the ions and increases in the burning voltage of the arc. It is demonstrated that the burning voltage of the vacuum arc can be ultimately increased to 160 V. Zh. Tekh. Fiz. 68, 39–43 (May 1998)     

Self-Similar Gas Motion Near The Evaporating Electrode of An Electric Arc

Simple solutions of 1Dt gas-dynamical equations based on similarity analysis are possible for the gas surrounding a point source of mass and energy such as an electrode (cathode) arc spot. To obtain nontrivial (non-zero temperature) solutions throughout, two-scale formulation is used that permits an additional boundary condition near the source. Three generalised gas flow variables, R, Z and V, related to gas density, temperature and velocity are calculated and presented as functions of a single similarity parameter, λ, related to position and time. The computational results are compared with data from two gas discharge experiments: on gas disturbances due to an electric arc of micrometer length in atmospheric air and on expansion of a metal-vapour plasma cloud generated by a low-pressure cold-cathode arc.     

Plasma Interaction with Boundary Surfaces in Low-Pressure Radio-Frequency Capacitive Discharge

A particular case of a problem on interaction of plasma with a surface is examined experimentally. We study interaction of its own plasma with boundary surfaces in a low-pressure radio-frequency (RF) capacitive discharge (RFCD) by considering their functions. On the basis of the physical model of RFCD substantiated earlier, we examine experimentally the physical conditions taking place in a near-electrode layer of space discharge, which lead to formation of pulsed electron beams and highly non-equilibrium plasma electron energy spectrum. We verify experimentally the known fact that in RFCD it is possible to generate natural oscillating LC circuits modulating the discharge current, and the conditions of their excitation by their own electron beams are clarified.     

“Titan,” a source of gas and metal ions based on a contracted discharge and vacuum arc

Titan ion sources are capable of generating wide aperture beams of both gas and metal ions of different types: Mg, Al, Ti, Cu, Cr, Fe, Co, Ni, Sm, Zn, W, Pb, Ta, Re, Y, C, He, N, Ar, Xe. This is made possible by combining two types of cold cathode arc discharges in the discharge system. Metal ions are obtained using a vacuum arc ignited between a cathode made of the ion-forming material and a hollow anode. Gas ions are obtained using a low-pressure contracted arc discharge ignited on the same hollow anode. In pulsed operation the accelerating voltage of the source is regulated from 10 to 100 kV. The pulse current of both gas and metal ions is 0.3–0.5 A with a pulse duration of approximately 400 µs and a pulse repetition rate of up to 50 Hz. During continuous operation at an accelerating voltage as high as 10 kV, the ion current reaches tens of milliamperes. In this article the operating principle of the source is discussed, along with some physical peculiarities which arise during the formation and transport of high-current ions beams, and the design of the ion source is presented.Institute of High-Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 53–65, March, 1994.     

Conditions of the Anode Spot Formation in a Vacuum Arc

A critical analysis of available experimental data and models of an anode spot formation shows their insufficiency for developing a clear-cut physical model of anode processes in a high-current vacuum arc. Based on new results of studying an anode medium- and low-pressure arc region, a qualitative physical model of an anode spot formation in a vacuum arc is proposed. The main idea of the model is that a change of the sign of the anode voltage drop (from negative to positive) is a necessary condition for an anode spot formation. Experimental data are qualitatively discussed from the point of view of the proposed model.     

Ion emission from arc discharge plasmas

Results are presented from studies of the ion-emission properties of the anode plasmas of low-pressure contracted arc discharges and vacuum arcs. It is shown that creating a longitudinal magnetic field in the anode region of a discharge changes the plasma parameters significantly and facilitates a large increase in the ion current. Space charge limited ion current in a vacuum arc leads to a reduction in the noise level of the total ion current and of its components with charges of up to +3, while creating Penning discharge conditions ensures that ions of different gases can be generated in this discharge system at fractions as high as 90%, depending on the type of plasma forming gas.Institute of High-Current Electronics, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vuzov, Fizika, No. 3, pp. 24–33, March, 1994.     

Interaction of a low-pressure mercury discharge with the discharge tube wall

The darkening of soda-lime glass envelopes of low-pressure mercury discharge tubes has nothing to do with the formation of sodium amalgam on the inner surface of the tube. It is, however, connected with the diffusion of mercury ions into the glass of the tube. By applying a high negative voltage to part of the outer surface of a burning tube a sodium depleted region is created at the corresponding part of the inner surface. After removal of the high-voltage electrode and continued normal operation the rate of darkening of the sodium-depleted part of the tube is about 50 times larger than the rate observed for the normal parts of the same tube.     

High current density spotless vacuum arc as a glow discharge

Vacuum discharge burning between a broad cathode and a point anode made of Mo, Cu, and Cd has been studied. This discharge operates in anode vapors and shows major arc characteristics, although no craters were examined on the cathode. The secondary electron emission is involved to explain current transport within the cathode region. This discharge is interpreted as a high density low voltage glow discharge. Having discussed the present and previous findings, the conclusion has been drawn that the secondary electron emission and “hump of potential” are dominant in the vacuum arc cathode spot     

Theory of a normal high-pressure glow discharge

In the present work, a theoretical model considering the processes of generation and losses of charged particles in the cathode region of a glow discharge in the drift approximation for ion and electron motion is developed. Exact analytical solutions, which can be used to calculate the current-voltage characteristics of the glow discharge in an arbitrary gas with the known Townsend ionization coefficient, are derived. The calculated parameters of the normal glow discharge (the current density, discharge burning voltage, and width of the space charge region) for different gases are in good agreement with the available experimental data. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 71–77, February, 2006.     

Surface properties of diamond-like carbon films prepared by CVD and PVD methods

Diamond-like carbon (DLC) films have been deposited using three different techniques: (a) electron cyclotron resonance---plasma source ion implantation, (b) low-pressure dielectric barrier discharge, (c) filtered---pulsed cathodic arc discharge. The surface and mechanical properties of these films are compared using atomic force microscope-based tests. The experimental results show that hydrogenated DLC films are covered with soft surface layers enriched with hydrogen and sp$^{3}$ hybridized carbon while the soft surface layers of tetrahedral amorphous carbon (ta-C) films have graphite-like structure. The formation of soft surface layers can be associated with the surface diffusion and growth induced by the low-energy deposition process. For typical CVD methods, the atomic hydrogen in the plasmas can contribute to the formation of hydrogen and sp$^{3}$ hybridized carbon enriched surface layers. The high-energy ion implantation causes the rearrangement of atoms beneath the surface layer and leads to an increase in film density. The ta-C films can be deposited using the medium energy carbon ions in the highly-ionized plasma.