The vacuum arc is a rich source of highly ionized metal plasma that can be used to make a high current metal ion source. Vacuum arc ion sources have been developed for a range of applications including ion implantation for materials surface modification, particle accelerator injection for fundamental nuclear physics research, and other fundamental and applied purposes. The beam parameters can be attractive, and the source has provided a valuable addition to the spectrum of ion sources available to the experimenter. Beams have been produced from over 50 of the solid metals of the periodic table, with mean ion energy up to several hundred keV and with beam current up to several amperes. Typically the source is repetitively pulsed with pulse length of order a millisecond and duty cycle of order 1%, and operation of a dc embodiment has been demonstrated. Here the source fundamentals and operation are reviewed, the source and beam characteristics summarized, and some applications examined.

https://cds.cern.ch/record/1693045/files/p311.pdf

Vacuum Arc Ion Sources

Electron configurations close to the tetrahedral hybridization are found in pure amorphous carbon at a concentration which depends on preparation conditions. Tetrahedral bonding at levels of approximately 80% is found in amorphous carbons formed from beams of carbon ions with energies in a `window' between 20 eV and approximately 500 eV. Suitable techniques for its formation include cathodic arc deposition, ion beam deposition and laser ablation. Similar material appears to be formed by pressure treatment of fullerene precursors and by displacement damage in diamond. Highly tetrahedral forms of amorphous carbon (ta-C) show electronic, optical and mechanical properties which approach those of diamond and are quite different from amorphous carbons with low content. Useful techniques for determining the content include electron energy loss spectroscopy, electron and neutron diffraction and Raman spectroscopy. Considerable progress has been made in the understanding of this material by simulating its structure in the computer with a range of techniques from empirical potentials to ab initio quantum mechanics. The structure shows departures from an idealized glassy state of diamond which would have a random tetrahedral network structure as used to describe amorphous silicon and germanium. A surprising feature of the structure simulated using ab initio methods is the presence of small rings containing three or four carbon atoms. The electronic and optical properties are strongly influenced by the residual of carbon. Applications to electronic devices are at an early stage with the demonstration of photoconductivity and some simple junction devices. Applications as a wear resistant coating are promising, since the theoretically predicted high values of elastic constants, comparable to but less than those of diamond, are achieved experimentally, together with low friction coefficients.

https://iopscience.iop.org/article/10.1088/0034-4885/59/12/002/pdf

Tetrahedral bonding in amorphous carbon

Diamond-like carbon (DLC) films deposited by cathodic vacuum arc evaporation (CVAE) have attracted worldwide interest from research groups and industry since the beginning of the 1990s. Hydrogen-free amorphous carbon (a-C) coatings were first deposited by CVAE about two decades after the first description of hydrogenated a-C coatings (a-C:H) deposited by glow-discharge techniques. This paper highlights the development and broad potential of hard a-C coatings deposited by direct (DCVAE) and filtered (FCVAE) cathodic arc evaporation, including pulsed arc. DLC films offer a wide range of exceptional physical (optical, electrical), chemical (interaction with media), mechanical (hardness, elastic modulus), biomedical and tribological properties. Monolithic tetrahedrally-bonded hydrogen-free coatings (ta-C) provide the highest hardness, while various softer a-C coatings are also useful in some applications. Many film properties such as electrical conductivity and surface energy can be modified by alloying with elements such as H, N, Si, B, F, P and metals. Recent research and industrial solutions for generating DLC coatings by CVAE of carbon-based cathodes are described, and hybrid methods using metal cathodes and gas-phase sources are discussed. Coatings containing additional elements and having complex architectures are also discussed, and selected properties for various coating types are presented. The number of industrial applications of ta-C and a-C coatings continues to increase, mainly for tribological coatings to reduce wear and friction. Various applications of coatings deposited by CVAE are described, including data hard disks, engine parts, razor blades, valve seals, decorative coatings, cutting and forming tools, biomedical products and others.

60 years of DLC coatings: Historical highlights and technical review of cathodic arc processes to synthesize various DLC types, and their evolution for industrial applications

A review is given on arc cathode spots, mainly based on the investigation of arcs in a vacuum with cold cathodes. For the latter and after a short description of general features and theoretical concepts, experiments are presented that study the temporal and spatial behaviour of the spots with high time and space resolution of less than 10 ns and less than 5 µm, respectively. With the help of these observations the various spot types described in the literature are ordered into three levels: level A corresponding to the proper spot with typical diameters of 50-100 µm, level B associated with spot fragments having a size of 10-20 µm and level C comprising a substructure of the fragments. The structures undergo periodic fluctuations of brightness and position with characteristic times that can be arranged in a hierarchy from a few nanoseconds through about 100 µs. The analysis of these fluctuations shows that the spot operates in cycles that include both extremely non-stationary periods with time constants of less than 10 ns and more stationary periods in the microsecond range. In the presence of an external magnetic field, the latter periods lead to unstable plasma configurations that give rise to retrograde motion. Finally, for vacuum arc spots the basic parameters are summarized. After that, the peculiarities of spots in gases with cold electrodes are discussed, followed by a presentation of spots with hot cathodes at high pressures.

https://iopscience.iop.org/article/10.1088/0022-3727/34/17/202/pdf

Topical Review: Cathode Spots of Electric Arcs

The composition of cathode mass loss was analysed for cadmium, copper and molybdenum vacuum arcs. It showed that two dominant flows are present, one consisting of ions, the other of molten droplets which have sizes in the order of microns to tens of microns. The droplet flow is mainly oriented along the cathode plane and is strongly dependent on the fusion temperature of the cathode metal and the charge transfer by the arc. The cathode mass loss in vapour form is considered to be small.

http://iopscience.iop.org/article/10.1088/0022-3727/9/16/009/pdf

Components of cathode erosion in vacuum arcs

The net erosion rate at the cathode spots of 100‐A vacuum arcs has been determined experimentally for Cd, Zn, Ag, Cu, Cr, Fe, Ti, C, Mo, and W electrodes. Ion currents to the metal walls surrounding each of these cathode materials have also been investigated. For each material, the dependence of the wall ion current on the electrode spacing and anode geometry is consistent with an arc model which assumes predominant vapor ionization in the cathode regions, with subsequent isotropic free flight motion from these regions. Comparison of the net erosion rate with the wall ion current indicates that, for high‐vapor‐pressure materials such as Cd and Zn, ≈ 15% of the vapor leaves the cathode regions ionized. For low‐vapor‐pressure materials such as C, Mo, and W, this fractional ionization is almost 100%. The ion current magnitudes observed at long electrode spacings are similar for each material, and lie in the range 7–10% of the arc current. Ion currents of this magnitude are also predicted for Mg, Al, and Ni u...

C. W. Kimblin

Papers

Erosion and ionization in the cathode spot regions of vacuum arcs