Vacuum Arc Discharge Research Articles

Generation of multiply charged metal ions in a high current short pulse vacuum arc

We have studied the plasma composition of a high current short pulse vacuum arc discharge with different cathode materials: lanthanum, gadolinium, lead, silver, and tin. We find that for optimal vacuum arc discharge parameters – arc current pulse duration about 2 μs and amplitude about 3 kA – the maximum ion charge state is 11+ and mean ion charge state from 7.8+ for tin to 9.6+ for lanthanum. The mean ion charge state for different materials depends on the discharge voltage and the energy required for ionization to maximum charge state. The cathode surface heats to a temperature of 700 °C–1100 °C in the course of the arc current pulse, depending on the cathode material, and the cathode surface of low melting point metals such as lead and tin melts to a depth of 5 μm and 10 μm, respectively. Surface melting does not lead to change in plasma ion composition, since the ion flux from the cathode considerably exceeds the evaporated atom flux.

Ion velocity separation mechanism during vacuum spark stage

Abstract Supersonic ion jets produced in vacuum arc discharges have a wide range of applications, where precise control of ion kinetic energy is crucial. However, a comprehensive understanding of the ion acceleration mechanism remains elusive, particularly regarding whether there is ion velocity separation in the vacuum spark stage. In this paper, a 1D spherical implicit particle-in-cell (PIC) with Monte Carlo collision (MCC) model is employed to investigate the ion velocity separation in multi-charged vacuum arc plasma with varying electrode bias voltages and plasma ion densities. The results show that ion kinetic energy can reach hundreds of electron volts due to continuous acceleration by the formed potential valley, which leads to ion velocity separation at low electrode bias voltage or low plasma density. An increasing electrode bias voltage flattens the potential valley, reducing the electric field acceleration. While increasing the plasma density deepens the valley and intensifies Coulomb collisions, resulting in nearly-equal velocities across ions in different charge states. These findings can theoretically explain the discrepancies observed in previous experiments regarding the dependence of the ion velocity on its charge state during the vacuum spark stage.

Issues of ensuring the resistance of high-voltage solar arrays of spacecraft to the effects of secondary arc discharges

We have considered the issues of ensuring the resistance of high-voltage solar battery (SB) of spacecraft to the effects of secondary arc discharges. Research in this area has been going on for more than 50 years, but the answer to all the questions has not yet been found. First of all, this is due to the complexity of the electrophysical processes occurring on the surface of the spacecraft in space and in laboratory conditions. The second reason is the random nature of secondary vacuum arc discharges, which requires the use of special test methods to confirm the effectiveness and reliability of selected design and technological solutions. Tests in conditions close to full-scale conditions do not allow us to solve this problem. We have given a retrospective review of publications on the physical features of secondary arcs arising on SB of spacecraft, the mechanisms of their initiation, experimental research and testing methods. We paid considerable attention to the issues of the occurrence of secondary arc discharges SB of the spacecraft in the conditions of ionospheric plasma and plasma generated by electric propulsion thrusters. We have shown that despite the large amount of accumulated data and knowledge, the transition from low-voltage SB to high-voltage SB remains a difficult scientific and technical problem, which requires additional research to solve. In addition, it is already necessary to start training personnel who possess a wide range of knowledge and are able to work on this topic. To do this, it seems advisable to organize sectoral research, as well as the allocation of targeted funds for the training of highly qualified specialists and their independent research. This approach will make it possible to solve the problem of creating high-voltage SB in the shortest possible time and prepare personnel for the development of this technology.

Plasma plume enhancement of a dual-anode vacuum arc thruster with magnetic nozzle

Vacuum arc thruster (VAT) is a type of pulsed electric propulsion device that generates thrust based on vacuum arc discharges, it has great candidate for micro-newton force applications in orbit. To improve both the thrust and longevity of the VAT, a novel dual-anode structure, comprising a central anode and a ring anode, was developed. We conducted an investigation into the plasma discharge and acceleration process within the influence of a magnetic nozzle. The dual-anode architecture resulted in a reduction in the initial plasma impedance, thereby enhancing ion current and velocity. Analysis of surface parameters during discharge revealed a synergistic mechanism between the two insulator-conducting films, enabling a co-cyclic distribution of energy and resistance fluctuations within the discharge. Consequently, the dual-anode setup demonstrated a lifespan extension of at least twofold. Comparative analyses of arc energy, plasma velocity, ion current, and thrust variations with magnetic field strength were conducted between the dual-anode and single-anode configurations under magnetic nozzle influence. Results showed that the dual-anode structure increased ion current and velocity when subjected to magnetic nozzle influence, resulting in a thrust increase of up to 303%. Additionally, we developed a theoretical model for the diffusion coefficient to elucidate the adaptive splitting phenomenon of the arc within the dual-anode structure under magnetic field influence. This model suggests that the dual-anode structure can achieve a more significant enhancement in beam current from the magnetic nozzle compared to the single-anode configuration.

Study on the properties of deuterium ions in a composite cathode vacuum arc discharge

A vacuum arc discharge with a metal-deuteride cathode can generate a supersonic deuterium ion jet, which finds important applications in vacuum arc ion sources. In this study, a 1D3V spherical particle-in-cell direct simulation Monte Carlo cathode spot model with a titanium-deuteride cathode is developed to investigate the ionization and acceleration of deuterium ions from vacuum breakdown to the steady-arc stage. The effects of cathode deuteration concentration on the deuterium ion fraction and kinetic energy are also analyzed. The results show that the released deuterium atoms start to be ionized at around tens of nanometers from the cathode and then become fully ionized at about 0.4μm as the cathode potential drop gradually builds up. The proportion of deuterium ions in the plasma is slightly higher than the proportion of deuterium atoms in the cathode material. Velocity separation of deuterium and titanium ions occurs due to the acceleration of the electric field during the vacuum breakdown stage; however, the predominant ion–ion Coulomb collisions wipe out this separation in the steady-arc stage. Shifting the deuterium atom concentration in the cathode under a constant arc burning voltage produces an approximately equal current density, and increases the velocities of all ion species. A higher ion kinetic energy is gained by reducing the ohmic heating dissipation, facilitated by the lower plasma resistivity under the increased deuterium ion density.

PULSED VACUUM-ARC PLASMA SOURCE WITH LASER ARC EXCITATION

A method of solution to the issue of contamination of the laser beam input window in pulsed vacuum-arc plasma sources with vacuum arc laser excitation is proposed. The method involves the periodic introduction of energy through an unfocused laser beam into a layer of condensate formed on the surface of the laser beam input window. The focus of such a cleansing laser beam is located outside the vacuum chamber, ensuring the absence of unauthorized activation of the plasma source, and the optical axis is perpendicular to the input window surface, providing optimal conditions for removing the formed condensate film. The periodicity of cleansing the laser beam input window, which determines the window throughput, is based on the condition of ensuring the probability of vacuum arc excitation not below a specified level. The area of the cleansing laser beam unfocusing spot Sunf on the laser beam input window surface facing the plasma source cathode is determined under the condition of ensuring the power density q of the laser radiation on the cleansed surface in the range of 104 ≤ q ≤ 105 W/cm2 and the condition Sunf ≥ Sexc, where Sexc is the area of the laser beam spot that excites the vacuum arc discharge on the input window surface facing the plasma source cathode. The vacuum arc excitation in the pulsed plasma source using the proposed method, which allows removing the condensate layer on the laser beam input window, is characterized by a stable 95% probability of exciting the vacuum arc at a pulse repetition frequency of 300 Hz, regardless of the plasma source operating duration.

Substrate surface processing in gas vacuum arc discharge

Problem. Preparation of the surface before the deposition of vacuum arc coatings is of great importance, as it affects not only the adhesive properties of the obtained coatings, but also the physical and mechanical properties of the substrate surface layer. The processes of ions interaction with the substrate surface during its ionic cleaning, before the deposition of coatings, have been relatively little studied and are almost not described in the literature. Goal. In this work, some of their features are considered in relation to the surface preparation of materials before the deposition of vacuum arc coatings. Methodology. The nature of the plasma interaction with the substrate material is determined by the ions energy and their flow density, other things being equal. The energy of the ions treating the substrate consists of their initial energy and the energy acquired in the Debye layer adjacent to the substrate when a negative potential is applied to it. The value of the potential at which the processes of condensation or sputtering are balanced is determined mainly by the nature of the vaporized material. When the value of the substrate potential increases, the deposited particles and its material are sputtered. At the same time, atoms on the substrate that are weakly connected to it, various impurities are removed, substrate temperature increases, especially in its surface layers. Results. The work investigates the influence of various metals and gases used to clean the surface of substrates made of cubic boron nitride PcBN and steels on the surface morphology. It was established that the use of gases (argon, nitrogen) for cleaning the surface of dielectric materials, in particular PcBN, showed the best results, which subsequently leads to an increase in the adhesion of the vacuum arc coating to the substrate. Practical value. The obtained results of investigation are of great practical importance. They can be used for the increasing of tool life and productivity of mechanical engineering.

Investigation of Changes in the Field Emission Characteristics of the Eroded Cathode Surface after Submicrosecond Vacuum Arc Discharges with Different Current Amplitudes

Investigation of Changes in the Field Emission Characteristics of the Eroded Cathode Surface after Submicrosecond Vacuum Arc Discharges with Different Current Amplitudes

Dependence of the Nonuniformity of Thickness of the Vacuum-Arc Discharge Plasma Coating on the Geometric Parameters of the Inter-Blade Channel

Dependence of the Nonuniformity of Thickness of the Vacuum-Arc Discharge Plasma Coating on the Geometric Parameters of the Inter-Blade Channel

Low-pressure high-current pulsed magnetron discharge with electron injection from a vacuum arc plasma emitter

We report our investigations on a planar (Ø 125 mm) high-current (up to 50 А) pulsed (100–400 μs) magnetron discharge with injection and acceleration of auxiliary electrons into the cathode layer. The injected electrons were from the plasma of a pulsed (300 μs) vacuum-arc discharge with current amplitude 10–60 A. The magnetron targets were Cu and Zn, and the operating gas was argon. The use of a gasless vacuum-arc electron emitter leads to further decrease in the minimum operating pressure of the high-current form of magnetron discharge, down to 0.18 mTorr (0.024 Pa). We present here the experimental results and a numerical model of the evolution of the ion mass-to-charge composition of the magnetron plasma as the operating pressure decrease to its ultimate lower limit.

Thermal vacuum evaporation peculiarities of perovskite-type barium-strontium hafnate

Experimental results are presented on the thermal vacuum evaporation of barium hafnate BaHfO3 and double barium-strontium hafnate Ba0.5Sr0.5HfO3, which are included together with finely dispersed tungsten as components in sintered composites. It is found that at T = 1900 K only barium and barium oxide are the products of BaHfO3 evaporation, i.e., congruent evaporation of BaHfO3 does not occur. Investigations of Ba0.5Sr0.5HfO3 evaporation at T = 1600 K showed that it also does not evaporate congruently. At the same time, the nucleation of a new phase of BaO·SrO in the form of structures with D6 symmetry was detected. Using a high-current vacuum arc discharge, congruent evaporation of Ba0.5Sr0.5HfO3 takes place, forming various crystalline formations of double barium-strontium hafnate on the substrate.

Features of the formation and diagnostics of powerful metal ion beams with submillisecond duration

The article presents the results of experimental studies on the formation of repetitively-pulsed beams of titanium ions with submillisecond pulse duration from the continuous vacuum arc discharge plasma. The influence of ion-electron emission on the overestimation of the measured ion current with a power density of tens and hundreds of kilowatts per square centimeter was studied using various methods. It has been established that at an average energy of titanium ions of about 80 keV, due to ion-electron emission, the measured current is three times higher than the real ion beam current. Complicating the measurement of the current and energy parameters of the ion beam, the ion-electron emission ensures the neutralization of its space charge during the entire duration of the pulse. An increase in the ion current density due to ballistic focusing to more than 1 A/cm2 does not change the ion-electron emission coefficient. It is shown that, as a result of incomplete ion beam space charge neutralization, its crossover is shifted by 20 mm beyond the geometric focus of the system. The possibility of forming submillisecond high-intensity titanium ion beams with a current density exceeding 2.8 A/cm2, a power density exceeding 200 kW/cm2, and a pulse energy exceeding 100 J has been experimentally demonstrated. Data are obtained on the change in the current density over the ion beam cross-section depending on the accelerating voltage amplitude, the vacuum arc discharge current, and the distance from the focusing electrode.

Development of multi-spectral pyrometer for measuring cathode surface temperature of pulsed vacuum arc discharge

The cathode surface temperature is a vital parameter in the pulsed vacuum arc discharge process, which has an important influence on the formation of vacuum arc plasma, electrode corrosion prediction and ion source lifetime. Currently, the research of cathode surface temperature measurement is mainly based on a high-speed charge coupled instrument (CCD) camera. However, there are no other temperature measuring instruments to verify the results of a high-speed camera. For this reason, a new type of multi-spectral pyrometer is developed. The developed pyrometer adopts optical filter instead of traditional prism splitting, which simplifies the calibration process of pyrometer. An optical sampling system is redesigned to ensure that a tiny target of 100 μm can be measured. On the built experimental platform, the synchronous experiment of multi-spectral pyrometer and high-speed camera are carried out. The experimental results show that the developed multi-spectral pyrometer can verify the measurement results of the multi-spectral pyrometer based on high-speed camera.

Implantation of tantalum ions into a dielectric coating synthesized by electron-beam evaporation of aluminum oxide ceramic in the forevacuum pressure range

We describe our investigations of the electrophysical properties, phase composition and structure of Al2O3 ceramic particles in coatings formed by electron-beam evaporation of alumina ceramic and modified by implantation of tantalum ions. The ceramic coatings were synthesized in a helium atmosphere in the forevacuum pressure range of 1–10 Pa, at characteristic temperatures of beam target and substrate about 2500 and 250 Celsius, respectively, at a deposition rate of 500 nm/min. Ion implantation was performed using a metal ion source based on a vacuum arc discharge, at pressure of order 10−4 Pa; the mean tantalum ion energy was 90 keV and the implantation doses investigated were 1 × 1016, 5 × 1016, and 1 × 1017 ion/cm2. The original and modified ceramic coating samples were studied using a transmission electron microscopy technique. Measurements of the surface resistivity showed that the treatment of coatings by high-energy tantalum ion implantation leads to increase in specific resistance and decrease in sheet resistance.

Spontaneous plasma formation via electrical explosion of nanostructured metal surface layers in plasma–surface interactions

The article is aimed at studying the issue of spontaneous, i.e., triggerless ignition of arcing plasma splashes due to explosive-electron-emission pulses at fiber-form nanostructured (W-fuzz) surface during plasma–surface interaction. There has been proposed an equivalent sputtering yield for arcing Yeff = 4.8 γ C/mg, where γ is the rate of plasma production (mass per charge) from a cathode by vacuum arc discharge. The ratio of the released-to-incident atoms Yeff can reach the value of about 10 for the plasma production rate of 2 mg/C. The increase in the plasma production rate γ has been estimated as (i) an increase in mass due to mechanical destruction of neighboring nanofragments and (ii) a decrease in ions average charge. The resulting twentyfold increase in γ at few-μm layers agrees with the experimental observations. The critical temperature Tcr (and corresponding cohesive energy Ecoh = 5 Tcr) for the W-fuzz nanostructure has been estimated as Tcr = 2 n/n0 eV, where n/n0 is the relative density of the W-fuzz nanostructure. It falls below 1 eV for typical fuzz layer thickness larger than few tenths of μm. This results in the experimentally observed reduction of the average W-ions charge in vacuum arc plasma.

Particle simulation on the ion acceleration in vacuum arc discharge

The supersonic ion jet generated in vacuum arc plasma has numerous applications, but the ion acceleration mechanism is incompletely understood. In this paper, a one-dimensional spherical vacuum arc discharge model is established, and the ion acceleration from vacuum breakdown to steady arc stage is investigated using particle-in-cell direct simulation Monte Carlo method. The results show that a potential hump exists and locates about far away from the cathode, but the potential drop provides a small contribution to the ion acceleration. A potential valley forms near the plasma–vacuum boundary and propagates towards the anode as the plasma expands during the vacuum breakdown stage. The ion mounting this valley experiences continuous acceleration by the dynamic electric field of the potential valley. As the plasma reaches the anode, a steady arc stage is gradually build-up, and the potential valley disappears. Consequently, the maximum mean ion velocity decreases. The source dominating the ion acceleration in this stage is turned into the electron–ion Coulomb collision.

Effect of ion collision on separation between light and heavy ions in multi-component vacuum arc

In multi-component vacuum arc discharge, light ions and heavy ions usually have different spatial distributions of density and velocity. Previous research has suggested that the difference in spatial distribution of light and heavy ions is due to the mixing effect of cathode spot jet. However, in this work, the ion collision is found to be an important factor leading to the separation of light and heavy ions. In this paper, multi-fluid model is used to study the effect of ion collisions on separation mechanism in multi-component vacuum arc. The simulation results show that, during the jet mixing process, the collisions between different ions will reduce the velocity of light ions, and greatly increase the density and temperature. As a result, the pressure expansion of light ions is significantly enhanced. In addition, the collision between different ions will also increase the size of jet mixing region for light ions, which makes the plasma jet of light ions mixing more fully. These effects make their isotropic expansion dominant, and the ion density at the center is not much different from that at the edge. However for heavy ions, the collision between different ions has little influence on their movement. The pressure is far less than the inertia force, so the density of heavy ion mainly distributes along the convection direction, and the center is greater than the edge. This is the main separation mechanism of ion angular flux. It is also found there are three main factors leading to the separation of light and heavy ions: ion mass, ion density and ion temperature. The separation effect can be enhanced by increasing ion temperature, decreasing ion density and selecting electrode components with significant differences in elemental mass. This paper provides an insight into the mechanism of ion separation in multi-component vacuum arc.

Dependence of electron and neutral vapor density distributions on anode mode of high current vacuum arc

The vacuum arc discharge makes transition to a footpoint mode, anode spot type 1 (type 1) mode and anode spot type 2 (type 2) mode under high current conditions. The mode dependence of the electron and metal vapor densities were experimentally quantified using dichroic Shack–Hartmann type laser wavefront sensors. In the type 1 mode, the electron and metal vapor densities were about 2.5 times higher than the footpoint mode. The electron density of the type 2 mode was three times higher than that of the type 1 mode, while significant difference was not found in the metal vapor density. Such higher electron density for the type 2 mode than the type 1 mode was coherent with a previous result obtained by Stark broadening. The present electron and metal vapor density measurement demonstrated that the amount of the electrode erosion was in the following order: footpoint mode < type 1 mode < type 2 mode, which agreed with a previous study.

Dielectric Properties of Copper(II) Oxide Nanoparticles Synthesized in a Vacuum Arc Discharge

Dielectric Properties of Copper(II) Oxide Nanoparticles Synthesized in a Vacuum Arc Discharge

Vacuum plasma erosion resistant 2D nanocomposite coating Avinit for compressor blades of gas turbine engines of aircraft engines

The work is devoted to the search for new vacuum-plasma coatings with high hardness to increase the durability of the compressor blades of the GTE of aircraft engines Ti-Al-N-based vacuum-plasma coatings obtained by Avinit technologies, which ensure the application of hard, high-quality coatings with dramatically reduced micro-arc damage, were selected as candidates. Avinit multilayer coatings have higher functional characteristics than TiN (microhardness, crack resistance, temperature resistance, erosion and corrosion resistance) and may be promising for applying erosion-resistant coatings for compressor blades. Avinit technologies are technologically closest to the vacuum-plasma technologies used in industrial production for applying TiN protective coatings. New multi-layered 2D nanocomposite wear-resistant ion-plasma hard coatings Avinit (TiN-AlN)n have been developed. The created software products made it possible to reach a qualitatively new level in terms of further modification and improvement of the designs of Avinit functional coatings, stability of technologies and improvement of their quality control when applying such coatings for use in the production of compressor blades of gas turbine engines of aircraft engines. Special attention is paid to methods of preliminary ion-plasma treatment of surfaces before coating. Metallographic studies of the chemical and phase composition and structure of Avinit (TiN-AlN)n coatings have been carried out. The thickness of the coatings is 7-9 μm, the microhardness is 34-35 GPa (compared to the serially used TiN coating: 27.4 GPa). The use of three-stage ion-plasma treatment in Avinit technologies using a double vacuum-arc discharge followed by the application of strengthening coatings in a single technological cycle eliminates the formation of cracks and ensures the production of tightly bonded, high-quality coatings of a given composition with the maximally reduced share of the droplet component. The developed coatings (TiN-AlN)n were applied to experimental batches of working compressor blades of GTE aircraft engines for bench tests.