Cathode Plasma Jet Research Articles

Array hollow-anode microsecond-pulsed plasma jets at atmospheric pressure: mode transition and influencing factors

Abstract Hollow cathode plasma jets are commonly utilized across various fields, yet there is limited research on hollow anode discharge, particularly on array hollow anode plasma jets. This letter presents the novel design of a array hollow anode discharge device excited by microsecond pulse. Systematical investigations about the discharge characteristics and mode transition process of the device are examined from the perspectives of electricity and space-time distribution to get insights into the formation mechanisms of array hollow anode plasma jets. Results show that three distinct discharge modes when the array hollow anode plasma jets interacting with ITO plate are identified based on the number and location of the discharged hollow anodes: Mode A involves all 16 hollow anodes discharging, Mode B entails 12 hollow anodes discharging, and Mode C comprises 4 hollow anodes discharging at the four vertices of the device. It is observed that experimental outcomes are influenced by the distance from the hollow anode tube port to the plate. The formation mechanism is determined by an increase in distance impacting spatial electric field distribution and facilitating mode transition. Furthermore, the impacts of pulse voltage, pulse frequency, and flow rate on the variation of interval length under different modes are investigated. The results indicate that voltage has the most significant effect on interval length, followed by frequency, while flow rate has a minimal effect. These findings hold significant implications for enhancing understanding of mode transition and influencing factors of array hollow anode plasma jets.

Operating voltage of a W-fuzz cathode arc and the mass/charge composition of the arc plasma depending on the fuzz thickness

The arc operating voltage and the mass/charge composition of the arc plasma were measured for W-fuzz samples with different fuzz thicknesses at different numbers of arc pulses. It was found that the formation of a fuzz structure led to a significant decrease in the arc operating voltage within the first few arc pulses. With an increase in the number of pulses, the operating voltage and the mean charge of tungsten ions in the arc plasma increased to values characteristic of conventional tungsten cathodes. The obtained experimental data were analyzed theoretically using an empirical cohesive energy rule and a magnetohydrodynamic model of the ionization processes occurring in a cathode plasma jet.

Nickel-Copper Oxide Catalysts Deposited on Stainless Steel Meshes by Plasma Jet Sputtering: Comparison with Granular Analogues and Synergistic Effect in VOC Oxidation

A novel method for the preparation of Ni-Cu oxide catalysts—deposition on stainless steel meshes using hollow cathode plasma jet sputtering—was studied. This method allows the preparation of thin oxide films. Consequently, the whole volume of the active phase is readily accessible for the reactants and can be employed in the catalytic reaction due to the negligible effect of internal diffusion. As a result, the activity of our sputtered catalyst was seven times higher in ethanol oxidation and 61 times higher in toluene oxidation than that of the corresponding granular catalyst. Moreover, due to stainless steel meshes used as a catalyst support, the pressure drop across the catalyst bed was lower. Finally, the catalytic activity of the sputtered Ni-Cu oxide catalyst with Ni:Cu molar ratio of 1:1 in ethanol oxidation was 1.7 times higher than that of the commercial EnviCat® VOC-1544 catalyst, while the amount of the active phase in the catalyst bed was 139 times lower. The outstanding performance of the Ni0.5Cu0.5 catalyst was ascribed to the synergistic effect between the copper and nickel components.

Structure and properties of Cr-TiBx composite coatings prepared by a hybrid technique of sputtering and arc evaporation

In this paper, Cr-TiBx coatings were deposited using a hybrid technique involving magnetron sputtering of TiB2 target and cathodic arc evaporation of Cr target. A baffle plate placed in front of the Cr target was used to adjust cathodic plasma jet area to control the deposition rate of Cr. The structure, mechanical properties and thermal stability of the coatings were researched by using scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy, nano-indentation and temperature static oxidation in muffle furnace. The results show that the pure TiB2 coating exhibited a typical columnar structure. The microstructure of the Cr-TiBx coatings changes from nano-composite structure to alternate nano-multilayered structure as the deposition rate of Cr from low to high. The nano-composite Cr-TiBx coating is consisted of TiB2 nanograins encapsulated in the Cr-B amorphous phase, which exhibits high hardness and oxidation resistance. However, the multilayered Cr-TiBx coating is composed of metallic Cr layers and amorphous TiBx layers. The soft metallic layers as well as the amorphization of the TiBx layers result in the decrease of the coating hardness.

Optical emission spectroscopy study of plasma parameters in low-pressure hollow cathode plasma jet and planar magnetron powered by DC and pulsed DC supply

Optical emission spectroscopy (OES) has become a non-intrusive and versatile method for plasma parameters determination. Each spectral line in emission spectroscopy corresponds to an optical transition between two quantum levels of atom/molecule. The spectral line intensities are controlled by densities of species in various upper states. We calculated the electron temperature (Te) and electron density (ne) in low-pressure discharge systems based on the modified Boltzmann equation and line intensity ratios. We have evaluated the mentioned plasma parameters in the low-pressure hollow cathode plasma jet (HC) and planar magnetron cathode system (PM) in the continuous DC and the pulsed-DC regime. We present the dependences of the electron temperature (Te) and electron density (ne) on the applied power and the argon flow rate in the mentioned two systems together with a qualitative discussion of the obtained results.

Ti–6Al–4V alloy deposition characteristics at electrode-negative polarity in the cold metal transfer–gas metal arc process

Although wire arc additive manufacturing (WAAM) of Ti alloys using gas metal arc yields a high deposition rate, cathode spots exhibit unstable behavior. In this study, the cold-metal-transfer process and an electrode-negative (EN) polarity were used in the WAAM process of the Ti–6Al–4V alloy. High-speed imaging was performed to investigate the mechanisms to stabilize cathode plasma jets, arc plasma, and molten metal transfer in the EN polarity. Arc plasma and cathode jets had the same direction, and sound cathode jets were shrouded by arc plasma in the EN mode. The metal transfer was also stabilized by balanced plasma formation under the EN mode, and inconsistent wire melting under the electrode-positive (EP) mode was mitigated. In the deposition test using the EN mode, distributed heating of the substrate and depressed molten pool were observed, which resulted in a 21.0% increase in the bead width and 27% decrease in the wetting angle compared with the EP mode. This study demonstrated that the instability of the gas metal arc WAAM process of Ti alloys can be overcome with the EN-mode cold metal arc process.

Iron Oxide and Iron Sulfide Films Prepared for Dye-Sensitized Solar Cells.

In this paper, the prospects of iron oxide films and their sulfidation for dye-sensitized solar cells (DSSC) are reviewed. Iron oxide thin films were prepared by hollow cathode plasma jet (HCPJ) sputtering, with an admixture of oxygen in the argon working gas and with an iron nozzle as the sputtering target. The discharge was powered by a constant current source in continuous mode and by a constant voltage source in pulsed mode. Plasma composition was measured by an energy-resolved mass spectrometer. Moreover, secondary electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), absorption and Raman spectra of the films are presented. Strong correlation between the color of the iron oxide film and its phase composition was revealed. Iron oxide films were sulfided at 350 °C. A relatively clean pyrite phase was obtained from the magnetite, while the marcasite with admixture of the pyrite phase was obtained from the hematite. Low influence of sulfidation on the films’ microstructure was demonstrated.

Influence of the laser plasma-expansion specific on a cathode jet formation and the current stability in a laser-ignited vacuum discharge

The formation of a current-plasma shell is studied during the expansion of a laser-ignited low-power vacuum-discharge cathode plasma jet into the interelectrode gap. The shell geometry is found to be determined by the mode of laser-plasma expansion at the discharge ignition stage. It is shown that the increase in the laser-beam focal spot area on the cathode surface leads to the increase in the matter density and the decrease in the density gradient in the discharge gap and to transition from the spherical laser-plasma expansion mode to the jet mode. The latter considerably stabilizes the current transfer in the discharge plasma, even during the development of the hydrodynamic sausage instability in it.

Application of microcracked columnar TiO2 thin films deposited by DC hollow cathode plasma jet in dye-sensitized solar cells

The deposition of nanostructured thin films with specific optical properties is of great importance for solar cell technology. In this work, the authors used a direct current hollow cathode plasma jet with a supporting anode to deposit highly microcracked columnar titanium dioxide thin films. For diagnostics of the morphology and crystalline structure of the films, they used scanning electron microscopy and x-ray diffraction methods. The light-harvesting ability of the films was tested in dye-sensitized solar cells at the AM 1.5 G conditions, where TiO2 was used as the photoelectrode. Photovoltaic tests were performed using platinum counter electrodes and an N719 dye-sensitizer. The effect of microcracks on the conversion efficiency and angular response of solar cells was discussed.

Influence of Axial Magnetic Field on Cathode Plasma Jets in High-Current Vaccum Arc

The cathode plasma jets in vacuum arc and the effect of magnetic field on them have been studied for several years and these studies are helpful to understand the arc characteristics and improve the controlling effect of magnetic field on arc plasma. In this paper, the experiments of the cup-shaped axial magnetic field (AMF) contacts were conducted in which a Helmholtz coil was introduced to generate different external imposed AMFs. It was found that the appearance of arc plasma was changed by variation of the external imposed AMF. If the composite AMF in arc column increased gradually, the obvious individual cathode plasma jets were detected, the arc constriction decreased, and the arc stability increased. Meanwhile, the inclination of cathode plasma jets was observed and the inclination direction was found to be consistent with the magnetic field vector direction which is closely related to the composite AMF. By variation of the external imposed AMF and its direction, the inclination direction of cathode plasma jets also changed. The criterion to detect obvious cathode jets in arc column is obtained that at the contact peripheral where R> 80.5% R0 (R0 is the contact radius), the AMF strength is no less than 4.5 mT/kA. It was also found that if the composite AMF in interelectrode gap points to different directions at a certain moment, it may lead to the transfer of arc column from the center to the edge of the interelectrode region and the arc instability until when the composite AMF in the interelectrode gap points to the same direction. It can be concluded that the appearance of individual cathode plasma jets can be manipulated by the variation of AMF, which is helpful to study the interaction between arc plasma and electrodes, especially the anode, and improve the interruption performance at higher current.

Features of the Growth Dynamics of Plasma Jets in Laser-Induced Vacuum Discharges with High Rates of Current Rise

An experimental study of the dynamics of formation of plasma jets and ion beams in laser-induced low-voltage discharges with high rates of current rise has been performed. It has been found that for given discharge characteristics (energy store voltage, discharge current, current rise rate, and discharge gap spacing) there exist optimum initial conditions, determined by the characteristics of the laser radiation, that provide stable single pinching of the cathode plasma jet at its maximum compression. Increasing the ion density and decreasing the temperature of the foreplasma by reducing the laser radiation power density at the cathode due to an increase in laser pulse duration improves the stability of the plasma pinching at a lower energy input.

TiO2 nanoparticle detection by means of laser beam scattering in a hollow cathode plasma jet

The distribution of TiO2 nanoparticles in a plasma plume of a hollow cathode plasma jet is being studied in this work. The method is based on the detection of light from a laser beam scattered on nanoparticles by three detectors: a photodiode, an optical spectrometer and a digital photo camera. The Rayleigh–Mie theory was used as a basis for the description of the results. Two lasers with wavelengths of 446 and 661 nm were used as light sources. 2D maps of the scattered light intensity were assembled from photo camera pictures at different discharge parameters. Dependencies of the signal intensity on the O2 flow rate and wavelength are discussed. Direct measurements of particle size on the substrate were carried out by means of a scanning electron microscope in order to verify the agreement of results with the theory. Aside from nanoparticles we detected TiO2 columnar structures in the deposited samples. Crystalline structure of the samples was investigated using x-ray diffraction analysis.

Ion acceleration in multi-species cathodic plasma jet

A general expression for ion-ion coupling in a multi-species plasma jet was obtained. The expression is valid for any value of the inter-species velocity. This expression has enabled us to review a hydrodynamic problem of expanding the cathodic plasma microjet with two ion species within the respective charge states Z1 = +1 and Z2 = +2 into a vacuum. We were able to illustrate that in scenario when the initial (i.e., acquired during a process of emission from cathode's surface) difference for ion's species velocity exceeds a threshold value, the difference remains noticeable (roughly about 10% of the average jet's velocity) at a distance of a few centimeters from the emission center. At this point, it can be measured experimentally.

Experimental investigation of cathode spots and plasma jets behavior subjected to two kinds of axial magnetic field electrodes

In this paper, cathode spot plasma jet (CSPJ) rotation and cathode spots behavior subjected to two kinds of large diameter axial magnetic field (AMF) electrode (cup-shaped and coil-shaped) are studied and analyzed based on experiments. The influence of gap distances on the CSPJ rotational behavior is analyzed. Experimental results show that CSPJ rotational phenomena extensively exist in the vacuum interrupters, and CSPJ rotational direction is along the direction of composite magnetic field (mainly the combination of the axial and azimuthal components). For coil-shaped and cup-shaped AMF electrodes, the rotational or inclination phenomena before the current peak value are much more significant than that after current peak value (for the same arc current), which is related to the larger ratio of azimuthal magnetic field Bt and AMF Bz (Bt/Bz). With the increase of the gap distance, the AMF strength decreases, when the arc current is kept as constant, the azimuthal magnetic field is kept invariable, the ratio between azimuthal magnetic field and AMF is increased, which results in the increase of rotational effect. For cathode spots motion, compared with cup-shaped electrode, coil-shaped electrode has the inverse AMF direction. The Robson drift direction of cathode spots of coil-shaped electrode is opposite to that of cup-shaped electrode. With the increase of gap distance, the Robson angle is decreased, which is associated with the reduced AMF strength. Erosion imprints of anode and cathode are also related to the CSPJ rotational phenomena and cathode spots behavior. The noise of arc voltage in the initial arcing stage is related to the weaker AMF.

Numerical studies of arc plasma generation in single cathode and three-cathode plasma torch and its impact on plasma spraying

This paper is to study the characteristics of arc plasma torch generated by single cathode and three-cathode structure and their potential impact on plasma spraying. A comprehensive physical model is developed, which is capable of describing plasma generation, compressible reacting flow and its interaction with particles involving heat, momentum and mass transfer as well as particle melting and re-solidification. A computational scheme is also developed to solve the Navier–Stokes equations, Maxwell’s equations and equations of particles’ momentum, heat and mass transfer with plasma jet and particles’ phase change. This scheme is applied to simulate thermal spraying processes using both single cathode and three-cathode plasma guns. Results show that plasma torch from the single cathode plasma gun shifts to one side, while that from the three-cathode plasma gun is axisymmetric along the jet axis with triangular structure on the jet cross sections. Temperature and velocity along the center axis are lower than those away from the jet axis in the three-cathode plasma torch. The regime with high temperature and velocity in the three-cathode plasma jet is larger than that in the single cathode plasma jet. By choosing a suitable injection position, the in-flight particles in the three-cathode plasma jet can be uniformly distributed within the high temperature and velocity region, and be heated and accelerated uniformly. The size of particles that can be fully melted is larger in the three-cathode plasma jet than in the single cathode plasma jet, therefore, beneficial to the coating quality.

Crystalline structure and morphology of TiO2 thin films deposited by means of hollow cathode plasma jet with supporting anode

TiO2 thin films with developed structure were deposited by means of a hollow cathode plasma jet (HCPJ) in a DC regime with a supporting anode. The influence of the plasma temperature on the surface morphology and crystalline structure of the thin films under different deposition conditions was studied. Diagnostics of the thin films structure was carried out using XRD, SEM, EDX and TEM methods. One batch of samples was annealed at a temperature of 400 °C in atmospheric conditions as a comparison with the crystalline structure and morphology of unannealed samples. The presence of two crystalline polymorphs of rutile and anatase in the films was discussed. The vacuum system was improved for an extended deposition of non-conductive materials without terminating the discharge and cleaning of the deposition chamber. The aim of this investigation was to prepare the vacuum system for the fabrication of photo electrodes which are the main functional part in dye-sensitized solar cells. The test DSSCs (dye-sensitized solar cells) were prepared from low-cost materials (raspberry/hibiscus natural dye-sensitizers and candle soot counter electrode) in order to check the quality of the films, with a highest conversion efficiency η = 0.66% and a fill factor FF = 62%.

Formation of a cathode plasma jet in a laser-induced vacuum discharge

The process of formation of micropinch structures in the plasma of a vacuum discharge initiated by a laser pulse on the cathode is studied. It is demonstrated that the micropinch formation takes place mainly in the substance evaporated by the laser pulse upon the discharge initiation. The size of the hot region of the plasma jet and the distance from the cathode to the micropinch increase with increasing laser pulse energy.

On plasma jet formation in vacuum arc with composite cathode

This paper deals with the computer modeling of vacuum arc with composite multicomponent cathode. This arc is typical for certain kind of ion sources, plasma generator and vacuum interrupters. The described hybrid model treats the electrons as an inertialess fluid and ions as macroparticles. The macroparticle dynamic is calculated with the use of particle-incell method. Ion-ion Coulomb collision is considered with the use of Monte Carlo method. The model can simulate vacuum arc as a whole including separate cathode plasma jets, mixing zone, and common plasma column. The dependence of ion angular current distribution on the cathode composition reproduced with the help of developed model agrees well with experimental results.

Mechanism of cathode spot splitting in vacuum arcs in an oblique magnetic field

Experiments in the last decade showed that for cathode spots in a magnetic field that obliquely intercepts the cathode surface, the current per spot increased with the transverse component of the magnetic field and decreased with the normal component. The present work analyzes the nature of cathode spot splitting in an oblique magnetic field. A physical model for cathode spot current splitting was developed, which considered the relation between the plasma kinetic pressure, self-magnetic pressure, and applied magnetic pressure in a current carrying cathode plasma jet. The current per spot was calculated, and it was found to increase with the tangential component of the magnetic field and to decrease with the normal component, which agrees well with the experimental dependence.

Hybrid Computational Model of High-Current Vacuum Arcs With External Axial Magnetic Field

This paper deals with the computer modeling of a high-current (total current $\ge 10$ kA) vacuum arc with an external axial magnetic field. This arc is typical for certain kind of vacuum interrupters. The described hybrid model treats electrons as a massless fluid and ions as macroparticles. The macroparticle dynamics are calculated with the use of the particle-in-cell method. Ion-ion Coulomb collision is considered with the use of the Monte Carlo method. The model can simulate high-current vacuum arcs as a whole including separate cathode plasma jets, mixing zone, and common plasma column. The hybrid model is able to calculate V-shape volt-tesla characteristics, which correlate well with experimental results.