Anode Spot Research Articles

An Investigation into the Behavior of Cathode and Anode Spots in a Welding Discharge

The effective development of modern welding technologies and the improvement of equipment and materials inevitably require deep theoretical knowledge about the physical phenomena occurring in the electric arc column and in the near-electrode region. However, there is still no convincing theoretical description of an arc discharge. This article demonstrates, through the generalization of known experimental facts and studies using a high-speed camera, that the conductive channel of an electric arc has a discrete structure, consisting of a set of thin channels through which the main discharge current passes. The cathode spot of an arc discharge is a highly heated and brightly glowing area on the cathode’s surface. Electron emission occurs from this region, which supports the discharge as well as the removal of the cathode material. We propose a new technique to study the reverse side of the cathode spot, revealing a structure consisting of individual cells or fragments of the cathode spot. For the first time, we present the anode spots captured by a high-speed camera. We carry out an analysis of the spots’ structure. We determine the parameters affecting the mobility of cathode and anode spots. We propose a hypothesis based on the obtained experimental facts about the heterogeneous structure of cathode and anode spots in an arc discharge and the existence of current filaments that affect the mobility of spots during arc combustion.

Comparative Analysis of Craters Formed on Cathode and Anode Spots of a Spark Discharge in Air on Iron Electrodes

Comparative Analysis of Craters Formed on Cathode and Anode Spots of a Spark Discharge in Air on Iron Electrodes

Investigation of the influence of opening speed on vacuum arc under transverse magnetic field

The objective of this paper is to investigate the vacuum arc characteristics on transverse magnetic field (TMF) contacts at different opening speeds. Experiments are carried out at different opening speeds. The experimental current ranges from 7 to 16 kA (peak current) at approximately 50 Hz. The contact material is CuCr30. The results show that increasing the opening speed increases the expansion speed of the arc after ignition. A higher opening speed increases the gap distance at which an anode spot occurs and reduces the duration of the instability stage, and it also reduces the duration of the motion stage. The arc motion can be optimized by adjusting the opening speed. The moment of contacts separation has no obvious influence on the gap distance at the transition of the arc mode. When the arc ignites between the arms, it expands slowly. This phenomenon is analyzed by a finite element method. The simulation results show that the ignition position influences the current direction, which influences electromagnetic force of the arc. The radial electromagnetic force is smaller when the arc ignites between the arms, causing a stagnation of the 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.

Parametrization of electron sheath expansion for Langmuir probe I-V traces

The Langmuir probe is a common plasma diagnostic widely utilized in various fields of plasma physics, and its associated methods of data analysis remains in active development. In this work, we present an attempt using a power law parametrization model similar to Sheridan's empirical formulation is to describe the sheath expansion effect on electron current in an argon plasma. The fitting results using the power law parametrization method show observably better consistency compared to those using conventional interception method and inflection method. It is also observed that when used to fit the electron saturation current at probe bias voltages well beyond the plasma potential plus the argon ionization energy, resultant curve fitted by power law parametrization, as with that by linear fitting, deviates significantly from the curve fitted at lower bias voltages, albeit the saturation obtained fitted using the power law method remained consistent with that fitted at lower probe bias voltages. Probable causes of this deviation include anode glow or spots near the probe and the changes of the global plasma parameters via electron absorption at very high probe bias. The fact that the resultant electron saturation current remained consistent hints that these non-trival effects can also be approximated by power law parametrization.

Research on the Energy Characteristics of a Transferred Arc Plasma-Chemical Reactor for Waste Treatment

This study has been performed to reveal the main characteristics of operating a direct current (DC) plasma-chemical reactor (PChR) designed for hazardous waste treatment. The PChR employs thermal plasma as the operating environment. The investigations presented in this paper were conducted to study the electrical and energy characteristics of the plasma torch and plasma-chemical reactor during the destruction of inorganic waste. The PChR is equipped with a plasma torch with a nominal capacity of 50 kW and a free-burning arc. The zone of heat release from the atmospheric pressure DC arc cathode and arc anode (melted waste) spot is combined with the area of chemical reactions. The plasma torch (PT) parameters vary in the range of arc current I = 120–180 A, arc voltage U = 250–280 V, arc length x = 0–100 mm, and gas flow rate G = 1–3 g/s at atmospheric pressure, using air as the plasma-forming gas. The experimental results confirmed that plasma technology has several advantages over conventional incineration, including higher temperatures, heat source independence from the waste being processed or additional fuel, and a shorter exposure time in the high-temperature area. It was determined that the arc current increases with increasing arc length. With increasing arc length, the initial part begins to operate in a turbulent regime. This study determines the dependence on the heat flux transferred by electrons to the anode on the arc current. The convective heat flux density distribution over the anode heating spot was measured and discussed.

A pre-Columbian galvanic technique able to explain the gilding of copper in northern Peru

Around 150 BCE and 700 CE, pre-Columbian goldsmiths in the Peruvian northern coastline developed a method for gilding copper. The characteristics of the resulting pieces are substantially different from those obtained by hammering, embossing, and casting. We discuss two electrochemical gilding methods that were possibly developed by pre-Columbian goldsmiths. The first method consists of electrochemical replacement where copper is immersed in a solution containing dissolved gold. The second method utilizes the same solution but includes pyrite to form a galvanic cell with copper as the cathode and pyrite as the anode. Characterizations via X-ray fluorescence (XRF) and Scanning electron microscopy with energy dispersion spectroscopy (SEM-EDX) allowed a comparison of the results of the two methods with archaeological samples. The electrochemical replacement method does not reach thicknesses observed in archeological samples and delivers irregular gilding due to the formation of anodic spots on copper. Meanwhile, including pyrite as an anode in the electrochemical cell leads to a more homogeneous deposition of gold with layer thicknesses similar to those found in archaeological samples. This work contributes to understanding pre-Columbian techniques lost before the Inca Empire.

Numerical simulation and performance analysis of the radiofrequency inductive cathode

The radiofrequency (RF) inductive cathode has great prospects in space missions with long mission cycles, large speed increments, and rapid response requirements as the main electron source and neutralizer in Hall thrusters and ion thrusters. This paper proposes a comprehensive multi-physics RF inductive cathode model in which the RF electromagnetic field, electrostatic field for extracting electrons, flow field, plasma transport and electrochemical reaction process are all accounted for. Each physical field mentioned above can form a closed partial differential equation. The two-dimensional finite element code COMSOL is used to solve the multi-physics model. With this model, the formation process of the anode spot is exhibited and demonstrates the non-bipolar flow theory in practice. The simulation results demonstrate that the current jump in the RF inductive cathode is caused by the anode spot. Furthermore, the influences of preset discharge parameters such as RF power, bias voltage and actuating gas flow as well as structural parameters like the coil structure, discharge chamber size and ion collector area, emission hole size, distance between the anode target and the emission hole etc on the cathode performance are investigated, and some important optimal parameters are proposed.

Плавка кварц-лейкоксенового концентрата при рассредоточенном дуговом нагреве

Separation of titanium and silicon oxides in the melt of quartz-leucoxene concentrate of the Yarega deposit under diffuse arc heating was investigated. Melting was carried out in argon at atmospheric pressure at direct current in a graphite crucible with an arc power of ≈ 25 kW. The crucible with the material was the anode of the arc. The arc heating was dispersed by applying an axial magnetic field. At the same time, a diffuse anode spot with a current density of 8 A/cm2 was formed on the surface of the material. The current-voltage parameters of the diffuse arc were investigated. As a result of melting, an oxide ingot consisting of two phases was obtained, one of which is enriched with titanium oxide, the other with silicon oxide. However, the separation of these oxides did not occur completely due to the high cooling rate of the melt. Despite the low current density in the heating spot, the melt evaporated intensively. Evaporation occurred congruently. Due to the high temperature of the bath mirror, no volatile titanium oxide evaporated along with the volatile silicon oxide. Condensation of the evaporated material occurred selectively. A condensate, consisting almost entirely of SiO2, was formed in the form of powder on the cooled surfaces near the crucible. A specific surface area of the powder was 120 m2/g. The evaporated TiO2 was removed with the exhaust gas.

The influence exerted by active cooling on the permanent connection formed as a result of electric arc welding

The problem of temperature stresses is solved in the work. The process of electric arc welding with guaranteed penetration of steel plates of various thicknesses is simulated. The possibility of reducing residual stresses formed as a result of welding by applying heat removal from the surface of the near-weld region of a steel plate is being investigated. The temperature distribution is determined by solving a non-linear heat equation, in which the specific heat and thermal conductivity depend on temperature. The heat source is modeled using the double ellipsoid method proposed by John A. Goldak. The horseshoe-shaped heat sink follows immediately after the anode spot and is set by the heat flux in such a way that the main temperature of the plate does not decrease below its initial temperature. This limitation reduces the level of the temperature gradient, thereby reducing the stresses in the metal plate. To illustrate the effect of active heat sink, the temperature distribution in the top layer at the moment of termination of welding is compared with and without active heat sink. The material is assumed to be elastoviscoplastic, the deformations are small and consist of reversible and irreversible ones. Reversible deformations are related to stresses by the Duhamel - Neumann law. Irreversible strains increase when the von Mises plastic flow condition is satisfied, in which there is a plastic strain rate component responsible for the plastic flow viscosity. The elastic moduli (Young's modulus, Poisson's ratio) and the yield strength are assumed to be temperature dependent. The solution of the mechanical part of the problem is found by the method of simple iterations. For plates with different thicknesses, diagrams of residual stresses are given, located in the center of the plate from the seam to the periphery. As a result of the work, according to the obtained distributions of residual stresses in the plate material, it is concluded that the use of an active horseshoe-shaped heat sink from the near-weld zone when welding thin steel plates reduces residual stresses, therefore it is recommended to use in the welding process. The use of an active heat sink on the reverse side of the plate leads to an increase in the stress level, therefore it is not recommended for use.

Formation of multiple anodic fire spots inside an electrostatic cavity

AbstractCharged particles exhibit self‐organized behaviour during the discharge state transitions inside an electrostatic cavity, along with the energy redistribution in different coherent modes with progressive anode potential. Multiple sheath formations around the spherical metallic ball anode placed inside the cavity transit to intensely glowing multiple anode spot formations (fireballs) on the anode surface with progressive anode potential. The intensely glowing anode spots reorganize over the anode surface and multiply quickly on increasing the anode potential. The nonlinear analysis of the fluctuating discharge current reveals the presence of self‐organized criticality (SOC) during different states of discharge along with a strong memory effect within (10–104) time lags in every state of discharge. The multiple anode spots exhibit long‐range correlation in the absence of a magnetic field, indicating SOC behaviour. The present study investigates energy distribution among the coherent modes of discharge through the application of the Empirical Mode Decomposition technique. The analysis indicates that the introduction of a magnetic field results in the interchange of coherent modes carrying most of the energy during multiple spot formations. The present experimental configuration produces stable multiple coherent modes along with the evolution of anodic sheath layers in the absence and then in the presence of the magnetic field. Relating SOC with such discharge transitions may help to understand the relation between complex structure formations in plasma with nonlinear aspects of glow discharge, which is of vital importance in the investigation of complexities in space plasma.

Anode Input Heat Flux Density in High-Current Vacuum Arcs as Anode Spot Formation

In vacuum interrupters, anode spot significantly decreases the current interruption capability. Generally, the anode spot is evaluated by the anode spot threshold current. Unfortunately, as a circuit parameter, arc current cannot explain the anode spot formation from the physical point of view. This work proposes the heat flux density as a new parameter to evaluate the anode spot. The objective of this study is to determine the anode input heat flux density as anode spot formation. The heat flux density is numerically obtained by a two-temperature magnetohydrodynamic model. Based on a previous systematic experimental work over a wide range of discharge conditions, the calculated critical anode input heat flux density located in a narrow range from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.3\times 10^{8}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$11.3\times 10^{8}$ </tex-math></inline-formula> W/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{2}$ </tex-math></inline-formula> . Compared with the arc current, the anode input heat flux density is a key parameter in the interaction between the vacuum arc column and the anode; moreover, the heat flux density has a close relationship with both the arc distribution and the anode activity. Therefore, heat flux density is a reasonable physical parameter to reveal the mechanism of the anode spot formation.

Numerical investigation on transient arc characteristics and anode surface temperature considering the electrode movement

This work investigates the transient anode temperature and plasma parameters considering the electrode movement and the arc expansion. A transient self-consistent model is established using the dynamic mesh approach. Two cases with different maximum arc currents, representing various anode activity, have been studied. The simulations predict significant changes in spatial distribution of species densities, electron temperature and anode surface temperature in case with the anode spot formation. Furthermore, the influence of opening velocity on the plasma parameters has been studied numerically. The model was validated by comparison with experimental data for anode surface temperature as well as spectrally filtered arc images. Results of this comparison are presented and discussed.

Experimental Verification of Anode-Induced Phenomena During Prebreakdown Conduction in Vacuum Gaps Under Alternating Voltages With Special Electrode System

The results presented in this article relate to the work conducted to verify the existence of anode-induced phenomena, predominantly anode vaporization and consequent prebreakdown (PBD) current enhancement due to the impact of positive ions and microparticles over a relatively larger area at the cathode (presumably ion-assisted field (I-F) emission like). The verification of this hypothesis is attempted using a three-electrode arrangement. One electrode is comprised of a needle insulated from and projecting through a plane electrode (collector) of 40-mm diameter. It was surmised that if the positive ion beam from the anode spot (due to electron beam impact) were to be macroscopically diffuse, at least the collector would gather a part of it. However, no currents could be detected in the collector circuit even at voltages close to breakdown. The needle currents continued to display the typical characteristics of PBD currents under alternating voltages. The needle currents depended on the spacing between the needle tip and the plane of the collector and the polytetrafluoroethylene (PTFE) insulation used to prevent emission from the immediate vicinity of the needle evaporated significantly. Typical broad-area electrode behavior displayed by needle currents indicated that I-F emission, if any, is limited to the needle itself, which is certainly broad compared to the positive ion beam. Dependence of the PBD currents and breakdown voltages on the melting point of the anode material lend support to such anode-triggered electrode phenomena.

Investigation on anode modes of vacuum arc under different contact opening speeds

This paper aims to investigate the anode modes of vacuum arc at different opening speeds, especially at a high opening speed that exceeds 3 m/s. The butt contacts made of CuCr30 and CuCr50 with a diameter of 15 mm are used. Experiments are conducted at the current of 3.3, 4.4, 5.5, and 6.3 kA with a frequency of 50 Hz. An electromagnetic repulsion actuator provides the average opening speed from 1.7 to 3 m/s. The experimental results show that the number of droplets splashing into electrodes increases as the arc current increases, while a higher opening speed decreases the droplets. A higher opening speed will reduce the transferred charge before the anode spot type 2, and a higher Cr content increases the transferred charge before the anode spot type 2. Increasing opening speed will decrease the starting time of anode spot type 2, but it increases the gap distance when anode spot type 2 appears. Meanwhile, the increase in Cr content delays the formation of anode spot type 2.

Optical Investigation of Excited Species Distribution in Low-Current Vacuum Discharges

It is well-known that when high currents flow through a vacuum gap, anode spots are formed on the anode surface. However, anode flare phenomena are also observed in low-current vacuum discharges. The objective of this article is to experimentally observe the spatial distribution of excited Cu atoms and ions generated from a single cathode spot (CS) and to interpret the mechanism of the anode flare at low currents (40–80 A). Optical emission spectroscopy (OES) and laser-induced fluorescence (LIF) techniques have been used for investigating low-current vacuum arc discharge confined to axial magnetic fields (AMFs). The effects of AMFs and arc currents on the axial distribution of the radiation intensity were investigated for different copper ionization states (Cu I and Cu II). The highest luminance was found near the electrodes for both excited neutral copper atoms and ions, and only weak spectral lines of excited Ni atoms were detected in the near-anode region. With increasing the external AMF, a bright “spot” appeared near the anode surface. In the visible light range, excited atoms were the main contributor to anode flare in low-current vacuum discharge. As measured by LIF, the density of copper atoms near the anode increased from 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 10^{17}$ </tex-math></inline-formula> to 14 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 10^{17}\,\,\text{m}^{-3}$ </tex-math></inline-formula> when the applied magnetic fields increased from 31 to 74 mT. The anode flare contains far more excited atoms from the cathode material than the anode material. They are the results of cathodic plasma expansion to reach the anode after charge neutralization and reflection on the anode surface. For the single CS, the observed fact that a tiny number of atoms leave the anode surface and participate in the anode flare is more likely the result of a sputtering effect rather than thermal evaporation by cathode electron stream.

Al2O3 and TiO2 flux enabling activated tungsten inert gas welding of 304 austenitic stainless steel plates

Gas tungsten arc welding (GTAW) is important in those manufacturing where it is significant to control the mechanical and metallurgical characteristics and its weld bead geometry. This work has been committed to study the influence of oxide fluxes on welding of 4 mm thick 304 austenitic stainless steel plates. The Al2O3 and TiO2 were used as an oxide flux in powder form and are mixed with the acetone. The prepared mixture is applied on bead plate without any joint preparation and without filler wire addition. The Taguchi method with L9 orthogonal array is used to determine the optimal parameters. The current work aims to explore the influence of weld parameters on weld bead geometry (i.e. weld bead width, penetration and angular distortion), and mechanical &amp; metallurgical characteristics for 304 stainless steel welds. The oxide flux seems to narrow the arc and thereby the current density increases at the anode spot, that results in high weld depth.

Numerical simulation of low-current vacuum arc jet considering anode evaporation in different axial magnetic fields

As the main source of the vacuum arc plasma, cathode spots (CSs) play an important role on the behaviors of the vacuum arc. Their characteristics are affected by many factors, especially by the magnetic field. In this paper, the characteristics of the plasma jet from a single CS in vacuum arc under external axial magnetic field (AMF) are studied. A multi-species magneto-hydro-dynamic (MHD) model is established to describe the vacuum arc. The anode temperature is calculated by the anode activity model based on the energy flux obtained from the MHD model. The simulation results indicate that the external AMF has a significant effect on the characteristic of the plasma jet. When the external AMF is high enough, a bright spot appears on the anode surface. This is because with a higher AMF, the contraction of the diffused arc becomes more obvious, leading to a higher energy flux to the anode and thus a higher anode temperature. Then more secondary plasma can be generated near the anode, and the brightness of the ‘anode spot’ increases. During this process, the arc appearance gradually changes from a cone to a dumbbell shape. In this condition, the arc is in the diffuse mode. The appearance of the plasma jet calculated in the model is consistent with the experimental results.

Self-Organized Space Charge Structure Formations in DC Glow Discharge

Experimental investigations of a hollow cathode discharge through the controlled variation of anode potential inside a hollow cylindrical cavity, in the absence and presence of the magnetic field, reveal the self-organization of uniform complex space charge structure formation around the spherical anode into concentrated localized anode spots. The discharge current&#x2013;voltage (<inline-formula> <tex-math notation="LaTeX">$I$ </tex-math></inline-formula>&#x2013;<inline-formula> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula>) characteristic along with the electrostatic floating potential and discharge current fluctuations measured during the glow discharge regime suggest that the initial stable multiple sheath formation around the anode dissociates into intermittent multiple localized anode spot formations while passing through transient states during anode potential variation. On introducing a magnetic field, the localized concentrated anode spot formations on the anode surface undergo random distribution through self-organized criticality (SOC) and pronounced low-frequency oscillations (&#x007E;52.4 kHz). These oscillations gradually develop into harmonics of 100 kHz on further increasing the anode potential in the presence of the external magnetic field. Various discharge regimes are investigated through the time-resolved floating potential variation measurements using a cylindrical Langmuir probe (LP). We report on the relation between the discharge variations with the nonlinear time series analysis of the discharge current and floating potential fluctuations through the reconstructed phase space in different time domains to analyze the dynamics of complex structure formations and the existence of SOC behavior during the present hollow cathode discharge regime. The study of self-organized pattern formations and SOC behavior is vital for understanding the complex behavior of plasmas in the field of strongly coupled plasmas, plasma-based surface treatments, and thrusters for further development.

Analyzing Cathode and Anode Spot Movements of Atmospheric Arc Plasma in Parallel Electrodes Using Thermal Field Theory and Thermal Nonequilibrium Model

It is necessary to elucidate the mechanism of atmospheric arc plasma movement and the variation in its physical properties for constructing an accurate virtual model while using digital twin technology to design a next‐generation direct current circuit breaker. In this study, the calculation setting for considering the thermal nonequilibrium effect on an electrode surface was established. Moreover, the thermal field theory was employed for simulating the cathode spot movement and a thermal nonequilibrium model was implemented for analyzing the triggering factor of the re‐strike phenomenon occurrence on the anode surface. It was found that heavy particles (ions and neutral particles) were transported forward by the cathode jet and not only caused an increment in the electrical conductivity on the anode surface, but also increased the electric field between the arc column and the anode surface. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.