High-current Vacuum Arc Research Articles

Advanced Temporal Analysis of Anode Activity during Mode Transitions in High Current Vacuum Arcs

Advanced Temporal Analysis of Anode Activity during Mode Transitions in High Current Vacuum Arcs

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.

Three-dimensional transient modeling and simulation of high-current multi-component vacuum arc under transverse magnetic field

This paper established a three-dimensional transient MHD model of a high-current multi-component vacuum arc under a transverse magnetic field (TMF) to simulate the dynamic characteristics of plasma parameters in the uniform motion mode of a contracted arc under lower TMF. The model considered the ionization–recombination process among the multi-components and used the P1 model to calculate the thermal radiation losses. The simulation results show that the ion number density of The TMF arc is on the order 1024 m−3, and when the plasma temperature reaches 4.3 eV, the effects of thermal radiation cannot be ignored. The majority of the plasma from the cathode and anode undergo acceleration and then deceleration before finally intersecting at the center of the arc, creating an extreme value of the density and the pressure, where a large amount of kinetic energy is converted into internal energy. The arc will be bent and deflected under the action of the ampere force, and the deflection of Cu3+ is especially obvious. The TMF affects the collision strength of the jet in the intersection area and, thus, affects the ion density, in which the change of Cu2+ is dominant. The ionization–recombination process of ions is mainly determined by the electron temperature, which is affected by the arc current. As the current decreases, Cu1+ increases and Cu2+ and Cu3+ decrease, and the change in ionization rate is the main reason for the change in the proportion of each ionic component; the heat flux density to the anode and cathode is on the order of 1010 W/m2, which heats the front of the arc and ensures the stable movement of the arc. Meanwhile, due to the high ion number density, the ion heat flux accounts for the main part of the heat flux, and the anode exhibits a higher proportion of ion heat flux.

Numerical Study of Large Contact Diameter and Gap High Current Vacuum Arc

Numerical Study of Large Contact Diameter and Gap High Current Vacuum Arc

Simulation of High Current Vacuum Arc with Hybrid Cathode Attachment

Simulation of High Current Vacuum Arc with Hybrid Cathode Attachment

Time-of-Flight Measurements in the Jet of a High-Current Vacuum Arc Thruster

Measurements of ion speed in the plume of a pulsed high-current vacuum arc thruster were performed by means of electrostatic probes. The probes were designed to provide direct speed measurements with minimum disturbance on the plasma jet. Typical mean values of vi for Ti and Cu cathodes are determined at different locations downstream of the electrodes, in the far field region. From one VAT discharge to another, the mean ion speed strongly varies which leads to a large statistical dispersion. Single-shot analysis allows the observation of the plume anisotropy and its high divergence as well as the existence of several ion groups of different speeds throughout a discharge.

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.

Influence of Electrode Surface Evolution on the Properties of High-current Vacuum Arcs in Switching Applications

Properties of high-current vacuum arcs in dependence on electrode surface status have been studied. The AC current pulses with 16kA (rms) at 50Hz have been applied to spiral contact system made of conventional CuCr material. Each contact pair was loaded with 20 shots. Arc diagnostics comprises arc current and voltage measurements as well as various optical diagnostics. Two high-speed cameras were used for analysis of arc dynamics. Near infrared radiation spectroscopy was applied for determination of the anode surface temperature after the arc extinguishing. The results show clear changes in arc dynamics and anode surface temperature with progressing surface ageing.

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.

Fractal dimension of cathode spots in a high-current vacuum arc thruster

The fractal dimension of cathode spots occurring in the discharge of a high-current vacuum arc thruster (VAT) are determined according to the Minkowski–Bouligand method. Photographs taken during operation of a 30 W VAT allowed observation of spots distribution over the surface depending on the cathode material. A machine learning model as well as a heuristic analysis permit to outline that work function, cohesive energy and ionization energy of the cathode material are the main driver in the magnitude of fractal dimension and total surface area covered by the spots.

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.

Experimental investigation on the evolution of vacuum arc in the quench protection switch based on forced current zero

In this paper, the evolution of vacuum arc under different conditions in the quench protection switch (QPS) based on forced current zero was investigated experimentally and analyzed quantitatively. Experiments were conducted with cup-shaped axial magnetic field (AMF) contacts in a demountable vacuum chamber. Images of the arc column were photographed through the observation window with a high-speed digital camera with exposure time of 2 μs. Arc appearance was analyzed quantitatively through digital image processing. Quantified arc appearance and arc voltage characteristics indicated that the high-current vacuum arc evolution in the QPS could be divided into four stages: arc formation stage, arc column merging stage, diffusing stage, and fast extinguishing stage. The influence of AMF on the evolution of high-current vacuum arc in the diffusing stage was also studied. Experiment results indicated that the vacuum arc at relatively low current had a simpler evolution process and the arc column merging had less correlation with voltage stability. It was found that the vacuum arc with a long gap distance developed faster and the time required to enter the stable burning state was shorter. In addition, the vacuum arc with long arcing time tended to constrict again, which is not beneficial to current interruption.

Radiation Power of a Short High-Current Vacuum Arc at High Current Densities

The radiation of a vacuum arc was measured in the spectral region <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200~\text {nm} \le \lambda \le 1100$ </tex-math></inline-formula> nm. The arc was initiated in the center of the cathode by breaking the current in the auxiliary circuit and was fed by the rectangular current pulse with a duration of 10 ms. The interelectrode gap was fixed at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$h = 4$ </tex-math></inline-formula> mm, and the butt <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2r =30$ </tex-math></inline-formula> -mm CuCr30 electrodes were used. The arc was stabilized by an external uniform axial magnetic field (AMF). The radiation was coming out of the vacuum chamber through quartz ultraviolet (KU)-1 quartz window. The radiation detector was a silicon photodiode with a diameter of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d =1.2$ </tex-math></inline-formula> mm. It was located on an axis intersecting the axis of symmetry of the discharge in the center of the interelectrode gap. The distance from the diode to the axis of symmetry was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L =1340$ </tex-math></inline-formula> mm. After amplification, the signal from the diode was recorded on an oscilloscope. The measurements were made in a range of currents from 10 to 25 kA in order to cover the modes with the anodic activity. It was found that under the conditions of these experiments, the anode activity begins to manifest itself at the end of the pulse, starting with currents exceeding 15 kA. As the current increases, the activity begins closer to the beginning of the pulse. Considering the type of the spectral sensitivity of the diode, two series of measurements were made—measurements without a filter and through a yellow filter ZhS-10 that cuts off radiation with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda \le400$ </tex-math></inline-formula> nm. The results obtained made it possible to analyze the dependence of the radiation power on the arc current. The results showed that at high current densities in the developed vacuum arc with anodic activity, a significant part of the power is transferred by radiation. At the end of a pulse with a current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 25$ </tex-math></inline-formula> kA, the radiation power is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {uv}}~\approx ~150$ </tex-math></inline-formula> kW, while in the discharge, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{a} ~\approx ~800$ </tex-math></inline-formula> kW is released. That is, at high current densities at the end of the pulse, the radiation power reaches almost 20% of the power released in the arc at this time. Estimates of lateral losses due to radiation are made.

Duration of Anode-Spot Mode Type 2 and Plume Mode in High-current Vacuum Arc

Duration of Anode-Spot Mode Type 2 and Plume Mode in High-current Vacuum Arc

Investigation on the arc root characteristics of vacuum arc between the iron-core cup-shaped transverse magnetic field contacts

The severity of the contact surface ablation determines the breaking capacity of the vacuum circuit breaker, and the interaction between the arc root and the electrode is the main cause of the contact surface ablation. The characteristics of the arc root determine the magnitude of the electromagnetic force received by the arc during the movement stage as well as the shape and speed of the arc movement. It will eventually affect the temperature of the contact surface and the ablation situation. This paper studied the arc root characteristics of high-current constricted vacuum arcs between the iron-core cup-shaped transverse magnetic field contacts and put forward the idea of using the ratio of cathode and anode arc root areas to quantitatively analyze the concentration of vacuum arc. The research on the arc root characteristics of the vacuum arc can help to improve the arc characteristics and arcing mechanism, and the proposition of the ratio can provide a new method for the study of constricted arc. This can provide a basis for improving the arc extinction performance of the switch, reducing the ablation of the contact material, and improving the contact life.

Numerical simulation of vacuum arc movement between transverse magnetic field contacts

The contact system of the vacuum switch is a crucial factor affecting the breaking performance of the vacuum switch. The study of the arc characteristics has significant impacts in improving the breaking ability of the vacuum switch. It is difficult to fully grasp the characteristics of the vacuum arc by experimental methods. The vacuum arc simulation model can obtain the internal parameters spatial distribution and motion characteristics more effectively. A high-current vacuum arc magnetohydrodynamic model was established, which considered the influence of ion and electron viscosity and the combined effect of the transverse magnetic field (TMF) and the axial magnetic field (AMF). The simulation obtained the plasma parameters of the arc column region as well as the temperature distribution characteristics of the cathode and anode surfaces. In addition, the changes in plasma parameters during arc movement under the action of different TMF and AMF components between TMF contacts were discussed. The simulation results are relatively consistent with the experimental results and the existing research results, which provide theoretical support for the research on the mechanism of vacuum arc motion characteristics.

On hybrid type of cathode attachment in high current vacuum arcs

This paper discusses the issues of a possible change of the type of cathode attachment of high-current vacuum arcs (HCVA) with an average cathode current density of more than 105 A/cm2. This type of HCVA is used as pumping plasma gun in experiments with plasma puff z-pinches. These experiments showed that the measured linear mass of the HCVA plasma jet is much higher (by a factor of 10 or more) than the expected mass, which can be obtained from the assumption that cathode attachment occurs only through a multitude of cathode spots emitting supersonic plasma jets. It is shown that in HCVA of the type under consideration, at some time instant there are two types of cathode attachments - cathode spots and thermionic erosion attachment (TEA). It can be said that HCVA of this type have a hybrid cathodic attachment. Unlike cathode spots, TEA produces a subsonic plasma flow, which contributes to an increase in the linear mass of the HCVA plasma jet.

Measurement of the expansion velocity of the plasma high-current vacuum arc discharge

In this work, we present experimental results on measuring the velocity of vacuum arc discharge plasma expansion. In the experiments, two designs of plasma guns were used. In the first version, the end of the arc discharge cathode was located below the plane of the anode, and the surface of the insulator separating them was parallel to the axis of symmetry of the plasma gun. In this design, the arc discharge plasma escapes the anode through a hole, the diameter of which coincides with the diameter of the cathode. In the second variant, the plane of the end face of the arc discharge cathode coincided with the plane of the anode, and the surface of the insulator separating them was located perpendicular to the axis of symmetry of the plasma gun. To obtain an image of plasma in the optical range, an FER-7 optical streak camera was used. Based on the results obtained, it can be concluded that the expansion velocity of the plasma of a high-current vacuum arc discharge does not depend on the design of the guns considered in this experiment.

Determination of the voltage drop on a high-current vacuum arc discharge under conditions of a limited cross-section of the plasma flow

The work is devoted to the study of the high-current vacuum arc discharge characteristics under conditions of a limited cross-section of the plasma flow. The experiments were carried out on the IMRI-5 setup with a sinusoidal arc current amplitude of 300–350 kA and a rise time of 500 ns. Aluminum rods with diameters from 3 to 7 mm were used as a cathode. The plasma flow was formed in a channel whose diameter was equal to that of the cathode. The features of the formation of a plasma jet with various configurations of the used plasma gun are described. The electrophysical parameters of the arc discharge are presented. Theoretical estimates of the voltage drop across the high-current arc during the outflow of a plasma flow through holes with a limited diameter are provided.

Investigation of the aluminum electrodes erosion of a plasma gun during the operation of a high-current vacuum arc discharge

The aim of this work was to obtain magnitude quantitative estimates of the “closed-type” plasma gun aluminum electrodes erosion that occurs during the course of a high-current vacuum arc discharge. The experimental setup consisted of two current generators. The first generator capable of generating a current with an amplitude of up to 450 kA and a rise time of 500 ns was used as a current source for a plasma gun. The second one was used as an X-ray radiograph to visualize the object under study in the soft X-ray range (hv ≈ 0.5–3 keV). Quantitative distributions of the plasma linear mass are obtained both along the radius and along the length of the jet at different times. It was shown that the erosion properties of the electrode material are related to the current characteristics of the arc discharge current.