Anode Plume Research Articles

Investigation on anode plume in high-current vacuum arc by experiments and simulations

The objective of this paper is to investigate anode plume in high-current vacuum arc through experiments and simulations. A series of experiments are carried out in a demountable vacuum chamber at different current levels with the CuCr40 contact. Combined with arc voltage and arc image, the formation and evolution of typical anode modes, especially anode plume, are analyzed. The contact erosion and scanning electron microscopy (SEM) results are also discussed after experiments. Based on the experimental results, a two-dimensional (2D) magneto-hydro-dynamic (MHD) model is adopted to study the physical characteristics of anode plume. The experimental results show that a larger current leads to a more intense anode mode forming at smaller gap distance with a bigger and brighter arc column. Anode plume is generated between anode spot type 2 and current zero due to the obvious pressure difference between anode vapor and cathode plasma, which is confirmed by the simulation results of different anode temperatures. The contact erosion is more severe in the area where anode plumes frequently appear. The spatial distribution of number density, temperature, pressure, and electrical conductivity of anode plume are analyzed by simulations, and therefore the related experimental phenomena are explained.

Experimental Investigation on Anode Spots and Anode Plumes in High-Current Vacuum Arc Under Different Contact Materials

The objective of this article is to investigate the effect of contact material on the formation and transition of high-current anode spots and anode plumes. A series of experiments are carried out in a demountable vacuum chamber at three current levels of 3, 4, and 6.5 kA. Plate contacts made of CuCr30 and CuCr40 with a diameter of 10 mm are adopted. Arc images are captured by a high-speed camera and synchronized with measurements of the arc current and voltage. The experimental results show that the three typical anode discharge modes, namely footpoint, anode spot type 1, and anode spot type 2, are formed at a smaller gap distance as the experimental current increases, and this tendency is independent of the contact material. The arc voltage is higher and the anode spot appears earlier and lasts longer under the CuCr40 contact than under the CuCr30 contact. As a result, the footpoint is formed at a smaller gap distance, whereas anode spot type 2 is formed at a larger gap distance. As a special anode discharge mode, an anode plume usually occurs between anode spot type 2 and arc current zero in various shapes at different locations on the anode surface. The anode plume of the CuCr40 contact appears at a larger gap distance and the corresponding threshold current and accumulated arc energy are also larger. Due to a stronger anode activity, the anode plume lasts a longer time under the CuCr40 contact than under the CuCr30 contact.

Modeling of vacuum arc plasmas in anode spot or anode plume mode taking into account multiple ion components

This work investigates the arc behaviors with CuCr25 electrodes considering anode vapor using a magneto-hydro-dynamic model. Different kinds of components are considered including ions (Cu and Cr) with different charge numbers, electrons, and atoms (Cu and Cr). The effect of the anode sheath is also considered. The density distributions of these components are analyzed and compared with the experiments during the anode spot mode and the anode plume mode. Simulation results show that the anode vapor can enter the arc column forming a cool and poorly conducting region (i.e., neutral atom vapor area, NAVA) under high anode temperature. Atoms and single-charged ions mainly gather near each electrode. The highest double-charged ion density can be seen in front of the NAVA. Triple-charged ion density is negligibly low and reaches its maximum where the electron temperature is high. Cr is more likely to be ionized to a higher ionization level compared with Cu. Our results agree with experimental measurements of density distributions of different components and plasma temperature.

Computer simulation of high current vacuum arc with developed anode spot

A self-consistent simulation of anode heating by 4.5 kA vacuum arc during the half-wave of 50 Hz current with 1 m/s contact opening was carried out. The calculations were done in the framework of hybrid high current vacuum arc model, which treats ions and atoms as macroparticles with the help of particle-in-cell methods, but electron subsystem is treated as massless fluid with quasineutrality assumed. The occurrence of an anode plasma plume (similar to that found in experiments) was obtained as a result of modeling. It is shown that the energy flux of line radiation from the interelectrode plasma to the anode is a critical reason of the appearance and maintenance of the anode plume.

Investigation of Anode Plume in Vacuum Arcs Using Different Optical Diagnostic Methods

This paper presents the results of different optical diagnostic methods to investigate an anode plume which forms after the extinction of anode spot type 2. The formation of the anode plume is investigated by means of three high-speed cameras. Two high-speed cameras, positioned perpendicular to each other, are used to observe the general anode plume evolution. The third camera is connected to a spectrograph enabling the video spectroscopy. The arc is driven by a damped 50-Hz ac between Cu/Cr 75/25 butt contacts with a diameter of 10 mm. The emission coefficients for atomic and ionic Cu lines during anode plume formation are calculated. The inner part of the anode plume is dominated by atomic line radiation, whereas the outer part is dominated by the emission of singly charged ionic lines. The radiator density of the Cu I 510.55 nm is about $3\times 10^{17}\,\,\text{m}^{-3}$ compared with a radiator density of Cu II of $9\times 10^{13}\,\,\text{m}^{-3}$ at the same position inside the anode plume. A broadband absorption spectroscopy is used to determine the ground-state densities of Cu and Cr after the extinction of anode plume at current zero (CZ). The density of Cu I is about 1.5 times higher than Cr I at the same time around CZ. Moreover, near-infrared spectroscopy together with thermography is used to determine the anode surface temperature around CZ after the extinction of an anode plume. The central anode surface temperature varies from 1530 to 950 K within 20 ms after CZ.

Study of vacuum arc behavior under anode spot and anode plume modes

Anode spot (AS) and anode plume (AP) phenomena are widely observed in vacuum arc experiments and are related to anode melting and evaporation under strong heating from the arc column. Anode vapor will then strongly influence the arc column through ionization-recombination and energy exchange among atoms, ions, and electrons. This work investigated the characteristics of the vacuum arc with AS or AP using the two-dimensional magnetohydro dynamic model. Formation of the AS and AP modes was studied and analyzed using numerical simulation. Friction forces between ions and atoms were also taken into account. Simulation results show that anode vapor expansion depends on the pressure balance between the anode jet and cathode plasma. Higher anode temperature produces a larger neutral atom vapor area (NAVA), which was dominated by neutral atoms. Inside the NAVA, ion and electron temperatures were low in the AS and AP mode due to ionization and energy exchange. Electric conductivity in this area was also so low that the location of the maximal current density was near the edge of the anode instead of the anode center. The asymmetric appearance of an AP was mainly caused by the asymmetric anode temperature distribution with respect to the AS center. Qualitative comparisons show that the simulation results are consistent with the experimental results.

Determination of Cr density during high-current anode modes in vacuum arc

The results of Cr density during high-current anode modes using broadband absorption spectroscopy are presented. The vapor density of atomic Cr is determined during the formation of anode spot type 1, anode spot type 2, and anode plume. Cr I resonance lines at 425.43 nm are used for the analysis. An AC current pulse with a maximum of about 7 kA and a frequency of 100 Hz is applied. By adjusting the opening time or contact opening speed, anode spot type 1 and type 2 may appear. The temporal evolution of the ground state density of Cr atoms shows about two times higher metal vapor during anode spot type 2 compared with anode spot type 1. The vapor density during an anode plume following anode spot type 2 is also determined and is compared with the same time instant in which no anode plume appears, i.e., only when anode spot type 1 appears.

Vapor density and electron density determination during high-current anode phenomena in vacuum arcs

This paper presents time and space resolved results of spectroscopic measurements in a vacuum circuit breaker experiment during high-current anode modes, i.e., anode spot type 1, anode spot type 2, and anode plume. Excited state densities for Cu I, Cu II, and Cu III transitions are determined during anode spot type 1 and type 2 as well as for the anode plume. Temporal evolution of excited state densities and Cu neutral gas densities are also determined during anode spot type 1 and type 2, which show that the Cu density in front of the anode during anode spot type 2 is about 6 times higher compared to anode spot type 1. Electron densities are also determined during both types of anode spot using Stark broadening. The electron densities during anode spot type 2 are remarkably higher than during anode spot type 1.

Determination of Cr Density After Current Zero in a High-Current Vacuum Arc Considering Anode Plume

Results of broadband absorption spectroscopy in high-current vacuum arcs after current zero (CZ) are presented. Vapor density of atomic Cr is determined within 3 ms after CZ in cases with an anode plume which appears at about 400 $\mu \text{s}$ before CZ and after extinction of anode spot type 2. The anode plume is a cloud of metal vapor which develops on the anode after the extinction of one specific high-current anode mode, namely, anode spot type 2. An ac current pulse of about 7 kA from a high-current generator with operation frequency of 100 Hz was applied. Cr I resonance lines at 425.43, 427.78, and 428.97 nm were chosen for the analysis. The temporal evolution of the ground state density of Cr atoms within first 3 ms after CZ starts with about $2.5 \times 10^{18}~\text{m}^{-3}$ and decreases almost linearly with $0.65 \times 10^{18}~\text{m}^{-3}$ /ms. The Cr I densities in cases with and without anode plume corresponding to anode spot type 2 and 1, respectively, are compared at 100 $\mu \text{s}$ after CZ. In cases with anode plume, the metal vapor density is about 60% higher than in cases without plume, although the interrupting current is the same. The general behavior of the copper component is expected to be very similar to that of chromium.

Optical and Electrical Investigation of Transition From Anode Spot Type 1 to Anode Spot Type 2

This paper presents differences between anode spot type 1 and type 2 and the discharge conditions for a transition from anode spot type 1 to type 2 are investigated by means of optical and electrical measurements. The transition from the diffuse mode to the high-current anode modes (footpoint, anode spot type 1, and anode spot type 2) is studied with respect to spatial and temporal distributions of different ionization levels of Cu lines, voltage–current waveforms, transferred charge, and aspect ratio. The driving current pulse was applied by a high-current generator which corresponds to a pulsed dc of 10-ms duration. Spectral lines of Cu I, Cu II, and Cu III are analyzed for various anode modes using a combination of an imaging spectrograph and a high-speed camera. The results show that during the formation of the anode spot type 2, the intensity of all lines change noticeably. Significant differences are found, for example, in the spatial structure of Cu III lines in the anode spot modes. A jump in the arc voltage corresponding to the time of intensity changes appears at the transition from anode spot type 1 to type 2. The impact of transferred charge, instantaneous current, and aspect ratio on the formation of the anode spot type 2 is also investigated. The transition from anode spot type 1 to type 2 is dominated by the ratio of electrode diameter to gap length. The formation of an anode plume is always observed after extinction of anode spot type 2 and before current zero.

Time and space resolved spectroscopic investigation during anode plume formation in a high-current vacuum arc

This paper presents time and space resolved results of spectroscopic measurements during the formation of an anode plume in the late current pulse phase of a high-current vacuum arc. The formation of the anode plume is investigated systematically based on the occurrence of high-current anode spots, depending on gap distance and current for AC 100 Hz and CuCr7525 butt contacts with a diameter of 10 mm. The anode plume is observed after the extinction of anode spot type 2 in which both the anode and cathode are active. It is concluded from the spatial profiles of the atomic and ionic radiation, parallel and perpendicular to anode surface, that the inner part of the plume is dominated by Cu I radiation, whereas a halo of light emitted by Cu II covers the plume. The radiation intensity of Cu III lines is quite low across the whole anode plume. Upper level excited state densities corresponding to Cu I lines at 510.55, 515.32, 521.82, 578.21 nm are determined. The temporal evolution of the resulting excitation temperature in the centre of the plume varies from 8500 K to 6000 K at 500 µs to 100 µs before current zero, respectively. The density calculated for Cu I at position in the plume is in the range of 1–5 × 1019 m−3.

Emission Spectroscopy During High-Current Anode Modes in Vacuum Arc

A vacuum interrupter reaches its interruption limit once high-current anode phenomena occur. High-current anode modes lead to an increase of the anode surface temperature and an increased generation of metal vapor, which may result in a weakening of the dielectric recovery strength after current zero. In this work, different discharge modes in a vacuum arc for AC 50 Hz including diffuse, footpoint, anode spot type 1 and type 2, and anode plume are investigated. Electrodes made of CuCr7525 with diameter of 10 mm are used. The final gap length is about 20 mm. Time and space resolved optical emission spectroscopy is used to examine the temporal and spatial distribution of atomic and ionic copper lines. The distribution of atomic and ionic lines parallel and perpendicular to the anode surface is investigated. Radiator density is also determined for CuI, CuII, and CuIII near the anode surface.

Experimental study of plasma parameters in a vacuum arc with a hot refractory anode

The spatial distributions of plasma density, electron temperature, plasma potential and ion energy were measured during hot refractory anode vacuum arc (HRAVA) development as functions of arc current and inter-lectrode gap distance. Plasma density increased with arc time and saturated (⩾1014 cm−3) in the developed HRAVA stage. While the ion energy in the anode plasma at the gap exit was relatively small, the ions were accelerated outside the gap in radially expanding plasma to ∼15 eV at 19 cm from the electrode axis. The electron temperature decreased during anode plume development and was ⩾1 eV in the developed HRAVA stage. Measured plasma parameters agreed well with previously developed theory.

Angular distribution of ion current in a vacuum arc with a refractory anode

The total ion current and its angular distribution were measured in the radially expanded plasma of a hot refractory anode vacuum arc (HRAVA). The ion current increased during the transition from the initial cathodic arc stage to the developed HRAVA stage. The total ion current in the HRAVA was found to be significantly higher (up to 50%) than that found in the conventional cathodic arc. On the initial cathodic arc stage the ion current angular distribution peak was shifted from the gap mid-plane to the anode direction due to the contribution of the cathode plasma jets. In contrast, in the developed HRAVA stage and with small gaps (<6 mm) ion current angular distribution was symmetric with respect to the gap mid-plane due to dissipation of the cathode jets in the dense inter-electrode plasma of the anode plume. With large gaps (>20 mm), the developed HRAVA stage was more stable than the initial cathodic arc stage, due to the increased plasma density in the gap.