Arc Lifetime Research Articles

Power supply output inductance effect on arc parameters of high-power impulse magnetron sputtering

The paper studies the influence of the power supply output inductance on the arc parameters, which form on the sputtered target surface during high-power impulse magnetron sputtering. The arc energy, lifetime and maximum current are measured by the up-to-date power source and the proposed arc simulation circuit at various output inductance values. The experimental data are compared with the simulation results. The paper presents a brief model description for the arc parameter calculations. According to the experimental data, the decrease in the output inductance leads to the increase in the peak current, arc lifetime and energy. It is shown that the energy recuperation stored in the output inductance allows reducing the arc energy. Also, self-locking of control transistor occurs at a lower value (∼1 µH) of the output inductance, leading to the reduction in the current amplitude and the additional decrease in the arc energy.

Modelling of Switching Characteristics of Hydrogen-Nitrogen Filled DC Contactor Under External Magnetic Field

<div class="section abstract"><div class="htmlview paragraph">The electric or hybrid vehicles need fast switching operation in order to ensure the quick-response of the motors. This process is carried out by compact direct-current contactors which are designed to perform the switching over multiple cycles. During the contact separation, the gas between the contacts breaks down and the resulting thermal arc provides a conductive channel that sustains the current. Until the arc is quenched, the current continues to flow through the contacts despite the physical separation. This unintended flow of current could lead to a larger response time than the safe operation limits. We perform high-fidelity simulation of thermal arc in hydrogen-nitrogen mixture environment under external magnetic field of 1 Tesla. The hydrogen enrichment level is kept at 0%, 40%, 50% and 80%. The contacts are separated at 8 m/s. It is demonstrated that the increase in hydrogen concentration leads to smaller arc lifetime thereby improving the circuit interruption performance.</div></div>

Phonon-limited transport and Fermi arc lifetime in Weyl semimetals

Weyl semimetals harbor topological Fermi-arc surface states which determine the nontrivial charge current response to external fields. We here study the quasiparticle decay rate of Fermi arc states arising from their coupling to acoustic phonons, as well as the phonon-limited conductivity tensor for a clean Weyl semimetal slab. Using the phonon modes for an isotropic elastic continuum with a deformation potential coupling to electrons, we determine the temperature dependence of the quasiparticle decay rate, both near and far away from the arc termination points. By solving the coupled Boltzmann equations for the bulk and arc state distribution functions in the slab geometry, we show how the linear response conductivity depends on key parameters such as the temperature, the chemical potential, the geometric shape of the Fermi arcs, or the slab width. The chiral nature of Fermi arc states causes an enhancement of the longitudinal conductivity along the chiral direction at low temperatures, together with a 1/T^2 scaling regime at intermediate temperatures without counterpart for the conductivity along the perpendicular direction.

Mathematical Modeling of Arc Faults in Networks with Low Single Phase-to-Ground Fault Currents

The article comprises the results of the research defining open-flame arcs self-quenching conditions in the event of a single phase-to-ground fault in overhead medium-voltage distribution networks according to existing theories of arc extinguishing. The calculations included metallic and arc faults modeling in a network with low phase-to-ground fault current. The arc gap simulation based on the mathematical channel model of a cylindrically symmetrical upright arc stabilized by rising convective gas flow was carried out in ATPDraw software program. The single phase-to-ground arc fault calculations results indicated an increase in high-frequency currents’ attenuation rate during transient processes as well as a reduce reduction in the electric arc lifetime from 8 ms to 2 ms in case of the breakdown voltage decrease from the peak value to zero. Notably, in case of low single phase-to-ground fault current the arc extinguishing took place at the first high-frequency current zero. For the cases of nonzero breakdown voltages, the electric arc extinguishing was detected at the fundamental frequency current component zero-crossing instant. The maximum overvoltage ratio of K = 2.8 was obtained as athe result of the single phase-to-ground fault at the peak phase voltage.

The heating sources of spots on the vacuum arc cathodes

We have considered two stages in the development of a spot on the surface of a vacuum arc cathode: the stage of ignition and the stage of the remaining arc lifetime which consists of arc spot operation until ultimately it is extinguished. A model for the near cathode region of electric arc has been applied to obtain different parameters involved in the cathode spot region during the spot ignition stage. This model is based on the construction of a thin sheath near the cathode wall and electron emission upon the thermo-field theory of electron emission. The model is time-dependent and hence the different parameters of the cathode, plasma and sheath can be derived as a function of time. In particular, we determine the required values of the plasma and sheath parameters for spot ignition on the smooth cathode surface. Based on these calculations and taking into consideration the fluctuation in plasma and sheath parameters, the contribution of different heating mechanisms at the spot initiation stage is evaluated. After spot ignition, some spot parameters such as temperature and mass density of spot material, electron current density and vapour pressure considerably increase. High values of the electron current density and low values of the electrical conductivity of the dense plasma in the spot region significantly increase Joule heating during the evolution stage of spot operation.

Influence of residual gases on cathode spot behavior

A residual gas in a vacuum arc chamber influences the behavior of the arc by two effects: it changes the state of the cathode surface, in particular the surface cleanness, and it influences the interelectrode plasma. Experiments are summarized dealing with the influence of the residual gas on the arc parameters in a pressure range of 10/sup -6/-10/sup -5/ Pa. With increasing pressure, general tendencies are a decrease in the fluctuations of the burning voltage, in the chopping current, and in the current density, and an increase in the arc lifetime, spot velocity, and spot diameter. The conditions at the cathode surface are decisive for the spot behavior and not the pressure. Surface contaminations render the arc more stable. The transition between the so-called cathode spot type 1 (on contaminated surfaces) and type 2 (on clean surfaces) was found to be smooth rather than abrupt.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The origin of current chopping in vacuum arcs

A semiempirical model is presented which relates the phenomenon of current chopping of vacuum arcs to rapid microscopic processes on the cathode surface. First, for a resistive circuit the approximate chopping current as a function of power-current amplitude was calculated using two DC arc lifetime parameters which were obtained experimentally. Secondly, it is shown that spontaneous arc extinction is the result of an accumulation of characteristic arc instabilities, each of which can be described as a randomly occurring transient arc resistance. Qualitatively, the 'severity' of these instabilities is demonstrated to depend on arc current, arc length, and circuit parameters. Thirdly, the presence of instabilities seems to be a manifestation of an ion deficiency in the near-anode region. This deficiency may be due to a discontinuity in the ionized mass flow into the plasma, occurring at a failure to initiate a new cathodic emission site in time. Based on these findings, the nature of the current-chopping phenomenon, hitherto explained by a minimum cathode spot operation current, can be coupled to the dynamics of the spot. >

The influence of cathode surface microstructure on DC vacuum arcs

The experimental results of the arc lifetime, the arc voltage, the cathode spot velocity and the erosion structure influenced by the cathode surface microstructure for low-current DC vacuum arcs are presented. The correlation between the arc voltage instability peak and the discontinuity in the cathode erosion trace has been shown when applying a transversal magnetic field. With increasing cathode surface roughness, an increase (of about a factor of 100) in the arc lifetime and a 30% decrease in arc voltage at the most, has been found for a drawn arc. The increase of the cathode spot velocity of the retrograde motion by cathode roughness is significant (a hundred times different at most) for triggered arcs. The mechanism of the cathode surface microstructure influence on the DC arc stability is discussed.

The influence of contact surface microstructure on vacuum arc stability and voltage

The authors present the results of DC vacuum arc lifetime and voltage measurements for contacts with different surface microstructures. This was realized by treating the contact surface with emery paper of varying roughness. The contact surface microstructure was found to have a large effect on the DC arc lifetime (several tens of times difference at the most) and arc voltage (30% difference at the most). The mechanism of the surface microstructure effect on DC arc stability was analyzed and is explained preliminarily. The rougher the contact surface is, the longer the arc lifetime and the more stable. The arc itself has a tendency to condition the surface in a way that is unfavorable for a sustained arc lifetime. The crater size for a rough surface is smaller than for a smooth one. The rougher the contact is, the lower the arc voltage (both DC and HF components). The arc erosion has a tendency to increase the arc voltage. It is probable that type I cathode spots (fast motion, small crater size) correspond not only to the surface contamination, but also to the surface roughness. >

Stability of low-current vacuum arcs

A detailed analysis of current and voltage 'noise' in a low-current vacuum arc is presented. The occurrence of typical instabilities in arc current is shown to be correlated to the DC arc lifetime. Influence of the parameters of the feeding circuit on the instability behaviour is investigated and explained qualitatively. A model of the interaction between circuit and arc is proposed on the basis of which arc extinction seems to be a result of an accumulation of instabilities at low currents (I<20 A).

Lifetimes of free-burning arcs in air

The stability of free-burning copper arcs in air has been investigated using a variety of electrode configurations. The longest lifetimes are obtained using a hollow-cratered cathode which yields lifetimes of more than 10s in the current range 50–250 A. These times are more than one order of magnitude higher than the lifetimes obtained with a pointed-rod cathode. Distortion of the electrode surface, due to prolonged arcing, reduces the arc lifetime.

Über die Lebensdauer von elektrischen Gleichstrombögen im Ultrahochvakuum

AbstractThe life time of de‐arcs in vacuum was found to be determined by thin film effects on the cathode surface. By removal of surface contaminations in UHV the average arc duration was greatly enhanced. A further enhancement occurs by deposition of clean metal films. This is demonstrated for Mo on Cu‐cathodes, and for Cu on Mo‐cathodes. Hence compound materials like MoCu show an extreme high arc duration. The vapour pressure of the cathode material, however, has a minor influence. Therefore an arc between MoCu‐electrodes emits more Mo‐ than Cu‐vapour, as it is shown by mass analysis. Measurements of dc‐field emission from arc cathodes (after the arc) show that the arc life time is correlated to the stability of field electron emission. The most intense field emitting sites are produced during the ignition of the arcs.

Der Einflu� der W�rmeleitung zur Kathode im elektrischen Feldbogen

For various cathode metalsKesaev has measured the arc lifetime as a function of current. RecentlyKingdon, assuming the field emission theory could not explain these experiments, suggested that the secondary electron emission produced by positive ions through a diffusion-controlled neutralization process determines the cathode mechanism. In this paper another assumption is made, based on the field emission theory: the cathode needs a minimal energy-supply for evaporation in order to maintain a higher vapourpressure and ion density near the cathode. For the mercury cathode this assumption seems to be valid. The temperature of the cathode spot and the voltage drop in front of it, for Bi, Pb, Zn, Tl, Cd, In, Sn, Cu, is not yet exactly known. Therefore the validity of the assumption made, concerning these materials can only be proved qualitatively.

The Arc Cathode Spot and Its Relation to the Diffusion of Ions within the Cathode Metal

Kesaev's recent data on the stability of vacuum arcs for a wide variety of solid and liquid cathodes furnish a greatly expanded range of criteria for determining the mechanism of the cathode spot. The large effects of phase and crystalline texture of the cathode suggest that an essential process occurs within the cathode metal itself. This is thought to be secondary electron emission produced by positive ions through a diffusion-controlled neutralization process. Each secondary initiates a short burst of thermal ionization in front of the cathode, which supplies practically all of the arc current. Survival of the arc depends on the emission of at least one new secondary within the period of the burst, and this depends on the current and on the rate of diffusion of ions into the cathode, the secondary emission being greater the larger the current and the slower the diffusion. Relative diffusion rates are estimated for most of the cathode metals used by Kesaev and it is found that the current required for a given arc lifetime increases regularly with the rate of diffusion of ions into the cathode metal. The analysis yields five new heats of diffusion—polycrystalline mercury and bismuth 16.2 and 18.3 kcal/mole, respectively; and liquid bismuth, thallium, and aluminum, 8.8, 3.2, and 3.4 kcal/mole, respectively. The diffusion rate is correlated with cathode temperature, dislocations, and vacancies, and the moving spot probes in all directions for areas of low diffusion rate. The arc is extinguished when all parts of the cathode line lie on micro-areas of high diffusion. The arc lifetime data furnish estimates of the concentrations of dislocations in all the solid and liquid (transient existence) metals as prepared by Kesaev. The concentration of edge dislocations is found to be approximately inversely proportional to the fourth power of the heat of vaporization. The statistics of arc lifetime as a function of current may be correlated by the Poisson formula, with each burst of ionization counting as a single Poisson trial, which is successful if it produces one or more secondary electrons. The analysis for liquid indium indicates that the bursts have a lifetime of about 5×10−7 sec. The random motion of the free spot on mercury is thought to be determined by random radial temperature-fluctuation gradients at the edge of the spot. The velocity of the free spot on mercury is limited to about 104 cm/sec because the spot must not outrun its secondary emission, which lags behind positive ion incidence on the cathode by about the 10−7 sec required for the diffusion secondary emission process in mercury. Retrograde motion of the spot in a magnetic field is found, qualitatively and semiquantitatively, to be due to the temperature gradient set up across the spot by the Righi—Leduc thermomagnetic effect. The retrograde velocity on bulk liquid mercury is subject to the same velocity limit of about 104 cm/sec as is the random velocity in zero field. A spot at a mercury—molybdenum boundary can jump to a substantially higher velocity when the Righi—Leduc gradient is high enough, and when, also, the increased velocity is great enough to permit the spot to operate on a mercury layer so thin that the diffusing ions have access to the molybdenum surface, where the more abundant supply of electrons accelerates the neutralization process, and thus decreases the time-lag of secondary emission. It is suggested that more sophisticated observation and analysis of cathode-spot statistics should furnish a valuable metallurgical tool for studying the texture and dislocation properties of metal surfaces. From the analysis of Kesaev's data some speculations are made about the origin and behavior of edge dislocations.

Experimental Study of Arc Stability. II. An Investigation of Mercury Arc Stability

The duration of an arc struck on a mercury pool has been studied under a variety of arc currents and vapor pressures. It is shown that at temperatures greater than −38°C the distribution of arc lifetimes follows an exponential decay law over the entire current range studied, whereas a distinct departure from this distribution occurs between −57° and −195°C. Over the current range 0.02–2.0 amp the mean arc lifetime varies from a few microseconds to 0.1 sec on a mercury cathode at 23.5°C. This study extends previous work and establishes that there is a sudden change in arc stability at the melting point. The data demonstrate, contrary to experience with liquid mercury, that an arc can be struck for very low currents in the case of solid mercury and, once struck, will burn for a finite length of time given by τ=τ0+KI, where τ0 is a residual lifetime for almost zero current. It is shown, however, that as the current is reduced, the probability of drawing an arc becomes diminishingly small.