Arc Channel Research Articles

Production of a large area diffuse arc plasma with multiple cathode**Project supported by the National Natural Science Foundation of China (Grant Nos. 11475174 and11035005) and the Fundamental Research Funds for the Central Universities, China (Grant No. WK2090130021).

An arc channel at atmospheric pressure tends to shrink generally. In this paper, a non-transferred DC arc plasma device with multiple cathode is introduced to produce a large area arc plasma at atmospheric pressure. This device is comprised of a 42-mm diameter tubular chamber, multiple cathode which is radially inserted into the chamber, and a tungsten anode with a nozzle in its center. In argon/helium atmosphere, a large area and circumferential homogenous diffuse arc plasma, which fills the entire cross section surrounded by the cathode tips, is observed. Results show that the uniformity and stability of diffuse arc plasma are strongly related to the plasma forming gas. Based on these experimental results, an explanation to the arc diffusion is suggested. Moreover, the electron excitation temperature and electron density measured in diffuse helium plasma are much lower than those of constricted arc column, which indicates the diffuse helium plasma probably deviates from the local thermodynamic equilibrium state. Unlike the common non-transferred arc plasma devices, this device can provide a condition for axial-fed feedstock particles. The plasma device is attempted to spheroidize alumina powders by using the central axis to send the powder. Results show that the powder produced is usually a typical hollow sphere.

Research on the “jump sidewall” behavior and its signal characteristics in narrow gap P-MAG welding

Arc “jump sidewall” phenomenon is observed during P-MAG welding in narrow gap conditions. The mechanism and formation conditions are analyzed, and the phenomenon is found to be the arc channel re-establishment process, which results from large changes in the welding current. The arc channel position is the result of the balance between the electric field force and the magnetic field force. The current characteristics of P-MAG welding in a narrow groove provide adequate conditions for a “jump sidewall” phenomenon. The influences of a narrow gap groove on droplet transfer and arc signal of P-MAG power supply with modified I-I external characteristics are discussed. The research results lay a foundation for arc sensor-based welding seam tracking technology in narrow gap P-MAG welding.

Adaptive single-phase autoreclosing of high-voltage transmission lines based on steady-state parameters

Conventional adaptive single-phase autoreclosing (ASPAR) of extra-high-voltage transmission lines that uses the RMS voltage on the disconnected phase as the information-bearing parameter may have a dead band when high power is transmitted via the transmission line. This is caused by excess voltage during arcing after the arc extinction. The line end voltage under grounding arcing is determined predominantly by the longitudinal emf induced by the currents in the healthy phase. At the limit power-transmission angles, this voltage exceeds the recovery voltage after extinction of the secondary arc, which does not allow monitoring the status of the arc by the voltage. Using simple mathematical models, the existence of dead bands for both uncompensated and shunt-compensated lines (using four- or three-beam reactors) is shown. To establish the secondary arc extinction, it is proposed to monitor the voltage phase. The feasibility of the “phase” method was studied using a transmission line model based on matrix n-poles. The model considers the wire transposition and the nonlinearity of the grounding arc. Fundamentally, the phase method does not have any dead bands; however, owing to low arc channel conductance, a minor dead band may occur at large transmission angles and short circuits near the side of the voltage measurement. The restrictions to application of the “phase” method to the ASPAR are established and its typical dead band is identified.

Active flow control on a NACA 23012 airfoil model by means of magnetohydrodynamic plasma actuator

The paper is devoted to the study of high speed flow control around the airfoil by means of the Lorentz force. The latter is formed by creating the pulsed arc filament, moving in the magnetic field along the upper airfoil surface. The research was performed for the NACA23012 airfoil model at flow velocities up to 60 m/s (134 mph). The dynamic measurement of the aerodynamic forces on the airfoil was made. Changes up to 5% in an average value of lift and pitching moment were obtained at pulse repetition frequency up to 13 Hz and average discharge power less than 200 W. The amplitude of lift force oscillation was obtained as high as 10%, with the integration time of the balance 30 ms. The dynamic flow visualization of an airfoil model after a single discharge ignition was performed. It is shown that interaction of the main flow with the arc-induced disturbance leads to the dramatic changes in the flow structure. It was shown that the upstream movement of the arc channel (I = 40-700 A) leads to the local flow separation and simultaneously to the formation of a high pressure region above the model surface. Current paper presents investigation of previous work.

Research on the Self-Magnetic Field Distribution Characteristics of the Triggered Vacuum Switch With Multirod System

The motion of vacuum arc has an important effect on the performance of triggered vacuum switch with multirod (MTVS), and the motion characteristics of vacuum arc are closely influenced by the amplitude and profile of the magnetic flux density in the MTVS. A 3-D simulation model of the MTVS is built up, and the distribution of magnetic field of MTVS is calculated and analyzed. The simulation results show that the magnetic field in the interred gap has transverse component and longitudinal component. The simulation results also show that the transverse magnetic field is dominant when the MTVS is conducted by one single vacuum arc channel; however, the longitudinal magnetic field (LMF) is dominant when all the gap of the MTVS is conducted by vacuum arc. When the current flowing through the MTVS is up to 100 kA, the transverse component of magnetic field is up to 2.96 mT/kA, and the maximum value of the longitudinal component is up to 3.8 mT/kA, which meets the critical value of the LMF, which can keep the vacuum arc spreading. The influence of the structure parameters and the conductivity of vacuum arc on the magnetic field distribution are also analyzed. In addition, the high current capacity was tested, and the motion of vacuum arc in the MTVS has been investigated by the use of a high-speed camera. The experimental results agree well with the simulation results.

Characterization of a high current pulsed arc using optical emission spectroscopy

In this paper, we present the investigation realized on an experimental setup that simulates an arc column subjected to the transient phase of a lightning current waveform in laboratory conditions. Optical emission spectroscopy is employed to assess space- and time-resolved properties of this high current pulsed arc. Different current peak levels are utilised in this work, ranging from 10 kA to 100 kA, with a peak time around 15 µs. Ionic lines of nitrogen and oxygen are used to determine the radial profiles of temperature and electron density of the arc channel over time from 2 µs to 36 µs. A combination of 192 N II and O II lines is considered in the calculation of the bound–bound contribution of the absorption coefficient of the plasma channel. Calculations of the optical thickness showed that self-absorption of these ionic lines in the arc column is important. To obtain temperature and electron density profiles in the arc, we solved the radiative transfer equation across the channel under an axisymmetric assumption and considering the channel formed by uniform concentric layers. For the 100 kA current peak level, the temperature reaches more than 38 000 K and the electron density reaches 5 × 1018 cm−3. The pressure inside the channel is calculated using the air plasma composition at local thermodynamic equilibrium, and reaches 45 bar. The results are discussed and utilised to estimate the electrical conductivity of the arc channel.

Streamlining of a cylinder with an electric arc rotating in a magnetic field

Streamlining of a circular cylinder with a localized heat source modeling an MHD actuator in which the plasma arc channel moves along the cylinder surface under the action of the Lorentz force in a radial magnetic field is studied experimentally and simulated numerically. It is shown that the presence of a moving heat release region leads to a break in the symmetry in cylinder streamlining by the external flow and the appearance of a nonzero lift force and circulation.

Electrical and hydrodynamic characterization of a high current pulsed arc

High current pulsed arcs are of significant industrial interest and, aiming to reduce time and cost, there is progressively more and more need for computation tools that describe and predict the behaviour of these arcs. These simulation codes need inputs and validations by experimental databases, but accurate data is missing for this category of electric discharges. The principal lack of understanding is with respect to the transient phase of the current, which can reach thousands of amperes in a few microseconds. In this paper, we present the work realized on an experimental setup that simulates in the laboratory an arc column subjected to five levels of high pulsed current, ranging from 10 kA to 100 kA, with the last one corresponding to the standard lightning current waveform used in aircraft certification processes. This device was instrumented by high speed video cameras to assess the characteristic sizes of the arc channel and to characterize the shock wave generated by the arc expansion. The arc channel radius was measured over time during the axisymmetric phase and reached 3.2 cm. The position and velocity of the shock wave was determined during the first 140 μs. The background-oriented schlieren method was used to study the shock wave and a model for the light deflection inside the shock wave was developed. The mass density profile of the shock wave was estimated and showed good agreement with Rankine–Hugoniot relations at the wave front. Electrical measurements were also used to estimate the time-dependent resistance and conductivity of the arc for times lasting up to 50 μs.

Store-operated Ca2+ Entry-associated Regulatory factor (SARAF) Plays an Important Role in the Regulation of Arachidonate-regulated Ca2+ (ARC) Channels

The store-operated Ca(2+)entry-associated regulatory factor (SARAF) has recently been identified as a STIM1 regulatory protein that facilitates slow Ca(2+)-dependent inactivation of store-operated Ca(2+)entry (SOCE). Both the store-operated channels and the store-independent arachidonate-regulated Ca(2+)(ARC) channels are regulated by STIM1. In the present study, we show that, in addition to its location in the endoplasmic reticulum, SARAF is constitutively expressed in the plasma membrane, where it can interact with plasma membrane (PM)-resident ARC forming subunits in the neuroblastoma cell line SH-SY5Y. Using siRNA-based and overexpression approaches we report that SARAF negatively regulates store-independent Ca(2+)entry via the ARC channels. Arachidonic acid (AA) increases the association of PM-resident SARAF with Orai1. Finally, our results indicate that SARAF modulates the ability of AA to promote cell survival in neuroblastoma cells. In addition to revealing new insight into the biology of ARC channels in neuroblastoma cells, these findings provide evidence for an unprecedented location of SARAF in the plasma membrane.

Study of the AC arc discharge characteristics over polluted insulation surface using optical emission spectroscopy

Flashover of contaminated insulators is one of the major problems for the power distribution. Laboratory experiments have shown that the arc characteristics have great influences on the study of flashover performance of contaminated insulators. In order to investigate the characteristics of AC arc discharge on the polluted insulation surface, an experimental system was designed. The emission spectroscopy of arc discharge was obtained by a CCD spectrometer, and lithium chloride was added in the artificial pollution to introduce lithium as the indicator element in the analysis of arc emission spectroscopy. Arc temperature was obtained by employing the relative line intensities method, and the electron density was determined by analyzing the Stark-broadening values of the profiles. It was indicated that the temperature of partial arc increased with the leakage current value, but electron density of partial arc barely changes with leakage current. Special attention was paid to the influence of gas pressure on the characteristics of partial arc. It was found that both the arc temperature and the electron density of the arc channel increased with pressure in the case of same leakage current.

Vacuum arc with a distributed cathode spot as a plasma source for plasma separation of spent nuclear fuel and radioactive waste

Results from experimental studies of a vacuum arc with a distributed cathode spot on the heated cathode are presented. Such an arc can be used as a plasma source for plasma separation of spent nuclear fuel and radioactive waste. The experiments were performed with a gadolinium cathode, the properties of which are similar to those of an uranium arc cathode. The heat flux from the plasma to the cathode (and its volt equivalent) at discharge voltages of 4-15 V and discharge currents of 44-81 A, the radial distribution of the emission intensity of gadolinium atoms and singly charged ions in the arc channel at a voltage of 4.3 V, and the plasma electron temperature behind the anode were measured. The average charge of plasma ions at arc voltages of 3.5-8 V and a discharge current of 52 A and the average rate of gadolinium evaporation in the discharge were also determined.

Evolution of magnetically rotating arc into large area arc plasma**Project supported by the National Natural Science Foundation of China (Grant Nos. 11035005, 11475174, and 50876101) and the Science Instrument Foundation of the Chinese Academy of Sciences (Grant No. Y201162).

An arc channel tends to shrink due to its conductivity increasing with the increase of temperature. In this study, to generate large area arc plasma, we construct a magnetically rotating arc plasma generator, which mainly consists of a lanthanide tungsten cathode (13 mm in diameter), a concentric cylindrical graphite anode chamber (60 mm in diameter) and a solenoid coil for producing an axial magnet field. By controlling the cold gas flow, the magnetically rotating arc evolves from constricted mode to diffuse mode, which almost fills the whole arc chamber cross section. Results show that the diffuse arc plasma has better uniformity and stability. The formation mechanism of large area arc plasma is discussed in this paper.

Anchoring protein AKAP79-mediated PKA phosphorylation of STIM1 determines selective activation of the ARC channel, a store-independent Orai channel.

Although both the calcium store-dependent CRAC channels and the store-independent ARC channels are regulated by the protein STIM1, CRAC channels are regulated by STIM1 in the endoplasmic reticulum, whilst ARC channels are regulated by the STIM1 constitutively resident in the plasma membrane. We now demonstrate that activation of the ARC channels, but not CRAC channels, is uniquely dependent on phosphorylation of a single residue (T389) in the extensive cytosolic domain of STIM1 by protein kinase A. We further demonstrate that the phosphorylation of the T389 residue by protein kinase A is mediated by the association of plasma membrane STIM1 with the scaffolding protein AKAP79. Together, these findings indicate that the phosphorylation status of this single residue in STIM1 represents a key molecular determinant of the relative activities of these two co-existing Ca(2+) entry channels that are known to play critical, but distinct, roles in modulating a variety of physiologically relevant activities. The low-conductance, highly calcium-selective channels encoded by the Orai family of proteins represent a major pathway for the agonist-induced entry of calcium associated with the generation and modulation of the key intracellular calcium signals that initiate and control a wide variety of physiologically important processes in cells. There are two distinct members of this channel family that co-exist endogenously in many cell types: the store-operated Ca(2+) release-activated CRAC channels and the store-independent arachidonic acid-regulated ARC channels. Although the activities of both channels are regulated by the stromal-interacting molecule-1 (STIM1) protein, two distinct pools of this protein are responsible, with the major pool of STIM1 in the endoplasmic reticulum membrane regulating CRAC channel activity, whilst the minor pool of plasma membrane STIM1 regulates ARC channel activity. We now show that a critical feature in determining this selective activation of the two channels is the phosphorylation status of a single threonine residue (T389) within the extensive (∼450 residue) cytosolic domain of STIM1. Specifically, protein kinase A (PKA)-mediated phosphorylation of T389 of STIM1 is necessary for effective activation of the ARC channels, whilst phosphorylation of the same residue actually inhibits the ability of STIM1 to activate the CRAC channels. We further demonstrate that the PKA-mediated phosphorylation of T389 occurs at the plasma membrane via the involvement of the anchoring protein AKAP79, which is constitutively associated with the pool of STIM1 in the plasma membrane. The novel mechanism we have described provides a means for the cell to precisely regulate the relative activities of these two channels to independently modulate the resulting intracellular calcium signals in a physiologically relevant manner.

Study of the Influence of External Environment to Arc Channel in Argon with Laminar Flow

A 3D model is used to simulate free burning arc, and the influence of external environment to arc channel are discussed. The commercial CFD code FLUENT is used to model the plasma and the solid anode part. The cross-flow (2m/s, 5m/s, and 10m/s) and external magnetic fields (2mT, 5mT, and 10 mT) are applied to deflect arc. And then the condition they work together have also be discussed. Because the mechanisms of the influence are different, they only influences are reflect on the arc root displacement. The influence of arc root displacement to potential drop has been explained.

Speckle measurements of density and temperature profiles in a model gas circuit breaker

Speckle imaging was used to measure the density and temperature distribution in the arc zone of a model high voltage circuit breaker during the high current phase and under conditions simulating those present during current-zero crossings (current-zero-like arc); the arc was stabilized by a transonic, axial flow of synthetic air. A single probe beam was used; thus, accurate reconstruction was only possible for axially symmetric gas flows and arc channels. The displacement of speckles with respect to a reference image was converted to a line-of-sight integrated deflection angle, which was in turn converted into an axially symmetric refractive index distribution using a multistep process that made use of the inverse Radon transform. The Gladstone–Dale relation, which gives the index of refraction as a function of density, was extended to high temperatures by taking into account dissociation and ionization processes. The temperature and density were determined uniquely by assuming that the pressure distribution in the case of cold gas flow (in the absence of an arc) is not modified significantly by the arc. The electric conductivity distribution was calculated from the temperature profile and compared to measurements of the arc voltage and to previous results published in the literature for similar experimental conditions.

Transmission line transformer for reliable and low-jitter triggering of a railgap switch.

The performance of railgap switch critically relies upon multichannel breakdown between the extended electrodes (rails) in order to ensure distributed current transfer along electrode length and to minimize the switch inductance. The initiation of several simultaneous arc channels along the switch length depends on the gap triggering technique and on the rate at which the electric field changes within the gap. This paper presents design, construction, and output characteristics of a coaxial cable based three-stage transmission line transformer (TLT) that is capable of initiating multichannel breakdown in a high voltage, low inductance railgap switch. In each stage three identical lengths of URM67 coaxial cables have been used in parallel and they have been wounded in separate cassettes to enhance the isolation of the output of transformer from the input. The cascaded output impedance of TLT is ~50 Ω. Along with multi-channel formation over the complete length of electrode rails, significant reduction in jitter (≤2 ns) and conduction delay (≤60 ns) has been observed by the realization of large amplitude (~80 kV), high dV/dt (~6 kV/ns) pulse produced by the indigenously developed TLT based trigger generator. The superior performance of TLT over conventional pulse transformer for railgap triggering application has been compared and demonstrated experimentally.

Simultaneous imaging of two-dimensional electron density and air-flow distribution over air-blast decaying arc

Sensitive Shack–Hartmann type laser wavefront sensors were applied to simultaneous imaging of two-dimensional electron density and air-flow distributions over decaying arc channels under air blasting with several pressures. Our experimental results showed that higher blasting pressures facilitated the rapid reduction of arc diameters and an increase in the electron densities around the gap centre due not only to the thermal pinch effect but also to air-flow disturbances, although there were no significant effects of the air blasting on the arc conductance.

Decreasing the influence of arc feed currents and transient recovery voltages in single-phase conditions in EHV lines

One of the most efficient ways to solve the problem of reactive power compensation connected with restriction of unacceptable levels of voltage on extrahigh voltage (EHV) power-transmission lines is installation of additional shunting reactors (SR) in the EHV networks. Moreover, installation of shunting reactors leads to the occurrence of resonance overvoltages under single-phase operation conditions of power transmission (for example within the one-phase automatic reclosing time), as well as to the occurrence of deenergized current phase of the arc feed in the arc channel, which prevents fast deionization of another channel and increasing transient recovery voltage. In this paper, measures for decreasing the influence of arc feed currents and transient recovery voltages in single-phase conditions of EHV lines are considered.

Note: computational estimation of sparkgap inductance in nitrogen medium.

In this Note, attempt has been made to analytically derive the inductance of a sparkgap arc channel using fundamental circuit theory, heat transfer theory, and gas plasma equations. Simulation of a picosecond phenomenon of arc channel formation is attempted using coupled codes. Arc channel is assumed to be cylindrical and modeled as finite number of small coaxial cylinders filled with gas plasma. Conductivity of each gas plasma cylinder is found by its temperature. Current distribution in the cylinders is calculated using circuit theory and change in the current distribution with time is simulated. Over all inductance of the arc channel is computed for the current density distribution. Simulation is done for fast sub-nanosecond rising pulse. Experiments are conducted to measure the arc channel inductance and validate the same with the value found using computation.

Complex role of STIM1 in the activation of store-independent Orai1/3 channels

Orai proteins contribute to Ca(2+) entry into cells through both store-dependent, Ca(2+) release-activated Ca(2+) (CRAC) channels (Orai1) and store-independent, arachidonic acid (AA)-regulated Ca(2+) (ARC) and leukotriene C4 (LTC4)-regulated Ca(2+) (LRC) channels (Orai1/3 heteromultimers). Although activated by fundamentally different mechanisms, CRAC channels, like ARC and LRC channels, require stromal interacting molecule 1 (STIM1). The role of endoplasmic reticulum-resident STIM1 (ER-STIM1) in CRAC channel activation is widely accepted. Although ER-STIM1 is necessary and sufficient for LRC channel activation in vascular smooth muscle cells (VSMCs), the minor pool of STIM1 located at the plasma membrane (PM-STIM1) is necessary for ARC channel activation in HEK293 cells. To determine whether ARC and LRC conductances are mediated by the same or different populations of STIM1, Orai1, and Orai3 proteins, we used whole-cell and perforated patch-clamp recording to compare AA- and LTC4-activated currents in VSMCs and HEK293 cells. We found that both cell types show indistinguishable nonadditive LTC4- and AA-activated currents that require both Orai1 and Orai3, suggesting that both conductances are mediated by the same channel. Experiments using a nonmetabolizable form of AA or an inhibitor of 5-lipooxygenase suggested that ARC and LRC currents in both cell types could be activated by either LTC4 or AA, with LTC4 being more potent. Although PM-STIM1 was required for current activation by LTC4 and AA under whole-cell patch-clamp recordings in both cell types, ER-STIM1 was sufficient with perforated patch recordings. These results demonstrate that ARC and LRC currents are mediated by the same cellular populations of STIM1, Orai1, and Orai3, and suggest a complex role for both ER-STIM1 and PM-STIM1 in regulating these store-independent Orai1/3 channels.