Observation of arc modes in a magnetically rotating arc plasma generator

An arc plasma can present various forms under the influence of an external magnetic field. In this study, a magnetically rotating arc plasma generator has been developed to produce three arc modes, namely rigid arc, distorted arc, and diffuse arc, which are obtained by controlling the gas flow rate. The evolution of these arc modes are experimentally studied and discussed. Results show that, as the gas flow rate increases, the arc mode is first transformed from the rigid to the distorted mode, and then to the diffuse mode. Comparisons show that the location of the arc attachment is a key factor in determining the rigid and distorted modes. The diffuse arc is observed under larger gas flow rates, but the completely diffuse arc can exist only within a narrow range of gas flow rates. Compared to the distorted arc, the diffuse arc has not only better stability but also a wider high‐temperature plasma zone, which indicates that the diffuse mode may be more useful in industry.     

Production of a large area diffuse arc plasma with multiple cathode

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.     

Experimental observation and numerical analysis of arc plasmas diffused by magnetism

At atmospheric pressure, an intensified charge-coupled device (ICCD) camera with a narrow-band filter is used to capture the unsaturated images of a magnetically rotating arc. Comparison of its configurations with different arc current and external axial magnetic field (AMF) strength shows that the strong electromagnetic force may impel the arc to diffuse. Under the fully diffuse mode, the plasma is distributed throughout the electrode gap and no anode attachment can be seen in the cross-section of the torch. The fully diffuse plasma runs more steadily and its intensity distribution is more uniform, while its voltage fluctuation is reduced significantly. Using a commercial CFD (computational fluid dynamics) code FLUENT, the fluid flow and heat transfer of the fully diffuse plasma in an assumed magnetron torch have been simulated for qualitatively discussing the AMF effects. Numerical results show that the AMF significantly impels the plasma to retract axially and expand radially. As a result, the plasma intensity distribution on the cross section of the torch gets to be more uniform.     

Enhancement and stabilization of cathodic arc using mesh anode

The performance and characteristics of a cathodic arc deposition apparatus consisting of a titanium cathode, an anode with and without a tungsten mesh, and a coil producing a focusing magnetic field between the anode and cathode arc investigated. The arc voltage V_a is measured with a fixed arc current for an anode diameter of 40 mm. The relationship between V_a and the magnetic field B with and without a mesh is obtained. In addition, the relationship between the arc current I_a and V_c, the voltage to which the artificial transmission line was charged, is measured with and without the mesh to determine the minimum ignition voltage for the arc when the anode hole diameter is 40 mm. The arc resistance increases with the focusing magnetic strength B and decreases when using the mesh. Our results indicate that the high transparency and large area of the mesh allows a high plasma flux to penetrate the anode from the cathodic arc. The mesh also stabilizes the cathodic arc and gives better performance when used in concert with a focusing magnetic field     

大面积分散电弧等离子体的ICCD图像分析

用增强型电荷耦合检测器(ICCD)和窄带干涉滤光片相结合的方法拍摄了未饱和氩等离子体的分散电弧的非饱和图像。对不同励磁电流下电弧形态的分析比较,证实了在强电磁力的作用下弧柱趋于扩散。在电弧完全分散条件下,对ICCD拍摄非饱和图像的光强分析,表明分散电弧具有较为均匀的分布。所采集的电弧电压的脉动幅度显著降低,分散电弧稳定运行。实验中观测到了稳定的多阴极弧根和弥散阴极弧根的现象,这表明电弧已扩散。     

Dynamic behaviour of alternating current arc discharge in a multi‐arc generator at atmospheric pressure

In this letter, a multi‐arc generator with three high‐voltage electrodes and a common grounded one was developed for the purpose of obtaining large area and steady arc plasma at atmospheric pressure. Three typical discharge states were found in the multi‐arc generator: independent movement of three arc columns, confluence of two arc columns, and confluence of three arc columns. The three discharge states cyclically occur on the evolution of the arc discharge and their duration is influenced by the power dissipation and plasma working gas flow rate. With an increase of discharge power and a decrease of the gas flow rate, the duration of multiple arc confluence increases, which contributes to the suppression of the fluctuation amplitude of each arc. Frequency domain analysis of the arc voltage envelope shows that the frequency of arc fluctuation increases in the multi‐arc mode in the multi‐arc generator compared to that in the single arc mode.     

Effect of acoustic field parameters on arc acoustic binding during ultrasonic wave-assisted arc welding

As a newly developed arc welding method, power ultrasound has been successfully introduced into arc and weld pool during ultrasonic wave-assisted arc welding process. The advanced process for molten metals can be realized by utilizing additional ultrasonic field. Under the action of the acoustic wave, the plasma arc as weld heat source is regulated and its characteristics make an obvious change. Compared with the conventional arc, the ultrasonic wave-assisted arc plasma is bound significantly and becomes brighter. To reveal the dependence of the acoustic binding force on acoustic field parameters, a two-dimensional acoustic field model for ultrasonic wave-assisted arc welding device is established. The influences of the radiator height, the central pore radius, the radiator radius, and curvature radius or depth of concave radiator surface are discussed using the boundary element method. Then the authors analyze the resonant mode by this relationship curve between acoustic radiation power and radiator height. Furthermore, the best acoustic binding ability is obtained by optimizing the geometric parameters of acoustic radiator. In addition, three concave radiator surfaces including spherical cap surface, paraboloid of revolution, and rotating single curved surface are investigated systematically. Finally, both the calculation and experiment suggest that, to obtain the best acoustic binding ability, the ultrasonic wave-assisted arc welding setup should be operated under the first resonant mode using a radiator with a spherical cap surface, a small central pore, a large section radius and an appropriate curvature radius.     

亚大气压六相交流电弧等离子体射流特性研究:实验测量

以临近空间高超声速飞行器以及航天器再入大气环境飞行过程"黑障"问题的研究为背景,进行了多相交流电弧放电实验装置的物理设计,建立了六相交流电弧等离子体实验平台(MPX-2015),在背景压力为500 Pa的亚大气压条件下获得了最大直径和长度分别达到14.0 cm和60.0 cm的等离子体射流.研究了工作气体流量、真空腔压强、电极间距以及弧电流等因素对等离子体自由射流和冲击射流特性的影响规律.结果表明:在实验参数范围内,真空腔压强对等离子体的射流特性影响最为显著,等离子体自由射流的长度和直径以及冲击钝体条件下的鞘套有效工作长度和厚度均随着压强的降低而增大;提高沿电极环缝注入的工作气体流量或弧电流亦有利于等离子体鞘套尺寸的增加.上述工作有助于进一步开展临近空间飞行器与其周围复杂介质环境间复杂的气动热效应和"黑障"问题的研究.     

A rotating arc gas pump for circuit breaking and other applications

A rotating arc circuit breaker is described which uses an auxiliary current source to generate the magnetic field for driving the arc. Test results obtained using optical fiber measurement systems have shown that there are three main arcing phases. Initially the arc rotates at an essentially constant but low velocity, subsequently its velocity oscillates between this and much higher values, and finally the are plasma may become diffuse in nature. Test results obtained with dielectric strength probes have indicated that a unidirectional flow of arc heated gas is generated. The flow is away from the moving contact of the interrupter so promoting good dielectric strength in this critical contact region. The combination of the optical fiber and dielectric probe results indicates two possible modes of gas pumping represented, respectively, by a fan and a piston-type action of the arc. Simplified analytical models for both modes are developed with predictions obtained showing good agreement with the experimental results. Discussion of experimental results suggests that the transition from oscillatory velocity changes to diffuse arcing represents an important parameter for scaling the geometries of future interrupters and arc heaters     

The short vacuum arc. I. Experimental investigations

High-current vacuum arcs drawn between commercial radial-magnetic field, chromium-copper contacts were studied by high-speed photography. The aim of the investigation was to study phenomena of relevance to high-current interruption, such as arc constriction and arc motion. The arcs were drawn at contact opening speeds typical of commercial devices, are duration being 10 ms or less. The arcs were `short' for much of their lifetime, and strong electrode-discharge coupling could be expected. Such arcs are also of principal interest. Arc behavior was found to be strongly influenced by the gap length d and the arc current I. No diffuse mode was observed at d less the d_min≈4 mm and at instantaneous currents I above I_max±25 kA. The diffuse discharge mode was assumed more readily when d was large. At d below 2 mm, the arcs could not be moved by a magnetic field. Increasing both I and d resulted in an increase of the probability and duration of arc motion and of the arc path length. Arc speed was often irregular, showing that arc motion is also affected by parameters other than the purely electrodynamic ones     

Investigations of the ignition of arc spots on cold cathodes in anoble gas atmosphere

To investigate the ignition of arc spots on cold cathodes under defined conditions, a special experimental setup was developed. An arc ignited between horn electrodes in a pure argon gas atmosphere is blown magnetically against a third so called commutation electrode, which is negatively biased against the arc plasma. The ignition of arc spots on this cathode was investigated by electrical measurements and high-speed photography. The arc traces of short current pulses were examined by in situ optical microscopy of the cathode surface. Two different modes of arc-spot ignition were observed: an initiation by a diffuse glow discharge, which may pass into a constricted arc spot, and an immediate formation of a constricted arc spot. The two modes of arc-spot ignition at atmospheric pressure were attributed to different surface structures, which are characterized by broad or narrow distributions of local ion current density enhancement factors. Ion current density enhancement may raise the field strength and temperature on the tips of microprotrusions so far that they emit electrons. A sufficiently high density of small emission sites produces locally such a high average current density that a plasma channel and an arc spot on the cathode surface arc formed. With lower pressure, the influence of the surface structure is reduced and pushed back by Townsend-γ emission     

Fluctuation of arc plasma in arc plasma torch with multiple cathodes

Fluctuation phenomena commonly exist in arc plasmas, limiting the application of this technology.In this paper,we report an investigation of fluctuations of arc plasmas in an arc plasma torch with multiple cathodes.Time-resolved images of the plasma column and anode arc roots are captured.Variations of the arc voltage, plasma column diameter, and pressure are also revealed.The results indicate that two well-separated fluctuations exist in the arc plasma torch.One is the high-frequency fluctuation(of several thousand Hz), which arises from transferring of the anode arc root.The other is the low-frequency fluctuation(of several hundred Hz), which may come from the pressure variation in the arc plasma torch.Initial analysis reveals that as the gas flow rate changes, the low-frequency fluctuation shows a similar variation trend with the Helmholtz oscillation.This oscillation leads to the shrinking and expanding of the plasma column.As a result, the arc voltage shows a sinusoidal fluctuation.     

Experimental investigations into the arc properties of vacuuminterrupters with horseshoe electrode, four pole electrode, and theirapplications

By using ferromagnetic material around electrodes to generate strong nonuniform magnetic fields, vacuum arcs can be kept in well-defined diffuse mode or multiple arc mode. As a result, the arc voltage is low and stable, the current is confined in certain areas, and high interrupting ability and small size are achieved. The different arc modes for different electrodes, the arc voltage versus arc current for flat electrodes, horseshoe, and four-pole electrode, and the vacuum arc distribution are measured. The criteria of choice of electrode diameter and electrode distance are given     

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利用自行设计的快速移动静电探针对大气压下以氩气为工质的大尺度磁分散电弧等离子体进行诊断,分析了探针电压与电流的波形,绘制探针伏安特征曲线(U-I曲线),得到了发生器轴线方向等离子体波动特性以及电子温度沿轴线的变化趋势.发现等离子体发生器中心具有回流区,得到了电弧等离子体的大致体积.     

Investigation of unstable motion characteristics of vacuum arc cathode spots between transverse magnetic field contacts

With the improvement of the current level of power grids, the requirements of the opening level of the vacuum switches are also increasing. Vacuum arc cathode spots provide steam and electrons and, to a certain extent, determine the opening capacity of the vacuum switch. In this paper, a vacuum arc cathode spot research platform based on the de-mountable vacuum chamber is constructed. The characteristics of the vacuum arc cathode spots under the transverse magnetic field (TMF) contacts are assessed by a high-speed charge coupled device. The experimental results show that the cathode spot diffusion process can be divided into three processes through cathode spot distribution, arc voltage and current: initial diffusion stage of cathode spots, unstable motion stage of cathode spots, and extinguishing stage. The motion mode of cathode spots during unstable motion stage can be divided into cathode spots group stagnation (CSGS) to multi-cathode jet (MCJ) switch mode, cathode spots group motion (CSGM) to MCJ switch mode, CSGM mode, and MCJ mode. The effects of peak current and contact diameter on unstable motion mode were analysed.     

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采用简化阴极的一维边界层模型,将同轴磁旋转电弧等离子体发生器的阴极与弧柱耦合求解,使用FLUENT软件,数值模拟了不同锥角阴极的形状对磁分散电弧等离子体、阴极弧根和阳极弧根位形的影响.结果表明:阴极弧根具有扩散特征,其电流密度为107A·m-2量级;阴极形状的改变引起阴极弧根位形和电流密度分布变化,从而影响等离子体参数分布;随着阴极锥角的增大,阴极弧根从阴极前端移动到阴极侧面,等离子体区域向下游偏移,等离子体轴向厚度减小.     

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采用横向磁场驱动的滑移弧等离子体发生器产生非平衡、大气压下的等离子体。用氮分子谱和OH基谱来估算滑移弧等离子体射流中的重粒子温度。从实验数据的比较来看,从氮分子谱获得的重粒子温度相对较低,而从OH基谱获得的重粒子温度与磁稳滑移弧放电的重粒子温度比较接近,大约在2400~ 2700 K的范围内。     

Pulse intense metal-ion diode with a vacuum arc plasma anode

An intense pulsed ion beam of metal was extracted from a magnetically insulated ion diode operated in a mode of plasma prefill generated from a vacuum arc discharge, anode plasma source. With this ion diode, an intense metal-ion beam of a high melting-point metal (Ta) was obtained. A variety of operational modes appeared, depending on the amount of plasma in the diode gap at the initiation of the high-voltage pulse. The energy, current, and duration time of the ion beam were 20~100 keV, ~1 kA, and 1 μs, respectively. Measurements of ions were performed with an ion energy analyzer or a biased ion collector located at the end of a long drift tube and a Thomson parabola ion spectrometer. The Ta ions in the first to fifth states of ionization were detected accompanied by C⁺, O⁺, F⁺, and H⁺ . A Ta ion beam current of about half the total ion flux was obtained in this experiment     

One-step synthesis of porous palladium nanostructures by H2+He arc plasma method

Porous palladium nanostructures were prepared on a copper sheet previously fixed over the plasma high-temperature area by H₂+He arc plasma method. However, dispersed palladium nanoparticles with diameters in 50–90 nm were obtained on the inner wall of vacuum chamber. SEM, TEM, EDXA, XRD and BET were employed to characterize the palladium porous materials. SEM images show that porous palladium nanostructures are composed of spherical particles with diameters of 35 ± 3 nm. This special structure with large surface to volume ratio can be recycled easily for application in the field of catalysis.