Three-dimensional non-equilibrium modeling of a DC multi-cathode arc plasma torch

In this paper, a three-dimensional non-equilibrium steady arc model is used to investigate the temperature, velocity and electromagnetic field in multi-cathode arc torch, and the formation mechanism of a large-area, uniform and diffused arc plasma is analyzed. The numerical simulation results show that a large volume plasma region can be formed in the central region of the generator during discharge. During this process, the maximum electron temperature appears near the cathode and in the central convergence region, while the maximum heavy particle temperature only appears in the central convergence region. This phenomenon is consistent with the experimental arc images. Near the cathode tip, the arc column is in a contraction state. In the area slightly away from the cathode, the six arc columns begin to join together. In the plasma generator, there is a large-scale current distribution in all directions of X, Y and Z, forming a stable arc plasma with a wide range of diffusion. The calculated electron temperature distribution is in good agreement with the measured electron temperature. The results suggest that the largearea diffused arc plasma in the multi-cathode arc torch is the combined effect of current distribution, convection heat transfer and heat conduction.     

Behavior of an indigenously fabricated transferred arc plasma furnace for smelting studies

The utilization of industrial solid waste for metal recovery requires high-temperature tools due to the presence of silica and alumina, which is reducible at high temperature. In a plasma arc furnace, transferred arc plasma furnace(TAP) can meet all requirements, but the disadvantage of this technology is the high cost. For performing experiments in the laboratory, the TAP was fabricated indigenously in a laboratory based on the different inputs provided in the literature for the furnace design and fabrication. The observed parameters such as arc length, energy consumption, graphite electrode consumption, noise level as well as lining erosion were characterized for this fabricated furnace. The nitrogen plasma increased by around 200 K(200 ℃) melt temperature and noise levels decreased by ~10 d B compared to a normal arc.Hydrogen plasma offered 100 K(100 ℃) higher melt temperature with ~5 d B higher sound level than nitrogen plasma. Nitrogen plasma arc melting showed lower electrode and energy consumption than normal arc melting, whereas hydrogen plasma showed lower energy consumption and higher electrode consumption in comparison to nitrogen plasma. The higher plasma arc temperature resulted in a shorter meltdown time than normal arc with smoother arcing. Hydrogen plasma permitted more heats, reduced meltdown time, and lower energy consumption, but with increased graphite consumption and crucible wear. The present study showed that the fabricated arc plasma is better than the normal arc furnace with respect to temperature generation, energy consumption, and environmental friendliness. Therefore, it could be used effectively for smelting-reduction studies.     

Discharge and jet characteristics of gliding arc plasma igniter driven by pressure difference

Stable combustion in an afterburner can help increase the thrust of the engine in a short time, thereby improving the maneuverability of a fighter. To improve the ignition performance of an afterburner, a twin-duct ignition platform was designed to study the performance of a gliding arc plasma igniter in close-to-real afterburner conditions. The research was carried out by a combination of experiments and simulations. The working environment of the igniter was explored through a numerical simulation. The results showed that the airflow ejected from the radiating holes formed a swirling sheath, which increased the anti-interference ability of the airflow jet. The influence of the pressure difference between the inlet and outlet of the igniter (Δp), the flow rate outside the igniter outlet (W₂), and the installation angle (α) on the single-cycle discharge energy (E) as well as the maximum arc length (L) were studied through experiments. Three stages were identified: the airflow breakdown stage, the arc evolution stage, and the arc fracture stage. E and L increased by 107.3% and 366.2%, respectively, with Δp increasing from 10 to 70 Torr. The relationship between L and Δp obtained by data fitting is L = 3 − 2.47/(1 + (Δp/25)⁴). The relationship of L at different α is L_α=0° > (L_α=45° and L_α=135°) > L_α=180° > L_α=90°. E and L decrease by 18.2% and 37.3%, respectively, when Δp = 45 Torr and W₂ is increased from 0 to 250 l min⁻¹.     

Particle flux characteristics of a compact high-field cascaded arc plasma device

A new compact cascaded arc device for plasma-wall interaction study is developed at the Institute of Plasma Physics,Chinese Academy of Sciences.A magnetic field up to 0.8 T is achieved to confine plasmas in a 1.2 m long and 0.1 m diameter vacuum chamber.Gas fluid type analysis in this compact vacuum system was done under high particle flux condition.The gas pressure obtained by calculation was consistent with the measurement result.Continuous argon plasma discharge with ion flux of～0.5×1024 m-2 s-1 is successfully sustained for more than 1 h.The effects of magnetic field configuration,gas flow rate,and discharge arc current on the ion flux to target were studied in detail.     

OH and O radicals production in atmospheric pressure air/Ar/H2O gliding arc discharge plasma jet

Atmospheric pressure air/Ar/H_2O gliding arc discharge plasma is produced by a pulsed dc power supply. An optical emission spectroscopic(OES) diagnostic technique is used for the characterization of plasmas and for identifications of OH and O radicals along with other species in the plasmas. The OES diagnostic technique reveals the excitation Tx?≈?5550–9000 K, rotational Tr?≈?1350–2700 K and gas Tg?≈?850–1600 K temperatures, and electron density n?(1.1-1.9) ′101 4 cm~(-3) e under different experimental conditions. The production and destruction of OH and O radicals are investigated as functions of applied voltage and air flow rate. Relative intensities of OH and O radicals indicate that their production rates are increased with increasing Ar content in the gas mixture and applied voltage. nereveals that the higher densities of OH and O radicals are produced in the discharge due to more effective electron impact dissociation of H_2O and O_2 molecules caused by higher kinetic energies as gained by electrons from the enhanced electric field as well as by enhanced n e.The productions of OH and O are decreasing with increasing air flow rate due to removal of Joule heat from the discharge region but enhanced air flow rate significantly modifies discharge maintenance properties. Besides, Tgsignificantly reduces with the enhanced air flow rate. This investigation reveals that Ar plays a significant role in the production of OH and O radicals.     

阴极真空弧源磁过滤弯管偏压模式研究

为了改进阴极真空弧等离子体通过磁过滤弯管的传输效率,测定了磁过滤弯管出口离子电流与阴极弧流的关系,结果表明：磁过滤弯管内表面中,靠近大径中心一侧的表面（内侧面）和远离大径中心一侧的表面（外侧面）与等离子体的相互作用是独立的,存在两种向磁过滤弯等内表面运动的离子流：离子碰撞导致的横向扩散离子流和从阴极弧出来的较高能量的惯性离子流。两种离子流通过磁过滤管的传输过程有不同的机制。整个磁过滤弯管偏压较仅仅Bilek板偏压有更高的离子传输效率,Bilek板偏压对磁过滤弯管离子传输起主要作用。     

阴极端面旋转弧根的数值分析

辅助电弧的阴极弧根在管状钨阴极端面旋转时,随着阴极弧根旋转频率的增加,在阴极端面形成一圈温度较高的区域;区域中各点的温度（除弧根处温度）趋于均匀,从而为主电弧的阴极弧根在这个区域中分裂成多弧根或形成扩散型弧根模式提供了必要的温度条件;弧根处的阴极端面温度随旋转频率的增加而下降并趋于一个稳定的值。本文利用三维热传导方程对此进行了分析。     

磁驱动滑移电弧非平衡等离子体的研究

提出了一种磁驱动滑移电弧放电产生大气压非平衡等离子体的方法,给出了这种装置的基本结构,主要性能及基本原理。在弧电流0．6A左右得到了约100m／s的电弧移动速度和约80V／mm的电场强度,产生了非平衡度较高的大气压非平衡等离子体。     

Numerical modelling of a low power non-transferred arc plasma reactor for methane conversion

Thermal flow characteristics and the methane conversion reaction in a low power arc plasma reactor for efficient storage and transport of methane, which is the main component of shale gas, were simulated. The temperature and velocity distributions were calculated according to the type of discharge gases and arc current level by a self-developed magnetohydrodynamics (MHD) code and a commercial ANSYS-FLUENT code; the transport of chemical species was analyzed as including the chemical reactions of methane conversion. The simulated results were verified by the comparison of calculated and measured arc voltages with permissible low error as under 4%. Three C₂ hydrocarbon gases with ethane (C₂H₆), ethylene (C₂H₄), and acetylene (C₂H₂) were selected as the converted species of methane from experimental data. The mass fraction of C₂ hydrocarbons and hydrogen as the product of the conversion reaction at the reactor was also calculated. Those values show good agreement with the actual experimental results in that the major conversion reaction occurred in C₂H₂ and hydrogen, and the conversions to C₂H₆, C₂H₄, and hydrogen were minor reactions of methane pyrolysis conversion.     

Dynamics of plasma bullets by nanosecond pulsed micro-hollow cathode discharge within air

In this paper, the air plasma jet produced by micro-hollow cathode discharge(MHCD) is investigated. The discharge is powered by a positive nanosecond pulse high voltage supply. The waveforms of the discharge, the images of the jet, the evolution of the plasma bullet and the reactive species are obtained to analyze the characteristics of the MHCD plasma jet. It is found that the length of the plasma jet is almost proportional to the air flow rate of 2–6 slm. Two plasma bullets appear one after another during a single period of the voltage waveform, and both of the two plasma bullets are formed during the positive pulse voltage off. The propagation velocity of the two plasma bullets is on the order of several hundred m/s, which is approximate to that of the air flow. These results indicate that the gas flow has an important influence on the formation of this MHCD plasma jet.     

Study of generation characteristics of glow-type atmospheric-pressure plasma jet based on DC discharge in air

In order to form an atmospheric-pressure plasma jet without airflow, a needle–ring electrode structure is proposed in this paper. When heteropolar potentials are applied to a needle and a ring, a marked electric field strength enhancement around the needle's pointed end has been found. When the same potential is applied to both the needle and the ring, the lateral electric field strength for the needle can be weakened. By using the above two methods, an increase of the difference between the pointed end electric field strength and the lateral one is achieved and stable plasma jets are formed. A symmetrical space electric field distribution is established at the pointed end of the needles when several sets of heteropolar needle–ring electrodes are uniformly arranged, which is conducive to forming a uniform array plasma jet. Under DC discharge conditions, a safe and stable plasma jet of high density and an array plasma jet are successfully achieved.     

Study of Metal and Ceramic Thermionic Vacuum arc Discharges

The thermionic vacuum arc （TVA） is a new type of plasma source, which generates a pure metal and ceramic vapour plasma containing ions with a directed energy. TVA discharges can be ignited in high vacuum conditions between a heated cathode （electron gun） and an anode （tungsten crucible） containing the material. The accelerated electron beam, incident on the anode, heats the crucible, together with its contents, to a high temperature. After establishing a steadystate density of the evaporating anode material atoms, and when the voltage applied is high enough, a bright discharge is ignited between the electrodes. We generated silver and Al2O3 TVA discharges in order to compare the metal and ceramic TVA discharges. The electrical and optical characteristics of silver and Al2O3 TVA discharges were analysed. The TVA is also a new technique for the deposition of thin films. The film condenses on the sample from the plasma state of the vapour phase of the anode material, generated by a TVA. We deposited silver and Al2O3 thin films onto an aluminium substrate layer-by-layer using their TVA discharges, and produced micro and/or nano-layer Ag-Al2O3 composite samples. The composite samples using scanning electron microscopy was also analysed.     

Decontamination of infected plant seeds utilizing atmospheric gliding arc discharge plasma treatment

In agriculture production,plant health is threatened by pathogens parasitic on seeds;hence,it is necessary to disinfect harvested seeds before germination.In this study,a technique of gliding arc plasma treatment was proposed and investigated.The experiment was conducted to treat Astragalus membranaceus (A.membranaceus) seeds that were artificially infected with Fusarium oxysporum (F.oxysporum).The plasma treatment duration varied from 30 s to 270 s.Direct and indirect treatments were compared to evaluate the inactivation efficiency of the F.oxysporum spores on the surface of seeds.The results indicated that the direct treatment behaved significantly better in disinfection than the indirect way.Meanwhile,experiments of the quantitative assessment of seed germination were also conducted,including the germination rate,the germination potential,and the germination index.The results showed that the inactivation efficiency increased as the plasma treatment time was extended.When the treatment time was 90 s,the inactivation efficiency reached more than 98％.The plasma treatment of 270 s had a complete devitalization of F.oxysporum spores on the surface of the seeds.After the treatment of 30 s and 90 s,the seed germination parameters improved significantly.This study verified the inactivation efficacy of gliding arc discharge plasma under atmospheric pressure.The technique of gliding arc treatment shows advantages of energy saving and adaptation and has the potential to be utilized in industry.     

Dependence of plasma structure and propagation on microwave amplitude and frequency during breakdown of atmospheric pressure air

The structure and propagation of the plasma in air breakdown driven by high-power microwave have attracted great interest. This paper focuses on the microwave amplitude and frequency dependence of plasma formation at atmospheric pressure using one two-dimensional model,which is based on Maxwell's equations coupled with plasma fluid equations. In this model, we adopt the effective electron diffusion coefficient, which can describe well the change from free diffusion in a plasma front to ambipolar diffusion in the bulk plasma. The filamentary plasma arrays observed in experiments are well reproduced in the simulations. The density and propagation speed of the plasma from the simulations are also close to the corresponding experimental data. The size of plasma filament parallel to the electric field decreases with increasing frequency, and it increases with the electric field amplitude. The distance between adjacent plasma filaments is close to one-quarter wavelength under different frequencies and amplitudes. The plasma propagation speed shows little change with the frequency, and it increases with the amplitude. The variations of plasma structure and propagation with the amplitude and frequency are due to the change in the distribution of the electric field.     

Penicilliumchrysogenum的低温空气等离子体诱变研究

以产黄青霉菌(Penicillium chrysogenum)Pc05为出发菌株,利用物理诱变方法低温空气等离子体技术对其进行诱变处理,结果表明:在处理时间为30 min内时,产黄青霉孢子的存活率随处理时间变化呈现出明显的“马鞍型”曲线;正突变株占所有突变株比例为44.19％,且负突变率很低.经过初筛、复筛获得突变株a...     

Cold atmospheric-pressure air plasma treatment of C6 glioma cells: effects of reactive oxygen species in the medium produced by the plasma on cell death

An atmospheric-pressure air plasma is employed to treat C6 glioma cells in vitro.To elucidate on the mechanism causing cell death and role of reactive species(RS) in the medium produced by the plasma,the concentration of the long-lived RS such as hydrogen peroxide,nitrate,and ozone in the plasma-treated liquid(phosphate-buffered saline solution) is measured.When vitamin C is added to the medium as a ROS quencher,the viability of C6 glioma cells after the plasma treatment is different from that without vitamin C.The results demonstrate that reactive oxygen species(ROS) such as H_2O_2,and O_3 constitute the main factors for inactivation of C6 glioma cells and the reactive nitrogen species(RNS) may only play an auxiliary role in cell death.     

Dynamic behavior of a rotating gliding arc plasma in nitrogen: effects of gas flow rate and operating current

The effects of feed gas flow rate and operating current on the electrical characteristics and dynamic behavior of a rotating gliding arc (RGA) plasma codriven by a magnetic field and tangential flow were investigated.The operating current has been shown to significantly affect the time-resolved voltage waveforms of the discharge,particularly at flow rate =21 min-1.When the current was lower than 140 mA,sinusoidal waveforms with regular variation periods of 13.5-17.0 ms can be observed (flow rate =21 min-1).The restrike mode characterized by serial sudden drops of voltage appeared under all studied conditions.Increasing the flow rate from 8 to 121 min-1 (at the same current) led to a shift of arc rotation mode which would then result in a significant drop of discharge voltage (around 120-200 V).For a given flow rate,the reduction of current resulted in a nearly linear increase of voltage.     

Conversion of coalbed methane surrogate into hydrogen and graphene sheets using rotating gliding arc plasma

The use of atmospheric rotating gliding arc(RGA) plasma is proposed as a facile, scalable and catalyst-free approach to synthesizing hydrogen(H_2) and graphene sheets from coalbed methane(CBM). CH_4 is used as a CBM surrogate. Based on a previous investigation of discharge properties, product distribution and energy efficiency, the operating parameters such as CH_4 concentration, applied voltage and gas flow rate can effectively affect the CH_4 conversion rate,the selectivity of H_2 and the properties of solid generated carbon. Nevertheless, the basic properties of RGA plasma and its role in CH_4 conversion are scarcely mentioned. In the present work, a 3D RGA model, with a detailed nonequilibrium CH_4/Ar plasma chemistry, is developed to validate the previous experiments on CBM conversion, aiming in particular at the distribution of H_2 and other gas products. Our results demonstrate that the dynamics of RGA is derived from the joint effects of electron convection, electron migration and electron diffusion, and is prominently determined by the variation of the gas flow rate and applied voltage. Subsequently,a combined experimental and chemical kinetical simulation is performed to analyze the selectivity of gas products in an RGA reaction, taking into consideration the formation and loss pathways of crucial targeted substances(such as CH_4, C_2H_2, H_2 and H radicals) and corresponding contribution rates. Additionally, the effects of operating conditions on the properties of solid products are investigated by scanning electron microscopy(SEM) and Raman spectroscopy. The results show that increasing the applied voltage and decreasing CH_4 concentration will change the solid carbon from its initial spherical structure into folded multilayer graphene sheets, while the size of the graphene sheets is slightly affected by the change in gas flow rate.     

Simulation and Experimental Study of Arc Column Expansion After Ignition in Low-Voltage Circuit Breakers

The dynamic process of arc pressure and corresponding arc column expansion, which is the main feature after arc ignition and has a significant effect on the breaking behaviour of low -voltage circuit breakers, is studied. By constructing a three dimensional mathematical model of air arc plasma and adopting the Control Volume Method, the parameters of arc plasma including temperature and pressure are obtained. The variations of pressure field and temperature field with time are simulated. The result indicates that there are six stages for the process of arc column expansion according to the variation of pressure in arc chamber. In the first stage, the maximal pressure locates in the region close to cathode, and in the second stage the maximal pressure shifts to the region close to the anode. In the third stage, the pressure difference between the middle of arc column and the ambient gas is very large, so the arc column begins to expand apparently. In the fourth stage, the pressure wave propagates towards both ends and the maximal pressure appears at the two ends when the pressure wave reaches both sidewalls. In the fifth stage, the pressure wave is reflected and collides in the middle of the arc chamber. In the last stage, the propagation and reflection of pressure wave will repeat several times until a steady burning state is reached. In addition, the experimental results of arc column expansion, corresponding to the arc pressure variation, are presented to verify the simulation results.     

Study on plasma sheath and plasma transport properties in the azimuthator

A physical model of transport in an azimuthator channel with the sheath effect resulting from the interaction between the plasma and insulation wall is established in this paper.Particle in cell simulation is carded out by the model and results show that,besides the transport due to classical and Bohm diffusions,the sheath effect can significantly influences the transport in the channel.As a result,the ion density is larger than the electron density at the exit of azimuthator,and the non-neutral plasma jet is divergent,which is unfavorable for mass separation.Then,in order to improve performance of the azimuthator,a cathode is designed to emit electrons.Experiment results have demonstrated that the auxiliary cathode can obviously compensate the space charge in the plasma.