真空放电中磁场对等离子体生成特性的影响

本文针对锥-筒、锥-螺旋电极结构,通过Ansoft Maxwell 3D电磁场仿真软件,分析了放电时,两种电极内部的电场分布与磁场分布。通过朗缪尔探针法,对真空放电生成的等离子体参数进行了测量,重点讨论了电极内部磁场对等离子体生成密度的影响。在上述讨论的基础上,针对锥-螺旋电极,进一步分析了螺旋电极的螺距对电极间的电磁场分布及等离子体生成和传播特性的影响。实验及仿真结果表明,锥-螺旋电极较传统的锥-筒电极,可以获得较高密度的金属等离子体。放电电流在螺旋状电极内部产生的磁场,对向四周扩散的等离子体有一定的约束作用,适当减小螺旋电极的螺距,既可以增大阴极尖端的电场强度,同时可以有效增大螺旋电极内部的磁场强度,更易于在电极轴向获得更高密度的等离子体。     

水下等离子体声源放电特性和声特性实测与分析

在小型消声水池中,同步测量水下等离子体脉冲声源的放电特性和声特性,实验分析研究了其在单电极和多电极下负载注入峰值功率和放电能量对声特性的影响。结果表明,在相同的电极数和间距下,直达波脉冲声源级仅与负载注入峰值功率有关,气泡脉冲声源级和气泡周期则主要受放电能量影响,多电极放电通过减小单根电极放的电能量来减小气泡脉冲声源级和气泡周期。此外,在相同的充电电压下,减小充电电容对电极数的比,可以增大直达波脉冲声源级并压制气泡脉冲;负载注入峰值功率对放电能量的比对声特性的影响也呈现出类似规律。实测及其分析结果可为进一步优化水下等离子体脉冲声源的声特性提供参考。     

石英板夹层中窄电极结构与材料对直流放电的影响

研究了一种石英板夹层窄电极放电装置的低气压直流放电过程,重点探讨了电极结构与电极材料对等离子体参数的影响,其中电极要求宽高为4mm,间距大于40mm。实验采用朗缪尔双探针法诊断,通过改变气压、放电功率等条件分析了电极结构对自制的直流等离子体放电装置的电子密度分布及电子温度的影响。结果表明:通过增加电极表面积,采取特殊的电极结构都可以有效地提高等离子体密度。实验中还发现,随着气压降低,正柱区逐渐缩小、等离子体密度沿电场方向变化趋于平缓,阳极的直流等离子体密度逐渐升高,这时等离子体空间分布均匀度提高,且在16Pa时取得最大值。     

电极锥角对真空沿面放电等离子体生成特性的影响

本实验采用持续时间为微秒级、放电电流为100 A～300 A的单脉冲电源形式,设计了三种不同锥角的铝电极.通过朗缪尔探针法测量放电生成的等离子体相关参数,讨论了电极锥角对真空沿面放电等离子体生成特性的影响.由于爬距相同时沿面放电的路径具有不确定性,导致探针法无法准确测得等离子体参数.本实验采用OPT101光电转化芯片对真空沿面放电瞬间的电弧发光强度进行测量,并通过双缝法对放电路径进行了筛选,从而保证探针法测量数据的可靠性.实验结果表明,阴极锥角越小,阴极三结合点处电场强度越大,越容易发生沿面放电;阴极三结合点处电场强度越大、阴极三结合点的分布范围越大,沿面放电得到的主放电电流越大,最终测得的等离子体密度也越大.     

水中脉冲电压放电形成等离子体通道模拟分析

为获得水中纳秒脉冲电压下放电形成等离子体通道的发展过程,建立水中放电流体模型的数学方程,利用COMSOL软件的有限元方法求解二维轴对称情况,模拟出针-板电极之间的电场强度、电子密度、氢离子密度以及氢氧根离子密度等随时间和空间的分布,并研究脉冲电压幅值、电极间距、电导率对这些物理量以及流注形貌的影响。模拟结果表明:针电极尖端的高场强使高纯水产生最初的电离,之后产生的空间电荷进一步加强了流注头部场强,使流注头部向前推进,形成等离子体通道;当针-板电极间距较小和所加脉冲电压幅值相对较低时,电极间只形成单流注通道,且通道内的电场强度与电子密度随着电压幅值的略微升高而增大,呈线性变化;当所加脉冲电压的幅值高到一定程度时,单流注通道出现"分叉",通道内的电子密度随电压幅值的变化不再是线性的。当针-板电极间距较大时,反应腔内则形成类似于"树枝"状的等离子体通道。当用电导率较高的自来水替代高纯水作为反应介质时,流注头部场强与等离子体通道内的电子密度明显提高。     

水下等离子体声源脉冲放电光谱测量与分析

本文采用HR4000CG-UV-NIR光纤光谱仪和NI-PCB压力传感器测量了水下等离子体声源脉冲放电光谱和强声波的压力幅值,分析了声与光之间的能量转换关系,并重点观察了不同放电参数对光谱特征的影响。实验结果表明,等离子体声源脉冲放电光谱为连续谱,能量主要集中在500 nm左右的谱段;放电产生的光能量和声波能量相互竞争,具有此消彼长的关系;提高放电电压,减小电极间隙距离可以提高光的辐射强度和半峰值谱宽度;增大电极间隙距离,将使发光能量向远紫外区移动;更换电极材料将明显改变光的谱分布和强度变化。     

不同气压下微间距气体放电特性分析

为了研究不同气压下微间距气体放电的过程,在1-100 kPa的可变气压环境下,在1-100 μm的电极间距范围内进行气体放电实验并对实验结果进行分析.在电极间距小于100μm,pd小于80 Pa· cm左右时,随着电极间距的减小,击穿曲线与传统Paschen曲线偏差增大,此时相同pd值对应多个击穿电压.分析各电极间距在...     

射频容性耦合等离子体阻抗影响因素研究

为了进一步探索射频容性耦合放电等离子体,本文建立了以容性耦合等离子体(CCP)为基础的板-板电极一维轴线简化仿真模型。仿真采用氦气为工作气体,使用约化电子传递属性并忽略重粒子对流,利用有限元算法,综合讨论了一定范围内放电参数(气体压强、输入功率、电极直径以及间隙长度)变化时,放电等离子体阻抗的变动情况,并根据仿真所得数据进行理论分析。结果表明:四种仿真条件下的等离子体均呈现容抗特性;当气压升高、放电间隙长度变大时,初期均有利于碰撞电离的发生,而后将成为限制因素,使得等离子体阻抗呈现先减小后升高的变化趋势;当电极直径增大、输入功率增加时,初期等离子体阻抗均呈下降趋势,但后续变化趋于平稳。     

不同激励参数对DBD等离子体放电功率的影响

为探索DBD等离子体放电功率与各激励参数之间的联系,本文建立了二维的板-板电极简化仿真模型,分别研究了脉冲、正弦交流两种激励的放电频率、电压与放电功率间的具体函数关系。仿真结果显示:一定条件下,放电功率正比于脉冲电压峰值的1.381次方、正比于脉冲放电频率的1.097次方,即放电功率与脉冲电压峰值及脉冲放电频率间均有幂函数关系;放电功率与正弦交流电压幅值呈现指数函数关系,放电功率与正弦交流放电频率间近似线性关系;实际工程中,需要增大DBD等离子体放电功率时,应尽量选用提高电压峰值(幅值),而避免选择提高放电频率。     

电加工8418钢的能量分配与表面粗糙度模型

针对电火花加工8418钢构建一种采用不同电极材料加工时的表面粗度模型。采用实验与有限元仿真分析相结合的手段,首先通过实验分别得到紫铜电极、CuW70电极加工8418钢的表面粗糙度Ra,然后采用ANSYS软件仿真分析单脉冲放电加工8418钢的电蚀凹坑半径与深度,结合表面粗糙度模型计算出仿真Ra,通过对比实验得到的表面粗糙度Ra,分析得出紫铜电极、CuW70电极加工8418钢时工件上的能量分配系数η分别为33%和24%。最后对能量分配系数和表面粗度模型进行了实验验证,通过误差分析,不同电极加工的表面粗糙度最大误差为9.59%,证明了能量分配系数和表面粗度模型是准确的。通过对比实验和分析结果,得出不同电极材料对能量分配系数的影响,同时随着脉冲放电能量的增加,η对凹坑半径与深度的影响增大,采用紫铜电极与CuW70电极加工8418钢时Ra差异增大。     

Plasma microthruster based on spark discharge with a liquid metal cathode

The parameters of low-inductance vacuum spark discharge with an In-Ga liquid metal eutectic cathode have been experimentally studied. The application of a constant magnetic field of a permanent magnet significantly modifies the character of plasma flow in discharge, which ensures a significant (1.5- to 2-fold) increase in the cathodic jet impulse. The proposed discharge provides high propulsion characteristics: jet impulse per unit energy stored amounts up to about 10 (μN s)/J, which is close to the best-known values for analogous ion sources with solid metal cathodes.     

A multichannel discharge between a stream electrolytic cathode and a metal anode at atmospheric pressure

An experimental investigation is performed of the structure and current-voltage characteristics (CVC) of a multichannel discharge (MD) between a stream electrolytic cathode (SEC) and a metal anode, as well as of the density of SEC and anode current in a wide range of values of current I = 0.02–10 A, interelectrode spacing l = 5–50 mm, and anode diameter d _a = 5–40 mm. The development of cathode spots on the SEC surface is studied. It is found that a cathode spot of SEC may have various shapes and structures (regular circle, horseshoes, filamentary spots, and so on). The CVC of a multichannel discharge between SEC and metal anode depends significantly on I, l, and d _a , as well as on the material of the anode and on the composition and concentration of electrolyte. The dependence of the density of SEC current on discharge current is nonmonotonic. It is for the first time that a bundle-like MD between SEC and metal anode and multichannel and diffuse discharges between the plasma region and stream electrolytic cathode are observed, and their characteristics are investigated.     

Conversion of toluene into carbon nanotubes using arc discharge plasmas in solution

In order to form nanocarbon materials, an arc discharge plasma method in hydrocarbon solvent is developed. In the case that the arc discharge is performed in toluene with nickel electrodes, tube-like nanocarbons were formed from toluene. The catalysis of the metal electrodes is found to be an important factor for the formation of the nanocarbons by the arc discharge in toluene. This method has a possibility of forming carbon nanotubes from liquid state solvents as a new carbon source by using catalyst ingredient as discharge electrodes.     

A Vapor-Air Discharge between Electrolytic Anode and Metal Cathode at Atmospheric Pressure

An experimental investigation is performed of the structure, mechanism, and electrical and thermal characteristics of a vapor-air discharge between an electrolytic anode (EA) and a metal cathode (MC) in a wide range of parameters at pressure P = 8×10⁴ to 10⁵ Pa, current I = 0.02 to 60 A, interelectrode spacing l = 0.1 to 40 mm, and metal cathode diameter d _c = 1 to 40 mm. The main types of vapor-air discharge with EA are identified. The possibility of burning of a multichannel discharge between a metal cathode and an electrolytic anode at atmospheric pressure is demonstrated for the first time, and a vapor-air discharge with a diffuse plasma column is investigated at high currents and large interelectrode spacings. It is determined that the electrical and thermal characteristics depend significantly on current, interelectrode spacing, electrolyte composition and concentration, geometric shape, diameter, and cooling of the MC. The significant effect of the vapor-air discharge on the electrolytic anode surface is revealed. Transverse waves are observed on the electrolyte surface. Significant turbulent mixing is observed for the first time on the electrolyte-plasma interface in the case of a vapor-air discharge with electrolytic anode at atmospheric pressure and high currents.     

新型荫罩式PDP中电极对放电特性影响模拟分析

SM-PDP中可以通过改变电极宽度,使放电空间的等位面沿电极增加的方向扩展,在等位面扩展的区域电场得到增强,从而改善SM-PDP的放电性能.但在性能改善的同时,相邻电极间的电感加大,输入功率增加,这对SM-PDP性能的提高是不利的.本文采用三维模拟方法,详细研究了在不同电极宽度情况下,SM-PDP放电单元的放电特性,为在设计SM-PDP时选择合适的电极宽度提供帮助.     

Correlation of electrical breakdown of supercritical helium in short gaps with partial discharge in cable samples

As part of a project to develop a superconducting power cable at Brookhaven National Laboratory (BNL), many experiments have been conducted on short coaxial cable insulation samples lapped with various polymeric tapes. These experiments have shown the partial discharge inception voltage to be a function of a sample construction and the density of the helium impregnant. It was concluded that the partial discharge inception voltage in the butt gaps of lapped tape insulation is determined by the product of helium density and gap depth, which corresponds to the tape thickness. This means that the inception voltage obeys the similarity law. This conclusion was based on additional experiments performed to determine the breakdown voltage of helium in a short gap between both bare metal electrodes and plastic insulation coated electrodes. The effects of the condition of the electrode surfaces and the area of the electrodes were essential in determining the breakdown voltage in a short gap of high density cryogenic helium.     

Effects of self-erasing discharge on panel-aging characteristics in AC plasma display panel

This paper investigates the changes in the surface morphology of the MgO thin film on the ITO and bus electrodes in ac plasma display panel under various sustain voltages during the panel-aging process. It is found that the achievement in the stable discharge in an AC-PDP by means of the panel-aging process strongly depends on whether the surface morphologies of the MgO thin film are identical on both the ITO and bus electrodes. It is also found that the self-erasing discharge during the panel-aging process is not effective in obtaining the uniform surface morphology of the MgO thin film on the ITO and bus electrodes, due to the difference in the amount of ion bombardment on the ITO and bus electrodes caused by the erasing of the wall charges during the self-erasing discharge. These experimental results are confirmed by monitoring the three-dimensional IR emission and simulating the wall charge distribution, the electric field strength, and the impulse on the MgO layer.     

AB5-type Hydrogen Storage Alloy Modified with Ti/Zr Used as Anodic Materials in Borohydride Fuel Cell

1. IntroductionFuel cells are attractive alternative energy conversiondevices due to their higher efficiency and low pollution.Some fuel cells such as the proton exchange membranefuel cell (PEMFC), the alkaline fuel cell (AFC), and thephosphoric acid fuel cell (PAFC) require gaseous hydro-gen as the fuel. Establishing an available hydrogen stor-age system for these fuel cells is a key to satisfy the re-quirement of practical application. Though researchersin the world developed all kinds …     

Discharge characteristics of a plasma display panel with hump-shape electrodes

The long gap discharge in a plasma display panel has an advantage of high luminous efficacy but has a deficiency of high firing voltage as well. A hump-shape electrode is suggested to reduce the firing voltage of a long gap discharge while maintaining high luminous efficacy. The effects of hump electrodes inserted between two sustain electrodes are investigated by experiment and with a three-dimensional fluid simulation. The experimental results show that hump structure has lower firing and sustain voltage than the conventional long gap structure. A three-dimensional fluid simulation shows that the hump electrode enhances discharge ignition while maintaining the same optical characteristics of the long gap discharge. Also, the hump structure guarantees the addressing reliability with a reduced discharge time lag.