射频激励铜离子激光器的功率消耗

通过对射频激励激光器放电电压、电流以及相位的精确测量，基于射频放电等离子体等效电路，得出等离子体总电阻(包括等离子体总电阻和鞘层电阻分量)，经非线性最小平方拟合分别得到等离子体电阻和鞘层电阻，进而定量地得到等离子体和鞘层功率消耗，鞘层电压以及鞘层厚度随放电电流变化的关系，借此可以诊断出射频放电处于α或γ放电。研究表明在中等气压氦气中随着气体压强的增加和电流的增加，气体的放电模式将从α放电为主转向γ放电为主。     

射频激励铜离子激光器的功率消耗

通过对射频激励激光器放电电压、电流以及相位的精确测量,基于射频放电等离子体等效电路,得出等离子体总电阻(包括等离子体总电阻和鞘层电阻分量),经非线性最小平方拟合分别得到等离子体电阻和鞘层电阻,进而定量地得到等离子体和鞘层功率消耗,鞘层电压以及鞘层厚度随放电电流变化的关系,借此可以诊断出射频放电处于α或γ放电。研究表明在中等气压氦气中随着气体压强的增加和电流的增加,气体的放电模式将从α放电为主转向γ放电为主。     

基于均匀离子密度的容性耦合射频放电等离子体的实验诊断研究北大核心CSCD

容性耦合射频(CCRF)放电可用于制备大体积、均匀、低温非热平衡等离子体,已得到了国内外的广泛关注。针对CCRF放电过程中等离子体参量的诊断问题,本文提供了一种基于均匀离子密度的描述CCRF放电的等效回路模型(ECM),并根据等效阻抗原理引入能量平衡方程,对等离子体特征参量电子密度n_e和电子温度T_e进行了诊断,诊断结果与等离子体发射光谱诊断结果相一致。实验结果表明:在一般的CCRF放电过程中,放电电流与放电电压波形呈正弦曲线,高次谐波成分较少且总的谐波强度小于基波信号的11%,可以采用ECM描述等离子体放电状态。随着射频输入功率的增加,等离子体电子密度线性增加,但电子温度变化不明显,鞘层厚度逐渐减小,主等离子体区厚度增加;随着工作气体压强的升高,电子密度和电子温度均减小。对于较高的气压,放电在不同的输入功率下分为低功率下的α模式和高功率下的γ模式,这主要是极板表面的俄歇发射过程引起的。     

基于均匀离子密度的容性耦合射频放电等离子体的实验诊断研究

容性耦合射频(CCRF)放电可用于制备大体积、均匀、低温非热平衡等离子体,已得到了国内外的广泛关注。针对CCRF放电过程中等离子体参量的诊断问题,本文提供了一种基于均匀离子密度的描述CCRF放电的等效回路模型(ECM),并根据等效阻抗原理引入能量平衡方程,对等离子体特征参量电子密度n_e和电子温度T_e进行了诊断,诊断结果与等离子体发射光谱诊断结果相一致。实验结果表明:在一般的CCRF放电过程中,放电电流与放电电压波形呈正弦曲线,高次谐波成分较少且总的谐波强度小于基波信号的11%,可以采用ECM描述等离子体放电状态。随着射频输入功率的增加,等离子体电子密度线性增加,但电子温度变化不明显,鞘层厚度逐渐减小,主等离子体区厚度增加;随着工作气体压强的升高,电子密度和电子温度均减小。对于较高的气压,放电在不同的输入功率下分为低功率下的α模式和高功率下的γ模式,这主要是极板表面的俄歇发射过程引起的。     

等离子体刻蚀提纯冶金硅研究

通过自行设计的冷等离子体粉粒纯化系统,将硅粉撒进辉光放电区,以Ar气为反应气体,利用鞘层区域辉光放电的冷等离子体对硅粉料的作用,进行一系列的处理后,硅粉表面形貌平整度明显提高,纯度从98.75 9,6提高到99.56%.在此基础上,设计射频感应放电等离子体的振动倾斜反应室,经实验,将硅粉纯度提高到99.96 9,6,接近太阳级硅的要求,也为该研究未来的发展提供了新的思路和理论参考.     

氟化乙丙烯共聚物薄膜驻极体电荷存储性能与电晕产生模式相关性

采用在直流稳态、高频脉冲和交变电场作用下的电晕放电对氟化乙丙烯共聚物(FEP)薄膜材料进行注极,通过等温表面电位测量和热刺激放电技术考察了FEP驻极体的电荷存储特性,依据电晕放电等离子体鞘层模型对实验结果进行了分析,研究了电晕产生模式对FEP薄膜驻极体电荷存储性能的影响。结果表明,电晕注极FEP薄膜驻极体的表面电位稳定性与电晕产生模式、电晕极性有关,但是电荷存储机制只与电晕极性有关。脉冲电晕注极时的稳定性优于稳态电晕注极,但其初始表面电位值较低。交变电场电晕注极获得的驻极体,呈现负极性。不同电晕放电模式在材料表面形成的等离子体鞘层的组成和厚度不同,是FEP驻极体性质不同的主要原因。     

大气压射频单介质阻挡放电中放电通道收缩现象的研究

大气压射频辉光放电产生的等离子体具有温和的温度、较好的稳定性和较强的化学活性而广泛应用于工业生产、生物处理等领域。为提高工作效率、增加放电均匀性,应避免产生放电收缩现象。为此,设计了一个带水冷铜电极的射频单介质阻挡放电系统,在大气压下研究氮气和氩气放电收缩形成的机制。纳秒级ICCD相机拍摄的放电图像揭示出在大气压下氮气和氩气放电中明显存在放电通道收缩现象,在放电周期内放电通道形状保持不变,但在不同位置的发光强度随射频电源的频率作周期性变化。通过分析放电图像的三维时空分辨图和二维时间分辨图,发现上下电极表面附近的发光强度在一个射频周期内交替出现一个峰,但峰出现时间上为非对称。这不同于射频裸电极放电,也不同于射频双介质阻挡放电。分析认为发光强度峰在一个射频周期内交替出现的时间非对称性是由于非对称电极表面电荷积累和二次电子发射差异造成。     

中子管射频离子源放电特性仿真研究北大核心CSCD

国外射频离子源中子管的中子产额已经达到10^14n/s,明显优于潘宁源中子管。为了深入了解用于中子管射频离子源的放电特性,从射频感应耦合等离子体的放电原理入手,建立用于氢气放电模拟研究的理论模型。设计中子管射频离子源几何结构,运用麦克斯韦方程组在理论上推导了等离子体放电过程中影响粒子密度的因素。结合Comsol软件中的二维轴对称的电感耦合等离子体模型,采用单一变量法,通过仿真实验得到了线圈匝间距、线圈匝数、线圈直径、线圈功率和放电气压等参数对H^+密度分布和大小的影响。总结出H+在不同参数下的变化规律,得到了一些有价值的结论,为优化中子管射频离子源的实验参数和结构设计提供重要依据。     

中子管射频离子源放电特性仿真研究

国外射频离子源中子管的中子产额已经达到10~(14) n/s,明显优于潘宁源中子管。为了深入了解用于中子管射频离子源的放电特性,从射频感应耦合等离子体的放电原理入手,建立用于氢气放电模拟研究的理论模型。设计中子管射频离子源几何结构,运用麦克斯韦方程组在理论上推导了等离子体放电过程中影响粒子密度的因素。结合Comsol软件中的二维轴对称的电感耦合等离子体模型,采用单一变量法,通过仿真实验得到了线圈匝间距、线圈匝数、线圈直径、线圈功率和放电气压等参数对H~+密度分布和大小的影响。总结出H~+在不同参数下的变化规律,得到了一些有价值的结论,为优化中子管射频离子源的实验参数和结构设计提供重要依据。     

等离子体鞘层中朗缪尔探针吸收离子电流理论的数值模拟

为了研究朗缪尔静电圆柱型探针半径对等离子体密度测量的影响以及鞘层空间电势分布等特性,在非热平衡条件下采用等离子体鞘层中探针吸收离子模型,对朗缪尔静电探针周围等离子体鞘层空间中的修正玻姆电流、OML理论鞘层空间电势分布、ABR理论鞘层空间电势分布、BRL理论鞘层空间电势分布以及三种理论对应的探针吸收离子电流进行了系统的数值模拟研究。计算结果显示,电子温度和等离子体密度对ABR理论鞘层空间电势分布存在显著影响,离子温度小于0.1倍电子温度时离子的温度效应对BRL理论鞘层空间电势分布的影响可以忽略;探针半径为1~3倍德拜长度时,OML理论、ABR理论及BRL理论预测的归一化离子电流近似相等,即三种理论给出近似相等的等离子体密度。     

方管内表面等离子体离子注入动力学GPU-PIC仿真

内表面改性近年日益受到人们重视。本文采用基于Graphic Processing Unit(GPU)的Particle-in-cell(PIC)模型对方形管内表面的离子注入动力学过程进行数值仿真研究。结果表明在注入过程中,辅助地电极周围形成离子空穴,随时间延长,离子空穴发生交联并不断扩展,直至所有离子注入到方管内壁。离子空穴的形成和扩展使得在管内部形成离子密度波,密度波的传播速度随时间增加。由于等离子体鞘层的不均匀重叠使得管内的初始鞘层厚度分布不均,其中位于拐角附近的鞘层较厚,从而又导致了方管内壁周向上的注入剂量和能量分布存在不均匀性,内壁平面附近位置的注入剂量和注入能量均相对较大,而拐角附近的离子注入剂量和能量最小。本文采用GPU加速PIC的算法取得了高达90的加速比,极大缩短了等离子体粒子模拟的计算时间。     

6063铝材微弧氧化最佳电流密度和槽液温度的探讨

目前的铝合金微弧氧化工艺存在电流密度高、槽液温度范围窄等不足,使其应用受到了限制.为此,从铝材低电流密度和宽槽液温度方面研究了6063铝材的微弧氧化工艺,探讨了微弧氧化工艺中电流密度及槽液温度对起弧电压、起弧时间及膜层厚度等的影响.结果表明,同等条件下,电流密度越大,则起弧电压越低,起弧时间越短,膜层越厚;槽液温度越高,则起弧电压越低,起弧时间越短,膜层越厚;在10 min内,得到12μm厚度的膜层,同等时间内比普通阳极氧化膜厚提高4倍;微弧氧化膜的表面显微硬度相对6063铝材高7倍以上.     

The observation of unipolar arc damage on stainless steel and TiC coatings on stainless steel

Unipolar arcing represents a plasma-surface interaction process leading to surface damage and metal impurity influx in tokamaks. It develops if the sheath potential formed in the plasma-surface contact is high enough to ignite and sustain a micro-arc. A laser-produced plasma was used for a comparison of the arc damage produced on stainless steel surfaces with that on surfaces protected with a coating of TiC a few microns thick. Smooth coatings of superior-quality TiC were produced by the activated reactive evaporation process, which is a plasma-assisted physical vapor deposition process. For a sufficiently high electron temperature in the laser-produced plasma a large number (about 300 000 cm^?2) of unipolar arc craters were observed on the stainless steel surface which had been exposed to the expanding laser-produced plasma cloud for a few hundred nanoseconds. In comparison, no similar arc craters were detected on the surfaces protected by the TiC coating which showed minimum damage limited to the laser beam impact area.     

Time evolution of electrode voltage distribution in large-area capacitively coupled plasmas

Time evolution of non-uniform voltage distribution on the powered electrode in a large-area very-high-frequency (VHF) capacitively coupled plasma processing system is studied based on a one-dimensional transmission-line model with an equivalent-circuit model of the plasma. With this model, time evolution of voltage and current distributions on the electrode is examined at its activation by the power supply with various frequencies, waveforms, and power-supply locations. It has been found, with the power supply of multiple frequencies, that effects of beat waves can significantly affect plasma uniformity especially if the difference in frequency is small. It has been also demonstrated that, with multiple power-supply locations combined with multiple frequencies, good voltage uniformity over the long electrode can be obtained.     

Nonideal electrochemical behavior of biomimetic iron porphyrins: interfacial potential distribution across multilayer films

The electrochemical behavior of multilayer films formed by iron porphyrins deposited on an edge plane graphite electrode has been examined under anaerobic conditions. In the scan rate interval (1-250 mV/s) where the electrode reaction is reversible, CV diagrams of these films demonstrate substantial deviations from ideality in broadening and separation of the peaks. A model that describes the observed behavior is proposed by taking into account the potential distribution at the electrode/film interface and the concentration dependence of surface activity coefficients. The peak separation is described in terms of the electric double layer that affects the potential difference driving the electrode reaction. The effective potential difference deviates from the applied value due to the potential distribution across the film. The interfacial potential distribution depends on the ionic concentration inside the film. When different ionic concentrations are assumed for oxidation and reduction, different shifts from the applied potential lead to a hysteresis of the peaks. The peak broadening is modeled by using the lattice theory expression for the surface activity coefficients. The model shows that the midpoint potentials of the redox centers depend on the ionic concentration inside the film. At low ionic concentrations, they are remarkably close to the midpoints of the cytochrome c oxidase heme a3/CuB site.     

Oxygen atom density in capacitively coupled RF oxygen plasma

The density of neutral oxygen atoms was determined in a plasma reactor for surface functionalization of polymer materials. Plasma was created in a stainless steel chamber by capacitively coupled RF generator at 13.56 MHz and adjustable forward power up to 100 W. Measurements were performed with a classical nickel catalytic probe. Systematic measurements were performed at a constant pumping speed, different flow rates from 15 to 100 sccm corresponding to pressures between 30 and 110 Pa, different powers between 40 and 100 W and different probe positions in the discharge chamber. The results showed that the O atom density did not depend much on probe position as long as it was between the powered electrode and grounded housing facing the electrode. The O density depended rather linearly with power at fixed pressure. At low power, the O density did not depend much on pressure, but at high power, it was increasing with increasing pressure. The O density was of the order of 10¹⁹ m⁻³ and increased slightly over 10²⁰ m⁻³ at the highest power and pressure. The results were explained by gas phase and surface reactions.     

A method of measuring electrode temperature for arc powercalculation

A technique for the construction of the thermocouple probe used for the measurement of electrode temperature under the influence of arcing in a low-power circuit breaker at break is reported. The problem of appreciable heat diffusion to the surroundings during the short time of arcing at break, typically 3-6 ms (depending on the speed of break), is dealt with by placing the thermocouple probe as near as possible to the electrode's surface, and in the center where, in most cases, the arc occurs. Under dc test conditions the amounts of the are power received by each electrode for various parameters such as current and electrode spacing are calculated     

Electrostatic Separation of Peeling and Gluten from Finely Ground Wheat Grains

Sieving and air classification are not efficient enough for the extraction of the high-nutritional-value constituents of wheat. The aim of this article is to validate a simple electrostatic separation method of peeling and gluten, which are two such nutriments contained in finely ground wheat grains. The electrostatic separator is composed of metallic grounded belt conveyer and a rotating roll electrode connected to a high voltage supply. The electrostatic behavior of peeling and gluten powders was characterized using surface potential decay and direct charge measurements. These first set of experiments pointed out the conductive behavior of these powders: in contact with a grounded electrode, they lose their charge in less than 10 s. In a second set of experiments, mixtures of 50% peeling and 50% gluten powders were processed by electrostatic separation. Experimental design methodology was used to model the outcome of the separation process as function of two control variables: the high-voltage applied to the roll electrode and the speed of the belt conveyor electrode. In this way, it was possible to determine the optimal operational conditions for the recovery of high-purity peeling and gluten fractions.     

桥式射频MEMS开关上电极薄膜的残余应力改进模型

桥式射频(RF)微机电系统(MEMS)开关的上电极薄膜残余应力影响开关的响应时间、下拉电压等性能参数,降低了开关的可靠性.在分析传统拉伸线模型的基础上,提出了一种改进的残余应力静力学模型,将残余应力扩展到压应力的情况,并可应用于非对称均布载荷.选取了一组典型的开关参数,计算了双轴残余应力对两端固支MEMS薄膜均布载荷下拉挠度的影响.结果表明,在选取的参数条件下,拉应力增大到1 MPa时,薄膜的最大挠度减少7.95%,压应力增大到-1 MPa时,薄膜的最大挠度增加9.47%,与传统模型的计算结果相比,改进模型消除了非线性叠加产生的约0.3%的误差.采用迭代方法计算下拉电压,对两组实验测试数据与模型计算结果进行了验证,模型计算结果与实验数据基本相符.     

Multi-harmonic test setup for RF breakdown studies

A multi-harmonic asymmetric cavity is predicted to obtain lower RF breakdown probability than a conventional pillbox cavity, when driven by two or more external RF harmonic sources. Experimental efforts are underway to study RF breakdown in a bimodal asymmetric cavity powered by dual frequency test stand. Details of design of the test stand are described.