�����װ�õĻԹ�ŵ�����

在四阳极直流放电装置上,测量并分析了辉光放电的电流-电压和发光特征随气压的变化关系。结果表明,采用稳流放电模式比稳压放电具有更宽的稳定放电气压和电流范围,能在从1～800Pa的较宽气压范围内实现氦气辉光放电,放电电流可达到500mA左右。随着电极表面亮斑的变化,对于同一气压,在低电流区,放电电压几乎成指数增长;随电流增大,电压的增长速度变缓;对于高的气压,碰撞频率的增大使得电压随电流升高的速率变小。分析表明,放电处于异常辉光区。从放电管的CCD图像可以看出,对于同一放电电流,随气压的升高,等离子体往阴极收缩。     

磁控溅射辉光放电特性的模拟研究

采用二维、自洽的PIC/MCC (particle-in-cell with Monte Carlo collision) 方法,模拟了磁控溅射辉光放电过程, 重点讨论了工作参数对放电模式和放电电流的影响. 模拟结果表明, 当工作气压由小到大或空间磁场从强到弱变化时, 放电模式会从阴极空间电荷主导的放电模式过渡到阳极空间电荷主导 的放电模式.在过渡状态,对应的工作气压与磁通密度分别为0.67 Pa和0.05 T; 随着工作气压的增大,放电电流先增大后趋向平衡,当工作气压超过2.5 Pa时,电流开始随工作气压的增大而减小; 而阴极电压增大时,放电电流近似线性增加.     

外磁场作用下的磁等离子体动力学过程仿真

磁等离子体动力学推力器是空间高功率电推进装置的典型代表,磁等离子体动力学过程是其核心工作机制.为深入理解外磁场对其工作特性的影响,本文采用粒子云(particle in cell,PIC)方法结合基于自相似准则的缩比模型,进行外加磁场作用下磁等离子体动力学推力器工作过程的建模仿真,通过与实验结果对比验证模型和方法的可靠性,并重点分析推力器点火启动过程的等离子特性参数分布,以及外磁场和阴极电流对推力器工作性能的影响.研究结果表明:阴阳极放电电弧构建是推力器启动和高效工作的关键步骤;外磁场强度较低工况不利于构建稳定放电电弧,等离子体束流集中于轴线附近,推力主要产生机制是自身场加速;外磁场强度较高时,阴阳极放电电弧稳定,推力产生主要机制是涡旋加速,推力、比冲随外磁场强度线性增大;推力器效率随阴极电流和外磁场强度增大而增大;放电电压随阴极电流增大而增大,但随外磁场强度的增大表现出先减小后增大的趋势.     

外磁场作用下的磁等离子体动力学过程仿真

磁等离子体动力学推力器是空间高功率电推进装置的典型代表,磁等离子体动力学过程是其核心工作机制.为深入理解外磁场对其工作特性的影响,本文采用粒子云(particle in cell,PIC)方法结合基于自相似准则的缩比模型,进行外加磁场作用下磁等离子体动力学推力器工作过程的建模仿真,通过与实验结果对比验证模型和方法的可靠性,并重点分析推力器点火启动过程的等离子特性参数分布,以及外磁场和阴极电流对推力器工作性能的影响.研究结果表明:阴阳极放电电弧构建是推力器启动和高效工作的关键步骤;外磁场强度较低工况不利于构建稳定放电电弧,等离子体束流集中于轴线附近,推力主要产生机制是自身场加速;外磁场强度较高时,阴阳极放电电弧稳定,推力产生主要机制是涡旋加速,推力、比冲随外磁场强度线性增大;推力器效率随阴极电流和外磁场强度增大而增大;放电电压随阴极电流增大而增大,但随外磁场强度的增大表现出先减小后增大的趋势.     

170 GHz回旋管大束流双阳极磁控注入电子枪的分析及设计

 基于绝热压缩原理和强流电子光学理论,设计了一只170 GHz回旋管双阳极磁控注入电子枪,经过理论分析及计算,采用仿真软件进行模拟和优化,最终得到的电子枪的电子注速度比为1.31,横向速度零散度为3.5%,纵向速度零散度为6.1%,束电流为51 A。讨论了阴极磁场、控制阳极电压和第二阳极电压等因素对电子注性能的影响,发现电子注的速度比和速度零散度对这些影响因子的变化都非常敏感:随着阴极磁场的增大,电子注的速度比减小,纵向速度零散度先增大后减小,横向速度零散度先减小后增大;阳极角越接近阴极倾角,纵向速度零散度越小;阳极角向着减小阴阳极间距的方向变化时横向速度零散度变小;增大第一阳极电压可以增大电子注的速度比和电子注的速度零散度。在两阳极电压不变的情况下,增大阴阳极之间的距离会使电子注的速度零散度和电子注的速度比减小。     

含氢电极真空弧放电等离子体时空分布特性研究

真空弧离子源在真空镀膜、材料表面改性、真空大电流开关、加速器离子注入等领域有广泛应用,目前国内外对真空弧放电等离子体的研究主要针对纯金属或合金电极,对含氢电极的研究和公开报道较少.本文利用高时空分辨的四分幅图像诊断系统,结合氢和钛原子特征线单色器件,研究了含氢钛电极的真空弧微秒级脉冲放电等离子体的轴向和径向时空分布特性.研究表明:在真空击穿阶段,阳极区域发光更为明显,阳极电极解吸附释放的氢原子是引发击穿的主要放电介质;在真空弧阶段,阴极-绝缘-真空三结合点处产生圆锥状阴极斑,喷射出大量的等离子体以维持弧放电,同时电极内壁非阴极斑区域也有少量等离子体产生,等离子体中H原子的轴向和径向空间分布均比Ti原子均匀.     

同轴电极结构下真空放电等离子体生成及传播特性

采用放电电流为100~300 A、持续时间为13 s的单脉冲电源,设计了两种同轴电极结构作为放电阳极,分别为筒状电极、喷嘴状电极。利用MAXWELL 3D电场仿真软件对两种电极结构下的电场分布进行了仿真分析,并采用探针法对放电生成的等离子体的参数进行了测量,分析讨论了同轴电极结构对真空放电等离子体生成特性的影响。选取喷嘴状电极结构作为阳极,分别测量了采用铅、铝、铜三种材质的阴极时生成的等离子体的扩散速度及能量。实验与仿真结果表明:当阳极为喷嘴状电极时阴极尖端的电场强度较大,测得放电电流较大,击穿电压较低,等离子体密度也较大;采用铝材质阴极时生成的等离子体扩散速度最快,采用铅材质阴极时生成的等离子体的离子动能最大。     

直流纯氩层流等离子体射流的长度变化

采用主要由阴极、阳极以及介于阴极和阳极之间的中间段组成的直流非转移式电弧等离子体发生器,在大气压条件下,比较系统地研究了纯氩层流等离子体射流的长度随着弧电流、气体流量以及发生器结构而变化的规律。结果表明:层流射流的长度随弧电流和工作气流量的增加而增长;层流向湍流流动转变的临界气流量值随弧电流增大而提高;在发生器的伏安特性呈大梯度变化的情况下,射流长度随弧电流的变化幅度增大。     

碳纳米管在大气压环境中的场致发射特性

研究了在大气压环境下,单根碳纳米管作为场致发射阴极,与阳极间距为100—200 nm时的场致发射特性.对比了碳纳米管在不同阴阳极间距和不同气体环境中的场致发射电流和噪声的特点. 关键词： 碳纳米管 场致发射 大气压     

大气压管板结构纳秒脉冲放电中时域X射线研究

纳秒脉冲放电能在大气压下产生高电子能量、高功率密度的低温等离子体,由于经典放电理论无法很好地解释纳秒脉冲放电中的现象,近年来以高能逃逸电子为基础的纳秒脉冲气体放电理论受到广泛关注.纳秒脉冲放电会产生高能逃逸电子,伴随产生X射线,研究X射线的特性可以间接反映高能逃逸电子的特性.本文利用纳秒脉冲电源在大气压下激励空气放电,通过金刚石光导探测器测量放电产生的X射线,研究不同电极间隙、阳极厚度下和空间不同位置测量的X射线特性.实验结果表明,在大气压下纳秒脉冲放电能产生上升沿约1 ns,脉宽约2 ns的X射线脉冲,其产生时间与纳秒脉冲电压峰值对应,经计算探测到的X射线能量约为2.3×10-3J.当增大电极间隙时,探测到的X射线能量减弱,因为增大电极间隙会减小电场强度和逃逸电子数,从而减少阳极的轫致辐射.电极间距大于50 mm后加速减弱,同时放电模式从弥散过渡到电晕.随着阳极厚度增加,阳极后方和放电腔侧面观察窗测得的X射线能量均有所减弱,在阳极后面探测的X射线能量减弱趋势更加明显,这说明X射线主要产生在阳极内表面,因此增加阳极厚度会使穿透阳极薄膜的X射线能量减少.     

Cold-hollow-cathode arc discharge in crossed electric and magnetic fields

A crossed-field cold-hollow-cathode arc is stable at low working gas pressures of 10⁻²–10⁻¹ Pa, magnetic-field-and gas-dependent arcing voltages of 20–50 V, and discharge currents of 20–200 A. This is because electrons come from a cathode spot produced on the inner cathode surface by a discharge over the dielectric surface. The magnetic field influences the arcing voltage and discharge current most significantly. When the plasma conductivity in the cathode region decreases in the electric field direction, the magnetic field increases, causing the discharge current to decline and the discharge voltage to rise. The discharge is quenched when a critical magnetic field depending on the type of gas is reached. Because of the absence of heated elements, the hollow cathode remains efficient for long when an arc is initiated in both inert and chemically active gases.     

回旋速调管双阳极磁控注入电子枪的设计与优化

 根据8 mm回旋速调管放大器对双阳极磁控注入电子枪的要求，分析了电极形状、阳极电压、磁场、注电流对电子注横纵速度比和速度零散的影响，并进行了粒子模拟。分析表明：这些因素可归根为电场和磁场的作用，阴极附近高的电场有助于提高横纵速度比和降低速度零散；而高的磁场及低的磁压缩比将降低横纵速度比，但对速度零散影响无明显规律。在此基础上通过优化电极形状、磁场分布、电流、第一阳极电压和第二阳极电压，模拟并试制出工作电压65 kV、电流12 A、磁场1.4 T的双阳极电子枪，得到的横纵速度比值为1.4，横向速度零散为4.5%， 为8 mm回旋速调管提供了稳定高质量的电子注。     

THE EFFECT OF MESH ANODE ON CATHODIC ARC IN FOCUSING MAGNETIC FIELD

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 are investigated. The arc voltage V_a is measured with a fixed arc current. 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. 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.     

Glow Discharge Characteristics of Hollow Needle-Plate Electrode in Atmospheric Pressure ArgonSCIEI北大核心CSCD

Atmosphere pressure uniform plasma has the broad application prospect in the industrial field. Using hollow needle cathode - plate anode device excited by direct-current voltage, a uniform and stable glow discharge is generated at atmospheric pressure in ambient air with argon used as working gas. The influence of the experimental parameters (including gas flow rate and the gas gap width) on discharge has been investigated by optical method. It can be found that a glow-discharge plasma column can bridge the two electrodes. The plasma column is uniform, and no filaments can be discerned. Near the plate electrode, the diameter of the plasma column is largest of all positions. The maximal diameter of the plasma column increases with increasing the discharge current or the gas flow rate. Through electrical method, the voltage-current characteristic has been investigated. It has been found that the discharge voltage decreases with increasing the current which is similar with the characteristic of glow discharge in low pressure. It increases with increasing the gas gap width or the gas flow rate. By analyzing the optical emission spectrum scanning from 330 to 450 nm emitted from the direct-current glow discharge, the molecular vibrational temperature and the intensity ratio of spectral lines I-391.4/I-337.1 have been investigated as functions of the gas flow rate and gas gap width. Results indicate that both the vibrational temperature and the intensity ratio of spectral lines I-391.4/I-337.1 decrease with increasing the gas flow rate or the gas gap width. In addition, the molecular vibrational temperature and the intensity ratio of spectral lines I-391.4/I-337.1 have been investigated in spatial resolution along the direction of gas flow(plasma column axial), and give a qualitative analysis as well. It is found that the vibrational temperature and the average electron energy increase with increasing the distance from the hollow needle cathode. These results are important to the industrial applications of glow discharge.     

ZnO:Zn低能电子发光的亮度饱和

本文讨论了ZnO:Zn低能电子发光亮度饱和的物理原因。指出,在Vg=Va(通常数字显示的情况)的条件下,亮度饱和的主要原因是ZnO:Zn次级电子发射和阴极发射疲劳;若取Vg=Va,则饱和亮度成倍提高,这时热猝灭将是亮度饱和的主要因素。同时指出,对于一定的输入功率,存在着一个与最佳效率相对应的最佳阳极电流密度;低阳极电流密度,高阳极电压往往是低效率的。作者根据本文的研究结果,制成了饱和亮度高达37,000cd/m2的发光管和饱和亮度为22,000cd/m2、能在5,000至10,000cd/m2稳定工作的高亮度数字显示管。后者配上适当的滤光片、在阳光直接照射或照度高达100,000lux的条件下仍能清晰地阅读。     

Onset of breakdown and formation of cathode spots

When an increasing diode voltage is applied, enhanced field emission of electrons begins from a growing number of small spots or whiskers on the cathode surface. This stimulates desorption of weakly bound adsorbates from the surface of a whisker. As the diode voltage increases, the 100-V equipotential surface moving toward the cathode is met by the desorbed neutrals moving away from the cathode, resulting in sharp risetime for the onset of ionization of desorbed neutrals by field-emitted electrons. Positive ions produced in the ionization region a few microns from the electron emitting spot are accelerated back to it. This bombardment leads to surface heating of the spot. The onset of breakdown by this mechanism requires much less current than the Joule heating mechanism. The localized buildup of plasma above the electron emitting spot leads to pressure and electric field distributions that ignite unipolar arcs. The high current density of the unipolar arc and the associated surface heating by ions result in the explosive formation of cathode spot plasma     

阴极帽结构L波段相对论磁控管的效率提升

提出了一种具有阴极帽结构的L波段相对论磁控管的设计方案,并给出了数值模拟结果。在相对论磁控管中引入阴极帽是为了降低轴向泄露电流并提高功率转换效率。三维粒子模拟用于研究引入阴极帽后产生的影响。结果显示,当在束波互作用区域的上游和下游同时添加阴极帽,并且将阴极延伸出阳极块结构,直至衍射输出结构时,轴向泄露电流不仅会从1 kA降至72 A,且功率转换效率会有明显提高。虽然如此,阴极帽的引入除了以上优点外,同样会带来微波反射。因此,阴极帽的半径和位置对于效率有至关重要的影响,它们之间存在一个最优数值来保证效率最高。当电压为563 kV, 磁场为0.34 T时,轴向衍射输出结构L波段相对论磁控管输出微波功率为2.13 GW,频率为1.59 GHz,相应的功率转换效率为75.5%。