棒-板电极下缩比气隙辉光放电相似性的仿真研究

建立了棒-板电极下氩气直流放电的流体模型,利用有限元法对几何位形相似的两个气隙放电过程进行了数值求解.两放电气隙外加电压相同,气隙线性尺寸的比值为10:1,气压分别为1 Torr和10 Torr.仿真得到了两相似气隙的放电的伏安特性曲线以及放电物理量(如电位、电场、电子密度、离子密度、电子温度等)的空间分布.根据气体放电相似性的基本结论,检验了气隙对应物理量之间的数值关系.结果表明:两相似气隙的放电类型为正常辉光放电,对应放电物理量之间存在相似性理论指出的比例关系,且在相同幅值的直流电压作用下,气隙放电的工作点相同.这将为利用气体放电相似性来外推相似气隙的放电特性提供一定的理论依据.     

X-pinch负载分流关系研究

研究了X-pinch和回流柱之间的分流关系,以及两个X-pinch之间的分流关系。在X-pinch和回流柱的分流实验中,X-pinch上的电流与回流柱上的电流大体相等,这表明电流分布不只与X-pinch或回流柱的特性有关,而且也与它们所在回路的其他部分有关。在两个X-pinch之间的分流实验中,X-pinch上的电流与X-pinch本身的材料和直径几乎无关,这确认了电流分布与回路中X-pinch之外的部分有关。离绝缘柱远的X-pinch上的电流总是比离绝缘柱近的X-pinch上的电流略大一些,这是并联回路之间的互感造成的。     

Determining the resistance of X-pinch plasma

The current and the voltage of an X-pinch were measured. The inductance of the X-pinch was assumed to be a constant and estimated by the calculation of the magnetic field based on the well-known Biot-Savart's Law. The voltage of the inductance was calculated with L · di/dt and subtracted from the measured voltage of the X-pinch. Then, the resistance of the X-pinch was determined and the following results were obtained. At the start of the current flow the resistance of the exploding wires is several tens of Ohms, one order of magnitude, higher than the metallic resistance of the wires at room temperature, and then it falls quickly to about 1 , which reflects the physical processes occurring in the electrically exploding wires, i.e., a current transition from the highly resistive wire core to the highly conductive plasma. It was shown that the inductive contribution to the voltage of the X-pinch is less than the resistive contribution. For the wires we used, the wires' material and diameter have no strong influence on the resistance of the X-pinch, which may be explained by the fact that the current flows through the plasma rather than through the metallic wire itself. As a result, the current is almost equally divided between two parallel X-pinches even though the diameter and material of the wires used for these two X-pinches are significantly different.     

Influence of Forbidden Processes on Similarity Law in Argon Glow Discharge at Low Pressure

The similarity law of gas discharge is not always valid due to the occurrence of some elementary processes, such as the stepwise ionization process, which are defined as the forbidden processes. To research the influence of forbidden processes on the similarity law, physical parameters （i.e., the electric field, electron density, electron temperature） in similar gaps are investigated based on the fluid model of gas discharge. The products of gas pressure p and dimensions are kept to be constant in similar gaps and the discharge model is solved with and without the forbidden processes, respectively. Discharges in similar gaps are identified as glow discharges and the typical similarity relations all are investigated. The results show that the forbidden processes cause significant deviations of similarity relations from the theoretical ones and the deviations are enlarged as the scaled-down factor k increases. If the forbidden processes are excluded from the model, the similarity law will be valid in argon glow discharge at low pressure.     

缩比间隙中辉光放电相似性的初步研究

为了研究缩比实验在气体放电中的有效性, 对缩比间隙中的低气压氩气放电进行了数值模拟. 根据气体放电相似性的猜想, 如果间隙气压p和间隙距离d的乘积为常量, 即p₁d₁=p₂d₂, 并且约化电场E/p 在两个间隙中的空间分布相同, 那么这两个放电间隙的放电特性存在相似性. 数值模拟中设置三个缩比间隙: 气隙A的长度为30 mm, 气压为1 Torr (1 Torr=133.322 Pa); 气隙B的长度为15 mm, 气压为2 Torr; 气隙C的长度为10 mm, 气压为3 Torr. 仿真结果表明, 三个间隙均为辉光放电, 并存在明显的阴极位降区. 间隙A, B, C 的阴极位降区的厚度d_C分别为2.71, 1.35和0.87 mm, 相对应的pd值几乎相同, 即pd_C≈2.70 Torr·mm. 这与氩气辉光放电Paschen曲线最低点(pd≈2.86 Torr·mm)相近. 缩比间隙的放电参数的特性(如工作电压、电场、电流密度、电子密度和离子密度的沿“空间”px的分布)的数值计算结果与放电相似性猜想所预计的结果一致. 所以, 可以认为放电相似性猜想适用于低气压氩气缩比间隙的辉光放电. 关键词： 放电相似性 辉光放电 缩比间隙     

Determination of Ionization Coefficient of Atmospheric Helium in Dielectric Barrier Discharge

A weakly luminous layer close to the anode is observed at time far ahead of the current pulse in dielectric barrier discharge of helium at atmospheric pressure and it is considered as the result of a very weak Townsend discharge. Based on the assumption that the space charge produced by this Townsend discharge is too small to distort the uniform electric field in the gas gap, the electrons have more or less the same energy over the entire gap and the spatial distribution of the discharge light is proportional to the distribution of electron density. This light distribution is obtained by processing side-view photograph of discharge gap using an intensified charge coupled device camera with an exposure time of 20ns. By fitting a theoretically derived formula with the measured curve of light distribution, the Townsend electron ionization coefficient α is determined to be 31 cm^-1 at E/p = 3.6 V·cm^-1·Torr^-1, which is much higher than that obtained by solving the Boltzmann equation of pure helium. It is believed that penning ionization of helium metastables with impurity of nitrogen molecules makes great contribution to the experimentally determined α value. The contribution of this penning ionization to α is roughly estimated.     

气流对氮气介质阻挡放电气体温度及放电模式的影响

利用光谱测量和高速照相的方法,对大气压氮气介质阻挡放电进行了研究.在气流的帮助下,2mm气隙中的均匀放电可以长时间得以维持.根据放电电流波形和1μs曝光时间的放电图像,这种均匀放电被判定为汤森放电.用氦氖激光器对实验中所用的光谱仪带来的谱线轮廓展宽进行了标定,并将得到的仪器展宽数据输入Specair软件,计算了不同气体温度下氮分子二正系0—2谱带的谱线轮廓.通过用计算谱线轮廓去拟合实验谱线轮廓,确定了氮分子的转动温度并将其近似为气体温度.结果表明:大气压氮气介质阻挡汤森放电并不能使气体温度大幅上升(ΔTg≤50K),气体温度的小幅上升不会引起热不稳定性而导致放电发展成为细丝放电.气流确实可以降低放电气体温度,但这不是使汤森放电得以维持的原因.通过比较加入气流前后的放电光谱可知,气流降低了气隙中杂质氧的含量,使得更多的氮分子亚稳态N2(A3Σu+)的寿命延长到下一次放电的起始时刻,为汤森放电提供了必需的大量种子电子.     

射频等离子体压力传感器及其在动态压力测量中的应用

为精确测量高温高压严苛环境下的动态压力数据,本文设计了一种基于射频等离子体原理的压力传感器,并研究了该传感器在不同电源输出功率时对气压变化的响应规律,及不同温度环境下的工作特性,最后利用该传感器在低速轴流压气机实验台上进行了叶顶动态压力场的测量。实验结果表明,射频等离子体压力传感器电极间隙为220μm时,气压从0.4 atm升高到4.5 atm,灵敏度为0.22 V/kPa;标准大气压下环境温度从25℃上升到400℃时,传感器两端维持电压基本不变,说明该传感器在此温度范围下不具有温度敏感性;低速轴流压气机叶顶动态压力场测量实验结果表明,等离子体压力传感器和Kulite压阻式传感器具有同样捕捉叶片通过频率和叶顶泄漏流的自激非定常特征频率的能力。     

全固态高重复频率LTD的性能测试和特性分析

全固态直线型变压器驱动源(LTD)是具有独特性能的新型高重频脉冲功率发生器。针对LTD的基础特性进行了较详细的实验研究。测量内容包括输出脉冲宽度与控制信号的关联、LTD模块上的信号延迟及其分散性，以及不同条件下LTD系统的能量效率分析。实验结果使我们对LTD取得了更加详细和深入的认识，同时为进一步改善和提高LTD脉冲功率发生器的技术水平提供了重要的参考数据。     

单丝及多丝Z箍缩的X射线背光成像

基于X箍缩软X射线辐射点源对单丝及多丝Z箍缩发展过程进行了背光成像研究,实验平台为清华大学电机系研制的脉冲功率装置PPG-Ⅰ（500 kV/400 kA/100 ns）。成像光路安排为:作为X射线源的X箍缩和作为目标物的单丝或多丝（双丝）Z箍缩分别安装在装置的输出主电极阴阳极之间或回流导电杆处,成像胶片采用高分辨力、高灵敏度的X射线胶片。利用自行设计的电流传感器和罗氏线圈对目标物实际流过的电流进行监测。为了测定目标物金属细丝的质量消融率,设计了m级厚度的阶梯光楔。通过大量成像实验,获取了Z箍缩等离子体融合、先驱等离子体形成及不稳定性发展等过程的相关物理图像以及质量消融率、丝芯膨胀率等重要定量参数。