气体放电相似性主要致力解决超大或超小尺寸放电研究所遇到的困难，同时有助于不同尺寸气体放电器件设计和放电特性预测，具有重要的理论与应用价值。本论文通过实验研究、数值模拟和理论分析，对低气压下气体放电相似性的某些相关问题进行了研究，主要工作如下： 建立了一套低气压气体放电装置，极限真空达10-5Pa，配置了相应的外加电源、气路系统、气压测量、电气及图像诊断系统，设计不同位形的几何相似的放电气隙、绝缘外筒以及用于电流密度测量的环形电极。在不同气隙长度d、电极半径r和放电管半径R的实验条件下，通过分别改变气隙的电场分布参数和径向扩散参数，对低气压下帕邢曲线不重合现象进行了系统研究，提出电场分布的差异是导致两个气隙帕邢曲线分离的主要原因。研究了低气压下帕邢曲线的“交叉”现象。实验和数值计算结果均发现：气隙长度相同但电极半径明显不同的帕邢曲线将在低气压区产生交叉现象，这是由汤森放电击穿条件以及电子碰撞电离系数 α= f(E/p)决定的。利用气体放电的流体模型，对三种不同位形（平行平板、棒-板、棒-筒）几何相似气隙的辉光放电进行了数值仿真，对比了两气隙放电同一物理参量（电位、电场、电子密度、离子密度等）之间的比例关系，结果表明：如果两个几何相似气隙缩比系数较小并且p1d1 = p2d2，那么两个几何相似气隙的辉光放电是相似的。通过建立两个略微不同的辉光放电物理模型，一个包含不允许过程（逐级电离、除彭宁电离以外的第二类非弹性碰撞)，另一个不包含不允许过程，比较不同缩比系数下几何相似气隙中的辉光放电数值仿真结果，研究了不允许过程对辉光放电相似性的影响。实验研究了不同位形（平行平板、棒-板）的几何相似气隙中低气压辉光放电的相似性。对于平行平板间隙，分析了缩比系数和气压对伏安特性的影响，确定了几何相似气隙放电相似时所对应的气压范围，并利用环形电极测量了正常和反常辉光放电的电流密度，比较了同种辉光放电条件下几何相似气隙中的电流密度。对于棒-板间隙，研究了不同极性下几何相似气隙中辉光放电的相似性，分析了棒电极上部绝缘屏蔽对放电相似性的影响。在平行平板气隙下，研究了低气压下反常辉光放电阴极位降区长度dc以及径向扩散条件对相似关系式pdc = f(J/p2) 的影响。
Similarity theory of gas discharge mainly deals with the difficulties encountered in research of ultra-large or ultra-small scale discharge; meanwhile it helps designing and predicting discharge properties of gas-discharge device of different size, which has a vital theoretical and applicative value. In this paper, some problems related to the low-pressure gas discharge similarities were given an in-depth exploitation, based on experimental study, numerical simulation and theoretical analysis. The main work includes:A low-pressure gas discharge experimental apparatus was constructed, in which the ultimate vacuum was up to 10-5Pa. The appropriate power supply, gas inlet and outlet path, pressure measurement, electrical diagnosis and gas-discharge imaging system were established. Geometrically similar gas gaps in different configurations were designed, as well as the insulation tube. A type of ring electrode was designed for current density measurement.In experimental conditions of different air-gap lengths d, electrode radius r and discharge-tube radius R, the “segregation” phenomenon of Paschen’s curves was studied, by changing the field distribution parameter d/r and the transverse diffusion parameter d/R, respectively. It was proposed that the difference in electric field distribution is the primary reason incurring separation of Paschen’s curves in the two gaps. The “intersection” phenomenon of Paschen’s curves at low pressure was investigated. Both the experimental results and numerical simulation indicate that, in different gaps whose length is the same but electrode radius is significantly different, the Paschen’s curves would cross over at low pressure. Occurrence of this phenomenon can be explained by the Townsend’s breakdown criterion and the divergence of electron impact-ionization coefficient α = f (E/p).Glow discharge in gaps of three different configurations (parallel plane, rod-plane and rod-tube) was studied adopting a two-dimensional fluid model. In each configuration, the ratios between physical quantities (electric potential, electric field, electron density, ion density, etc.) of two geometrically similar gaps were compared. The results showed that the glow discharges in the two gaps are similar, as long as the scale-down factor is relatively small and the reduced length relation meets the condition p1d1 = p2d2.Two different physical models of glow discharge were established. The forbidden processes, i.e. stepwise ionization, inelastic collision of second kind (except Penning ionization), were included in one model, whereas excluded in the other. The influence of forbidden processes on similarity law of glow discharge was discussed, by comparing simulation results in gaps with different scale-down factors.Experimental research on similarity of glow discharge was carried out in geometrically similar gaps of different configurations (parallel plane, rod-plane). In the parallel plane gap, the effect of scale-down factor and gas pressure on the voltage-ampere (VA) characteristic was analyzed, and the pressure range where the same VA characteristic holds in geometrically similar gaps was confirmed. The current densities of normal and abnormal glow discharge were measured by using the dedicatedly designed ring electrodes, and the current densities of glow discharge in geometrically similar gaps were compared. For the rod-plane gap, the similarity of glow discharge in different polarities was investigated, and the influence of insulation shielding (on upper rod electrode) on similar discharge was surveyed. As for the parallel-plane gap, by measuring the cathode fall thickness of low-pressure abnormal glow discharge under different experimental conditions, the influence of transverse diffusion of charged particles on the similarity relation pdc = f (J/p2) was inspected.
