Studies on Electrode Surface Conditions and Vacuum Breakdown Phenomena by an Electron Emission Microscope

本项目的目的是利用我们实验室研制的电子发射显微镜来发现真空间隙电极上电子发射位点形态的变化。开发的电子发射显微镜的特点是电子发射成像不仅可以瞄准点电极，而且可以瞄准大面积电极。1997年，即研究学期的第一年，澄清了以下内容： 1．获得了电子发射位点的图像，验证了电子发射显微镜的工作性能。 2．观察到场电子发射部位振动。这可能是由于排放地点的移动造成的。为了确认排放点的移动，还需要进行进一步的实验。 3．利用该显微镜对真空间隙大面积无氧铜电极上的场电子发射位点进行了观察。观察结果表明，宏观上单个发射位点由多个位点组成。1998年，即本项目的最后一年，连续进行了真空间隙电极的观察，结果总结如下： 1．通过紫外光激发下50μm直径铝丝的光电子发射图像来标定显微镜的放大倍数。 2．真空间隙无氧铜电极的观察表明，宏观单场电子发射位点由多个位点组成。 3．此外，对无坑电解抛光铝电极的观察表明，击穿前后电子发射位点的形态发生了显着变化。通过这项研究，可以阐明电子发射位点形态的变化。该仪器将提供一种强大的手段来评估电极表面处理以获得真空间隙的更高电压保持能力。

The aim of this project is to find changes of the aspect of electron emission sites on electrodes of a vacuum gap by using an electron emission microscope developed by our laboratory. The electron emission microscope developed has the feature that imaging of electron emission sights on not only a point electrode but also a broad area electrode is possible.In 1997, the first year of the research term, followings were clarified.1. The images of electron emission sites were obtained and operating performance of the electron emission microscope was confirmed.2. It was observed that field electron emission sites vibrated. This may be due to moving of emission sites. To confirm moving of emission sites it is necessary to make further experiments.3. Field electron emission sites on broad area oxygen-free copper electrodes of a vacuum gap were observed by this microscope.The observations revealed that macroscopicaly single emission site consists of several sites.In 1998, the last year of this project, observations of electrodes of vacuum gaps were carried in succession, and the results were summarized as follows.1. The magnification factor of the microscope was calibrated by photoelectron emission images of 50 mu m diameter Al wire excited by ultra-violet light.2. Observations of oxygen-free copper electrodes of vacuum gaps clarified that a macroscopically single field electron emission site consists of several sites.3. In addition, observations of pit-free electropolished aluminum electrodes revealed that the aspect of electron emission sites changed significantly before and after breakdowns.By this research it becomes possible to clarify changes of aspect of electron emission sites. The instrument will provide a powerful means to asses electrode surface treatments to obtain higher voltage hold-off capability of a vacuum gap.