| 摘要 |
Conventional electron guns in electron beam columns utilize a thermionic triode configuration. A tetrode (four electrode) gun is described which allo ws the adjustment of both variable high brightness and illumination uniformity in t he profile of the electron beam. This is achieved by adding an electrostatic focusing electrode between the cathode and the anode within the electron gun. The focusing electrode is positively biased to a few keV and allows the image of the cathode to be focused at infinity. The addition of a focusing electrode enables both variable brightness and illumination uniformity by adjustment of the bias of a grid which is mounted below the cathode to maintain constant emission. while adjusting the bias of the focusing electrode to obtain the optimal beam cross-sectional uniformity.
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