| 摘要 |
A set of three cathodes, a control electrode, an accelerating electrode, a first focus electrode, a second focus electrode, a third focus electrode, a fourth focus electrode, a final accelerating electrode and a shield cup electrode are provided successively in an electron beam travelling direction. The shield cup electrode has a pair of screen-shaped electrodes that sandwich electron-beam through-holes in a vertical direction. A quadrupole lens that has a horizontal convergent action and a vertical divergent action is generated by an electrical potential difference between the screen-shaped electrodes and the final accelerating electrode. Accordingly, even if vertical and horizontal convergence power difference in a main lens formed by the fourth focus electrode and the final accelerating electrode is not large, a composite lens formed through a combination of the quadrupole lens and the main lens has strong horizontal convergence power and weak vertical convergence power.
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