| 摘要 |
PURPOSE:To form all of the three beam spots into the required shape, by providing auxiliary electrodes near each round hole in the grid No.4. CONSTITUTION:In parallel to the surface connecting each central axis of each round hole (a4) in the grid No.4 4, auxiliary electrodes 10 are provided near each round hole (a4), and by adjusting length or width of said auxiliary electrodes 10 the shape of each beam is longitudinally changed to make its adjustment in such a manner as to obtain the required shape. While concentrically with the central round hole an adjusting cylinder is provided, and the adjustment of its length and position can adjust the shape of the central beam. |
