| 摘要 |
PURPOSE:To obtain required shapes for three beam spots by placing aux. electrode between each circular hols of third grid at the side of main lens. CONSTITUTION:A planar aux. electrode 10 is additinally provided between each circular hole a3 of grid No.3 5 at the side of main lens. By adjusting the length and the width of said aux. electrode 10, required beam shapes can be obtained at both side. While an adjusting cylinder 11 is provided concentrically with the central hole, and when adjusting the length and the position of said cylinder 11 the shape of central beam can be adjusted. When an oval beam shape is required, the planar aux. electrode and the adjusting cylinder are provided at the side of grid No.4 4. |
