| 摘要 |
PURPOSE:To correct the influence due to the distortion near the axis along which the charged particle to be selected will advance, by providing a correction electrode for producing an auxiliary field in addition to the field due to the electrode. CONSTITUTION:The surface of magnetic poles 13, 14 are enlarged thereby the distortion of magnetic field near the central axis 23 is low and uniform. But the surface of an electrode arranged between said fields is small thereby the field near the central axis 23 where the charged particle is projected will distort and the magnetic and electric field crossing accurately in perpendicular can not be formed near said central axis. Here suitable voltage is applied from a power source 22 to auxiliary electrodes 20, 21 thereby the distortion near the central axis 23 formed by the electrodes 11, 12 is corrected by the field due to said correction electrodes 20, 21, to produce the magnetic and electric field crossing perpendicularly near said central axis 23 thus to select the desired charged particle. |
