| 摘要 |
PURPOSE:To obtain the stigmatic image formation by making only the first- order term zero when a Wien filter constituting an energy analyzer has proportional terms of the first order and higher in the uniform electric field and magnetic field superimposed at a right angle or in the electric field direction or the magnetic field direction only. CONSTITUTION:A Wien filter is constituted so that a charged beam passes through the uniform electric field and magnetic field or one of the electric field and magnetic field inclined proportionally to the first term and is dispersed in response to the magnitude of the energy. Thereby, the magnetic pole size becomes inevitably large, and a magnet becomes enormous. Therefore, even if the electric field has a gradient of the first order or higher, the first-order term is eliminated 80 that an image is formed at the correct position without being adversely affected by the beam. Accordingly, the condition of the stigmatic image formation can be obtained even if the ratio D/S(De/Se, Dm/Sm) between the top length D and the gap length S is compressed to 1.0 or less in magnetic poles 1, 2 and electrodes 3, 4.
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