| 摘要 |
PURPOSE:To make it possible to correct the deflecting aberration efficiently without losing the performance, by making furnishing positions and forms of four electrode pieces composing a quadrupole electrode in a position and form almost axis-symmetrical to the elctron beams. CONSTITUTION:A pair of opposing electrode pieces 6a and 6c, and a pair of opposing electrode pieces 6b and 6d compose a horizontal and vertical electric fields respectively. The crossing angle theta of two diagonal planes l and m which combine the middle points in the four gaps 9 formed between the peripheral sides of the four electrode pieces is made within 90 deg.+ or -5 deg., the crossing line p of the two diagonal planes l and m is made almost on the center line of the space surrounded by the four electrode pieces, and the elctron beams 7 are made to pass on the line p. Therefore, the symmetry of the electric field at the center of the space of the quadrupole electrode 6 is maintained, and the section form of the electron beams 7 is converted only from a circular section to a longish oval section including no other excessive deformation. Therefore, the spot image of the electron beams 7 displayed on the fluorescent screen is almost a regular circle, removing only the deflecting aberration.
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