| 摘要 |
PURPOSE:To make beam current vs optimum focusing voltage characteristics of central electron beams be almost identical with those of both side electron beams by making an annular top part of an aperture for central electron beam transmission be lower than two annular top parts of apertures for both side electron beam transmission and making flat surface parts in the vicinity of the apertures be formed in approximately similar height. CONSTITUTION:A peripheral part 13b of a central aperture 10b, which faces a second grid electrode 11, is formed in a first grid electrode 10 and at a position lower than both side apertures 10a and 10c, and a peripheral part 15b of a central aperture 11b, which faces a first grid electrode 10, is formed in the second grid electrode 11 and at a position lower than peripheral parts 15a and 15c of both side apertures 11a and 11c. Thereupon, a mutual parallel degree between the first grid electrode 10 and the second grid electrode 11 cen be upgraded. Distances between cathodes 1A to 1C and the apertures of the first grid electrode 10, distances between the apertures of the first grid electrode 10 and those of the second grid electrode 11, can be made essentially equivalent concerning the central electron beams and both side electron beams. Hence, electron-optical characteristics of both their electron beams are made identical with each other at three electrode positions, and optimum focusing voltages of both their electron beams become equal to each other in the end.
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