| 摘要 |
PURPOSE:To enable a small diameter and a high resolution to be realized even during the existence of a large beam current while sufficiently narrowing the distance between a G2 and a G3 electrode by restricting the maximum value of the primary differential of an electric potential on the axis and the positions of the local maximum and minimum values of the secondary differential to within specified ranges. CONSTITUTION:In the region in which the second grid 19 and the third grid 28 face each other, when the maximum value of the primary differential of an electric potential (V) on the axis (an electric field on the axis) is in the range of 5X10<4>-5X10<5> V/cm, the relationships of 1.0D1<=Z1<=2.0D1 and 0.5D1<= Z2-Z1<= 1.2D1 should be satisfied in the electrode constitution according to this invention; the positions of the local maximum and minimum values of the secondary differential (V'') are supposed to be Z1 and Z2 relative to the electron-discharging surface of a cathode 1 and the diameter of the electron-beam passing hole of the first grid 18 is supposed to be D1. As a result, the lens effects of the focusing and the divergent lens sections 23a and 23b of a prefocusing lens 23 are both intensified, an astigmation-suppressing effect newly appears and the diameter of a crossover virtual image 24 is extremely reduced.
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