| 摘要 |
PURPOSE:To improve the stream line flow property of beams, by making the inside diameter of the electron beam passage aperture of a Whenelt electrode 1 to 1.2 times the outer diameter of the electron emitting face of a cathode, bending the peripheral nonmesh part of the second grid electrode at the position 1 to 1.2 times the outer diameter of the electron emitting face, and inclining the extension thereof at 65 to 80 deg. to the electron gun axis. CONSTITUTION:The inside diameter DW of the aperture 23 of a Whenelt electrode 22 is made 1 to 1.2 times the outside diameter DK of the electron emitting face 12 of a cathode 11. The second grid 18 is bent P at a nonmesh part 19 at the periphery thereof, making the angle theta to the electron gun axis Z, and welded to a flange 21. The diameter DP of the second grid 18 is made 1 to 1.2 times the diameter DK of the cathode, and the theta is made 65 to 80 deg.. In such a composition, the scattered electrons at the outer side of the grid mesh are fewer, the beam permeability can be maintained 90% or more, and the assembly is also easier.
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