| 摘要 |
PROBLEM TO BE SOLVED: To provide a hollow beam aperture of a great strength, in which a narrow opening can be easily manufactured. SOLUTION: The hollow beam aperture consists of a 3-layered structure: a shielding layer 1, which has a function to shield the beam; a holding layer 3, which has a function to hold the shielding layer 1; and a reinforcing layer 4, which has a function to keep total aperture strength. The holding layer 3 is comprised of a beam passage, which consists of four holes 5, and it has the function to hold a circular beam absorber 2 at the gap 6 between the holes 5. The shielding layer 1 is comprised of a circular hole, which is concentric with the circular beam absorber 7, and between them is a ring band opening 7. By making the holding layer 3 to have a sufficient thickness to hold the circular beam absorber 2, the holding strength of the circular beam absorber 2 can be kept without increasing the depth of the ring band opening 7.
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