| 摘要 |
PROBLEM TO BE SOLVED: To prevent the thermal deformation of cooling crosspieces, while restraining the numerical aperture of an irradiation window from degrading. SOLUTION: This irradiation window 4a is equipped with two rows of reinforcing crosspieces, which are coupled with each of the cooling crosspieces 8 so as to be orthogonal to each of them at two points closer to both ends than to the center of the longitudinal direction Y of each of them. Each of both ends of the longitudinal direction (X-direction in Figure) of both reinforcing crosspieces 22 is fixed on a frame 10, on which both ends of the longitudinal direction Y of each of the cooling crosspieces 8 are fixed.
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