Design and Construction of Coil Supporting Structure and Cryostat Vessel for LHD
The Large Helical Device is a fusion experimental machine with all superconducting coils. Electromagnetic force generated by the coils is supported by the torus shaped “supporting structure” of 100 mm thick 316 stainless steel. This structure consists of 20 fan shaped parts that were welded together on site. The coils needed to be positioned within 2 mm accuracy in the absolute coordinates so that the supporting structure had to be assembled within 5 mm accuracy prior to the coil setting. After completion of the welding, the overall accuracy of < 5 mm was achieved.
The cryostat vessel for the cryogenic structures of LHD has also been assembled on site. The material used in this vessel is 304 stainless steel. The thickness is 100 mm for the base plate and 50 mm for the outer and inner cylinder parts and the upper cover. Calculations for the deformation of this vessel under atmospheric pressure were carried out by using the finite element method and the displacement of ports for plasma diagnostics was confirmed to be less than 4 mm.
KeywordsWelding Process Supporting Structure Welding Zone Electron Beam Welding Minor Radius
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