Structural Analysis of the Large Helical Device

Abstract

Structural analysis by finite element method has been carried out for the supporting structures of the Large Helical Device (LHD). The LHD has one pair of helical coils and three pairs of poloidal coils, all of which are superconducting coils. The electromagnetic forces loaded on the coils are in the order of 10 MN/m. Accuracy of the location of the coils is very important for the helical device. All coils, therefore, are firmly fixed to a cylindrical supporting structure to confront the large electromagnetic force. In order to suppress the error field within 1x10 ^-4 of the central toroidal field, it was provided that the permissible value of asymmetric deformation of each coil caused by electromagnetic force would be within 3.4 mm for 4 T operation. After minor reformation of the thickness and the shape of the supporting structures, the detailed structural analysis has been carried out. As the results of analysis with considering the rigidness of poloidal coils, the maximum displacement can be suppressed within 2.39 mm. The maximum stress is calculated to be 264 MPa. This is allowable for SUS 316 that will be the main material of the structures.