Rigidity evaluation of a superconducting helical coil for an LHD-type fusion magnet

The large helical device (LHD) type fusion power reactor has many advantages in operations such as steady state and no active plasma current. The magnet system of the LHD-type fusion device consists of superconducting helical coils and superconducting poloidal coils. Since the helical coil is a complicated three-dimensional structure, designs of the coil and the supporting structure have to be performed carefully. Clarifying the mechanical behavior during coil excitation is very important for a design of the coil system. The mechanical behavior for components in the helical coil can be estimated using a simplified two dimensional axisymmetric model which has a mean radius of curvature of the actual helical coil. To evaluate the accuracy of this simplified model, stress distribution was calculated with three-dimensional finite element model and the result was compared with that of the simplified model. The stress distribution of a candidate design of LHD-type helical reactor was estimated by using the simplified model and the result showed that the stress / strain level were within the reasonable range for composed materials.