Optimal design of a Bi-2223/Ag coil for superconducting magnetic energy storage at different operating temperatures

We carried out optimal design of a Bi-2223/Ag toroidal coil for a superconducting magnetic energy storage system. The objective was to minimize the total length of Bi-2223/Ag tape at fixed conditions of operating temperature, stored energy and upper limit of the loss. The energy loss was calculated by means of the 3D finite element method (FEM) with the use of J-E expressions, which can quantitatively estimate the experimental data obtained from the tape in wide ranges of temperature (20-77 K), external magnetic field (0.02-3 T) and its applied direction (arbitrary). On the other hand, the optimal solution was obtained by a genetic algorithm (GA), which was a particularly effective optimization method when the objective function had a number of local minimum points. We performed such optimal design under various constraint conditions, and found that the optimal configuration of the coil drastically changed as its operating temperature varied.