Development of superconducting conductors for Large Helical Device

The superconducting helical coils of the Large Helical Device (LHD) require superconducting conductors with large current capacities (from 20 kA to 30 kA) and high current densities (55 A/mm² at 8 T). An NbTi superconductor/bin with pool boiling is being used because of the large electromagnetic force and the complicated helical windings. Several conductors are designed to show how the difference of the position of pure aluminum in the conductors affects the stability and the mechanical properties. Scaled-down R&D conductors with operational currents from 7 kA to 10 kA were made on an experimental basis. The superconducting characteristics, stability, and mechanical properties of these scaled-down conductors were tested. The design and the test results concerning the superconducting characteristics are described