Development of variable field-direction superconducting magnet

Magnetic field direction often has a great influence on material properties, such as critical current densities of tape-shaped superconductors. To determine the influence, an object is usually rotated in a fixed magnetic field. This method, however, is not always effective. We are developing a superconducting magnet that can change its field direction continuously in a two-dimensional plane. Two sets of split-pair coils are placed perpendicularly to each other, and the perpendicular magnetic fields generated by each split-pair coil are superimposed. By independently controlling the operating current of each split-pair coil, the direction of the superimposed magnetic field can be changed continuously. The coils are wound with Ni-Ti conductors. The variable field-direction magnet is designed to rotate a field of 1 T. The field homogeneity is estimated to be less than 1% in a 10-mm diameter sphere volume. This is a conduction-cooled superconducting magnet with 4K-GM refrigerators. Predictions derived by numerical calculations show that the electromagnetic forces among coils are quite large.