Patent ID: 8513527

Claim:
A superconducting circuit comprising a superconducting joint that joints a niobium titanium superconducting wire having a structure where a filament made of niobium titanium alloy is arranged in a matrix made of copper or copper alloy and other superconducting wire, wherein, in operation, a magnetic field intensity where the superconducting joint is placed is smaller than the magnetic field intensity where a main coil of the niobium titanium superconducting wire in a portion other than the superconducting joint is placed, wherein a volume ratio or a surface density of an α-Ti precipitation in the niobium titanium alloy of the filament in the superconducting joint is smaller than the volume ratio or the surface density of the α-Ti precipitation in the niobium titanium alloy of the filament in the niobium titanium superconducting wire in the portion other than the superconducting joint, and wherein a critical current density of the filament in the superconducting joint is 5% to 80% of a critical current density of the filament in the niobium titanium superconducting wire in the portion other than the superconducting joint in a case where the critical current densities are measured in the same magnetic field intensity.