The development of a 2.5 T/100 kV a AC superconducting magnet using a high-J_c NbTi superconducting wire having Nb artificial pins

High critical current densities, such as 1.61*10¹⁰ A m^-2 at 1 T, 6.10*10⁹ A m^-2 at 3 T and 2.89*10⁹ A m^-2 at 5 T were achieved by optimizing the artificial pin number, the pin size and the pin interval inside the NbTi filaments for ultrafine-multifilamentary NbTi superconducting wires having Nb island-type artificial pins. The obtained critical current densities above 0.5 T are two or three times higher than in most conventional NbTi superconducting wires for AC use, because the position of the peak value of pinning-force density could be shifted in the wide range of the magnetic field by controlling the designed artificial pin parameters. On the basis of these results, we designed and fabricated a high-J_c, AC superconducting wire having Nb island-type pins for the purpose of AC use under medium magnetic field above 2 T, and successfully completed an AC superconducting solenoid magnet. This magnet was the first magnet wound by NbTi multifilamentary wires with artificial pins, and could generate the peak value of 2.5 T at 60 Hz AC mode without quench, where the electrical capacity of the magnet corresponded to about 100 kV A.