Development of high-field a.c. superconducting magnet using ultrafine multifilamentary Nb-Ti superconducting wire with designed Nb artificial pins

A 2.5 T/100kVA a.c. superconducting magnet has been developed using Nb-Ti superconducting wire with artificially introduced pins. Investigations have been conducted regarding the suitability of critical current density J_c design using artificial pins and the effectiveness of magnets using wires with high J_c. Studies on pin design suggested that the maximum pinning force density F_p would be reached at a magnetic field of 2.5 T. As anticipated, the maximum F_p was achieved at 2.5T, and a high J_c of 4.7 × 10⁹ A m^-2 was obtained. Using an a.c. magnet fabricated from this wire, current operation at 60 Hz and 4.2 K was effected, and steady state operation at a capacity of 104.8 kVA, a current of 105.8 A_rms and a voltage of 991.2 V_rms was achieved. At the same time, a central magnetic field of 2.5 T was obtained. In addition, it was demonstrated that the total a.c. losses were 4.8 W at a central magnetic field amplitude B₀ of 2 T, a mere 0.007% with respect to the capacity of 69 kVA and much lower than in a.c. magnets of the 100 kVA class made using conventional a.c. wires. This confirmed the effectiveness of reducing magnet size through the use of wires having high current density.