Abstract
Electromagnetic properties of powder-metallurgy processed superconducting Nb3Sn wires are usually similar to those of single core wires due to strong coupling among filaments. In this study, it has been demonstrated that the effective filament diameter of the powder-metallurgy processed wire can be decreased by twisting and the wire can be practically used for magnets.
Firstly, Cu-22.5wt% Nb powder-metallurgy processed Nb3Sn wires with a diameter of 0.25mm were fabricated in a semi-industrial scale, and electromagnetic properties were measured. With theoretical consideration about twist effect and magnetic instability based on the experimental results, a magnet with an inner diameter of 34mm, an outer diameter of 147mm and a length of 160mm was designed and wound by a 21-strand cable, of which the effective filament diameter was decreased to 53μm by twisting with the pitch of 11mm. In a d.c. operation, the magnet generated a field of 4.1T at the current of 450A, though this value corresponded to only 60 percent of the critical current of a short sample, which might resulted from the ununiformity of critical current in the wires. The magnet could be operated to the current of this value also in a pulse mode at the maximum sweep rate of 7.8T/sec. Therefore, the wire fabricated in this way was confirmed enough stable.
