Measuring method of critical current for NbTi superconductors with Cu and CuNi matrices

Quench characteristics of NbTi superconducting wires with Cu and CuNi matrices have been experimentally studied to standardize a measuring method of critical current (Ic) for the wires. In the previous work, the superconducting wires frequently quenched caused by abrupt wire motions before reaching their Ic. Hence, we tried to measure Ic under various fixing conditions of the wires (1, 5, and 10 N of winding tensions to the wires, dry windings and impregnation by two types of grease (silicone and Apiezon(R)), non-metallic and metallic sample mandrels). The experimental results showed that 10 N of the winding tension was best in the three tensions, and Apiezon grease impregnation was effective. However, the wire currents in the above conditions did not reach their Ic at low magnetic fields. When the wires were fixed by solder on the metallic mandrels, the wire currents always reached their Ic with no premature quenches due to the wire motions. We obtained a prospect to standardize the measuring method of Ic for the three-component superconducting wires.