Increased critical current density in Nb–Ti wires having Nb artificial pinning centers

Abstract

Artificial pinning center (APC) wires containing Nb 47 wt.% Ti with 24 vol.% of round Nb pins have produced very high critical current densities (Jc) which are attributed to a sharply defined, nanometer-scale Nb-pin array. By reducing both the number of warm extrusion steps from four to three and the temperature of the third extrusion from 650 °C to 250 °C, the degree of pin-matrix interdiffusion has been reduced and Jc values at all applied magnetic fields increased by 25–45% over those for a previous composite of almost identical design. The best wire achieved the very high Jc(5 T, 4.2 K) value of 4600 A/mm2. These results underscore the importance of the thermomechanical treatment in determining the maximum flux pinning properties of APC Nb–Ti wires.