Artificial pinning centre Nb–Ti superconducting wire for AC applications

Abstract

The present work presents the steps for the manufacture of an Nb–Ti artificialpinning centre (APC) multifilament wire for AC applications. The wire productionstarts from a Ti bar inserted in a Nb tube. The superconductor Nb–Ti alloywas obtained using heat treatments during the wire production steps throughthe growth of the diffusion layer between the pure Nb and Ti regions. The finalwire is composed of many filaments dispersed in a Cu–Ni matrix. The transportcritical current density was measured in samples for different conditions of heattreatment, followed by wire diameter reduction. Magnetization hysteresis loops weremeasured to extract the hysteretic losses in wires with filament diameters of 76 and92 µm and compared to the results in commercial wires with comparable filamentdiameters. We obtained an Nb–Ti APC wire with hysteretic losses of the sameorder of magnitude as the commercial wires. However, critical current densitiesJc are higher for fields lower than 2 T, where AC applications are most important. TheJc results confirmed a previous result that the decrease of normal region sizes is a lessimportant pinning source in this material than the pinning from variations in thecomposition of the diffusion layer.