Size and arrangement effect of Nb artificial pinning centers on flux pinning in Nb-Ti multifilamentary wires

Abstract

Flux pinning properties of niobium-titanium multifilamentary wires with artificial pinning centers (APC) were studied. Previous investigations on the effects of different APC materials (Nb, Nb-7.5 wt.% Ta, Ta) on the flux pinning properties found that Nb pins had larger pinning force in comparison with other material and improved critical current density drastically in magnetic fields up to 5 T. In this paper, to increase the flux pinning force, 1, 7, 19 and 37 Nb pins were introduced into Nb-46.5 wt.% Ti filaments, and the volume fraction of Nb pins was varied from 0 to 25%. The effect of the size and arrangement of the Nb pins on the flux pinning properties was investigated. Consequently, a peak of the bulk flux pinning force density (F/sub P/) as a function of magnetic field shifts to a higher field as the pin interval becomes smaller. This behavior becomes more pronounced with decreasing a pin size because the pin deforms into a ribbon-like configuration. Furthermore, we investigated the effect of heat treatment on flux pinning to study the effect of boundary conditions between pin and Nb-Ti matrix. We also discuss the scaling behavior of F/sub P/.