Development of high performance multifilamentary Nb-Ti-Ta superconductor for LHC insertion quadrupoles

Abstract

-A preliminary investigation of a new Nb-Ti-Ta (39wt%Nb, 44wt.%Ti, 17wt.%Ta) alloy has been investigated as a possible material for application at 1.9 K and 10.5 T in the insertion quadrupoles of LHC. 1550 A/mm*, the highest yet reported critical current density at 10.5 T (1.9 K), was achieved in a monofilament of this material. The initial multifilamentary production strand produced a lower 10.5 T (1.9 K) critical current density of 1370 A/mmz. Large variations in precipitate size were produced in the microstructures, which have yet to be fully optimized. Quantitative analysis of the microstructures in a Nb-44 wt.%Ti-15 wt.%Ta alloy reveals a linear relationship between volume % of a-Ti precipitate and critical current density at 5 T and 8 T (4.2 K). The increase in critical current with precipitate volume is less than for Nb-47 wt.%Ti. High resolution FESEM electron backscatter images suggest a high atomic number region adjacent to the grain boundaries after heat treatment.

Analysis Method of High-Field Pinning Centers in NbTi Wires and MgB2 Wires

“…This is very important because it allows us to understand why the critical current density is low near B irr . The magnetic and non-magnetic particles decrease J c in NbTi wires in high magnetic fields [57][58][59][60].…”

Prospects for MgB2superconductors for magnet application

“…NbTi has T C ∼ 9 K, H C2 (4.2 K) ∼ 10-12 T [12,13] and very high J C of more than 3 × 10 5 A cm −2 at 5 T, 4.2 K and ∼1.5 × 10 5 A cm −2 at 8 T [14]. Doping improves the J C significantly and for the Fe added NbTi samples the J C is ∼1.45 × 10 5 A cm −2 and for NbTiTa ternary alloy the J C is nearly 1.37 × 10 5 A cm −2 ; these two values are at 1.9 K and 10.5 T [15,16]. NbTi cannot be used for fields above 9 T. Though it has high strength, ductility, critical current density, and relatively low cost, the thermal stability of NbTi is less, due to the low T C .…”