Flux Pinning in Bronze-Processed Nb₃Sn Wires

Abstract

With the increasing importance of multifilamentary Nb₃Sn conductors for technological uses such as for the production of very high magnetic fields in fusion magnets, means of improving the superconducting critical current density J_c at very high magnetic fields (H > 10 tesla) have been sought intensively, and it has been found that metallurgical factors such as heat treatment conditions,¹ alloying additions,² and mechanical strains³ can strongly influence the critical current density. The correlation of changes in J_c with such metallurgical variations in the Nb₃Sn wires has been facilitated by the use of scaling laws for magnetic flux pinning in hard süperconductors, and the scaling law developed by Kramer⁴ has been used frequently.⁵ We have found in the course of our investigations of the properties of monofilamentary Nb₃Sn wires produced by the “bronze process” that the magnetic field dependence of J_c at high fields can qualitatively be characterized well by Kramer’s scaling law. However, when a detailed comparison of the scaling law and available experimental results was made, we found serious inconsistencies in the values of the parameters which appear in the scaling equation.

Work performed under the auspices of the U.S. Department of Energy.