Flux Pinning in Bronze-Processed Nb3Sn Wires
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 Jc 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 Jc 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 Jc 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.
KeywordsHigh Magnetic Field Magnetic Field Dependence Flux Pinning Flux Line Lattice Nb3Sn Layer
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