A method for measuring interface roughening

Document Type

Conference Proceeding

Publication Title

AIP Conference Proceedings


A common problem with manufacture of composite Nb3Sn superconductor wire which contains a tantalum diffusion barrier is an increasing roughness of the interface between the Cu and Ta regions as the wire is drawn down. As the Ta layer thins, the scale of this interface roughening can become large relative to the Ta layer thickness. When this happens, the chance of layer fracture increases. Breaches in the Ta layer lead to Cu contamination by diffusing Sn and a dramatic decrease in the local residual resistance ratio (RRR) of the Cu stabilizer material adjacent to the Ta layer. This occurrence limits the maximum continuous length of wire that can be made, increases wire manufacturing costs, and leads to lower efficiency magnets wound from shorter lengths of wire which requires a larger number of resistive joints. The authors have developed a method for measuring the surface roughness of the Ta diffusion barrier in Nb3Sn superconducting wires. The method has been applied to find the Ta interface roughness in test monofilament Cu-Ta conductors as well as commercially manufactured superconductors. Interpretation of the data and application of the technique to various scenarios is presented. © 2008 American Institute of Physics.

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