Critical Current and AC Loss of Coevaporated Nb₃Sn Superconductors

Abstract

Stanford University has a program devoted to gaining an understanding of the material parameters of type II superconductors that are important for the achievement of high critical currents and minimum ac losses in the low magnetic fields encountered in superconducting power transmission lines. To that end, electron beam deposited Nb₃Sn has been investigated. This method of fabrication is attractive because of the ease by which samples of differing grain size, thickness, and multiple components (layered samples) can be made. The present stage of this work has dealt mainly with tubular samples because this geometry is convenient for making induced critical current [^1,2] and electronic ac loss measurements as described in more detail in a companion paper[³]. However, this configuration somewhat complicates the sample preparation process, as deposition is done on a heated, rotating tube, rather than a flat substrate. This paper provides observations on the film growth morphologies encountered in this process and relates them to the measured superconducting properties.

Research supported by National Science Foundation-RANN and by the Electric Power Research Institute.