Low AC loss Nb3Sn tape for transmission line applications

A process for modifying the surface topography of Nb3Sn tapes so as to achieve low ac losses has been further developed by experimental operation at pilot plant scale. Diffusion process Nb3Sn tapes are treated by etching followed by hot dip coating with tin. Problems involved in control of the etch process and the Nb3Sn input have been studied for the purpose of optimizing the product superconductor with respect to minimum losses in combination with high values of critical current. Performance capability has been demonstrated by processing a group of four tapes totaling about 3,000 feet. The average ac loss for the group, as determined from measurements at each end of each tape, is at the target specification: 10 μW/cm²(500 rms A/cm, 60 Hz, 4.2 K, unclad). The target specification for critical current was also met.