Microwave superconductivity of Nb3Sn
James Stimmell, Ph.D.
Cornell University 1978
Abstract
Nb3Sn superconducting resonant cavities were fabricated using two different techniques; the first consisting of ionplating thin Sn layers onto Nb substrates and then firing in vacuum at approximately 1000 C, and the second consisting of the vapor diffusion technique developed by Rinderer, Saur and Wurm. Measurements of the superconducting surface resistance and breakdown field at 8.6 GHz are reported, and the structure and composition of the Nb3Sn layers are analyzed using optical microscopy of anodized specimens and Secondary-Ion-Mass-Spectroscopy. Growth rates of vapor diffused samples are measured. Results indicate that surfaces produced by vapor diffusion have superior r.f. properties, yielding surface resistances of 1 microhm and breakdown fields of 380 gauss at 4.2 K. Results depend critically upon control of the Sn condensation rate. The correspondence between condensation rate, microstructure and r.f. performance is discussed.
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