Speaker
Description
Due to the higher superconducting critical temperature (Tc ~18.3 K) and superheating field (Hsh ~400 mT) compared to Nb (Tc ~9.25 K, Hsh ~200 mT), Nb3Sn is a promising material as a surface coating on Nb superconductive radio frequency (SRF) cavities. Nb3Sn coated Nb cavities can deliver a higher quality factor and acceleration gradient when operated at 4 K replacing the bulk Nb SRF cavity operated at 2 K, hence reducing the operation cost significantly. A cylindrical magnetron sputtering system was commissioned at Old Dominion University and used to coat Nb3Sn into a 2.6 GHz Nb SRF cavity. Using two identical cylindrical magnetrons, Nb3Sn was fabricated on Nb substrates mounted on the equivalent positions of the beam tubes and the equator of the SRF cavity. Microanalysis of the films confirms the growth of single phase Nb3Sn. The Nb3Sn films from all three positions showed good superconducting properties (Tc = 17.61-17.76 K and Δ Tc = 0.06-0.1 K). We then coated ~1.2 μm Nb3Sn inside of the 2.6 GHz Nb SRF cavity. We will discuss the design and commissioning of the cylindrical magnetron sputtering system, first results from Nb3Sn fabrication on Nb flat substrates, and the Nb cavity coating by ~1.2 μm Nb3Sn and results on cavity testing.
