The high critical temperature (~18K for Nb3Sn) and very low Bardeen-Cooper-Schrieffer (BCS) surface resistance of A15 intermetallics makes them a promising category of materials alternative to niobium to be used in Superconducting Radio Frequency (SRF) cavities. Despite these benefits, the excessive brittleness of this group of materials means that they cannot be used as the bulk material in cavity manufacturing. They could thus be encouraging candidates for superconductor coated copper cavity technology. This thin film based approach could offer desired characteristics together with significant cost reduction compared to the standard niobium cavities, by replacing expensive superconducting substrates with copper ones and improving cryogenic efficiency by increasing the operational temperature of the cavity to 4.2K.
In this study, magnetron sputtering was used to synthesise Nb3Sn thin films onto a copper substrate, designed to closely mimic a cavity coating. Investigations into the deposition and annealing response of films manufactured using different coating pressures and sputtering gases have been performed using a broad range of techniques. These include X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) analysis, Energy Dispersive X-ray Spectroscopy (EDS), Focused Ion Beam (FIB) cross-sectional milling and Superconducting QUantum Interference Device (SQUID) magnetometer testing. A maximum critical temperature of 16.5K has been obtained up to now by refining the process parameters. The challenges inherent to the use of copper as a substrate and proposals to tackle them down will be exposed.