Speaker
Description
Superconducting radio frequency (SRF) cavities based on Nb$_3$Sn superconductor can exceed the performance of conventional Niobium SRF cavities and would open many new industrial applications for small scale accelerators. The material quality-especially the surface non-homogeneity and microstructural defects, is the crucial challenge to realize the full potential of Nb$_3$Sn SRF cavities. In this work, we present our recently developed route for effectively reducing the intrinsic defects in magnetron sputter coated Nb$_3$Sn SRF cavities and eventually improve the overall RF performance.
In our study, we introduced a small variable fraction of Zr in Nb$_3$Sn host matrix using co-sputtering process. Post-annealing, the elemental Zr forms ZrO$_2$ precipitates of average dimensions ranging from 20-100 nm. We noted that the density of the surface and bulk voids as well as their average sizes are dramatically reduced on increasing the Zr content in Nb3Sn. We also observed that increasing Zr concentration up to an optimal level can substantially improve both superconducting transition temperature and upper critical magnetic field. Additionally, increasing the Zr concentration is also noticed to prevent the oxygen diffusion and resulting to a thinner formation of primary surface oxides. These results indicate that inclusion of Zr in Nb$_3$Sn sputtered coating will be a promising method to improve the material quality and might help to reduce the overall RF power dissipation.
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