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arXiv · 1503.03410

Analysis of Nb3Sn surface layers for superconducting RF cavity applications

Chaoyue Becker·Samuel Posen·Nickolas Groll·Russell Cook·Christian M. Schlepuetz·Daniel Leslie Hall·Matthias Liepe·Michael Pellin·John Zasadzsinski·Thomas Proslier
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Abstract

We present an analysis of the Nb3Sn surface layers grown on a bulk niobium (Nb) coupon prepared at the same time and by the same vapor diffusion process used to make Nb3Sn coatings on 1.3 GHz cavities. Tunneling spectroscopy reveals a well-developed, homogeneous superconducting density of states at the surface with a gap value distribution centered around 2.7 meV and superconducting critical temperature (Tc) up to 16.3 K. Scanning Electron microscopy (STEM) performed on cross section of the sample's surface region shows a 2 microns thick Nb3Sn surface layer. The elemental composition map exhibits a Nb over Sn ratio of 3 and reveals the presence of buried sub-stoichiometric regions that have a ratio f 5. Synchrotron x-ray diffraction experiments indicate a polycrystalline Nb3Sn film and confirm the presence of Nb rich regions that occupy about a third of the coating volume. These low Tc regions could play an important role in the dissipation mechanism occurring during RF tests of Nb3Sn-coated cavities and open the way for further improving a very promising alternative to pure Nb cavities for particle accelerators.

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Chaoyue Becker, Samuel Posen, Nickolas Groll, Russell Cook, Christian M. Schlepuetz, Daniel Leslie Hall, Matthias Liepe, Michael Pellin, John Zasadzsinski, Thomas Proslier. 2015-03-11. Analysis of Nb3Sn surface layers for superconducting RF cavity applications. https://doi.org/10.1063/1.4913617

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