Superconducting thin films, e.g., Nb₃Sn, are the next-generation materials for RF accelerator cavities. However, the large surface roughness and non-stoichiometry of Nb₃Sn are two critical issues that limit their RF performance. Here, we achieved smooth, homogenous Nb₃Sn through our novel electrochemical recipes. The resultant surface roughness is five time smaller than the values from conventional vapor diffusion. Quantitative mapping using chemical and atomic probes confirm the uniform stoichiometry, i.e., the Nb/Sn ratio, of our electrochemical Nb₃Sn. The new process and the resultant Nb₃Sn film has been applied to a large-scale (0.2 m² surface area) 1.3 GHz SRF cavity, yielding outstanding RF performance, e.g., ultra-low BCS resistance.

This work is part of CBB’s efforts on developing advanced methods and materials for game-changing SRF cavities so as to achieve the ultimate goal of high efficiency and high fields for beam acceleration.

Reference:

Z. Sun, G. Gaitan, M. Ge, K. Howard, M. U. Liepe, R. D. Porter, T. Oseroff, T. A. Arias, Z. Baraissov, M. Kelley, D. A. Muller, J. Sethna, N. Sitamaran, and K. D. Dobson, “Toward Stoichiometric and Low-Surface-Roughness Nb₃Sn Thin Films via Direct Electrochemical Deposition,” in Proc. SRF ’21, Lansing, MI, Jun. 2021, doi:10.18429/JACoW-SRF2021-WEOTEV03 [Online]. Available: https://srf2021.vrws.de/papers/weotev03.pdf