Caption: A (top) Dark field scanning TEM image of a Nb₃Sn layer grown on Nb using standard vapor diffusion. This growth method results in a rough Nb₃Sn surface atomic Sn concentration map (bottom) determined using Energy Dispersive X-ray Spectrometry (EDX) and showing Sn deficient grains and Nb inclusions. B (top) Nb₃Sn layer grown on Nb using the new electrodeposition method. This growth method results in smooth Nb₃Sn surface (bottom) and uniformly rich Sn deposition on the surface. While the Sn composition decreases near the Nb₃Sn/Nb interface, there are no Nb inclusions or voids.

Nb₃Sn is a next generation material for superconducting accelerating cavities. Unlike traditional niobium cavities, Nb₃Sn cavities can operate at higher temperatures, eliminating the need for expensive and complex cryogenic refrigeration systems.  As a result, Nb₃Sn opens the door to far wider application of high-power beams.In prior efforts to coat superconducting accelerating cavities with Nb₃Sn, the Nb₃Sn layer exhibited two structures with different critical temperatures.  One of these had a high critical temperature (T_c), consistent with expectations for ideal Nb₃Sn, while the other had a lower T_c with degraded performance.  Working together, CBB grad students Nathan Sitaraman, Zhaslan Barraisov and Ryan Porter combined their ab initio calculations, microscopic sample characterization, and growth expertise to diagnose the problem and modify the Nb₃Sn growth procedures, resulting in better uniformity and a 50% reduction in intrinsic energy losses.  

CBB is sharing its procedures with scientists at JLAB and Fermilab, who are now assembling the first full-scale Nb₃Sn accelerating cavities.  Future Nb₃Sn cavities could increase the performance of high energy accelerators and enable new environmental applications such as the purification of city wastewater in order to eliminate parasites, pharmaceuticals and other persistent contaminants.

References:

Workshop on Energy and Environmental Applications of Accelerators, S. Posen, M. Liepe, G. Eremeev, U. Pudasaini, C.E.Reece, "Nb₃Sn Superconducting Radiofrequency Cavities: a Maturing Technology forParticle Accelerators and Detectors",  [Online] Available: https://arxiv.org/pdf/2203.06752.pdf 

R. D. Porter, N. Banerjee, and M. U. Liepe, “Dynamic Temperature Mapping of Nb3Sn Cavities,” in Proc. SRF ’21, Lansing, MI, Jun. 2021, doi: 10.18429/JACoW-SRF2021-SUPCAV003 [Online]. Available: https://srf2021.vrws.de/papers/supcav003.pdf 

Z. Sun, M. U. Liepe, T. Oseroff, R. D. Porter, T. A. Arias, Z. Baraissov, D. A. Muller, N. Sitaraman, D. Johnson-McDaniel, M. Salim, and C. Dukes, “Surface Oxides on Nb and Nb3Sn Surfaces: Toward a Deeper Understanding,” in Proc. SRF ’21, Lansing, MI, Jun. 2021, doi: 10.18429/JACoW-SRF2021-THPTEV004 [Online]. Available: https://srf2021.vrws.de/papers/thptev004.pdf

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