Abstract
Nb3Sn is a promising next-generation material for superconducting radiofrequency cavities, with significant potential for both large scale and compact accelerator applications. However, so far, Nb3Sn cavities have been limited to continuous wave accelerating fields <18 MV m−1. In this paper, new results are presented with significantly higher fields, as high as 24 MV m−1 in single cell cavities. Results are also presented from the first ever Nb3Sn-coated 1.3 GHz 9-cell cavity, a full-scale demonstration on the cavity type used in production for the European XFEL and LCLS-II. Results are presented together with heat dissipation curves to emphasize the potential for industrial accelerator applications using cryocooler-based cooling systems. The cavities studied have an atypical shiny visual appearance, and microscopy studies of witness samples reveal significantly reduced surface roughness and smaller film thickness compared to typical Nb3Sn films for superconducting cavities. Possible mechanisms for increased maximum field are discussed as well as implications for physics of RF superconductivity in the low coherence length regime. Outlook for continued development is presented.
Highlights
Superconducting radiofrequency (SRF) cavities are widely used for particle beam acceleration because of their ability to generate large amplitude accelerating electric fields (Eacc) with small heat dissipation (Pd)
There are a number of methods to create Nb3Sn, but so far, the method that has been most successful in terms of cavity performance is vapor diffusion [4], [11], [12], which takes advantage of the phase diagram at high temperatures to “phase-lock” to the desired e.g. a large cryogenic plant has a coefficient of performance approximately 3-4 times better at 4.4 K vs 2 K
If thermal runaway were the key limitation in this test, one might expect that the heating pre-quench would have been higher or that the higher temperature observed by the T-map after quench would have resulted in a significantly lower maximum field
Summary
Superconducting radiofrequency (SRF) cavities are widely used for particle beam acceleration because of their ability to generate large amplitude accelerating electric fields (Eacc) with small heat dissipation (Pd). There are a number of methods to create Nb3Sn, but so far, the method that has been most successful in terms of cavity performance is vapor diffusion [4], [11], [12], which takes advantage of the phase diagram at high temperatures to “phase-lock” to the desired e.g. a large cryogenic plant has a coefficient of performance approximately 3-4 times better at 4.4 K vs 2 K This manuscript has been authored by Fermi Research Alliance, LLC under Contract No DE-AC02-07CH11359 with the U.S D1epartment of Energy, Office of Science, Office of High Energy Physics. We show measurements of several types of SRF cavities with smooth, thin films, showing significantly improved performance compared to the previous state-of-the-art
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