Development and characterization of Nb3Sn/Al2O3 superconducting multilayers for particle accelerators

Chris Sundahl,Chang-Beom Eom,Lin Xie,Junki Makita,Lian Li,Yi-Feng Su,Alex Gurevich,Huimin Zhang,Paul B Welander,Fumitake Kametani

doi:10.1038/s41598-021-87119-9

Abstract

Superconducting radio-frequency (SRF) resonator cavities provide extremely high quality factors > 1010 at 1–2 GHz and 2 K in large linear accelerators of high-energy particles. The maximum accelerating field of SRF cavities is limited by penetration of vortices into the superconductor. Present state-of-the-art Nb cavities can withstand up to 50 MV/m accelerating gradients and magnetic fields of 200–240 mT which destroy the low-dissipative Meissner state. Achieving higher accelerating gradients requires superconductors with higher thermodynamic critical fields, of which Nb3Sn has emerged as a leading material for the next generation accelerators. To overcome the problem of low vortex penetration field in Nb3Sn, it has been proposed to coat Nb cavities with thin film Nb3Sn multilayers with dielectric interlayers. Here, we report the growth and multi-technique characterization of stoichiometric Nb3Sn/Al2O3 multilayers with good superconducting and RF properties. We developed an adsorption-controlled growth process by co-sputtering Nb and Sn at high temperatures with a high overpressure of Sn. The cross-sectional scanning electron transmission microscope images show no interdiffusion between Al2O3 and Nb3Sn. Low-field RF measurements suggest that our multilayers have quality factor comparable with cavity-grade Nb at 4.2 K. These results provide a materials platform for the development and optimization of high-performance SIS multilayers which could overcome the intrinsic limits of the Nb cavity technology.

Highlights

Superconducting radio-frequency (SRF) resonator cavities provide extremely high quality factors > 1 010 at 1–2 GHz and 2 K in large linear accelerators of high-energy particles
These experiments have shown an increase of the dc field onset of penetration of vortices on Nb surfaces coated with different SIS s tructures[4,11,12,13,14,15,16,17,18,19], such key SRF characteristics as the surface resistance and quality factors of SIS multilayers under high-amplitude RF fields have been investigated to a much lesser extent
We developed a technique of high-temperature confocal sputtering of Nb and Sn from elemental targets to grow stoichiometric N b3Sn multilayers with A l2O3 interlayers

Summary

Introduction

Superconducting radio-frequency (SRF) resonator cavities provide extremely high quality factors > 1 010 at 1–2 GHz and 2 K in large linear accelerators of high-energy particles. Technological advances have resulted in the development of Nb cavities which can exhibit extremely high quality factors Q > 1 010 @ 1–2 GHz and 2 K while sustaining accelerating gradients up to 50 MV/m1–3 Such exemplary performance and low RF losses can only be achieved if the cavities operate in a Meissner state which can persist up to the maximum magnetic field at the inner cavity surface reaches the superheating field Bs = 240 mT1–3. In this work we report results on growth and characterizations of N b3Sn/Al2O3 multilayers which exhibit good superconducting properties and low-field SRF performance on par with the cavity-grade Nb

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