Advances in Nb3Sn superconducting radiofrequency cavities towards first practical accelerator applications

TL;DR

This paper reports significant advancements in Nb3Sn superconducting RF cavities, achieving higher accelerating fields up to 24 MV/m and demonstrating a full-scale 9-cell cavity, highlighting its potential for practical accelerator applications.

Contribution

It presents the first high-field Nb3Sn cavities reaching 24 MV/m and the first 9-cell Nb3Sn-coated cavity, advancing towards practical accelerator use.

Findings

Achieved accelerating fields up to 24 MV/m in single-cell cavities.

Demonstrated a full-scale 9-cell Nb3Sn-coated cavity.

Showed potential for cryocooler-based industrial accelerator applications.

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 cw accelerating fields <18 MV/m. In this paper, new results are presented with significantly higher fields, as high as 24 MV/m 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.