Advances in Nb₃Sn superconducting radiofrequency cavities towards first practical 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 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.

Key directions for research and development of superconducting radio frequency cavities

“…Extrapolation from high power pulsed RF experiments is in agreement with this prediction [36]. In CW regime, Nb 3 Sn deposited on bulk niobium cavities show promising results [37], reaching high Q ∼ 10 10 even at temperatures ∼ 4 K. So far, R&D cavities demonstrated accelerating gradients up to 24 MV/m in single-cell cavities and 15 MV/m in 9-cell TESLA-shape cavities [38]. Such gradients might already be useful for small-scale accelerators.…”

Detecting High-Frequency Gravitational Waves with Microwave Cavities

“…Indeed, this sort of strategy is being pursued by ADMX for their small "sidecar" cavities [122]. A similar approach could be implemented in multi-cell cavities of the type typically used for RF acceleration [124].…”

Next-Generation Superconducting RF Technology based on Advanced Thin Film Technologies and Innovative Materials for Accelerator Enhanced Performance and Energy Reach

“…The most widely developed technique to form the A15 Nb 3 Sn phase on Nb is Sn vapor diffusion in bulk Nb, initially developed by Siemens in the 90s and rekindled in 2010s by Cornell, Fermi Lab and Jefferson Lab. Improvements in understanding the materials science and refinement of the coating process have led to resolving the precipitous Q-slope, increasing the maximum attainable accelerating gradient by a factor of 5 with Q 0 > 10 10 at 4.2 K [39][40][41][42]. However, Nb 3 Sn cavity performance has yet to reach its full potential.…”