Preservation of the High Quality Factor and Accelerating Gradient of Nb3Sn-coated Cavity During Pair Assembly

TL;DR

This paper reports on the successful preservation of high quality factor and accelerating gradient in Nb3Sn-coated cavities during pair assembly, demonstrating improved superconducting performance post-assembly.

Contribution

It presents new methods to mitigate degradation of Nb3Sn cavities during pair assembly, achieving high gradients after assembly.

Findings

One cavity reached over 80 mT gradient after assembly.

Vertical tests showed preserved superconducting properties.

Assembly challenges were effectively mitigated.

Abstract

Two CEBAF 5-cell accelerator cavities have been coated with Nb3Sn film using the vapor diffusion technique. One cavity was coated in the Jefferson Lab Nb3Sn cavity coating system, and the other in the Fermilab Nb3Sn coating system. Both cavities were measured at 4 K and 2 K in the vertical dewar test in each lab and then assembled into a cavity pair at Jefferson Lab. Previous attempts to assemble Nb3Sn cavities into a cavity pair degraded the superconducting properties of Nb3Sn-coated cavities. This contribution discusses the efforts to identify and mitigate the pair assembly challenges and will present the results of the vertical tests before and after pair assembly. Notably, one of the cavities reached the highest gradient above 80 mT in the vertical test after the pair assembly.