Development and Performance of the First Nb₃Sn Thin Film Cavity via Bronze Process

Abstract Low-temperature synthesis of Nb$_3$Sn thin film on a cavity is of great significance for the industrialization of superconducting RF cavities.The bronze process can grow phase-pure Nb$_3$Sn at 700 $^\circ$C, making it very promising to synthesize a Nb$_3$Sn thin-film cavity at low temperature. In this work, we have successfully fabricated the world's first Nb$_3$Sn thin-film cavity via the bronze process. We solved the technical problems for the precursor preparation, and characterized the uniformity of the Nb$_3$Sn film by testing the performance of samples distributed in the cavity. During the vertical test, a $Q_0$ value of 1.2$\times10^{9}$ was obtained at 4.2 K, higher than that of a bulk niobium cavity under the same conditions. This result means that the preparation of Nb$_3$Sn via the bronze process can potentially lead to copper-based Nb$_3$Sn thin-film cavities, which can substantially improve the SRF cavity performance and promote its practical applications.