We report the first successful production of a Cu-based Nb3Sn sample specifically designed for Quadrupole Resonator (QPR) testing, representing a significant step toward scalable RF superconducting coatings of Nb3Sn on copper substrates. The sample was fabricated using an optimized electrochemical thermal synthesis (ETS) via the bronze route, incorporating several key advancements: electropolishing of the Cu substrate, electroplating of the bronze precursor layer, a tailored heat treatment at approximately 700 ∘C to promote grain growth and suppress tin-rich impurity phases, and a newly developed chemical etching procedure for effective removal of surface bronze residues and contaminants. These improvements address longstanding challenges in the fabrication of high-quality Cu-based Nb3Sn thin films. Subsequent QPR measurements yielded the peak magnetic field and temperature dependent surface resistance Rs, as well as the superconducting transition temperature and quench field. Although the achieved RF performance -- characterized by a minimum Rs of 43.4 nΩ at 4.5 K and 15 mT -- is not yet optimal, the results clearly demonstrate the feasibility of this approach and its potential for further enhancement through process refinement.
@article{arxiv.2509.11224,
title = {Preparation of the First Cu-based Nb$_3$Sn Sample via Bronze Route for Quadrupole Resonator Testing},
author = {Ming Lu and Sebastian Keckert and Felix Kramer and Alena Prudnikava and Jens Knobloch and Aleksandr Zubtsovskii and Oliver Kugeler},
journal= {arXiv preprint arXiv:2509.11224},
year = {2026}
}