Speaker
Description
Nb₃Sn (Tc ≈ 18.3 K, μ₀H_sh ≈ 400 mT) is a leading candidate for next-generation SRF cavities, and its deposition on copper offers further gains in cost and cryogenic heat load. Uniform coating and reliable adhesion on the curved inner surface of a closed cavity, however, remain a key challenge for magnetron sputtering.
A 6 GHz oxygen-free copper cavity was therefore fabricated as two half-cells split along the cavity axis, providing line-of-sight access for uniform coating and in-situ sample co-deposition. Nb₃Sn films were grown by co-sputtering from independent Nb and Sn targets, with stoichiometry tuned via the relative target power. Curved witness coupons attached to the half-cell inner surface were coated simultaneously for compositional, structural, and superconducting characterization. Under optimized conditions the films reproducibly reached Tc = 16.2 K with a narrow transition, and repeated liquid-nitrogen thermal cycling produced no peeling, delamination, or cracking.
The coated half-cells were then assembled into a complete resonator with indium-wire seals, including the stainless-steel vacuum flanges. The cavity maintained stable vacuum with no detectable leakage through multiple cool-down cycles, and the Nb₃Sn coating remained intact. These results demonstrate the feasibility of a demountable Cu cavity + Nb/Sn co-sputtering + indium-sealed assembly route at 6 GHz, and lay the groundwork for Q₀–Eacc measurements and scaling to lower-frequency cavities.
Funding Agency
The Institute of High Energy Physics of the Chinese Academy of Sciences
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