We have investigated the coating of an inner surface of superconducting radio frequency cavities with a magnesium diboride thin film by hybrid physical-chemical vapor deposition (HPCVD). To simulate a 6 GHz rf cavity, a straight stainless steel tube of 1.5-inch inner diameter and a dummy stainless steel cavity were employed, on which small sapphire and metal substrates were mounted at different locations. The ${\mathrm{MgB}}_2$ films on these substrates showed uniformly good superconducting properties including $T_c$ of 37–40 K, residual resistivity ratio of up to 14, and root-mean-square roughness $R_q$ of 20–30 nm. This work demonstrates the feasibility of coating the interior of cylindrical and curved objects with ${\mathrm{MgB}}_2$ by the HPCVD technique, an important step towards superconducting rf cavities with ${\mathrm{MgB}}_2$ coating.

• Received 31 October 2013

DOI:https://doi.org/10.1103/PhysRevSTAB.17.012001

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Published by the American Physical Society