Evaluations of MgB$_{\mathrm{2}}$ Coatings on 2'' Copper Discs for Superconducting Radio Frequency Applications.

We propose that coating the inner walls of copper RF cavities with superconducting MgB$_{\mathrm{2}}$ ($T_{c} \quad =$ 39 K) can result in a viable alternative to the already established niobium-based SRF technology. This approach improves the thermal conductivity, allows for operation at higher temperatures, and reduces the need for large helium refrigeration, thereby resulting in lower operational costs. For our studies, we grew MgB$_{\mathrm{2}}$ films via hybrid physical chemical vapor deposition (HPCVD) on 2'' Cu substrates. Since Mg and Cu readily form an alloy at higher temperatures, the HPCVD setup was modified in order to achieve lower deposition temperatures, minimize alloy formation, and provide high quality MgB$_{\mathrm{2}}$ films. This method yielded MgB$_{\mathrm{2}}$ coatings on 2'' Cu discs with transition temperatures around 38 K. The samples were characterized with regards to their RF attributes and showed similar performance in comparison to Nb reference samples. The presented results show that MgB$_{\mathrm{2}}$ coated copper can be a suitable alternative for use in SRF cavities.