Niobium on Copper (Nb/Cu) is being considered as the current technology of choice for the realization of superconducting radio frequency (SRF) accelerating cavities for the future circular collider (FCC). It provides, in fact, a significant reduction of the costs involved . This conclusion assumes the feasibility of niobium coated copper cavities with RF performances at T=4.5 K and 400 MHz, such that the cryogenic power consumption is comparable to the bulk Nb technology at 800 MHz and T=2 K. The cryogenic power consumption depends on the surface resistance Rs of the superconducting material employed, and thence on the ability of making high quality Nb coatings.
Alternative superconducting materials can enable the possibility to further reduce the power consumption significantly. In this respect, materials in the A15 family, like Nb3Sn, are among the most promising.
In this work, we have investigated the RF performances of both Nb and Nb3Sn films coated on a copper substrate, employing a quadrupole resonator cavity (QPR). The QPR allows for the measurement of the Rs of small samples at different temperatures, frequencies and RF field values . The main results will be presented in comparison with those from a Nb bulk sample, measured with the same technique.
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