Speaker
Description
A degradation of the RF performance at high fields has been historically observed in SRF thin film coated cavities. It is known that the presence of defects in the superconducting thin film causes a local increase of the surface resistance, which is correlated to power being dissipated in the surroundings of the defect. This leads to the observed Q drop which becomes more important when testing at high fields. Thus, it is imperative to avoid defects in order to mitigate this phenomena. Efforts have been made not only to improve the deposition techniques, but also to produce high quality substrates, as defects are propagated to the thin film deposited on top. To this end, seamless copper substrates have been produced by two different methods: chemical electroplating and machining of a bulk Cu billet. Two 1.3 GHz cavities have been manufactured, each one with the aforementioned methods, followed by a Nb film deposition via HiPIMS technique. In this work we will present the preliminary results of the RF performance of those cavities, which have been measured down to 1.85 K using a mobile coupler to ensure a good matching between the input coupler and the cavity, hence reducing the measurement uncertainty.
