Measurement station for the critical temperature of SC thin films on copper for SRF applications

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Figure 1: (a) Measurement system. (b) Complete experimental setup. (c) A typical measurement of the SC transition of bulk niobium. Figure 2: bulk Nb sample (left) and Cu substrate sample (right).

A consistent R&D program for the development of SC thin-film coated copper cavities is ongoing at CERN, which implies the synergy of the Vacuum, Surfaces and Coatings, Radio Frequency, Cryogenics and Mechanical and Materials Engineering groups. The measurement of the Tc is needed as first assessment of the film quality, and can turn out to be costly in terms of both time and financial resources. Hence the measurement station at the CryoLab has the role of providing a service with fast feedback in the initial part of the production process. The measurement station consists of a contactless two-coil system operated inside a large neck, liquid helium vessel cryostat. The required sample size is 11x35x1 mm^3. A complete description can be found in the conference proceedings of CERN Based Tc Measurement Station for Thin-Film Coated Copper Samples and Results on Related Studies (vrws.de)The stand also has the capability of measuring bulk samples films on different substrates than copper, provided that the sample size is compatible with the system and that the expected transition temperature lies between 4.2 K and 30 K.