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The required combination of performance properties for internal tin Nb3Sn wires for high energy physics includes high critical current density (J c) and RRR values as well as low magnetization and effective diameters (Deff ) value. It is quite a challenge to achieve them all at once. A comprehensive study has been carried out on two internal tin Nb3Sn wires with essentially different layouts and 37 sub-elements each. The first type of wires has distributed diffusion barriers. The second one has common diffusion barrier with sub-elements internally divided by resistive separators. Two sets of data for two types of wires have been obtained, which include transport measurements of J c(B), magnetization loops M(B), superconducting transition temperature (Tc), RRR values, Sn-concentration by EDAX measurements and XRD analysis. XRD analysis of the superconducting layers has shown that the compressive macrostress is larger for the wire with overall barrier than for the wire with distributed diffusion barriers. This observation correlates with a shift of the stress-dependent curves of the superconducting transition. The difference in the volume fractions and the homogeneities of the Nb3Sn phase leads to a significant difference of the J c(B) dependences and the values of the Kramer critical field (BKr) for these types of wires. In summary, the high critical current density for the first type of wires and the low hysteresis losses for the second type of wires have achieved with high RRR values in both cases.

The 3-Tesla superconducting magnetic system (SMS) project for the magnetic refrigerator machine is proposed. The second-generation high-temperature superconducting tapes for SMS are developed, fabricated and tested in NRC "Kurchatov Institute". The magnet consists of 12 non-insulated double pancake coils. The SMS is installed in the vacuum chamber and cooled by a cryo refrigerator.