First Prototypes of the Superconductive Reference Device SRD1000

In the framework of the European Project "Ultra-Low Temperature Dissemination (ULT)," a superconductive reference device (SRD1000) and dedicated external measurement electronics were developed to provide direct traceability to the new Provisional Low Temperature Scale (PLTS-2000). The SRD1000 includes 10 reference points in the temperature range 15 mK to 1 K: W (TC = 15 mK), Be (TC = 23 mK), Ir80Rh20 (TC ≈ 35 mK), Ir92Rh08 (TC ≈ 65 mK), Ir (TC = 100 mK), AuAl2 (TC = 160 mK), AuIn2 (TC = 208 mK), Cd (TC = 520 mK), Zn (TC = 850 mK) and Al (TC = 1180 mK). After extensive research and development in the preparation and in the ultra-low temperature characterization of superconductive reference materials during the past years, eventually a final selection of the materials to be included in the first SRD1000 prototype sensors was made. In this paper, the superconducting transitions observed for the selected materials and the sample preparations are reported, the SRD1000 sensor and external electronics technology are described with some detail, and the ULT facility set up to calibrate the prototype sensors and the future commercial devices is presented.