The use of critical current measurements for the development of technological superconductors

The development of superconductors of technological interest is studied in our institute. The quality of the products is controlled in an apparatus for measuring critical currents up to 1000 A at 4.3 K in magnetic fields up to 13 tesla. The "short sample" is a one meter long wire in the form of a helix. A shunt limits the power generated in the cryostat at the quench. A data acquisition system, with digital voltmeters of 0.1μV sensitivity, is adapted to the apparatus. The data are transferred to the main computer of the institute for further processing. The reliability of the apparatus has been checked measuring critical currents of commercial superconductors, the agreement with the producer's data being good. The apparatus is used to optimize the thermal treatments of home made niobium-tin superconductors. The power supply and the data acquisition system were also used for the study of small superconductive coils which were wound with commercial niobium-titanium multifilament wire. One of these coils generates fields up to 8 tesla.