International Laboratory of High Magnetic Fields and Low Temperatures: how it was set up and how it evolved

the Coordination of Research and Further Developments in This Field within the Section of Physico-Technical and Mathematical Sciences of the Presidium.'' The Commission was to monitor a wide range of superconductivity research projects, the latest search for new superconductors, and the expansion of applications-oriented work. The RAS Presidium assigned eleven institutes of the Academy (Institute for High Pressure, Institute of Solid State Physics, P N Lebedev Physical Institute, IFP, PTILT, Institute of Chemical Physics, Institute for High Temperatures, etc.) specific tasks covering the entire spectrum of research activities and applications of superconductivity. A P Aleksandrov, as a member of the Presidium, was chosen to head the Commission on Superconductivity. As he was already responsible for an immense field of atomic power research, the entire work of the Commission on Superconductivity lay on the shoulders of his deputy, namely N E Alekseevskii. At the same time, the RAS Presidium submitted to the State Committee on Science and Technology under theUSSR Council of Ministers its recommendations to greatly expand the industrial production of superconducting wire and devices requiring it. It looked as if the road was opened for the Nb-Sn tape, all the more so since the General Electric factories (USA) had begun to work on a technology for depositing the Nb3Sn coating onto the tape from the gas phase. At the beginning, the solid-diffusion technique appeared to be simpler, but the actual process proved to be much more complicated: liquid tin through which the niobium tape was drawn collected pollutants, perhaps because of insufficient purity of niobium; as a result, it was impossible to produce long specimens of a superconductor with the same high critical parameters. Later on, another drawback inherent in the tape itself was revealed. In 1974, the Intermagnetics company brought toMoscow superconducting magnets with coils implemented as Nb-Sn wafers made of General Electric tape. The magnets produced a magnetic field of 17.5 T. This was phenomenal! It was soon found, however, that wafer coils were not very reliable. After a few transitions to the normal state (these are unavoidable), the superconductor irreversibly degraded, and the magnetic field dropped by 2±3 T. This deterioration was caused by the low mechanical strength of niobium, which formed the base of the tape. The reputation of the tape was greatly `marred', and in the race to lower costs it soon lost the battle to a new, `bronze' technology. The essence of the bronze technology consists in the fact that niobium rods were immersed into the matrix of tin bronze (Cu‡ 13%Sn). This half-product was drawn through a die until the required wire diameter was achieved. The cable wire obtained in this way was coated with a heatresistant insulator and then used for winding the solenoid. The prepared coil was placed in a furnace at T ˆ 900 C. Tin diffused out of bronze, and a micron-thick layer of Nb3Sn formed on the surface of the niobium. The technology of manufacturing the original wire became simpler, while that of magnet assembly became more complex. In the USSR, the bronze technology was initiated by researchers at the AllUnion Research Institute of Inorganic Materials (currently known as the A A Bochvar All-Russian Research Institute of Inorganic Materials): V Ya Fil'kin, A D Nikulin, and A K Shikov. This technology is nowadays the main one in the industry of superconducting cable wires for high-field magnetic systems. Although the maximum field produced by magnets with wire coils is 1 or 2 T lower than that of tape (wafer) magnets, their stability and reliability are higher. The bronze technology offered several advantages: the absence of other stannides in the diffusion layer, in addition to Nb3Sn, high strength of the cable wire, automatically produced current and magnetic stabilization, the high current-bearing ability, andÐ the main advantageÐ the constancy of parameters over great lengths of the wire. In the mid-1970s, all work on tape superconductors was discontinued. Interest in them returned to some extent with the advent of high-temperature superconductors. It is possible that the method of fabricating superconducting tape using solid-state diffusion, which N E Alekseevskii started to develop, may resurface, provided the latest technologies and multilayer (reinforced) niobium tape are merged into an integrated process. The author acknowledges E Nikolaev's help in searching for the archival documents of the USSR Academy of Sciences.