The development of a high-temperature superconducting magnetic sensor (SQUID) has been reported. It is relatively easy to handle in comparison with a Nb SQUID because it can work at liquid nitrogen temperature. This high Tc SQUID has great potential for application in medical diagnostics, nondestructive tests and geological survey, and in other areas. Recently a single channel of the high Tc SQUID was placed on the market. It is expected that this SQUID will accelerate the development of SQUID applications.
The superconducting magnet levitation railway system will make its debut as a new high-speed mass transport system in the 21st century. In conjunction with the Central Japan Railway Company, the Railway Technical Research Institute (RTRI) started test running of the system in April 1997 on the Yamanashi Test Line. Eight months thereafter, or in December 1997, the test vehicles recorded the world's highest speed of 550km/h, which had been the first target of the development. Various tests related to the system are successfully being promoted to verify the high technical level attained so far. This paper outlines the developmental processes of the superconducting magnet, on-board refrigeration system, and other cryogenic systems; reports the results and operation during the past year; and introduces some of the key technologies that led to the unprecedented speed of 550km/h.
The mechanical properties of superconductors such as Young's modulus and yield strength, are very important for their applications. There has been an urgent need to test the mechanical properties, but no standard method exists worldwide. We have discussed, evaluated through a round-robin test, and standardized the method of room temperature tensile tests for Cu/Nb-Ti composite superconductors because Cu/Nb-Ti composite is now the most popular superconductor. This paper provides critical examination of this method and is concerned with double-yielding phenomena, strain measurement, reliability, and accuracy, which are the items to be elucidated. The first draft is prepared and submitted to IEC/TC90 as an international standard. It will soon be issued as International Standard IEC61788-4.
A new-type structure of multifilamentary oxide-superconducting wire and tape is proposed. It is expected that this structure will be effective in reducing transport losses produced when they carry changing currents. The fabrication method of such a wire or tape with low transport losses has more flexibility in the design of its parameters, such as the pitch and the direction of twisting or the number of filament layers, than the existing method does. Theoretical analyses of transport current distributions and resultant transport losses are made for a cylindrical two-layer wire with a twist in the same or the opposite direction for each layer. The theoretical result shows that uniformity in transport current distribution is achieved by optimizing the wire parameters regardless of the twist direction. Moreover, the possibility that the obtained uniformity reduces transport losses by one order compared with the existing type, which has strongly localized current distribution, is theoretically shown for a new multilayer wire or tape.
It had been found that the indentation scar made at cryogenic temperatures disappeared at room temperature in plastics such as epoxy and glass fiber reinforced plastic (GFRP); thus we could not measure Vickers hardness numbers at cryogenic temperatures. We then measured the indentation depth with load. The specimens used were GFRP, polyethylene fiber reinforced plastic (DFRP), epoxy and SUS304 steel. The results showed that the elastic recovery ratio, defined as a ratio of the decrement in depth during unloading to the maximum depth at the loaded condition, was up to 90% for epoxy and up to 30% for SUS304 steel in liquid helium temperature. This paper suggested a new hardness evaluation method obtained from displacement-load curve during indentation. The new hardness HVd was defined as HVd=P/(24.5δ2), where P was load and δ was the indentation depth. Consequently, we could get the hardness number for plastics from 4 to 293K, and it monotonically increased with decreasing temperature.