A three-terminal superconducting devise composed of a semiconductor coupled Josephson junction and an oxide-insulated gate was described. It was possible to control the superconducting coherence length ξn in the semiconductor by applying a gate voltage; consequently, the junction's superconducting critical current, which depends on ξn, was changeable. Power dissipation and switching time constant would be expected to be approximately 1μW and 10ps, respectively.
Mechanical properties of carbon-glass hybrid composite materials have been studied in order to check the applicability of hybrid composite materials at low temperature. Four types of interlaminate hybrid composites, which were reinforced by high-modulus carbon and glass or high-tensile carbon and glass cloth, were prepared. Their volume fraction of reinforcement were identical but the geometrical arrangement of the reinforcements was different. Tensile and dynamic flexural elastic modulus were measured and the law of mixture was found to be valid. Tensile tests were also performed and the breaking stress of hybrid materials was confirmed to follow the law of mixture at both room and low temperature. Not only the elastic modulus but the breaking stress of hybrid materials could be improved compared with those of glass fiber reinforced plastics even at low temperature.
The forced-convective heat transfer to supercritical helium has been investigated. The test section is a 1.25mm I.D., 200mm long vertical straight tube through which helium flows upward or downward and heated uniformly. The conditions covered are inlet fluid temperature between 4.7 and 10.8K, system pressures of 0.3, 0.5 and 0.8MPa, mass velocities of 20, 40 and 80kg/(m2·s) and heat fluxes of 500, 1000, 2000 and 4000W/m2. Experimental results on the distribution of wall temperature and heat transfer coefficient are presented. A comparison of the experimental results between upward and downward flow directions and discussion about the differences between them, in the light of the buoyancy effect, are done.
A thin-film platinum resistance thermometer (SDT101A, Tama Electric Work Company), which is available commercially, has useful characteristics for thermometry in the range of 20 to 300K and in high magnetic fields up to 5T. The Z function-table of this platinum resistance thermometer (PRT) was obtained experimentally. We comfirmed a possibility of the two point calibration with a precision of ±0.1K above 30K. The magnetoresistance of this PRT at 30K is about 1.5% for a magnetic field of 5T, whose value is one order of magnitude smaller than that of a precision type PRT.
A-15 Nb3Al tape superconductor has been prepared by high power density and continuous wave CO2 laser beam irradiation onto moving Nb-Al composite tapes made by the powder method. The irradiated area was melted and then immediately resolidified, which resulted in a fine dendritic microstructure consisting of Nb dendrites embedded in Nb3Al matrix. Nb2Al phase was also observed in the heat-affected zone nearby the melted area by laser beam irradiation.
Laser irradiated Nb3Al superconductors showed critical temperatures TC above 16.0K and subsequent heat-treatment at 750°C enhanced the TC to 18.6K. For laser irradiated and then heat-treated specimens, critical currents IC were little decreased, even over 20T, as compared with specimens which were only heat-treated. A maximum critical current density JC for reacted area of 4.8×104A/cm2 was obtained at 23T and 4.2K. The effects of temperature change and magnetic field direction on IC were also discussed.
It is expected that a superconducting wire is exposed to an elliptically rotating field, when it is used for AC 50Hz equipments such as superconducting armature- and exciting-windings of a cryoturbogenerator. This paper provides an expression for AC losses of a multifilamentary composite in an elliptically rotating transverse field H with the index of an ellipticity η(=Hn/Hm), where Hn and Hm are the shortest and the longest radii of the ellipse, respectively. The coupling-current loss is simply given by a sum of two losses in the cases of reciprocative alternating fields with amplitudes Hn and Hm. The hysteresis loss increases as η increases in the case of Hm>>Hdc, where Hdc is a superposed DC bias field. For the case of Hdc=0, on the other hand, the hysteresis loss first decreases rapidly as η increaes from zero, takes a minimum at η=0.5, and then increases gradually as η approaches 1. The rapid decrease of the loss in the low η region is important for AC applications such as the armature winding, in which the field rotates with a small η. The present result cannot be expected from earlier works in which only the case of the circular rotation (η=1) was investigated.