The database (DB) on organic composites and organic materials for cryogenic use has been established and the usage of the DB is described. There are two characteristics of the DB, that is (i) only the measured data are accumulated, and (ii) the name of the suppliers and the trade names are considered as one of the specifications of the material. The problems originated from the different measuring methods which exist potentially in DB can be avoided. The user of the DB can obtain easily the materials accumulated in the DB because the trade names or the suppliers names are described. The DB will be supplied in the form of floppy disk in which data are accumulated using the commercially available software. The data which do not exist in the DB can be obtained using the measuring systems installed in the laboratory.
Thermoacoustic theory gives two types of heat flux. One is proportional to thermal expansion coefficient of working fluid and contributes to heat-pumping effect of cryocoolers. The other is proportional to the heat capacity and axial gradient of temperarture. This acoustically enhanced heat-conduction term corresponds to one of regenerator losses, shuttle loss of displacer and a part of heat-flux in conventional “Dream Pipe.” Heat transports in the “Dream Pipe” are discussed in terms of thermoacoustics of inviscid fluid. Results of thermoacoustic theory are compared with experiments of dream pipe of which working fluid is liquid water. Good agreements of thermoacoustic theory with experiments suggest that thermoacoustic theory of inviscid fluid is useful for accounting regenerator loss and shuttle loss of cryocoolers.
The AURORA is a compact synchrotron light source optimaized for X-ray lithography. The system consists of 150MeV racetrack microtron as an injector, a compact electron storage ring, and light beam lines. The superconducting magnet system is composed of a cylindrical single-body magnet and a helium refrigeration system. The magnet generates Bz=4.34T at the 650MeV storage energy. The diameter of the central orbit is 1m. Iron york and poles are used for shielding the magnetic field, reducing the electromagnetic force between superconducting coils, and making the magnetic field distribution adequate for beam injection and storage.
Single crystals of the superconductor with the composition, Bi2.2Sr1.8 Ca1.0Cu2.0 O8.2, were grown by the travelling solvent floating zone method with changing the oxygen partial pressure, PO2, and measurements of physical properties were carried out. Stabilization of molten zone during the crystal growth can easily be attained with feed rods which were uniformly densified by a quick zone-pass. Oxygen partial pressures from 22 to 100kPa do not show any effect on the crystal size nor the formal charge of Cu ions. Density measurement suggests the coexistence of cation defects and excess anion oxygen. Zero resistance temperature, Tc, is 83K in case of crystals grown at PO2=22, 60 and 100kPa, while 57K at PO2=0kPa. Magnetization hysterisis loops in the applied field, H, parallel to the c-axis at 4.3K show that the critical current density, Jc, is insensitive to the applied field, indicating a large pinning potential in the single crystal. By the bean model a value of Jc is estimated as 2.5×106A/cm2 at 4.3K and 0 Oe for the crystal grown at PO2=100kPa.
We investigated Tc, Bc2 and Jc in a residual strain state of pre-strain for bronze processed multifilamentary Nb3Sn wires. The influence of a sample holder to the measured Jc value due to the thermal contraction and the relationship between a Jc criterion and an n-value in the form of V=KIn were clarified. It turned out that the temperature dependence of Bc2 under strain obeys [1-(2/3)(l.c.T/1.75 Tc)2] near T=0 and (1-T/Tc) near Tc. Moreover, the establishment of the temperature scaling law on the global pinning force Fp was confirmed in practical Nb3Sn wires.
Thermal stability of an immersion-cooled single-pancake superconducting coil has been numerically analyzed. The unsteady heat-conduction equation with source terms allowing for heat conduction across electric insulation film, thermal disturbance, helium cooling and Joule heat generation has been solved. The effect of the transport current, the magnetic flux density, and the energy density, duration, and spatial size of thermal disturbance on the stability of a superconducting coil is clarified.
Repulsive forces by the Meissner effect act on Y-Ba-Cu-O superconductors (polycrystalline superconducting oxides) at 77K in a magnetic field. The forces are measured experimentally in the cases of bulk and thin strip superconductors. Also, the forces are calculated by the numerical method under the assumption that the superconductor is a perfect diamagnetic body. Compairson between the both values in the bulk superconductor reveals that the experimental values have a range from 20 to 40% of the calculated values because the magnetic fluxes penetrate the superconductor even below the lower critical magnetic field. It is proposed that the real forces produced by the Meissner effect of the Y-Ba-Cu-O superconductors are estimated using the magnetic susceptibility of the superconductors, Although the estimated values using the proposed method are not good approximate values of the real forces in the thin strip superconductors, it is found that the method is valid for the bulk superconductor.
The preparation conditions for as-deposited superconducting films of Y-Ba-Cu-O have been investigated. By DC magnetron sputtering using single sintered targets with different compositions, films have been deposited onto heated substrates of single crystal MgO and further have been heat-treated at 450-550°C for 30 minutes in an oxygen pressure of 160 Torr during the course of cooling. The film thickness ranges from 100 to 6, 000Å. The rate of deposition for Y-Ba-Cu-O films highly depends on the oxygen partial pressure PO2 and total gas pressure PAr+O2. A small increase in PO2 from 0.1 to 10m Torr anomalously reduces the deposition rate, despite high PAr+O2 exceeding 200m Torr. However, in the case of PAr+O2=300m Torr, the deposition rate becomes constant with increasing the PO2 to above 1m Torr and the resputtering effect seems to be reduced. Ba-poorer targets than stoichiometry normally provide films with high-Tc (transition temperature) and low ρn (normal state resistivity). The distance L between target and substrate has also a benefical effect on the growth of high-Tc films and depositions at L=38mm provide high-Tc films with c-axis preferred orientation and homogeneous surface. The maximum zero resistance temperature Tc, end reaches 87K and even thin films with thicknesses of -500Å still maintain Tc, end above 85K.