Search

A multi-laminated HTS tape conductor has recently been developed for large coils. If the HTS tapes are simply laminated to form the conductor, the current distribution in the laminated tape conductor of the coil is unbalanced because of the differences among all tape inductances. Transposition of the tape in the conductor is effective for homogeneous current distribution, but the tape may be damaged due to the lateral bending. In our previous paper, we proposed a new theory to analyze and control current distributions in the multi-laminated tape conductor for a solenoid coil with arbitrary layers. We applied the Maxwell integral equation to the region contoured by adjacent laminated tapes to analyze the current distributions of the tapes in the infinite solenoid coil, demonstrated that the flux across the region is conserved as long as the tapes are not saturated, and finally induced fundamental equations as functions of coil construction parameters, such as layer radius, laminated tape space, and winding pitch. In order to verify the theory, we designed two kinds of coils with homogeneous and inhomogeneous current distributions in the two-laminated tape conductor by adjusting the space between the tapes in the second layer, and fabricated them. In the case when the space between the tapes in the second layer is the same as that of the first layer, 0.31 mm in thickness, we measured the tape currents of 7:3 for the inner and outer tape of the first layer, respectively. We adjusted the space between the tapes of the second layer, 1.78 mm in thickness, while the space of the first layer remained unchanged, 0.31 mm in thickness. We obtained the homogeneous current distribution in the tape conductor. The experimental data were in good agreement with the theory.

This paper describes a cryocooler cooled NbTi superconducting magnet system. The technical features of this magnet system are a 4K-Gifford-McMahon (GM) refrigerator using magnetic regenerator material and a high-Tc Bi2Sr2CaCu2Oy superconducting current lead. The NbTi coil was directly cooled by the 4K-GM refrigerator without liquid helium and it took about 21 hours for the NbTI coil to be cooled from room temperature to below 4 K. The stable magnetic field of 6 T at 3.5 K and the maximum magnetic field of 6.45 T were obtained in the 180 mm room temperature bore.

Demand for electric power in Japan has been steadily increasing in recent years.To meet this demand, power networks have been more robustly connected with a view to improving their reliability. However, this has been accompanied by a trend toward a greater incidence of fault currents in these power networks. If a fault current limiter is used to connect these systems, electric power utilities will be able to accommodate electric power through the superconducting limiter from a system with excess capacity to another system in which the available power is insufficient, while the limiter protects systems from the influence of faults in a system. The authors have developed a 6.6 kV/2.0 kA class superconducting fault current limiter used for power distribution substations, as the preliminary stage of development of current for trunk power systems. In order to reduce impedance under normal operating conditions and quickly switch to high impedance in a fault condition, the limiter consists of a pair of double-layer non-inductive superconducting windings connected in series. Each winding is wound with a 36-stranded AC superconducting wire having ultra-fine NbTi filaments in a high-resistivity matrix. The device successfully limited a 6.9 kA short-circuit current to 3.4 kA and transmitted continuous power at 2.0 kArms.

Japanese maglev system consists of on-board superconducting magnets(SCMs) and ground coils. When SCMs vibrate due to magnetic fluctuation from ground coils, the heat load of SCMs increases not a little. To estimate this heat load of SCMs with different structures, we have done electromagnetic vibration tests by changing the inner structures of the SCMs. And then, we have tried to measure the eddy current on the inner vessel, and we got available knowledge. As a result, we have found that the increase of the heat load is influenced by vibration characteristics and resistivity of structures.

An adiabatic demagnetization cooler with an indirectly cooled superconducting magnet was fabricated for an infrared detector. The operating temperature was designed to be 0.2 K. The temperature of the sensor, which replaced the infrared detector, was successfully maintained at 0.200–0.205 K for 7 h by active magnetic field control, using single crystal chromic potassium sulphate as a magnetic working substance. Using manganese ammonium sulphate, a temperature below 0.300 K was maintained for over 12 h, although the lowest sensor temperature was 0.237 K. Yttrium aluminium garnet doped with the magnetic impurity neodymium ion (Nd 3+ ) was also tested, it being a substitute for paramagnetic salts from the viewpoint of easy processing and handling. Using this garnet a temperature of 0.203 K could be obtained, though this could only be maintained for 6 min. A proposal for improvement in the garnet cooling capacity has been made.