The saturation and non-saturation phenomena for pinning force density are described. Models for these phenomena are introduced and compared experimentally. It can be concluded that the non-saturation phenomenon observed in commercial Nb-Ti belongs to the pinning regime of higher pinning performance than the saturation phenomenon observed in Nb3Sn. Such classification is determined by the number density and elementary pinning force of the pinning centers. The peculiar behavior of flux lines in the saturation phenomenon can be clarified by a small AC ripple field measurement called Campbell's method. An avalanching flux flow model based on this experimental result explains the saturation and non-saturation properties well.
This paper describes a fundamental study on the generation characteristics of a high Tc superconducting induction/synchronous machine (HTS-ISM), with a structure the same as squirrel-cage induction machines. Bi-2223/Ag multifilamentary tapes are utilized for the fabrication of the secondary windings, and a commercialized 3-phase, 4-pole stator is introduced. The fabricated HTS-ISM is immersed in liquid nitrogen, and then operated at a frequency of 60 Hz. It is shown for the first time that our HTS machine can generate active power at synchronous speed when the primary windings are excited. This indicates that synchronous generation can be realized with the simple structure of HTS-ISM.
The magnetic superconductor FeSr2YCu2O6+y exhibits superconductivity below 59 K, only when it is properly annealed in a N2 flow and subsequently annealed in an O2 flow and under high O2 pressure. FeSr2LnCu2O6+y (Ln = Nd, Eu, Gd and Tb), where Ln is substituted for Y, was also studied. While FeSr2GdCu2O6+y and FeSr2EuCu2O6+y show superconductivity below 37 K and 31 K, respectively, FeSr2NdCu2O6+y and FeSr2TbCu2O6+y do not show superconductivity. A peak was observed at 20 K in the temperature dependence of susceptibility under a magnetic field of 1 T for FeSr2YCu2O7.65, and this implies the magnetic order of the Fe ion. To study the magnetism of the Fe ion in FeSr2YCu2O7.65, non-superconducting FeSr2Y(Cu0.95Zn0.05)2O7.65 was studied. The magnetism of the Fe ion is mainly antiferromagnetic.
Alternately-layered MgB2/B thin films were prepared on silicon (100) substrates by an electron-beam evaporation technique without any post-annealing. The thickness of each MgB2-layer was designed to be 42, 24 or 15 nm. Cross-sectional transmission electron microscopy observations confirmed that the layered structure was successfully obtained. The critical temperature Tc of the MgB2/B thin film decreased as the MgB2-layer became thinner. We then compared the magnetic field dependence of the critical current density Jc and the global pinning force Fp between the alternately-layered MgB2/B and pure MgB2 thin films. In the MgB2/B film, Jc was higher in fields parallel to the substrate than in perpendicular fields. The Fp -B curve in parallel fields had a clear peak at 4 T, indicating that the maximum Fp was achieved when the quantized fluxon line spacing matched the B-layer spacing. The results suggest a high possibility that the alternately-layered nanostructure improves the superconducting performance of MgB2.