Continuous rapid heating to about 2, 000°C and rapid quenching to Ga bath, and additional transformation annealing at about 800°C for Nb3Al superconductors, the so-called RHQT (rapid heating, quenching and transformation) process, makes Jc characteristics of the Nb3Al superconductors promising in a high magnetic field. These RHQT processed Nb3Al superconductors show no so-called peak effect, i.e., they show a high Jc even in a lower magnetic field; thus these conductors are expected also to be available around 10T, e.g., for accelerator magnets. So far the jelly-roll-processed RHQT Nb3Al superconductors have been developed for high magnetic field applications, e.g., 1GHz NMR magnet; thus the matrix ratio has been reduced as much as possible to improve the overall Jc. However, excessive reduction of the matrix ratio would be one possible reason for the electromagnetic filament coupling, especially when these conductors are used in a middle magnetic field region around 10T. The increase of the effective filament size degrades the stability, especially in the lower magnetic field, where the Jc becomes much higher. In this paper, the filament coupling for the RHQT-processed jelly-roll Nb3Al multifilamentary superconductors is discussed, referring to the results of the magnetization measurement with a vibrating sample magnetometer and Jc measurement. It was found that the proximity effect might occur even if the designed thickness of the Nb barrier between the filaments was about 10μm. An observation of the cross-sections with SEM shows that this would be due to the partial reduction of the barrier thickness during the RHQ process.
Fabrication of YBCO superconductor by the MOD method has many advantages: precise controllability of metal components, wide flexibility to coating objects, and low-cost nonvacuum approach. We succeeded in the preparation of a high-quality coating solution that enables us to obtain YBCO films having high critical currents (Ic). We also investigated processing conditions: proper control of water vapor in furnace, suppression of the reaction between substrate and fluoride during heat treatments, and other process conditions. By their optimization, we can successfully fabricate the film, which has Jc of 4.6MA/cm2 at 77K, 0T. The results show the potentiality of the TFA-MOD method for high-temperature superconductor applications.