Kengo Iwafuchi

Homogenizing field-trapping capabilities of bulk Y–Ba–Cu–O superconductors fabricated using Ba–Cu–O oxide substrates for practical applications

We employed Ba–Cu–O substrates for fabrication of bulk Y–Ba–Cu–O superconductors using the top-seeded melt-growth method. There were several advantages of using a Ba–Cu–O substrate as compared to conventional substrate materials such as MgO, ZrO2, Al2O3, RE123 (RE = rare earth) and RE211. The Ba–Cu–O substrate avoided crystallization from the substrate, suppressed liquid loss and scarcely reacted with the precursor. Furthermore, the introduction of large-sized cracks into a grown bulk was greatly suppressed by propagation along the interface between the grown bulk and the substrate. We were able to obtain bulk Y–Ba–Cu–O superconductors with uniform trapped magnetic field distributions and equal maximum trapped field values on both top and bottom surfaces, which indicates that the field-trapping capabilities were homogenized along the c-axes of the bulks fabricated on the Ba–Cu–O substrates.

Improvement of the field-trapping capabilities of bulk Nd-Ba-Cu-O superconductors using Ba-Cu-O substrates

We used Ba–Cu–O substrates to fabricate bulk Nd–Ba–Cu–O superconductors using a top-seeded melt-growth method. There were several advantages for the use of Ba–Cu–O substrate compared to conventional substrate materials such as MgO, ZrO2, Al2O3, RE123 and RE211 (RE = rare earth). The Ba–Cu–O did not react with the precursor and minimized liquid loss. Accordingly, the introduction of large-sized cracks was suppressed. We also found that Tc values were high at the bottom regions, which was ascribed to the beneficial effect of Ba–Cu–O in suppressing Nd/Ba substitution. As a result, we obtained bulk Nd–Ba–Cu–O superconductors that exhibited fairly good field-trapping capabilities, even at the bottom surfaces.

Application of Neutron Diffraction Technique to Industrial Materials

As an important industrial problem, the rolling contact fatigue damage is accumulated in rails during the repeated passage of trains over the rails, and rail failures may occur from the cracks grown in the rails. In order to prevent such rail failures, the estimation of the behavior of internal rail cracks is required based on the exact engineering analysis model as well as conducting rail test to search rail defects. The purposes of this paper are to apply the neutron stress measurement to rails, and to obtain residual stress state in the rails for the above purpose. The rail samples used were those that have been used in service line in Japan for about six years (222 million gross tons). The neutron measurement was conducted using the Residual Stress Analyzer (RESA) of the Japan Atomic Energy Agency (JAEA). The present measurement of stresses in rails by the neutron diffraction method was the first attempt in Japan.

Homogenizing field-trapping capabilities of bulk Y-Ba-Cu-O superconductors using Ba-Cu-O oxide substrate for practical applications

We employed Ba-Cu-O substrates for fabrication of bulk Y-Ba-Cu-O superconductors in the top-seeded melt-growth method. There were several advantages for a use of a Ba-Cu-O substrate compared to conventional substrate materials such as MgO, ZrO2, Al2O3, RE123 and RE211 (RE = rare earth). The Ba-Cu-O substrate avoided crystallization from a substrate, suppressed a liquid loss and then scarcely reacted with a precursor. Furthermore, the introduction of large-sized cracks into a grown bulk greatly was suppressed by propagating along the interface between a grown bulk and a substrate. We could obtain bulk Y-Ba-Cu-O superconductors with uniform trapped magnetic filed distributions and equal maximum trapped filed values on both top and bottom surfaces, which indicates that the field-trapping capabilities were homogenized along the c-axes of the bulks fabricated on the Ba-Cu-O substrates.