Toshiki Herai

Resin-impregnated bulk YBCO current leads for Maglev

Abstract Recent advancement in the fabrication techniques has allowed the production of large grain bulk RE–Ba–Cu–O (RE: rare earth elements) superconductors with large critical current density. The current leads can be machined from such large disks. However, the stress produced by refrigeration or electromagnetic induction sometimes causes cracking. It is therefore essentially important to improve mechanical properties of bulk materials to enhance their current carrying capability. In this study, we report on a novel technique to dramatically improve the mechanical properties of the current lead made of bulk superconductors, in which epoxy resin is impregnated into the bulk materials. At 77 K, a large current of 1000 A could be passed along the RE–Ba–Cu–O current lead without the transition from superconducting to normal state. The heat generation was also found to be much smaller than the current lead employed in the present Maglev model, showing that bulk RE–Ba–Cu–O is promising for current lead applications for Maglev.

Preliminary design of magnetic shielding by FEM

In this paper, we propose an optimization method for magnetic shielding. Our main purpose is the weight reduction of shield material. Assuming that the permeability of shield material is infinite, we simplify the magnetic shielding problem. Under this assumption, we design optimal passage for magnetic flux through the shield. We apply this method to designing the magnetic shielding for Maglev and show the effectiveness of this method by experimental and numerical data.

Resin-impregnated bulk RE–Ba–Cu–O current leads for the superconducting magnet on maglev train

Abstract Bulk RE–Ba–Cu–O (RE: rare earth elements) superconductors exhibit high critical current density ( J c ) and low thermal conductivity, that are the characteristics desired for the current lead applications. In this study, we studied whether the resin-impregnated Y–Ba–Cu–O rods can be used as the current lead for the superconducting magnet on a magnetically levitated train. The fatigue test showed that the mechanical properties of resin-impregnated Y–Ba–Cu–O rods are sufficiently good for maglev applications. We could also pass the electric currents of 500 A without heat generation. This was further confirmed by field distribution measurements, which showed that the superconducting state of the current lead was well maintained when the currents of 500 A were passed.

Study of the mechanical heat generation inside the inner vessel installed with a superconducting coil

In this study, the mechanical heat loss inside the inner vessel installed with a superconducting coil (SC-coil) was investigated which increases the heat load in the on-board superconducting magnets for the JR MAGLEV system. Vibration tests for the SC-coil-installed inner vessel were performed to investigate the relation between heat load and vibration. Strain distribution analysis of the SC-coil was performed to evaluate the heat generating area inside the inner vessel. These results proved that the SC-coil strain distribution analysis would be an effective method to evaluate the mechanical heat generating area inside the inner vessel.

Study of the relation between evaluation of strain distribution on superconducting coil and mechanical heat generation

In the superconducting Maglev system, on-board superconducting magnets (SCMs) are vibrated at various frequencies according to the train speed by the electromagnetic disturbance which is caused when the train passes over ground coils. Then a mechanical loss is generated inside the inner vessel in the SCM. This phenomenon increases the heat load on the cryogenic equipment in the SCM. It has been surmised that the mechanical heat inside the inner vessel is generated by the frictional heat caused by the relative microscopic slips between fasteners and superconducting coil (SC coil). Nevertheless, heat generation mechanisms inside the inner vessel have not been studied sufficiently. In this study, we suggest a hypothesis that the frictional heat generated by the relative microscopic slips between fasteners and a SC coil will be indicated if the calculated strain distribution on the SC coil is evaluated. The results of this study supported this hypothesis.