As the 4th lecture of the series on high-temperature superconducting materials, this article provides an overview of REBa 2 Cu3Ox (RE: Y and rare earth) wires (so-called coated conductors) from the fabrication process to future prospects. Development of coated conductors has progressed rapidly in the last decade and the properties of coated conductors are approaching the market requirements for practical superconducting devices such as power cables, transformers, SMES and rotating machinery. Several venders have started to sell coated conductors. The fabrication processes of coated conductors and their properties are briefly reviewed so that non-specialists can understand coated conductors during their use in designing HTSC devices. The future prospects of coated conductors for practical applications are discussed as well.
This paper reports thermal diffusivities of Bi-system and Y-system tape conductors. First, we measure temperature traces of the bundled conductors for the heater disturbance at conduction cooling conditions. Obtained results are modeled and analyzed using one-dimensional as well as two-dimensional heat balance equations. We show that the analysis results can successfully reproduce the experimental results for a wide temperature range from 20 to 77 K. On the basis of such results, we also clarify that the thermal diffusivity, in the perpendicular direction to the tape surface, of the Y-system conductors are five orders of magnitude lower than that of the Bi-system ones. Our results indicate that the consideration of such low thermal diffusivity is important for the conduction-cooled magnet design.
A trapped field magnet is one application for a melt-processed bulk high-Tc superconductor (HTS). In the magnetization process via field cooling of the bulk HTS, stresses are induced by the Lorentz force between shielding currents and magnetic fields. Evaluation of the maximum stress during magnetization is important from the viewpoint of destruction of the bulk HTS. In the present paper, stresses in a hollow cylindrical bulk HTS are numerically evaluated using an axisymmetric threedimensional model. Shielding current distributions are obtained through macroscopic numerical simulation using Maxwell equations and the critical-state model. Hoop stress distributions are obtained for both open and fixed boundary conditions. In the analysis of field-cooled magnetization, the maximum hoop stresses are discussed for both a hollow model and a stacked model.