This paper reviews the progress of studies about one-, two- and three-dimensional artificial pinning centers (APCs) into REBa2Cu3Oy (REBCO) films. In particular, the doping techniques for the three-dimensional APC in film and coated conductor are reported. For example, nano-Y2BaCuOx, REBCO and RE2O3 particles and nano3 (M=Hf, Zr, Sn) rods in REBCO films and coated conductors have been investigated for creating nano-size for flux This paper includes reviewing the results on REBCO films and coated conductor processing for a high-performance conductor under a high magnetic system and power cable.
The development of environment-friendly material as a substitute for glass fiber reinforced plastics (GFRP) is required for cryogenic electrical insulation. Our laboratory has studied the A.C. breakdown properties of solidified alcohol solutions at 77 K. In many cases, the A.C. breakdown voltages of solidified solutions were higher than that of ice. From these results, it is suggested that the breakdown voltage can be improved by mixing with alcohol. However, the breakdown voltage dispersion of solidified solutions was large.The suppression of dispersion is required for practical application.Therefore, an attempt was made to suppress dispersion of the breakdown voltage by combination with cotton fabric.In this paper, we observed A.C. breakdown voltages of cotton fabric-solidified alcohol (ethylene glycol, 1,3-propanediol, propylene glycol or glycerin) solution composite systems.The following results were obtained.1) The dispersion of breakdown voltage in cotton fabric solidified alcohol solution composite systems was suppressed. 2) The minimum breakdown voltages of cotton fabric-solidified solution composite systems were higher than those of solidified solutions.3) The average breakdown voltage of cotton fabric solidified solution composite systems was higher than that of the cotton fabric-ice composite system.
Ferroelectric ice, ice XI, existing at the cryogenic temperature of 1 atm is a very interesting material because of its high electrical stability at low temperature and its low environmental impact. However, the ice XI formation process is very difficult. The dielectric properties of ice are governed by the behavior of the hydrogen ions, protons. Protons in ice can hop along lattice defects at a relatively high temperature, e.g., 253 K. At a cryogenic temperature such as 77 K, proton movement in ice is difficult. To obtain polarized ice, we applied DC voltage to normal ice, ice Ih, at 253 K and cool it down to 77 K with voltage application. In this process, protons in ice hop to the cathode side at 253 K and stop moving at 77 K, therefore polarization fixed there. The polarized ice is called "ice electret." The electrical properties and structure of ice electret have not yet been clarified. We produced ice electret using the aforementioned method and observed its depolarization current. We changed the application time and magnitude of voltage in during the formation process and measured the charged stored in the ice electrets produced. The results show that the stored charge in ice electret increases with application time and amplitude of voltage.