Fabrication of YBCO Small Test Coils for Accelerator Magnet Development

A research program for studying coil winding technologies using YBa₂Cu₃O_x (YBCO) coated conductors is now in progress. In this program, we are attempting to develop high-T_c superconducting magnets for highly functional, efficient, and compact accelerator systems. In designing superconducting coils with thin tape conductors, we must be concerned about magnetization of the superconducting layer. In order to experimentally evaluate the influence of the additional field resulting from the magnetization current, prototype racetrack coils were constructed with YBCO coated conductors. A 62 m length of coated conductor was wound to form each of the coils, which were then impregnated with epoxy resin. For precise analysis of the additional magnetic field, it is essential to fabricate superconducting coils without degradation because the voltage generated at such a degraded part would affect the behavior of the additional magnetic field. In a liquid nitrogen environment, the racetrack coils were energized to evaluate the voltage-current (V-I) characteristics. It was found that there was no degradation in the superconductivity. The V-I characteristics showed sufficiently high index values of 28 and 34 throughout an electric field range of 10^-9 V/cm. Magnet design derived from accelerator design, as well as construction of an experimental reduced-scale coil in a typical shape, are also discussed.