The development of a superconducting Maglev system in Japan was started more than 30 years ago. Since 1997, the running tests have been successfully continued on the Yamanashi test line. A manned run in 1999 attained a speed of 552km/h, The Yamanashi test results proved a remarkable stability of the onboard superconducting magnet system, In these 30 years, we have encountered many difficult problems during this development. In this paper, the history of the Maglev development will be introduced with focus on these problems, especially in regard to the superconducting magnets and onboard refrigerators.
We fabricated 2.1GHz TM010-mode microwave resonators with (Bi, Pb)2Sr2Ca2Cu3Ox (Bi2223) superconducting thick films on a Ba(Sn, Mg, Ta)O3 dielectric disk with a relative dielectric constant of εr=24. The Bi2223 thick films were screen-printed on both sides of the dielectric disk and subjected to a double repetition of cold isostatic pressing at 0.4GPa and sintering at various temperatures ranging from 820 to 840°C. An increase of the sintering temperature raises the Bi2223 phase purity up to 98% on the surfaces of the thick films, but high-temperature sintering above 830°C causes a chemical reaction at the interface between the Bi2223 thick film and the dielectric disk. An optimization of the sintering temperature to 830°C gives the unloaded quality factors Qu as much as 74, 000 at 70K and 158, 000 at 25K, which correspond to surface resistances Rs of 0.34 and 0.15mΩ for Bi2223 thick films, respectively. These values are approximately 20 times higher than those for the resonator using Ag electrodes with the same structure.