An experimental 2-GHz band Cryogenic Receiver Front-End (CRFE) has been newly developed for IMT-2000 cellular radio base stations. It uses a high-Q high-temperature supercon-ducting filter (HTSF), a cryogenic low-noise amplifier (CLNA), and a highly reliable cooler that is very compact. The ideal frequency selectivity realized with the HTSF and the virtually noise-free receiver performance made possible by the cryogenic operation are expected to achieve various system improvements that are not available with any existing normal temperature receiver frontend. First, the basic radio zone design for a nationwide cellular system is introduced as well as fundamental radio base station construction. It is shown that existing superconducting devices are most effective when applied to the receiver front end of the base station. Next, the basic circuit configuration of the CRFE is considered, and fundamental characteristics of the developed CRFE are measured to confirm that ultralow noise and high selectivity can be achieved. Moreover, the influence of antenna noise, including ground thermal noise and man-made noise, on CRFE is experimentally estimated. Finally, the system merits obtained by applying CRFE to IMT-2000 are predicted, and expectations of future developments in superconducting devices are discussed.

View full abstract

Since the discovery of High-T_c superconducting (HTSC) materials, elementary technologies of an HTSC cable system have been developed such as the manufacturing technology of a conductor wound with HTSC wires, cold dielectric properties, and thermally insulated pipes. HTSC cable models have also been constructed to evaluate these technologies. As a next step, new test project of a 100m, 66kV/1, 000A/100MVA class, three-core HTSC cable system, integrating these elementary technologies, are planned to verify the practicability of an HTSC cable system as an actual power system equipment. It is a joint project of Tokyo Electric Power Company and Sumitomo Electric Industries, Ltd., and is being conducted in collaboration with the Central Research Institute of Electric Power Industry. The purposes of this project are to prove newly developed technologies satisfying the requirement as actual deployments, to prove manufacturing abilities and installation technologies, and to conduct long-term current-voltage loading tests. The cable consists of three-core conductors placed in thermally insulated pipes having a vacuum insulation layer between them. Each conductor consists of a copper former, superconducting layers, PPLP/LN₂ composite insulating layer, and superconducting shielding layers. The cable is placed at a CRIEPI test yard and is bent into U-shape at its center, partially installed into a duct 150mm in inner diameter. The following tests are scheduled, using this cable system, such as an initial cooling test, continuous rated current-voltage loading tests, load fluctuation tests, cooling cycle test between room temperature and LN₂ temperature, and overloading and overvoltage withstand tests. Through these tests, problems are expected to be extracted that may be difficult to foresee in individual part tests for development of an actual level HTSC power cable system.

View full abstract

Electromagnetic and thermal phenomena on multistrand cables are studied for the purpose of large-scale applications, e.g., fusion machines and SMES. The conductors in these machines (generally cable in conduit conductors [CICCs]) must be designed to aim at a reduction of interstrand coupling loss and promotion of current redistribution ability in the normal generation. So far, most analytical studies have been carried out for single-stage twisted cable or multiplestage twisted cable with insulation among strands, and current redistribution phenomena have been revealed well. In this study, we evaluated both minimum quench energies (MQEs) and recovery current of multistrand cables without insulation among strands by numerically solving the electric circuit and thermal equations. The validity of segregated copper strands to enhance the stability in the multistrand cable was also evaluated. The results show that the MQE is not improved, but the recovery current becomes larger when segregated coppers are added.

View full abstract

High strength Ag based alloy tubes with homogeneously dispersed very fine (Mg0.8Ni0.2at%)oxides and (Mg0.5Ni0.2at%)oxides were prepared by internal oxidation. Using the tubes we fabricated high strength Bi-2223 and Bi-2212 multifilamentary tapes with 7 filaments by the powder in tube technique, which have three different arrangements of sheath material such as inner/outer sheaths of Ag alloy/Ag alloy, Ag/Ag alloy and Ag/Ag. For the tapes we examined the microstructures and the critical current I_C, especially I_C under tensile stress and strain in a self magnetic field at 77K and also usual critical current density J_C vs. magnetic field curves at 4.2K. The I_C under tensile stress and strain are improved for the high strength sheath tapes, especially those tapes with Ag/Ag alloy arrangement. The J_C strongly depends on the inner sheath material, showing high J_C for the Ag/Ag and Ag/Ag alloy arrangements. For the tapes with Ag alloy/Ag alloy arrangement some swellings appear in each filament on fabrication and heat-treatment process. Around the swellings observed are some voids and highly mis-aligned grains. This induces the decrease in J_C on the connectivity of superconducting grains and also J_C under the stress and strain.

View full abstract