Development of Ag-sheathed Bi2223 superconducting wires and their application to magnets

Abstract

Silver-sheathed BiPbSrCaCuO 2223 superconducting wires with long length and high Jc of over 10/sup 4/ A/cm/sup 2/ were developed by using the powder-in-tube method. Future possibilities to obtain much higher Jc's are discussed in relation to crystal alignment, connectivity between grains and flux pinning. High amperage wires and high strength wires were also developed for large scale magnet application. High I/sub c/ of over 300 A at 77 K were obtained for the wire with large cross sectional area. Good stress and strain tolerant characteristics were also obtained for silver alloy sheathed wires. In order to apply the HTS wires for AC use, it is necessary to reduce AC loss. So, the AC loss of the wires are also discussed. As a progress of wire technology, we have fabricated many types of magnets, such as pancake magnets and solenoidal magnets. In the case of 77 K application, it is promising to apply for AC use because of large heat capacity of HTS wires and liquid nitrogen. So, we are developing the 500 kVA transformer and pulse magnet for SMES. A refrigerator cooled magnet operated near 20K was fabricated. This magnet was operated at 21 K and generated 3 T inside a /spl phi/40 mm room temperature bore, stably generated 2.5 T continuously for over 150 hours and could be operated at high ramp rate of over 12 T/min. As for the 4.2 K operation, high field insert magnet for 1 GHz NMR application are developed. Highest magnetic field of 24 T was achieved using the hybrid magnet at MIT and persistent current mode operation was done by using the layer wound coil with persistent current switch.