Microstructure controls and their effects on the properties of Bi2Sr2Ca1Cu2Ox superconductors

This paper reports our recent progresses in the development of Bi2Sr2Ca1Cu2 Ox/Ag tape conductors for the applications of magnetic field generation in liquid helium or around 20 K, using a refrigerator. We have carried out ext ensive work to optimize the processing parameters, investigating the relati onship between the microstructure and transport Jr(c). We have found that t he partial melting in oxygen atmosphere is effective to have large transpor t J(c) with good reproducibility. The pre-annealing and intermediate rollin g (PAIR) process has been successfully applied to the multilayer conductors to improve the grain alignment and transport J(c). The J(c) of 5 x 10(5)A/ cm(2) at 4.2 K and 10 T has been achieved, which is the highest value repor ted so far. Two magnets fabricated by using different types of Bi-2212/Ag c onductors were tested. One is a magnet designed as an insert magnet for a 1 8 T-class large bore Nb-Ti/Nb3Sn superconducting magnet, The conductor of t his magnet Was multifilamentary tape processed by powder-in-tube method, Th e I, was 98 A in the backup field of 18 T, which generated the self field o f 1.79 T. A large pancake coil was fabricated with multilayer conductor and tested under the operation of cryocooler system. The coil was stably opera ted up to the J(c) of the coil at the temperatures below 30 K.