Magnetic Field Dependence of Critical Current Density for Silver Sheathed Bi_2Sr_2CaCu_2O_x Wires(High-T_c Superconducting Materials Research)

The critical current density (J_c) of Bi(2212) tapes were measured at 77K and 4.2K in magnetic fields up to 30T. J_c of the tape specimen was significantly improved due to the high c-axis oriented Bi(2212) superconducting laminate grains. Consequently, high J_c of 3.5x10^4 was obtained at 77K and 0T. However, the superconducting properties at 77K were still insufficient for magnet applications because of the large field dependence and high anisotropy of J_c. On the contrary, J_c at 4.2K was not so sensitive to magnetic field and anisotropy of J_c was very small. A fine multifilamentary composite conductor is not necessary in the Bi(2212) superconductor on the basis of the calculation of the limiting size of stability for D.C. operations. Therefore, we fabricated double pancake coils using Bi(2212) superconducting tapes. This coil generated magnetic field of 360G at 4.2K in a external field of 10T. This result indicated that the Bi(2212) superconductor was quite useful for making a inner magnet of a high field hybrid magnet