PINNING-FORCE DENSITY OF SUPERCONDUCTING BI-2223 TAPE WIRES

The pinning-force density and the irreversibility field are measured f or Bi-2223 tape wires at various temperatures under the magnetic field s normal and parallel to the c-axis. It is found that the scaling laws of pinning-force density in the low and high-temperature regions and the temperature dependence of the irreversibility field are formally t he same between the two field directions in spite of some anisotropy f actor, suggesting that the pinning mechanism is essentially the same f or the two field directions. These results are compared with the numer ical calculation based on the flux-creep model. The experimental resul ts are well explained by the theory including the anisotropic property . The pinning potential estimated from the flux-creep theory at 80 K a nd 1.0 T is of the order of several 10 meV and the factor of the aniso tropy is about 1.3. The value of the pinning potential under the magne tic field along the c-axis suggests that the flux lines are strongly c onnected along this direction. The longitudinal elastic correlation le ngth of the flux lines is of the order of several mu m and this suppor ts the hypothesis. The pinning characteristics of a Bi-2223 tape wire to which the strong pinning centers are successfully introduced are di scussed using the flux-creep theory for evaluating the potential of th is material for application. The irreversibility field for the directi on parallel to the c-axis is estimated to be sufficiently high even at 77.3 K and it is concluded that Bi-2223 has a sufficient potential fo r application.