Hysteresis loss in a superconducting Bi-2223 tape with fine filaments

The energy loss density was measured for a Bi-2223 tape wire with superconducting filaments of average thickness 2.5 μm to confirm the reduction of energy loss density due to the reversible fluxoid motion. The energy loss density is compared with the prediction by the modified Kim model. It is lower than the prediction at AC field amplitudes below the penetration field at temperatures above 77 K. The slope of the minor magnetization curve is less than unity and the estimated AC penetration depth is longer than the filament thickness in the same regime. This result supports the speculation that the reduction of the energy loss density is due to the reversible fluxoid motio

Characterization of critical current density in silver-sheathed Bi-2223 tape

The critical current property of a superconducting Bi-2223 tape produced by the over pressure processing at the final heat treatment was investigated. The critical current density increased by a factor of 1.6-1.8 at 77.3 K in comparison with the tape produced by the usual process. Thus, the critical current increased in spite of a reduction in the filament thickness. It was also found that the irreversibility field increased by a factor of 1.34 at 77.3 K by the new process. As a result, the enhancement of the critical current density at higher fields is remarkable. These results suggest that the over pressure process not only enriches the mass concentration of the superconducting phase but also contributes to the c-axis alignment. This is supported directly by the reduction of FWHM of rocking curve and indirectly by an enhancement the n value. The critical current property at lower temperatures is also investigated and the possibility of the further improvement of the property is discussed

Critical current properties in multifilamentary Bi-2223 tape produced by the over pressure processing

Investigation is done on the effect of ConTrolled Over Pressure (CT-OP) processes on the critical current properties in multifilamentary Bi-2223 tapes. It is found that the critical current density at low magnetic fields is remarkably improved by the new CT-OP process. This result with those on irreversibility field and n-value are compared with the numerical calculation based on the flux creep and flow model. The analysis reveals that the most probable value is increased, although the statistical distribution width is increased for the flux pinning strength. This result indicates that the critical current density at high magnetic fields is deteriorated by the widened distribution. If such an inhomogeneity can be reduced to the level of previous tapes by improving the CT-OP process, the high field performance is shown to be significantly improved

Effects of over pressure sintering for Bi-2223 silver-sheathed tape

The critical current properties of a superconducting Bi-2223 tape produced by the over pressure processing at the final heat treatment were investigated. The critical current density increased more than the factor of densification of the superconducting region. In addition, the irreversibility field also increased. This means that the quality of flux pinning is improved by the new process. From the numerical calculation based on the flux creep and flow model, it is speculated that the fraction of weakly pinning regions decreases due to the improved connectivity of grains

Evaluation of field-angle anisotropy of critical current in multifilamentary Bi-2223 tapes prepared by CT-OP process

The critical current property of Bi-2223 silver sheathed tape has been significantly improved by application of ConTrolled Over Pressure (CT-OP) process with adjusting temperature and oxygen partial pressure at the final heat treatment. In this paper, the field-angle dependence of the critical current density was measured at 77.3 K and the crystalline misorientation angle was estimated for four specimens with different critical current densities. It is found that in a parallel magnetic field, the critical current density of the latest Bi-2223 tape of 190 A class is remarkably higher than the other specimens over a wide region of magnetic field. On the other hand, although the critical current density of the latest tape in a normal magnetic field is higher than the other specimens, the difference is relatively small especially at high magnetic fields. Thus, the field-angle anisotropy of the latest tape is higher than the other specimen. The observed results can be explained by the improved condensation energy density and the better c-axis alignment in the latest tape