Current-voltage characteristics in a superconducting Bi-2223 tape in the range of very low electric field

Current-voltage characteristics in the range of very low electric field were analyzed from a relaxation of the magnetization using a SQUID magnetometer in a superconducting Bi-2223 tape. It was found that the observed current-voltage characteristics in this range were scaled well as predicted by the vortex glass-liquid transition theory. However, the obtained transition field was much lower than that obtained from a scaling in the higher electric field range. At the same time, the dynamic critical index, z, was much larger than usual values. Hence, it is concluded that these parameters are not uniquely determined independently of the level of electric field. The experimental result was compared with the theoretical analysis using the flux creep-flow theory in which the distribution of the effective flux pinning strength was taken into account. It was found that the theoretical result explains approximately the observed result. This shows that the essential mechanism which governs the transport property in the superconducting tape is the flux pinnin

Theoretical analysis of E–J characteristics in a Bi-2223 silver-sheathed tape

From an analysis of E–J curves with the aid of the flux creep-flow model, it is found that most of the electric field is caused by the flux creep even in the range of electric field in usual resistive measurement. This result is consistent with the fact that the mechanism of flux creep generally explains various phenomena such as the critical current density, the irreversibility field and so on. On the other hand, it is much easier to use the parameters used in the percolation flow model to describe the E–J characteristics phenomenologically. The two models are compared and it is found that the two models are consistent. This gives a theoretical proof for the parameters of the percolation flow model

E–J characteristics in a wide range of electric field for a Bi-2223 silver-sheathed tape wire

The E–J characteristics are measured for a Bi-2223 silver-sheathed tape wire using the four probe method and a relaxation method of DC magnetization in the high and low electric field regions, respectively. The obtained results in the two regions are approximately explained by a theoretical analysis based on the flux creep-flow model in which the distribution of flux pinning strength is taken into account. It was found that the value of the pinning force density and its peak magnetic field are largely different between the two measurements

Irreversibility field of Bi-2223 silver-sheathed tape determined with different electric field criteria

Dependence of the irreversibility field (Bi) on the electric field criterion (Ec) was measured for a Bi-2223 silver-sheathed tape wire using various measuring methods. It was found that Bi increased monotonically with the electric field criterion. A good agreement was obtained for Bi between experiments and the theoretical analysis using the flux creep-flow model. This implies that the resistive property of superconducting wires can be well described by the mechanism of flux creep and flow. The vortex glass–liquid transition field (Bg) was also determined from E–J curves which measured in the low and high electric field regions. It was found that Bg also depends on the ranges of electric field. This is incompatible with the prediction of the vortex glass–liquid transition theory