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Abstract: The superconducting Ba1-xKxFe2As2 (x = 0.4) single crystals were prepared by the so-called FeAs self-flux method. The critical temperature by ac susceptibility measurement was estimated to be about 36 K. The magnetic field and temperature dependences of critical current densities were investigated by an ac inductive measurement (Campbell''s method). Unlike the phenomenon of co-existence of the global and local critical current densities observed in many polycrystalline Fe-based superconducting pnictides, it was found that only a uniform critical current density (Jc) flows through the whole sample. The value of Jc at 20 K and 1 T was about 5×108 A/m2, which is much smaller than the local critical current density observed in polycrystalline samples. The force-displacement characteristic of fluxoids in sample was investigated. The Labusch parameter was found to increase monotonously with increasing magnetic field, while the interaction distance was proportional to the fluxoid spacing. These results are consistent with the prediction based on a simple flux pinning mechanism. [Copyright &y& Elsevier]

Abstract: It is important to investigate condensation energy density of superconducting material, since it determines its pinning property. According to the heavy-ion irradiation, the columnar defects are introduced to the superconductor which act as the strong pinning centers, and the critical current density is enhanced by the new pinning centers. Since the number density and the size of the columnar defects can be observed, the condensation energy density is estimated by using the pinning summation theory. In the present study, we prepared Ba(Fe0.93Co0.07)2As2 (Ba-122) pnictide superconductors by self-flux method. 200 MeV Au ions were irradiated into the specimens along c-axis and the matching field was 2 T. After the irradiation, the critical current density was 6 times larger than that before the irradiation. The estimated condensation energy density is in the order of 104 J/m3 and is slightly smaller than those of cuprate superconductors. The temperature dependence is similar to that of YBa2Cu3Ox oxide superconductors, since the anisotropy parameter is small in Ba-122. Therefore, it is expected to use Ba-122 at high temperatures near the critical temperature. [Copyright &y& Elsevier]

An innovative superconducting DC power cable using high-temperature superconducting wires is introduced. The new cable design is proposed to utilize the longitudinal magnetic field effect that was discovered about a half-century ago. It was shown that the critical current density of a superconducting wire could be significantly increased when the superconductor is in a parallel field configuration. It is empirically known that a force-free structure is attained for the current flowing in the superconductor in this case. In the new cable, the outer layer is twisted in such a way that the shielding current flowing in this region generates a magnetic field that is parallel to the inner conductor. As a result, a force-free structure is realized for the wiring in the inner conductor. It is shown that the current carrying capacity of the proposed cable is dramatically improved in comparison with other cables and that the improvement becomes more pronounced with the increase of the current level. [ABSTRACT FROM AUTHOR]

In this study, we focused on the estimation of the global critical current density, super-current path, grain connectivity and their relationships with the faults volume fraction in the MgB2 bulks prepared by a modified PIT (powder in tube) method. Campbell's method was applied for the purpose of acquiring the penetrating AC magnetic flux profile and the characteristic of AC magnetic field vs. penetration depth from the specimen's surface. A computer simulation on the penetrating AC flux profile in MgB2 bulks with certain amount of randomly distributed voids, oxidized grains and other faults was also carried out. The global critical current density obtained by Campbell's method turned out to be smaller than that obtained from the SQUID measurement, implying that the global super-current was reduced by the existence of various kinds of faults and the lack of the electrical connectivity between grains. It was verified that the relationship between the global critical current characteristics and the faults contained in MgB2 specimens can be quantitatively clarified by comparing the simulated critical current densities and other factors with the experimental results. [ABSTRACT FROM AUTHOR]

• Crack may occur at the junction and the critical current deteriorates. • A very thin solder or a silver diffusion junction is necessary to recover it. • Trapezoid junction can reduce the stress at the junction. • FEM is useful to evaluate the electrical and mechanical properties at the junction. In the present study, in order to clarify the electrical and mechanical properties of the junction of superconducting wires, a junction was numerically simulated using the finite element method, and the electrical and mechanical properties were evaluated. We used a 1 µm-thick YB a 2 C u 3 O 7 − δ superconducting coated conductor to act as a superconducting wire and joined two films together for current density simulation. The magnetic field dependence of the critical current density is based on the experimental results for YB a 2 C u 3 O 7 − δ . We introduced a crack in the superconducting junction and confirm that the critical current is drastically reduced by increasing the width of crack. We then attempted to reinforce the crack using solder and superconducting film. The effectiveness of reinforcement of I c was clarified using very thin solder or a silver diffusion junction. [ABSTRACT FROM AUTHOR]

In this study, we focused on the estimation of the global critical current density, super-current path, grain connectivity and their relationships with the faults volume fraction in the MgB2 bulks prepared by a modified PIT (powder in tube) method. Campbell's method was applied for the purpose of acquiring the penetrating AC magnetic flux profile and the characteristic of AC magnetic field vs. penetration depth from the specimen's surface. A computer simulation on the penetrating AC flux profile in MgB2 bulks with certain amount of randomly distributed voids, oxidized grains and other faults was also carried out. The global critical current density obtained by Campbell's method turned out to be smaller than that obtained from the SQUID measurement, implying that the global super-current was reduced by the existence of various kinds of faults and the lack of the electrical connectivity between grains. It was verified that the relationship between the global critical current characteristics and the faults contained in MgB2 specimens can be quantitatively clarified by comparing the simulated critical current densities and other factors with the experimental results. [ABSTRACT FROM AUTHOR]