S. Safran

Critical Current and AC Loss of DI-BSCCO Tape Modified by the Deposition of Ferromagnetic Layer on Edges

Modification of local magnetic field with the help of a ferromagnetic layer could be utilized to improve the performance of multifilamentary Bi-2223/Ag tapes. We investigated the case of the horseshoe-shaped cover on the tape edges, characterized by layer thickness and total length. Numerical simulations have been carried out to find the critical currents of tapes with different covers. According to the indications obtained from these calculations, samples with covered edges have been prepared with the primary aim of increasing the self-field critical current. We observed up to 7% enhancement of this quantity. AC loss was also investigated theoretically and experimentally in a case of applied ac transport current or ac magnetic field applied perpendicular to the tape wide surface. Reduction of both the transport loss and the magnetization loss has been observed. Good agreement is obtained between the experimental data and the calculations.

Mechanical, microstructural and magnetic properties of the bulk BSCCO superconductor prepared by two different methods

BSCCO bulk samples have been prepared by solid-state reaction and ammonium nitrate precipitation methods with Bi1.65Pb0.35Sr2Ca2Cu3O10±y stoichiometry. Structural, mechanical and magnetic characterizations of the samples were performed by the X-ray powder diffraction (XRD), the scanning electron microscopy (SEM), Microhardness measurements, AC susceptibility measurements. The XRD patterns showed that the diffraction peaks for our samples belong to the two main phase, namely 2223 and 2212 of the BSCCO. In this study we have focused on microhardness measurements to investigate the mechanical properties. Vickers microhardness, Young’s modulus and yield strength values were calculated separately for all samples. In addition to these, we calculated the load independent hardness values of samples. Experimental results of hardness measurements were analyzed using the Meyer’s law, proportional sample resistance (PSR) model, Elastic–Plastic deformation model (EPD) and indentation induced cracking (IIC) model. The critical transition temperature, phase purity, lattice parameter, surface morphology and crystallinity of the prepared bulk samples were compared with each other.

Effect of re-pelletization on structural, mechanical and superconducting properties of BSCCO superconductors

We have examined the effect of re-pelletization on structural, mechanical and superconducting properties of high temperature superconducting (HTS) bulk samples using Bi1.85Pb0.35Sr2Ca2Cu3Oy stoichiometry. Conventional solid state reaction method is used for preparation of three different bulk samples. XRD measurement of the samples shows that a high percentage of high-Tc phase is determined. Superconducting critical transition temperature of the samples have been obtained from the curves of ρ-T and χ-T. Vickers micro-hardness are also calculated for all samples. Re-pelletization has a positive effect on structural, mechanical and superconducting properties of bulk samples.

AC loss in stacks of Bi-2223/Ag tapes modified with ferromagnetic covers at the edges

We investigated the magnetization loss of stacked Bi-2223/Ag tapes with a ferromagnetic cover on the edges. Such modification has been found recently to reduce the AC loss of a single tape; however, the behavior in a coil winding could be different. With experiments and numerical calculations we show that a ferromagnetic cover on the edges of a superconducting tape could reduce its magnetization loss also when the tapes are arranged in a stack. The effect is weaker for larger numbers of tapes but nevertheless remained significant in a stack of four tapes, which was the maximum number studied here. The effects observed experimentally are nicely explained by the results of numerical calculations.

Switching and Decoupling Effects in a Single-Phase Transformer Using Extra DC Current

A single-phase current-limiting transformer has been developed based on flux transfer. The transformer consists of two independent iron cores, one primary coil, two separate secondary coils, and superconducting windings/loops. Two iron cores are in a mechanical contact and clamped. Superconducting windings/loops act as coupling/decoupling mechanism between two iron cores. The transformer has been made operational via a switchgear of the applied dc current for a potential use in the current limitation when the transition between the superconducting and normal (quench) states can be triggered. DC and ac currents can be applied simultaneously in fault and no-fault conditions to mimic the realistic cases of use. With decoupling ac energy transfer, we propose that conventional switching off may be replaced with the approach described.