Ryoji Inada

Total AC loss of Ag-sheathed Bi2223 tapes with various filament arrangements carrying AC transport current in AC parallel transverse magnetic field

For the applications of Bi2223 tapes as the strands to power cables with multilayer structures, the tapes must carry the AC transport current in an AC parallel transverse field with various field amplitudes depending on the layer positions. In this study, we experimentally investigated the total AC loss characteristics under parallel transverse field for Bi2223 tapes with various filament arrangements in their cross sections. The tapes with different filament arrangements in the final tape sections were prepared by a conventional powder-in-tube (PIT) process with drawing using round dies and a rectangular deformation process using a two-axial rolling (TAR) technique. Total AC losses in the tapes carrying AC transport current in an AC parallel transverse field were measured by means of the electromagnetic method. The measured loss values in the tapes were compared with several analytical models. Based on the experimental results, the influence of filament arrangements on total AC loss behaviour is discussed, under the different operating conditions with various amplitudes of current and applied field.

Field-free core, current distribution, and alternating current losses in self fields for rectangular superconductor tapes

A method is proposed to calculate the shape of field-free core, the current distribution, and accordingly the alternating current (ac) losses in self fields as a parameter of current amplitude I0 for straight superconductor tapes with the arbitrary sectional geometry. The validity for this is justified by showing that magnetic fields inside the field-free core are negligibly small and by checking that calculation results of ac losses for elliptic tapes agree with the prediction by the theory of Norris. The ac losses for rectangular tapes behave as a thin strip superconductor in high I0 values near critical current, while showing a gradual deviation from this behavior as I0 is lowered. A decrease in the aspect ratio of width to thickness in the rectangular tape makes the deviation more remarkable.

Current distributions and AC losses in self-fields for superconductor tapes and cables

The alternating current losses in self-fields for superconductor tapes are investigated using numerical calculations. In the calculation, the current distributions and self-field losses for straight superconductors with the arbitrary sectional geometry are calculated as a parameter of current amplitude. For the 7-filamentary tapes, the losses depend on the filament configurations, which is also observed experimentally in the 7-filaments samples. In the case of cables, the values of the losses are strongly influenced by the tape arrangements. The losses for altered cables, which are composed of a number of similar tapes, are different from each other. These results suggest that the optimization of tape and cable structure, i.e. the arrangement of the superconductor cores in the cables, is useful to reduce the loss generation in the cables.

Fabrication and characterization of Bi2223 tapes with interfilamentary SrZrO3+Bi2212 barriers for AC loss reduction

To suppress interfilamentary coupling in (Bi, Pb)2Sr2Ca2Cu3Ox (Bi2223) multifilamentary tapes under an AC external magnetic field it is necessary to increase the transverse resistivity by using a high-resistivity Ag alloy sheath as a matrix. Alternatively, oxide layers can be introduced as resistive barriers among the filaments, together with filament twisting. In this paper, we fabricated twisted Bi2223 tapes with interfilamentary oxide barriers and evaluated the effect of the introduction of such a barrier on the AC magnetization loss properties in a perpendicular transverse magnetic field. The conventional powder-in-tube method was used for tape fabrication. In order to avoid affecting the Bi2223 phase during the sintering process, SrZrO3 was selected as the barrier material. Moreover, 20 wt% Bi2Sr2CaCu2Oy (Bi2212) was mixed with SrZrO3 to improve its ductility for cold working. Monocore Ag-sheathed rods were coated with an oxide barrier using a slurry, before being stacked into honeycomb structures. By twisting the filament with a twist pitch length below 9 mm and introducing interfilamentary barriers, the coupling frequency ( fc) in a perpendicular field, which is inversely proportional to the decay time constant (τc) of coupling current, exceeded 100 Hz and perpendicular field losses around the power-grid frequency were reduced from the analytical prediction for fully coupled filaments. Avoiding physical connections among the irregular deformed filaments in twisted barrier tapes should lead to further loss reduction in a perpendicular field.

Influence of locally varying Jc distribution on AC transport losses for superconductor wires and tapes with various cross sections

Abstract The influence of locally varying J c value on AC transport losses in self-fields is investigated on superconductor wires and tapes with various cross sections through numerical calculations. For round wires, the loss values depend on the J c variation along a radial direction in their cross sections. The distribution that J c increases in going from the center to the edge along a radial direction lowers the loss value, below the theoretical prediction for an elliptic superconductor without any J c variation. For tapes, the loss values are mainly influenced by the J c variation along a width direction. The rectangular tapes with high aspect ratio and also with nearly uniform J c value behave as a thin strip superconductor. The distribution that J c decreases in going from the center to the edge along a width direction raises the loss value, and the loss value approaches the theoretical prediction for an elliptic superconductor as the J c variation becomes significant.

Reduction in alternating-current transport losses of a (Bi, Pb)2Sr2Ca2Cu3Ox multifilamentary tape-form conductor by the introduction of resistive barriers

We succeeded in reducing alternating-current (ac) transport losses at 77 K and 50 Hz for the (Bi, Pb)2Sr2Ca2Cu3Ox tape-form conductor with 39 filaments, fabricated by a four-roller machine to make a rectangular deformation and also by the introduction of Bi2Sr2CuOx sheets as resistive barriers in an arrangement parallel to a tape surface. Although the main contribution to the losses comes from the hysteresis loss of the superconductor, the loss value for the conductor is reduced by approximately 70% compared with the value for the (Bi, Pb)2Sr2Ca2Cu3Ox multifilamentary tape prepared by an ordinary powder-in-tube process without the resistive barriers. Using numerical calculations we ascribe this loss reduction to the division of field-free-core under ac current transmission, caused by introduction of the barriers.

Development of Lithium-Stuffed Garnet-Type Oxide Solid Electrolytes with High Ionic Conductivity for Application to All-Solid-State Batteries

All-solid-state lithium-ion battery (LiB) is expected as one of the next generation energy storage devices because of their high energy density, high safety and excellent cycle stability. Although oxide-based solid electrolyte materials have rather lower conductivity and poor deformability than sulfide-based one, they have other advantages such as their chemical stability and easiness for handling. Among the various oxide-based SEs, lithium stuffed garnet-type oxide with the formula of Li7La3Zr2O12 (LLZ) have been widely studied because of their high conductivity above 10-4 Scm-1 at room temperature, excellent thermal performance and stability against Li metal anode.Here, we present our recent progress for the development of garnet-type solid electrolytes with high conductivity by simultaneous substitution of Ta5+ into Zr4+ site and Ba2+ into La3+ site in LLZ. Li+ concentration was fixed to 6.5 per chemical formulae, so that the formulae of our Li garnet-type oxide is expressed as Li6.5La3-xBaxZr1.5-xTa0.5+xO12 (LLBZT) and Ba contents x are changed from 0 to 0.3. As results, all LLBZT samples have cubic garnet structure without containing any secondary phases. The lattice parameters of LLBZT decrease with increasing Ba2+ contents x < 0.10 while increase with x from 0.10 to 0.30, possibly due to the simultaneous change of Ba2+ and Ta5+ substitution levels. Relative densities of LLBZT are in the range between 89% and 93% and not influenced so much by the compositions. From AC impedance spectroscopy measurements, the total (bulk + grain) conductivity at 27oC of LLBZT shows its maximum value of 8.34 x 10-4 S cm-1 at x = 0.10, which is slightly higher than the conductivity (= 7.94 x 10-4 S cm-1) of LLZT without substituting Ba (x = 0). Activation energy of the conductivity tends to become lower by Ba substation, while excess Ba substitution degrades the conductivity in LLBZT. LLBZT has wide electrochemical potential window of 0-6 V vs. Li+/Li and reversible Li+ insertion and extraction reactions of TiNb2O7 film electrode formed on LLBZT by aerosol deposition are successfully demonstrated at 60oC. The results indicate that LLBZT can potentially be used as a solid electrolyte in all-solid-state batteries.

Numerical analysis for AC losses in single-layer cables composed of rectangular superconducting strips with various lateral Jc distributions

The critical current density (Jc) in the superconducting layer in the typical coated conductor is known to be not uniform along a lateral direction of its cross section. Non-uniformity of Jc values in a superconducting layer is the dominant factors of the AC loss characteristics together with its geometrical shape and arrangement in an actual power device. In this paper, we investigated the AC loss characteristics on the single-layer cable composed of thin rectangular superconducting strips with various lateral Jc distributions through the numerical analysis. In our analysis, several rectangular strips were arranged on a cylindrical former, in a parallel way to the conductor length. Numerical calculation of magnetic field distributions and loss values under AC current transmission were performed, by taking into account the locally-varying Jc values in a tape strand and geometrical factors of cables. The influence of non-uniformity of Jc values along a tape width on loss under AC current transmission in the cable conductors was discussed.

Effect of Bi2223 addition in precursor on the formation and Jc property of Bi2223 tapes sheathed with the Ag–Cu alloy

The use of an alloy sheath is effective in improving the mechanical strength of Bi2223 tapes although it easily decreases Jc properties. In the case of the tape sheathed with Ag?Cu alloy, the Jc value was decreased by the formation of non-superconducting (Sr,Ca)14Cu24Ox (14:24) particles. In this study, the effect of Bi2223 addition in precursor on the formation and the properties of Bi2223 tapes was investigated. The addition of Bi2223 in precursor was found to be effective in reducing the number and size of the 14:24 particles and in increasing the formation speed of the Bi2223 phase. This rapid formation of Bi2223 is probably due to the skipping of nucleation of Bi2223 since the Bi2223 crystals added in precursor act as nuclei. In addition, the crystal size after the first sintering decreased on increasing the content of 2223 powder. Due to the reduction of 14:24 particles, Jc values of about 2 ? 104?A?cm?2 were attained in the tapes with 2223 up to 5%, although the Jc values were decreased by further addition of 2223 to more than 10%. This reduction of Jc would be caused by the poor alignment of Bi2223 crystals because of the small size in the rolling step.

Phase formation mechanism and properties of Ag-sheathed (Bi, Pb)-2223 tapes prepared by two-powder method

Abstract The effects of two-powder method on the J c properties were investigated through the microstructure and c -axis orientation observations. Three kinds of Ag-sheathed (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x tapes from one-powder and two-powder precursors were fabricated. The microstructures, phase constructions and J c properties were compared in these tapes. The tapes from two-powder and one-powder calcined at 780 °C precursors show good J c values compared to the samples from one-powder calcined at 825 °C. No clear difference in microstructures and c -axis orientations were not observed in the final tapes, while the high J c samples had large amount of non-reacted residual phases before the second sintering step. This suggests that the residual phases may promote the improvement of the grain connectivity during second sintering step to lead the high J c values.