Bi 2Sr2Ca2Cu3O10 Research Articles

Comparison of Heat Assisted Lap Joints of High-Temperature Superconducting Tapes With Inserted Indium Foils

Easy and simple fabrication of a lap joint of high-temperature superconducting (HTS) tapes is desirable for various HTS applications such as power cables and current feeders. We have developed mechanical joints with a low-temperature heat treatment at around 370 K where indium foils are inserted between joint surfaces. Though the joint showed a good performance, it took over 10 min to fabricate one joint and ideally the fabrication time should be further shortened. In this study, we proposed to use ultrasonic welding (UW) to assist a heat generation at the joint for lap joints with indium foil, which can be completed within 1 s. We prepared various lap joint samples of HTS tapes: REBCO (REBa 2 Cu 3 O 7 , RE: rare-earth) or BSCCO (Bi 2 Sr 2 Ca 2 Cu 3 O 10 ) tapes were pressed together with an indium foil using a UW machine or pressing machine with cartridge heaters. Then, the current-voltage curve was evaluated at 77 K and the joint resistance characteristics were discussed depending on the joint methods and HTS tapes. The samples with copper-stabilized REBCO tapes all showed joint resistivities of 31.6-35.6 nΩcm 2 without critical current (I C ) degradation for both joint methods. The samples with silver-sheathed BSCCO tapes showed joint resistivities of 18.6-46.5 nΩcm 2 for both joint methods; however, some of those fabricated by the UW showed I C degradation. The degradation was able to be prevented by optimizing UW conditions.

Measurement of AC transport current loss in different kinds of superconducting tapes andwires in liquid helium

Low-temperature and high-temperature superconductors are used in liquid helium (LHe) asmagnets and in other applications. AC transport current loss study is important for the useof these superconductors in alternating current regimes. The measurement of AC transportcurrent loss under LHe conditions requires a measurement system with a specialmeasurement device. A possible way to carry out the measurement is presented in thispaper. The device described in this paper is based on the principle of a currenttransformer. The transport current is induced into one secondary turn formedby a superconducting sample. The LHe evaporation caused by the heating ofthe current leads at high currents and the measurement system dimensions areminimized. Our experimental setup enables us to determine the AC transportcurrent loss of a superconducting tape or a wire in the self-field, in LHe up to acurrent of 2000 A at a frequency up to 300 Hz. The measurements are based ona lock-in technique. This paper presents and compares AC transport losses ofYBa2Cu3O7 − x (YBCO) coatedconductor, Bi2Sr2Ca2Cu3O10 (BSCCO)tape, NbTi wire and Nb3Sn tape measured up to their quench currents in LHe.

Time-Varying Magnetic Field Coupled Noise Reduction in Low-Voltage Measurements in Superconductors

Noise generated by time-varying magnetic fields interferes in the measurements of low voltages particularly with superconductor materials. The measured values can alter significantly if it is not compensated appropriately or if suitable protocols are not followed. Measurements on inductive loads, like superconducting wires and coils, considerably generate high magnetic field in the surrounding, which couples electromagnetic noise through measurement leads and circuits. Twisted pair cables are adopted and used as a classical solution to avoid magnetically induced voltages. However, the magnetic field produced by large inductive load couples imposed electromagnetic interference (EMI) with the cable loop created by voltage taps, which are soldered over part of the load. The effects are severe when there is a big loop area due to large sample size or when there is a high rate of change in the magnetic field due to high-current ramp rates. A finite uncompensated flux is invariably linked in such cases. Three simple, yet effective, techniques were implemented for the cancellation of EMI noise which couples in a cable loop formed by voltage-measuring leads of superconductor sample in low-temperature experiments. In all these methods, the basic principles are to detect and measure signal portion and coupled-noise portion with dedicated voltage taps, use subtraction mathematics to cancel the noise portion, and derive actual voltage-drop signal across a superconducting load. These techniques were tested successfully on low-resistance joint of high-temperature superconducting Bi2Sr2Ca2 Cu3O10 tape in a bath-cooled condition (77 K). EMI noise coupling was simulated with background field coil and a permanent magnet. This paper describes the detailed experimental procedure, results, and observations. The concept can be extended to DC joint-resistance measurement of Toroidal and Poloidal field coils of Steady State Superconducting Tokamak-1.

Evaluation of delamination properties of coated conductors by means of MELT method using epoxy resin

Abstract Coated conductors (CCs) are prospective for application to electric power conductors due to not only better cost performance but also high Jc–B properties compared with Bi2Sr2Ca2Cu3O10 (BSCCO) tapes. However, CCs are composed of multi-layered thin films and metal substrate, and post-treatments are essential to putting CCs to practical use, which are slitting and/or making thin film multi-filaments. For this reason, CCs delaminate between multi-layers. The delamination prevents CCs from functioning as superconducting wire, and therefore there is a need to evaluate delamination toughness of CCs quantitatively. In this study, we applied the Modified Edge Lift Test (MELT) using epoxy resin to evaluation of delamination properties. Then, we investigated delaminated surfaces by the means of scanning electron microscope.

Magnetic field dependence of vortex activation energy: A comparison between MgB2, NbSe2 and Bi2Sr2Ca2Cu3O10 superconductors

The dissipative mechanism at low current density is compared in three different classes of superconductors. This is achieved by measuring the resistance as a function of temperature and magnetic field in clean polycrystalline samples of NbSe2, MgB2 and Bi2Sr2Ca2Cu3O10 (BSCCO) superconductors. Thermally activated flux flow behaviour is seen in all the three systems and clearly identified in bulk MgB2. While the activation energy at low fields for MgB2 is comparable to Bi2Sr2Ca2Cu3O10, its field dependence follows a parabolic behaviour unlike a power-law dependence seen in Bi2Sr2Ca2Cu3O10. We analyse our results based on Kramer’s scaling for grain boundary pinning in MgB2 and NbSe2.

Development of a laser scribing process of coated conductors for the reduction of AClosses

Expectations are high for using coated conductors for electric powerapplications not only because of better cost performance but also higherJc–B propertiescompared with Bi2Sr2Ca2Cu3O10 (BSCCO) tapes. Furthermore, the coated conductors could also reduce AC losses bythe use of various methods in post-treatment. When a YAG laser was used forscribing the superconductive layer, an AC loss reduction due to a decrease inthe width of the superconductivity layer could be confirmed in short samples.In the case of AC applications using long tapes, high resistance between scribed filaments isnecessary. However, the resistance between the filaments scribed by a laser was as low as10−3 Ω cm−1. The reason for the low resistance was the existence of dross in the filament spacings,which was confirmed by a cross-sectional compositional mapping observation.Although the superconductivity layer was divided by the laser, the dross of the metalsubstrate made a bridge over the superconductivity filaments. Post-annealing in anO2 atmosphere to oxidize the dross was carried out in order to increase the resistance.Consequently, the resistance between the filaments was improved to be as high as50 Ω cm−1. We succeeded in controlling the resistance value between filaments in a range five ordersof magnitude higher than that of the as-scribed YBCO film, through oxygen atmospherepost-annealing.

Processing of bulk Bi-2223 high-temperature superconductor

The Bi2Sr2Ca2Cu3 O10+x (Bi-2223) is one of the main high temperature superconductors for applications. One of these applications is the Superconductor Fault Current Limiter (SCFCL), which is a very promising high temperature superconducting device. SCFCL's can be improved by using bulk superconductors with high critical currents, which requires a sufficiently dense and textured material. In the present work, a process for improving the microstructure of Bi-2223 bulk samples is investigated. Pressed precursor blocks are processed by sintering with a further partial melting step, in order to enhance the Bi-2223 grain texture and to healing cracks induced by pressing. In order to improve the microstructure, the precursor is mixed with silver powder before pressing. Samples with and without silver powder have been studied, with the aim of investigating the influence of silver on the microstructure evolution. The phase contents and the microstructure obtained have been analyzed through XRD and SEM/EDS. The electromagnetic characterization has been performed by Magnetic Susceptibility Analysis. We present and discuss the process and the properties of the superconducting blocks. High fractions of textured Bi-2223 grains have been obtained.

Phase relations study on the melting and crystallization regions of the Bi-2223 high temperature superconductor

The melting and solidification behavior of Bi2Sr2Ca2Cu3 O10 (Bi-2223) precursors has been studied. Nominal compositions corresponding to excess of liquid, Ca2CuO3 and CuO have been investigated. Each sample was made by packing a precursor powder into a silver crucible, in order to approximately simulate the situation found in 2223 silver-sheathed tapes. The samples were partially melted and then slow-cooled, being quenched from different temperatures and analyzed through X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDS). The precursors decomposed peritectically during melting, forming liquid and solid phases. Very long plates with compositions falling in the vicinity of the 2223 primary phase field formed upon slow-cooling. The 2223 phase may have been formed and the results suggest that long grains of this phase might be obtained by melting and crystallization if the exact peritectic region and the optimum processing conditions are found.

Glass-derived superconducting ceramics with zero resistance at 107 K in the Bi1.5Pb0.5Sr2Ca2Cu3Ox system

A melt of composition Bi1.5Pb0.5Sr2Ca2Cu3Ox was fast quenched to form a glass. This was subsequently air annealed and the influence of annealing time and temperature on the formation of various crystalline phases was investigated. X-ray powder diffraction indicated that none of the resulting samples were single phase. However, for an annealing temperature of 840 °C, the volume fraction of the high Tc phase (isostructural with Bi2 Sr2 Ca2 Cu3O10 ) increased with annealing time. A specimen annealed at this temperature for 243 h followed by slow cooling showed a sharp transition [ΔTc (10–90%) ∼2 K] and Tc (R=0)=107.2 K. To our knowledge, this is the highest Tc yet reported for any superconductor prepared via the glass route.