Bi-2223 Tapes Research Articles

Conceptual Design of a HTS CICC Coil for Fusion Devices Based on Bi-2223 Tapes

Conceptual Design of a HTS CICC Coil for Fusion Devices Based on Bi-2223 Tapes

Improving phase transformation and superconducting performance of Bi-2223 tapes via Cu addition

Improving phase transformation and superconducting performance of Bi-2223 tapes via Cu addition

Flux Pinning Enhancement of Bi-2212 Tapes by Increasing Sr Content

Flux Pinning Enhancement of Bi-2212 Tapes by Increasing Sr Content

Influences of oxygen partial pressure on the phase composition of the (Bi, Pb)-2212 precursor powder

Bi-2223 tapes, synthesized through the two-powder method, exhibit distinctive features such as high current density and a controllable secondary phase. Traditionally, the two-powder method involves the separate preparation of Bi-2212 and CaCuO powders followed by their mixing. However, during this process, it is necessary to dope the Bi-2212 powder with an appropriate Pb content to achieve a stable lattice structure in the Bi-2223 phase. The alteration of ion valences between Pb2+ and Pb4+ influences the oxygen content, thereby affecting the phase formation of (Bi, Pb)-2212 and, consequently, the final properties of Bi-2223 tapes. Surprisingly, limited research has explored the impact of the heat treatment process on (Bi, Pb)-2212. Consequently, this study investigates the phase composition and microstructure of (Bi, Pb)-2212 under various oxygen partial pressures to deepen our understanding of the effect of Pb on the composition of (Bi, Pb)-2212. Simultaneously, the behavior of Pb in the lattice of Bi-2212 is analyzed. Ultimately, the findings reveal that low oxygen conditions are advantageous for fabricating (Bi, Pb)-2212 powder with a high main phase content and a reduced secondary phase, thereby demonstrating excellent current-carrying performance in Bi-2223 tapes.

Resistance at 77 K of two Bi-2223 coils with superconducting joints prepared by incongruent melting

A superconducting joint for multi-filamentary Bi2Sr2Ca2Cu3O10+δ (Bi2223) tape, which has applications in nuclear magnetic resonance and magnetic resonance imaging, has been developed based on incongruent melting and multi-junction methods. In this study, the critical current limit, optimal oxygen annealing conditions, and reproducibility of this joint are experimentally evaluated. The results indicate that the critical current limit of the joint at 77 K is determined by that of the tape. The critical current limit was estimated to be about 40 A. Additional oxygen annealing after heat treatment below 1143 K. appears to have no effect on the critical current, and that above 1153 K slightly increases the critical current. It is found that the multi-junction method effectively increases the reproducibility of obtaining a high critical current. To obtain a high critical current at 77 K, the highest temperature in the joint creation process should be lowered to near the incongruent melting temperature of Bi2223 (about 1133 K in air). Two Bi2223 coils, each with one joint (four junctions), were prepared and their persistent current at 77 K was tested. A persistent current of above 20 A was measured with a resistance of about 10 pΩ.

Study on Electromagnetic-Thermal Characteristics of Bi-2223 Tape by Homogenization Model

Study on Electromagnetic-Thermal Characteristics of Bi-2223 Tape by Homogenization Model

Initial Study on Press Welding With Indium Applied to High-Temperature Superconducting DC Feeder Cables

High-temperature superconducting (HTS) DC feeder cable has been proposed for reducing energy loss in railway systems. The feeder cables are required to be installed during the night using a quickly-fabricable low-resistive joint. A soldering technique has been widely used for connecting HTS round-shaped cables in transmission or feeder cable systems. In this study, we proposed applying press welding with indium at room temperature (cold pressure welding) or with heat treatment at 90–120 °C as an alternative candidate for the cable-to-cable joint. First, we examined the necessity of the pre-joint process, polishing the HTS tape, and pickling indium foil with 10% HCl as well as the joining temperature. The examination was performed using tape-to-tape joints with copper-alloy-laminated Bi-2223 tapes. The joint resistance and mechanical strength for railway application were satisfied even by a joint fabricated at room temperature skipping the above two pre-joint processes. Then, we fabricated straight and spiral joints of the model cable made of copper-alloy-laminated Bi-2223 tapes with various joining processes and spiral pitches. The joint resistivity for the model cable joint was less influenced by the joining process and spiral pitch and it was comparable to that of a single tape-to-tape joint. As a conclusion, press welding with indium with a simplified process, joining at room temperature, and skipping some of pre-joint processes can be applied to quick and simple joint fabrication of HTS DC feeder cable.

Systematic investigation of a NbTi-Bi2223 hybrid low-resistive joint

In this study, a NbTi-Bi2223 hybrid low-resistive joint fabricated by the superconducting solder method was systematically investigated. The joint is a necessary component of gigahertz nuclear magnetic resonance (NMR) with Bi2223 as the insert coil. The joint resistance and current capability under different applied magnetic fields were measured, and the resistance exhibited a near-linear relationship with the applied field. Beyond the superconducting properties, the allowed mechanical criteria for the Bi2223 tape in the joint were also briefly studied. Based on the above two properties, a 1.3 GHz NMR design with a NbTi-Bi2223 hybrid low-resistive joint was shown as an application demonstration. Although the current resistance can fit the magnetic-field decay criteria, obtaining a lower resistance value was attempted by extending the joint length but failed. The main source of the resistance in NbTi-Bi2223 was studied. We attempt to show an engineering-feasible NbTi-Bi2223 hybrid low-resistive joint to help improve the development of gigahertz NMR.

Analysis of critical current and hot spot behavior in Bi-2223 stacked-tape cable for fusion reactor

The cable-in-conduit-conductor (CICC) based on Bi2Sr2Ca2Cu3Ox (Bi-2223) tape has potential to be used in fusion magnets duo to its high current-carrying capacity under high field and low temperature. In this study, the optimized study on the stacked tape cable based on Bi-2223 tape was performed. The effect of the quantity of grooves and tapes on the critical current is studied by the finite element method, respectively. The comparison between the copper and aluminum frame on the quench behavior of cable is also discussed. The results shows that the critical current of cable is mainly determined by the quantity of tape in cable where the self-field effect has little impact on the critical current in 4.2 K and 15 T. The minimum quench energy (MQE) is proportional to the tape numbers where the MQE with copper frame is higher than that with aluminum frame. The hot spot temperature is decreased with tape numbers for cable with aluminum frame, however, the effect of tape numbers on the hot spot temperature of cable with copper frame is not obvious where the quench is triggered by MQE. Moreover, the cable with lower quantity of grooves shows higher stability compared with other variants containing the same number of tapes.

Predictable and robust performance of a Bi-2223 superconducting coil for compact isochronous cyclotrons

The development of ever smaller medical particle accelerators is motivated by a desire to make proton therapy accessible to more patients. Reducing the footprint of particle accelerators and subsequently proton therapy facilities allows for cheaper and broader usage of proton therapy. By employing superconducting technologies for field shaping, the size of particle accelerators can be reduced further below what is possible with saturated iron. This article discusses experiments on a first-of-its-kind double pancake (DP), and an assembly of six DP coils, designed to be used as a so-called ‘flutter coil’ for a compact isochronous cyclotron for proton therapy, fabricated from high-temperature superconducting (HTS) BiPb x Sr2Ca2Cu3O y (Bi-2223) tape. The coils were mounted under pre-stress within a stainless-steel structure to maintain mechanical stability during the experiments. The critical current as a function of the temperature of both coils was measured in a conduction-cooled setup. A model describing the coils, based on tape data, was created and revealed that the measurements were in excellent agreement with the predictions. Additional experiments were performed to study the quench and thermal runaway behaviour of the HTS coils, determining whether such coils can be protected against fault scenarios, using realistic quench-detection levels and discharge extraction-rates. These experiments demonstrate that the coils are very robust and can be well protected against quenches and thermal-runaway events using common quench-protection measures with realistic parameters.

An Improved Critical Current Calculation Method of HTS Field-Excitation Coil for Double-Stator HTS Generator With Stationary Seal

In this article, a calculation method for critical current of high-temperature superconducting (HTS) excitation coils made by Bi-2223 tapes is proposed, which can provide a reference for the design and manufacture of HTS excitation coils. Based on the test data provided by the manufacturer, the suppression effect of the applied parallel and perpendicular magnetic field on the critical current density is separately described by the proposed Jc-B model of the Bi-2223 tapes. Then, taking a 10 kW double-stator HTS machine (DS-HTSM) as an example, the target excitation magnetomotive force (MMF) required to meet its designed electromagnetic properties is obtained. After then, the turns number and the critical current of the HTS excitation coils required to meet the target MMF are calculated by the finite element analysis (FEA). Further, the FEA model of the DS-HTSM will be built by using the homogenization modeling method of HTS coils, and the influence of the armature reaction magnetic field on the critical current of the HTS excitation coils is analyzed. Finally, the correctness and effectiveness of the proposed improved critical current calculation method is verified by fabricating the 10 kW DS-HTSM prototype and conducting experimental test.

Vortex glass phase transition in two-dimensional Bi2Sr2Ca2Cu3O sub-microbridge

Vortex dynamics is crucial for practical applications and to understand the nature of the mixed state for high-T c superconductors. Mechanically exfoliated ultra-thin single crystals provide a unique platform for exploring vortex physics in the two-dimensional (2D) limit. Here, we systematically investigated the current–voltage (I–V) characteristics as functions of the temperature and magnetic field in a single-crystalline Bi2223 sub-microbridge of 2.5 unit cells thickness. The nonlinear I–V characteristics are excellently described by the scaling theory for a quasi-2D vortex glass (VG) phase transition, and a phase diagram revealing the VG and vortex liquid phase is drawn. The scaling parameter v is consistent with previous reports, while the critical exponent z is far smaller than that in most investigations. Moreover, the VG transition temperature T g of the present sample is higher than that in the reported Bi2223 epitaxial thin films and tapes. In addition, the pinning force density of our sample is calculated, which is stronger than that reported in Bi2223 epitaxial thin films and tapes. Our results indicate that a high pinning force density may suppress the dynamical critical exponent z and enhance the VG phase transition temperature, providing new insight into the flux dynamics in cuprates.

The effect of intermediate layer densification on the critical current of a Bi-2223 superconducting joint

The effect of intermediate layer densification on the critical current (I c) of Bi-2223 superconducting joints was quantitatively studied. First, we evaluated the phase purity, density, and intergrain critical current density (J c) of Bi-2223 thick film samples simulating the intermediate layer. The samples were uniaxially pressed to increase the film density. After two heat treatments of the pressed film, an increase in J c was achieved. Second, we fabricated superconducting joints by synthesizing an intermediate layer between two Bi-2223 tapes. Applying a uniform uniaxial pressure on the joint resulted in the formation of a homogeneous structure. This process enables the reproducible fabrication of superconducting joints with high n values. The I c of the superconducting joint was increased by intermediate pressing (IP) and two heat treatments. However, pressing at high pressures can mechanically damage filaments in the Bi-2223 tapes, leading to a decrease in I c. Sample characterization showed that the optimum IP pressure range to produce high I c was 1.5–2 × 108 Pa. We confirmed that pressing densified the intermediate layer of the superconducting joints. Our experimental results and analyses reveal that densification of the intermediate layer increases the I c of Bi-2223 superconducting joints.

Measurement of In-Field E-J Characteristics in Multi-Filamentary Bi-2223 Tapes at Ultra-Low Electric-Field Down to Around 10−13 V/m

We have developed a method to investigate in-field electric-field v.s. current-density (E-J) characteristics at ultra low electric field criterion around 10-13 V/m in a multi filamentary Bi-2223 tape at 5 K based on scanning Hall probe microscopy (SHPM). Bi-2223 is widely used in high field applications, e.g. a 30.5 T NMR magnet system is currently being developed in Japan. Ultra-low electric field is induced in such magnets operating in persistent current mode with extremely steady field. Namely, E-J characteristics need to be clarified around that criterion. E-J characteristics can be estimated from decay of magnetization in the whole sample, assuming the uniformity of J. But for multi filamentary Bi-2223 tape, magnetization current path should be clarified. In this study, we measured local magnetic field profile as a function of time for Bi-2223 tapes using SHPM. Additionally, we carried out flux annealing measurements to realize ultra-low electric field induced in the tape. As a result, two main messages we obtained. Experimental field profile or sheet current density obtained from the inverted Biot-Savart law indicated that filaments remain coupled up to high field, and even at ultra-low E criterion. Moreover, local E-J characteristics around 10-13 V/m are obtained at 5 K and 4.5 T of perpendicular magnetic field, which is comparable perpendicular field component in a Bi-2223 insert coil in the high field NMR magnet system. Ic properties at 10-12 V/m decrease to nearly 50%, in comparison to the transport Ic properties at 10-4 V/m.

Measurement of AC Loss Characteristics of HTS Sample Coils Under the Conditions Assumed for use in Power Electronics Devices

To examine the applicability of superconducting technology to fields of industrial applications such as linear conveyor, transfer, and transport systems, we investigated the AC loss characteristics of HTS sample coils under conditions assumed for use in power electronics devices. Since inverters are used in the drive circuit of power electronics devices in a linear transfer system and so on, the drive current contains harmonic components, and then it is expected that the AC losses increase. In this study, we measured the AC loss characteristics of the HTS sample coil by the liquid nitrogen boil-off method under various conditions in which the amplitude and frequency of the harmonic current were changed. The HTS sample coils were wound by a Bi-2223 tape. The outer diameter of the sample coil is about 60 mm, and the height is about 25 mm. As the result of the measurement, the AC loss increased in proportion to the square of the harmonic current amplitude and increased in proportion to the 1.5th power of the harmonic frequency. Based on the measured results, the increase of AC losses due to the harmonic current component was discussed.

Development of a Persistent Current Mode 9.39 T (400 MHz) LTS/Bi-2223 NMR Magnet With a Bi-2223 Superconducting Joint

We developed and operated a persistent current (PC) mode 9.39 T (400 MHz for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> H NMR) LTS/Bi-2223 NMR magnet using a Bi-2223 insert coil with a superconducting joint. Firstly, we developed a basic joining procedure to achieve the superconducting joint for the high-strength Bi-2223 tape used for the insert coil. We applied this procedure to the coil. Secondly, a stand-alone PC mode operation test for the coil at 4.2 K was performed. No apparent field decay was observed owing to the superconducting joint. Finally, we installed the coil inside the LTS outer coil's bore to form a PC mode LTS/Bi-2223 NMR magnet system. We successfully demonstrated a 9.39 T PC mode operation of the magnet though the current of the insert coil was limited to 5 A. The field drift rate was as low as 0.4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> ppm h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . The joint resistance was estimated to be < 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−12</sup> Ω at 4.2 K and 0.26 T. To our best knowledge, this is the first demonstration of a Bi-2223 superconducting joint that realized a PC mode LTS/Bi-2223 NMR magnet. This is an important step towards full-scale PC mode Bi-2223 magnets, including a 30.5 T (1.3 GHz) LTS/HTS NMR magnet.

Enhancement of Bi-2223 Intergrain Connections by Heat Treatment Parameters Optimization

Aiming at the improvement of current capacity in Bi₂Sr₂Ca₂Cu₃O_{10&#x002B;&#x03B4;} (Bi-2223) superconducting tapes, both the calcination process of precursor powders and the sintering process of Bi-2223 tapes have been modified to tune the intergrain connections. By adopting different calcination atmosphere of air and oxygen during the pre-calcination process, the phase composition of final precursor powder kept almost the same, while the particle size decreased in oxygen pre-calcinated powders, which thus led to the appearance of more secondary phases. On the other hand, due to the optimization of crystallization process of Bi-2223 phase, the microstructure with less pore density has been obtained, which proved that the increase of heating rate could obviously lead to the enhancement of intergrain connections of Bi-2223 tapes. Finally, critical current of 116 A has been achieved with the air pre-calcinated powders and 400 &#x00B0;C &#x002F;h heating rate during HT2, which was &#x223C;40&#x0025; increase comparing with the <i>I</i>_c of Bi-2223 tape with oxygen pre-calcinated powders and 100 &#x00B0;C&#x002F;h heating rate in HT2 process.

Progress in superconducting joints between Bi-2223 tapes

Abstract This is a viewpoint on the letter by Takeda, Kobayashi, Uchida et al. 2022 Supercond. Sci. Technol. 35 02LT02.

Critical current improvement and resistance evaluation of superconducting joint between Bi2223 tapes

We improved the critical current (I c) of the superconducting joint between the Bi2223 tapes by introducing the two-step sintering process. The in-field transport I c of ∼300 A at 4.2 K and 1 T under a 10−9 Ω criterion was successfully demonstrated. The I c improvement can probably be attributed to the enhancement of the intergrain critical current density for a Bi2223 intermediate layer. Ultra-low in-field joint resistance below 10−14 Ω at 4.2 K and 1 T was also demonstrated using current decay measurement. To the best of our knowledge, this study is the first to demonstrate a practical level of in-field transport I c and ultra-low in-field joint resistance for the superconducting joint between Bi2223 tapes. We believe that this superconducting joint technology will facilitate development of persistent current mode Bi2223 superconducting magnets.

Measurement of critical current of superconducting cable

The critical current of a coaxial cable made of Bi-2223 tapes was investigated to survey underlying problems, especially for the resistive voltage caused by current transfer, for the standardization of test method of the critical current of superconducting AC power cables. Five voltage taps were attached on the copper sheath of 80 mm long, which is used as a part of the current lead, on both ends for the inner conductor layer and outer shield layer. The current transfer was theoretically examined especially for the outer shield layer of a simple structure. The resistive component in the measured voltage was calculated as a function of the position of the voltage tap, and it can be shown that the critical current is correctly obtained using the electric field criterion after subtracting the resistive component, as is usually done in experiments. These results are compared with the observed results.