REBCO Wires Research Articles

Effect of epoxy impregnation on strain distribution of materials in Bi2223 superconducting coils by using synchrotron X-ray diffraction

Synchrotron X-rays have been used to observe strain distributions in composite materials such as superconducting wires with a thickness of less than about 2 mm. In applications that employ wound coils of superconducting wire, it is necessary to understand the strain distribution within the coiled wire. Superconducting wires such as Bi2223 and REBCO wires approximately 4–5 mm wide are commercially available. Coiled wires of this width are too thick to easily measure using conventional X-ray techniques, especially the inner strain, because the penetration depth tends to be around 2 mm. Therefore, the beam penetration must be improved, and it is known that the penetration depth of an X-ray beam depends upon the beam energy, beam intensity, measurement material, and measurement method. In this study, we used a white X-ray diffractometer at SPring-8 to develop a method of observing the strain distribution in Bi2223 superconducting coils winded by a 4.5 mm wide Bi2223 wire. We successfully observed a clear (400) peak of the Bi2223 phase by an appropriate measurement condition, and then observed the strains of each material in the Bi2223 coils with and without epoxy impregnation. This is the first time that we have obtained the strain of a Bi2223 phase in coiled wire using synchrotron X-ray diffraction. Further synchrotron-based study of superconducting coils will be useful in the development of advanced high-field magnets. The appropriate measurement method and the obtained measurement results are presented in this paper.

Development of Non-Circular REBCO Pancake Coil for High-Temperature Superconducting Cyclotron

A series of feasibility studies are carried out on the applications of a high-temperature superconducting (HTS) magnet system to a heavy-ion accelerator for particle cancer therapy. A novel HTS cyclotron is expected to be more compact and have higher efficiency than a conventional heavy ion synchrotron accelerator. A high current density is required for the HTS magnet to realize a compact HTS cyclotron. Further, a high-strength reinforcing structure is absolutely essential for the HTS magnet owing to the large Lorentz force caused by the high current density to prevent the magnet deformation and maintain the required high accuracy field. In a previous study, a novel coil structure called the Y-based oxide superconductor and reinforcing outer integrated “YOROI coil” was proposed and tested at 4.2 K in 8-T backup fields. The YOROI model coil exhibited no degradation after the excitation test with a maximum hoop stress of 1.7 GPa determined by the product of the magnetic field, current density, and coil radius. The mechanism of stress sharing between the coil winding and the reinforcing structures of the YOROI coil was numerically determined. In addition, the electromagnetic and mechanical properties of a reinforcing structure based on the YOROI coil for circular REBCO coils assuming part of the HTS cyclotron magnet system was also numerically simulated in the previous paper. In this study, a new reinforcing structure is proposed on the basis of the YOROI coil for a non-circular REBCO coil assuming part of the HTS cyclotron magnet system. The electromagnetic and mechanical properties for the new reinforcing structure are numerically determined. As a result, the proposed reinforcing structure has great ability to reduce the stress and strain acting on the coil winding to maintain the coil shape and prevent degradation in the REBCO wire.

An applicable calorimetric method for measuring AC losses of 2G HTS wire using optical FBG

We present a new calorimetric method for measuring alternative current (AC) losses of high-temperature superconducting (HTS) tapes by optical fiber Bragg grating (FBG), which is particularly well suited for the AC loss measurement of ReBCO wires, so-called the second generation (2G) HTS wires. Compared with conventional calorimetric methods, the suggested method is both free of electromagnetic disturbance, magnetic field, and fast as well as simple. Self-field AC losses are measured by the optical FBG method and the conventional lock-in-amplifier (LIA) technique, respectively. The results show that the measured AC loss is in good agreement with those measured by the electric method, thus the presented calorimetric method would be available for measuring the AC loss of 2G wire and is expected to be generalized for the measurement of AC loss or thermal performances of HTS bulk.

Project Overview of HTS Magnet for Ultra-high-field MRI System

A project to develop an ultra-high-field magnetic resonance imaging (MRI) system based on HTS magnets using (RE)Ba2Cu3O7 (REBCO; RE=rear earth) coils is underway. The project is supported by the Japanese Ministry of Economy, Trade and Industry and aims to establish magnet technologies for a whole-body 9.4 T MRI system. REBCO wires have high critical current density in high magnetic fields and high strength against hoop stresses, and therefore, MRI magnets using REBCO coils are expected to have cryogenic systems that are smaller, lighter, and simpler than the conventional ones. A major problem in using REBCO coils for MRI magnets is the huge irregular magnetic field generated by the screening current in REBCO tapes. Thus, the main purpose of this project is to make the influence of this screening current predictable and controllable. Fundamental technologies, including treatment of the screening currents, were studied via experiments and numerical simulations using small coils. Two types of model magnets are planned to be manufactured, and the knowledge gained in the development of the model magnets will be reflected in the magnet design of a whole-body 9.4 T MRI system.

Development of REBCO HTS Magnet of Magnetic Bearing for Large Capacity Flywheel Energy Storage System

A flywheel energy storage system (FESS) is a promising electrical storage system that moderates fluctuation of electrical power from renewable energy sources. The FESS can charge and discharge the surplus electrical power repetitively with the rotating energy. Particularly, the FESS that utilizes a high temperature superconducting magnetic bearing (HTS bearing) is lower loss than conventional FESS that has mechanical bearing, and has property of longer life operation than secondary batteries. The HTS bearing consists of a HTS bulk and double-pancake coils used 2nd generation REBCO wires. In the development, the HTS double-pancake coils were fabricated and were provided for a levitation test to verify the possibility of the HTS bearing. We successfully confirmed the magnetic field was achieved to design value, and levitation force in the configuration of one YBCO bulk and five double pan-cake coils was obtained to a satisfactory force of 39.2kN (4 tons).

A Suitable Design Method of SMES Coil for Reducing Superconducting Wire Usage Considering Maximum Magnetic Flux Density

Generally, high magnetic flux density is adopted in superconducting magnetic energy storage (SMES) coil design to reduce superconducting coil size and increase energy density. However, critical current density of the SMES coil is degraded by applying the high magnetic flux density to superconducting wire. This means that adopting the high magnetic flux density is not necessarily suitable for the superconducting wire reduction of the SMES coil. In this paper, the relationship between the maximum magnetic flux density within coil and superconducting wire usage of the SMES coil composed of solenoid or toroidal coil wound by MgB2, Bi2223, or REBCO wire was investigated. As a result, most suitable magnetic flux density within SMES coil for realizing the minimum superconducting wire usage in MgB2 , Bi2223, and REBCO wires were clarified. How to estimate the most suitable maximum magnetic flux density within coil for realizing the minimum wire usage in each superconducting wire was also investigated. Comparison between the rate of change of coil radius times maximum magnetic flux density and critical current density with respect to the maximum magnetic flux density is useful for obtaining the suitable maximum magnetic flux density for the minimum superconducting wire usage.

Recent R&D on Superconducting Wires for High-Field Magnet

Development for superconducting wires of materials such as Nb3Al and the high-temperature superconductors (HTS such as REBCO, Bi2223, and Bi2212) has been carried out for high-field magnet applications. It is known that these types of wire exhibit very different characteristics and performance for different applications. The development of Nb3Al wire for high-field accelerator magnet has resulted in remarkable achievements in critical current using a Rapid Heating and Quenching (RHQ) method by High Energy Accelerator Research Organization (KEK) and National Institute for Materials Science (NIMS). As one example of a characteristic of Nb3Al, the strain sensitivity of the critical current in the RHQ-Nb3Al wire is better than that of Nb3Sn wire. A strain study is needed to further the development of a high-filed magnet; therefore, we have carried out experimental studies using the neutron diffractometer at J-PARC Takumi. Researchers have recently achieved the highest critical current density for REBCO wires in a high-field above 15 T. For this reason, REBCO wire has been considered for high-field magnet NMR applications in Riken. But several obstacles remain, including coil degradation, shielding current and thermal runaway. In this paper, R&D on recent advances for applications will be presented.

Small Layer-wound ReBCO Solenoids

Abstract The development of the next generation of high field superconducting magnet systems demands studies of new technological approach for its internal sections. Several small HTS solenoids (21 mm inner diameter, 32 layers) were fabricated by layer-winding technique from SuperPower type SCS-4050 ReBCO wire insulated by polyimide wrapping. Different designs of external and internal joints also were also tested. The highest field generated by HTS coil was 2.4 T in a 10 T background field (total field was 12.4 T) at 4.2 K and achieved current density in the coil was 498 A/mm 2 . The results will be used in development of HTS inner sections for 25 T superconducting magnet.

Design and Evaluation of 66 kV-class “3-in-One” HTS Cable Using REBCO Wires

Abstract Sumitomo Electric (SEI) has been involved in the development of 66 kV-class HTS cables using REBCO wires. One of the technical targets is to reduce the AC loss to less than 2 W/m/phase at 5 kA. SEI has developed a clad-type textured metal substrate with lower magnetization loss than NiW substrate. REBCO tapes 30 mm-wide were slit into 4 mm-wide strips, and these strips were wound spirally on a former with small gaps. The measured AC loss of the manufactured cable was 1.8 W/m/phase at 5 kA, achieving the AC loss goal.

Development of 66kV class REBCO superconducting cable

Abstract Sumitomo Electric Industries (SEI) has been involved in the development of 66 kV/5 kA-class HTS cables using REBCO wires. One of the technical targets was to reduce the AC loss to less than 2 W/m/phase at 5 kA. SEI developed a clad-type textured metal substrate with lower magnetization loss than NiW substrates. REBCO wires of 30 mm wide were slit into 4 mm-wide strips, and these strips were wound spirally on a former with small gaps. The measured AC loss of the manufactured cable was 1.8 W/m/phase at 5 kA, achieving the AC loss goal. Another important target was to manage fault current. The copper protection layers were designed based on simulation findings. Fault current tests (max. 31.5 kA, 2 sec) showed that the designed HTS cable has the required withstanding performance. The development of the elemental technologies was finished on schedule, and a 15 m-long HTS cable system will be constructed to demonstrate that it meets all the required specifications.

Evaluation of the Screening Current in a 1.3 GHz NMR Magnet Using ReBCO

NMR magnets using high-Tc superconductors (HTS) are currently by several organizations designed to generate high fields exceeding 25 T. In such designs, the HTS are used for the inner coils, and the outer coils consist of NbTi and Nb3Sn wires. A ReBCO wire with a Hastelloy substrate has excellent critical current performance over wide range of magnetic fields and tolerates high tensile stress up to 700 MPa. We have previously shown conceptual designs in which the main coils are assumed to use ReBCO wires. The designs suggest the potential to realize much more compact and lightweight magnets than conventional magnets with low-Tc superconductors (LTS) and HTS. On the other hand, the problem of screening current induced by the perpendicular field remains to be solved. In this study, we evaluate numerically the amount of the magnetic field generated by the screening current in ReBCO coils. Compensation coils for improving field homogeneity were found to reduce the shielding current by several percentage points. The improved coil arrangement is reported considering the shielding current effect.

Design and Evaluation of 66 kV Class HTS Power Cable Using REBCO Wires

High temperature superconducting (HTS) cables achieve large power capacity and low-loss power transmission in a compact package. In a new Japanese national project, Sumitomo Electric Industries, Ltd. is working to develop a 66 kV–5 kArms HTS cable with REBCO wires. One of the important technical targets is to reduce AC loss to less than 2 W/m/ph at 5 kArms. To investigate the effect of wire width on the AC losses in multi-layer cable conductors, 30-mm-wide REBCO tapes were divided into 4-mm-wide or 2-mm-wide strips, and two 4-layer cable conductors were manufactured with these strips. The measured AC loss characteristics of the two cable conductors were comparable. The measured AC loss in the cable conductor with 4-mm-wide wire was in good agreement with numerical calculations. However, the AC loss in the cable conductor with 2-mm-wide wires was larger than the numerical prediction. The difference may be due to the wires' non-uniform <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$J_{c}$</tex> </formula> distribution in the width direction, because the AC losses in cable conductors with narrow wires are strongly influenced by the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$J_{c}$</tex></formula> profiles of the wires. AC loss simulations assuming that the wire's <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$I_{c}$</tex> </formula> will be higher show that a 14000 A- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$I_{c}$</tex></formula> class cable with 4-mm-wide wires is expected to achieve the AC loss target. For cables with 2-mm-wide wires, the improvement of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$J_{c}$</tex> </formula> distribution in the width direction will reduce the AC loss level, and the goal will be achieved with lower <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$I_{c}$</tex></formula> wires.

Design and evaluation of 66 kV-class HTS power cable using REBCO wires

Sumitomo Electric (SEI) has been involved in the development of 66kV-class HTS cables using REBCO wires. One of the technical targets in this project is to reduce the AC loss to less than 2W/m/phase at 5kA. SEI has developed a clad-type of textured metal substrate with lower magnetization loss compared with a conventional NiW substrate. In addition, 30mm-wide REBCO tapes were slit into 4mm-wide strips, and these strips were wound spirally on a former with small gaps. The AC loss of a manufactured 4-layer cable conductor was 1.5W/m at 5kA at 64K. Given that the AC loss in a shield layer is supposed to be one-fourth of a whole cable core loss, our cables are expected to achieve the AC loss target of less than 2W/m/phase at 5kA. Another important target is to manage a fault current. A cable core was designed and fabricated based on the simulation findings, and over-current tests (max. 31.5kA, 2s) were conducted to check its performance. The critical current value of the cable cores were measured before and after the over-current tests and verified its soundness. A 5kA-class current lead for the cable terminations was also developed. The current loading tests were conducted for the developed current leads. The temperature distribution of the current leads reached to the steady-state within less than 12h, and it was confirmed that the developed current lead has enough capacity of 5kA loading.

Progress in Scale-Up of RE-123 Coated Conductors With $I_{c}$ of 300 A/cm by IBAD/PLD Process

By an IBAD/PLD method, a 500 m-length high-performance GdBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (GdBCO) coated conductor with BaZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BZO) was fabricated. End-to-end I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of the 503.5 m tape was 349.6 A/cm at 77 K, corresponding I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> times L value of 176,023 Am. New approaches to decrease the thickness of IBAD buffer layers were developed by combination of IBAD-MgO(111) and IBAD-Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (GZO). The maximum Jc of the GdBCO on the buffer layer was 550 A/cm. We also started to investigate IBAD-MgO(OOl) by using a large IBAD system with a 110 cm times 15 cm ion source. A 50 m-length IBAD-MgO tape with DeltaPhi of 13deg was fabricated at a 100 m/h-1 pass. Insulated REBCO wires with Cu or Ni-Cr lamination were developed using 5 mm-wide conductors sliced from 10 mm-wide IBAD/PLD tapes. Practical long insulated wires were supplied for several prototypes of motors, transformers and fault current limiters in fiscal 2007.