Experiment and numerical simulation of the combined effect of winding, cool-down, and screening current induced stresses in REBCO coils

This paper overviews the combined effects of winding, cool-down, and screening current-induced stresses in REBCO coils. First, a simulation method to model the circumferential stress modification effect due to the screening-current is overviewed. The simulation includes coil winding, cooling down, and coil charge up to the operating current. Second, we will compare the numerical simulation results with the experimental results. The numerical simulations for a dry coil and an epoxy impregnated coil agree well with the experimental results. Third, the enhanced circumferential stress did not degrade the performance of a dry winding REBCO coil, but the improved increased compressive stress buckled the coil structure. Finally, it is demonstrated that epoxy impregnation has beneficial effects in reducing the stress modification effect. However, the circumferential stress is enormously enhanced at the coil ends, sometimes resulting in degradation of the coil performance

Microstructural Analysis of Superconducting Joint Fabricated Using CJMB Between Gd123-coated Conductors

A superconducting joint between two Gd123-coated conductors was successfully formed using crystal growth in the bulk (CJMB). An intermediate Yb123 layer was used at the junction, and was melted to form a joint by heat treatment at a temperature below the melting point of the RE123 (such as Gd123) in the coated conductor. This liquid-phase bonding results in high tensile strength, which has exceeded 100 MPa in previous studies. Nevertheless, the joint principle has not been sufficiently clarified. In this study, we performed microstructural analysis of the joint using X-ray diffraction and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy to form a clearer understanding of the joint formation mechanism in order to achieve a high critical current in the junction

Fabrication of 16-main-core RE123 split wire using inner split method

For application to ultrahigh-field nuclear magnetic resonance spectroscopy (e.g., 30 T), we have started to develop a REBa2Cu3O7-δ (RE123, RE: rare earth) multi-core coated conductor in which the ceramic layers (RE123 and buffer layers) are electrically separated to create multiple filaments. This method is called electrical separation by inner splitting, and the wire is called a split wire. The multi-core structure is fabricated using electrical separation by a phase stress, which utilizes the difference in toughness between ceramics and metal, such as partial V-bending by stress along the longitudinal direction of the coated conductor using a commercially available single-core RE123 coated conductor. In addition, about 10 narrow cores (width: 5-15 μm) can be formed by one bending. These cores are called subcores. The wire is composed of main cores and subcores. In this study, a 4 mm wide multifilamentary RE123 split wire with 16 main cores and 150 subcores was fabricated and evaluated. The manufacturing method, microstructure, and critical current properties under an external magnetic field and tension are presented

Simplified and optimized multispectral imaging for 5-ALA-based fluorescence diagnosis of malignant lesions

5-aminolevulinic acid (5-ALA)-based fluorescence diagnosis is now clinically applied for accurate and ultrarapid diagnosis of malignant lesions such as lymph node metastasis during surgery. 5-ALA-based diagnosis evaluates fluorescence intensity of a fluorescent metabolite of 5-ALA, protoporphyrin IX (PPIX); however, the fluorescence of PPIX is often affected by autofluorescence of tissue chromophores, such as collagen and flavins. In this study, we demonstrated PPIX fluorescence estimation with autofluorescence elimination for 5-ALA-based fluorescence diagnosis of malignant lesions by simplified and optimized multispectral imaging. We computationally optimized observation wavelength regions for the estimation of PPIX fluorescence in terms of minimizing prediction error of PPIX fluorescence intensity in the presence of typical chromophores, collagen and flavins. By using the fluorescence intensities of the optimized wavelength regions, we verified quantitative detection of PPIX fluorescence by using chemical mixtures of PPIX, flavins, and collagen. Furthermore, we demonstrated detection capability by using metastatic and non-metastatic lymph nodes of colorectal cancer patients. These results suggest the potential and usefulness of the background-free estimation method of PPIX fluorescence for 5-ALA-based fluorescence diagnosis of malignant lesions, and we expect this method to be beneficial for intraoperative and rapid cancer diagnosis

Observation of an Unusual Magnetic Anomaly in the Superconducting Mixed State of Heavy-Fermion Compound UBe13 by Precise dc Magnetization Measurements

We have performed precise dc magnetization measurements for a single crystal of UBe13 down to 0.14 K, up to 80 kOe. We observed a magnetic anomaly in the superconducting (SC) mixed state at a field, named H*_[Mag] (～26 kOe, at 0.14 K), implying that UBe13 has a magnetically unusual SC state. We studied the magnetization curves of UBe13, assuming that the H*_[Mag] anomaly originates from (1) and unusual SC diamagnetic response, or (2) a peculiarity of the normal-state magnetization due to vortices in the SC mixed state. The origin of the H*_[Mag] anomaly is discussed

Experiment and numerical simulation of the combined effect of winding, cool-down, and screening current induced stresses in REBCO coils

This paper overviews the combined effects of winding, cool-down, and screening current-induced stresses in REBCO coils. First, a simulation method to model the circumferential stress modification effect due to the screening-current is overviewed. The simulation includes coil winding, cooling down, and coil charge up to the operating current. Second, we will compare the numerical simulation results with the experimental results. The numerical simulations for a dry coil and an epoxy impregnated coil agree well with the experimental results. Third, the enhanced circumferential stress did not degrade the performance of a dry winding REBCO coil, but the improved increased compressive stress buckled the coil structure. Finally, it is demonstrated that epoxy impregnation has beneficial effects in reducing the stress modification effect. However, the circumferential stress is enormously enhanced at the coil ends, sometimes resulting in degradation of the coil performance