Faculty Profiles - UEDA Hiroshi

Papers - UEDA Hiroshi

Division display 21 - 40 of about 161 ／ All the affair displays >>

Turn-to-Turn Contact Resistance Measurement of NI REBCO Double Pancake Coils Reviewed International journal

Takanobu Mato, Ryota Inoue, Hiroshi Ueda, SeokBeom Kim, So Noguchi

IEEE Transactions on Applied Superconductivity 34 ( 3 ) 1 - 5 2024.5

Contact Resistance and Current Characteristics of NI HTS Coils in Low Frequency AC Method Reviewed International journal

SeokBeom Kim, Hirotaka Kobayashi, Daiki Sato, Ryota Inoue, Hiroshi Ueda, Takanobu Mato, So Noguchi

IEEE Transactions on Applied Superconductivity 33 ( 5 ) 1 - 5 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

The development of high-performance HTS magnets requires a method to correctly measure the contact resistance between turns of no-insulation (NI) coils. We have proposed a method to measure the turn-to-turn contact resistance of NI coils using low frequency alternating current (LFAC). In the LFAC method, AC current is used, and it is assumed that all the AC current flows in the radial direction of the NI HTS coil. To confirm the reliability of the proposed measurement method, AC current distribution characteristics were evaluated using four (quarter circle, 1/4 size) pickup coils in a previous study. The pickup coils were mounted under the NI test coils and the current bypass characteristics from circumferential to radial direction were evaluated as a function of frequency. However, the size of the fabricated four pickup coils was relatively large compared to the test coil, so its sensitivity and spatial resolution were not sufficient. Therefore, in this article, we prepared eight pickup coils smaller than the 1/4 size pickup coil used in the previous study. Two test coils with winding tensions of 0.5 and 1 kg were prepared, and the non-uniformity of the contact resistance of both NI coils was detected using eight pickup coils.**We also identified locations in the test coil where the contact resistance changed due to multiple cooling cycles by liquid nitrogen.

DOI： 10.1109/tasc.2023.3248519

Analyses of deformation due to screening-current-induced force in layer-wound REBCO insert coil for 1.3-GHz LTS/HTS NMR Reviewed International journal

Keisuke Naito, Ryo Harada, Ryota Inoue, SeokBeom Kim, Hiroshi Ueda, Yu Suetomi, Yoshinori Yanagisawa, Hideaki Maeda

IEEE Transactions on Applied Superconductivity 33 ( 5 ) 1 - 5 2023.8

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

REBCO wires have high critical current density and thermal stability, and are being applied in various fields such as NMR, MRI, and accelerators. We are currently designing a 1.3-GHz LTS/HTS NMR magnet that operates in a persistent current (PC) mode. However, there are issues with using REBCO coils that need to be resolved. One problem unique to REBCO coils is non-uniform electromagnetic forces caused by screening currents. During the charging and discharging of the coil, screening currents are induced, resulting in a significantly non-uniform current distribution within the coil. As a result, non-uniform electromagnetic forces are generated within the coil due to these screening currents. In this study, we performed an electromagnetic stress analysis using a two-dimensional axisymmetric structural analysis that considered tension during winding, thermal stress during cooling, and electromagnetic force during charging. First, we compared the results of the numerical simulation of the layer-wound REBCO coil with the experimental results. Then, we conducted numerical simulations of an insert REBCO coil in a design example of a 1.3-GHz NMR to evaluate the stress and deformation of the REBCO coil.

DOI： 10.1109/tasc.2023.3259923

Investigation of HTS Coil Structure Robustness Against Misalignment Between Coils in a Wireless Power Transmission System for Railway Vehicles Reviewed International journal

Ryota Inoue, Yuta Inoue, Hiroshi Ueda, SeokBeom Kim

IEEE Transactions on Applied Superconductivity 33 ( 5 ) 1 - 5 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

A wireless power transmission (WPT) system using high-temperature superconducting (HTS) coils has been investigated. However, it is difficult to precisely match the positions of the primary and secondary coils. Thus, the HTS coil structure with high misalignment tolerance is required. In this paper, we investigated the non-circular HTS coil structure with a high quality factor for the WPT system, such as a rectangular coil and a racetrack coil. Also, we evaluated the power transmission characteristics of the WPT system using the non-circular HTS coils. As a result, the quality factor of the non-circular HTS coils was maximum when the radial gap between turns was almost the same as the HTS wire width, and increased with increasing coil length in a rail longitudinal direction. Also, the receiving power and the system efficiency using the non-circular HTS coils were more robust against misalignment between coils than those using the circular HTS coils. On the other hand, the receiving power decreased with increasing the coil length of the non-circular HTS coils in the rail longitudinal direction due to thermal radiation from normal temperature. From the above, the receiving power of the WPT system with small lateral misalignments can be improved by using the rectangular coils with a short coil length in the rail longitudinal direction in parallel. Moreover, the system efficiency of the WPT system with large lateral misalignments can be improved by using the rectangular coils or the racetrack coils with a long coil length in the rail longitudinal direction.

DOI： 10.1109/tasc.2023.3252490

Experimental Study on the Critical Current Properties of Flexible Nb₃Al Superconducting Wires in Cryocooler System Reviewed International journal

Hibiki Fukuda, Riku Onoue, Tomoya Sakamoto, Ryota Inoue, Hiroshi Ueda, SeokBeom Kim, Akihiro Kikuchi, Yasuo Iijima

IEEE Transactions on Applied Superconductivity 33 ( 5 ) 1 - 5 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

In recent years, Jelly-rolled Nb/Al composite monofilament Nb3Al superconducting wires with an outer diameter of 30 μm, and multi-stranded Nb3Al wires were successfully fabricated by NIMS in Japan. So, it is necessary to measure the temperature dependence of the critical current of Nb3Al wires in cryocooler system for development of superconducting applications cooled by conduction cooling method. The single and multi-stranded ultrafine Nb3Al superconducting sample wires with different outer diameter were prepared to evaluate the critical current properties. The critical currents of sample wires were evaluated by the current sweep method and constant current method. In this study, the sample wires were soldered to the copper wire to prevent burnout of the sample wire during critical current measurements. Therefore, the amount of current shunted to the copper wire was estimated to accurately evaluate the critical current of the superconducting wire. Also, the critical current of Nb3Al wires due to bending strain (bending radius of 5 to 15 mm) was experimentally investigated. From the critical current measurement results of Nb3Al wires with different cross-sectional structures, it was confirmed that the superconducting properties of the wires were improved by reducing the wire diameter. It was shown that the critical current density of the developed Nb3Al wire is lower than that of REBCO wire, but higher than that of commercial NbTi and Nb3Sn wires.

DOI： 10.1109/tasc.2023.3258911

Basic Study of a Wireless Power Transmission System Using Superconducting Coil as a Ground-Side Coil for Electric Vehicles Reviewed International journal

Yuta Inoue, Ryota Inoue, Hiroshi Ueda, SeokBeom Kim

IEEE Transactions on Applied Superconductivity 33 ( 5 ) 1 - 5 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

We proposed a large-capacity wireless power transmission (WPT) system for the electric vehicle in which a high-temperature superconducting (HTS) coil is installed only on the ground side. On the other hand, the design guideline of the 100 kW class WPT system using the HTS and the copper coils for EVs has not been sufficiently discussed. Therefore, we analyzed the electric power transmission characteristics of the 100 kW class proposed WPT system using the HTS coil and the copper coil by an electromagnetic field analysis using the finite element method (FEM) and an equivalent circuit analysis. Also, we investigated the effect of a cooling temperature of the HTS coil on the receiving power and the transmission efficiency of the proposed WPT system for EVs. As a result, we found that the proposed WPT systems using the high-inductance primary and secondary coils are suitable for a low-frequency operation around 1 kHz. On the other hand, the proposed WPT systems with high-frequency operation above 10 kHz are suitable for reducing the weight of the secondary coil. In addition, although the system efficiency considering the cryocooler power loss is reduced by decreasing an operating temperature of the primary HTS coil, it is possible to realize a large-capacity WPT system with the receiving power of more than 100 kW.

DOI： 10.1109/tasc.2023.3247685

Investigation into accuracy of turn-to-turn contact resistance measurement in low-frequency AC method by 3D numerical simulation Reviewed International journal

Takanobu Mato, Ryota Inoue, Hiroshi Ueda, Seok Beom Kim, So Noguchi

Superconductor Science and Technology 36 ( 1 ) 2023.1

Language：English Publishing type：Research paper (scientific journal)

In this paper, we discuss two points: (a) the accuracy of contact resistance measurement using the low-frequency AC (LFAC) method and (b) the relation between the contact resistance and the contact resistivity. The LFAC method is used to measure the turn-to-turn contact resistance of a no-insulation (NI) rare-earth barium copper oxide (REBCO) pancake coil. We have previously shown the validity of the LFAC method by experiment. In this paper, the current distribution of aNI REBCO pancake coil on the applyication of the LFAC method is investigated using numerical simulation. The simulation results show the possibility of improving the measurement accuracy. Hence, a correction method is also proposed using the phase difference of the coil voltage and current. The LFAC simulation results also indicate the inconsistency of the well-known relation between contact resistance and contact resistivity. Therefore, we investigated the relation through the LFAC and sudden-discharging test simulations.

DOI： 10.1088/1361-6668/aca5b9

Mechanical Strength Evaluation of a Yoroi-Coil Structured Non-Circular REBCO Pancake Coil in High Magnetic Field Reviewed International journal

Tomonori Watanabe, Shigeo Nagaya, Atsushi Ishiyama, So Noguchi, Hiroshi Ueda, Gen Nishijima

IEEE Transactions on Applied Superconductivity 32 ( 6 ) 2022.9

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

In order to achieve a high intensity and compact multifunctional air-core cyclotron, the behavior of non-circular coils in a high magnetic field at 4.2 K were investigated. Two types of isosceles triangle shaped double-pancake coils: a coil with reinforcement by Yoroi-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structuring and a coil without reinforcement, were manufactured and their behaviors were observed when current was applied to each coil in a high magnetic field. The non-reinforcement coil showed in 10 T external magnetic field that the superconducting properties of the coil were partially lost and a voltage generated in the coil winding was observed when the applied current exceeded 160 A. After disassembling this coil, it was found that the superconducting tape in the coil winding was plastically deformed and permanently bent at the corners. The reinforced coil due to Yoroi-coil structuring was powered up to the coil current of 300 A in a magnetic field of 14 T. A voltage of 0.3 mV was observed when the coil current was 277 A, and the excitation was terminated when the voltage reached 0.6 mV at 300 A. The coil winding, after the current flowing up to 300 A in 14 T field, indicated that the deformation of it was significantly limited. It was confirmed that the Yoroi-coil type structural reinforcement, even for triangular coils, has sufficient mechanical strength under the conditions of our air-core cyclotron.

DOI： 10.1109/TASC.2022.3149232

Numerical Evaluation of Screening Current-Induced Magnetic Field in REBCO Coil System for Skeleton Cyclotron Using a Full-Scale Model Reviewed International journal

Kodai Shirai, Atsushi Ishiyama, Hiroshi Ueda, So Noguchi, Tomonori Watanabe, Shigeo Nagaya, Mitsuhiro Fukuda

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 32 ( 6 ) 2022.9

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

We have been developing a new-generation accelerator named high-temperature superconducting skeleton cyclotron (HTS-SC), an extremely compact and high-intensity accelerator capable of producing At-211 for targeted alpha-particle therapy, which is expected to be effective in treating advanced cancer. The coil system for HTS-SC consists of multiple air-core REBCO coils that create a magnetic field of high intensity and precision required for particle acceleration. The HTS-SC needs high-precision magnetic field distribution and temporal stability in the particle acceleration plane. However, the magnetic field induced by the screening current in the REBCO tape (SCIF: Screening Current-Induced magnetic Field) deteriorates the quality of the generated magnetic field spatially and changes it temporally. Therefore, in this paper, the SCIF is evaluated based on numerical analysis for a full-scale REBCO coil system designed for targeted alpha-particle therapy. In addition, the effect of the overshoot method, which is one of the current waveform control methods used to reduce the effect of SCIF on temporal stability, is investigated.

DOI： 10.1109/TASC.2022.3171195

An Optimal Configuration Method of Superconducting Magnet With Iron Shield Using Model Order Reduction Reviewed International journal

So Noguchi, Hiroshi Ueda, Tomonori Watanabe, Shigeo Nagaya, Atsushi Ishiyama, Mitsuhiro Fukuda

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 32 ( 6 ) 2022.9

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

We have been developing a cyclotron accelerator for radioisotope production of medical use. The features of developed cyclotron system are compactness, light weight, and multi energy outputs. To achieve such features, coils are wound with rare-earth barium copper oxide (REBCO) tapes and the magnet has no iron core to generate an azimuthal varying field (AVF). To install the developed cyclotron accelerator into hospitals, an iron shield is needed for protection of leakage radiation and magnetic field. In this paper, to optimally design main coils with iron shield, a fast field computation method called "Model Order Reduction (MOR)" is adopted. Using MOR technique, the field computation is accelerated similar to 50 times. The error of MOR field computation is sufficiently small. Hence, the MOR is effective in the optimal configuration design of coils with iron shield. The optimized configuration of a miniaturized cyclotron accelerator magnet is also shown.

DOI： 10.1109/TASC.2022.3175454

Basic study on power transmission characteristics for high-temperature superconducting cable termination applying a wireless power transmission system Reviewed International journal

Ryota Inoue, Hiroshi Ueda, Seokbeom Kim

IEEE Transactions on Applied Superconductivity 32 ( 6 ) 1 - 1 2022.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

We devised an HTS cable termination applying a wireless power transmission (WPT) system. The WPT system for the HTS cable termination can mechanically separate the HTS cable (low temperature part) from the copper cable (normal temperature part). In order to clarify the feasibility and design guidelines of the WPT system for the HTS cable termination, it is necessary to investigate the power transmission characteristics of the WPT system using the HTS and copper coils. In this study, we analyzed the power transmission characteristics of the simple WPT model system for the HTS cable termination by an equivalent circuit model and a finite element method analysis, and investigated the basic coil structure for the HTS cable termination applying the WPT system. As a result, the high-efficiency WPT system for the HTS cable termination can be realized by increasing the transport current of the HTS coil more than that of the copper coil. Also, we found that the HTS-Cu system using the primary-side HTS coil and the secondary-side copper coil is suitable for the HTS cable termination applying the WPT system.

DOI： 10.1109/tasc.2022.3167933

Study on Low-Loss and High-Energy Density Coil Structure of a Wireless Power Transmission System Using High Temperature Superconducting Coils for Railway Vehicle Reviewed International journal

Ryota Inoue, Hiroshi Ueda, Seokbeom Kim

IEEE Transactions on Applied Superconductivity 32 ( 6 ) 1 - 1 2022.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

We have been investigating a wireless power transmission (WPT) system using a high-temperature superconducting (HTS) coil for a railway vehicle. In the previous research, we investigated the conceptual design of the WPT system using the HTS coils for the railway vehicle. However, in order to suppress the AC loss per HTS coil below the cooling power of a cryocooler, it was necessary to install multiple HTS coils in parallel on the vehicle and ground sides. Therefore, we investigated the low-loss and high-energy density coil structure in the WPT system for the railway vehicle. In this study, we analyzed the AC loss and the coupling coefficient of various HTS coil structures using the narrow REBaCuO (RE: Rare Earth elements, REBCO) wires in parallel by finite element method (FEM) calculation, and evaluated the power transmission characteristics of the WPT system using the HTS coil structures using the narrow REBCO wires in parallel for the railway vehicle. As a result, we found that the AC loss of the HTS coil structure using the narrow REBCO wires in parallel was lower than that using the wide REBCO wire. The coupling coefficient between coils using a single pancake coil structure was higher than that using a double pancake coil structure. Also, the receiving power density of the WPT system was improved by the HTS coil structures using the narrow REBCO wires. Particularly, the receiving power density of the single pancake coil using the twisted narrow wire in parallel in the coil radial direction increased to about 1.5 times that of the single pancake coil using the wide wire.

DOI： 10.1109/tasc.2022.3169997

Study on the magnetic properties of metal substrates at low temperature by fabricated compact SST Reviewed International journal

Kazuki Kume, Ryota Inoue, Hiroshi Ueda, Seokbeom Kim

IEEE Transactions on Applied Superconductivity 32 ( 6 ) 1 - 1 2022.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

In recent years, a development of a high magnetic field magnet using a high temperature superconducting (HTS) wire has been advanced. On the other hand, we are planning to use the HTS wires for superconducting applications cooled by cryocooler. So, it is necessary to measure the temperature dependence of the magnetic properties of the metal substrates (Hastelloy, stainless steel and NiW) for HTS wire under conduction cooling conditions. We have been developing a single sheet tester (SST) that can evaluate the magnetic properties of electromagnetic steel sheets and other materials. However, since the size of an excitation coil in the conventional SST is large, it is difficult to install them in the conduction cooling system. In this study, we fabricated the compact SST and its measurement accuracy was compared with the conventional SST. The magnetic properties of metal substrates were measured at room temperature and liquid nitrogen temperature (77 K). As a result, although the measurement accuracy of the compact SST was slightly reduced by decreasing the coil size, we found that the error of the magnetic field homogeneity of the compact SST was within 2% at the center region of the 5 mm length. The magnetic properties of Hastelloy and stainless steel were almost unchanged at both room temperature and liquid nitrogen temperature. However, the magnetic properties of the NiW substrate changed significantly at liquid nitrogen temperature. The B-H characteristics of the NiW substrate in the rolling and transverse directions were clearly different, and the iron loss increased significantly at liquid nitrogen temperature.

DOI： 10.1109/tasc.2022.3159499

Critical Characteristics of Ultrafine Nb₃Al Superconducting Wires Under Conduction Cooling Conditions Reviewed International journal

SeokBeom Kim, Hibiki Fukuda, Ryo Kimura, Ryota Inoue, Hiroshi Ueda, Akihiro Kikuchi, Yasuo Iijima

IEEE Transactions on Applied Superconductivity 32 ( 6 ) 1 - 5 2022.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

In recent years, an ultrafine Nb3Al wires with a diameter of less than 50 mu m has been developed by a research group at the National Institute for Materials Science (NIMS) in Japan. Therefore, we are planning to use the developed high performance Nb3Al wires for superconducting applications operated by cryocooler. In order to design the superconducting applications cooled by cryocooler, it is necessary to measure the temperature and magnetic field dependence of the critical current of Nb3Al wires under conduction cooling conditions. Single and seven-stranded Nb3Al wires with different diameters (phi 67 mu m and phi 81 mu m) fabricated by the Jelly-rolled method were prepared. The barrier material of the two samples is the same Nb, but the core materials are Nb (phi 67 mu m) and Ta (phi 81 mu m), respectively. The Cu/nonCu ratio of the two samples is 1. In this study, the critical currents of sample wires were measured by a four-probe method with current sweep and constant current, and they were compared to define a reasonable critical current value under conduction cooling. Under conduction cooling, it was confirmed that the critical current measurement by the constant current method was more accurate than the current sweep method.

DOI： 10.1109/tasc.2022.3156927

Numerical Evaluation on Mechanical Behavior of No-Insulation REBCO Pancake Coils in Small-Scale Model of Skeleton Cyclotron Reviewed International journal

Yuta Miyake, Yuki Nakai, Ryota Inoue, SeokBeom Kim, Hiroshi Ueda, So Noguchi, Tomonori Watanabe, Shigeo Nagaya, Mitsuhiro Fukuda, Atsushi Ishiyama

IEEE Transactions on Applied Superconductivity 32 ( 6 ) 1 - 5 2022.9

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

We are developing a high-temperature superconducting (HTS) air-core compact cyclotron, named Skeleton Cyclotron (Ueda et al. 2013), (Ueda et al. 2019), that can accelerate various particles and variable energy for radioisotope (RI) production. The coil system of Skeleton Cyclotron consists of circular main coils and noncircular sector coils which are wound by REBa2Cu3O6+delta (REBCO) tape applied no-insulation (NI) winding technique for both high current densities and thermal stabilities. The electromagnetic and thermal behaviors in NI coil differs from those in conventional insulated coils during charging, discharging, and quenching. Therefore, it is necessary to investigate the mechanical behavior and reinforcement structure of multiple NI coils in Skeleton Cyclotron. In this study, we report on the numerical evaluation of mechanical properties of NI REBCO coils in Skeleton Cyclotron at charging and quenching considering the current distributions and electromagnetic stresses unique to NI coils. In the quenching process, the radial current in a quenching pancake of the sector coil became dominant, resulting in generating the rotating force and non-symmetric deformation. YOROI-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structure is effective for the additional magnetic stress.

DOI： 10.1109/tasc.2022.3163693

Numerical Evaluation on Quench Behavior of No-Insulation REBCO Coil System in Small-Scale Model of Skeleton Cyclotron Reviewed International journal

Yuki Nakai, Yuta Miyake, Ryota Inoue, SeokBeom Kim, Hiroshi Ueda, So Noguchi, Tomonori Watanabe, Shigeo Nagaya, Mitsuhiro Fukuda, Atsushi Ishiyama

IEEE Transactions on Applied Superconductivity 32 ( 6 ) 1 - 5 2022.9

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

We have proposed a cyclotron for cancer therapy, called Skeleton Cyclotron, which is based on non-insulation (NI) high temperature superconducting (HTS) technology. The Skeleton Cyclotron consists of circular main coils for the isochronous field and non-circular sector coils for the azimuthally varying field (AVF). In order to establish the development technology of HTS multi-coil system for the skeleton cyclotron, we have now designed a small half-size multi-coil system for demonstration, called Ultra-Baby Cyclotron, at the operating current of 540 A, the operating temperature of 20 K and the magnetic field of 1.6 T at the extraction radius of 0.2 m. The NI HTS coil can make both high current density and high magnetic field, so it can achieve miniaturization of its size and high intensity beams. Furthermore, in NI coils, the current flows not only in the coil winding direction but also in the radial direction. Therefore, even if the local normal transition occurs in the coil windings, the current can bypass into the neighboring wires and thermal stability can be improved. On the other hand, when the normal transition and quench occur, the electromagnetic and mechanical behaviors in NI coils are different from those of conventional insulated coil. Therefore, we developed a current distribution analysis code for non-insulation HTS coils and simulated the current distributions during the normal transition and quench in NI REBCO coil system for Skeleton Cyclotron.

DOI： 10.1109/tasc.2022.3174811

Deformation Analysis of No-Insulation REBCO CDeformation Analysis of No-Insulation REBCO Coils Considering Turn-to-Turn Contact Configurationoils Considering Turn-to-Turn Contact Configuration Reviewed International journal

Hiroshi Ueda, Keisuke Naito, Ryota Inoue, SeokBeom Kim

IEEE Transactions on Applied Superconductivity 32 ( 6 ) 1 - 5 2022.9

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

In recent year, there has been remarkable progress in the use of high-field rare-earth barium copper oxide (REBCO) coils in NMR, MRI, and accelerator applications. No-insulation (NI) winding techniques are adopted to achieve high thermal stability and high current density. Thus, each winding in a non-impregnated NI REBCO coil can deform separately and move freely because of the thermal strain and electromagnetic force. The additional force and stress due to a screening current has also become an issue in REBCO coils. The screening current leads to a non-uniform force distribution in REBCO tapes and forces exceeding an acceptable value. It has been reported that REBCO coils have experienced mechanical deterioration or damage when operating under high magnetic fields. However, the detailed mechanism for this damage or deterioration has not been clarified. In order to clarify the detailed mechanism of this damage to a REBCO coil, the stress and strain during the winding, cooling down, charging, and discharging processes need to be evaluated. Furthermore, in NI REBCO coils, the turn-to-turn contact configurations are very important for the current bypassing, the thermal and mechanical stability. In previous studies, we have developed the numerical simulation code on the electromagnetic behavior of screening current and mechanical behavior of the turn-to-turn contact state. This study numerically evaluated the deformation and stress in REBCO tape and the turn-to-turn contact in NI REBCO coils.

DOI： 10.1109/tasc.2022.3171160

Numerical Evaluation of Reinforcement Structure Against Electromagnetic and Thermal Stresses in Stacked REBCO Pancake Coils Reviewed International journal

Keisuke Naito, Ryota Inoue, SeokBeom Kim, Hiroshi Ueda

IEEE Transactions on Applied Superconductivity 32 ( 6 ) 1 - 5 2022.9

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

In recent years, high field REBCO coils have been applied with great interest to NMR and accelerators due to their high thermal stability and high current density. However, deteriorations and damages of REBCO coils are occurring. During the charge and discharge of REBCO coils, screening currents are induced to circulate in the windings, resulting in a non-uniform current distribution in the wires. It has been reported that the electromagnetic force distribution in the wire becomes significantly non-uniform, resulting in degradation of REBCO coils. In this study, the effects of stress and deformation of REBCO coils were investigated through electromagnetic stress analysis using two-dimensional axisymmetric structural analyses, taking into account thermal stress during cooling, tension during winding and electromagnetic force during not only charge and but also discharge, and the suppression of stress and deformation by the currently devised YOROI-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structure and over-banding was evaluated.

DOI： 10.1109/tasc.2022.3177389

Experimental Study on the Accuracy of the Proposed LFAC Method for Measuring the Contact Resistance of NI HTS Coils Reviewed International journal

SeokBeom Kim, Kohei Miyamoto, Hirotaka Kobayashi, Ryota Inoue, Hiroshi Ueda, So Noguchi

IEEE Transactions on Applied Superconductivity 32 ( 6 ) 1 - 5 2022.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

No-insulation (NI) winding technique provides high thermal stability, and the turn-to-turn contact resistance is an important factor to characterize the thermal stability and charging delay of NI HTS magnets. Therefore, a method that can accurately measure the contact resistance between turns of NI HTS magnets was required. We have previously proposed a turn-to-turn contact resistance measurement method using a low frequency AC current. The proposed low-frequency-AC-current (LFAC) can accurately evaluate the contact resistance between turns only when the whole AC current flows in the radial direction of the NI HTS pancake coil (there is almost no coil inductance). In addition, the AC current flowing in the radial direction needs to have a uniform current distribution in the plane of winding wire (REBCO wire). Therefore, in this study, an experimental study was conducted to prove the reliability of the proposed LFAC method. In the experiment, three NI test coils with different winding tension (0.5, 1 and 2 kg) were prepared, and four pickup coils were placed under each test coil to evaluate the radial current bypass characteristics. The contact resistance of each test coil was decreased from a few percent to several tens of percent by multiple cooling cycles from room temperature to liquid nitrogen temperature. Although it is a qualitative observation, the validity of the LFAC method was proved by the prepared pickup coils, and it was shown that even a small change of contact resistance in NI coils can be measured.

DOI： 10.1109/tasc.2022.3175791

Numerical Evaluation on Electromagnetic and Thermal Stresses in Non-Circular REBCO Pancake Coils of Multi-Coil System For Skeleton Cyclotron Reviewed International journal

Hiroshi Ueda, Yuta Miyake, Yuta Awazu, Ryota Inoue, SeokBeom Kim, So Noguchi, Tomonori Watanabe, Shigeo Nagaya, Mitsuhiro Fukuda, Atsushi Ishiyama

IEEE Transactions on Applied Superconductivity 31 ( 5 ) 4603705 2021.8

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)

We proposed the air-core cyclotron using high-temperature superconducting (HTS) technology, named Skeleton Cyclotron, as high intensity compact, variable-energy and multi-particle cyclotron for RI production. Skeleton Cyclotron consists of HTS split circular main coils generating the isochronous field and HTS non-circular sector coils generating the azimuthally varying field (AVF). Now, we are currently developing the small-scale cryocooler-cooled HTS coil system of Skeleton Cyclotron, which accelerates the proton up to energy of 5 MeV at an extraction radius of 20 cm. Skeleton cyclotron is multi-coil system consists of HTS split circular main NI (no-insulation) coils and HTS non-circular sector NI coils. Therefore, the electromagnetic, thermal, and mechanical behaviors are expected to be very complicated. In this study, the structure analysis based on finite element method using COMSOL Multiphysics is performed for a non-circular sector coil. The coils in Ultra-Baby Cyclotron are reinforced with YOROI-coil structure. Therefore, the effect of YOROI-coil structure was numerically investigated during cool-down process and excitation process. YOROI-coil structure is effective for non-circular sector coil against the electromagnetic force.

DOI： 10.1109/tasc.2021.3072871

　 PREV - NEXT 　

1
2
3
4
5
6
7
8
9