Faculty Profiles - UEDA Hiroshi

Papers - UEDA Hiroshi

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Current bypassing and transient stability in a partially insulated HTS coil Reviewed International journal

SeokBeom Kim, Haruyoshi Okusa, Kentaro Tami, Hiroshi Ueda

IEEE Transactions on Applied Superconductivity 28 ( 3 ) 4603105 2018.4

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

The no-insulation (NI) winding technique to improve the transient stability of high-temperature superconducting (HTS) magnets has been studied and a cowinding method using a metallic tape was tested. Normally, the operating current in NI HTS coils is bypassed into the transverse direction due to the normal region generated within the coils. Therefore, a method that controls such current bypassing into the turn-to-turn direction of NI HTS coils was investigated as a means to regulate the effective number of turns. In this study, we experimentally investigated the characteristics of current bypassing in the transverse direction within a test coil wound with a GdBCO tape. First, to find an optimized heater location, a 20-turn HTS pancake with two partial insulation shapes was prepared and tested experimentally. The current bypassing characteristics in the normal region created by heaters (strain gauges) were studied while varying the number of heaters, heater positions, and the amount of heating at liquid nitrogen temperature. Using both short and long heating periods, we found that we could effectively control the number of turns (coil inductance) via long-duration heating.

DOI： 10.1109/TASC.2017.2787108

An Extended Thin Approximation Method to Simulate Screening Current Induced in REBCO Coils Reviewed International coauthorship International journal

So Noguchi, Seungyong Hahn, Hiroshi Ueda, Seokbeom Kim, Atsushi Ishiyama

IEEE Transactions on Magnetics 54 ( 3 ) 7201904 2018.3

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

Superconducting magnets wound with second-generation high-temperature superconductors, i.e., REBa2Cu3O7-x (REBCO, RE = Rare Earth) tapes, are desired to apply high magnetic field nuclear magnetic resonance, MRI, and accelerators. However, a major problem for practical application is an undesirable irregular magnetic field caused by screening currents induced in REBCO tapes. To investigate the screening current-induced magnetic field, a few simulation methods have been proposed. One of the effective simulation methods employs a finite-element method with a thin approximation method. Although the thin approximation method was developed to simulate eddy currents in magnetic steel sheets, and it is not applicable to REBCO tapes carrying a transport current. Therefore, the thin approximation method is extended to simulate screening currents in REBCO tapes considering a carrying transport current. To show the validity of the proposed extended thin approximation method, the screening currents of an REBCO magnet are computed, and the results are compared with the measurement and simulation results of the conventional thin approximation method. The more accurate solution is available by using the proposed methods.

DOI： 10.1109/TMAG.2017.2752083

Study on the Persistent Current Switch in HTS Coils Wound with 2G Wire for Compact NMR Magnets Reviewed

K. Sugo, S. B. Kim, R. Nomura, H. Ueda

Journal of Physics: Conference Series 871 ( 1 ) 2017.7

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Institute of Physics Publishing

High temperature superconducting (HTS) magnets wound with REBCO wires are used in many applications, and the superconducting magnet which is operated in persistent current mode has many advantages. Therefore, we have been developing compact NMR relaxometry devices using HTS coils operated at liquid nitrogen temperature. The required strength and homogeneity of magnetic field of proposed NMR relaxometry devices are 1.5 T and 150 ppm/cm3 respectively. The proposed HTS magnet for NMR relaxometry device consists with stacked HTS double pancake coils wound with REBCO wires and operated by persistent current mode (PCM) using superconducting joint between REBCO wires. In PCM operation, the ability of persistent current switch (PCS) is very important, so, in this study, the thermal properties of YBCO wire against the various thermal inputs by heater were investigated experimentally to design the PCS for PCM HTS magnets. The thermal behaviors of the YBCO wires were measured as functions of amount of heat input using two types of epoxy resin. The current bypassing properties on the YBCO loop coil with developed PCS were studied experimentally.

DOI： 10.1088/1742-6596/871/1/012087

Numerical Evaluation of the Reinforcing Effect of the Advanced YOROI Coil Structure for the HTS Coil Reviewed

Yuji Kashiwazaki, Atsushi Ishiyama, Xudong Wang, Hiroshi Ueda, Tomonori Watanabe, Shigeo Nagaya

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 27 ( 4 ) 4601804 2017.6

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

REBCO coils applied to superconducting magnetic energy storage system, magnetic resonance imaging, medical accelerator, and so on, are expected to result in high efficiency and compactness due to the realization of higher magnetic field and current density. Because these devices require large coil radius, huge hoop stress "BJR" (= magnetic field x current density x coil radius) is produced in the coil winding and the damage to these devices is likely to cause. In our previous study, we proposed a novel coil structure called the Y-based oxide superconductor and reinforcing outer integrated (YOROI) structure to achieve a highstrength REBCO pancake coil. The YOROI structure comprises upper and lower plates and the outer frame of the winding outer periphery. The frames are forcibly expanded by the superconducting coil winding situated inside when the coil winding is subjected to an electromagnetic force. The outer frame is connected to the upper and lower plates and transfers a part of the electromagnetic force from the coil winding to the reinforcing outer plates. The reinforcing outer plates then support the coil to suppress the coil deformation against the electromagnetic forces. The YOROI structure achieved the resistance to a maximum hoop stress of 2 GPa, which was calculated from the BJR in an excitation test at 4.2 K in 8-T backup fields. In this study, we investigated the effect of the stress control structure to realize the HTS coil with a mechanical strength of over 2 GPa using a three-dimensional finite-element structural analysis.

DOI： 10.1109/TASC.2017.2652918

Progress in the Development of Conduction-Cooled REBCO Magnets for Ultrahigh-Field MRI Systems Reviewed

Hiroshi Miyazaki, Sadanori Iwai, Tatsuro Uto, Yasumi Otani, Masahiko Takahashi, Taizo Tosaka, Kenji Tasaki, Shunji Nomura, Tsutomu Kurusu, Hiroshi Ueda, So Noguchi, Atsushi Ishiyama, Shin-ichi Urayama, Hidenao Fukuyama

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 27 ( 4 ) 4300805 2017.6

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

We started developing REBa2Cu3O7-delta (REBCO) magnets for ultrahigh-field magnetic resonance imaging (MRI) systems in 2013. Our final targets are 9.4 TMRI systems for whole-body and brain imaging. In this paper, a conduction-cooled 1.5 T REBCO MRI magnet having a room-temperature bore of 396 mm was fabricated and tested in order to evaluate the magnetic field homogeneity and stability. The magnet was composed of 60 single pancakes whose inner diameter was 500 mm. The total conductor length was 10.3 km, and the total inductance was 12.4 H. The size of the homogeneous magnetic field region was 200 mm diameter spherical volume. The central magnetic field was as high as 1.5 T at 192.7 A, and the current density of single pancakes was 301 A/mm(2). The magnet was cooled from room temperature to 4.7 K in 55 hours, and the temperature difference among the coils was 0.1 K or less during both initial cooling and excitation. The magnetic field inhomogeneity was 249.7 parts per million (ppm), and the Z(2) coefficient was largest at 579.6 ppm. The main reason for the error magnetic field was dimensional errors in the positions on the z-axis. The magnetic field inhomogeneity was improved to 4.1 ppm by passive shimming using iron pieces. The magnetic field stability was about 2 ppm/h because of a reduction in screening-current induced in the REBCO-coated conductors. Current sweep reversal improved the magnetic field stability from 2 ppm/h to 0.8 ppm/h.

DOI： 10.1109/TASC.2017.2656858

Current Behavior Simulation in Stacked NI REBCO Pancake Coils during Local Normal-State Transition Reviewed

So Noguchi, Ryosuke Miyao, Katsutoshi Monma, Hajime Igarashi, Hiroshi Ueda, Atsushi Ishiyama

IEEE Transactions on Applied Superconductivity 27 ( 4 ) 4603205 2017.6

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

This paper presents the current behavior and axial Lorenz force of stacked no-insulation (NI) REBa2Cu3O7-x (REBCO, RE = Rare Earth) double-pancake coils during local normal-state transition. The NI winding technique enhances the thermal stability and increases the engineering current density in REBCO pancake coils. The high thermal stability of NI REBCO coil has been verified in experiments of overcurrent test. In addition, the numerical simulations of NI REBCO single-pancake coils have been performed to confirm the high stability. However, REBCO magnets usually consist of some stacked double-pancake coils to generate a high magnetic field for practical applications. When a normal-state transition occurs in one of the stacked pancake coils, it may affect the other pancake coils. For the more reliable verification, the current and electromagnetic force behavior of stacked NI REBCO pancake coils during a normal-state transition should be simulated. To examine the stacked NI REBCO pancake coils, we extend the previously proposed partial element equivalent circuit (PEEC) model to deal with a few double-pancake coils. In this paper, an NI REBCO double-pancake coil and their three stacked coils are simulated by using the extended PEEC model.

DOI： 10.1109/TASC.2017.2656381

Screening-Current-Induced Magnetic Field of Conduction-Cooled HTS Magnets Wound With REBCO-Coated Conductors Reviewed

Hiroshi Miyazaki, Sadanori Iwai, Tatsuro Uto, Yasumi Otani, Masahiko Takahashi, Taizo Tosaka, Kenji Tasaki, Shunji Nomura, Tsutomu Kurusu, Hiroshi Ueda, So Noguchi, Atsushi Ishiyama, Shin-Ichi Urayama, Hidenao Fukuyama

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 27 ( 4 ) 4701705 2017.6

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

Superconducting magnets for magnetic resonance imaging systems require homogeneous, stable magnetic fields. The homogeneity of the magnetic field is highly dependent on the coils shape and positions. Furthermore, in REBa2Cu3O7-delta (REBCO) magnets, the screening-current-induced magnetic field, which changes the magnetic field distribution of the magnet, is one of the most critical issues. In the work described here, a small REBCO coil that can generate a magnetic field of over 10 T was fabricated and tested. The small REBCO coil was composed of a stack of 22 single pancake coils whose inner and outer diameters were 50 mm and 130 mm, respectively. The total conductor length was 1.5 km. The small REBCO coil could generate a central magnetic field of 8.27 T at 10 K. A magnetic field of over 10 T was achieved by replacing 12 of the single pancake coils with new ones wound with the latest REBCO-coated conductors. The measured value of the central magnetic field at 10 K was 13.53 T, which was lower than the calculated value of 13.94 T obtained without taking account of the screening-current-induced magnetic field. Furthermore, it was examined whether the current sweep reversal would be effective for 10 T-class magnetic field conditions.

DOI： 10.1109/TASC.2017.2657636

Numerical Evaluation on Irregular Field Generated by Screening Current in High-Field REBCO Coil for Whole-Body MRI Reviewed

Kohei Nakazono, Hiroshi Ueda, Atsushi Ishiyama, So Noguchi, Hiroshi Miyazaki, Taizo Tosaka, Tsutomu Kurusu, Shunji Nomura, Shinichi Urayama, Hidenao Fukuyama

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 27 ( 4 ) 4400405 2017.6

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

In recent years, high-field magnets wound with RE-BCO tape and their applications to magnetic resonance imaging (MRI) have undergone considerable research and development. MRI coil systems require a highly accurate field in the imaging space. However, in REBCO coils, the irregular magnetic field generated by the screening current is induced by the radial component of the magnetic field in the REBCO tape, and may deteriorate the field quality both spatially and temporally. Therefore, a design process with consideration for the effect of the screening-current field is required for the reduction and correction of this field for a high-accuracy-field REBCO coil. In this study, the screening-current distribution in the REBCO tape and the irregular magnetic field were analyzed by using the simulation we developed for a REBCO model coil system for whole-body MRI. We additionally discuss the effect of the screening-current field in the REBCO coil based on the coil shape and arrangement to use it as feedback to the design stage.

DOI： 10.1109/TASC.2016.2645839

Loss Measurement in a Cryogen-Free Bi-2223 HTS Dipole Magnet for Beam Line Switching Reviewed

Jun Yoshida, Takaaki Morie, Atsushi Hashimoto, Hitoshi Mitsubori, Yukio Mikami, Keiichi Watazawa, Kichiji Hatanaka, Hiroshi Ueda, Mitsuhiro Fukuda, Tetsuhiko Yorita

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 27 ( 4 ) 4701905 2017.6

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

High-temperature superconducting (HTS) magnets have several advantages for ac and pulse operation due to having a high critical temperature. However, fast magnetic field changes generate severe ac losses and eddy current losses. Therefore, loss estimation and reduction is a significant issue for HTS magnet cooling design. For future cooling design, we have measured losses of a Bi-2223 HTS magnet for beamline switching in the cyclotron facility at the Research Center of Nuclear Physics, Osaka University. The time-varying magnetic field losses for triangular wave excitation with a perpendicular magnetic field amplitude of 0.8 T in wire and a minimum period of 42 s were obtained from measured cryocooler temperatures and preliminary measured cooling capacity curve. The eddy current losses of the metal components were calculated using transient electromagnetic finite element analysis. The ac losses of the Bi-2223 wire were derived from the measured time-varying magnetic field losses and the calculated eddy current losses. The frequency dependence of their losses indicates the importance of accurate evaluation and reduction of the eddy current losses for the future magnet with higher charging speed.

DOI： 10.1109/TASC.2017.2653222

Optimal Configuration Design of MRI REBCO Magnet Taking into Account Superconducting Layer Reviewed

So Noguchi, Hiroshi Miyazaki, Taizo Tosaka, Shunji Nomura, Tsutomu Kurusu, Hiroshi Ueda, Atsushi Ishiyama, Shinichi Urayama, Hidenao Fukuyama

2016 IEEE CONFERENCE ON ELECTROMAGNETIC FIELD COMPUTATION (CEFC) 2017.1

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

The development of ultra-high-field (similar to 10 T magnetic resonance imaging (MRI) device is underway. It is, therefore, required to achieve the extremely high field homogeneity at a magnet design stage, where the field homogeneity is evaluated using the Legendre polynomials. Commonly, it is supposed that the current uniformly flows on the cross section of coils. However, for REBCO magnet, the no-current-flowing region has to be taken into account, such as a copper stabilizer. In addition, the REBCO layer inside REBCO tape is very thin, 1 - 2 mu m, so the current-flowing region is 1/100 of the REBCO tape area. Therefore, it is necessary to consider that the current flows only in the REBCO layer, for accurate evaluation of field homogeneity.

DOI： 10.1109/CEFC.2016.7815982

Electromagnetic Analysis on Magnetic Field and Current Distribution in High Temperature Superconducting Thin Tape in Coil Winding Reviewed International journal

Hiroshi Ueda, SeokBeom Kim, So Noguchi, Atsushi Ishiyama, Hiroshi Miyazaki, Sadanori Iwai, Taizo Tosaka, Shunji Nomura, Tsutomu Kurusu, Shinichi Urayama, Hidenao Fukuyama

2016 IEEE CONFERENCE ON ELECTROMAGNETIC FIELD COMPUTATION (CEFC) 2017.1

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

High temperature superconducting (HTS) wires are high aspect ratio cross-section tapes. Therefore, the applications of HTS tapes lead to various problems such as AC loss, nonuniform current, and screening current. In practice, we must investigate the detail of current distribution in HTS tapes using the electromagnetic analysis technique dealing with high aspect ratio tape and nonlinearity of superconductor. We developed the numerical simulation code of electromagnetic field analysis in HTS tape using a finite element method (FEM) and fast multipole method (FMM).

DOI： 10.1109/CEFC.2016.7816041

Design of a conduction-cooled 9.4T REBCO magnet for whole-body MRI systems Reviewed

Hiroshi Miyazaki, Sadanori Iwai, Yasumi Otani, Masahiko Takahashi, Taizo Tosaka, Kenji Tasaki, Shunji Nomura, Tsutomu Kurusu, Hiroshi Ueda, So Noguchi, Atsushi Ishiyama, Shinichi Urayama, Hidenao Fukuyama

SUPERCONDUCTOR SCIENCE & TECHNOLOGY 29 ( 10 ) 104001 2016.10

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

A project on the development of REBa2Cu3O7-delta (REBCO) magnets for ultra-high-field magnetic resonance imaging (MRI) was started in 2013. Since REBCO-coated conductors feature high mechanical strength under tensile stress and high critical current density, use of REBCO coils would allow superconducting magnets to be made smaller and lighter than conventional ones. In addition, a conduction-cooled superconducting magnet is simpler to use than one cooled by a liquid helium bath because the operation and maintenance of the cryogenic system become simpler, without the need to handle cryogenic fluid. Superconducting magnets for MRI require homogeneous, stable magnetic fields. The homogeneity of the magnetic field is highly dependent on the coil shape and position. Moreover, in REBCO magnets, the screening-current- induced magnetic field, which changes the magnetic field distribution of the magnet, is one of the critical issues. In order to evaluate the magnetic field homogeneity and the screening-current- induced magnetic field, a 1 T model magnet and some test coils were fabricated. From an evaluation of the 1 T model magnet, it was found that the main reason for magnetic field inhomogeneity was the tolerances in the z-axis positions of the coils, and therefore, it is important to control the gap between the single pancakes. In addition, we have already demonstrated the generation of an 8.27 T central magnetic field at 10 K with a small test coil. The screening-current-induced magnetic field was 0.43 T and was predictable by using an electromagnetic field simulation program. These results were reflected in the design of a conduction-cooled 9.4 T REBCO magnet for whole-body MRI systems. The magnet was composed of six main coils and two active shield coils. The total conductor length was 581 km, and the stored energy was 293 kJ. The field inhomogeneity was 24 ppm peak to peak and 3 ppm volume-root-mean-square (VRMS) for a 500 mm diameter spherical volume (DSV). The axial and radial 5 gauss line locations were less than 5 m and 4.2 m respectively.

DOI： 10.1088/0953-2048/29/10/104001

Developments of HTS Magnets towards Application to Accelerators

K. Hatanaka, M. Fukuda, K. Kamakura, H. Ueda, Y. Yasuda, T. Yorita

Proceedings of the 7th International Particle Accelerator Conference 1180 - 1182 2016.6

Development of a Rapid Beam Emittance Measurement System using a Real-Time Beam Profile Monitor Reviewed

Keita Kamakura, Kichiji Hatanaka, Mitsuhiro Fukuda, Tetsuhiko Yorita, Hiroshi Ueda, Takane Saito, Shunpei Morinobu, Keiichi Nagayama, Hitoshi Tamura, Yuusuke Yasuda

IEEE TRANSACTIONS ON NUCLEAR SCIENCE 63 ( 3 ) 1710 - 1714 2016.6

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

We have developed a rapid beam emittance measurement system for the injection beam of the K140 azimuthally varying field (AVF) cyclotron at Research Center for Nuclear Physics (RCNP). So far, a conventional emittance monitor has been used in a section of a medium energy beam transport (MEBT) system to evaluate the quality of the injected beam to the K400 ring cyclotron. Two kinds of emittance monitors were supplemented in the low energy beam line for evaluation of ion beams from ion sources. One of them is a conventional type consisting of two sets of position-variable slits and a three-wire profile monitor (TPM), similar to the one installed in the MEBT system of the AVF cyclotron. It takes about 30 min to get emittances in both the horizontal and vertical planes. For quick emittance measurements, we have developed a new system equipped with a set of fast moving slits with a fixed gap and a real-time beam profile monitor (BPM83) with a rotating helical wire. With this system the measurement time was considerably reduced to 70 s for both the horizontal and vertical emittances. Moreover the data analysis and graphical processing were completely automated. The overall measurement and analysis time was successfully minimized within 75 s. This rapid emittance measurement system has contributed to improve the beam quality by optimizing parameters of ion sources and the beam transport system.

DOI： 10.1109/TNS.2016.2542865

Experiment and Simulation of Impregnated No-Insulation REBCO Pancake Coil Reviewed

So Noguchi, Katsutoshi Monma, Sadanori Iwai, Hiroshi Miyazaki, Taizo Tosaka, Shunji Nomura, Tsutomu Kurusu, Hiroshi Ueda, Atsushi Ishiyama, Shinichi Urayama, Hidenao Fukuyama

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 26 ( 4 ) 4601305 2016.6

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

It is important to investigate the stability and behavior of an epoxy-resin-impregnated no-insulation (NI) REBCO pancake coil to implement high-field applications, such as ultra-high-field magnetic resonance imaging. We have performed sudden discharging and overcurrent tests for the impregnated NI REBCO pancake coil. From the discharging test, the contact resistivity is estimated, and it changes depending on the initial current. From the overcurrent test, the high thermal stability of the impregnated NI REBCO pancake coil is confirmed. The REBCO pancake coil is charged up to 67 A though the critical current is only 46 A, and no degradation has been found. To investigate in detail the electromagnetic behavior of an impregnated NI REBCO pancake coil, the simulation is performed by means of the partial element equivalent circuit (PEEC) model. In the sudden discharging test, the simulation results for the case of lower initial current are in good agreement with the experimental data. As can be inferred from the simulation results, the current drastically decreases from the inside of the impregnated NI REBCO pancake coil. The result of the overcurrent simulation is almost identical to the experimental one. However, since the contact resistivity is presumed to be constant in the simulation, the difference is observed in the high current region.

DOI： 10.1109/TASC.2016.2536736

R&D Project on HTS Magnets for Ultrahigh-Field MRI Systems Reviewed

Taizo Tosaka, Hiroshi Miyazaki, Sadanori Iwai, Yasumi Otani, Masahiko Takahashi, Kenji Tasaki, Shunji Nomura, Tsutomu Kurusu, Hiroshi Ueda, So Noguchi, Atsushi Ishiyama, Shinichi Urayama, Hidenao Fukuyama

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 26 ( 4 ) 4402505 2016.6

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

An R&D project on high-temperature superconducting (HTS) magnets using (RE) Ba2Cu3O7 (REBCO; RE = rare earth) wires for ultrahigh-field (UHF) magnetic resonance imaging (MRI) systems is described. Our targets are 9.4-T MRI systems for whole-body imaging and brain imaging. REBCO wires are promising components for UHF-MRI because REBCO wires have high critical current density in high magnetic fields and high strength against hoop stresses, which allows MRI magnets to be smaller and lighter than conventional ones. The aim of the project is to establish basic magnet technologies for adapting REBCO coils for UHF-MRI. The project term is three years, and this year is the final year. We have already demonstrated the generation of an 8.27-T magnetic field with a small test coil composed of 22 REBCO pancake coils. A magnetic field spatial distribution with inhomogeneity of several hundreds of parts permillion within 100-mm diameter spherical volume (DSV) was demonstrated with a 1-T model magnet. A stable magnetic field of a few parts per million per hour was also demonstrated with the 1-T model magnet. The targets of the project, to be achieved by March 2016, are to demonstrate the generation of a 9.4-T field with the small REBCO coil, and to demonstrate a homogeneous magnetic field in 200-mm DSV with a 1.5-T magnet having three pairs of split coils. Imaging will be performed with the 1.5-T magnet.

DOI： 10.1109/TASC.2016.2535863

Evaluation of Irregular Magnetic Field Generated by Screening Current in REBCO Coils for High Accuracy Field Reviewed

Ayako Matsumi, Hiroshi Ueda, So Noguchi, Tao Wang, Atsushi Ishiyama, Hiroshi Miyazaki, Taizo Tosaka, Shunji Nomura, Tsutomu Kurusu, Shinichi Urayama, Hidenao Fukuyama

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 26 ( 4 ) 4702305 2016.6

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

In recent years, research and development of applications for a high field magnet wound with a REBCO tape into nuclear magnetic resonance and magnetic resonance imaging have been carried out. These applications require a very high accuracy field, that is, the spatial uniform and temporally stable field. However, in the REBCO coils, the irregular magnetic field is generated by the screening current, which is remarkably induced by the radial component of the magnetic field in a REBCO tape. Therefore, a nonconventional approach is required for the reduction or correction of the irregular magnetic field generated by the screening current in the stage of design for a high-accuracy-field REBCO coil. The prediction and improvement of the irregular magnetic field generated by the screening current is a serious issue for the development and design of REBCO coils and correction shims. In this study, we numerically investigated the screening current distribution in the winding and the irregular magnetic field generated by the screening current. Moreover, we discuss the irregular effect of the magnetic field generated by the screening current in the REBCO coil from the arrangement of the coil windings and excitation pattern.

DOI： 10.1109/TASC.2016.2535966

Evaluation of Magnetic Field Distribution by Screening Current in Multiple REBCO Coils Reviewed

Ayumu Mochida, Hiroshi Ueda, So Noguchi, Tao Wang, Atsushi Ishiyama, Hiroshi Miyazaki, Taizo Tosaka, Shunji Nomura, Tsutomu Kurusu, Shinichi Urayama, Hidenao Fukuyama

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 26 ( 4 ) 4702805 2016.6

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

Coil systems are fabricated with various combinations of multiple coils in order to generate homogenous fields for NMR and MRI applications. In multiple coil systems using REBCO coils, the behavior of the screening current, which deteriorates field homogeneity, depends on the patterns of the transport current, the charging sequence of the coils, and the various resulting magnetic fields. It is therefore important to investigate and clarify the behavior of the irregular magnetic field and screening current in multiple coil systems under different operating environments. In a previous study, we experimentally and numerically clarified the different behaviors of irregular magnetic fields based on the charging sequence of coils in multiple-model REBCO coils [1], [2]. In this paper, we constructed the multiple-model REBCO coils in order to obtain the fundamental data for reducing or improving the resulting irregular magnetic field. Furthermore, the distribution of the irregular magnetic field in terms of the screening current was measured by using the reversal current method [3], [4]. We also calculated the spatial and temporal behavior of the irregular magnetic field by using our developed 3-D numerical simulation. Based on the experimental and numerical results, we discuss the behavior of the magnetic field in terms of the screening current when using the current sweep reversal method in multiple-model REBCO coils.

DOI： 10.1109/TASC.2016.2542980

Experimental Results of Screening-Current Field With 10-T Class Small REBCO Coil Reviewed

S. Iwai, H. Miyazaki, Y. Ohtani, T. Tosaka, K. Tasaki, S. Nomura, T. Kurusu, H. Ueda, S. Noguchi, A. Ishiyama, S. Urayama, H. Fukuyama

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 26 ( 4 ) 4302305 2016.6

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

A REBCO-coated conductor has a tape shape and is suitable for forming a stack of single pancakes for generating a high magnetic field. However, the magnetic flux going through the tape surface causes a screening current, which reduces the magnetic field in conventional coil designs. Magnetic resonance imaging systems need high uniformity of the magnetic field, both spatially and temporally, and thus, the screening field resulting from the screening current is one of the critical issues. In this paper, a 10-T class small test coil using REBCO-coated conductors was fabricated and tested in a conduction-cooled configuration from 10 to 60 K for investigating the effect of the screening field on the generated magnetic field in the inner space of the coil. The coil was composed of a stack of 22 single pancakes using 4-mm-wide REBCO tapes with an inner diameter of 50 mm, an outer diameter of 129 mm, and a height of 104 mm. For different stacking orders based on the coil critical currents, the measured values of the central magnetic field at 10 K were 7.66 and 8.27 T, which were lower than the calculated values of 8.07 and 8.70 T obtained without taking account of the screening-current fields.

DOI： 10.1109/TASC.2016.2530301

Performance Test of Cryogen-Free Bi-2223 HTS Dipole Magnet for Beam Line Switching Reviewed

Jun Yoshida, Atsushi Hashimoto, Hitoshi Mitsubori, Yukio Mikami, Keiichi Watazawa, Kichiji Hatanaka, Hiroshi Ueda, Mitsuhiro Fukuda, Tetsuhiko Yorita, Eisaku Ueno, Takeshi Kato

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 26 ( 3 ) 4005004 2016.4

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

We have developed a Bi-2223 high-temperature superconducting dipole magnet for beam line switching at the cyclotron facility of the Research Center for Nuclear Physics, Osaka University. Exit beam lines are periodically switched by increasing and decreasing the magnetic field between 0 and 1.6 T with a switching time of 10 s. The magnet is equipped with two sets of Bi-2223 coil assemblies, which are conduction cooled by two 10-K Gifford-McMahon cryocoolers. We evaluated the superconducting property of the Bi-2223 coil assemblies in liquid nitrogen before installation in the cryostat. There were no degradation in wire performance during the assembly process. Magnetic field, strains, and temperatures of the coil assembly were investigated for performance verification after the magnet fabrication. The magnetic field and the temperatures meet specifications, and the deformation of the coil assembly is considered to be successfully suppressed by reinforcing structure. Furthermore, from a viewpoint of temperature, it is indicated that the magnet can make switching time and cycle time faster than that of the specified operation.

DOI： 10.1109/TASC.2016.2528543

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