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ABSTRACT: This paper addresses adverse effects of dimensional uncertainties of an HTS insert assembled with double-pancake coils on spatial field homogeneity. Each DP coil was wound with Bi2223 tapes having dimensional tolerances larger than one order of magnitude of those accepted for LTS wires used in conventional NMR magnets. The paper presents: 1) dimensional variations measured in two LTS/HTS NMR magnets, 350 MHz (LH350) and 700 MHz (LH700), both built and operated at the Francis Bitter Magnet Laboratory; and 2) an analytical technique and its application to elucidate the field impurities measured with the two LTS/HTS magnets. Field impurities computed with the analytical model and those measured with the two LTS/HTS magnets agree quite well, demonstrating that this analytical technique is applicable to design a DP-assembled HTS insert with an improved field homogeneity for a high-field LTS/HTS NMR magnet.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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ABSTRACT: The electromagnetic stress distribution inside a HTS insert is one of the key issues for construction of a high field high/low temperature superconductor (HTS/LTS) magnet. The r middot J middot B formulae is widely used for the stress calculation of the coil, due to its simplicity. However, the assumption of this calculation makes it impossible to consider the effects of the bobbin, an epoxy impregnated structure, on stress of the coil. In this work, stress analysis methods are reported. The governing equation defined from the force equilibrium state was adopted and used to analyze what the stress of the HTS coil wound with Bi2223/Ag conductor. The validness of the stress analysis method was confirmed by comparison with experimental results, especially in the coil with epoxy impregnation. The numerical and experimental procedures are described and both results are discussed.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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ABSTRACT: Recently, the performance of high temperature superconducting (HTS) bulks such as critical current density, size, and mechanical strength has been improved rapidly. So, various applications with HTS bulks such as motors, bearings, and flywheels have been investigated by many research groups. A compact nuclear magnetic resonance (NMR) magnet is one of the new applications after the technique to enhance maximum trapped field of the HTS bulk more than 11.74 T, a corresponding <sup>1</sup>H NMR frequency of 500 MHz, has been developed. This new compact NMR magnet out of HTS bulks is far less expensive than those conventional NMR magnets and expected to be widely used in food and drug industry. In design and manufacture of those compact NMR magnets, spatial field homogeneity of large trapped magnetic field in HTS bulk annuli is essential. This paper presents the magnetic field distribution in single and three assembled HTS bulk annuli, measured by a 3-axis hall sensor, and experimental results of its spatial homogeneity improvement by mounting an iron ring inside or outside of the HTS bulk annuli.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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[show abstract]
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ABSTRACT: This paper addresses adverse effects of dimensional uncertainties of an HTS insert assembled with double-pancake coils on spatial field homogeneity. Each DP coil was wound with Bi2223 tapes having dimensional tolerances larger than one order of magnitude of those accepted for LTS wires used in conventional NMR magnets. The paper presents: 1) dimensional variations measured in two LTS/HTS NMR magnets, 350 MHz (LH350) and 700 MHz (LH700), both built and operated at the Francis Bitter Magnet Laboratory; and 2) an analytical technique and its application to elucidate the field impurities measured with the two LTS/HTS magnets. Field impurities computed with the analytical model and those measured with the two LTS/HTS magnets agree quite well, demonstrating that this analytical technique is applicable to design a DP-assembled HTS insert with an improved field homogeneity for a high-field LTS/HTS NMR magnet.
IEEE transactions on applied superconductivity : a publication of the IEEE Superconductivity Committee. 06/2009; 19(3):2281-2284.
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ABSTRACT: This paper reports results, experimental and analytical, of the nonlinear behavior of a shim coil in the presence of an HTS coil assembled with double-pancake (DP) HTS-tape coils. The experimental results are from: 1) operation of a 700 MHz LTS/HTS NMR magnet (LH700) consisting of a 600 MHz LTS NMR magnet (L600) equipped with superconducting shim coils and a 100 MHz DP-assembled HTS insert (H100) and; 2) an experiment with a room-temperature (RT) Z1 shim coil coupled to a 50 MHz DP-as-sembled HTS insert (H50). A field mapping theory with a harmonic analysis is applied to interpret both results. Based on experimental results and analyses, we conclude that the screening-current-induced field (SCF) generated by a DP-assembled HTS insert is primarily responsible for the nonlinear behavior, including strength degradation, of a shim coil.
IEEE transactions on applied superconductivity : a publication of the IEEE Superconductivity Committee. 06/2009; 19(3):2285-2288.
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ABSTRACT: This paper describes two general methods: field map processing and NMR lineshape analysis, that we are currently using for the on-going research of field improvement techniques specifically applied to our 700 MHz LTS/HTS NMR magnet. The validity of the methods is verified with comparison between calculations and experiments. Also, a simple but effective analysis has been used to identify the principal source of a remanent magnetic field measured in the bore of the 700 MHz LTS/HTS NMR magnet: the screening current induced field (SCF) from the 100-MHz HTS insert, comprised of 48 double pancake coils, each wound with Bi2223 tape.
IEEE Transactions on Appiled Superconductivity 07/2008; · 1.04 Impact Factor
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Myung-Jin Park,
Sang-Yeop Kwak,
Woo-Seok Kim,
Seung-Wook Lee, Seung-Yong Hahn,
Ji-Kwang Lee,
Jin-Ho Han,
Kyeong-Dal Choi,
Hyun-Kyo Jung,
Ki-Chul Seong,
Song-yop Hahn
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ABSTRACT: Auto tuning niching genetic algorithm was used to design optimal HTS magnets for the 600 kJ class SMES system under several design constraint conditions. Constraint conditions were operation loss of magnet (less than 2 W), inductance of magnet (less than 24 H), the number of double pancake coils (about 10 DPCs), the number of turns of DPC (less than 300 turns), outer diameter of DPC (close to 800 mm) and total length of HTS wire in a DPC (less than 500 m). As a result of optimum design, we obtained design parameters for the 600 kJ SMES magnet according to two operating currents, 360 A and 370 A. However, even though the HTS magnet was designed optimally in respect to the electromagnetics, consideration of mechanical integrity due to the stress by Lorentz force must not be neglected for the stable operation of the SMES system. Therefore, we developed a program, through the finite element method (FEM), for stress analysis due to Lorentz force in operation of the SMES system. In this paper, the stresses (radial and hoop stress) imposed on the designed HTS magnets were calculated by the program, and the results of stress analysis were discussed.
IEEE Transactions on Appiled Superconductivity 07/2007; · 1.04 Impact Factor
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ABSTRACT: This paper presents the results of a study, experimental and simulation, of normal zone propagation (NZP) in winding pack models comprised of several lengths of YBCO tapes, each sandwiched by insulating spacers. A heater strip extending over the entire length of, and placed at the midpoint of, each winding pack model was energized over the entire length to trigger a quench in the middle YBCO tape. In each winding pack model, the YBCO tapes were connected electrically in series in such a way that a transport current through the YBCO tapes zigzagged from the YBCO tape at one side of the winding pack model to that at the other side of the winding pack model. The transverse speed of normal zone propagations through the different insulating spacers were measured by experiments and estimated by simulations.
IEEE Transactions on Appiled Superconductivity 07/2007; · 1.04 Impact Factor
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ABSTRACT: As a component of Phase-2 LTS/HTS NMR magnet of a 3-phase program to complete a 1-GHz LTS/HTS NMR magnet by 2009, an HTS insert magnet has been assembled from 48 double-pancake (DP) coils, each wound of high-strength Bi-2223/Ag/stainless steel composite tape. The paper describes the design and actual parameters; and preliminary performance results of the insert. The results include: 1) voltage vs. current data of double pancakes; and 2) splice resistances between adjacent double-pancake coils.
IEEE Transactions on Appiled Superconductivity 07/2005; · 1.04 Impact Factor
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ABSTRACT: The paper presents results, experiment and simulation, of quench/recovery study of coated YBCO "composite" test samples, cooled by boiling liquid nitrogen and subjected to an over-current pulse. To operate stably and be protected from damage under adverse operating conditions of a real device, the YBCO tape must be a "composite", loaded with normal metal of a sufficient thickness that significantly increases the thickness of the original YBCO tape.
IEEE Transactions on Appiled Superconductivity 07/2005; · 1.04 Impact Factor
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ABSTRACT: A new type of "persistent-mode" magnet, assembled from YBCO annuli, appears promising for "microcoil" NMR, in which compactness and simple manufacturability are vital. To develop an annular magnet for micro NMR, a YBCO-annulus Helmholtz coil was studied. The paper describes the new magnet concept and results of our study on the Helmholtz coil.
IEEE Transactions on Appiled Superconductivity 07/2005; · 1.04 Impact Factor
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ABSTRACT: By periodically injecting a quantified amount of flux in a "slightly" resistive NMR magnet, a digital flux injector (DFI) enables the magnet to effectively operate in persistent mode. This paper presents: 1) parameters of the first full-scale DFI, specifically designed and built to operate with an LTS/HTS NMR magnet; and 2) its preliminary results when coupled to an LTS insert magnet in a bath of liquid helium.
IEEE Transactions on Appiled Superconductivity 07/2005; · 1.04 Impact Factor
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ABSTRACT: The trapped field variation of a high temperature superconducting (HTS) bulk before and after a crack happens, which was impossible to simulate using 2D analysis method, was calculated in this paper. 3D finite element method (FEM) and iteration method were used to find screening current distribution inside an HTS bulk. In 3D analysis of an HTS bulk with a crack, calculated current distribution inside an HTS bulk should obey the equation of current continuity. For this purpose, ∇φ variable was set to satisfy the equation of current continuity, which was impossible to be considered directly by the FEM governing equation using critical state model. Also, boundary condition at the surface of an HTS bulk was applied to consider the equation of current continuity. Simulation results were compared with experimental ones to verify the validity of the suggested simulation method.
IEEE Transactions on Appiled Superconductivity 07/2004; · 1.04 Impact Factor
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ABSTRACT: This paper describes an effective method to calculate hysteresis loss of high-temperature superconducting (HTS) bulk material under time varying magnetic field. In the proposed method, the inner product of current and electric field in a HTS bulk is integrated to calculate hysteresis loss. To consider the nonlinear relation between the current and the electric field of HTS bulk material, critical state model and iteration method are adopted. According to the critical state model, if different types of time varying magnetic field are applied, the current distribution in a HTS bulk is affected not by applied field types but by peak-to-peak field values on the assumption of same critical current density regardless of different field types. This is the basic idea to compute hysteresis loss more effectively. This paper shows how to reduce total calculation time using the suggested method. To verify the validity of the suggested method, numerical results are compared with experimentally measured ones.
IEEE Transactions on Appiled Superconductivity 07/2003; · 1.04 Impact Factor
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ABSTRACT: In this paper, optimization of an HTS SMES coil as a part of a 200-kJ HTS SMES system has been realized. A 1+1 evolution strategy with the line element method was used to optimize the shape of the coil. In order to ensure the desired energy storage capacity, final dimensions of the coil were recalculated with the finite element method (FEM).
IEEE Transactions on Appiled Superconductivity 04/2002; · 1.04 Impact Factor
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ABSTRACT: A new flywheel energy storage (FES) system that has a heavy flywheel which rotated in low angular velocity was proposed. In this FES, an induction machine of which the winding connection was controllable was used to eliminate the power converter from the conventional FES system. This reduced the total cost of the FES system, because the price of the electronic power converter is a large part of the total FES system cost. In this paper, the new system configuration was proposed and the operation of the suggested FES system using the induction motor/generator was explained in detail. A new levitation system which consisted of the HTS wire and bulks was proposed. This levitation system was designed to produce a very high levitation force to store the same amount of energy compared to that of the high-speed conventional FES system. At the end of the paper, a conceptual design of a 5 Mj low-speed large-inertia FES system with an induction motor/generator was done.
IEEE Transactions on Appiled Superconductivity 04/2002; · 1.04 Impact Factor
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ABSTRACT: Magnetic field can be trapped in a superconducting bulk by using
the field cooling method. In this paper, trapped field was calculated by
3-D numerical analysis. The existing 1-D critical state model was
expanded to 3-D. With this model and iteration method, the nonlinearity
of J-E constitutive relation of a superconducting bulk was numerically
modeled. The field cooling system with a hexahedral bulk and cylindrical
magnet, which is impossible to be analyzed by 2-D or axisymmetric
numerical analysis, was analyzed by the presented method. Being compared
with experimental data, the validity of the presented method was
verified. The finite element method was adopted for numerical
calculation
IEEE Transactions on Appiled Superconductivity 04/2001; · 1.04 Impact Factor
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ABSTRACT: The electromagnetic stress distribution inside a HTS insert is one of the key issues for construction of a high field high/low temperature superconductor (HTS/LTS) magnet. The rmiddotJmiddotB formulae is widely used for the stress calculation of the coil, due to its simplicity. However, the assumption of this calculation makes it impossible to consider the effects of the bobbin, an epoxy impregnated structure, on stress of the coil. In this work, stress analysis methods are reported. The governing equation defined from the force equilibrium state was adopted and used to analyze what the stress of the HTS coil wound with Bi2223/Ag conductor. The validness of the stress analysis method was confirmed by comparison with experimental results, especially in the coil with epoxy impregnation. The numerical and experimental procedures are described and both results are discussed. Budget for Nuclear Research of the Ministry of Education, Culture, Sports, Science and Technology Japan Science and Technology (JST) System Development Program for Advanced Measurement and Analysis (SENTAN)
IEEE.
