S. Hahn

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (42)45 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: The thermal and electrical characteristics of two GdBCO-coated conductor racetrack coils, one insulated with Kapton insulation and the other without turn-to-turn insulation, were investigated by typical voltage–current measurement, charge–discharge, sudden discharge, and over-current tests with respect to external pressures applied to the straight sections of the coils. The test results show that the thermal and electrical stabilities of the racetrack coil without insulation were enhanced considerably with increasing external pressure up to 0.5 MPa, whereas those of the insulated coil were not affected by the pressure. The non-insulated HTS racetrack-type coil with improved turn-to-turn thermal contact in the straight sections may have the potential to be manufactured into field coils for HTS wind turbine generators with highly enhanced thermal and electrical stabilities.
    Superconductor Science and Technology 07/2013; 26(8):085025. · 2.76 Impact Factor
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    ABSTRACT: A compact high temperature superconducting (HTS) magnet, which consists of a stack of 500 HTS thin film annuli, was constructed and tested. Each thin film annulus, manufactured by the AMSC using the Rolling Assisted Bi-axially Textured Substrate (RABiTS) method, has a square cross-section of 40 mm × 40 mm with a thickness of 80 m. It has a 25-mm center hole created by machining. This paper reports a study on the anisotropic Jc issue due to the rolling procedure of the Ni substrate direction and its impact on field homogeneity. Also, three different stacking methods with rotation angles of 22.5°, 90°, and 0° against the rolling direction have been tested to study their impacts on strength, spatial homogeneity, and temporal stability of trapped fields. Finally, the 500-annulus magnet was tested at 21 K under a cryogen-free environment using a GM cryocooler. The spatial field homogeneity and temporal stability were measured at 21 K and compared with those obtained in a bath of liquid nitrogen at 77 K.
    Physica C Superconductivity 01/2013; 484:295–299. · 0.72 Impact Factor
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    ABSTRACT: High temperature superconducting (HTS) magnets are expected to play a prominent role in future nuclear magnetic resonance (NMR) systems because not only are they an essential item to surpass the current record of NMR frequency, 1 GHz, but also they may even enable an all-HTS NMR device that can be operated without a liquid helium cryogenic environment. The HTS magnets, however, introduce many new challenges as an NMR magnet, including the large high-order harmonic field errors originated from manufacturing errors of the HTS insert, particularly the one comprised of double-pancake (DP) coils. These harmonic errors are dependent on a choice of magnetic center, i.e., a magnetic center can be defined in a way to minimize the harmonic errors in an HTS NMR magnet. This paper proposes a new algorithm to automatically find a magnetic center of an HTS magnet to minimize the target harmonic components after a “single” field mapping. With a field map given, field gradients are calculated by a harmonic analysis, and then a new magnetic center is determined, using the proposed algorithm, to minimize the target harmonic errors. These steps are recursively repeated until the “best” magnetic center is defined. A test coil was constructed and 3-D field mapping tests were performed to verify the proposed algorithm. An in-house 3-D field mapping system was used for field mappings during the experiment.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):4900204-4900204. · 1.20 Impact Factor
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    ABSTRACT: Upon the totally unexpected theft of the original 600 MHz HTS insert that occurred in December 2011, we were forced to examine our entire 1.3 GHz NMR Magnet program anew and determined that a combination of a 600 MHz LTS magnet and a 700 MHz HTS insert (H700) would yield a 1.3 GHz LTS/HTS magnet that meets the technical specifications consistent with economic constraints. Although this new 700 MHz HTS insert still comprises, as H600, a YBCO inner coil and a Bi2223 outer coil, it incorporates innovative design features. In addition to presenting the major design parameters of the new H700, we discuss here its key electromagnetic and mechanical issues.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):4400304-4400304. · 1.20 Impact Factor
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    ABSTRACT: This paper presents our latest experimental results on high-temperature superconducting (HTS) splice joints for HTS insert coils made of YBCO and Bi2223, that comprise a 1.3 GHz low-temperature superconducting/HTS nuclear magnetic resonance magnet currently under development at Francis Bitter Magnet Laboratory. HTS splice joint resistivity at 77 K in these insert coils must be reproducible and <; 100 Ω·cm2. Several YBCO tape to YBCO tape (YBCO-YBCO) splice joint samples were fabricated, and their resistivity and Ic were measured at 77 K. First, we describe the joint splicing setup and discuss the parameters that affect joint resistivity: pressure over joint surface, solder, and YBCO spool batch. Second, we report results on YBCO-YBCO joints at 77 K in zero field. Measurements have shown that spool batch and solder are primary sources of a wide range of variation in YBCO-YBCO joint resistivity. By controlling these parameters, we expect to reproducibly achieve HTS-HTS resistive joints of resistance <; 100 nΩ·cm2.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):6800704-6800704. · 1.20 Impact Factor
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    ABSTRACT: In fabrication of a compact NMR (Nuclear Magnetic Resonance) magnet which consists of a stacked HTS (High Temperature Superconducting) bulk annuli, generally there are three key issues: spatial homogeneity, temporal stability, strength of trapped magnetic fields. This paper presents a study on the effects of axial gap length between stacked HTS bulks on the three key issues of a bulk HTS magnet for compact HTS NMR applications. The HTS bulk magnet of which the ID and OD are 20 and 60 mm respectively has a 50 and 80 mm heights depending on the axial gap lengths between HTS bulks. The gap length between each HTS bulk varied from 0 mm to 10 mm and were used as parameters to optimize, analytically as well as experimentally, the overall field homogeneity of the HTS bulk magnet. The optimized axial gap length was obtained by analytical results, and the better magnetic field homogeneity and temporal stability of trapped magnetic field were achieved by lower magnetization field. The improved spatial homogeneity and strength of generated magnetic field by a new compact NMR magnet will be presented.
    IEEE Transactions on Applied Superconductivity 01/2012; 22(3):4302004-4302004. · 1.20 Impact Factor
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    ABSTRACT: In design and manufacture of a compact NMR (nuclear magnetic resonance) magnet which consists of a stack of high temperature superconducting (HTS) bulk annuli, spatial homogeneity and temporal stability of trapped magnetic fields are key issues. This paper presents a study on optimized configuration of stacked HTS bulk annuli for the compact NMR application. A three-stack bulk magnet was designed and tested at two different temperatures of 20 and 77 K, and two different background fields of 3 and 5 T. The test results were compared with analytic results to verify the validity of the calculation. Then, various optimized patterns were investigated numerically to find out an optimized stack pattern of HTS bulk annuli in a given condition. The results prove that with the proposed optimized method trapped field strength as well as its homogeneity of a bulk-annulus stack can be improved.
    IEEE Transactions on Applied Superconductivity 07/2011; · 1.20 Impact Factor
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    ABSTRACT: The partial insulation winding was examined to ameliorate the slow charge–discharge shown by coils wound without insulation. Single pancake coils of GdBCO coated conductor were wound without insulation, with kapton tape every five turns, and with the full use of kapton tape. They were characterized by charge–discharge, sudden discharge, and over-current testing. The improved charging and discharging and high thermal and electrical stabilities of the partially insulated coil demonstrate its potential for use in HTS power applications.
    Superconductor Science and Technology 01/2011; 24(12). · 2.76 Impact Factor
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    ABSTRACT: A compact nuclear magnetic resonance (NMR) magnet is one of the new applications after a technique to enhance maximum trapped field of an high temperature superconducting (HTS) bulk. In design of a compact NMR magnet which consists of the stacked HTS bulk annuli, the issues of strength, spatial homogeneity and temporal stability by trapped magnetic fields are very important. This paper presents a study on the effects of magnetization field strength and gap length between stacked bulks for the compact HTS bulk NMR applications. Four-stacked HTS bulk magnet with ID 20mm and OD 60mm was prepared to investigate the optimized configuration. The thickness of each HTS bulk is 5mm, and the gap lengths from 0mm to 10mm were used as parameters in analysis and experiment, respectively. Four-stacked HTS bulk magnets with various gap lengths were tested at two different background magnetic fields of 0.5T and 2T at 77K. The optimized axial gap length was found out by analytical results, and the better magnetic field homogeneity and temporal decay property of trapped magnetic field were obtained by lower magnetization field in this experiments.
    Physica C Superconductivity 01/2011; 471(21):1454-1458. · 0.72 Impact Factor
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    ABSTRACT: We have proposed continuously transposed coated conductor (CTCC) in striation for power devices reducing AC loss. It consists of a number of coated conductors with filaments made by striation. The transport of current may distribute non-uniformity in the filament particularly while CTCC conducts AC current. The array of Hall sensors is capable of measuring the current distribution in the filaments and in conductors. However, the search coil array may be applied as ersatz for Hall array in case of existing AC current. The filamentary CTCCs are prepared and the current distribution is then measured by the array of search coils.
    IEEE Transactions on Applied Superconductivity 07/2010; · 1.20 Impact Factor
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    ABSTRACT: A solid cryogen cooled 500 MHz/200 mm RT bore MRI magnet has been built and tested. The magnet is a low temperature superconductor (LTS) Nb3Sn system of compensated coils that can operate in persistent mode at 250 A and in the range from 4.2 K to 6 K. Here we present details of the magnet integration to the cryostat and also test data of the magnet immersed in solid nitrogen (SN2). Test included a cooldown/freezing of the cryogen to 4.2 K and operation of the magnet in the 4.2 K-6 K range, while the magnet remained in persistent mode.
    04/2010;
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    ABSTRACT: The stabilizer of a YBCO coated conductor (CC) plays a very important role in bypassing the over-current and transferring the heat generated at the moment of a fault. Therefore, one of big issues is to determine the best material for the stabilizer and its dimensions for high performance in a HTS power application system. In the case of a superconducting fault current limiter (SFCL), which requires it to react immediately to any fault, the characteristics of the stabilizer are decisive in limiting the fault current and recovering the superconducting properties during and after quenching. This study examined the electrical and thermal behavior of YBCO CCs with various stabilizer thicknesses in fault mode to determine the effects of the stabilizer thickness on the quench/recovery characteristics of YBCO CCs. In particular, the electric field intensity (E) of YBCO CCs in fault mode were calculated and compared with the experimental results.
    IEEE Transactions on Applied Superconductivity 01/2010; 20(3):1246-1249. · 1.20 Impact Factor
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    ABSTRACT: In 2008, the Phase 3 program to complete a 1.3GHz (30.5T) NMR magnet started at the Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology. It comprises two sub-phases, 3A and 3B. In Phase 3A, a 600MHz high temperature superconductor (HTS) insert magnet (H600) will be designed, constructed, and operated in the bore of a 500MHz low temperature superconductor (LTS) background magnet. This will be followed by Phase 3B, in which the H600 will be combined with a 700MHz LTS background magnet to complete a 1.3GHz NMR LTS/HTS magnet. This paper presents and discusses design issues for two conductor options for H600: BiSCCO-2223 (Bi2223) and coated-YBCO or its variants, here designated as YBCO. For each conductor option, we focused on the following issues: (1) elastic and thermal properties; (2) critical current vs. field performance; (3) splice and index heat dissipations; (4) mechanical and thermal stresses; and (5) protection.
    Physica C Superconductivity 01/2010; 470(20):1721-1726. · 0.72 Impact Factor
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    ABSTRACT: Recently, the performance of high-temperature superconducting (HTS) bulks such as a critical current density, size, and mechanical strength has been improved. In consequence, various applications with HTS bulks such as motors, bearings, and flywheels are being investigated by many research groups; Compact nuclear magnetic resonance (NMR) magnet is one of the new applications after a technique to enhance maximum trapped field of an HTS bulk more than 11.7T, 500MHz 1H NMR frequency, 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, the issues of spatial homogeneity and temporal stability of trapped magnetic fields in HTS bulk annuli are very important. In this paper, the characteristics of the trapped magnetic fields in a stack of assembled HTS bulk annuli were investigated with various axial spaces between HTS bulks, experimentally and analytically.
    Physica C Superconductivity 01/2010; 470(20):1740-1744. · 0.72 Impact Factor
  • H. Lee, S. Hahn, B. Ham, J. Paik, M. Lee
    European Neuropsychopharmacology - EUR NEUROPSYCHOPHARMACOL. 01/2010; 20.
  • Source
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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 07/2009; · 1.20 Impact Factor
  • Source
    SeokBeom Kim, T. Nakano, R. Takano, Seung-yong Hahn
    [show abstract] [hide abstract]
    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 Applied Superconductivity 07/2009; · 1.20 Impact Factor
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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.
  • [show abstract] [hide abstract]
    ABSTRACT: For the design of a high temperature superconductor (HTS) power transformer the AC loss is a critical issue because the energy is dissipated as heat in the low temperature. It is necessary to study the AC losses theoretically and experimentally. For the analysis of AC losses in an HTS power transformer, two-dimensional numerical analysis has been carried out until now. However, AC losses which are calculated by using two-dimensional numerical analysis differ from those using three-dimensional numerical analysis because the geometry of the HTS transformer is not symmetric.AC losses of a 1 MVA-single-phase HTS transformer were calculated using both two-dimensional and three-dimensional numerical analysis. To prove the effectiveness of the calculations, the numerical results were compared with the measured results for a transformer fabricated using Bi2Sr2CaCu2O8+δ tapes in 2004.
    Physica C Superconductivity 01/2009; · 0.72 Impact Factor
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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 Applied Superconductivity 07/2008; · 1.20 Impact Factor

Publication Stats

112 Citations
34 Downloads
2k Views
45.00 Total Impact Points

Institutions

  • 2004–2013
    • Massachusetts Institute of Technology
      • Francis Bitter Magnet Laboratory
      Cambridge, Massachusetts, United States
  • 2009–2011
    • Okayama University
      Okayama, Okayama, Japan
    • Korea Polytechnic University
      Sŏul, Seoul, South Korea
  • 2007
    • Electronics and Telecommunications Research Institute
      Sŏul, Seoul, South Korea
  • 2001–2004
    • Seoul National University
      • Department of Electrical and Computer Engineering
      Sŏul, Seoul, South Korea