S. Hahn

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

Are you S. Hahn?

Claim your profile

Publications (21)21.21 Total impact

  • Y.G. Kim · S. Hahn · K.L. Kim · D.G. Yang · H.G. Lee
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper reports the optimization procedure for a no-insulation (NI) multi-width (MW) REBCO magnet, which enables the fabrication of a highly compact and competitively priced superconducting magnet. In order to identify the design considerations for the NI-MW magnet, the electromagnetic performances of 3 different magnets were investigated using the finite element method (FEM). Based on the comparison results, it was verified that the critical current distribution-factor (CCD-factor), which is the ratio of the highest pancake critical current (Ic) to the lowest pancake Ic within the magnet, should be close to 1.00 for the MW configuration to be most effective. In the optimized MW magnet, the center Bz (7.54 T) remarkably exhibited an ∼ 51 % increase compared to the 4-mm single width magnet (5.00 T). Furthermore, the CCD-factor of the optimized MW magnet was 1.04, which is quite close to 1.00, sufficiently demonstrating the validity of the optimization process and result.
    No preview · Article · Jul 2015 · Current Applied Physics
  • [Show abstract] [Hide abstract]
    ABSTRACT: Herein, we report a feasibility study for elimination of the screening current-induced field (SCIF) in fully insulated (INS) and no-insulation (NI) GdBCO coated conductor (CC) coils exposed to an external AC magnetic field generated by background solenoid copper coils. Prior to investigating the effects of external AC magnetic fields on SCIF in the GdBCO CC coils, the magnetic flux density (B z ) was calculated using the equivalent circuit model and compared to the B z obtained empirically to quantify the SCIF in the INS and NI coils. The value of the SCIF in the NI coil was smaller than that in the INS coil without the use of an external AC magnetic field, due to the current paths originating from the turn-to-turn and layer-to-layer contacts, suggesting that the screening current dissipated by contact resistance during charging. When the INS and NI coils were exposed to the external AC magnetic field, the B z of the coils increased gradually, and eventually saturating to the calculated B z values, indicating full removal of the SCIF. In addition, the SCIF of the NI coil could be removed under subjection to a lower external AC magnetic field compared to the INS coil, due to the lower SCIF occurring in the NI coil after charging.
    No preview · Article · Jan 2014 · Journal of Superconductivity and Novel Magnetism
  • O J Kwon · K L Kim · Y H Choi · H J Shin · S Hahn · Y Iwasa · H G Lee
    [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.
    No preview · Article · Jul 2013 · Superconductor Science and Technology
  • S.B. Kim · T. Kimoto · S. Hahn · Y. Iwasa · J. Voccio · M. Tomita
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jan 2013 · Physica C Superconductivity

  • No preview · Article · Jan 2013
  • Y H Choi · S Hahn · J B Song · D G Yang · H G Lee
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Dec 2011 · Superconductor Science and Technology
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Nov 2011 · Physica C Superconductivity
  • S.B. Kim · M. Imai · R. Takano · J.H. Joo · S. Hahn
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jul 2011 · IEEE Transactions on Applied Superconductivity
  • S. Hahn · J. Bascuñán · W. Yao · Y. Iwasa
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Nov 2010 · Physica C Superconductivity
  • S.B. Kim · M. Imai · R. Takano · K. Kashima · S. Hahn
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Nov 2010 · Physica C Superconductivity
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jul 2010 · IEEE Transactions on Applied Superconductivity
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jun 2010 · IEEE Transactions on Applied Superconductivity
  • J. Bascuñán · S. Hahn · M. Ahn · Y. Iwasa
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Apr 2010
  • Source
    K.L. Kim · S.J. Hwang · S. Hahn · S.H. Moon · H.G. Lee
    [Show abstract] [Hide abstract]
    ABSTRACT: The properties of the conductor.mechanical, thermal, and electrical-are the key information in the design and optimization of superconducting coils. Particularly, in devices using second generation (2G) high temperature superconductors (HTS), whose base materials (for example, the substrate or stabilizer) and dimensions are adjustable, a design process for conductor optimization is one of the most important factors to enhance the electrical and thermal performance of the superconducting system while reducing the cost of the conductor. Recently, we developed a numerical program that can be used for 2G HTS conductor optimization. Focusing on the five major properties, viz. the electrical resistivity, heat capacity, thermal conductivity, Z-value, and enthalpy, the program includes an electronic database of the major base materials and calculates the equivalent properties of the 2G HTS conductors using the dimensions of the base materials as the input values. In this study, the developed program is introduced and its validity is verified by comparing the experimental and simulated results obtained with several 2G HTS conductors.
    Preview · Article · Jan 2010 · Progress in Superconductivity and Cryogenics (PSAC)/Journal of the Korea Institute of Applied Superconductivity and Cryogenics
  • S. Choi · S. H. Park · S.Y. Lee · W. Kim · C. Park · J. B. Song · H. Lee · K. Choi · S. Hahn
    [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.
    No preview · Article · Oct 2009 · Physica C Superconductivity
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The operation of the SMES system can be divided into three modes such as charging, operating and discharging. During the charging and the discharging modes, a magnetic field variation due to the current increase and decrease generate eddy current losses in the SMES system. The eddy current loss in discharging mode is the major factor to be considered because the operating time in the mode is fixed, whereas the charging mode has the arbitrary operating time which is not fixed. In this paper, we present the analysis results of the eddy current losses which are generated in the 600kJ class HTS SMES system during the discharging mode.
    Preview · Article · Sep 2008 · Physica C Superconductivity
  • Source
    S. Hahn · J. Bascunan · H. Lee · E. S. Bobrov · W. Kim · Y. Iwasa
    [Show abstract] [Hide abstract]
    ABSTRACT: For the first time in nuclear magnetic resonance (NMR) magnet development, a magnet configuration comprising an insert wound with high-temperature superconductor (HTS) and a background-field magnet wound with low-temperature superconductor (LTS) has been proven viable for NMR magnets. This new LTS/HTS magnet configuration opens the way for development of 1 GHz and above NMR magnets. Specifically, a 700 MHz LTS/HTS NMR magnet (LH700), consisting of a 600 MHz LTS magnet (L600) and a 100 MHz HTS insert (H100), has been designed, built, and successfully tested, and its magnetic field characteristics were measured and analyzed. A field homogeneity of 172 ppm in a cylindrical mapping volume of 17 mm diameter by 30 mm long was measured at 692 MHz and corresponding <sup>1</sup> H NMR signal with 1.9 kHz half-width was captured. Two techniques, room-temperature and ferromagnetic shimming, were analytically examined to investigate if they would be effective for further improving spatial field homogeneity of the LH700.
    Preview · Article · Mar 2008 · Review of Scientific Instruments
  • [Show abstract] [Hide abstract]
    ABSTRACT: Superconducting magnetic energy storage (SMES) systems with high temperature superconducting (HTS) wires have been actively developed world-wide. In this paper, we researched decreasing effect of eddy current loss according to a shape of a cooling plate by division and slit. The cooling plate having less eddy current loss was designed by division and slit and analyzed for three models which have different poison of the cooling plate by 3D finite element method for a 600 kJ class SMES magnet.
    No preview · Conference Paper · Nov 2007
  • S.W. Lee · Y.I. Hwang · H.W. Lim · W.S. Kim · K.D. Choi · S. Hahn
    [Show abstract] [Hide abstract]
    ABSTRACT: Because of the shape of the HTS tapes, the layer winding is not good for high voltage power transformer. The double pancake winding which is one of disk windings is good for the insulation and limitation of voltage stress, but it makes high AC losses. So we have proposed a new winding method which is called continuous disk winding (CDW) for high voltage HTS transformers and has advantages from both layer and double pancake windings. In this paper, we calculated numerically and measured AC losses in the HTS continuous disk winding. 4 kinds of short samples with different numbers of stacked HTS tapes were made and their AC losses were measured. These data were used in the process of calculation, making the result more precisely. Other properties such as the critical current, inductance and capacitance were analysed numerically and tested also.
    No preview · Article · Jul 2007 · IEEE Transactions on Applied Superconductivity
  • R Mai · S Hahn · H Lee · J Bascuñán · Y Iwasa
    [Show abstract] [Hide abstract]
    ABSTRACT: By periodically injecting a quantified amount of flux in a ''slightly'' resistive magnet, a digital flux injector (DFI) enables the magnet to effectively operate in persistent mode. This paper presents the operation and performance results of DFI coupled to a 50-MHz HTS insert coil for an NMR magnet.
    No preview · Article · Jul 2006 · Journal of Physics Conference Series

Publication Stats

113 Citations
21.21 Total Impact Points


  • 2006-2015
    • Massachusetts Institute of Technology
      • Francis Bitter Magnet Laboratory
      Cambridge, Massachusetts, United States
  • 2004-2010
    • Seoul National University
      • Department of Materials Science and Engineering
      Sŏul, Seoul, South Korea
  • 2007
    • The Seoul Institute
      Sŏul, Seoul, South Korea