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An LTS/HTS NMR Magnet Operated in the Range 600–700 MHz
Bascunan, J.,Wooseok Kim,Hahn, S.,Bobrov, E.S.,Lee, H.,Iwasa, Y. Institute of Electrical and Electronics Engineers 2007 IEEE transactions on applied superconductivity Vol.17 No.2
<P>As part of our 3-phase program to develop a high resolution 1 GHz LTS/HTS NMR magnet, a system composed of a 600 MHz LTS background NMR magnet and an HTS insert operating in the range 75 to 100 MHz has been built and tested. Operated at 4.2 K, immersed in a bath of liquid helium, the Phase 2 LTS/HTS magnet, the LTS magnet in persistent mode and the HTS insert powered by a stable supply, generated an NMR frequency of 692.2 MHz (16.26 T): the LTS magnet, with 234.4 A, at 588.7 MHz (13.83 T); and the HTS insert, with 115.95 A, at 103.5 MHz (2.43 T). This paper presents results of the magnet operation during test geared to the design of room temperature shim coils and ferromagnetic tiles. Magnetization effects of the HTS insert on field distribution are also reported.</P>
Quench Analyses of the MIT 1.3-GHz LTS/HTS NMR Magnet
Institute of Electrical and Electronics Engineers 2019 IEEE transactions on applied superconductivity Vol.29 No.5
<P>The MIT 1.3-GHz LTS/high-temperature superconducting (HTS) nuclear magnetic resonance (NMR) magnet is currently under development. The unique features of this magnet include a three-nested formation for an 800-MHz REBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>x</SUB> (RE = Y, Gd) (REBCO) insert (H800) and the no-insulation (NI) winding technique for H800 coils. Because when it is driven to the normal state, an NI REBCO magnet will respond electromagnetically, thermally, and mechanically that may result in permanent magnet damage, analysis of a quenching magnet is a key aspect of HTS magnet protection. We have developed a partial element equivalent circuit method coupled to a thermal and stress finite-element method to analyze electromagnetic and mechanical responses of a nested-coil REBCO magnet each a stack of NI pancake coils. Using this method, quench simulations of the MIT 1.3-GHz LTS (L500)/HTS (H800) NMR magnet (1.3G), we have evaluated currents, strains, and torques of H800 Coils 1 to 3 and L500, and center fields of 1.3G, L500, and H800. Our analyses show H800 is vulnerable to mechanical damage.</P>
MIT 1.3-GHz LTS/HTS NMR Magnet: Post Quench Analysis and New 800-MHz Insert Design
Institute of Electrical and Electronics Engineers 2019 IEEE transactions on applied superconductivity Vol.29 No.5
<P>We present post-quench analyses of the MIT 800-MHz REBCO insert magnet (H800), unexpectedly quenched during operation in March 2018, and design study of a new 800-MHz HTS insert (H800N). The as-wound H800 was supposed to contribute 18.7 T and, with an LTS background magnet (L500), produce 30.5 T corresponding to a proton resonance frequency of 1.3 GHz. The H800 was operated at 4.2 K in liquid helium and, about 5 min after the power supply reached a target operating current of 251.3 A, it experienced a quench. Because the damage in the H800 was more widespread than it first appeared, we decided to design and build a new insert magnet, H800N. In designing H800N, we tried to eliminate unanticipated flaws in our H800 design. H800N has been designed to be more stable and reliable against quench without permanent damage by: 1) adopting a single solenoid structure composed of 40 stacked double pancake coils with improved cross-over sections; 2) enhancing thermal stability; and 3) reducing excessive current margin for quench protection.</P>
High-temperature superconductors for NMR/MRI magnets:opportunities and challenges
Iwasea, Yukikazu,Bascunan, Juan,Hahn, Seung-Yong,Yao, Wejun The Korean Society of Superconductivity and Cryoge 2009 한국초전도저온공학회논문지 Vol.11 No.4
The unique features of HTS offer Opportunities and challenges to a number of applications. In this paper we focus on NMR and MRI magnets, illustrating them with the NMR/MRI magnets that we are currently and will shortly be engaged: a 1.3GHz NMR magnet, an "annulus" magnet, and an $MgB_2$ whole-body MRI magnet. The opportunities with HTS include: 1) high fields (e.g., 1.3GHz magnet); 2) compactness (annulus magnet); and 3) enhanced stability despite liquid-helium-free operation ($MgB_2$ whole-body MRI magnet). The challenges include: 1) a large screening current Beld detrimental to spatial field homogeneity (e.g., 1.3 GHz magnet); 2) uniformity of critical current density (annulus magnet); and 3) superconducting joints ($MgB_2$ magnet).
High-temperature superconductors for NMR/MRI magnets:opportunities and challenges
Iwasa, Yukikazu,Bascunan, Juan,Hahn, Seungyong,Yao, Weijun The Korea Institute of Applied Superconductivity a 2009 초전도와 저온공학 Vol.11 No.2
The unique features of HTS offer opportunities and challenges to a number of applications. In this paper we focus on NMR and MRI magnets, illustrating them with the NMR/MRI magnets that we are currently and will shortly be engaged: a 1.3 GHz NMR magnet, an "annulus" magnet, and an $MgB_2$whole-body MRI magnet. The opportunities with HTS include: 1) high fields (e.g., 1.3 GHz magnet); 2) compactness (annulus magnet); and 3) enhanced stability despite liquid-helium-free operation ($MgB_2$whole-body MRI magnet). The challenges include: 1) a large screening current field detrimental to spatial field homogeneity (e.g., 1.3 GHz magnet); 2) uniformity of critical current density (annulus magnet); and 3) superconducting joints ($MgB_2$magnet).
A REBCO Persistent-Current Switch (PCS): Test Results and Switch Heater Performance
Michael, Philip C.,Timing Qu,Voccio, John,Bascunan, Juan,Hahn, Seungyong,Iwasa, Yukikazu Institute of Electrical and Electronics Engineers 2017 IEEE transactions on applied superconductivity Vol.27 No.4
<P>In this paper, we report preliminary results of our on-going effort to develop a superconducting persistent-current switch (PCS) for REBCO pancake coils that will be operated in liquid helium. In the first part of this paper, we briefly describe experimental results of our PCS operated in the temperature range 77-57 K, i.e., liquid-and solid-nitrogen environments. The rest we devote to a new PCS heater design in which we target a heating power of < 1 W in liquid helium.</P>
Seungyong Hahn,Seok Beom Kim,Min Cheol Ahn,Voccio, John,Bascunan, Juan,Iwasa, Yukikazu IEEE 2010 IEEE transactions on applied superconductivity Vol.20 No.3
<P>This paper presents experimental and analytical results of trapped field characteristics of a stack of square YBCO thin film plates for compact NMR magnets. Each YBCO plate, 40 mm × 40 mm × 0.08 mm, has a 25-mm diameter hole at its center. A total of 500 stacked plates were used to build a 40-mm long magnet. Its trapped field, in a bath of liquid nitrogen, was measured for spatial field distribution and temporal stability. Comparison of measured and analytical results is presented: the effects on trapped field characteristics of the unsaturated nickel substrate and the non-uniform current distribution in the YBCO plate are discussed.</P>
Min Cheol Ahn,Yagai, T.,Seungyong Hahn,Ando, R.,Bascunan, J.,Iwasa, Y. IEEE 2009 IEEE transactions on applied superconductivity Vol.19 No.3
<P>This paper presents experimental and simulation results of a screening current induced magnetic field (SCF) in a high temperature superconductor (HTS) insert that constitutes a low-/high-temperature superconductor (LTS/HTS) NMR magnet. In this experiment, the HTS insert, a stack of 50 double-pancake coils, each wound with Bi2223 tape, was operated at 77 K. A screening current was induced in the HTS insert by three magnetic field sources: 1) a self field from the HTS insert; 2) an external field from a 5-T background magnet; and 3) combinations of 1) and 2). For each field excitation, which induced an SCF, its axial field distribution and temporal variations were measured and compared with simulation results based on the critical state model. Agreement on field profile between experiment and simulation is satisfactory but more work is needed to make the simulation useful for designing shim coils that will cancel the SCF.</P>