• Progress in Superconductivity and Cryogenics
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• v.14 no.1
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• pp.14-19
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• 2012

Shimming, active and/or passive, is indispensable for most MR (magnetic resonance) magnets where homogeneous magnetic fields are required within target spaces. Generally, shimming consists of two steps, field mapping and correcting of fields, and they are recursively repeated until the target field homogeneity is reached. Thus, accuracy of the field mapping is crucial for fast and efficient shimming of MR magnets. For an accurate shimming, a "magnetic" center, which is a mathematical origin for harmonic analysis, must be carefully defined, Although the magnetic center is in general identical to the physical center of a magnet, it is not rare that both centers are different particularly in HTS (high temperature superconducting) magnets of which harmonic field errors, especially high orders, are significantly dependent on a location of the magnetic center. This paper presents a new algorithm, based on a field mapping theory with harmonic analysis, to define the best magnetic center of an MR magnet in terms of minimization of pre-shimming field errors. And the proposed algorithm is tested with simulation under gaussian noise environment.

• Progress in Superconductivity and Cryogenics
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• v.25 no.4
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• pp.75-80
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• 2023

Rare earth barium copper oxide (REBCO) materials have shown the possibility of high-temperature superconductor (HTS) magnetic resonance imaging (MRI) magnets due to their elevated transition temperature. While numerous MRI magnet designs have emerged, there is a growing emphasis on estimating the cost before manufacturing. In this paper, we propose two designs of REBCO whole-body MRI magnets: (1) 1.5 T and (2) 3.0 T, the standard center field choices for hospital use, and compare their costs based on conductor usage. The basis topology of the design method is based on discretized solenoids to enhance field homogeneity. Magnetic stress calculation is done to further prove the mechanical feasibility of their construction. Multi-width winding technique and outer notch structure are used to improve critical current characteristic. We apply consistent constraints for current margins, sizes, and field homogeneities to ensure an equal cost comparison. A graph is plotted to show the cost increase with magnetic flux growth. Additionally, we compare our designs to two additional MRI magnet designs from other publications with respect to the cost and magnetic flux, and present the linear relationship between them.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.6
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• pp.651-659
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• 2016

Korea Institute of Machinery & Materials (KIMM) has developed a high efficient Stirling cryocooler with moving magnet linear compressor for precooling hydrogen liquefier and cooling high temperature superconductor (HTS) devices, such as superconductor cable and superconductor fault current limiters. Hydrogen liquefier and HTS electric devices require cryocooler with cooling capacity of hundred watts to kilowatts at 77 K. The compressor in the Stirling cryocooler uses opposed moving magnet linear motors to drive opposed pistons. High efficient Stirling cryocooler is designed by SAGE-software, manufactured and tested systematically. A cooling capacity of 1 kW at 77 K with an electric input power of 9.6 kW has been analyzed. But prototype test results of the Stirling cryocooler have the cooling capacity of 0.65 kW at 76.8 K with an electric input power of 8.1 kW. And then, 21.5% Carnot COP (Coefficient of performance) of the prototype Stirling cryocooler is achieved. The comparison analysis between SAGE-model and experimental results has shown the direction for further design optimization of the Stirling cryocooler.

• Progress in Superconductivity and Cryogenics
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• v.16 no.4
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• pp.7-16
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• 2014

Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes have already been commercialized but still possess some issues in terms of manufacturing cost, anisotropic in-field performance, $I_c$ response to mechanical loads such as delamination, homogeneity of current transport property, and production length. Development on improving its performance properties to meet the needs in practical device applications is underway and simplification of the tape's architecture and manufacturing process are also being considered to enhance the performance-cost ratio. As compared to low temperature superconductors (LTS), high temperature superconductor (HTS) REBCO CC tapes provide a much wider range of operating temperature and a higher critical current density at 4.2 K making it more attractive in magnet and coil applications. The superior properties of the REBCO CC tapes under magnetic field have led to the development of superconducting magnets capable of producing field way above 23.5 T. In order to achieve its optimum performance, the electromechanical properties under different deformation modes and magnetic field should be evaluated for practical device design. This paper gives an overview of the effects of mechanical stress/strain on $I_c$ in HTS CC tapes due to uniaxial tension, bending deformation, transverse load, and including the electrical performance of a CC tape joint which were performed by our group at ANU in the last decade.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.285-286
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• 2008

In practical applications of HTS tapes for electric devices such as coils and power cables, the jointing of HTS tapes is needed. In magnet applications superconducting joints are needed to achieve very low resistance at the joint, but for power device applications, a slightly higher joint resistance may be acceptable. In this study, an economical joint with good mechanical and electrical integrity could be achieved for Bi-2223 tapes which can be applicable to electric power applications. A lap joint method has been used. The joint resistance and strength of the jointed Bi2223 tapes have been evaluated. Electro-mechanical properties of the joint sample under tension have been examined and compared with the case of the single tapes.

• Progress in Superconductivity and Cryogenics
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• v.10 no.3
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• pp.23-26
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• 2008

Constructions of coated conductor which is differently from Bi-2223 is comprised multiple coatings on a base material or substrate and designed to achieve the highest degree of alignment possibility of the atoms in the superconductor material. In this study, we are measured and analyzed degradations of critical current according to diameter. In addition to study the effects of bending strain, we observed the AC loss of coated conductor and carried out analytical study for relation between Ic degradation and AC loss as well. The measurement of AC loss and numerical calculation was carried out based on Norris theory to compare with experimental results. The relationship between critical current and AC loss of HTS tapes with partial deformation by mechanical stress was studied. These results will amount the most important basis data in the of HTS cable, magnet, etc that winding work is required.

• Progress in Superconductivity
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• v.2 no.2
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• pp.76-80
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• 2001

We have fabricated YBa$_2$Cu$_3$$O_{7-x}$ (YBCO) ramp-edge Josephson junctions by modifying ramp edges of the base electrodes without depositing any artificial barrier layer. YBa$_2$Cu$_3$O/7-x//SrTiO$_3$ (YBCO/STO) films were deposited on SrTiO$_3$(100) by on-axis KrF laser deposition. After patterning the bottom YBCO/STO layer, the ramp edge was cleaned by ion-beam and then reacted with deionized water under various conditions prior to the deposition of counter-electrode layers. The top YBCO/STO layer was deposited and patterned by photolithography and ion milling. We measured current-voltage (I-V) characteristics, magnetic field modulation of the critical current at 77 K. Some showed resistively shunted junction (RSJ)-type I-V characteristics, while others exhibited flux-flow behaviors, depending on the dipping time of the ramp edge in deionized water. Junctions fabricated using optimized conditions showed fairly uniform distribution of junction parameters such as I$_{c}$R$_{n}$ values, which were about 0.16 mV at 77 K with 1$\sigma$~ 24%. We made a dc SQUID with the same deionized water treated junctions, and it showed the sinusoidal modulation under applied magnetic field at 77 K. 77 K.

• Progress in Superconductivity and Cryogenics
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• v.25 no.4
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• pp.60-64
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• 2023

The manufacturing process of antibody drugs comprises two main stages: the upstream process for antibody cultivation and the downstream process for antibody extraction. The domestic bio industry has excellent technology for the upstream process. However, it relies on the technology of foreign countries to execute downstream process such as affinity chromatography. Furthermore, there are no domestic companies capable of producing the equipment for affinity chromatography. High gradient magnetic separation technology using a high temperature superconducting magnet as a novel antibody separation and purification technology is introduced to substitute for the traditional technology of affinity chromatography. A specially designed magnetic filter was equipped in the bore of the superconducting magnet enabling the continuous magnetic separation of nano-sized paramagnetic beads that can be used as affinity magnetic nano beads for antibodies. To optimize the magnetic filter that captures superparamagnetic nanoparticles effectively, various shapes and materials were examined for the magnetic filter. The result of magnetic separation experiments show that the maximum separation and recovery ratio of superparamagnetic nanoparticles are 99.2 %, and 99.07 %, respectively under magnetic field (3 T) and flow rate (600 litter/hr).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.23-30
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• 2017

Most superconducting magnets which generate more than 20 T consist of nested magnets. A combination of LTS and HTS magnets is conventionally used, but high field magnets which use only HTS magnets have been developed recently. As HTS wires have very strong magnetic anisotropy, appropriate techniques should be used to consider this effect properly. The load line method has been conventionally used to design nested magnets for high field generation. Because this method considers only parallel and perpendicular magnetic fields, the effect of their orientation is not taken into account. In this paper, the actual orientation of the magnetic fields from 0 to 90 degrees is considered. The critical currents of the two kinds of high field nested magnets designed using the proposed method are calculated. The finite element method is used to calculate the distribution of the magnetic fields and the evolution strategy is used to find the critical current which maximizes the central magnetic field.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1288-1289
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• 2011

세계가 점차적으로 "전화(電化)"됨에 따라 전기 에너지의 효과적인 분배와 사용이 급격히 중요하게 되었다. 일반 도체를 통한 전류의 흐름은 도체의 저항에 의해 줄열을 발생시켜 전기 에너지의 손실을 일으키고 결국은 에너지와 경제적 자원의 낭비를 초래하게 된다. 초전도체의 저항은 직류 전류에서는 0, 교류 전류에서는 거의 0이기 때문에 초전도체를 이용하면 전력 소자 및 기기의 부피와 무게를 현저히 줄일 수 있는 반면에 모든 전기 시스템의 효율을 향상시킬 수 있고, 에너지 사용의 절감에 따라 환경 문제에 도움을 줄 수 있다. 사고 전류 제한기의 설계에 있어서, 권선형태에 따른 솔레노이드 마그네트와 팬케이크 마그네트를 설계, 제작하여 자장 특성 및 한류 특성을 비교 하였다. 2세대 고온 초전도 선재로 불리는 YBCO 박막형 초전도 선재를 이용하여 동작 전류 증대를 위한 다병렬 솔레노이드 마그네트와 다병렬 팬케이크 마그네트를 제작하였다. 이를 이용하여 440 V/ 630 A급 초전도 사고 전류 제한기와 2 kA 급 대전류 통전 사고 전류 제한 모듈을 설계, 제작하여 단락 특성 시험을 수행하였다. 한편, 자장 응용 기기에 적용 가능한 더블 팬케이크 마그네트를 제 2 세대 초전도선재를 이용하여 설계, 시작하였다. 2세대 선재는 1세대 선재에 비하여 20 T 이상의 외부 자장에 대한 특성이 우수하여 고자장 마그네트 시스템에 더욱 적합하다. 이에 초전도 마그네트 보호를 위한 상전도 영역 전파 실험을 수행하여 CC 선재의 안정도를 측정하였다. 또한 영구전류모드 운전과 플럭스 펌프를 통한 전류 충전에 대한 연구도 병행하였다.