• Nuclear Engineering and Technology
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• 제51권3호
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• pp.877-883
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• 2019

Superconducting multi-spoke cavities are outstanding alternative choice for acceleration of heavy ions in medium velocity regimes. Based on the scheme of China ADS, several researches on the superconducting double-spoke cavities were done and two prototype cavities have been developed. In this paper, the RF design, the mechanical design and fabrication considerations of the bare cavity will be described in detail. After Buffered Chemical Polishing and High Pressure Rinsing, one of the prototype cavities was installed into the Vertical Test Stand for high gradient RF testing at 4.2 K. The measurement results of the quality factor as a function of the accelerating field and the maximum surface field will be presented. An accelerating gradient of more than 15 MV/m is achieved during the test, with maximum surface electric field of 58 MV/m, and maximum surface magnetic field of 117 mT.

• Journal of Magnetics
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• 제3권3호
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• pp.69-73
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• 1998

A drum type magnetic separator was designed and optimized by computer simulation. The separator consisted of rotating outer shell of drum, magnetic flux generator drum which was assembled with numbers of disk type magnet holders, and drum axis around which the magnet holders were fixed. NdFeB magnet blocks were inserted into the disks, and the disks were assembled layer by layer along the drum axis. Magnetic circuits of the separator were simulated on the basis of highest magnetic strength, least cost, and high yield of separation by using a Vector Field S/W employing the Opera-2D program. The separator proved a separation yield of 95% in removing fine iron-base particles, and installed at Hot Rolling Mill of Pohang Iron & Steel Co. In Korea.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1990년도 추계학술대회
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• pp.19-23
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• 1990

A new technique for reducing the susceptibility artifact in gradient echo imaging which uses a tailored RF pulse is proposed. It is applied to the case of imaging where artifacts and distortions arise due to the high local magnetic field inhomogeneity i. e., the susceptibility. The signal loss and void phenomena due to susceptibility in a voxel are studied and a correction method using a tailored RF pulse is proposed. Applications of this method in imaging are given and experimental results obtained using an human volunteer with a 2.0 T KAIS NMR system are presented.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 춘계학술대회 논문집
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• pp.4-4
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• 2009

Paper factories use a large amount of water and same amount of wastewater is generated. It is important to recycle the wastewater because of water shortages and water pollution. The existing water treatment facilities like precipitation process need large-scale equipment and wide space to purify the wastewater of paper factory. High gradient magnetic separation (HGMS) system has the merits to purify rapidly because of large voids at filter and to occupy small space. In this paper, two types of superconducting magnets were used for HGMS systems. Cryo-cooled Bi-2223 superconducting magnet system with 70 mm room temperature bore and 200 mm of height was prepared. Cryo-cooled Nb-Ti superconducting magnet with 100 mm room temperature bore and 600 mm of height was used for magnetic separator. Magnetic filters were designed by the analysis of magnetic field distribution at superconducting magnets. The various magnetic seeding reactions were investigated to increase the reactivity of coagulation. The effects of magnetic separation of wastewater were investigated as variation of magnetic field strength and flow rate of wastewater.

• Progress in Superconductivity
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• 제10권1호
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• pp.50-54
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• 2008

A conduction-cooled superconducting magnet system is developed for material separation. The superconducting magnet for material separation has to be designed to have a strong magnetic field in a control volume. Since the magnetic field gradient is larger at the end rather than at the center of the magnet, we developed a design method to optimize the superconducting magnet for material separation. The safety of the superconducting magnet is evaluated, taking into account the electro-magnetic field, heat and structure. The superconducting coil is successfully wound by the wet-winding method. The superconducting coil is installed in a cryostat maintaining high vacuum, and cooled down to approximately 4 K by a two-stage GM cryocooler. The performance of the conduction-cooled superconducting magnet system is discussed with respect to the supplied current, cooling medium and cooling power of a cryocooler.

• 천문학회보
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• 제40권1호
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• pp.66.3-67
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• 2015

Without scrutinizing reflection, the plasma comprising a coronal loop is usually regarded to reside within a flux rope. This picture seems to have been adopted from laboratory plasma pinches, in which a plasma of high density and pressure is confined in the vicinity of the flux rope axis by magnetic tension and magnetic pressure of the concave inward magnetic field. Such a configuration, in which the plasma pressure gradient and the field line curvature vector are almost parallel, however, is known to be vulnerable to ballooning instabilities (to which belong interchange instabilities as a subset). In coronal loops, however, ideal MHD (magnetohydrodynamic) ballooning instabilities are impeded by a very small field line curvature and the line-tying condition. We, therefore, focus on non-ideal (resistive) effects in this study. The footpoints of coronal loops are constantly under random motions of convective scales, which twist individual loop strands quite randomly. The loop strands with the axial current of the same direction tend to coalesce by magnetic reconnection. In this reconnection process, the plasma in the loop system is redistributed in such a way that a smaller potential energy of the system is attained. We have performed numerical MHD simulations to investigate the plasma redistribution in coalescence of many small flux ropes. Our results clearly show that the redistributed plasma is more accumulated between flux ropes rather than near the magnetic axes of flux ropes. The Joule heating, however, creates a different temperature distribution than the density distribution. Our study may give a hint of which part of magnetic field we are looking to in an observation.

• Investigative Magnetic Resonance Imaging
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• 제5권1호
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• pp.57-65
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• 2001

목적 : 초고속 Echo Planar Imaging (EPI) 의 데이터 측정시간을 반으로 단축시킨 half courier EPI와 임상에서 널리 사용하는 $T_2$ 강조 영상을 결합한 $T_2$-weighted half courier EPI(T2HEPl) 영상기법을 제안하였다. 제안한 방법으로 강한 $T_2$ 대조도를 갖는 $128{\times}128$의 고해상도 EPI 영상을 single scan으로 얻고자 한다. 대상 및 방법 : 초고속 EPI 기법의 데이터 측정시간을 줄이기 위하여 k-space의 절반만을 측정하고, 나머지 절반은 conjugate symmetry 성질을 이용하여 재구성한다. 따라서 64개의 에코로 $128{\times}128$의 고해상도 single shot 영상을 얻을 수 있다. 또한 k-space 데이터의 순서를 시간 축에서 조절하여 강한 $T_2$ 대조도를 갖는 영상을 얻을 수 있다 Eddy current의 영향으로 phase encoding 방향으로 잔류 경사자계가 있을 경우 측정된 데이터들은 k-space에서 이동이 되며 , 이것은 재구성 영상에 심각한 문제점을 초래하게 된다. 본 논문에서는 pre-scan에서 얻은 기준 데이터와 dc에 해당하는 에코간의 상관도를 측정하여 이동을 추정하며, 초기의 phase encoding gradient의 크기를 조정하여 이러한 이동을 제거한다. 결과 : 제안한 $T_2$-weighted half courier EPI 영상기법을 1.0 Tesla 전신 MRI 시스템에 적용하였다. 실험 조건은 single shot으로 TR은 무한대이고, TE는 72ms와 96ms로 설정하였다. 제안한 영상기법을 이용하여 single scan으로 강한 $T_2$ 대조도를 갖는 128x128의 고해상도 EPI 영상을 얻을 수 있었다. 결론 : 제안한 Half Fourier기법을 이용하여 기존의 $64{\times}64$ 영상보다 해상도를 높인 $128{\times}128$ EPI영상을 single scan으로 얻을수 있었으며, 에코의 적절한 배치를 통해 임상에서 널리 사용되는 $T_2$ 대조도를 얻을 수 있었다. 제안한 방법은 특별한 하드웨어의 추가 없이, 펄스 시퀀스와 tuning 및 재구성 알고리즘 등의 소프트웨어적인 방법만으로 구현이 가능하여 많은 임상 응용이 기대된다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.342-343
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• 2009

Paper factories use a large amount of water and same amount of wastewater is generated. It is important to purity and recycle the wastewater because of water shortages and water pollution. The existing water treatment facilities like precipitation process need large-scale equipment and wide space to purity the wastewater of paper factory. High gradient magnetic separation (HGMS) system has the merits to purity rapidly because of large voids at filter and to occupy small space. In this paper, two types of superconducting magnets were used for HGMS systems. Cryo-cooled Bi-2223 superconducting magnet system with 70 mm room temperature bore and 200 mm of height was prepared. Cryo-cooled Nb-Ti superconducting magnet with 100 mm room temperature bore and 600 mm of height was used for magnetic separator. Magnetic filters were designed by the analysis of magnetic field distribution at superconducting magnets. The various magnetic seeding reactions were investigated to increase the reactivity of coagulation. The effects of magnetic separation of wastewater were investigated as variation of magnetic field strength and flow rate of wastewater.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.44-44
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• 2010

Conventional water treatment facilities like precipitation process need large-scale equipment and wide space to purify the wastewater of paper factory. In case of massive waste water, high gradient magnetic separation (HGMS) parts are more effective to purify it rapidly and to occupy relatively small space, since large voids at filter with HGMS are adopted. Cryo-cooled Nb-Ti superconducting magnet with room temperature bore in diameter of 100 mm and 600 mm in height was used for magnetic separator. Magnetic filters were designed by the analysis of magnetic field distribution at superconducting magnets.

• Investigative Magnetic Resonance Imaging
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• 제25권3호
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• pp.141-155
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• 2021

Purpose: To develop a 3D magnetic resonance fingerprinting (MRF) method for application in high resolution knee cartilage PD, T₁, T₂ mapping. Materials and Methods: A novel 3D acquisition trajectory with golden-angle rotating radial in k_xy direction and interleaved echo planar imaging (EPI) acquisition in the k_z direction was implemented in the MRF framework. A centric order was applied to the interleaved EPI acquisition to reduce Nyquist ghosting artifact due to field inhomogeneity. For the reconstruction, singular value decomposition (SVD) compression method was used to accelerate reconstruction time and conjugate gradient sensitivity-encoding (CG-SENSE) was performed to overcome low SNR of the high resolution data. Phantom experiments were performed to verify the proposed method. In vivo experiments were performed on 6 healthy volunteers and 2 early osteoarthritis (OA) patients. Results: In the phantom experiments, the T₁ and T₂ values of the proposed method were in good agreement with the spin-echo references. The results from the in vivo scans showed high quality proton density (PD), T₁, T₂ map with EPI echo train length (N_ETL = 4), acceleration factor in through plane (R_z = 5), and number of radial spokes (N_spk = 4). In patients, high T₂ values (50-60 ms) were seen in all transverse, sagittal, and coronal views and the damaged cartilage regions were in agreement with the hyper-intensity regions shown on conventional turbo spin-echo (TSE) images. Conclusion: The proposed 3D MRF method can acquire high resolution (0.5 mm³) quantitative maps in practical scan time (~ 7 min and 10 sec) with full coverage of the knee (FOV: 160 × 160 × 120 mm³).