• 한국초전도ㆍ저온공학회논문지
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• 제12권1호
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• pp.56-60
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• 2010

Recently, many researches have been carried out for a high temperature superconducting (HTS) magnet which is advantageous in high critical current density and critical temperature. In HTS magnet, however, critical current is decreased by perpendicular magnetic field and persistent current is hard to maintain due to a low index value and high joint resistance compared with low temperature superconducting (LTS) magnet. In this paper, the HTS magnet using BSCCO wire was simulated through finite element method (FEM) and manufactured. we experimentally investigated operating characteristics of the compensating mode of the HTS magnet for current decay and made a comparison between persistent current mode and compensating mode. A feedback control unit was used to sustain current within specified ranges with defined upper and lower limits.

• 센서학회지
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• 제32권4호
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• pp.232-237
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• 2023

This paper presents a system for estimating the position of a magnet using a magnetic sensor. An algorithm is presented to analyze the waveform and output voltage values of the magnetic field generated at each position when the magnet moves and to estimate the position of the magnet based on the analyzed data. Here, the magnet is sufficiently small to be inserted into a blood vessel and has a micro-magnetic field of hundreds of nanoteslas owing to the small size and shape of the guide wire. In this study, a highly sensitive magneto-impedance (MI) sensor was used to detect these micro-magnetic fields. Nine MI sensors were arranged in a 3×3 configuration to detect a magnetic field that changes according to the position of the magnet through the MI sensor, and the voltage value output was polynomially regressed to specify a position value for each voltage value. The accuracy was confirmed by comparing the actual position value with the estimated position value by expanding it from a 1D straight line to a 3D space. Additionally, we could estimate the position of the magnet within a 3% error.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.741-742
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• 2006

This paper deals with an efficient superconducting joint method between 2G high superconducting(HTS) wire, YBCO coated conductor(CC). Recently CC is one of the most promising superconducting wire due to high n-value and critical current independency from external magnetic field. It is expected to be used many superconducting application such as fault current limiter, persistent current system and cable etc. In most HTS applications, superconducting magnet is used, and it is necessary to joint between superconducting wire to fabricate superconducting magnet system. A CC tape used in this research consists of copper stabilizer, silver layer, YBCO layer, buffer and substrate. Direct joint using soldering method was inefficient due to resistance of copper, then copper lamination is removed by chemical etching method to reduce resistance between CC tapes. Jointed tapes were fabricated and tested. Transport current through jointed area and induced voltage were measured to characterize the I-V curve. Resistance between CC wire using chemical etching was compared with resistance of direct jointed tapes using soldering method in this paper.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.27-34
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• 2000

HTS wires processed by PIT method are now available for magnet applications. But, those wires can not be used over 40 K due to weak link. This leads to necessity of development of coated conductor which can retain high $J_c$ at high field in liquid nitrogen. In this paper, various technical issues and the R&D status for both PIT wires and coated conductor were discussed. The difference of coated conductor's processes were also investigated and summarized. Various requirements for a design of HTS magnets were discussed. Anisostropic $J_c$ property with respect to magnetic field was considered to determine the coil's critical current. Low n value is a critical parameter to degrade a field stability with respect to time for a persistent mode HTS magnet. The relation between the margin of operation current and n value was investigated. Prototype HTS magnets with PIT wires are being developed for various applications such as crystal growth, MRI, magnetic separator and etc. HTS magnets will come into wide use in various fields of industries if the HTS wires with a low performance cost is developed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.856-860
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• 2008

Wire-suspensions in the conventional actuators mechanically support the moving part and guarantee the accuracy of the actuator without tangential tilt actuation. However, such a suspension configuration has considerable stiffness in the tangential tilt direction with two additional wire beams for the tangential tilt. Thus, we performed a design sensitivity analysis for the wire-suspension stiffness of 4-axis actuator and controlled the main parameters such as distance among wire-suspensions and wire-suspension length to allow tangential tilt flexibility. The elasticity of frame PCB that supports the moving part by wire-suspensions was also exploited to improve the flexibility of wire-suspension in the tangential tilt direction. A novel suspension structure was devised by establishing eight wire-suspensions at both sides of the moving part for electrical connection to coils. The magnetic circuit according to the proposed 4-axis actuator using multi-polar magnet and coils was also suggested for the generation of electromagnetic forces in the focusing, tracking, radial and tangential tilt directions.

• E2M - 전기 전자와 첨단 소재
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• 제11권10호
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• pp.40-45
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• 1998

This paper describes a collaborative work between SEI and KEPCO on the Superconducting Magnetic Energy Storage system (SMES). We have studied two types of magnets. One is the 400kJ class LTS-SMES for testing the power stabilization operated at liquid helium temperature (4.2K) and the other is the 100J class HTS-SMES for confirming the possibility of applying HTS wire to SMES at liquid nitrogen temperature (77k). In this paper, the design of the magnet and the test results are described. Each magnet performed completely at rated operation.

• 한국초전도ㆍ저온공학회논문지
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• 제19권1호
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• pp.51-55
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• 2017

To obtain Nuclear Magnetic Resonance (NMR) measurement of membrane protein, an NMR magnet is required to generate high intensity, homogeneity, and stability of field. A High-Temperature Superconducting (HTS) magnet is a promising alternative to a conventional Low-Temperature Superconducting (LTS) NMR magnet for high field, current density, and stability margin. Conventionally, an HTS coil has been wound by several winding techniques such as Single-Pancake (SP), Double-Pancake (DP), and layer-wound. The DP winding technique has been frequently used for a large magnet because long HTS wire is generally difficult to manufacture, and maintenance of magnet is convenient. However, magnetic field generated by the slanted turns and the splice leads to field inhomogeneity in Diameter of Spherical Volume (DSV). The field inhomogeneity degrades performance of NMR spectrometer and thus effect of the slanted turns and the splice should be analyzed. In this paper, field gradient of HTS double-pancake coils considering the slanted turns and the splice was calculated using Biot-Savart law and numerical integration. The calculation results showed that magnetic field produced by the slanted turns and the splice caused significant inhomogeneity of field.

• 한국초전도ㆍ저온공학회논문지
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• 제20권4호
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• pp.65-69
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• 2018

Due to large in-field current carrying capacity and strong mechanical strength, a REBCO wire has been regarded as a viable high temperature superconductor (HTS) option for high field MRI and > 1 GHz (>23.5 T) NMR magnets. However, a REBCO magnet is well known to have an inherent problem of field inhomogeneity, so-called 'Screening Current induced magnetic Field (SCF)'. Recently, 'field shaking' and 'current overshoot operation' techniques have been successfully demonstrated to mitigate the SCF and enhance the field homogeneity by experiments. To investigate the effectiveness of current overshooting operation technique, a numerical simulation is conducted for a test REBCO magnet composed of a stack of double pancake coils using '2D edge-element magnetic field formulation' combined with 'domain homogenization' scheme. The simulation result demonstrates that an appropriate amount of current overshoot can negate the SCF. To verify the simulation results, current overshoot experiments are conducted for the REBCO magnet in liquid nitrogen. Experimental results also demonstrate the possible application of current overshoot technique to mitigate the SCF and enhance the field homogeneity.

• 한국초전도ㆍ저온공학회논문지
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• 제2권1호
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• pp.31-34
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• 2000

this paper deals with the initial magnetic field decay for a large scale superconducting magnet e.g. NMR/MRI magnet. The high resolution image can not be obained during the periods of the initial field decay. It is known that all superconducting materials have the property of diamagnetism. This diamagnetism is usually explained with the concept of screening current. We assumed that the existence of the screening currebt. we assumed that the existence of the screening current makes the current distribution in the superconducting wire non-uniform. And the initial magnetic field decay is caused steady current state in the view of its pattern. The initial magnetic field decay is caused by the change of the current distribution between the energizing state and persistent current mode. in this paper the theoretical analysis for the current distributions has been introduced for each state. The experiments have been carried out to verify transport currents in order to veperiments, it small at the higher transport current.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1904-1906
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• 1996

Transient voltage distribution tests are carried out to evaluate effects of a high frequency oscillating voltage generated in a superconducting magnet as a result of the arc discharge extinction. Especially, the effects of temperature and conduction state of the magnet conductor on surge behavior are carefully investigated. Based on the results of simulation tests, it is shown that internal voltage waveforms are influenced by its transmission along the superconducting wire and reflection at the terminal and that attenuation process of the waveforms depends considerably on the conductor resistance which decreases with lowering the temperature.