• 한국초전도학회:학술대회논문집
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• v.9
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• pp.373-377
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• 1999

HTS magnet operated at 20${\sim}$40 K was fabricated using three pieces of 100 m Bi-2223 high temperature superconductors fabricated by powder-in-tube process. It was composed of 6 double pancakes with 75 ID. and 113 OD. connected by lab splice. Coil I$_c$ of each DP.(double pancake) obtained for a 140 turn, fabricated using react and wind procedure was 6${\sim}$8 A at 77 K, self field. The maximum field was measured 0.06 T at lop = 5 A, 77 K. The joint resistance due to lap splice of HTS tapes affect badly to operate HTS magnet with persistent current mode, total effective magnet resistance included lap splice was 55 ${\mu}$ ${\omega}$ at 77 K.

• Progress in Superconductivity
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• v.2 no.1
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• pp.20-26
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• 2000

A 40-channel superconducting quantum interference device (SQUID) system was constructed for measuring neuromagnetic fields. Main features of the system are the use of double relaxation oscillation SQUIDs (DROSs), and planar gradiometers measuring magnetic field components tangential to the head surface. The DROSs with high flux-to-voltage transfers enabled direct readout of the SQUID output by room-temperature dc preamplifiers and simple flux-locked loop circuits could be used for SQUID operation. The pickup coil is an integrated first-order planar gradiometer with a baseline of 40 mm. Average noise level of the 40 channels is around 1.2 $fT/cm/{\surd}Hz$ at 100 Hz, corresponding to a field noise of 5 $fT/{\surd}Hz$, operated inside a magnetically shielded room. The SQUID insert was designed to have low thermal load, minimizing the loss of liquid helium. The constructed system was applied to measure auditory-evoked neuromagnetic fields.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.117-119
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• 2003

YBa$_2$Cu$_3$O$_{7-{\delta}}$(YBCO) high temperature superconducting thin films were grown on SrTiO$_3$single crystal substrates by pulsed laser deposition(PLD). The texture and lattice parameter of the YBCO films were analysed using the GADDS (general area detector diffraction system) which enables XRD analyses to be done faster and with fewer sample movement than with the XRD system with point detector. The XRD results of the films grown in different deposition conditions are reported together with the SEM microstructure analysis results.ysis results.

• Progress in Superconductivity and Cryogenics
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• v.3 no.2
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• pp.15-20
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• 2001

This paper describes a model flux pump experiment recently performed at the MIT Francis Bitter Magnet Laboratory. The results of the model flux pump will be used in the development of a prototype flux pump that will be couple to a high-temperature superconductor (HTS) insert coil of a high-field NMR (Nuclear Magnetic Resonance) magnet, Such an HTS insert is unlikely to operate in persistent model because of the conductors low index(n) The flux pump can compensate fro field decay in the HTS insert coil and make the insert operate effectively in persistent mode . The flux pump, comprised essentially of a transformer an two switches. all made of superconductor, transfers into the insert coil a fraction of a magnetic energy that is first introduced in the secondary circuit of the transformer by a current supplied to the primary circuit. A model flux pump has been designed. fabricated, and operated to demonstrate that a flux pump can indeed supply a small metered current into a load superconducting magnet. A current increment in the range of microamperes has been measured in the magnet after each pumping action. The superconducting model flux pump is made of Nb$_3$ Sn tape, The pump is placed in a gaseous environment above the liquid helium level to keep its heat dissipation from directly discharged in the liquid: the effluent helium vapor maintains the thermal stability of the flux pump.

• Progress in Superconductivity and Cryogenics
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• v.5 no.2
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• pp.1-7
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• 2003

Nowadays, one of the serious problems in KEPCO(Korea Electric Power Co-Operation) system is the more higher fault current than the SCC(Short Circuit Capacity) of circuit breaker. There are many alternatives to reduce the increased fault current such as isolations of bus ties, enhancement of SCC of circuit breaker, applications of HVDC-BTB(High Voltage Direct Current-Back to Back) and FCL(fault current limiter). But, these alternatives have some drawbacks in viewpoints of system stability and cost. As the superconductivity technology has been developed, the HTS-FCL(High Temperature Superconductor -Fault Current Limiter) can be one of the attractive alternatives to solve the fault current problem. Under this background, this paper presents the EMTDC(Electro-Magnetic Transient Direct Current) model for resistance type HTS-FCL considering the nonlinear characteristic of final resistance value when quenching phenomena occur.

• Bulletin of the Korean Chemical Society
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• v.9 no.5
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• pp.280-282
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• 1988

The structural, electrical and magnetic properties were investigated for the high-Tc superconductor $YBa_2Cu_3O_{7-x}$, where x was 0.13. The results of temperature dependence of the resistivity and the magnetization in $YBa_2Cu_3O_{6.87}$ whose structure and phase are confirmed by arialysis of X-ray powder diffraction pattern have been reported. A very sharp superconductivity transition appears at 92K in the specimen whose chemical composition is determined from redox titration, strongly suggesting that this specimen consists of a single-phase superconductor. From the results of X-ray diffraction analysis, magnetization curves, levitation and resistance measurements, it is suggested that the observed superconductivity is bulk property in nature and that the $YBa_2Cu_3O_{6.87}$ phase is responsible for the superconductivity of the present reproducible specimen.

• 한국초전도학회:학술대회논문집
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• v.11
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• pp.19-19
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• 2001

• Progress in Superconductivity and Cryogenics
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• v.3 no.1
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• pp.16-21
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• 2001

Bubble behavior is studied with an electrode system which consists of coaxial spiral coil-to-cylindrical electrode with an insulation barrier and spacers and is immersed in liquid nitrogen for simulation of insulation environments in high temperature superconducting(HTS) coils The results show that the bubble behavior Is affected severely by electric field: (1) under low applied voltage bubbles rise by buoyancy, but at higher applied voltage they are trapped in a lower electric field region below the coil electrode, and (2) the trapped bubble flows along the downside of coil electrode if no obstruction is in a groove between coil turns. but it splashes out of the groove after its growing if the obstruction such as spacer-exists.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.185-188
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• 2002

In the design of superconducting power equipments such as transformer, cable and fault current limit, knowledge of the dielectric behavior of both liquid and gaseous at very low temperatures is very importance. Especially, Electrical properties of liquid nitrogen($LN_{2}$) and gaseous nitrogen($GN_{2}$) have become of great interest again since the discovery of high temperature superconductors. However, many sources of $LN_{2}$and $GN_{2}$ problems in the test of pancake coil model arising form the deficiency of insulation data. Therefore, this paper describes the results of an experimental study on the ac breakdown voltage($V_{B}$) properties of $LN_2$ and Air under the electrode of simulated HTS pancake coil. The ac breakdown voltage of $GN_{2}$ have been measured by pancake coil-pancake coil gaps over the temperature range of 293 K to 77 K.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.312-314
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• 2002

Magnetic circuit design of HTS (High Temperature Superconducting) motor is important to achieve the power at a given load condition, and it is essential to the thermal design for HTS motor rotors. To determine the result of thermal design, the magnetic field distribution has to be known exactly. On the basis of the 2 dimensional magnetic field analysis, the magnetic field distributions due to several cases are calculated by using Biot-Savart equation and magnetic image method. And the I$_{c}$ of HTS field coil was calculated by using I$_{c}$-B(equation omitted) curve and 3D FEA(Finite Element Analysis).is).