• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.543-546
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• 2004

The melting temperature and critical temperature(Tc) of $YBa_2Cu_3O_x$ with deferent content impurities of PbO and $BaPbO_3$ were studied. When the PbO was used as addition in $YBa_2Cu_3O_x$, although the melting point could be reduced, the superconductivity(the transition width, ${\Delta}T_c$) became poor. From the XRD pattern of the sintered mixture of $YBa_2Cu_3O_x$ and PbO it was known that there is a reaction between $YBa_2Cu_3O_x$ and PbO, and the product is $BaPbO_3$. In the process of the reaction the superconducting phase of $YBa_2Cu_3O_x$ was decreased and in the sample $BaPbO_3$ became the main phase. Therefore the superconductivity was reduced. $BaPbO_3$ was chosen as the impurity for the comparative study. The single phase BaPbO3 was synthesized by the simple way from both mixtures of $BaPbO_3$ and PbO, $BaPbO_3\;and\;PbO_2$. Deferent contents of $BaPbO_3$(10%, 20%, 30%) were added in the $YBa_2Cu_3O_x$. By the phase analysis in the XRD patterns it was proved that there werenot reactions between $YBa_2Cu_3O_x$ and $BaPbO_3$. When $BaPbO_3$ was used as impurity in $YBa_2Cu_3O_x$ the superconductivity was much better than PbO as impurity in $YBa_2Cu_3O_x$. But the melting point of $YBa_2Cu_3O_x$ with $BaPbO_3$ could not be found when the temperature was lower than $1000^{\circ}C$ in the DTA measurement.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.54-56
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• 2005

In this paper, we investigated the quench characteristics of HTSC elements in the integrated three-phase flux-lock type SFCL according to fault types such as the single-line-to-ground fault, the double-line-to-ground fault, the line-to-line fault and the three-line-to-ground fault. The integrated three-phase flux-lock type SFCL was the upgrade version of the single-phase flux-lock type SFCL. The structure of the integrated three-phase flux-lock type SFCL consisted of three-phase flux-lock reactor wound on an iron core with the ratio of the same turn between coil 1 and coil 2 in each phase. When the SFCL is operated under the normal condition, the flux generated in the iron core is zero because the flux generated between two coils of each single phase is canceled out. Therefore, the SFCL's impedance is zero, and the SFCL has negligible influence on the power system. However, if a fault occurs in any single-phase among three phases, the flux generated in the iron core is not zero any more. The flux makes HTSC elements of all phases quench irrespective of the fault type, which reduces the current of fault phase as well as the current of sound phase. It was observed that the fault current limiting characteristics of the suggested SFCL were dependent on the quench characteristics of HTSC elements in all three phases.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.52-53
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• 2005

$Y_2O_3$ film was directly deposited on Ni-3at%W substrate using DC reactive sputtering technique. Metallic yttrium was used for DC sputtering target and water vapor was used for oxidizing the deposited metallic Yttrium atoms on the substrate. The window of the water vapor turned out to be broad. The minimum partial pressure of water vapor was determined by sufficient oxidation of the $Y_2O_3$ film, and the maximum partial pressure of water vapor was determined by the non-oxidation of the target surface. As the sputtering power was increased, The deposition rate increased without narrowing the window. The fabricated $Y_2O_3$ films showed good texture qualities and surface morphologies. The YBCO film deposited directly on the $Y_2O_3$ buffered Ni-3at%W substrate showed $T_c$, $I_c$ (77 K, self field), and $J_c$ (77 K, self field) of 89 K, 64 A/cm and 1.l $MA/cm^2$, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.282-283
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• 2005

Ion beam assisted deposition(IBAD) technique was used to produce biaxially textured polycrystalline MgO thin films for high critical current YBCO coated conductor. Hastelloy tapes were continuous electropolished with very smooth surface for IBAD-MgO deposition, RMS roughness of Hastelloy tape values below 2 nm and local slope of less than $1^{\circ}$. After the polishing of the tape an amorphous $Y_2O_3$ and $Al_2O_3$ are deposited Biaxially textured MgO was deposited on amorphous layer bye-beam evaporation with a simultaneous bombardment of high energy ions. We had developed the RHEED to measure in-situ biaxial texture of film surface as thin as tens angstrom. And also ex-situ characterization of buffer layers was studied using XRD and SEM. The full-width at half maximum(FWHM) out of plane texture of IBAD-MgO template is $4^{\circ}$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.639-642
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• 2005

HTS Transformer developing is developing a power distribution and transmission class HTS transformer that is one of the 21st century superconducting frontier projects. Therefore, we prepared the model, that is Z continuous winding from Kapton insulated Cu tape for a small simulated the HTS transformer. For the development of electrical insulation design of a HTS transformer with Z continuous winding, we have been discussed insulation composition and investigated breakdown characteristics such as breakdown of liquid $N_2(LN_2)$, polymer and surface flashover on FRP and breakdown-surface combination in $LN_2$. Also we have been designed and manufactured a bobbin that has spiral slot for the Z continuous winding. The Z continuous winding mini-model from Kapton film insulated Cu tape for simulated 22.9kV class HTS transformer has been constructed using 0.1 % breakdown strength obtained by Weibull distribution. The widing model was measured their insulation characteristics such as ac (50kV, 1min) and impulse (154kV, $1.2\times50{\mu}s$ full wave, 3 times) withstand test and its excellent performance was confirmed.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.486-487
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• 2007

$Bi_2Sr_2Ca_{n-1}Cu_nO_x$(n=0, 1, 2) thin films have been fabricated by co-deposition at an ultra-low growth rate using ion beam sputtering(IBS) method. The growth rates of the films was set in the region from 0.17 to 0.27 nm/min. MgO(100) was used as a substrate. In order to appreciate stable existing region of Bi 2212 phase with temperature and ozone pressure, the substrate temperature was between 655 and $820^{\circ}C$ and the highly condensed ozone gas pressure in vacuum chamber was varied between $2{\times}10^{-6}{\sim}4{\times}10^{-5}$ Torr. Bi 2212 phase appeared in the temperature range of 750 and $795^{\circ}C$ and single phase of Bi 2201 existed in the lower region than $785^{\circ}C$. Whereas, $PO_3$ dependance on structural formation was scarcely observed regardless of the pressure variation.

• 한국콘텐츠학회논문지
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• 제17권7호
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• pp.437-442
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• 2017

최근 자기공명신호를 형성시키지 않는 보상물질을 이용하여 신호강도를 높이려는 연구가 활발히 진행되면서 검사부위에 보상물질을 직접 부착함에 따른 환자감염의 우려가 나타나고 있다. 이에 본 연구에서는 발상의 전환으로 보상물질을 코일에 간접 부착함으로써 기존의 직접 부착방식을 대체할 수 있는지 알아보고자 하였다. 연구방법은 보상물질인 실리콘을 원통형 bar의 형태로 제작하여 8채널 head 코일의 element에 부착한 후, 실리콘 부착 전 후 water phantom의 신호강도를 측정하였다. 영상획득은 3.0T 초전도 자기공명영상장치와 8채널 head 코일을 이용하여 T1, T2강조영상을 획득하였으며, 획득한 영상은 영상측정프로그램을 이용하여 신호강도를 측정한 후, 대응표본T검정을 이용하여 유의한 차이가 있는지 판단하였다. 부착 전 후 신호강도는 T1 강조영상은 3.39%, T2 강조영상은 2.62% 유의하게 증가하였다. 결론적으로 간접 부착방식은 증가율이 낮아 모든 환자를 대상으로 대체하기에는 한계가 있을 수 있지만, filling factor의 증가로 인한 신호강도의 의미있는 상승이 있으므로 당뇨병 등 감염성 질한 우려 환자에 적용 시 유용하리라 판단된다.

• 한국자기학회지
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• 제22권1호
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• pp.15-18
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• 2012

Olivine 구조인 $LiFe_{0.9}Mn_{0.1}PO_4$ 분말 시료를 직접합성법(solid state method) 으로 제조하였으며, 결정학적 및 자기적 특성을 x-선 회절(x-ray diffractometer), 초전도 양자 간섭계(superconducting quantum interference devices) 및 뫼스바우어 분광(M$\ddot{o}$ssbauer spectroscopy) 실험을 이용하여 연구하였다. $LiFe_{0.9}Mn_{0.1}PO_4$ 시료의 결정구조는 공간그룹이 Pnma인 orthorhombic 구조임을 Rietveld 정련법으로 분석하였다. $LiFe_{0.9}Mn_{0.1}PO_4$ 시료의 닐온도 (N$\acute{e}$el temperature; $T_N$)는 50 K으로 나타내었고 닐온도에서 자기 상전이가 일어나는 것을 초전도 양자 간섭계 실험을 통하여 확인하였다. Fe(Mn)-O 이온간 거리를 분석하여 $FeO_6(MnO_6)$ 팔면체 구조가 비대칭임을 확인하였고 그 구조로 인하여 강한 결정장에 영향을 받으며, 닐온도 이상에서 자기 2중극자 상호작용은 사라지고, 강한 결정장에 의한 전기 4중극자 작용만이 존재하여 두 개의 흡수선이 나타나는 것을 뫼스바우어 분광 실험을 통하여 분석하였다.

• Nuclear Engineering and Technology
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• 제40권6호
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• pp.451-458
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• 2008

After more than 10 years construction, KSTAR (Korea Superconducting Tokamak Advanced Research) had finally completed its assembly in June 2007, and then achieved the goal of first-plasma in July 2008 through the four month's commissioning. KSTAR was constructed with fully superconducting magnets with material of $Nb_3Sn$ and NbTi, and their operation temperatures are maintained below 4.5K by the help of Helium Refrigerator System. During the first-plasma operation, plasmas of maximum current of 133kA and maximum pulse width of 865ms were obtained. The KSTAR Integrated Control System (KICS) has successfully fulfilled its missions of surveillance, device operation, machine protection interlock, and data acquisition and management. These and more were all KSTAR commissioning requirements. For reliable and safe operation of KSTAR, 17 local control systems were developed. Those systems must be integrated into the logically single control system, and operate regardless of their platforms and location installed. In order to meet these requirements, KICS was developed as a network-based distributed system and adopted a new framework, named as EPICS (Experimental Physics and Industrial Control System). Also, KICS has some features in KSTAR operation. It performs not only 24 hour continuous plant operation, but the shot-based real-time feedback control by exchanging the initiatives of operation between a central controller and a plasma control system in accordance with the operation sequence. For the diagnosis and analysis of plasma, 11 types of diagnostic system were implemented in KSTAR, and the acquired data from them were archived using MDSpius (Model Driven System), which is widely used in data management of fusion control systems. This paper will cover the design and implementation of the KSTAR integrated control system and the data management and visualization systems. Commissioning results will be introduced in brief.

• 한국초전도ㆍ저온공학회논문지
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• 제26권2호
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• pp.9-18
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• 2024

The current study deals with the possible interplay between superconductivity and spin density wave in two band model high temperature iron based superconductor (FeBSC) Ba_1-xNa_xFe₂As₂. The electron and hole bands in the presence of the inter-band interaction between the two bands is becoming a vital issue to deal with the high temperature physics of the iron-based superconductors. In this research work, a model Hamiltonian appropriate for the system under consideration has been developed and the temperature dependent Green's function technique has been employed to get the solution for the equations of motion constructed for the two band model high temperature FeBSC Ba_1-xNa_xFe₂As₂. By making use of the decoupling procedure, the equations of motion for the dependence of superconducting transition temperature (T_C) on spin density wave(SDW) order parameter (Δ_SDW) in the electron intra-band (Δ_sc(e)) , hole intra-band (Δ_sc(h)) and inter-band (Δ_sc(eh)) for Ba_1-xNa_xFe₂As₂ have been obtained. We have also obtained the expression for the dependence of spin density wave transition temperature(T_SDW) on Δ_SDW for Ba_1-xNa_xFe₂As₂. Using some plausible approximations and appropriate experimental values for the parameters in the obtained equations of motion, phase diagrams of T_C versus Δ_sc(e), Δ_sc(h) and Δ_sc(eh) are plotted. Furthermore, a phase diagram of T_SDW versus Δ_SDW is plotted for the material under consideration. Finally, using the above mentioned phase diagrams, the interplay between superconductivity and spin density wave in the two band model high temperature FeBSC Ba_1-xNa_xFe₂As₂ has been demonstrated to be a very distinct possibility. The agreement of the current finding with the experimental observations is quite commendable.