The critical currents I$_c$ of the YBCO grain boundaries of 90-degree [100] symmetric tilt showed a hysteretic behavior depending on how the external magnetic fields were applied. Near 77K for fields less than ${\sim}$1 T, the field-cooled I$_c$ of grain boundaries was larger than the zero-field-cooled I$_c$. This result is consistent with the model in which the grain-boundary vortices can be pinned by neighboring Abrikosov vortices in the nearby grains.

The recent progress in new cooling techniques of the high Tc superconductor(HTS) systems is reported and discussed with some practical examples. At the beginning stage of the HTS development in research laboratories, liquid nitrogen(LN$_2$) is the standard medium for an effective cooling. The success of HTS in many different application areas, however, has required a variety of need in the cooling temperature and the cooling capacity with specific design restrictions. While the utilization of alternative liquid cryogens such as liquid neon (LNe) or liquid hydrogen (LH$_2$) has been tired in some of them, even solid cryogens such as solid nitrogen (SN$_2$) or solid hydrogen (SH$_2$) may be another option in special applications. The gaseous helium cooled by a cryogenic refrigerator has also been a good candidate in many cases. One of the best cooling methods for the HTS is the direct conduction-cooling by a closed-cycle refrigerator with no cryogen at all. The refrigeration may be based on Joul-Thomson, Brayton, Stirling, Gifford-McMahon, or pulse tube cycles. The pros and cons of the newly proposed cooling methods are described and some significant design issues are presented.

A Josephson sampler circuit using high-Tc superconductor (HTS) ramp-edge junctions has been designed, fabricated, and experimentally tested. It consists of five ramp-edge junctions with a stacked groundplane and is based on single-flux-quantum (SFQ) operations. The sampler was used to measure current waveforms at picosecond and microampere resolutions. We are developing a system based on the sampler for measuring the current waveform in a room-temperature sample. And measuring current flowing through wiring in a semiconductor large-scale integrated circuit is a promising application for the HTS sampler system.

This paper is to present the general descriptions and their research trend of MRl/NMR which has already commercialized and also is more successful than any other applications of superconducting magnet, Superconducting Single Crystal Growing Equipment and Superconducting Magnetic Separation technology which are practically used in the related areas, and power electric application machine, which is the most effective and efficient one among the applications using high magnetic field. Therefore, it is hoped that this study will help to establish the ground of the industrial application of superconductivity in Korea.

We apply the nonperturbative parquet approximation method, which was previously used to study the effect of thermal fluctuations in two-dimensional vortex systems, to vortices in a layered superconductor. We set up the parquet equations for the Lawrence-Doniach model and present two different numerical methods to solve them. The results for a superconductor consisting of two and four layers are also discussed in connection with an observed first order transition line in the vortex liquid regime.

We developed a 40-channel superconducting quantum interference device (SQUID) system for neuromagnetic measurements. The main features of the system are use of double relaxation oscillation SQUID (DROS), and planar gradiometer for measuring tangential field components. The DROSS with high flux-to-voltage transfers enabled direct readout of the SQUID output by room-temperature electronics 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. The average noise of the 40 channels is around 1.2 fT/cm/${\sqrt{Hz}}$ at 100 Hz, corresponding to the field noise of 5 fT/${\sqrt{Hz}}$ at 100 Hz, operated inside a magnetically shielded room. The 40-Channel system was applied to measure auditory-evoked neuromagnetic fields.

We have fabricated YBCO/STO/YBCO multilayer by the pulsed laser deposition method varing the deposition condition of insulating STO layer. Superconducting properties of both YBCO layers are sensitively affected by the deposition condition of STO layer. We obtained the upper YBCO layer of T$_{c(zero)}\;{\sim}\;$90 K with a good reproducibility, however, T$_{c(zero)}$ of lower YBCO layer was decreased to about 80 K maybe due to the oxygen loss during the deposition of STO layer. Superconducting properties of both YBCO layers at every fabrication step were measured in order to study the reason for the deterioration of superconducting properties.

We prepared hish T$_c$ Josephson junctions that have different I$_c\;'s$ and R$_n\;'s$ and studied their microwave properties. We measured the current-voltage characteristics of the junctions under the irradiation of 22 GHz electromagnetic wave at various temperatures. from the Shapiro steps, we calculated the maximum detectable frequency and the microwave received power of the junctions. Increasing critical current values increase both maximum detectable frequency and sensitivity. However, increasing temperature increase sensitivity but decrease maximum detectable frequency.

Instead of using KrF excimer lasers( ${\lambda}$ = 248 nm) in depositing oxide thin films, as in the most of the laboratories in Korea, we have used an ArF excimer laser( ${\lambda}$ = 197 nm) which has a shorter wavelength. By using a beam which has a shorter wavelength, we could obtain higher quality and smoother surface YBCO thin films. We fabricated YBCO thin films with the various substrate temperature conditions and analyzed the characteristics of these films. We also studied the charateristics of the films fabricated under the various conditions of the power of laser and the oxygen pressure. The characterization tools used in this work were a transport measurement setup, an XRD , and a SEM. We also fabricated STO/YBCO multilayers to use in SFQ devices fabrication. XRD patterns of the multilayers showed that the multilayer films were grown epitaxially.

We demonstrate small-scale high-T$_c$ superconductor RSFQ(Rapid Single Flux Quantum) circuits using multilayer bicrystal technology. An RSFQ balanced comparator is demonstrated with good current resolution, and its operating conditions are discussed in some detail. A single-loop delta-sigma modulator is realized adding a feedback loop to the comparator. The effect of the feedback is confirmed by dc measurement and simulation. A design of an RSFQ toggle flip-flop with the same multilayer bicrystal technology is suggested.

본 연구에서는 SQUID를 이용한 비파괴 평가 시스템을 제작, 측정하였다. 이 시스템은 비자기 차폐 환경에서 작동할 수 있도록 설계하였고, 측정 자기 센서로는 dc 및 rf-SQUID gradiometer를 사용하였다. 비자기 차폐 환경에서 ${\sim}$nT의 미세 자기 신호를 검출하였고, 공간적으로 변화하는 외부 자기 신호를 측정, 분석하였다. 또한, 측정된 자기 신호를 통해 dc-SQUID와 rf-SQUID에 대한 비교를 했다.

We fabricated a new hairpin type HTS 2-pole microstrip Bandpass filter to operate at 5.8GHz. The fabrication method was pulsed laser deposition and YBCO films were deposited on ${\alpha}$-A1$_2O_3$ substrates with a CeO$_2$ thin layer as a buffer layer. We developed a new style hairpin type filter by using interdigitide innerpole. Compared to the saute size regular hairpin type filters, our filter had a lower center frequency, bandwidth and loss by an amount of 14.5%, 29.6%, 0.5488dB, respectively. The size of the filters were 13.7${\times}$3.3mm. We did simulations on the several types of band pass filters by using HFSS and serenade. We measured growth rate and Tc of YBCO films grown on CeO$_2$/ ${\alpha}$-A1$_2O_3$ substrates which were rotated while growing films.

We fabricated ramp-edge Josephson junctions with barriers formed by interface treatments instead of epitaxially grown barrier layers. Low-dielectric Sr$_2AITaO_6$(SAT) layer was used as an ion-milling mask as well as an insulating layer for the ramp-edge junctions. An ion-milled YBa$_2Cu_3O_{7-x}$ (YBCO)-edge surface was not exposed to solvent through all fabrication procedures. The barriers were produced by structural modification at the bottom YBCO edge using plasma treatment prior to deposition of the top YBCO electrode. We investigated the effects of pre-annealing and post-annealing on the characteristics of the interface-treated Josephson junctions. The junction parameters were improved by using in-situ RF plasma cleaning treatment.

We have fabricated YBa$_2Cu_3O_{7-x}$ thin films by cylindrical hollow cathode sputtering. For 2 inch diameter of MgO (100) substrate, we obtained the zero resistance temperature in the range from 83 K to 86 K and thickness uniformity better than 5 % over the whole area. Also, the average deposition rate was 100nm/h which is higher than 10 times compare to conventional off-axis sputtering method. These results indicate that cylindrical hollow cathode sputtering seems to have unique capabilities for high rate and homogeneous deposition of large area thin film.

접지면을 가지는 정사형 조셉슨 결합을 제작하기 위한 기본 단계로 YBCO/STO/YBCO 구조의 다층 박막을 제작하였다. 상하부 YBCO 박막은 그 사이에 존재하는 STO 절연층에 형성된 홀을 통해 서로 연결되어 있으며 이것의 저항-온도 특성을 측정한 결과 임계 온도가86 K로 나타났다. 이 결과는 시편을 매우 장시간동안 열처리한 후 얻은 결과로서 YBCO/STO/YBCO 다층 구조의 박막 제작시 하부 YBCO 박막의 특성이 많이 저하되고 이를 복원하기 위해서는 열처리 공정이 매우 중요함을 알 수 있었다. 현재 우수한 특성을 가지는 YBCO/STO/YBCO 다층 구조의 제작 공정을 최적화하기 위한 연구를 계속 수행 중에 있다.

TE$_{01\;{\delta}}$ mode Cavity Resonators with a low loss dielectric rod and YBa$_2Cu_3O_{7-{\delta}}$ (YBCO) endplates were prepared and their microwave properties were studied at temperatures above 30 K. Both sapphire and rutile were used as the dielectrics. The TE$_{01\;{\delta}}$ mode Q$_0$ of the resonator, designed to work as a tunable resonator with variations in the gap distance (s) between the dielectric rod and the top YBCO, was more than 1000000 at s = 0 mm and at 30 K and .the resonant frequency of 19.56GHz when a sapphire rod was used for the dielectric. The TE$_2Cu_3O_{7-{\delta}}$ mode resonant frequency (f$_0$) appeared to decrease as the temperature is raised. Meanwhile, the temperature dependence of the TE$_2Cu_3O_{7-{\delta}}$ mode f$_0$ of the rutile-loaded resonator appeared different with f$_0$ increasing according to the temperature and Q$_0$ more than 300000 at 30 K and f$_0$ = 8.56 CHz. Comparisons were made between the microwave properties of the sapphire-loaded and the rutile-loaded resonators. Also, applications of the TE$_2Cu_3O_{7-{\delta}}$ mode cavity resonator for a tunable resonator with a very high Q$_0$ as · well as a characterization tool for surface resistance measurements of HTS films are described.

We have fabricated $_2Cu_3O_7$ step-edge junctions with different step orientations and studied their transition properties. Steps with different orientations were prepared on the substrate. Josephson junctions were made on a single substrate with step orientations ranging from 0$^{\circ}$ to 165$^{\circ}$ at 15$^{\circ}$ interval. We measured current-voltage characteristics, the critical current, and the superconducting transition temperature as a function of the angle. The critical current showed a modulation that has a maximum near 0$^{\circ}$ or 90$^{\circ}$ and a minimum near 45$^{\circ}$ and 135$^{\circ}$. We believe that the critical current modulation with the step orientation could be associated with the symmetry of high T$_c$ superconductor.

We have studied the annealing effects of 570 (SrTiO$_3$) single crystal substrate and the I-V properties of step-edge junctions after Ar ion milling. YBa$_2Cu_3O_7$ (YBCO) thin films are fabricated on the substrates by using pulsed laser deposition (PLD) and photolithography. The surface of Ar ion milled substrate was characterized with atomic force microscope (AFM) and scanning electron microscope (SEM) images. After the substrate was damaged by milling, the critical current density of YBCO thin films deposited on the substrate was lowered. The annealing of the damaged substrate at about 1000 $^{\circ}C$ recovered the critical current density to that before the milling. Futhermore the annealing helped junction formation due to high quality film and increased the yield rate for the fabrication of high quality step-edge junction.

A new type of high-T$_c$ superconducting Josephson junctions has been prepared by Ar ion beam etching and electron beam lithography. YBa$_2Cu_3O_{7-x}$ (YBCO) films deposited on (001) SrTiO$_3$ single crystal substrate by pulsed laser deposition were patterned by Ar ion milling with photolithography. The narrow slit with a electroresist mask, about 1000 ${\AA}$ wide, was constructed over a 3 ${\sim}$ 5 ${\mu}$m bridge of a 1200-${\AA}$-thick YBCO film by electron beam lithography. The slit was then etched by the Ar ion beam to form a damaged 600-${\AA}$-thick YBCO. Thus prepared structure forms an S-N-S (YBCO - damaged YBCO - YBCO) type Josephson junctions. Those junctions exhibit RSI-like I-V characteristics at 77 K. The properties of the Josephson junctions such as I$_c$ R$_N$, and J$_c$ were characterized.

The crystalline alignment of Ni substrates textured by RABiTS have a probability distribution in the surface plane. This makes it difficult to obtain a high quality of textures over all the range of a long Ni tape. In order to improve the textures of Ni tape, we have investigated a new method of texturing. We obtained non-cube textured Ni tapes by rolling and annealing a high purity Ni. In these tapes, the [001]-axes were tilted around the rolling direction, and the [100]-axes were parallel to the rolling direction. The average grain size was several cm$^2$. We deposited buffer layer (CeO$^2$/YSZ/CeO$^2$) and YBCO on those tapes. We found out that a YBCO film with grows normal with respect to the surface and this feature is independent of the tilting angles of the Ni [001]-axes.

To improve the texture and the hardness of Ni substrates, we added impurities such as Mn, Fe, Co, Cu and Cr and investigated the effect of impurities on the texture and the hardness of Ni tapes. The Ni tapes with 0.2% Co, Cr, Cu, showed poor in-plane textures. However, the Ni tapes with 0.1 ${\sim}$ O.2% Mn (or Fe), showed much better textures. We'll describe the detailed effects of the amount of Mn impurities.

We have designed and fabricated a four-bit shift register circuit using YBCO bicrystal junctions and experimentally tested its operations by a computer-controlled digital measurement set-up. Laser ablated YBCO thin films with clean surface were used in this work. The circuit consists of the shift register and two read SQUIDs placed next to each sides of the shift register. The SQUIDs were inductively coupled to the nearby shift register stages. A probe equipped with high speed coax lines were used in this experiment. The major obstacle in testing the circuit was the interference between the read SQUIDs and we solved the problem by finding the correct operation points of the SQUIDs from the simultaneously measured modulation curves. Loaded Data("1" or "0") were successfully shifted from a stage to the next one by a controlled current pulse injected to the bias lines located between the stages and the data shifts were correctly monitored by the read SQUIDs

A high-temperature superconducting 1.78 GHz bandpass filter, designed for PCS applications, is presented. The structure consists of microstrip pseudo-lumped elements, which make the miniaturization of the filter possible. A 5-pole microstrip filter can be realized on 37 mm ${\times}$ 9 mm LaAlO$_3$ substrate, using double-sided high-temperature superconducting YBa$_2Cu_3O_{7-{\delta}}$ thin film. This filter shows 0.7% fractional bandwidth, 0.3 dB insertion loss, and 12 dB return loss in the passband at 60 K.

Superconducting multiplexer consisting of hairpin type filters has been designed for the reduction of the physical size of the device. Pulsed laser deposition with a Nd:YAG laser has been used to grow high quality YBCO superconducting films on MgO substrates. Multiplexer has been designed to have the center frequencies at 13.6 CHz and 13.9 GHz on MgO substrate with the size of 20 ${\times}$ 20 ${\times}$ 0.5mm$^3$. It is possible to implement superconducting multiplexer having two passbands on the limited 20 ${\times}$ 20 ${\times}$ 0.5mm$^3$ MgO substrate by adopting hairpin type filters. This type of superconducting device will be useful for the integration of microwave subsystem.

Ba$_2Cu_3O_{7-{\delta}}$ (YBCO) thin films were deposited by pulsed laser deposition using differently prepared targets: One was a conventionally solid-state sintered (SSS) target and the other was a modified melt-textured grown (MTC) target. Compared with SSS targets, MTG targets showed a well-connected microstructure consisting of much larger grains and the surface was Bess roughened with the cumulative laser incidence. YBCO films deposited from MTC targets showed a denser and smoother surface of the basal film than the case of SSS targets. The investigations of ${\alpha}$-axis outgrowths in the films indicated that the deposition using MTG targets would result in a more homogeneous and stable film growth as compared to the SSS targets. Also, TEM analysis revealed that the film deposited from MTG targets had a less granular microstructure that would reduce weak-link effects in the film.

We designed and constructed a non-destructive evaluation system using an HTS DC SQUID electronic gradiometer. Our DC SQUID electronic gradiometer is composed of two DC SQUID magnetometers. The system included a non-magnetic stainless steel cryostat and a set of coaxial exciting coils, which were used to induce an eddy current in the test material. We also have calculated the eddy current density produced by an exciting coil in any direction of the testing object. We could compute the eddy current density distribution in 3D. The SQUIDs were computer controlled and the output data from the electronic gradiometer was obtained by using a Labview software.

We report microwave properties of high-T$_c$ superconducting (HTS) microstrip antennas without impedance matching circuits, where the impedance mismatching is obvious under the critical temperature (T$_c$). The superconducting thin films used in this report were YBa$_2Cu_3O_{7-x}$ (YBCO) films deposited on MgO substrates produced by pulse laser deposition (PLD) technique. At around T$_c$, 86 K the reflection coefficient rapidly drops, and the standing wave ratio (SWR) becomes almost unity, and the characteristic impedance based on the Smith chart is nearly 50 ${\Omega}$. The reflection coefficient and the SWR of the HTS microstrip antenna were - 62.52 dB and 1.0015, respectively, at the resonant frequency of 11.812 CHz at 86 K.

A new single solution source MOCVD technique for the deposition of YBCO film has been developed, using a ultrasonic atomizer to feed the precursors into an evaporation zone. This method being investigated as a basis for future long wire fabrication, for example the electric power use, the magnatic applications, etc.. YBCO films were prepared on MgO(100) substrate, using mixture of Y, Ba, and Cu ${\beta}$ -diketonate chelate was dissolve in tetrahydrofuran as a solution sources. X-ray diffraction measurement indicated that the thin film grew epitaxially with the c-axis orientation perpandicular to the surface of the surface.

We have fabricated and tested a simple circuit of the rapid single-flux-quantum(RSFQ) four-stage shift register using a single layer high-T$_c$ superconducting (HTS) YBa$_2Cu_3O_{7-x}$ (YBCO) thin film structure with 9 step-edge Josephson junctions. The circuit includes two read superconducting quantum interference devices(SQUID) and four stages. To establish a robust HTS RSFQ device fabrication process, we have focussed the reproducible process of sharp and straight step-edge formation as well as the ratio of film thickness to step height t/h. The spread of step-edge junction parameters was measured from each13 junctions with t/h=l/3, l/2, and 2/3 at various temperatures. We have demonstrated the simplified operation of the shift register at 65 K..

It is certain that the power quality will be very important at 21 century. Especially instant power shortage or power fault will occur serious problems. Accordingly stable power supplication is very technical problem. There are many way to make stable supplication as auxiliary generator, but this is long time delay complement. To solve this problem the superconducting magnetic energy storage is introduced. High Tc superconductor is more commercial.

For the enhancement of communication system performance, high quality filters are required. Conventional metal filters made of copper can be substituted by high quality high temperature superconductivity(HIS) flms for better performance. In order to reduce the size of the filter for the integration of device in the limited area, we have fabricated hairpin type filters using pulsed laser deposition(PLD) technique. The superconducting YBCO thin films have been grown on MgO substrates by PLD with Nd:YAC laser. The YBCO films were patterned by conventional wet-etching process. We have compared YBCO filters and copper filters which were made with the same spec. Simulated and measured frequency responses reveal that HIS YBCO hairpin type bandpass filters show better performance than copper filters.

CeO$_2$ buffer layers and in-situ YSa$_2Cu_3O_{7-{\delta}}$ (YBCO) thin films were grown by pulsed laser deposition method on R-plane sapphire substrates. Superconducting properties and surface morphologies of YBCO thin films exhibit strong dependence on the crystallinity of CeO$_2$ buffer layer. The best a-axis oriented CeO$_2$ buffer layers could be grown at 800 $^{\circ}C$ of deposition temperature, 1.5 J/ cm$^2$ of laser energy density and 50 mTorr of oxygen pressure. The YBCO thin films on the a-axis CeO$_2$ buffer layer have Tc (R=0) ${\ge}$ 89.5 K, ${\delta}$Tc ${\sim}$ 0.5 K, and Jc ${\ge}$ 3.2 ${\times}$ 10$^6$ A/ cm$^2$ at 77 K.

YBCO step-edge Josephson junction were fabricated on sapphire substrates. The steps were formed on R-plane sapphire substrates by using Ar ion milling with PR masks. The step angle was controlled in the wide range from 25$^{\circ}$ to 50$^{\circ}$ by adjusting both the Ar ion incident angle and the photoresist mask rotation angle relative to the incident Ar ion beam. CeO$_2$ buffer layer and in-situ YBa$_2Cu_3O_{7-{\delta}}$ (YBCO) thin films was deposited on the stepped R-plane sapphire substrates by pulsed laser deposition method. The YBCO film thickness was varied to obtain the ratio of film thickness to step height in the range from 0.5 to 1. The step edge junction exhibited RSJ-like behaviors with I$_cR_n$ product of 100 ${\sim}$ 300 ${\mu}$V, critical current density of 10$^3$ ${\sim}$ 10$^5$ A/ cm$^2$ at 77 K.

YBa$_2Cu_3O_{7-{\delta}}$ (YBCO) films grown on CeO$_2$-buffered r-cut sapphire substrates (CbS's) were prepared and their structural and electrical properties were measured. Post-annealed CeO$_2$ films were used as buffer layers for the experiments. It turned out that the YBCO films grown on post-annealed CbS's had the rms roughness of less than 20 ${\AA}$ and peak-to-peak roughness of about 30 ${\AA}$ when the YBCO film thickness was 3000 ${\AA}$. Meanwhile, YBCO films on in-situ grown CeO$_2$ buffer layers on r-cut sapphire substrates appeared to have the peak-to-peak roughness of more than 450 ${\AA}$. X-ray diffraction data revealed that the YBCO flms were epitaxially grown along the c-axis with the typical FWHM of(005) ${\theta}$ -2 ${\theta}$ peak about 0. 16 $^{\circ}$ and ${\Delta}$ ${\omega}$ of the (005) peak about 0.5 $^{\circ}$. T$_c$ > 87 K, ${\Delta}$T < 1 K and R(look)/R(100K) ${\ge}$3 were observed from the YBCO films. Applicability of the YBCO films for high-frequency applications was described.

We have fabricated the direct-coupled planar type 1st-order SQUID gradiometers. The gradiometer consists of moats or slots in SQUID loop. It is made by YBa$_2Cu_3O_7$ thin films using pulsed laser deposition method on SrTiO$_3$ single crystal and bi-crystal substrates. We have studied the effects of slots and moats in SQUID loop by measuring the voltage modulation signals under uniform field and 1st-order gradient, and the noise properties under non-shielded environment.

We have investigated the mixed-state Hall effect in HgBa$_2CaCu_2O_6$, HgBa$_2Ca_2Cu_3O_8$, and Tl$_2Ba_2Cau_2O_8$ thin films as functions of the magnetic field up to 18 T. At high fields and low temperatures, the scaling exponent in ${\rho}_{xy}$ = A${\rho}_{xx}\;^{\beta}$ shows a universal behavior, ${\beta}$ = 1 ${\pm}$ 0.1, regardless of the field, the number of CuO$_2$ layers, the types of defects, and even the types of compounds. At low fields and high temperatures, p = 1 ${\pm}$ 0.1 also appears as a universal number although the observed field range is rather limited. These observations show the universal scaling of Hall resistivity in the regions of the clean and the moderately clean limit, consistent with a theory based on the midgap states in the vortex core.

We have characterized solid solution Y$_{l-x}Ca_xBa_2Cu_3O_y$ (0${\le}$x${\le}$0.3) materials by measuring the XRD pattern, resistivity and hole concentrations, etc. As Ca concentration increases, T$_c$, is decreased monotonically because the hole concentration on the superconducting plane increases beyond the optimum region in the electronic phase diagram due to the hole transfer from the Cu-O chain to the CuO$_2$ plane. A very small amount of secondary phase have large effects on the analysis of oxygen content and hole concentration etc. The results before the correction of impurity phase are compared with those after the correction.

Hg-1223 박막에서의 비저항(${\rho}$)을 임계온도 근처에서 은도와 자기장의 세기의 변화에 따라 측정하였다. 전도도(${\sigma}$)의 임계요동 부분은 3차원-XY 모델과 일치하는 임계현상을 보였다. 동적임계지수 z값은 1.5${\pm}$0.1로써 YBCO에서와 같았다. 정적임계지수 v값은 1.19${\pm}$0.3으로 YBCO에서보다 더 컸으며, 이것은 Hg-1223의 c축을 따라 층간의 약한결합 정도가 z값에는 영향을 미치지 않고, v값을 크게 증가시키는 것을 보여준다.

We have measured I-V characteristics of Bi$_2Sr_2CaCu_2O_{8+{\delta}}$ mesa containing a small number of intrinsic stacked Josephson junctions in a magnetic field. We fabricated mesa with an area of 40${\times}$40 ${\mu}$m$^2$ containing 3${\sim}$20 intrinsic junctions. We applied magnetic field perpendicular to He CuO$_2$ planes up to 5T. We observed flux-flow branches and flux-flow steps in the I-V characteristics which might be due to collective motion of Josephson vortices in the long junction limit. In a parallel field, critical current I$_c$ varies as I$_c$(B) ${\sim}$ exp(-B/B$_0$), where B$_0$ is about 2T, which is consistent with the theoretical model. DC and AC intrinsic Josephson effects are also discussed.

Biepitaxial Y$_1Ba_2Cu_3O_{7-x}$ (YBCO) and La$_{0.2}Sr_{0.8}MnO_3$ (LSMO) thin films have been prepared on SrTiO$_3$ buffer layer and MgO seed layer grown on Al$_2O_3$(11${\bar{2}}$0)substrates by dc-sputtering with hollow cylindrical targets, respectively. We charaterized Josephson properties and significantly large magnetoresistance in YBCO and LSMO films with 45$^{\circ}$ grain boundary junction, respectively. The observed working voltage (I$_cR_n$) at 77 K in grain boundary junction was below 10${\mu}$V, which is typical I$_cR_n$ value of single biepitaxial Josephson junction. The field magnetoresistance ratio (MR) of LSMO grain boundary juncoon at 77K was enhanced to 13%, which it was significant MR value with high magnetic field sensitivity at a low field of 250 Oe. These results indicate that inserting the insulating layer instead of the grain boundary layer with metallic phase can be possible to apply a new SIS Josephson junction and a novel magnetic device using spin-polarized tunneling junction.

We have studied the vortex dynamics in YBa$_2Cu_3O_7$ single crystals with columnar defects using micro Hall-probe array. The Hall-probe array technique allowed a simultaneous measurement of the time and spatial dependence of the vortex density so that more detailed information on flux dynamics could be obtained. We found that field profiles inside sample were similar to the Bean's critical state model from the magnetic hysteresis measurement. Normalized relaxation rates were maximum near the center and decreased toward the edge if applied field H$_{app}$ is greater than the penetration field H. But applied magnetic field H$_{app}$ is less than H, relaxation rates were minimum near the center and increased toward edge. We found that glassy exponent ${\mu}$ has the value of ${\sim}$ 1 whose corresponding vortex motion is half-loop excitation. However, single vortex creep, ${\mu}$ ${\sim}$ 1/7, was also found at 30 K and H$_{app}$ ${\cong}$ H'. Calculation of activation energy, U, was possible from direct analysis of the local relaxation data using the basic diffusion equation. From these results, we found that U increases logarithmically with time and U around center was lower than that at the edge.

The coexistence of the superconductivity and magnetism in the Ho1-xDyxNi2B2C is studied by using Ginzburg-Landau theory. This material violates the standard do Gennes scaling showing the coexistence and complex interplay of superconducting and magnetic order yielding an anomalous phase diagram. We propose a phenomenological model which includes two magnetic and two superconducting order parameters accounting for the multi-band structure of this material. We describe the magnetic fluctuations and order and demonstrate that they lead to anomalous behavior of the upper critical field. The doping dependence of Tc in Ho1-xDyxNi2B2C showing a reentrance behavior are analyzed yielding a very good agreement with experimental data.

In the ferromagnetic phase with electrons for La$_{1-x}$(Ca or Sr)$_x$MnO$_3$, films, a remnant resistivity of the order of 10$^{-8}$ ${\omega}$m is observed up to 100 K and increases exponentially with temperature up to T$_c$ and above one Tesla as a function of magnetic field strength (a positive magnetoresistivity). The phase below T$_c$ is regarded as a polaronic state with a polaronic tunneling conduction. Possible p-wave condensation (or superconductor) with a parabolic density of states and the phase separation are discussed on the basis of the two-fold degeneracy of ${\varrho}_{\delta}$ orbitals.

Magnetic and superconducting properties in a series of intermetallic compounds Y$_{1-x}Tb_xNi_2B_2C$ were investigated by measuring the temperature dependent magnetization, M (T), and resitivity, ${\rho}$ (T). As Tb concentration, x, is increased, the superconducting transition temperature, T$_c$, decreases and eventually disappears in the vicinity of x = 0.5 while Neel temperature, T$_N$, appears abruptly near x = 0.4 and increases linearly. Of particular interest is the collision of superconductivity and antiferromagnetism around x = 0.4. The linear decrease of T$_c$ for dilute Tb concentration seems to follow the Abrikosov-Gor'kov behavior, while the decay of T$_c$ below T$_c$ is expected to originate from the effective magnetic field on the conduction electrons. The Ginzburg-Landau theory was phenomenologically constructed to explain this competition of superconducting order parameter and antiferromagnetic order parameter with the multi-band model.

Magnetoresistance and magnetization of Sr$_{l-x}K_xBiO_3$ were both measured as functions of temperature and magnetic field. Resistivity goes to zero at T=10.1K and the overall superconducting transition behavior under applied magnetic fields is similar to that of other BiO based superconductors. Also, below T<5K we have observed the reappearance of finite resistivity with a power law temperature dependence( ${\rho}$ ${\sim}$T$^1$); the reentrant superconducting transition of resistivity. Contrary to the Josephson weak link effect in polycrystalline samples, which gives the depression of the superconducting state with increasing electrical current or magnetic field, the superconducting state for T<5K is resumed by applying a higher current or magnetic field. Magnetic susceptibility( ${\chi}$ ) of Sr$_{l-x}K_xBiO_3$ for T<5K also shows similar trends to that observed in transport measurements: increase of ${\chi}$ (paramagnetic-like behavior) at a low magnetic fields(B=50 Oe) and, the resumption of perfect diamagnetism at high fields.

We investigated the quench characteristics of meander line type resistive superconducting fault current limiters based on YBCO thin films grown on 2" diameter LaAlO$_3$ substrates. A gold layer was deposited onto the 0.4 ${\mu}$ m thick YBCO film to disperse the heat generated at hot spots, prior to patterning into 1 mm wide meander lines by photolithography. The limiters were tested with simulated fault currents of various amplitudes. The quench started at 10 A and was completed within 1 msec at the fault current of 65 A$_{peak}$. The dynamic quench characteristics were explained based on the heat conduction within the film and the heat transfer between the film and the surrounding liquid nitrogen. The heat transfer coefficient per unit area was estimated to be 3.0 W/cm$^2$K.

Magnetization measurements have been carried out on grain aligned Hg-1223 with the applied field parallel to the c-axis. The temperature dependence of the lower critical field H$_{cl}$(T) was determined by considering the effect of the surface barrier on the magnetization. H$_{cl}$(T) have been determined .from magnetic hysteresis loops within the framework of the modified Kim-Anderson critical-state model, where the surface barrier and the lower critical field are explicitly considered. At high temperature, H$_{cl}$(T) is identified as H$_p$(T). This results are agreed with the theory of Bean-Livinston surface barriers.

From extensive measurements of the resistance and the dynamic resistance as functions of magnetic field and temperature, we find that the transport in the insulating state beyond the superconductor-insulator (S-I) transition is dominated by bosons(Cooper pairs and/or vortices) and cannot be described by the theory of the fermionic insulating phase. The maximum of the magnetoresistance at B = B$_m$ and the following negative slope in R(B) with increasing field can be explained by the crossover from the "Bose-glass" to the "Fermi-glass" phase as suggested by Paalanen, Hebard, and Ruel. The zero bias peak in dv/dl for biases below the characteristic voltage V$_c$ (or current $I_c$), gives a clue for the assumption of the "dirty boson" model which states that the insulating state above the critical magnetic field is the phase where Cooper pairs are localized due to the Coulomb blockade with a nonvanishing order parameter. The shift to a lower value of the critical magnetic field by overlaying thin Au layer, which is known as a strong spin-orbit scatterer, also supports the bosonic nature of the S-I transition.

We have investigated the microwave properties of a high-T$_c$. superconducting Josephson junction by Shapiro step measurements. A Josephson junction was fabricated on the bicrystal MgO substrate using pulsed laser deposition method. We have measured Shapiro steps in the I-V characteristics under the irradiation of 1.36 cm wavelength up to 45 K and found inclined current steps above 50 K. In order to understand these results, we introduced an additional resistance connected in series to RSJ model. Using this modified RSJ model, we could explain the inclined current steps as a result of superposition of the junction and an additional resistance above certain temperatures. Also, we presented the received power of the Josephson junction above 50 K.

We have measured the temperature dependence of thermoelectric power (TEP) and resistivity for the Sr$_{1-x}K_xBiO_3$ superconductor (x=0.45-0.6). At T=10.2K, the resisitivity starts to increase from zero and a rather broad superconducting phase transition (${\Delta}$T ${\sim}$ 2.3K) is observed. TEP at room temperature has a small negative value ( S =-1.96${\mu}$V/K), characteristic of metallic-like TEP. The temperature dependence of TEP shows two distinct features. With decreasing temperature from room temperature, the absolute value of TEP decreases and the sign of TEP changes from negative to positive around 200k. Also, the negative slope of TEP(dS/dT) decreases substantially and becomes rather flat at around 160k, which is a feature already noted in Ba$_{1-x}K_xBiO_3$[1].

To investigate the effect of interference current between pairs and quasi-particles, we have calculated the change I-V characteristic curve of resistively and capacitively shunted Josephson junction with external microwave by simulation of modified Stewart-McCumber model. Such rf-induced constant-voltage steps and the immunity against to noise were found to be changed in the presence of interference current.

We have observed that a stable and reproducible Negative Differential Resistance(NDR) is induced by external microwave at low power in Nb/AlO$_x$/Al/Alo$_x$/Nb junctions. To study the erratic and pozzling NDR observations we have simulated Stewart-McCumber model in the region. Experimental results and simulation results will be presented with a discussion to draw a dynamic interpreration of the NDR.

Analog-to-digital converter has attracted a lot of interests as one of the most prospective area of an application of Josephson Junction technology. Recently, the development of a digital-to-analog converter has been pursued to achieved the high performance. One of the main advantage in using single flux quantum logic in a digital-to-analog converter is the low voltage drop in a single Josephson Junction and hence the resolution of the output voltage of this digital-to-analog converter can be very high. In this work, we have used a software, called WRspice, to study a voltage multiplier circuit which is the basic block in building a digital-to-analog circuit. In simulation, we operated a voltage multiplier with .4 Josephson Junctions per stage and studied the dependence on the circuit bias currents and the circuit inductors of the voltage multiplier. Our simulation results showed a fast operation and reasonable circuit margins.

For the fabrication of fault current limiting device using HTSC thick film, YBa$_2Cu_3O_x$ superconducting thick film was formed by surface diffusion process of the Y$_2BaCUO_5$ and the mixed compound of (3BaCuO$_2$+2CuO) expected to be liquid phase above the peritectic temperature of YBa$_2Cu_3O_x$. For the surface diffusion, the compounds of 3BaCuO$_2$+2CuO mixed with binder material was patterned on Y$_2BaCUO_5$ substrate by the screen printing method. After proper sintering, the characteristics of current limit on thick film fabricated was measured. The thick film was able to limit the current from 2.8213 mA$_{rms}$nu to 4.2034 mA$_{rms}$ with 500${\omega}$ load resistance, and from 4.1831 mA$_{rms}$ to 4.2150 mA$_{rms}$ with 10${\omega}$ load resistance.

We have performed $^{63,65}$Cu nuclear quadrupole resonance (NQR) measurements on Zn and Ni doped YBa$_2Cu_3O_7$ (YBa$_2Cu_{3-x}M_xO_7$, M=Zn or Ni, x = 0.00 ${\sim}$ 0.09). Doping effects are markedly different in relaxation rates as well as in superconducting transition temperatures. Both the spin-lattice and the spin-spin relaxation rates decrease for Zn doped YBCO. However, those increase for Ni doped YBCO. This contrast in local electronic dynamics provides a clear microscopic evidence that Zn forms no local moment, while Ni develops a local moment. Consequently, the antiferromagnetic spin fluctuation is suppressed by Zn doping whereas it is preserved by Ni doping.

Local field distribution in the mixed state of type II superconductors has been numerically calculated and compared with $^{11}$B NMR spectra for YNi$_2B_2C$ single crystals. We find that only small distortion of vortex positions from the perfect lattice points is enough to smear out the low frequency shoulder. As the vortices are further distorted, the line shape changes from an asymmetric shape with a high frequency tail to a symmetric Gaussian line shape. It is found that the second moment of the field distribution has a major contribution from the high frequency tail. Consequently, a linewidth of the full width at half maximum calculated from the second moment assuming for a Gaussian line shape is overestimated.

새로운 구리산화물 (Pb$_{0.5}$V$_{0.5}$)Sr$_2$(Ca$_{1-x}$Pr$_x$)Cu$_2$O$_z$를 상압의 산소 분위기 열처리를 통해 합성하였다. X선 회절실험결과 x=0.5 이상일 때 Pb-1212의 단일상이 형성됨을 확인했으며, 비저항 측정결과 x=0.5 인 시편에서 T$_c$(zero)=29 K T$_c$(onset)=40 K 가 관측되었다. x=0.6 이상일 때는 초전도 특성이 관측되지 않았으며 이는 Pr의 도핑량 x 가증가할수록 a 축이 증가하고 c 축이 감소 하는 것과 밀접히 연관되는 것으로 논의되었다.

We compared c-axis tunneling characteristics of small stacked intrinsic Josephson junctions prepared on the surface of pristine, I-, and HgI$_2$-intercalated Bi$_2Sr_2CaCu_2O_{8+x}$ (Bi2212) single crystals. The R(T) curves are almost metallic in I-Bi2212 specimens, but semiconducting in HgI$_2$-Bi2212 ones.· The transition temperatures were 82.0 K, 73.0 K, and 76.8 K for pristine Bi2212, I-Bi2212, and HgI2-Bi2212 specimens, respectively, consistent with p-T$_c$ phase diagram. Current-voltage (IV) characteristics of both kinds of specimens show multiple quasiparticle branches with well developed gap features, indicating Josephson coupling is established between neighboring CuO$_2$ planes. The critical current I$_c$ of I-Bi2212 is almost the same as of that of pristine crystals, but I$_c$ is much reduced in Hgl$_2$-Bi2212. In spite of expanded interlayer distances, the interlayer coupling is not significantly affected in I-Bi2212due to holes generated by iodine atoms. The coupling in HgI$_2$-Bi2212 is, however, weakened due to inertness of HgI$_2$ molecules and the expansion of interlayer distance. Relation between the superconducting transition temperature T$_c$ and the critical current I$_c$ seems to contradict Anderson's interlayer-pair-tunneling theory but agree with a modified version of it.

We observed leveling-off of the resistance in granular In/InO$_x$ thin films in the zero-temperature limit. The temperature T$_b$ at which the leveling-off appears gets larger as the sheet resistance R$_n$ increases. This is consistent with the concept that the leveling-off of the resistance is due to the dissipation of the bosonic phase and that the dissipation is enhanced as the resistance increases. The magnetic field dependence of the saturated resistance R$_b$ at low temperatures fits the modified square-root cusp-like form R$_b$/R$_n$=α exp[-b(B/B$_c$-1)$^{-1/2}$] for the magnetic field in the range B$_c$$_f$ where B$_c$ is the onset magnetic field of the resistance leveling-off. α and b are constants of order 1. For B>B$_f$ tansport properties are described by the theory of the fermi insulator. From the results, we attribute the leveling-off to the dissipative quantum tunneling of vortices, which supports the models predicting the vortex-motion-induced insulating phase related with the concept like"dirty boson" [1]l and "hose metal" [2].

We report the activation energies which is calculated by adding a term being neglected usually, and magnetic relaxation effects for the surface barrier. The activation energies U at initial magnetization m (m$_{en}$ and m$_{ex}$) and equilibrium magnetization m$_{eq}$ are nearly similar to those of Burlachkov, but the m dependence of the activation energy U is remarkably different. The relaxation effects, which were determined by the m dependence of the activation energies U, are nonlinear for vortex entry, but linear at the initial stage and nonlinear at m(Int) ${\simeq}$ m$_{eq}$ for vortex exit. During relaxation process, the vortex entry at m = m$_{en}$ is faster than the vortex exit at m = m$_{ex}$ by about factor 90. The vortex exit at m = m$_{eq}$ is faster than one at m = m$_{ex}$ by about factor 1.3

A SQUID magnetometer or a SQUID gradiometer can be used to measure the field or gradient distribution, respectively. We describe the magnetic dipole model of the eddy currents in a nondestructive evaluation. Such a theoretical calculation of the magnetic dipole fields produced by a deep flaw in metallic materials can be used in aerospace and transportation industries.

We are investigating epitaxially grown YBa$_2Cu_3O_x$(123) on MgO single crystal by partial melting process for high power application. After fabricating of BaCuO$_2$(011), Y$_2BaCuO_5$(211) powder, we made YBa$_2Cu_3O_x$(123) Paste with just mixing of (211), (011) and CuO(001) powders. Screen printing method was used to coat YBa$_2Cu_3O_x$(123) paste on MgO single crystal. To reduce the reaction in low temperature, rapid heating was conducted at partial melting temperature. The film was analysed with the difference of cooling-rate, thickness, reaction temperature by XRD, SEM, in-plane alignment, out-of-plane alignment, temperature-resistivity characteristics.

It is well known that HTS current lead minimizes helium vaporizations much less than the conventional current lead. To estimate the helium vaporizations in the design step, we need to compute the exact the temperature distributions on the lead. Unfortunately, the thermal parameters such as thermal conductivity and electrical resistivity depend strongly on the temperature. That is, heat equation itself has a nonlinear characteristics in the current lead. Furthermore, the uncertainties of helium vaporizations make it more difficult to estimate the boundary values. So far, numerical analyses using constant parameters in finite intervals have been used. In this paper, we calculate the temperature distribution in the current lead in considerations of temperature dependent parameters. The results showed self consistencies.

The microstructures of a Tl$_{0.8}Pb_{0.2}Bi_{0.2}Sr_{1.6}Ca_2Cu_3O_{9+{\delta}}$/Ag tape (tape I ) with J$_c$ of 17,600 A/cm$^2$ at 77 K and 0 T and three Tl$_{0.8}Pb_{0.2}Bi_{0.2}Sr_{1.8}Ba_{0.2}Ca_{2.2}Cu_3O_{9+{\delta}}$/Ag tapes with J$_c$'s of 9,300 (tape II), 16,700 (tape III) and 25,200 A/cm$^2$ (tape IV)prepared using the powder-in-tube method and an in-situ reaction method, were investigated using scanning electron microscopy and high-resolution transmission electron microscopy, and compared each other. ln the tape preparation, an intermediate rolling process was incorporated during final heat-treatment for the last tape, but not for the rest of the tapes. The microstructural analysis revealed clear differences in grain-texturing, crystallographic defects and impurity phases, depending on the chemical composition of the tape. Tendency of directional grain-alignment increased in an order of tapes I, II III and IV. In tape IV, T1-1223 grains are textured, at least in local regions. In crystallographic defects, while stacking faults were prevalent in the former composition, dislocations and voids were frequently observed in the latter. Also impurity phases were appeared to be more abundant in the former than in the latter. The relationship between 1,and the microstructure in the tapes was attempted to explain in a term of grain-linking.

Long 19-filamentary Bi-2223 tapes were prepared using the so called "powder-in-tube" method. In the preparation, two types of precursor powders and two different reduction rates during rolling were used. Also two rolling method, which resulted in different filament geometry, were used. The characteristics of the tapes will be presented. Also A coil was prepared using two 56 m-long 19-filament tape. It was consisted of two double pancake coils. Each pancake, which is separated by FRP spacer, was composed of 98 turns. The experimental results will be presented and compared to the simulation result.

We investigated the effects of Pd impurities on cube-textures in cold rolled and recrystallized PtPd tapes The sample were made from Pt$_{1-x}Pd_x$ alloys (x from 0 to0.34) by rolling at low temperature. The thickness of the tapes were about 100 ${\mu}$m. The PtPd[111] pole figures of X-ray Diffraction for all the samples indicated similar deformed textures. But the recrystallized textures after annealing showed that a better cube texture was formed in the sample of larger x. The final textures were sensitive to annealing time and temperature when x was increased.

Bi$_2Sr_2CaCu_2O$(Bi-2212) thick films were fabricated on Y2l1 substrate by screen printing method. And the samples were annealed in various atmospheres, respectively. Though samples had many voids, the sample annealed in N$_2$ ; O$_2$ = 1:0 atmosphere and the sample in N$_2$ : O$_2$ = 0:1 showed some Bi 2212 low phase in comparison to other samples. The thickness of Bi-2212 on Y2ll substrates was about 20 ${\mu}$m.

To tap the feasibility of exploiting the 2$^{nd}$ phases as flux-pinning centers in the (Bi,Pb)$_2Sr_2Ca_2CuO_{10}$ superconductor, the size and the distribution of the precipitates have been controlled by changing reaction temperature and time, oxygen partial pressure Po$_2$ and annealing condition. Various annealing heat treatments were also conducted on the as-received 61 filament Bi-2223 tapes with Bi$_{1.8}Pb_{0.4}Sr_2Ca_{2.2}Cu_3O_8$ starting composition and annealed specimen were analyzed with XRD, SEM, EDS and TEM.. The grain size of (Ca,Sr)$_2$(BiPb)O$_4$ or Bi$_{0.5}Pb_3Sr_2Ca_2CuO_{\delta}$ was controllable by optimizing the heat treatment condition and critical current density (J$_c$) showed dependence on the size of the 2$^{nd}$ phases.

This paper presents an high efficiency energy conversion system for very high-speed flywheel energy storage system using high Tc superconducting bearings. Main configuration of power convertor is designed to replace of the conventional battery with EMB(Electro Mechanical Battery). PMSM(Permanent Magnet Synchronous Motor) using Halbach array is used as the energy conversion system of motor and generator. Some PWM methods for the high frequency inverter is described and the power factor effects to the torque characteristics and efficiency of the motor and generator is analyzed. As the results, it is verified that the inverter output current is well regulated to be in-phase or inverse-phase sinusoidal waveform to have the wide operational range from 2,500rpm to 42,000rpm. Proposed circuit is designed to obtain the very high speed, high efficiency and stable rotational characteristics, and to be applied to1.2r[kW]/65[Wh] system.

A prototype of Flywheel Energy Storage System with high Tc superconducting bearings was fabricated and tested to verify its applicability for the energy industry. The moment of inertia of assembled wheel with rotor magnets is about 1.072${\times}$10$^{-1}$ Kg-m$^2$. The wheel was designed to withstand its integrity up to the rotation speed of 20,000 rpm. YBCO bulk superconductors prepared by seed growth method were used as bearing to levitate and stabilize the rotating wheel. High speed rotation of the flywheel without mechanical contact was achieved by using specially designed Halbach type motor. The flywheel system showed very high stability during test operation performed up to the speed of about 10,000rpm. The energy loss measured by free decay test performed between 9,300 rpm and 7,000 rpm was calculated as about 45 W.

Bi$_{2}Sr_{2}CaCu_{2}O_{\delta}$ superconducting films were rapidly fabricated on copper tape by liquid reaction between a Cu-free precursor and Cu tape (LiReac-PreCu) method. Those thick films were well oriented along the c-axis. The precursor was made by melt-quenched technology using twin roller. The melt-quenched films were transparent and glossy yellow in appearance. These films which were the compostion of Bi$_2SrCaO_y$, Bi$_3Sr_2CaO_z$ were placed on copper tape and then heated at various temperatures for several minutes in air. They were analyzed using X-ray powder diffraction, SEM, a DC four-probe method. The mechanism of superconducting phase formation . from the melt-quenched precursor on Cu tape was studied

To solve the problems in the present ree1-to-reel deposition method, we have developed a new deposition system for a 12m long YBCO coated conductor. The system comprises two chambers, a reaction chamber and a evaporation chamber which are connected through window. A tan long fi tape textured by RABiTS was wound around a cylinderical sample holder of 20cm diameter. The cylinder was rotated in the reaction chamber during deposition of YBCO film by coevaporation. We'll describe the details of the performance of this system as well as the RABiTS process for a 12m long Ni tape.

We fabricated 18cm YBCO coated conductor comprising a YBCO superconducting film and CeO$_2$/YSZ/CeO$_2$ buffer films deposited on a biaxially textured Ni tape. For those film fabrications, we developed a new method, the cylindrical holder in a double chamber. This is alternative to the reel-to-reef method which is commonly tried to fabricate a long YBCO coated tape. We will discuss about the superconducting properties of the 18cm long YBCO coated tapes.

We investigated the effects of residual gas partial pressure on the property of a CeO$_2$ buffer layer on a textured Ni tape, where the buffer layer was deposited by e-beam evaporation. The oxygen partial pressure were varied from 10$^{-7}$ to 10$^{-4}$ Torr. we also changed the surface condition for the surface oxygenation. We'll describe the detail of the resultant textures of the buffer layers and effects of YBCO growth on them

The BSCCO 2223 Ag-sheathed tapes were prepared with spray dried precursor powders, which are of different starting condition. The J$_c$ in the short tapes varied from 24 kA/ cm$^2$ to 47 kA/ cm$^2$ at 77K and 0T. The largely improvement of J$_c$ in certain tape, which characterized with the large textured BSCCO 2223 grains, homogeneity of reactant and fewer tracks of second phases in final superconducting matrixes, could be due to optimization in the precursor powder.

High T$_c$ (${\sim}$21,500 A/cm$^2$, at 77K) of 100m length of BSCCO 2223 tapes have been achieved using optimized precursor powders with carefully controlling variables in heat treatment. Prototype 500A class multistrand conductor for HTS power cable was fabricated using these tapes. Also discussed are the transportation properties of prototype 500A class multistrand conductor.

전력계통에 저항형과 유도형 초전도 한류기를 적용하였을 때 사고각별 전류제한 효과를 살펴보았다. S1 변전소로부터 S2 변전소까지 거리의 약 60%지점에서 사고가 발생하였을 때, 1선 지락사고에서 S1측 고장전류는 사고각 0 $^{\circ}$ 의 경우 약 39kA이었으며 이는 정상전류의 약 87배이었고, 5주기 이후의 전류값도 53배에 달하는 약 23 kA값을 보여주었다. 차단기 전단에 저항형과 유도형 초전도 한류기를 적용하였을 때 사고각별 전류제한효과를 보면, 사고각 0 $^{\circ}$ 인 경우 저항형은 사고발생 직후 최대 한류전류값이 최고 39 kA, 최종 한류전류값이 약 15 kA이었다. 이때 과도상태에서 직류분은 거의 발생하지 않았다. 유도형은 사고발생 직후 최고 39 kA와 최종 12 kA의 전류값을 나타내었다. 이때 직류분은 약 3 kA이었다. 2선 지락사고에서 고장전류는 사고각 0 $^{\circ}$ 의 경우 최고 약 56 kA이었으며 이는 정상전류의 약124배이었고, 5주기 이후의 전류값도 76배에 달하는 약 34 kA값을 보여주었다. 선로에 저항형과 유도형 초전도 한류기를 적용한 경우 사고각별전류제한 효과를 보면, 사고각이 0 $^{\circ}$ 일때 저항형은 사고발생 직후 최대 한류전류값이 최고 44kA, 최종한류전류값이 약 15 kA이었다. 이때 과도상태에서 직류분은 거의 발생하지 않았다. 유도형은 사고발생 직후 최고 44 kA와 최종 14 kA의 전류값을 보여주었다. 이때 직류분은 약 4 kA이었다. 1, 2선 지락사고를 종합해 보면 2선 지락사고가 사고전류의 크기와 유도형의 직류분 감쇄폭이 약간 컸을 뿐 전력계통에서 초전도 한류기의 적용은 같은 조건(초전도 한류기의 최종 임피던스100${\omega}$)하에서 전류제한 능력면에서는 유도형이 유리하고 초기 과도상태에서 직류성분의 발생측면은 저항형이 장점을 가지고 있음을 알 수 있었다. 아울러 앞으로는 quench 시간에 따른 전류제한 현상에 관한 simulation을 수행 하고자 한다.

YBCO film을 이용한 meander 형태의 저항형 한류기에서 고장이 발생하였을 때 초기의 과도상태에서 볼수 있는 첨두전류를 억제하기 위하여 shunt 저항을 병렬로 취부한 경우의 전기적특성을 살펴보았다. 인가전압을 16.5 V$_{peak}$로 가하고 R$_0$는 1 ${\omega}$,R$_L$을 7.7 ${\omega}$으로 하고 shunt 저항을 5 ${\omega}$으로 하였을 때 약 12.2 A$_{peak}$의 전류값에서 최초quench가 발생하였으며 초전도 한류소자에 quench 발생으로 인한 저항이 발생함과 동시에 I$_1$으로 흐르던 사고전류의 일부가 shunt 저항이있는 I$_2$으로 서서히 분로하여 첨두전류가 거의 발생하지 않았다. 이때 초전도 한류기를 적용하지 않은 경우 최대 사고전류는 약 16.5 A$_{peak}$이었으며 초전도 한류기를 적용한 경우는 최대 한류전류값이 9 A$_{peak}$에서 4주기후에는 5.8 A$_{peak}$이었다. 인가전압 V$_0$=113 V$_{peak}$이고 표준저항 R$_0$는 1${\omega}$, 그리고 R$_L$을 7.7 ${\omega}$으로 하고 shunt 저항을 5 ${\omega}$으로 하였을 때 사고각 0 $^{\circ}$에서 사고전류값이 최고 23.0 A$_{peak}$까지 상승하고 이후 일정한 값을 유지하였다. 일반적으로 사고발생 직후에는 전류변화율에 의하여 전류값의 급격한 상승을 보이지만 shunt 저항이 전류분류의 역할을 수행하여 첨두전류는 거의 발생하지 않았다. 또한 상온의 gold층의 저항을 감안했을 때 사고발생후 약 36msec 후에 상온에 도달하였으며 shunt 저항이 없는 경우의 11 msec에 비하여 약 3배이상 길어졌다. 사고각 45 $^{\circ}$와 90 $^{\circ}$인 경우는 반복실험에 의한 시편의 특성저하(degradation)에 의하여 정상상태에서 초전도체에 흐르는 전류가 약간 발생하였다. 계통의 신뢰성이 중요한 요소로 작용하는 실제운전에서는 시편의 특성저하에 의한 quench전류의 감소를 감안하여 적절한 운전조건을 도출하여야 한다. 이상에서 앞으로는 장기간의 실제운전 조건을 고려하여 시편의 특성저하(degradation)와 가혹조건에 대한 전기적 특성에 대한 연구를 병행하고자 한다.

Cold 층을 입힌 저항형 초전도 한류기의 전류 제한 특성을 통하여 다음과 같은 결론을 얻었다. 고장발생후 3.2 msec 후에 quench가 발생하였으며, 부분적인 quench가 발생한 다음 시간이 지나면서 완전한 quench로 진행되었다. 즉, 선로고장에 따른 quench 발생 후 YBCO 초전도체의 gold층으로 대부분의 전류가 흐르게 되고, quench 되면서 발생하는 열도 대부분 gold층에서 흡수하여저항이 증가하였으며 이에 따른 전류감소, 전압증가 및 소비전력증가가 발생하였다. 인가전압 V$_0$=65 V$_{peak}$이고 R$_0$는 1 ${\omega}$, 그리고 R$_L$을 7.7 ${\omega}$으로 하였을 때 사고모의 위상각 0$^{\circ}$에서 고장발생후 0.9 msec 후인 9.6 A$_{peak}$ 되는 지점에서 quench가 발생하여 13.0 A$_{peak}$의 최대한류전류값을 보인후 11.4 A$_{peak}$의 전류값에서 fast quench가 완료되었다. 이때 quench 시간은0.63 msec 이었다. 저항값은 gold층에서 발생한 열때문에 점진적인 상승을 보이다가 약 3주기후에 일정한 값에 도달하였다. 한류소자의 온도는 약 11 msec 후에 상온에 도달하였으며, 3 주기후인 54 msec에는 150 $^{\circ}C$까지 상승하였다. gold 박막을 입힌 meander line은 임계전류 이상의 전류를 통전하였을 때에 용단되지 않았으며 ??치된 상태에서 3 사이클 이상 유지하였다. 약65 A$_{rms}$가 흘렀을 때에야 ??치후 3 사이클 지나용단되었다. 이러한 YBCO/gold에 의한 초전도한류기의 용량은 gold에 발생하는 열을 gold가감당할 수 있는 전류의 크기와 관련이 있으며, gold층이 YBCO 한류소자가 quench되었을 때 발생하는 열을 효과적으로 분산시킬 뿐만 아니라 전기적으로 shunt 회로 역할을 하고 있음을 확인할 수 있다. 이에 더하여 앞으로 quench 후 한류소자에서 발생할 수 있는 인덕턴스의 저감방안에 대한 설계 및 모델 탐구를 통하여 좀더 효율적인 한류소자 구성에 대한 연구를 병행하고자 한다.

The Cu sheets were selected for the substrate of the superconductor films. Pure Cu sheets with the thickness of 50${\mu}$m were fabricated using hot and cold rolling. The Cu sheets were heat treated to induce the biaxial texturing. The z-axis and x-y plane texturing of Cu sheets heat treated at different conditions were analyzed using XRD and a best heat treatment condition for the texturing was selected. ZrO$_2$ film was dip coated on Cu sheets heat treated at the best condition to prevent possible reaction between Cu sheets and YBCO superconductors, to reduce possible cracking due to thermal expansion mismatch and to decrease the lattice mismatch for biaxial texturing. The texturing of the oxide buffer layers were also studied.

Magnetic levitation forces and trapped magnetic fields of top-seeded melt growth-processed YBCO superconductors with multiseeding were studied. The number of seeds was varied from one to six. The surface magnetic field of the prepared YBCO samples was dependent on the number of the seeds. The trapped magnetic field of the top surface decreased with increasing the number of the seed. Particularly, it drastically decreased at the YBCO grain boundary, probably due to the weak rink nature of the boundary. The magnetic levitation force also decreased with increasing the number of the seeds, similar to the variation of the surface magnetic field.

Multiseeding 방법을 사용하여 Y-Ba-Cu-0 초전도_ 시료를 제조하였다. Multiseeding은 여러개의 종자를 동시에 사용함으로써 단시간에 큰 size의 시료를 제조하고자 하는 의도에서 시도되었다. 또한 field-cooled 상태에서 포획 자기장의 크기를 측정함으로써 입자간 결합 상태와 시료의 품질을 평가하였다. 일반적인 방법으로 제조할 경우 포획 자기장 값은 입계를 지나면서 크게 감소하였는데, 이는 입계에 존재하는 잔류액상 및 미반응 211 입자 등에 기인한 결과이다. 입계를 따라 미반응상들이 잔류하는 현상을 억제하기 위해 본. 연구에서는 종자들간의 간격을 조절하였다. 그 결과 종자결정들간의 간격을 최대한 좁게 배열하였을 때 포획자기장의 크기가 입계에서 감소하지 않는 결과를 얻었다. 이와 같이 종자간의간격이 충분히 가까울 경우에는, 결정성장 초기에 두 입자가 하나로 결합될 수 있으므로 입계에 미반응 액상이 잔류하는 현상을 억제할수 있었던 것으로 생각된다.

Using Ag sheathed multi filamentary Bi-2223 tape, stability against heat pulse has been investigated. The measured normal zone propagation(NZP) velocity of the tape was found to be faster due to increase of operating current and magnetic field, and agree well with calculated data from one dimensional heat balance equation. Minimum quench energy(MQE) was found to be larger than 17 J at 30 K zero magnetic filed at operating current of 96.5 with respect to I$_c$.

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.

We evaluated the effect of joining process such as contact method, shape of joined area and pressure on the electrical property of Bi-2223 superconducting tape. It was observed that the current capacity was reduced at the transition area of the joined tape and was significantly dependent on the uniaxial pressure. The lap-joined tape, fabricated with a pressure of 1,000-1,600 MPa, show the highest value of current capacity(80-90%) of the tape itself. It is believed the highest value of current capacity results from improvement in core density, contacting area and grain alignment, etc. In addition, the irreversible strain( ${\varepsilon}$ irrev) for the joined tape· was measured to be 0.1%, smaller than that of enjoined tape( ${\varepsilon}$ irrev = 0.3%). The decrease in the strength and irreversible strain for joined tape is believed to be due to the irregular geometry/morphology of the transition area of the tape.

A new multi-seeding process for the growth of YBa$_2Cu_3O_x$ single crystals was developed. This process introduces an additional heating step to peritectic temperature and a subsequent slow cooling step to the growth temperature following the point when the crystals contacted. The crystal growth was resumed thereafter. The results obtained with this new process were compared with those of the conventional growth process, in which materials were only kept at the growth temperature. There was significant improvement in trapped magnetic field over the conventional multi-seeding process, which is believed to be due to complete elimination of liquid phase between crystals.

Well oriented Bi2212 superconductor thick films were formed successfully on a copper substrate by liquid reaction between a Cu-free precursor and Cu tape method in which Cu-free BSCO powder mixture was' printed on copper plate and heat-treated. And we examined the effect of heat-treatment atmosphere for the superconducting properties and microstructure of Bi2212. The composition of Cu-free BSCO powder mixture was Bi$_2O_3$ : SrCO$_3$ : CaCO$_3$ = 1.2~2 : 1 : 1 and the heat-treatment for the superconducting formation reaction was performed in air, oxygen, nitrogen and low oxygen pressure. At heat-treatment temperature, the printing layer partially melt by reacting with CuO of the oxidizing copper plate, and the nonsuperconducting phases present in the melt are typically Bi-free phases and Cu-free phases. Among the nonsuperconducting phases, it is known that the (Sr,Ca)CuO$_3$ phase restrain the formation of the Bi2212 superconducting phase. Because a kind of the nonsuperconducting phases is controled by the oxygen partial pressure, the optimum condition in which the remnants of the second phases don't leave in the fully processed conductor was determined by XRD and the critical tempera to re (Tc) analysis.

Superconducting YBa$_2Cu_3O_{7-{\delta}}$(YBCO) thin films were grown on Hastelloy(Ni-Cr-Mo alloys) with CeO$_2$ buffer layer in-situ by pulsed laser deposition in a multi-target processing chamber. To apply superconducting property on power transmission line, we have deposited YBCO thin film on flexible metallic substrate. However, it is difficult to grow the YBCO films on flexible metallic substrates due to both interdiffusion problem between metallic substrate and superconducting overlayers and non-crystallization of YBCO on amorphous substrate. It is necessary to use a buffer layer to overcome the difficulties. We have chosen CeO$_2$ as a buffer layer which has cubic structure of 5.41 ${\AA}$ lattice parameter and only 0.2% of lattice mismatch with 3.82 ${\AA}$ of a-axis lattice parameter of YBCO on [110] direction of CeO$_2$ In order to enhance the crystallization of YBCO films on metallic substrates, we deposited CeO$_2$ buffer layers with varying temperature and 02 pressure. By XRD, it is observed that dominated film orientation is strongly depending on the deposition temperature of CeO$_2$ layer. The dominated orientation of CeO$_2$ buffer layer is changed from (200) to(111) by increasing the deposition temperature and this transition affects the crystallization of YBCO superconducting film on CeO$_2$ buffered Hastelloy.

We have fabricated BSCCO 2223 by modified two powder process and investigated 2223 phase formation and grain growth. Phase evolution and reactivity of 2223 were remarkably sensitive to size of 2212 grains and liquid phase. Larger size of 2212 phase increased liquid formation temperature. The Avrami relation was well suited for describing the kinetics of grain growth in BSCCO 2223.

본 논문은 고온초전도한류기가 투입된 회로에 사고가 발생했을 경우 사고각에 따른 사고전류의 패턴에 관한 연구이다. 계통에 심각한 영향을 끼치는 이러한 사고전류의 순간 특성을 해석하기 위해 유도형 고온초전도한류기를 직접 제작하였으며 임의로 다른 각도에서 사고를 발생시켜 실험하였다. 임의의 사고각을 위해 triac으로 구성되어있는 위상각제어 및 사고 발생기를 부하와 직렬로 연결하였다. 또한, 순간적으로 큰 사고전류의 유입은 철심을 포화시키기에 충분하며 철심의 포화로 인해 상대투자율이 작아짐으로서 고온초전도한류기의 임피던스가 작게 발생하게 된다. 본 논문에서는 이러한 영향으로 인한 사고전류의 패턴에 관하여 연구하였다.

A prototype of solenoidal superconducting magnet using Bi-2223/Ag multi-filamentary tapes was fabricated and tested to investigate its performance. The Bi-2223/Ag tapes were prepared by powder-in-tube method. The dimensions of magnet, which was stacked with 9 double pancakes, were 90 mm in height, 74 mm in outer diameter and 40 mm in clear core. The axial maximum magnet field at the center of the solenoidal magnet was about 0.12 T, and the critical current of coil conductor was about 9 A at 77.3 K.