The infinite layer compound $ACuO_2$, (A-Alkaline earth) consists of infinite stacking of $CuO_2$ planes separated only by alkaline earth ions. This compound attracted much attention because it contains only key ingredient of all cuprate high temperature superconductor; $CuO_2$ plane with controllable carrier concentration without charge reservoir block. High pressure synthesis method has been found to be preferable for this system due to its ability of doping various lanthanide ion into A site with larger superconducting volume fraction. But rigorous study on this rudimentary compound has been hindered by insufficient quality of sample. Especially superconductlng volume fraction was often too small to identify its origin. In this presentation, we report high pressure synthesis of $Sr_{0.9}Ln_{0.1}CuO_2$ (Ln=La, Sm). By controlling the heating temperature precisely during high pressure synthesis we could have superconductors with quite high superconducting volume fraction for this compound. The magnetic properties of the graln aligned samples show very different behavior compared to the cuprate high temperature superconductors. Details will be discussed.

We have developed an extremely sensitive radio frequency amplifier based on the dc superconducting quantum interference device (dc SQUID). Unlike a conventional semiconductor amplifier, a SQUID can be cooled to ultra-low temperatures (100 mK or less) and thus potentially achieve a much lower noise temperature. In a conventional SQUID amplifier, where the integrated input coil is operated as a lumped element, parasitic capacitance between the coil and the SQUID washer limits the frequency up to which a substantial gain can be achieved to a few hundred MHz. This problem can be circumvented by operating the input coil of the SQUID as a microstrip resonator: instead of connecting the input signal open. Such amplifiers have gains of 15 dB or more at frequencies up to 3 GHz. If required, the resonant frequency of the microstrip can be tuned by means of a varactor diode connected across the otherwise open end of the resonator. The noise temperature of microstrip SQUID amplifiers was measured to be between $0.5\;K\;{\pm}\;0.3\;K$ at a frequency of 80 MHz and $1.5\;K\;{\pm}\;1.2\;K$ at 1.7 GHz, when the SQUID was cooled to 4.2 K. An even lower noise temperature can be achieved by cooling the SQUID to about 0.4 K. In this case, a noise temperature of $100\;mK\;{\pm}\;20\;mK$ was achieved at 90 MHz, and of about $120\;{\pm}\;100\;mK$ at 440 MHz.

A high $T_c$ SQUID system is developed for the application to biological immunoassay. In this application, magnetic nanoparticles are used as magnetic markers to perform immunoassay, i.e., to detect binding reaction between an antigen and its antibody. The antibody is labeled with ${\gamma}-Fe_2O_3\;(or\;Fe_3O_4)$ nanoparticles, and the binding reaction can be magnetically detected by measuring the magnetic field from the nanoparticles. Design and set up of the system is described. The system consists of (1) SQUID magnetometer or gradiometer made of 30-deg. bicrystal junctions, (2) field and compensation coils to apply the magnetic field of about 1 mT, (3) special Dewar to realize a 2 mm-distance between the SQUID and the sample, (4) two layers of cylindrical shielding to reduce the extemal magnetic noise to about 1/100, and (5) an electric slider to move the sample with a speed of 10 mm/sec. The sensitivity of the system is studied in terms of detectable magnetic flux. For the measurement bandwidth from 0.2 Hz to 10 Hz, minimum-detectable amplitude of the magnetic flux is $0.8\;m\;{\Phi}_o$ and $0.25\;m{\Phi}_o$ for the magnetometer and the gradiometer, respectively, when the magnetic field of 1 mT is applied. The difference between them is due to the residual environmental noise, and the applied magnetic field does not increase the system noise. The corresponding weight of the magnetic markers is 1 ng and 310 pg, respectively. An experiment is also conducted to measure antigen-antibody reaction with the present system. It is shown that the sensitivity of the present system is 10 times better than that of the conventional method using an optical marker. A one order of magnitude improvement of sensitivity will be realized by the sophistication of the present system.

Recently the study of the pseudo-gap in high temperature superconductivity become critical issue because it contains key information of the pair formation of the high temperature superconductivity. Specially angle resolved photoemission study shows the various information of the gap formation. In this talk, I will review the recent theories as will as experiments on the pseudo-gap in high temperature superconductors. Specially I will introduce the possible observation of the Andreeve reflection in the underdopped high temperature superconductors.

We report on the novel nonequilibrium nlicrowave emission from quasiparticle-injected high-Tc superconductors. The phenomena have been observed for the current-injected YBCO/I/Au or BSCCO/I/Au thin-film tunnel junctions and BSCCO single-crystal intrinsic Josephson mesa junction samples. For the thin-film tunnel junctions, the emitted radiation appears as broadband. For the intrinsic BSCCO mesa samples, the radiation appears as three different modes of emissions depending on the bias point in the hysteretic current-voltage characteristics; Josephson-emission, nonequilibrium broad emission and sharp coherent microwave emission. The results were interpreted by the Josephson plasma excitation model due to quasiparticle injection.

We demonstrated a single balanced mixer of the combination of high-T. superconductor (HTS) and III-V GaAs beam lead Schottky diodes operating in the mini-cryogenic chamber. The HTS hybrid mixer was designed with a center frequency of 27.5 GHz and a bandwidth of 1 GHz, and consisted of a rat-race coupler circuit with beam-lead diodes attached to its balanced ports. The HTS hybrid mixer with 1 GHz RF bandwidths exhibits a conversion loss of 6 dB. A LO-to-RF isolation was greater than 40 dB in the range of operating frequencies. Since the HTS/III-V hybrid mixer devices have lower noise and conversion loss, this technique provide us with new capabilities that can be effectively utilized in the field of local-point distribution service (LMDS) systems.

The Josephson Plasma resonance in single crystalling Bi2Sr2CaCu2O8 has been investigated at a microwave frequency of 35 GHz in a cavity resonator. A sharp resonance is observed in a perpendicular oscillating magnetic field. The former is independent of the sample dimension, shile the latter shift to higher field as the sample size L is reduced, and it disappears when L becomes smaller than the critical length. The longitudinal plasma mode is a Nambu-Goldston mode in a superconductor, the experimental distinction between the longitudinal and the transverse mode leads to the conclusion that the existence of the Nambu-Goldston mod as predicted by Anderson was experimentally confirmed by direct observation of the Josephson plasma resonance with longitudinal excitations. The finite gap found in Josephson plasma resonance also provides a direct proof of the Anderson-Higgs mechanism within the context of the spontaneously broken phase symmetry of the Gauge-field theory in a superconductor.

The discoveries of high temperature superconductors received great attention due to their high critical temperatures. These materials also exhibit extremely high critical magnetic fields and high critical current density at low temperature, high magnetic field. Thus, they are the most promising materials for superconducting magnets above 20 T. In this talk, progress in the development of HTS materials and insert coils at the National High Magnetic Field Laboratory will be reviewed. In 1999, a Bi-2212 stack of double pancakes generated 3 T in a 19 T background field. These results will be reviewed in terms of implications for future systems. Individual double pancakes of Bi-2223 have also been tested and their performance will also be discused. The present goal of a 57 system will be presented and the key technical requirements for larger, higher field systems will be addressed. It will be shown that in addition to increased critical current density, improved mechanical performance (stain resistanced) is necessary for high field systems. Furthemore, improvements in the conductor n-value will improve prospects for operational systems.

초전도변압기는 효율이 높고 무게가 가벼울 뿐 아니라 부피도 적은 등의 장점을 갖고 있을 뿐만 아니라 가까운 장래에 실현될 것으로 예상되는 전초전도전력시스템을 구성하는 핵심적인 전력기기이다. 이에 따라 외국에서는 상업화가 가능한 초전도변압기를 개발하기 위해서 연구개발이 진행되고 있다. 국내에서도 초전도변압기를 개발하여야 할 시기가 도래했다.

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.

Large-area high-temperature superconducting (HTS) films, filter design and damage-free processing technique have been developed to fabricate low insertion loss and sharp skirt filters. Further, long life cryocooler, low temperature low noise amplifier (LNA) and cryocable have been developed to assemble HTS filter subsystem for IS-95 and IMT-2000 mobile telecommunication. The surface resistance of the films was about 0.2 milli-ohm at 70 K, 12 GHz. An 11-pole HTS filter for IS-95 telecommunication system and a 16-pole HTS filter for IMT-2000 telecommunication system were designed and fabricated using 60 {\times}$ 50 mm$^2$ and one half of 3-inch diameter YBCO films on a 0.5-mm-thick MgO substrate, respectively. We have assembled the filter and low temperature LNA in a dewar with the cryocooler. Ultra low-noise (noise figure: 0.5 dB at 70 K) and ultra sharp-skirt (40 dB/1.5 MHz) performance was presented by the IS-95 filter subsystem and the IMT-2000 filter subsystem, respectively.

The mixed-state Hall angle has been measured in Hg-based superconducting thin films as functions of magnetic fields (H) up to 18 T. The temperature dependence of the Hall angle shows a peak (T$^{\ast}$) at low temperature, which is consistent with a crossover point from the thermally activated flux flow (TAFF) to a critical region (CR). At low fields below 10 T, T$^{\ast}$ shifts to low temperature with increasing fields. Interestingly, however, we found that T$^{\ast}$ is independent of fields above 10 T, suggesting unusual vortex state. A physical implication of H - T$^{\ast}$ line will be discussed.

We have investigated the influence of columnar defects (CD) on the vortex dynamics in pristine and iodine-intercalated Bi$_2$Sr$_2$CaCu$_2$O$_{8+{\delta}} single crystals from do SQUID magnetization measurements. Especially, the temperature dependence of the irreversibility fields, H$_{irr}$(T), were studied. Anisotropy ratio ${\gamma}$, estimated from the fitting to the 2-dimensional melting model (A. Schilling et al., Phys. Rev. Lett. 71 1899 (1993)) in higher fields than the matching field B$_{\phi}$ at low temperature region, turns out to be decreased by the iodine-intercalation and additionally by the heavy-ion irradiation.

Using modified melt-textured grown targets, YBa$_2$Cu$_3$O$_{7-{\delta}}$ thin films were prepared by pulsed laser deposition technique at the laser energy density from 1 J/cm$_2$ to 4 J/cm$_2$. All the films showed c-axis preferred orientations, however, a-axis outgrowths on the film surface were considerably increased with an increase of the laser energy density. To examine the origin of the a-axis outgrowth formation, the microstructures of films deposited at 2 J/cm$_2$ and 4 J/cm$_2$ were investigated using X-ray diffraction, transmission electron microscopy, and high-resolution electron microscopy. It was shown that a significant number of Y$_2$O$_3$ inclusions were formed during the growth of c-axis oriented films at 4 J/cm$_2$. These inclusions formed nucleation sites for the a-axis outgrowths. It is considered that, due to the unstable growth conditions with a high flux density of incident vapor species and the strain induced by the surrounding c-axis films, the Y$_2$O$_3$ inclusions would prefer the nucleation of α-axis grains.

Cube texture를 갖는 Ni기판위에 MOCVD(Metal Chemical Vapor Deposition)를 이용하여 NiO, CeO$_2$, YBCO 박막을 제조하였다. NiO(200)와 CeO$_2$(200) buffer layer는 450${\sim}$470$^{\circ}$C에서 10분간 MOCVD방법으로 (100)<001>Ni 기판위에 직접 증착하였다. 제조된 NiO, CeO$_2$ buffer layer는 조직이 치밀하며 표면의 상태가 매우 좋으며 Ni기판 위에 epitaxial하게 성장하였다. NiO는 Ni기판과 NiO<100>//Ni<100>의 방위관계를 가지고 성장하였으며, CeO$_2$는 증착조건에 따라 CeO$_2$ <100>//Ni<100> 및 CeO$_2$ <110>//Ni<100> 의 방위관계를 가지고 성장하였다. 증착된 NiO막과 CeO$_2$막에서 균열은 발생하지 않았다. MOCVD법으로 표면에 biaxial texture를 갖는 ceramic buffer를 증착시킨 NiO/Ni및 CeO$_2$/Ni 기판위에 YBCO박막을 MOCVD법으로 제조하였다. YBCO막은 기판온도 800$^{\circ}$C,증착압력 10torr, 산소분압을 0.7torr로 하여 10분간 행하였다. 공급원료의 조성에 따라 YBCO의 막의 texture와 형성되는 상이 변화되었다. NiO/Ni및 CeO$_2$/Ni 기판 위에 증착된 YBCO막은 c축 배향성을 가지고 성장하였으며, -scan 및 ${\varphi}$ -scan으로 측정한 (500)면의 in-plane과 (110)면의 out-of-plane의 FWHM(Full Width Half Maximum)값은 각각 10$^{\circ}$ 미만으로 우수하였다.

$^{11}$B NMR measurements have been performed to investigate local electronic structure and 4f spin dynamics for TbNi$_2$B$_2$C single crystal. $^{11}$B NMR spectra show three resonance peaks due to the quadrupolar interaction. Shift and linewidth are huge and strongly temperature-dependent. In addition, both are proportional to magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the 4f spins of Tb. $^{11}$B NMR shift and relaxation rates show high anisotropy for field parallel and perpendicular to the c-axis. Anisotropy of the shift and the relaxation rates suggests that the hyperfine field perpendicular to the c-axis is larger.

Microwave response of intrinsic Josephson junctions in mesa structure formed on HgI2-intercalated Bi2Sr2CaCu2O8+x single crystals was studied in a wide range of microwave frequency. With irradiation of 73${\sim}$76 GHz microwave, the supercurrent branch becomes resistive above a certain onset microwave power. At low current bias, the current-voltage characteristics show linear behavior, while at high current bias, the resistive branch splits into multiple sub-branches. The voltage spacing between neighboring sub-branches increase with the microwave power and the total number of sub-branches is almost identical to the number of intrinsic Josephson junctions in the mesa. All the experimental results suggest that each sub-branch represents a specific mode of collective motion of Josephson vortices generated by the microwave irradiation. With irradiation of microwave of microwave of frequency lower than 20 GHz, on the other hand, no branch splitting was observed and the current-voltage characteristics exhibited complex behavior at hlgh blas currents. This result can be explained in terms of incoherent motion of Josephson vortices generated by non-uniform microwave irradiation.

본 연구에서는 STO(100) 기판 위에 PLD법으로 YBCO 박막을 제작할 때, YBCO 상과 outgrowth의 형성과정과 구조 등을 관찰하였다. 증착의 각 과정별로 박막의 표면 및 단면을 AFM과 SEM으로 관찰한 결과, YBCO 상은 작은 씨앗에서부터 계속 성장해 가며, YBCO 상은 구조를 약 한층 정도 형성하는 불과 10 ${AA}$ 정도만 증착되어도 YBCO의 XRD 피크를 보인다. 반면에 생성되며, YBCO처럼 작은 씨앗에서 서서히 성장해 가는 것은 아니라고 생각된다.

We report results of a comparative study of the normal-state and superconducting properties in the GdBa$_2$(Cu$_{2.9}$Al$_{0.1}$)O$_z$ system with substitutions by Pr for the Gd and Ba sites. It is observed that, fur both Pr-doped systems, the superconducting transition temperature(T$_c$) decreases almost linearly with the Pr-content, but Pr at Ba sites results in a faster T$_c$ drop than that of Pr at Gd sites. The thermoelectric power measurements indicate that there is a strong correlation between the T$_c$ and the room temperature value of thermoelectric power. The experimental results are discussed in connection with existing models.

The effect of Ba substitution for Sr on the lattice parameters and the temperature dependence of the thermoelectric power and electrical resistivity has been investigated for Y(Sr$_{2-x}$Ba$_x$)Cu$_{2.7}$Mo$_{0.3}$O$_z$ (x=0${\sim}$2.0). Both a and c lattice parameters increase as the Ba content, x increases. The correlation between Tc and the carrier concentration estimated from the thermoelectric power data indicates that the change of hole concentration is negligible for x ${\le}$ 1.0 in contrast to the large change for x > 1.

High temperature superconductor shows a good electric and magnetic properties and is known as a good candidate in various electronic device application. At present the technique to construct multilayers composed of HTS films and insulator films has not been fully studied in domestic research institutes. Since the construction of any reasonable eletronic devices require the use of multilayers, the development of HTS eletronic devices has been limited. To manufacture multiplayer, several processing steps which involve deposition and ion millings are required. To manufacture a good quality multilayerd structure, not only the deposition techniques but also the proper patterning have to be developed. In this work, we have fabricated a YBCO/STO/YBCO multiplayer and studied the electronic properties of it.

The normal state of high-Tc superconducting materials has been believed to contain important clues to finding the correct mechanism of the high-Tc superconductivity. One example is the existence of pseudogap in the normal state even above Tc, as observed in various measurements such as photoemission spectroscopy and tunneling conductance. In this pseudogap regime the existence of preformed pairs only with local phase coherence has been debated. Recently Choi, Bang, and Campbell[1] have proposed the occurrence of the zero-bias conductance enhancement due to Andreev quasiparticle reflection from the preformed pairs even with the local phase coherence. In this study we examine the zero-bias enhancement of the differential conductance near or slightly above Tc, using c-axis tunneling in mesa structure of Bi2Sr20a0u208+d single crystals. In slightly overdoped samples zero-bias conductance enhancement (ZBCE) has been observed over a range of 2 K above Tc. In contrast, in underdoped samples with Tc${\sim}$72K the ZBCE appears over a range of 5-6 K above Tc, a much wider temperature range than in overdoped samples. This result may pose as positive signs of the existence of prefurmed pairs in the normal state of high- Tc superconducting materials.

Ni tapes were textured by taking advantage of their secondary recrystallization. The obtained 18cm long tapes had textures of single crystalline qualities with their [001] axes tilted with respect to the surface and their [010] axes parallel to the rolling direction. YBCO/CeO$_2$/YSZ/CeO$_2$ films grown on the Ni tape had the same crystalline orientations. Magnetic field dependent I-V relations were measured on a 5cm section of the tape. Jc defined by 1mV criterion was 1.5 ${\times}$ 10$^5$A/cm$^2$ at 77K under zero field and was reduced by ${\sim}$50% under the applied magnetic field of 5T.

A ring comprising a coated conductor was fabricated. A ring was made first using a biaxially textured Ni tape whose two ends were connected by means of the atomic diffusion bonding technique. Then buffer layers and a YBCO film were deposited on it. All the films were well textured as confirmed by XRD pole figures. The B-H loops, where B and H are the magnetic field at the center of the ring and the applied field respectively, were measured as a function of temperature. The persistent current density (J$_c$) flowing circularly was estimated from the remanent field of B. In the range of temperature from 72K to 20K, J$_c$ changed from zero to 2${\times}$1 0$^5$A/cm$^2$.

We have studied the effects of d-wave symmetry on the critical current of YBa$_2$Cu$_3$O$_7$ step-edge Josephson junctions. The critical current along various misorientation angle was measured and analyzed with the concept of grain-boundary junctions with d-wave symmetry. Experimental results of c-oriented YBCO step-edge junctions with various in-plane misorientation angles were qualitatively in good agreement with the theory. The out-of-plane misorientation angle is usually formed between two grains with the c axes perpendicular to each other and is normally not controllable.

We have studied the magnetic properties in Bi$_2$Sr$_2$CaCu$_2$O$_8$ single crystal with columnar defects using micro Hall-probe array. We found that fold profiles inside sample were similar to the Bean's critical state model from the magnetic hysteresis measurement. In the magnetic relaxation measurement, the normalized relaxation rates were maximum near the center and decreased toward the edge of the sample expect zero gauss. The relaxation rates as a function of the temperature were maximum near the 40K and rapidly decreased both sides of the peak.

($^{11}$B NMR measurements have been performed on single crystals of LuNi$_2$B$_2$C superconductor to investigate vortex lattice structures and dynamical behavior. The spectrum in the superconducting state is significantly broadened by local field inhomogeneity due to the vortex lattice and the peak point of the spectrum shifts toward low magnetic field due to the imperfect field penetration. The linewidth of the spectrum reflecting local field variation is much smaller than expected for conventional vortex lattices and shows peculiar increase at low temperature. Furthermore, the transverse relaxation rate, 1/T$_2$, probing the slow motion of vortices, exhibits a single peak as temperature decreases. These prominent results highlight significant fluctuation of vortices even for this low T$_c$, and nearly isotropic 3D superconductor.

Recently, metal oxide films such as MgO or ZrO$_2$ have been studied as buffer layers to fabricate the superconductor with preferred orientation and as diffusion barriers to prevent the reaction between superconductor and metal substrate. In this research, we focused fabrication and characterization of MgO and ZrO$_2$ films on textured metal substrates. We fabricated MgO and ZrO$_2$ films on the Ni metal sheets by sol-gel dipping method. The microstrcures of the films were investigated by SEM and AES analyses. The films were coated with different cycles and dryed at 400$^{\circ}$C and 500$^{\circ}$C . The final films were heat-treated at 700$^{\circ}$C, 800$^{\circ}$C, and 1000$^{\circ}$C, in air atmosphere. We investigated the alignment of MgO and ZrO$_2$ films on Ni metal sheets by XRD and pole figure. The grain growth of metal oxide films was improved by the increase of the drying temperature and annealing temperature. The grain growth was increased with the annealing temperature. The alignment of metal oxide films depended on the thickness.

The time dependence of irreversible magnetization of grain aligned infinite layer superconductor Sr$_{0.9}$La$_{0.1}$CuO$_2$ was measured in temperature range of 2 K < T < 30 K for H= 0.5 T, 1.0 T and 1.5 T parallel to c-axis. From this, we calculated normalized flux creep rate S(T) ${\equiv}$ dlnM/dlnt and found that the temperature independent region in S(T) is significantly wide in comparision with other cuprate superconductors. Using the method of Maley et al., we also deduce the current density dependence of pinning potential and glassy exponent ${\mu}$.

We report high pressure synthesis of Sr$_{0.9}$Sm$_{0.1}$CuO$_2$. Powder x-ray diffraction showed that the synthesized compounds have infinite layer structure as a major component. Slow heating at the first stage of heating processes after pressurization resulted in several larger grains. The largest grain was found to have the longest edge length of about 100 micrometer. Through magnetic property measurement in superconducting state, we found that pinning in this compound has substantial difference from that of La doped infinite layer, which has no unpaired spin at Sr site.

We report high pressure synthesis of electron doped infinite layer superconductor Sr$_{0.9}$La$_{0.1}$CuO$_2$. Structural and low-field magnetization study demonstrated that the superconducting quality of our samples were best among all kind of bulk samples reported until now. With these good samples, many new findings are under going by our collaborators and us.

Magneto-resistances of the YBa$_2$Cu$_3$O$_{7-{\delta}}$ based coated conductors fabricated on the tilted single crystalline Ni substrates and RABiTS (rolling assisted bi-axially textured substrate) were measured under various magnetic fields. The activation energies of vortices were estimated from them by fitting equation of p = p$_o$ exp(-U(H,T)/k$_B$T). When currents flew in the rolling direction for the case of the tilted single crystalline YBCO on the RATS, the activation energies were similar to those of c-axis normal YBCO films on the SrTiO$_3$ single crystal substrates [5] and were slightly larger than those of the RABiTS coated conductors. On the contrary, for the currents flowing in the transverse direction, the magnetoresistances show double transitions in the temperature with much smaller activation energies.

The relations between tensile stresses and critical current densities (J$_c$) of coated conductors were measured. Around 320 MPa of tensile stress, the critical current densities of coated conductor fabricated on pure Ni tape were reduced to zero at 77K, where J$_c$ for zero stress was order of 10$^5$A/cm. The critical tensile stress was much enhanced for the coated conductors fabricated on NiCr alloy tapes. However fabrication conditions for the growth on such alloys are much different from those on the pure Ni and it was not easy to get good textures and large critical currents. The detailed fabrication methods on those alloys will be presented.

The effects of partial pressures of various gases on the qualities of coated conductors are studied, where the long samples were fabricated in a vacuum of a large physical vapour deposition system. The various gases such as $0_25,$H_2$,H_20$,$C_n H_m$, and CO come out from the large heating system and gives somewhat complicated effects on the interfacial chemistry at CeO/Ni which Is Important for the epitaxial growth of the film. The results of XRD measurements on the films fabricated in the controlled partial pressures of thoes gases will be presented.

We report on the influence of d-wave pairing symmetry in high-T$_c$ superconductor by tunneling spectroscopy. The zerobias conductance peak(ZBCP) which is produced by tunneling through the ab-plane is observed on both of metal Au/YBa$_2$Cu$_3$O$_y$(N/S) tunnel junctions and ferromagnet Co/Au/ YBa$_2$Cu$_3$O$_y$(F/N/S) tunnel junctions. The effects of Andreev reflection on the differential conductance of each junctions are dependent on the tunnel direction. For the S/N/F junction, it appears the suppression of the ZBCP due to the suppression of Andreev reflection at the interface between a ferromagnetic material and a d-wave superconductor. By comparing these experimental results with recent theoretical works on Andreev reflection, the existence of Andreev bound state is verified in high-T$_c$ superconductor, due to the d-wave symmetry of the pair potential.

Large area YBCO - films are series produced by thermal co-evaporation using a deposition scheme known as Garching process, which allows intermittent oxygen supply in a high vacuum ambient by an oxygen cup spaced closely underneath the moving substrates. The deposition area of 9" diameter is capable to handle very large wafers up to 8" diam. or numerous smaller wafers. The large distance between substrates and boat sources and an elaborate heater design guarantee excellent film uniformity over the entire deposition area. YBCO - films deposited by this technique are commercially fabricated for a variety of applications - the most prominent are resistive fault current limiters and microwave filters for mobile or satellite communications. IMUX and OMUX - filters are currently space qualined by Robert Bosch GmbH and are expected to be launched and installed on an experimental platform of the international space station ALPHA in 2001. Both of the above applications require quite different film specifications on the one hand, but at the same time extremely high uniformity and reproducibility on the other hand, since hundreds of YBCO - films are combined to large systems or have to be approved for manned space missions. The success of such projects is direct evidence that the technique of thermal evaporation is readily capable to meet these high demands and has become the major deposition technique to support the emerging HTS market.

Two methods have been investigated to fabricate good quality step-edge Josephson junctions on STO, MgO, and LAO single crystal substrates. One is the annealing of substrates at 1050$^{\circ}$C in 1 atmospheric oxygen after Ar-ion milling. The other is the cleaning of step-edge by using Ar ion milling. The step-edge is characterized with atomic force microscope (AFM) images. And YBCO thin films are deposited by using pulsed laser. The I-V properties of step-edge junctions are characterized. The yield rate of step-edge junction is increased by new fabrication methods.

We have developed a YBCO SQUID gradiometer system for the measurement of a very weak magnetic field in an unshielded environment. The system consists of a SQUID gradiometer sensor, low noise pre-amp, and FLL(fluxlocked loop) control electronics. The gradiometer sensors have been fabricated on STO bicrystal substrates, and exhibit a magnetic noise of 300 fT/${\surd}$ Hz/cm at 100 Hz. The overall magnetic field noise of the SQUID gradiometer system was about 10 pT/${\surd}$ Hz/cm at 10 Hz without any magnetic shield. The system demonstrated a high stability for a long time, and real-time measurement resolution ${\le}$ 100 pT/cm in the unshielded environments.

YBCO step-edge dc SQUID magnetometers on sapphire substrates have been fabricated. CeO2 buffer layer and YBCO films were deposited in situ on the low angle (${\sim}$35$^{\circ}$) steps formed on the sapphire substrates. Typical 5-${\mu}$m-wide junction has R$_n$ of 5 ${\omega}$ and I$_c$ of 50 ${\mu}$A with large I$_c$R$_n$ product of 250 ${\mu}$V at 77K. According to applied bias current, depth of voltage modulation was changed and maximum voltage was measured 16 ${\mu}$V. Field noise of do SQUID was measured 100${\sim}$300 fT/${\surd}^{Hz}$ in the 1 $^{kHz}$, and about 1.5 pT/${\surd}^{Hz}$ in the 1/f region. For ac bias reversal method, field noise was decreased in the 1/f region. The QRS peak of magnetocardiogram was measured 50 pT in the magnetically shielded room.

Digital to analog converters based on the Josephson effect are promising for voltage standard, because they produce voltage steps with high precision and good stability. In this paper, we made a simulation study on RSFQ D/A converter. RSFQ D/A converter was composed of NDRO cells, T(toggle) flip-flops, D flip-flops, Splitters and Confluence Buffers. Confluence Buffer was used to reset the D/A converter. We also obtained operating margins of the important circuit values by simulational experiments.

We fabricated ramp-edge Josephson junctions with barriers formed by interface treatments instead of epitaxially grown barrier layers. A low-dielectric Sr$_2$AlTaO$_6$(SAT) layer was used as an ion-milling mask as well as an insulating layer for the ramp-edge junctions. An ion-milled YBa$_2$Cu$_3$O$_{7-x}$ (YBCO)-edge surface was not exposed to solvent through all fabrication procedures. The barriers were produced by structural modification at the edge of the YBCO base electrode using high energy ion-beam treatment prior to deposition of the YBCO counter electrode. We investigated the effects of high energy ion-beam treatment, annealing, and counter electrode deposition temperature on the characteristics of the interface-controlled Josephson junctions. The junction parameters such as T$_c$, I$_c$c, R$_n$ were measured and discussed in relation to the barrier layer depending on the process parameters.

We have constructed a multi-channel SQUID magnetometer system. The system is designed to operate normally with 10 high temperature direct coupled SQUIDs. The main features of the system include a remote control by serial communication, low noise with wide bandwidth and high slew rate by several MHz modulation, signal conditioning and calibration by digital signal processing.

A prototype for a highly sensitive, automated measurement system for the microwave surface resistance of high-T$_c$ superconductor films was set up, and tested by measuring the microwave surface resistances of high-T$_c$ YBa$_2$Cu$_3$O$_{7-{\delta}}$(YBCO) films at the frequency of about 19.6 GHz and the temperature of 30 K ${\sim}$ 90 K. An open-ended TE$_{011}$ mode sapphire-loaded cylindrical cavity resonator was used as the measurement probe, where YBCO films were used as the endplates of the cylindrical cavity. The characteristics of the measurement system include functions to display the unloaded ${\varrho}$ and the resonant frequency of the TE$_{011}$ mode resonator as well as the microwave surface resistance of the YBCO films, all simultaneously as a function of temperature. Applicability of the measurement system for investigating the homogeneity in the microwave properties of large high-T$_c$ superconductor films is discussed.

For a ground plane in high-temperature superconducting ramp-edge junction devices, YBa$_2$Cu$_3$O$_{7-{\delta}}$/SrTiO$_3$/YBa$_2$Cu$_3$O$_{7-{\delta}}$ multilayer structures were fabricated using pulsed laser deposition and ECR ion milling. Various process parameters were adjusted to enhance the device characteristics. By etching the STO layer to form a tapered edge of about 15$^{\circ}$ and in-situ RF plasma treatment of bottom YBCO surface prior to deposition of top YBCO, the top-to-bottom YBCO showed T$_c$ of 75${\sim}$80 K and I$_c$ of about 40 mA through holes. It was found that the deposition of bottom YBCO at a reduced laser repetition rate of 1Hz increased the T$_c$ of top YBCO to 79.9 K. The resistivity of 570 layer was about 10$^6$ ${\Omega}$cm at 60 K, which ensures good electrical isolation between successive YBCO layers.

We have fabricated directly-coupled single-layer second-order high-Tc SQUID gradiometer. The gradiometer consisted of 3 parallel-connected square pickup loops, and each loop was directly coupled to SQUID. YBCO thin film was deposited by pulsed laser deposition and patterned by photolithography with ion milling technique. Optimum balancing condition was achieved by varying the outer diameter of the center loop. We have investigated nearly zero response of the SQUID to uniform and 1 st-order field gradient.

We fabricated rapid single-flux-quantum RS flip-flop circuits with and without Y$_1$Ba$_2$Cu$_3$O$_{7-{\delta}}$(YBCO) ground plane. The circuit consists of SNS-type ramp-edge Josephson junctions that have cobalt-doped YBCO and Sr$_2$AITaO$_6$(SAT) for barrier layer and insulator layer, respectively. The fabricated Josephson junction showed a typical RSJ-like current-voltage(I-V) characteristics above 50K. We sucessfuly demonstrated RS flip-flop at temperatures around 50K. The RS flip-flop fabricated on ground plane showed more definite set and reset state in voltage-flux(V-${\phi}$) modulation curve for read SQUID, which may be attributed to a shielding effect of the YBCO ground plane.

A new type low-pass filter design method based on a coupled line and transmission line theory is proposed to suppress harmonics by attenuation poles in the stop band. The design formula are derived using the equivalent circuit of a coupled transmission line. The new low-pass filter structure is shown to have attractive properties such as compact size, wide stop band range and low insertion loss. The seventh-order low-pass filter designed by present method has a cutoff frequency of 0.9 CHz with a 0.01 dB ripple level. The coupled line type low-pass filter with strip line configuration was fabricated by using a high-temperature superconducting (HTS : YBa$_2$Cu$_3$O$_{7-{\delta}}$ thin film on MgO(100) substrate. Since the HTS coupled tine type low-pass filter was proposed with five attenuation poles in stop band such as 1.8, 2.5, 4, 5.5, 6.2 GHz. The fabricated low-pass filter has improved the attenuation characteristics up to seven times of the cutoff frequency.

In this paper, we present a novel methodology for a wideband HTS antenna of finite length placed on a dielectric substrate. A methodology used in this work is based on a moment-method techniques with Green function singularity when the field point is in the source triangle. The designed resonance frequency of our HTS antenna is 11.85 GHz. The return loss is -26 dB. The bandwidth obtained is a significant 10.6 %. Experimental measurements for a HTS antenna designed in X-band are shown to agree well with the simulated prediction.

Effects of the post-annealing temperature of CeO$_2$ buffer layers on the properties of YBCO films on CeO$_2$-buffered sapphire were investigated. 45 nm-thick CeO$_2$ buffer layer was prepared in-situ on r-cut sapphire using an on-axis rf magnetron sputtering method, which was later post-annealed at temperatures between 950$^{\circ}$C and 1100$^{\circ}$C in an oxygen-flowing environment. YBCO films were prepared on CeO$_2$-buffered sapphire (CbS), for which the surface morphology, crystal structures and electrical properties of the YBCO films were studied. YBCO films on post-annealed CbS appeared to have better properties than those on as-grown CbS with regard to the morphological, structural and electrical properties when the YBCO films were prepared on CeO$_2$ buffer layer post-annealed at temperatures of 1000 - 1050$^{\circ}$C. A TE$_{011}$ mode rutileloaded cylindrical cavity resonators was fabricated with the YBCO films placed as the endplates, for which the unloaded Q of the resonator was measured. It turned out that the resonator with the endplates prepared from the YBCO films on postannealed CbS at 1000 $^{\circ}$C showed the highest unloaded Q with the value more than 8 ${\times}$ 10$^5$ at 30 K and 8.6 CHz, revealing that the YBCO films on post-annealed CbS at 1000$^{\circ}$C the temperature could be the lowest among the YBCO films on post-annealed CbS.

Properties of SrTiO$_3$ thin films were characterized under the influence of an applied dc voltage utilizing a gold resonator with a flip-chip capacitor. The measurements were performed at microwave frequency ranges and low temperatures cryogenic temperatures. The dielectric constant of 830 and the low loss tangent of 6X10$^{-3}$ at 3.64 GHz were observed at 90 K and 100 V. The quality in the SrTiO$_3$ film was presented in terms of fractional frequency under the bias voltages and cryogenic temperatures.

Bi-2212 HTS tube was fabricated by CFP(Centrifugal Forming Process). Slury was prepared in the mixing ratio of 8:2 between powder and binder and ball-milled for 24 hrs. Slurry was initially charged into the rotating mold with 300${\sim}$450 rpm and heated at the temperature ranges of 840${\sim}$860$^{\circ}$C for partial melting to finally obtain a uniformly textured tube shape. It was observed the plate-like grains with more than 20 ${\mu}$m were well oriented along the rotating axis and the measured T$_c$ was around 67K. In this paper we will discuss and analyze the tube characteristics depending on many different processing parameters such as, powder composition, binder mixing ratio between powder and binder, motor speed, heating temperature and etc.

AC Superconducting Generators (ACSG) are featured by 3D magnetic flux distribution, which decreases in the direction of axis. For this reason, when ACSG is optimal designed, 3D magnetic field analysis is required. This paper proposes 2D Finite Element Analysis (FEA) results normalized by 3D FEA according to the position of armature coil and the ratio of field coil width to axial length in order to reduce the analysis time. By using the proposed data, the reasonable 3D FEA results of ACSG can be only predicted by 2D FEA results. The validity of the 3D FEA results is verified by comparison with the experimental results of 30kVA superconducting synchronous generator.

The effect of twisting on the microstructural evolution and critical current of BSCCO superconductor tape has been evaluated. Twisting pitches of the tapes are in the range of 8-70 mm and uniformly deformed. The critical current of twisted tape was dependent on the twist pitch. Specifically, it was observed that the critical current decreased with decreasing twist pitch, and only 50% of critical current was retained when the tape was twisted to a pitch of 8 mm. This reduction of the critical current may be related to the interface irregularity, smaller grain size, worse texture and the presence of cracks due to the induced strain during the twisting processing.

Long lengths (<100m) of BSCCO 2223 tapes were fabricated of optimal process. We have I$_c$${\sim}$22A, J$_c$${\sim}$22,000A/cm$^2$(77K, 0T) at last heat treatment, and then prototype 1000A class current lead (length ${\sim}$50cm) fur HTS applications was fabricated using these tapes. Surface of current lead except both end part (${\sim}$1cm) was clothing with fiber glass. Also the transportation properties and thermal loss was studied on prototype 1000A class current lead.

The extrusion process for long-length multi-filaments of BSCCO 2223 superconductor tape has been investigated with aids of Finite Element Method and experimental inspection. Since the arrangement of filaments in matrix material has characteristic of rotational symmetry, a 2-dimensional commercial FEM package, DEFORM-2D, was adopted to simulate extrusion process with different variables such as hardness of sheath material, lengths of each filament and arrangement. From the FEM analysis, since the inner filaments move faster than the outer one, distribution of filaments is needed to be optimized. In the case of pure Ag matrix, undesirable non-uniform distribution of filament was obtained due to low hardness of sheath material. Dummy sample(brass (sheath) and talc powder(filament)), however, which has relatively high hardness of sheath material, had been produced with desirable results. Therefore, it is necessary to optimize hardness of sheath material, extrusion temperature and billet design.

Bi-2223 HTS current leads for a superconducting magnetic energy storage(SMES) magnet were designed and manufactured. The HTS leads composed of Bi-2223/AgAu tapes and stainless steel former were connected to conventional vapor-cooled copper leads. The heat input to the liquid helium through the HTS lead was 0.39 W/lead when the warm end part's temperature is 65 K. And, the critical current of the HTS leads was about 1.6 kA when the warm end part's temperature is 80 K. The measured those values are well consistent with computed values.

77 K와 self-field에서 22 A 의 Ic 를 갖는 길이 120 m, 19-심 Bi-2223상 선재를 제조하여, 두 개의 double pancake 코일로 구성된 proto-type 고온초전도 자석을 설계, 제작하여 이 자석에서의 4.2 K와 77 K에서의 I-V 특성과 운전 특성을 평가한 결과, 이 자석은 77 K 등온조건에서는 9.5 A 의 Ic를, 77 K 헬륨가스 속에서는 8.3 A 의 Ic를 나타내었고, 4.2 K 등온조건에서는 93.7 A 의 Ic와 102 A 의 Iq를, 4.2K헬륨가스 속에서는 88.4A의 Ic 와 92.0 A 의 Iq를 나타내어, 이 자석은 4.2 K 와 77 K 의 등온조건에서 각각 0.58 T 와 0.06 T 의 자장을 발생하였는데, 이는 해석적 방법으로 계산한 결과와 잘 일치하였다. 그리고 이 자석이 전도냉각되어 4.2 K 에서 운전될 때의 안정성 특성평가로서, Ic 보다 약간 큰 전류인 89 A 를 인가한 결과, 전류인가 후 82.6초 후에 quench가 발생하였는데, 이 quench는 네 번째 pancake의 전류도입선부 연결부에서와 약간 늦지만 첫 번째 pancake의 전류도입선부 연결부에서 거의 동시에 개시되어 전체로 파급된 것으로 사료되었는데, Ic 가 낮은 첫번째 pancake에서 더 높은 전압 강하가 나타났다. 또한 장착된 heater를 통하여 77 K 에서 8.9 A 의 전류로 운전되고 있는 코일에 146 joule 의 열을 가했을 때 quench 가 일어났는데, 이때 quench 는 방위각 방향의 Bi-2223/Ag 선재를 따라서 보다 Kapton 절연층을 관통하는 선재의 반경방향으로 훨씬 빨리 전파하였다.

The fabrication and characteristics of HTS race-track type field coil for generators was carried out. Field coils are composed of 3 pancake coils wound by 37-filamental Bi-2223/Ag-alloy tapes. The winding machine is horizontal type. The critical currents (I$_c$) of the superconducting tapes were measured with variation of bending strain and external magnetic fields. I$_c$ of both whole field coils and 3 pancake coils were measured as a function of temperature. At 77K under the self-field, I$_c$ of whole field coils was 12A, while in the case of middle pancake coil, I$_c$ was 15A. The distribution of magnetic field B was obtained, using 3-D FEM. Our simulation showed that maximums of B${\bot}$A in x-y plane were locally distributed in both the upper and the lower coils. In addition, the fabrication processes and the characteristics of field coil are described.

We investigated resistance development in Au/YBCO thin film meander lines during quench. The meander lines were fabricated by coating YBCO films insitu with a gold layer and patterning them by photolithography. The center stripe quenched fastest even though the flux flow resistance that appeared upon the current passing the critical current was uniform. Quench started at an area of the center stripe and propagate both through the gold layer and the sapphire substrate. Quench propagation speed was uniform and 60 cm/s at 30 V$_{rms}$.

The value of I$_c$(critical current) in HTS (High Temperature Superconductor) tape has a great influence on B${\bot}$(vertical field). Therefore, in shape design of field coil for the HTSG(High Temperature Superconducting Generator), a method to reduce the B${\bot}$ should be considered in order to maintain the stability and substantial improvement on the performance. On the basis of the magnetic field analysis, this paper deals with various field coil shape according to the iron plate to obtain small B${\bot}$ by using Biot-Savart's law, image method and 2D FEA(2 Dimensional Finite Element Analysis) considering the stress condition of HTS. Moreover, the analysis is verified by comparison with experimental results. And also this paper presents the advanced model by using 3D FEA, in which flux density at armature is calculated in 5kVA class HTSG.

To tap the possibility of exploiting the precipitates as flux-pinning center in the Bi-2223 superconducting system, as-received Bi-2223/Ag tapes with the starting composition of Bi$_{1.8}$Pb$_{0.4}$Sr$_2$Ca$_{2.2}$Cu$_3$O$_8$ were post-annealed at various temperature, oxygen partial pressure, and annealing time. The 2$^{nd}$ phases in the annealed specimen were analysed with XRD, SEM, TEM, and EDS. The size and the distribution of the precipitates such as (Ca,Sr)$_2$(Pb,Bi)O$_4$ and Bi$_{0.5}$Pb$_3$Sr$_2$Ca$_2$CuO$_{12+{\delta}}$ (3221) in the Bi-2223 matrix was controllable by varying heat-treatment condition without breaking the connectivity of the 2223 grains. The nano-size precipitates within the 2223 grains are conjectured as working as flux-pinning sites, resulting in increased J$_c$ value.

We simulated the current limiting characteristics of a resistive SFCL with 16 ${\Omega}$ of resistance for a single line-to-ground fault in the 22.9 kV system. The transient current during the fault increased up to 6.33 kA, 5.80 kA and 3.71 kA without SFCL at the fault angles of 0${\circ}$,45${\circ}$ and 90${\circ}$, respectively. An resistive SFCL limited the fault current to 2.27 kA in a half cycle. The quench resistance of 16 ${\Omega}$ was suggested to be appropriate to limit the fault current in the 22.9 kV distribution system.

We investigated a resistive superconducting fault current limiter (SFCL) fabricated using YBCO thin films on 2-inch diameter sapphire substrates. Nearly identical SFCL units were prepared and tested. The units were connected in series and parallel to increase the current and voltage ratings. A serial connection of the units showed significantly unbalanced power dissipation between the units. This imbalance was removed by introducing a shunt resistor to the firstly quenched unit. Parallel connection of the units increased the current rating. An SFCL module of 4 units in parallel, each of which has minimum quench current 25 Ap, was produced and successfully tested at a 220 V circuit. From the resistance increase, we estimated that the film temperature increases to 200 K in 5 msec, and 300 K in 120 msec. Successive quenches revealed that this system is stable without degradation in the current limiting capability under such thermal shocks as quenches at 220 V.

When high temperature superconducting tapes is fabricated using the PIT (Powder In Tube) method, the length of HTS tapes is increased more than 500 ${\sim}$ 1,000 times of initial powder packed billet. On mechanical processing, heterogeneous properties between the ceramic superconducting core and Ag/Ag alloy sheath occur the non-uniformity deformation as like sausaging that deteriorate the critical current properties of HTS tapes. In this study, we investigated the workability of Bi-2223/Ag/Ag alloy sheath tapes fabricated by the PIT method involving a number of different mechanical processes, multi drawing and rolling. In order to obtain the high critical current density and high uniformity of Bi-2223/Ag sheath tapes, the influences of powder packing density, drawing die angle and rolling parameters were studied. We found that the roll diameter is an important variable in the rolling process, as critical current of tapes rolled using 250 mm rolls was higher than that using 150 mm rolls.

The prototype high-T$_c$ superconducting (HTS) power transmission cables have been designed and fabricated multi layers of spirally wound HTS tapes. The cables were made Bi-2223 based Ag-sheathed HTS tapes, and tested in LN$_2$. Critical currents of 700A dc and better were achieved. The magnetic flux density and field direction were analyzed in the cable configuration. In this paper the results of analysis and tests of HTS power transmission cables were described.

The effect of the initial BSCCO 2212 grain size on the final gain size and the formation of the BSCCO 2223 was studied using a powder precursor synthesized by two-powder method. 2212 and CaCuO$_2$ tapes were prepared by dip coating and joined by pressing and then followed by the repeated thermo mechanical treatment. The samples were characterized by XRD and SEM analysis. The formation and grain size of the BSCCO 2223 depended on the initial BSCCO 2212 grain size.

In order to evade the patent of Oak Ridge National Laboratory (RABiTS process) and search for more economical process, a new process for producing the biaxially textured Ni tape by electrodeposition has been investigated. Electrodeposition was performed in the modified Watts bath. The crystal orientations of electrodeposited Ni were analysed by X-ray pole figure, ${\phi}$-scan and ${\omega}$-scan. The electrodeposited Ni tape showed cube texture with good out-of plane(< 8${\circ}$) and in-plane alignment(< 20${\circ}$).

Multiseeding with (100)/(100) grain junctions of top-seeded melt growth (TSMG) processed YBCO superconductors was studied. The effect of the number of seeds and the distance between two seeds on the levitation forces and the trapped magnetic fields of the TSMG-processed YBCO samples was investigated. Multiple seeding shortened the processing time for the fabrication of TSMC-processed YBCO superconductors. The large magnetic field was trapped at the grain junction when two seeds was placed without spacing, while the amount of the magnetic field decreased when the seed distance increased. This is attributed to the increased amount of the residual melt phases around the grain junctions.

We evaluated the electric properties of Bi-2223 jointed tapes processed by both resistive- and supercondcuting-joint methods. For the resistive-joint, filler materials of wood metal, Pb/Sn, In, and silver paste were used, whereas, for the superconductive-joint, the lap joint method were used. In the resistive-joint tape, it was observed that the electrical properties such as current transport property, n-value, and contact resistance of the tape were significantly related to the resistivity of filler materials. On the other hand, in the superconducting-joint tape, the current transport property was dependent on the uniaxial pressure. Specifically, the current transport property varied 50 to 80% with uniaxial pressure, probably due to the irregular microstructure in the transition region.

고순도 니켈분말을 사용하여 성형, 소결, 압연 및 중간소둔 공정을 통해 cube-texture를 갖는 니켈테이프를 제조하였다. 제조된 니켈테이프의 texture는 성형압력, 성형체의 소결 온도 및 시간, 냉간 압하율 및 중간열처리에 따라 달라지는 것을 관찰하였다. 200kgf/cm$^2$ 의 성형압력으로 제조한 성형체를 1000$^{\circ}$C의 온도에서 8시간열처리한 소결체를 100${\sim}$50 $_{\mu}$m로 압연된 tape을1000$^{\circ}$C 1시간 열처리 할 때 가장 우수한 texture를 가지는 tape을 제조할 수 있었다. 긴 니켈테이프를 제조하기 위해 50cm 길이의 mold에서 성형한 green-pellet을 불활성 분위기(Ar:96%-H$_2$:4%)에서 1000$^{\circ}$C, 8시간동안 열처리하여 소결하였다 400mm길이에 17${\sim}$20mm 두께의 소결체를 압연하여 100$_{\mu}$m두께의 긴 니켈 테이프를 제조하였다. 제조한 테이프의 texture는 소형으로 제조한 테이프에 비해 떨어졌으며 이는 압연 시 시료에 너무 큰 인장력을 가했기 때문으로 사료된다.

일반적으로 Bi계 고온초전도선재(HTS Tape)는 저온초전도선재(LTS Tape)에 비해서 비열이 수백 배 이상 크므로 열적으로 상당히 안정한 성격을 가진다. 그러므로 이러한 HTS Tape를 TQ(Thermal Quench)시켜주는 일은 매우 어렵게 되는데, 일반적으로 HTS Tape를 이용한 초전도응용 분야에서 TQ를 이용한 스위칭 동작이 매우 중요하므로, 응응에 앞서 이에 관한 연구가 반드시 이루어져야 할 것이다. 본 연구에서는 Bi-2223 Short Sample의 TQ 특성을 실험하여 온도특성과 전압특성 등을 비교하였으며, 또한 이론적으로 HTS Tape를 TQ시켜주기 위한 열량과 실제 실험에서 사용된 열량의 값을 비교하였다.

자기차폐형 고온초전도한류기에서 철심의 포화 문제와 더불어 가장 문제가 되는 것은 공극의 크기이다. 고온초전도 tube 와 철심 또는 일차 권선과 초전도 tube 사이에서의 공극은 정상상태에서 불필요한 전압강하의 원인이 된다. 이러한 전압강하는 시스템에서의 불안정성을 초래할 수 있기 때문에, 공극의 결정은 고온초전도한류기의 설계에 있어 가장 중요한 요소가 된다. 또한, 사고 발생시 나타나는 고온초전도한류기의 임피던스는 사고 전류를 제한하는 주요한 요소이다. 다양한 parameter의 변화를 통하여 고온초전도한류기의 임피던스변화를 관찰하였고, 임피던스 변화에 따른 전류제한 효과를 시뮬레이션을 통해 확인하였다. 시뮬레이션의 결과를 이용하여 440v급 Rod type 고은초전도한류기를 설계하였으며, 동작 특성을 해석하였다.