We evaluated the electrical properties of 37 multifilamentary jointed tapes processed by superconducting joint. In the superconducting joining method. a lap-joint was used. Tapes were selectively etched and exposed superconducting cores of the two tapes were brought into contact with each other and then only the joined region was uniaxially pressed in the range of 1,000 to 2,500 MPa. The current carrying capacity and n-value of the jointed tape were evaluated as a function of uniaxial pressure. The highest current carrying capacity and n-value were obtained to be 58%, 26% for the jointed tape to the tape itself.

We evaluated the degree of texture through depth of the superconductor core of Bi-Sr-Ca-Cu-O(BSCCO) superconductor tape. The degree of texture was characterized by pole figure analysis, indicating that the degree of texture varied significantly with depth of the superconductor core. It was observed that the degree of texture was higher near the interface than inside the superconducting core. Based on the result of degree of texture, the region near the interface is thought to carry significant current compared to that inside the core.

The microstructure evolution and the peritectic solidification of Sm$Ba_{2}$$Cu_{3}$ $O_{7-\delta}$ superconducting materials during the isothermal annealing were studied over the temperature range 1030-$1060^{\circ}C$ The faceted growth of the peritectic phase and its dependence upon Sm-diffusion in the liquid phase are discussed. A growth model is proposed to explain the growth shape of Sm123 crystals.

In the practical sense, it is important to assess the Young modulus and the degradation of $I_{c}$ due to mechanical deformation in HTS tapes for designing superconducting magnets. In order to establish a test method of mechanical properties in oxide composite superconductors, the committee of VAMAS/TWA 16-Subgroup proposed an international round robin test. The first effort has been focused on the multifilamentary Bi-2223 tapes. Eight groups participated in the RRT activity and each group carried out the tensile test by their own professional technique to three kinds of Bi-2223 tapes. The experimental details were reported and discussed for your information.

Stress/strain dependencies of the critical current I$_{c}$ in AgMgNi sheathed multifilamentary Bi(2212) superconducting tapes were evaluated at 77K. The external reinforcement was accomplished by soldering Ag-Mg tapes to single side or both sides of the sample. With the external reinforcement, the strength of tapes increased but I$_{c}$ decreased. The I$_{c}$ degradation characteristic according to the external reinforcement was improved markedly in terms of the stress although it appeared less remarkable on the basis of the strain. Effects of external reinforcement were discussed in a viewpoint of monitoring sensitivity of cracking in superconducting filaments by considering n-value representing the transport behavior of the current, which is closely associated with the location of them relative to the voltage-monitoring region in the tape. tape.

A series of superconducting Hg$Ba_{2}$Cu$O_{4+7}$ materials, containing $Ag_{x}$ additions with molar fraction x = 0, 0.05, 0.1, 0.3, and 0.5, have been studied. This study has showed that Ag additions lead to changes in superconducting properties of Hg-1201 materials. In addition, according to the amount of $Ag_{x}$ additions with molar fraction x up to 0.5, both $T_{c}$ and $J_{c}$ of Hg-1201 materials generally decrease with Ag-content. These and other results are discussed in this paper.

Bi-2212 HTS tube was fabricated by centrifugal forming process(CFP). As a variation of melt casting process(MCP) or centrifugal casting technique, the centrifugal forming process is a flexible method for manufacturing Bi-2212 bulk tubes and has been optimized to achieve smooth surface and uniform thickness. At this process, the slurry was prepared in the mixing ratio of 10:1 between Bi-2212 powder and binder and initially charged into the rotating mold under the speed of 300~450 rpm Heat-treatment was performed at the temperature ranges of 860 ~ $890^{\circ}C$ in air for partial melting. The HTS tube fabricated by centrifugal forming process at $890^{\circ}C$ under the rotating speed of 450 rpm was highly densified and the plate-like grains with more than 20$\mu$m were well oriented along the rotating axis. The measured Tc and Jc at 10K were around 85K and 3,000A/cm2 respectively.

Internal tin processed Nb$_3$Sn wires of intermediated worked state of were took from Mitsubishi and fabricated with various diameters ranging from 0.76 mm to 0.2 mm. These specimens were heat-treated at $460^{\circ}C$ for 70 h and at $570^{\circ}C$ for 100h to form bronze and at $700^{\circ}C$ for 100h to form Nb$_3$Sn compound. Bending strain Ic s of the wires were measured with various bending diameters ranging from flat to 76 mm. In order to investigate the sensitivity for strain, small diameters of wires were strain Ic at 6 T, 4.2 K. There were no breakage decrease during cold working to 0.2 mm of diameter and no decrease Jc to the diameter of 0.3 mm. The values of bending strain Ic of 0.2 mm and 0.3 mm diameters of the wires were not decreased at 76 mm of bending diameter.

A free piston and free displacer(FPFD) Stirling cryocooler for cooling infrared and cryo-sensors is currently under development at KIMM(Korea Institute of Machinery & Materials). The FPFD Stirling cryocooler employs 1) the Stirling cycle for refrigeration, 2) linear motors for driving the cryocooler, 3) spring and gas support systems, and 4) fine gap for clearance seals. It is the most suitable design for a mechanical cryocooler utilized in night vision environment. The experimental results show KIMM-E1 Stirling cryocooler (with expander manufactured by KIMM) has the higher cooling power and faster response time at optimum charging pressure.

A free piston and free displacer (FPFD) Stirling cryocooler for cooling infrared and cryo-sensor is currently under development at Korea Institute of Machinery & Materials. In this study, performance tests of stirling cryocooler with different length of split tube were performed to get characteristics of cryocooler. The Experimental results show the Stirling cryocooler with small volume of split tube has higher cooling power and faster response time.

Mechanical test of the Carbon Fiber Reinforced Plastics (CFRP) composite specimen was performed based on the ASTM code at the ambient and low temperature. Tension, compression in-plane shear, and inter-laminar shear properties of the composite laminates were evaluated experimentally using the Universal Testing Machine(UTM) system at the temperature of $24^{\circ}C$,$-76^{\circ}C$ , and $-196^{\circ}C$. From the test results it was found that the CFRP chosen for the Korea Superconducting Tokamak Advanced Research(KSTAR) magnet supporting post had smaller tensile strength and larger compressive strength at the low temperature than those of the ambient temperature because of material ductility.

The function of the thermal shield(TS) is to eliminate the thermal radiation from the room temperature side to the coil temperature(4.5K) region so as to reduce the thermal load on the He refrigerator. The TS is composed of multilayer insulation(MLI) which is coated very thin aluminum on the insulating material, cryopanel which is cooled by cold gaseous He, and supports which stand the cryopanel and MLI on the room temperature part. The thermal shield for the TF coils and PF coils has been located between the coils and vacuum vessel. The thermal shielding cryopanel is cooled under 80 K by a forced flow of helium gas using cooling pipes on the cryopanel.

Cryogenic technology is one of the key technologies for fusion reactor equipped with superconducting coil for plasma confinement. The KSTAR(Korea Superconducting Tokamak Advanced Research)Project is in progress since 1996. Major parameters of the KSTAR tokamak are : major radius 1.8m, minor radius 0.5m, toroidal field 3.5 Tesla and plasma current 2MA with a strongly shaped plasma cross-section and double -null diverter. Considering practical engineering constraints, the KSTAR device is designed for a pulse length of 300 sec in up-graded operation mode but in the initial configuration would provide a pulse length of 20 sec provided by the poloidal coil system in base-line operation mode. The cryogenic system is composed as follows : cold box, helium compressor system, distribution box, helium gas buffer tank, helium gas purifying system, gas recovery system, liquid helium storage dewar, current lead box, current bus line and liquid nitrogen storage tank.

The stability of PF 6-7 has been studied according to the transient analysis code TOKSCPF and quench analysis code QSAIT. We compare the stability and temperature rise with various Cu/SC ratios of 2.8 and 3.5 under the KSTAR normal operating conditions. It shows that the Cu/SC ratio has an influence on the quench propagation and stability margin. In transient operating condition, the Cu/SC ratio weakly influences on the temperature rise in PF magnet.

In this paper, a design scheme of SMES coil with HTS wire(BSCCO 2223) for least stray field and conductor consumption is presented. Three types of coils (solenoid, multiple solenoid, and modular toroid) have been considered. Shape and size of the coil was decided by line element method with evolution strategy and confirmed with Finite Element Method. Modular toroid displayed least stray field with given conductor length. The goal of the study is to establish designing technology of a HTS coil for SMES which works in relatively high magnetic field.

Levitation force of a new magnetic levitation system using a super-conducting bulk magnet(SBM) and a permanent magnet(PM) was numerically calculated. The non-linear J-E relation of a SBM was modeled using a critical state model and iteration method, and demagnetization of a PM was considered using a demagnetization curve of a real PM. The maximum limitation of levitation force was found according to increasing the trapped field in a SBM. Finite element method was used for numerical calculation.

Temperature and resistance of a Bi-2223 tape for fault currents up to 10 $I_{c}$ were measured in two types of samples taking into account real applications. The results indicate that the Bi-2223 tape is safe from burn-out for fault currents with a few cycles up to 10 I$_{c}$. For fault currents of over an order of magnitude higher than the nominal current, the temperature of the Bi-2223 tape depends strongly on fault durations.s.

This paper deals with the operational characteristics of the three-phase modified bridge type fault current limiter(FCL) for 3.3kV/200A power system. This is a preliminary step to develop the FCL's faculties for an application to high voltage transmission line. A three-phase modified bridge type FCL consists of transformers, diodes, and a high-Tc superconducting coil. As the results of simulations, when the FCL of 1.5H inductance was installed in the power system. the fault current was reduced to be about 90% of that without FCL.

The persistent current mode operation of HTS coils is one of the key technologies required for very high-field MRI magnets composed of LTS and HTS coils. But to date, the fabrication of persistent current mode system using HTS is not investigated well. In this paper, we fabricated the magnet and PCS using by BSCCO-2223 tape and jointed them with solder. The current decay behavior of the circuit was measured in liquid nitrogen by monitoring the magnetic field in the centre of magnet with a Hall sensor. To enhance the characteristic of persistent current mode system, superconducting joint method should be investigated.

The heater-triggered switching system for charging of a high temperature superconductor(HTS) is prepared by simulation and investigated its characteristic by experiment. heater-triggered switching system consists of two nickel-chrome alloy heater, an electromagnet and YBCO bulk HTS. There are three important parameters to generate the pumping-current in this system. The timing sequential control of two heters and electromagnet is an important factor to generate pumping-current in the YBCO bulk HTS. Thermal analysis of the switching part in YBCO bulk HTS according to the heater input current was carried out. Electromagnet of 0.6[T] and DC heater input current of 2.3[A] were optimally derived. In this experiment, the maximum pumping current is reaches about 12[A].

We studied on effective quench protection method to prevent damage from unexpected quench of superconducting magnet for magnetic resonance imaging. And we suggested quench protection circuit that is combined with several protection techniques. This circuit has the capacity to maintain the symmetric nature of the magnetic field and the active shielding effect and to protect shim coils during a quench.

The optimum cross-sectional area Profile of gas-cooled high-temperature superconductor (HTS) current lead is analyzed to have minimum helium boil-off rate. The conventional constant area HTS lead has much higher helium consumption than the optimum HTS lead considered in this study. The optimum HTS lead has variable cross-sectional area to have constant safety factor. An analytical formula of optimum shape of lead and temperature profile are obtained. For multi-step HTS current leads, the optimum tape lengths and minimum heat dissipation rate are also formulated. The developed formulations are applied to the Bi-2223 material, and the differences between constant area, constant safety-factor, and multi-step current leads are discussed.

For the development of a small-sized superconducting magnetic energy storage (SMES) system we designed, fabricated and tested the model coil consisting five coils with different features, e.g. winding tensions, bore diameters and materials, cooling channels. The results show that even in the highly pre-stressed small coil A, about 70 % of the coils critical current are degraded The quench current of the coils A, B and E with narrow cooling channels is two times as high as that of the coil C without them though they are similar except spacers. The test results also indicate that the usual training effect depends on the winding tensions of the coils but the quench characteristic does not change according to materials of a bobbin.

We investigated quench recovery characteristics of Au/YBCO thin film meander lines. YB$a_{2}$$Cu_{3}$ $O_{7}$films were coated in-situ with a gold layer and patterned into 2 mm wide meander lines by photolithography. The limiters were tested with simulated fault currents at various source voltages. Resistance decreased first slowly and then rapidly to zero. Resistance vs. time curves for different source voltages fell on top of each other when translated horizontally. The slowly varying portion of data fell on straight lines of a slope on a semi-log scale at all source voltages. A heat balance equation reflecting heat loss from meander lines to surroundings explains these results quantitatively.

This paper deals with cryogen, which is used solid nitrogen to keep the operating temperature of High Temperature Superconducting (HTS) synchronous machine. To make the solid nitrogen of liquid nitrogen, liquid helium (LHe) passes into and cools the heat exchanger to its own temperature. Two types of heat exchangers are designed and manufactured to make the solid nitrogen, and temperature characteristics of those compare with each other. The rotor cooled by latent heat of solid nitrogen and it is kept under 40K during 2 hours and 30 minutes without LHe.

This work presents racetrack High Temperature Superconducting (HTS) magnet with iron plates to achieve the maximum current-carrying capacity and the simple shape that can easily be wound and jointed. The shape, position and kinds of iron plates are chosen by using 3 Dimensional Finite Element Analysis (3d FEA) considering magnetic saturation of iron plates. The racetrack HTS magnet with iron plates, magnet having optimized current distribution and initial magnet are compared with each other through 3D FEA, manufacturing and testing these magnets. The measured performance of the magnet with iron plates improved by 50% on the basis of initial magnet.

In this paper we calculate the AC Loss in the superconducting slab carrying ac transport current. Magnetic diffusion equation for computation of the electric field and current distribution are based on Maxwell's equations and non-linear constitutive equation. The E-J characteristics of superconductor are applied to computation. We will present the result of the high-temperature superconductor case comparison with the slab of low temperature superconductor.

Racetrack coils are used in many areas of superconductivity applications such as generators, motors, maglev, wiggler magnets and so on. Especially now a days a few advanced nations including U.S., Japan are developing high temperature superconducting(HTS) wire which has better performance than low temperature superconducting(LTS) wire. Most of HTS wires such as BSCCO-2223 are manufactured with PIT(Power In Tube) process, so the shape of the wire looks like tape different from LTS wire with round cross-sectional appearance like normal conductors. Generally HTS racetrack coils are composed of a few partial double-pancake colis and then the double-pancakes are jointed each other according to their applications.

This paper presents the possible application of a HTS superconducting power cable for transmitting electric power in metropolitan areas, reflecting its important distinction such as compactness for installation in underground ducts and considerably economical efficiency comparable to present underground cables. In this paper, we investigated characteristic and market scale compact HTS transmission cable which is possible to install in underground ducts. And reviewed its economical efficiency comparing to present existed CV cable from point of view such as cost for cable construction and duct or tunnel installation.

In this paper, we propose an electrical method which is to estimate Ag ratio to Bi-2223/Ag tape.

This paper deals with the design and fabrication of loop superconducting Persistent Current Switch(PCS) circuit. The self and mutual inductances of the circuits are calculated and compared to the measured values. The size of loop circuits was determined using the calculated inductances, and the fabrication processes of the superconducting persistent current switch are described.

In this paper we present the results of manufacturing and tests of prototype cryostat for micro-SMES. The prototype cryostat with HTS current leads and refrigerator had been designed and manufactured for micro-SMES. The cryostat had been tested the helium boil-off and mechanical stress during transfer and vibration test. These results will be applied to micro-SMES cryostat.

The research results on the superconducting magnet for whole body MRI are presented. The magnet consists of main coil with 6 solenoid coils, shielding coil with 2 solenoid coils and 6 sets of cryogenic shim coil. The ferromagnetic shim assembly is installed on the inside wall of the room temperature bore for shimming inhomogeneous field components generated due to manufacturing tolerances, installation misalignments and external ferromagnetic materials near the magnet. Also, the magnet is enclosed with the horizontal type cryostat with 80cm room temperature bore to keep the magnet under the operating temperature. The magnetic field distributions within the imaging volume were measured by the NMR field mapping system. Through the test, the central field of magnet was 1.5 Tesla and the field homogeneity of 9.3 ppm has been obtained on 40cm DSV(the diameter of spherical volume) and using this magnet, comparatively good images for human body, fruits and water phantoms have been achieved.

For the development of a SMES system we fabricated and tested the 1 MJ superconducting magnet The test results show that the magnet is excellent in comparison with previously fabricated magnets outside. The recovery current of the conductor plays an important role in the fabrication of the stable magnets for a SMES system.

FY2000, Japanese government has started three new projects on superconductive power application. Two are succeeding projects of flywheel energy storage and superconducting generator. The other one is fully new project on ac application of superconductivity. Therefore, there are four national projects in Japan on power application of superconductivity, including SMES project Though each project will be reviewed in detail in my talk, outlines are as follows; SMES : FY1999-FY2003, carried by ISTEC Superconducting generator: FY2000-FY2003, carried by Super-GM AC application: FY2000-FY2004, carried by Super-GM Flywheel energy storage: FY2000-FY2004 carried by ISTEC.

Cryogenic air separation unit(ASU) was developed about 100 year ago in Europe. However, because there is not any ability of process design or manufacturing of ASU in Korea, many ASUs come from advanced countries every year. The purpose of this study is the development of cryogenic air separation unit by our own ability, especially cold box for nitrogen production. On this study, we developed the computer program for physical properties of gases and process simulation. We also did process design and manufactured of cold box, including air separation column, liquid air heat exchanger and condenser. The result of cold box test was successful.

YBCO superconductors were prepared by top-seeded melt growth process using various numbers of seeds. The levitation forces and trapped magnetic fields of the top surfaces of the samples were measured using Nd-B-Fe permanent magnets It was found that the processing time was greatly reduced by multiple seeding, but the properties were decreased as the number of seeds was increased. The degradation of the properties is attributed to the presence of the nonsuperconducting phases at the grain boundaries as result of the entrapment of a residual melt at grain boundaries during melt processing.

We designed superconducting four-element patch array antenna which has single-feed circularly polarization and a resonance frequency of 11.85 GHz for DBS receiving system. Antennas have been fabricated from both gold conductor and $YBa_{2}$$Cu_{3}$$O_{7-x}$(YBCO) superconductor (thin films) for comparison. Simulated and measured results, and analysis on resonant frequency(fr), return loss, and bandwidth are presented.

Bi-2223/Ag HTS tapes fabricated by PIT process are used to make the power transmission cable, motor, fault current limiter, transformer etc. But some problems are still remained as like bubbling, sausaging to got the high Jc. In this study. we carried out the experiment to prevent bubbling in the HTS tape. The bubbling mainly occurred when HTS tape was heat-treating. Therefore, additional vacuum annealing at 400 ~ $600^{\circ}C$and slowly ramp-up sintering method were used to decrease the bubbling. slowly ramp-up sintering was more effective to decrease the bubbling than the vacuum annealing, but Jc was also decreased after heat treatment. Optimum ramp-up sintering schedule was searched to get the high critical current and prevent bubbling at same time.

The Linear compressor is widely used in Stirling cryocooler for cooling of infrared sensor. The performance of Stirling cryocooler was mainly depending on how much pressure difference can be generated by compressor. The gap between cylinder and piston should be minimized to get high pressure difference, but too small gap cause failure in the cryocooler. In this study, the leakage rate through gap was investigated by using CFD method and simple thermodynamic relation. The results show compression ratio is decreased and leakage rate increased according to increasing gap.

An intermediate cooling is indispensible to reduce the refrigeration power at superconducting system that is cooled conductively by a cryocooler without liquid cryogens. The cooling load at the intermediate stage is caused by the mechanical supports, the radiation shield and the current lead. From the cooling load calculation, a thermodynamic analysis that take into account the temperature-dependent properties of the materials and the actual performance of the cryocooler is developed. For any given physical dimensions of the various components, it is shown that there exist a unique optimum for the intermediate temperature to minimize the overall refrigeration power. The results of this study can be usefully applied to the selection of the cryocooler as well as the design of the conduction-cooled cryostat.

A Stirling cryocooler is relatively compact, reliable, commercially available, and uses helium as a working fluid. The FPFD stirling cryocooler consists of two compressor pistons driven by linear motors which makes pressure waves and a pneumatically driven displacer piston with regenerator. It is the most suitable design for a mechanical cryocooler utilized in night vision environment. In order to get optimum operating frequency, natural frequency of piston and displacer, optimum phase angle between piston and displacer, cooling capacity, performance tests of the Stirling cryocooler by the frequency characteristics were performed.

KEPCO has a plan to construct TRF (tritium removal facility) in wolsong nuclear power plant site by 2005. In advance of WTRF construction, the pilot plant was installed at KEPRI in order to show process reliability of WTRF. The main processes of this pilot plant are LPCE(liquid phase catalytic exchange) and CD (cryogenic distillation). Deuterium is separated from heavy water in LPCE process and concentrated in CD process. CD process consists of cold box, where are a distillation column and heat exchangers, vacuum system, cryogenic refrigerant supply system and instrument & control system. The experience of the pilot plant will be used in WTRF design review, operating procedure revision and fundamental education for the operators.

The transport loss of a Bi-2223 tape exposed to external magnetic field was investigated. The results show that the transport loss is independent on voltage lead arrangements in case the magnetization loss is compensated. An serious increase of the transport loss due to external magnetic fields is observed. The loss is described well by dynamic resistance loss in relatively high fields, but another mechanism than the dynamic resistance must be responsible for the increase of the loss in low fields. The transport loss is also dependent strongly on the orientation of the applied field.

AC loss which is generated in an HTS wire varies with the direction of the external magnetic field. This paper calculates the AC loss in an HTS tape, where effects of the perpendicular direction of the magnetic field are considered. Brandt equation is used to calculate the loss by perpendicular magnetic field. In the calculation, current densities are varied along the variation of the magnitude of the external magnetic field. Results of calculation are compared with those of the conventional method.

Three nearly identical superconducting fault current limiters (SFCLs) were connected in series to increase the voltage ratings. A slight difference in the quench starting point of individual SFCL units produced significantly imbalanced power distribution when connected in series. The imbalance was successfully removed by connecting a shunt resistor to one SFCL in parallel. 1.2 kV SFCL was designed with five current limiting elements and two or three shunt resistors.

Two methods can be used to correct the undesirable magnetic field of MRI. One is active shimming method and the other is ferro-magnetic shimming. Ferro-magnetic shimming method is more inexpensive, more convenient in operation and more effective on correcting magnetic field. So, nowadays, it is the general method for shimming the commercialized MRI magnet. We have developed a 1.5T MRI magnet and its ferromagnetic shimming system. Using the ferro-magnetic shimming system, we have improved the field homogeneity of the 1.5T MRI magnet.

Magnetization loss of a Bi-2223 tape in magnetic fields parallel to the tape surface was measured by a magnetization method. The results indicate that the magnetization loss is hysteretic because the measured loss agrees well with calculated one from a critical state model. In the full field penetration case the magnetization loss increases with the frequency but in the partial field penetration case the influence of the frequency is opposite.

In order to design thermally trigger controlled persistent current switch (PCS) for superconducting magnet system, it is very important to know information of applied adiabatic method and condition to get designed resistance and characteristics In this paper, we used cotton-gummed tape as thermal insulator and derived experimentally averaged thermal conductivity of it around 10K on the assumption that adiabatic structure of PCS is shape of pipe. The result value is about 0.29 W/mK and it is verified reasonable value by computer simulation and experiment of test PCS. Test PCS was designed and manufactured different dimensions. The experimental results of test PCS were in good agreement with the calculated results.

This paper deals with the fabrication and characteristic experiment of a high-Tc superconducting(HTSC) power supply using by Bl-2223 tape. The purpose of this research is to apply real HTSC load. This system consists of two heaters, an electromagnet, a Bi-2223 solenoid and a Bi-2223 pancake load. In the experiment. 17sec and 8.5sec were used for pumping period. Mechanism of the superconducting switch is used for heater-trigger. In experiment, the pumping-current has reached about 1.2A.