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The turn-to-turn contact resistance of second-gene-ration (2G) HTS coil with metal insulation is a very important parameter in the viewpoint of the stability and current charging speed of the HTS coil. Controllability of the contact surface resistance of the 2G HTS coil with advanced metal insulation was observed in contrast with the case of the stainless steel (SS) metal insulation (MI). Three types of model coils—a no insulation coil, a metal insulation coil cowound with SS tape, and an MI coil cowound with copper (Cu) electroplated SS tape—were prepared and evaluated. The contact surface resistances between two Cu-plated 2G HTS tapes, between a Cu-plated 2G HTS tape and an SS tape, and between a Cu-plated 2G HTS tape and a Cu-plated SS tape are 6.3, 362.4, and 7.9 μ Ω·cm2, respectively. Dramatic reduction of the turn-to-turn contact surface resistance in model coils was achieved by using MI coil cowound with the Cu-plated SS tape. Also, the possibility of changing such contact surface resistance will be useful for designing the MI magnet.

The first quadrupole magnet at the in-flight fragment (IF) separator of heavy ion accelerator should withstand intense radiative heat load of neutron beam. Most of the HTS magnets are cooled by liquid cryogen or conduction cooling methods. However, the quadrupole magnet is exposed to the intense radiation heat load, and the quadrupole magnet can be cooled by the circulation of cold gaseous helium. The gaseous helium cooling system is composed of a liquid nitrogen precooler, a recuperator, a compressor at room temperature, and a single-stage GM cooler. Nichrome wire inside bobbin simulates the radiative heat load by neutron beam. The prototype magnet consists of two single pancake coils and has the half length of the full-scale HTS quadrupole magnet. HTS wire is wound on an aluminum bobbin without insulation layer. This paper describes the thermal stability test results of the prototype HTS magnet using additional heater to simulate the large radiation heat load. The operating current is transported while applying the additional heating on the bobbin surface, and the thermal characteristic is investigated. The experimental data will be used to design the thermal structure of the HTS magnets used in the first quadrupole magnet at the IF separator.

A dc reactor is operated under a dc current to reduce the current's ripple or harmonics in the power system. General dc reactors in high-voltage dc systems use a metal conductor. This has some disadvantages such as large reactor size, leakage flux, wide install space, heavy weight, and electrical losses due to the large operating current. This paper describes the design of the toroid-type high-temperature superconductor (HTS) dc reactor magnet. Target operating current and inductance of the HTS dc reactor are 1500 A and 400 mH, respectively. The HTS dc reactors were designed through electromagnetic analysis and a 3-D CAD program. The two-layered 12-mm-width 2G GdBCO wire was considered. In addition, we analyze the operating performance of the double pancake coil module for the 1500-A 400-mH HTS dc reactor magnet under the liquid nitrogen condition.

The substantial improvement of the signal-to-noise ratio (SNR) can be achieved with small-size samples or low-field MRI system by high-temperature superconducting(HTS) RF coil. The typical HTS RF coil made of HTS thin film is expensive and is limited the coil geometry to planar surface coil. In this study, commercial Bi-2223 HTS tapes was used as RF coil for a 0.35T permanent MRI system. It has advantages of both much lower cost and easier fabrication over HTS thin film coil. SNR gain of the image obtained from the HTS RF coil over a conventional Cu RF coil at room temperature was about 2.4-fold and 1.9-fold using the spin echo pulse sequence and gradient echo pulse sequence respectively.

A conduction-cooled high temperature superconducting (HTS) magnet for the SPMS was fabricated and tested. To achieve an adequate uniformity of background magnetic field, a split-pair winding configuration is used. Room temperature bore of this magnet was 38 mm (length) × 134 mm (width) × 360 mm (depth) in dimension. The magnetic field uniformity of HTS magnet was achieved lower than 1% within the virtual sample region 15 mm (width) × 100 mm (depth). Also, this HTS magnet could be operated to generate 3 T for 7 h.

This paper describes the design results, loss analysis, and experiment testing of the real manufactured toroid-type superconducting magnetic energy storage (SMES). We analysed heat load through the conduction and radiation of the cryostat and magnetization loss caused by the charging and discharging of the toroid-type SMES system. We also measured the characteristics of toroid-type SMES under three different types of operating conditions (steady state, one-cycle charging and discharging, series charging and discharging). The fundamental design specifications and the data obtained from the experiment will be applied to a large-scale toroid-type SMES system design.

This paper proposes a quench detection method applied to a HTS coil and also discusses the results of tests on an HTS BSCCO wire and an HTS YBCO coil. A series-type thermocouple was fabricated to detect quench, where several thermocouples were welded in series. As the series-type thermocouple has many points of detection, variation in temperature was detected at each point by using thermo-electromotive force. The feasibility of the proposed method was investigated through the quench detection tests on the YBCO coil. This method has advantages such as a simple structure and cost effectiveness and also protects the HTS coil by detecting partial quench and its propagation.

The authors designed and manufactured a toroidal-type superconducting magnetic energy storage (SMES) system. The toroidal-type SMES was designed using a 3D CAD program. The toroidal-type magnet consists of 30 double pancake coils (DPCs). The single pancake coils (SPCs), which constitute the double pancake coils, are arranged at an angle of 6° from each other, based on the central axis of the toroidal-type magnet. The cooling method used for the toroidal-type SMES is the conduction cooling type. When the cooling method for the toroidal-type SMES was designed, the two-stage Gifford–McMahon (GM) refrigerator was considered. The Bi-2223 HTS wire, which was made by soldering brass on both sides of the superconductor, is used for the magnet winding. Finally, the authors connected the toroidal-type SMES to a real-time digital simulator (RSCAD/RTDS) to simulate voltage sag compensation in a power utility.

Superconducting magnetic energy storage (SMES) can overcome fluctuations in frequency because of its fast response time in charging and discharging energy. To stabilize the fluctuations in frequency of wind power generation systems (WPGSs), HTS SMES systems should be connected to the terminal of the WPGSs. Ulleung Island's power network in Korea was modeled with a real-time digital simulator (RTDS) to demonstrate the effectiveness of SMES at stabilizing frequency. A toroid-type HTS SMES cooled by conduction cooling and a DC/DC chopper to charge and discharge current were fabricated for the experiment. The simulation results show the frequency stabilization effected by the HTS SMES system with its operational characteristics such as real time variation in current and temperature.

A superconducting property measurement system (SPMS) is used to acquire electrical and thermal properties of short HTS tape samples. The SPMS is composed of a specimen holder for mounting an HTS tape and magnet for applying a magnetic field externally. The magnet consists of two split racetrack windings and is designed to produce maximum 3 T of center field at 20 K. In this paper, an HTS magnet for the SPMS cooled by a cryocooler was designed. A HTS magnet consists of several pancakes winding wound from YBCO CC tape. We report out design for a conduction-cooled magnet using YBCO CC tape. For varying the number of double pancake coils (DPCs) and the bending radius, an electromagnetic field analysis is used. We subsequently find a suitable HTS magnet type for an SPMS. This paper describes the quench protection system for an HTS magnet of the SPMS. The detection of any normal zone must be preceded to protect the HTS magnet. We use simulated protection circuit to estimate the trigger conditions. The presented results in this paper will be verified using fabricated protection circuit.

Superconducting high gradient magnetic separation (HGMS) has advantages to treat wastewater because it can generate high magnetic field and achieve rapid purification. In this study superconducting HGMS was applied to remove impurities from the condenser water in thermal power plant. The condenser water contained mainly hematite and maghemite and it was highly magnetized than hematite. In the HGMS tests using a 6-T cryo-cooled Nb-Ti superconducting magnet, the turbidity of the condenser water was effectively reduced up to 99.6% and the result showed better performance than that of the 0.5-T permanent magnet test. The higher magnetic field was applied in the range of 1-6T, the more iron oxides were removed. The effect of magnetic filter configuration on the condenser water treatment was also investigated. Consequently superconducting HGMS system can be applicable to remove iron oxide impurities from condenser water in thermal power plant.

This paper analyzes the operational characteristics of conduction cooling Superconducting Magnetic Energy Storage (SMES) through a real hardware based simulation. To analyze the operational characteristics, the authors manufactured a small-scale toroidal-type SMES and implemented a Real Time Digital Simulator (RTDS) based power quality enhancement simulation. The method can consider not only electrical characteristics such as inductance and current but also temperature characteristic by using the real SMES system. In order to prove the effectiveness of the proposed method, a voltage sag compensation simulation has been implemented using the RTDS connected with the High Temperature Superconducting (HTS) model coil and DC/DC converter system, and the simulation results are discussed in detail.

Output power of the wind power generation system (WPGS) fluctuates due to wind speed variation and affects the frequency and voltage fluctuations of the utility. Superconducting Magnetic Energy Storage (SMES) can overcome these fluctuations because of fast response time for energy charging and discharging. To stabilize the frequency fluctuation, HTS SMES should be connected to the terminal of the WPGS. Ulleung island power network in Korea was modeled to demonstrate the effectiveness of SMES for frequency stabilization. Based on the simulation results using EMTDC, a toroidal-type HTS SMES cooled by conduction cooling method and a DC/DC chopper for current charging and discharging were fabricated for experiment. Power network including WPGS was implemented through a Real Time Digital Simulator (RTDS). The simulation and experimental results for frequency stabilization using real HTS SMES and RTDS are discussed in detail.

2nd generation high temperature superconducting (2G-HTS) tape consists of multi-layers such substrate, buffer layer, superconducting layer and reinforced lamination tapes. 2G HTS tape is a candidate of good materials for current lead of superconducting magnet system owing to its low thermal conductivity. However, joint resistance between 2G HTS tapes and terminal block can be a major problem because of high electrical resistivity of substrate, buffer layer and reinforced lamination tapes of 2G HTS. So specially considering joint resistance between 2G tapes and terminal block, 2G HTS current lead for 400 A was designed and fabricated. This current lead was consisting of two terminal blocks, a support bar or tube, protection tube and six 2G HTS tapes. Its total length was 300 mm and body diameter 18.3 mm. At liquid nitrogen temperature (77 K) critical current (Ic) of this HTS current lead was 600 A, about 1.5 times the operating current 400 A. Conductive heat loss of 2G HTS current lead between 60 K and 7 K was 50 mW.

Studies on (YBCO) coated conductor (CC) are actively underway for the practical application of high temperature superconducting (HTS) devices such as magnets, cables and fault current limiting devices because the CC has higher critical current characteristics under high temperature and magnetic field. However, it is hard to make a long-length of YBCO CC tape with uniform critical current density using the present processing techniques. The hot spot will emerge in a local region if the critical current is non-uniform along the HTS tape, and eventually, the hot spots may cause serious damage to the HTS tape. Therefore, it is important to examine the thermal stability characteristic of the YBCO CC tape from the quench protection point of view. In this paper, the segmental critical current of a YBCO CC sample tape is measured in liquid nitrogen, and a heater is installed at the center of the sample tape in order to examine the normal zone propagation characteristics in the longitudinal direction under the adiabatic condition with a Gifford-McMahon cryocooler. Measurements are performed as a function of heat input and transport current for the operating temperatures of 77 K, 65 K and 40 K, respectively, and the results are discussed in detail.

It is environmentally important to recycle the wastewater, since paper factories use a large amount of water and equivalent amount of wastewater is generated. Conventional water treatment facilities like precipitation process need large-scale equipment and wide space to purify the wastewater of paper factory. In case of massive waste water, high gradient magnetic separation (HGMS) parts are more effective to purify it rapidly and to occupy relatively small space, since large voids at filter with HGMS are adopted. In this respect, we prepared two types of superconducting magnets in order to apply HGMS parts for wastewater purification process. We made cryo-cooled Bi-2223 (HTS) superconducting magnet parts with room temperature bore in diameter of 70 mm and 200 mm in height. Also, cryo-cooled Nb-Ti superconducting magnet with room temperature bore in diameter of 100 mm and 600 mm in height was used for magnetic separator. Magnetic filters were designed by the analysis of magnetic field distribution at superconducting magnets. The faster wastewater's flow rate was, the worse the degree of clarity in treated water was. The ability of wastewater treatment in the case of magnetic separation used with 10 of magnetite particles was better than that in the case of 5 of magnetite particles.

A laboratory-scale conduction cooled high temperature superconducting (HTS) magnet is fabricated and tested. This HTS magnet was designed in order to generate 2 T at center of room bore in operating current 120 A. It consists of eight double-pancake sub-coils, two HTS current leads, a GM cryocooler and a cryostat without a radiation shield vessel. Sub-coils were wound with 1G HTS tapes of Sumitomo Electric Industries Ltd. using wet winding method. Assembled magnet was impregnated with epoxy resin in vacuum. Room bore diameter of this magnet was 70 mm. Each bobbin of double-pancake coils was of GFRP and aluminum alloy. Upper and lower supporting plates of coils is made by aluminum alloy in order to improve thermal conduction. In this paper, fabrication and test results of HTS magnet including magnetic field and temperature variation are reported.

This paper describes design, fabrication, and evaluation of the conduction cooled high temperature superconducting (HTS) magnet for superconducting magnetic energy storage (SMES). The HTS magnet is composed of 22 of double pancake coils made of 4-ply conductors that stacked two Bi-2223 multi-filamentary tapes with the reinforced brass tape. Each double pancake coil consists of two solenoid coils with an inner diameter of 500 mm, an outer diameter of 691 mm, and a height of 10 mm. The aluminum plates of 3 mm thickness were arranged between double pancake coils for the cooling of the heat due to the power dissipation in the coil. The magnet was cooled down to 5.6 K with two stage Gifford McMahon (GM) cryocoolers. The maximum temperature at the HTS magnet in discharging mode rose as the charging current increased. 1 MJ of magnetic energy was successfully stored in the HTS magnet when the charging current reached 360A without quench. In this paper, thermal and electromagnetic behaviors on the conduction cooled HTS magnet for SMES are presented and these results will be utilized in the optimal design and the stability evaluation for conduction cooled HTS magnets.

In order to investigate the possibility of using mixed rare earth (Nd1/3Eu1/3Gd1/3)Ba2Cu3O7-x (NEG123) as the superconducting layer of the HTS coated conductor, the NEG123 thin film was deposited epitaxially on LAO(100) single crystal and IBAD_YSZ metal templates by pulsed laser deposition. Systematic studies were carried out to investigate the influences of deposition parameters of PLD on the microstructure, texture and superconducting properties of NEG-123 coated conductor. Deposition at oxygen partial pressure of 600 mTorr was needed to routinely obtain high quality NEG123 films with JC's (77 K) over 2 MA/cm2 and Tc's over 90 K (DeltaT ~ 2 K) . We verified from magnetization study that the NEG123 has an improved in-field Jc as the field increases at temperatures between 10 K and 77 K compared with Gd123. The JC (77 K, self field) and the value of onset TC of NEG123 thin film on LAO substrate was 4.0 MA/cm2 and 92 K, respectively. This is the first report, to the best of our knowledge, of coated conductors with NEG123 film as the superconducting layer which have Ic and Jc over 40 A/cm-width and 1.6 MA/cm2 at 77 K, self field. This study shows the possibility of using NEG123 film as the superconducting layer of the HTS coated conductor which can be used in high magnetic field power electric devices.

The increasing use of high-temperature superconducting (HTS) materials for advanced power applications has generated much interest in the acquisition of the voltage–current ( V – I ) characteristic curve to measure the critical current ( I c ) of HTS tape. Cryogen free I c measurement system for HTS wires or coils was designed and fabricated by using a GM-cryocooler and two HTS current leads. The sample cools conductively by 2nd stage of SRDK-408D cryocooler manufactured by Sumitomo Heavy Industries Ltd. (SHI). Each high temperature end of HTS current leads is thermally connected to 1st stage of the cryocooler and electrically disconnected. HTS tape samples cooled down by about 10 K. I c measurements were conducted on a BSCCO-2212 tape, a BSCCO-2223 tape with joints and a BSCCO-2223 small coil under self-field. A description of cryogen free I c measurement system design and results from a series of measurements will be presented.

The important merit of Bi-2212/Ag high Tc superconducting wire is to apply cable as round wire geometry. Bi-2212/Ag wires were fabricated in order to develop Rutherford cable for SMES near the future. Various Ag ratio and various numbers of filaments for PIT (Powder-In-Tube) process were applied to investigate the workability during drawing and to improve critical current property of the wires. Rutherford cabling machine for B-2212/Ag strands was designed and manufactured. We designed and manufactured Rutherford cabling machine with 32 bobbins which had 2 km length of wire. This machine was constituted with Turks head, caterpillar tread and take-up facility. In order to obtain uniform working conditions without defects, Turks head's rolling system and Ag ratio of Bi-2212/Ag strands were modified. We tried to fabricate Rutherford cables with 20 and 30 Bi-2212 strands. Proper working conditions for without breakage strand in cable were investigated. We made successfully Bi-2212 Rutherford cable. The critical current of Bi-2212 Rutherford cable with 30 strands showed 420 A at 64 K and 4008 A at 4.2 K. The critical current of Bi-2212/Ag wire with 847 filaments was 398 A at 4.2 K and self field.

A 600 kJ HTS SMES is under development in Korea. Before the specific design of the HTS SMES, its model coil is fabricated and tested to verify the thermal and electrical characteristics. The model coil consists of two single pancakes and one double pancake coil with copper conduction plates between the coils. Each pancake is fabricated with a soldered 4-ply HTS conductor to increase the coil current. The model coil is cooled by two GM-cryocoolers and cooled down to below 20 K. Copper conducting plates between the coils are used as the thermal path to the cryocooler. With the model coil, experiments are performed to investigate the thermal stability related with the transport current and the charge/discharge rate. The results are used to develop the 600 kJ HTS SMES by clarify the several source of the heat generation.

A conduction-cooled high-temperature superconducting (HTS) coil consisting of two double pancake coils was fabricated. The current–voltage ( I – V ) characteristics of HTS coil were obtained at different temperatures by using GM cryocooler. Using OPERA 2D, magnetic field ( B r ) perpendicular to the surface of the tape at each layer of HTS coil was obtained. In order to compare with the measured values, I – V curve of the HTS coil was simulated, in the basis of the magnetic field dependence of the critical current ( I c ) in Bi-2223 tapes and index of n -value. Results showed pretty good agreement between the simulated and the measured critical currents at 77.3 K and 40 K, with a bit difference under simple assumption of index of n value.

HTS sample magnet having two double pancake sub- coils was manufactured. In HTS magnet coil, lab joint method has been conventionally, used. Such joint has some disadvantage: while handling, easy damage on HTS tapes occurs. On the contrary, parallel joint method has merits: easy handling to solder, less damage. Accordingly, such method was adopted to connect between two sub-coils. At 77.3 K, resistance of parallel joint with 20 cm in length was 55 nOmega up to about current 130 A. At 21.0 K, resistance of parallel joint was 31 nOmega and critical current (Ic) of HTS magnet higher than 500 A. In simple calculation, Joule heat was calculated 7.8 mW in the joint region under operating current 500 A, and Joule heat in HTS magnet was 565 mW. From such consideration of Joule heat generation, this joining method is available for fabricating HTS magnet.

This paper presents the influence of current distribution on AC transport current loss in multi-strand high-temperature superconductor (HTS) tapes. The current-distribution-dependent-AC loss is analyzed by introducing a current distribution parameter. We calculated AC loss of multi-strand HTS tapes numerically and performed AC loss measurements as well. Though the effect of current distribution on AC transport current loss is relatively insignificant for a low applied transport current, the effect of nonuniform current distribution seriously increases AC loss for a high applied transport current. The AC loss measurement method used in this paper is also confirmed by comparison with numerical results: the experimental and computational results showed good agreement for various current distribution parameters

Synchronous reactance is an important parameter of synchronous rotating machine because it affects on the machine output capacity, voltage variation and steady-state stability. The superconducting synchronous rotating machine has very small synchronous reactance about 1/5 of the conventional synchronous machine. This reason comes from the fact that the superconducting rotating machine is air-cored structure. In this paper, it is estimated how much this synchronous reactance has influences on many design parameters of superconducting synchronous machine such as machine volume and weight, efficiency, voltage variation and so on. In the case of a synchronous motor, the power factor can be adjusted according to the excitation voltage. This paper also deals with the effects of power factor on the design parameters and the performance of a HTS (High-temperature Superconducting) synchronous motor. This kind of analysis was used to design 1 MW class HTS motor

This paper proposes an effective design process for 1 MW HTS superconducting motor by using 3-dimensional equivalent magnetic circuit network method (3D EMCN) and response surface methodology (RSM). During the process, 3D EMCN is used with a simplified 3D analysis model to get electric parameters in short time. RSM is used for the motor optimal design to improve power density. The usefulness of this method is verified through the comparison of the performances of the optimal geometry and those of the initial geometry

This paper investigates the magnetization loss of stacked Bi-2223/Ag tapes. A numerical code was developed to estimate the magnetization loss of stacked tapes in parallel and perpendicular external magnetic fields. To calculate magnetization loss and current distribution across the tapes, we used magnetic field dependent current-voltage characteristics of a tape. The numerically calculated result showed good agreement with the measured magnetization loss in a tape. In a perpendicular field, it was observed that the loss per unit volume decreased as the stacking number increased because of the screening current across the tapes. In a parallel field, the loss per unit volume remained virtually unchanged as the stacking number increased. The influence of stacking effect on magnetization loss is addressed with the induced current distribution obtained from numerical calculation.

This paper proposes a design method for optimizing the rotor winding shape of HTS motor. The design objective is to maximize the flux-linkage of stator winding with a given amount of superconductor volume. The increase of flux-linkage results in output-power increase, compact size and quench-reliable characteristic. The optimization algorithm is a design sensitivity analysis where the HTS critical current condition is taken into account. First, the shape of rotor winding is optimized to give a boundary shape of smooth curves. Second, with the shape the rectangular sizes of windings are approximately obtained for easy manufacture. Finally, the rectangular sizes are also optimized for fine-size tuning. The proposed design method is applied to the 100-hp HTS motor.

A 100 HP rated synchronous motor with superconducting rotating field winding has been designed based on the formulated equations established from 2 dimensional magnetic field distributions in a cylindrical coordinate. The cross-section was drawn based on calculated design results via Fortran program and then modeled with FEM (finite element method) to investigate the machine performances. First of all, the magnetic field distributions are analyzed in many ways according to the field directions and the armature currents. Especially after the rotating field winding is arranged with BSCCO-2223 high-temperature superconducting (HTS) pancake coils, the exerted magnetic field normally on the HTS tape is calculated through FEM. And the machine output power is calculated according to the torque angles that lie between the field and the armature main flux lines. Moreover, this paper includes the eddy-current loss variations of a copper damper located between the field and the armature coils. Finally, 3 dimensional magnetic field distribution is also calculated via FEM. The radial components of magnetic field are compared along the center line of an armature conductor section between 2 dimensional and 3 dimensional results. By the comparison we make sure that about 30% of machine output is added from the end effect of HTS field coil and more accurate design approach is possible.

A superconducting motor consisting of high temperature superconducting (HTS) rotor and air-core stator is under development in Korea Electrotechnology Research Institute. HTS motor was designed for having the rated power of 100 HP at 1800 rpm. HTS field winding is composed of sixteen HTS race track shaped coils wound with stainless steel-reinforced Bi-2223 tape conductor by react and wind fabrication method. Nomex paper was used for electrical insulation. Each of four field coil assemblies was constructed with four double pancake sub-coils, mechanically stacked and electrically connected in series. Four field coil assemblies were fixed on an aluminum support structure to make effective heat transfer. Voltage terminals were attached to both ends of joints to measure joint resistances. HTS field winding was tested at 77 K, and the Joule heats generated at all the joints was calculated. In this paper, design, construction and testing of HTS field winding, Joule heat generated by the joints, and operating current were discussed.

A 100 hp class superconducting motor in the 21st Century Frontier R&D Program of Korea has been designed. A theoretical model of high temperature superconducting (HTS) motor was presented by two-dimensional electromagnetic field analysis. The motor is composed of HTS field winding, cold damper shield, air-gap armature winding and laminated machine shield. The HTS field winding consists of racetrack type double pancake coils wound with Bi-2223 HTS tapes operated at about 30 K. The operating current of the HTS tape conductor could be determined by the magnetic field distribution calculated in the HTS field winding and the I/sub c/ - B characteristics of a practical HTS conductor, taking account of its anisotropy.

Superconducting motors have high efficiency as well as reduced size and weight. In superconducting motors, the field winding is composed of HTS tapes (Bi-2223) without any iron core because of magnetic saturation, and the current in the field winding is limited by the maximum magnetic field in the field winding. To enhance the performance of superconducting motor, we need to maximize the critical current of field winding as much as possible. This paper introduces the shape optimization method with the constraint of HTS characteristic (I/sub c/-B curve), and proposes a shape that improves the critical current of the field winding. Finite element analysis and discrete sensitivity approach are used for calculating the magnetic field of coil and shape optimization.

We have successfully fabricated single-filament composite MgB/sub 2//Stainless-Steel (SS) tapes using powder-in-tube processes such as swaging and cold rolling. The transport critical currents, that were measured by a standard dc four-probe method, I/sub c//spl sim/316 A and /spl sim/105 A were observed at T=4.2 K with H=0 G for as-rolled and sintered MgB/sub 2//SS tapes, respectively. In addition, the isothermal magnetizations M(H) of sintered MgB/sub 2//SS tapes and commercial MgB/sub 2/ powder were measured at temperatures T between 5 and 50 K in fields up to 6 T, employing a PPMS. The critical current density (J/sub c/) values obtained from the M(H) data, using Bean model, were >5 /spl times/ 10/sup 5/ A/cm/sup 2/ and >5 /spl times/ 10/sup 7/ A/cm/sup 2/ at T=10 K with H=0 G for the sintered MgB/sub 2//SS tapes and the commercial MgB/sub 2/ powder, respectively. On the other hand, we investigated the cross sections of both the sintered and the as-rolled tapes, using SEM and EPMA. No evidence of significant diffusion between MgB/sub 2/ and SS tube was found in the SEM/EPMA. However, traces of reaction can be seen in the interface region between MgB/sub 2/ core and SS tube for the sintered MgB/sub 2//SS tapes, from the EPMA line profiles. In addition, impurity phases such as MgO or MgB/sub 4/, which can be generated inside the superconductor MgB/sub 2/ core during fabrication, were observed by XRD analyses.

A superconducting solenoid with large inner diameter has much lower current capacity than expected from short wire sample tests, and a solenoid of multi-strand cable has worse results. It is known that this degradation is observed when the inner diameter of the solenoid is bigger than a certain value (30 cm usually). However the reason is not clarified yet and some people called this just the "size effect." To obtain some clues to understand the size effect and to develop big solenoids with higher operating current, we prepared and tested two sample solenoids made of Rutherford type cables with and without soldering. Quench currents and AC losses of the two solenoid coils are measured and compared. The test results show that the soldering on the Rutherford cable improves the current capacity, but makes the AC loss much higher.

This paper deals with cryogen, which is used as solid nitrogen (SN 2 ) to keep the operating temperature of high temperature superconducting (HTS) synchronous rotating machine. To solidify liquid nitrogen, liquid helium (LHe) passed into the heat exchanger and cools its own temperature. Two types of heat exchangers were designed and fabricated for making the SN 2 , and the temperature characteristics of both case was compared. The rotor of HTS synchronous rotating machine was cooled by latent heat of SN 2 and it was kept under 40 K for 2 h and 30 min without the additional supplement of LHe.

We report the successful fabrication of single-filament composite MgB 2 /stainless-steel ribbons, as an ultrarobust conductor type. The transport critical current of the non-sintered MgB 2 /stainless-steel ribbons is remarkably high, as an unexpected result. Transport critical currents I c ∼316 A at T =4.2 K and I c ∼82 A at T =20 K were observed at self-field for the non-sintered composite MgB 2 /stainless-steel ribbons. The I c value of 316 A is the higher than any other value reported so far. In addition, the persistent current density, that was estimated by Bean formula, of the sintered composite MgB 2 /stainless-steel ribbons was more than J p ∼6×10 5 A/cm 2 at T =5 K with H =0 G, and J p ∼1.1×10 5 A/cm 2 at T =30 K with H =0 G.

This paper deals with high temperature superconducting (HTS) synchronous motor, which has two characteristics: the HTS magnet with iron plates as field coil, and the solid nitrogen (SN/sub 2/) as a cryogen. The HTS magnet has iron plates to achieve the maximum current-carrying capacity and the simple shape that can easily be wound and jointed. The HTS magnet with iron plates, magnet optimized current distribution, and initial magnet are presented through FEA (finite element analysis), manufacturing and testing these magnets. SN/sub 2/ is employed for keeping the operating temperature of HTS synchronous motor. To make the SN/sub 2/ of liquid nitrogen (LN/sub 2/), liquid helium (LHe) passes into the heat exchanger and cools its own temperature. Two types of heat exchangers are designed and manufactured to make the SN/sub 2/, and each of the temperature characteristics is compared.