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High temperature superconducting dynamos are capable of low loss contactless pumping large dc currents into superconducting magnet coils. We present a mathematical model of such devices and use it for computing the 2-D loop currents and electric fields induced by a dynamo rotor-mounted permanent magnet in a thin superconducting stator strip. Two numerical methods for thin film superconductivity problems, the mixed finite element method, and the fast Fourier transform based method, are employed and compared. We find voltages generated in the stator under open-circuit conditions and losses in the stator. It is shown that if the length of a permanent magnet is comparable to or smaller than the strip width, the 1-D model employed in the previous works can be inaccurate. [ABSTRACT FROM AUTHOR]

The influence of Gd addition on the microstructure and superconducting properties of Y-Ba-Cu-O (YBCO) bulk superconductors has been studied. Precursor powders YBa2Cu3O7-δ (Y-123), Y2O3, and CeO2 were enriched with different amounts of GdBa2Cu3Oy (Gd-123) powder with the aim to increase critical current density Jc by introducing additional pinning centers. YBCO bulk superconductors with GdBa2Cu3Oy (Y123-Gd) addition were prepared by the optimized top seeded melt growth process in the form of single grains. Microstructure of prepared samples was studied by polarized light microscope. The superconducting properties were measured using a vibrating sample magnetometer in magnetic fields up to 6 T at 77 K. In spite of decreasing critical current density Jc in zero field at 77 K with increasing Gd concentration x almost all the samples with Gd-123 addition posses a maximum trapped magnetic field Btmax higher than that for YBCO sample without any addition. In the contribution, the effect of Gd addition on Y2BaCuO5 (Y-211) particle size, critical transition temperature Tc, critical current density Jc, and maximum trapped magnetic field Btmax is reported. [ABSTRACT FROM AUTHOR]

The critical current degradation of coated conductors was investigated at 77 K s.f., after heating the samples in a solder bath to temperatures between 200 °C and 300 °C for durations between 30 s and up to 2 h to simulate possible soldering conditions. We found that the critical current degradation is strongly dependent on temperature and time, but independent from the number of thermal cycles. At 225 °C for 10 min a degradation of about 5%was measured. At 300 °C for 10 min the degradation was about 45%. Slight variations among different manufacturers were observed. Across production batches of the same manufacturer no variations were found for tapes of the same structure. Slight variations of tapes with different stabilizer thicknesses were detected after heat treatment. [ABSTRACT FROM AUTHOR]

Most of the latest models of HTS bulk magnetization take into account the thermal and electromagnetic coupling, but, they still lack the implementation of the mechanical deformation under strong magnetic fields. The following work tries to fill up partly the gap by proposing a model of the dependence of the electrical conductivity upon mechanical deformation during field-cooling magnetization. This dependence is carried out by the critical current density as a function of induced thermal and mechanical strain in the bulk. As a first approximation and bearing in mind the obvious discrepancies, a simplemodel inferred from HTS thin films and generic knowledge on ceramics is proposed. This first approach allows drawing some generalities on the expected thermal, magnetic, and mechanical response of disk-shaped YBCO pellets during magnetization. The utter goal is to assess design parameters to insert those pellets in electrical rotatory machines. [ABSTRACT FROM AUTHOR]

Sm-doped single-grain YBCO bulk superconductors were fabricated by the Top Seeded Melt Growth process in the system YBa2Cu3O7-δ/Y2BaCuO5 with CeO2 addition and with added liquid-rich powder at the bottom pellet. According to microstructure analyses, Sm2O3 addition led to the refinement of Y-211 particles, which was reflected in higher critical current density, Jc, at 77 K and zero fieldmeasured for doped sample. Missing of expected secondary peak in Jc field dependence for doped sample was related to lowering of Sm concentration in the sample by its diffusion into additional liquid-rich phase pellet. Sm-doped pellet exhibited higher maximum trapped field, Bc, measured at 77 K. [ABSTRACT FROM AUTHOR]

The eventual goal of high-voltage direct-voltage (HVDC) systems is to implement HVDC grids. One of the key obstacles in realization of the HVDC grid is the absence of a dc circuit breaker (DCCB). Several prototypes of DCCBs for the HVDC grid have been proposed, but no commercial solution has been developed yet due to insufficient dc fault current breaking capabilities and an unreliable protection-coordination scheme. In this respect, application of the suitable fault current limiter is necessary, and the use of a superconducting fault current limiter (SFCL), which has already been developed for the ac grid, is a viable solution, but there is no fundamental research about performance evaluation of SFCLs for the dc grid. Therefore, we aim to verify the applicability of the conventional SFCL in HVDC grids and perform a comparative analysis of the performance of several types of SFCLs. To analyze the performance of the conventional SFCL in the HVDC grid, three well-known representative types of SFCLs are modeled inMATLAB/Simulink, and their current limiting and recovery characteristics and energy dissipation are examined in voltage-source converter HVDC system application. From the simulation results, we deduced the strengths and the weakness of different types of SFCLs. Consequently, the likely SFCL candidate for commercialization in dc grid applications is suggested. [ABSTRACT FROM AUTHOR]

Toward the practical and rational insulation design of a resistive superconducting fault current limiter, it is necessary to consider the electrical breakdown (BD) due to the transient bubble generation in liquid nitrogen (LN2 ) at the quench of the HTSmaterials. We have been investigating the intrinsic BD characteristics of LN2 without bubbles and the dynamic BD characteristics of LN2 under transient bubble disturbance, respectively. In this paper, we have investigated the dynamic BD characteristics of LN2 for different electrode diameters and gap lengths, and have discussed in terms of the volume effect of dynamic BD strength. [ABSTRACT FROM AUTHOR]

Transformer-type superconducting fault current limiter (TSFCL) interruption system is a current breaking technology proposed by applying a transformer, superconductor, andmechanical dc circuit breaker. When the fault occurs, the fault current is limited due to the operation of the counter electromotive force by the transformer and the quenching of the superconductor. The fault current is then interrupted by the mechanical dc circuit breaker. In this paper, the transition and the interrupting behavior was analyzed according to the applied voltage to secure the stability and reliability of a TSFCL interruption system using the PSCAD EMTDC program. As a result, it was able to improve the current breaking time and the breaking capacity. Also, the burden imposed on a mechanical dc circuit breaker was reduced fivefold. [ABSTRACT FROM AUTHOR]

The effect of a rapid internal magnesium diffusion synthesis on the electrical, magnetic, and microstructural properties of binary MgB2 bulk samples has been investigated. We have used a laboratory-made induction furnace to reduce the reaction time, typically of many hours, to fewminutes. We report a comparison between two samples reacted at the same temperature with the induction furnace and with a commercial resistance oven. We have observed that the critical temperature and the width of the superconducting transition are not affected by the heat treatment. The induction heating leads to an increase of the critical current density at high fields, correlated with an enhancement of the upper critical field. This paper exposes the potentiality of the proposed fast process, which allows tuning the parameters of the heat treatment in ranges that would not be accessible with traditional ovens. The technique can be scaled for the preparation of wires and powders. [ABSTRACT FROM AUTHOR]

A transformer type field shielding superconducting fault current limiter (SFCL), which is made of rare-earth bariumcopper-oxide (REBCO) for primary and secondary windings, is designed andmade for demonstration of not only fault current limiting but also power system stability improvement performance. A lab-scale test power system consists of one machine (18.26 kVA, 200 V) and double transmission route to an infinite bus. The simulated fault occurs at the sending end of one of the transmission route and after a certain time (fault clearing time), the fault route was rejected by circuit breakers. While the clearing time is short, the generator can continue to operate with one healthy transmission route, however, it becomes longer than a certain time critical clearing time (CCT), the generator loses its synchronism and fails into step out. The test SFCL was installed at the generator side bus of the fault route. The peak fault current was reduced to less than half of that without SFCL and the generator terminal voltage did not fall below 20% of rated voltage. It was confirmed experimentally that CCT can be enhanced by introducing the SFCL. It is confirmed that the SFCL cannot only limit the fault current but also improve the system stability. [ABSTRACT FROM AUTHOR]

Polarized Drell-Yan measurements require a strong homogeneousmagnetic field. A 2.5 T longitudinal field is generated with a superconducting solenoid carrying a nominal current of 650 A, while high homogeneity is obtained by using additional shim--and compensation coils. Since the target needs to be transversely polarized, a second main coil is required. A superconducting dipole coil encloses the solenoid and together they are integrated in a common cryostat. Field rotation, from longitudinal to transverse and vice versa, is possible by simultaneously powering both coils. During the complete procedure, the absolute field strength is never allowed to drop below0.48 T to guarantee a high polarization percentage. In the meantime, the forces between the coils need to be controlled, and therefore the coils cannot both be carrying the nominal operational current, since this will destroy the system. The magnetic field rotation procedure is therefore uniquely developed for this system. In this paper, the magnet system is described and a summary of the operational experience gained during data taking is provided. [ABSTRACT FROM AUTHOR]

The no-insulation (NI) winding technique to improve the transient stability of high-temperature superconducting (HTS) magnets has been studied and a cowinding method using a metallic tape was tested. Normally, the operating current in NI HTS coils is bypassed into the transverse direction due to the normal region generated within the coils. Therefore, a method that controls such current bypassing into the turn-to-turn direction of NI HTS coils was investigated as a means to regulate the effective number of turns. In this study, we experimentally investigated the characteristics of current bypassing in the transverse direction within a test coil wound with a GdBCO tape. First, to find an optimized heater location, a 20-turn HTS pancake with two partial insulation shapes was prepared and tested experimentally. The current bypassing characteristics in the normal region created by heaters (strain gauges) were studied while varying the number of heaters, heater positions, and the amount of heating at liquid nitrogen temperature. Using both short and long heating periods, we found that we could effectively control the number of turns (coil inductance) via long-duration heating. [ABSTRACT FROM AUTHOR]

Identifying the location of an electrical fault (mainly short-circuit or circuit break) in close systems, such as superconducting magnet, is very difficult, especially when a problem appears only at cold conditions (no resistance). The time domain reflectometry (TDR) method could be useful notwithstanding that there is a commonly known limitation on the use of TDR to test the inductive circuit results of the high attenuation of incident and reflected pulses. This paper describes a method for locating electrical faults in superconducting magnets by means of measurements of the pulse response of magnet coil circuits (TDR principle). As a result of adapting TDR to test a circuit characterized by high values of equivalent capacitance and inductance, which is a winding of superconducting magnet, a study of the relationship between the frequency response of magnets and the injected pulse transient parameters is presented. The cutoff frequency of the investigated circuit is crucial information for pulse shaping. A TDR reflectometer with a pulse shaping circuit is described. The instrument consists of commonly available laboratory-measuring equipment: a pulse generator and a 50-MHz oscilloscope, which significantly facilitates the performance of the measurements. Test measurements were carried out for both the undamagedmagnets and themagnets with various locations of coil shorts. Advantages and limitations of the proposed method are discussed. [ABSTRACT FROM AUTHOR]

The high-temperature superconducting (HTS) bulk is the core component of HTS maglev systems. For the potential application of evacuated tube transportation, it is necessary to verify the loading capacity of the bulk under a low-pressure environment. Based on a home-made pressure-reducing platform, we investigated the levitation force of two kinds of typical bulks, that is, the same sized YBaCuO and GdBaCuO, above a Halbach permanent magnet guideway under different pressure conditions. The levitation force in the cases of zero-field-cooling (ZFC) and fieldcooling (FC) were measured and analyzed. Experimental results show that the reduced air pressure can significantly improve the levitation force of the two kinds of bulks. The levitation force of YBaCuO and GdBaCuO has increased by 11.6% and 4.4% in the FC case, 20.3% and 13.7% in the ZFC case under 20 kPa compared with the atmospheric pressure (100 kPa), respectively. This universal phenomenon was explained by the increasing critical current density Jc of HTS bulks due to cooler liquid nitrogen under the low-pressure condition. It is interesting to find that the YBaCuO bulk was more sensitive to the pressure variation compared with the GdBaCuO bulk. This difference reflects the improvement extent of levitation force of HTS bulks with different Jc performance working in a low-pressure environment. [ABSTRACT FROM AUTHOR]

Fluxmodulation permanentmagnet machines (FMPMMs) exhibit many superiorities over regular permanent magnet machines (PMMs), such as simple and robust configuration, high torque density, and efficiency; thus they are promising candidates for the motors in wind turbine powertrains, electric vehicles, and ship propulsion systems. However, since the PM flux linkage is almost constant, the flux-weakening capability of FMPMMs is usually inferior to that of thewound field machines (WFMs).Moreover, the power factors of FMPMMs are also lower. In order to incorporate the merits of FMPMMs and WFMs, this paper proposes a double-stator flux modulation machine with low-temperature superconducting field windings, which can exhibit higher torque density, stronger flux weakening capability, and larger power factor than the conventional FMPMMs. The configurations and working mechanism of the proposed machine are introduced, and its key performances are comparatively analyzed to a regular FMPMM based on a finite-element algorithm. [ABSTRACT FROM AUTHOR]

comprehensive study of upper critical (Hc2) and irreversibilitymagnetic fields (Hirr ) in (Ba0.6 K0.4 )Fe2As2 (critical temperature Tc = 38.3 K), Ba(Fe0.95 Ni0.05 )2As2 (Tc = 19.2 K), Ba(Fe0.94 Ni0.06 )2As2 (Tc =18.5 K),Ba(Fe0.92Co0.08 )2 As2 (Tc = 23.2 K), and Ba(Fe0.91Co0.09)2As2 (Tc = 25.3 K) polycrystalline bulk pnictide superconductors with different average grain sizes was made in pulsed fields at the Los Alamos National Laboratory. Themagnetic field-temperature (Hc2 -T) phase diagramswithHc2 as high as 65 T at 28Kfor theK-doped samples and critical current density (Jc) measurements as high as 105 A/cm2 for the smallest, submicrometer grain size samples were obtained. The high Hc2, Hirr, and Jc data show the suitability of these materials for magnet design as their mechanical strength and random grain alignment show promise in the manufacturing of next-generation magnets. [ABSTRACT FROM AUTHOR]

The large hadron collider (LHC) at CERN has been operating and generating physics experimental data since September 2008, and following its first long shut down, it has entered a second, 4-year-long physics run. It is to date the largest superconducting installation ever built, counting over 9000 magnets along its 27-km long circumference. A significant operational experience has been accumulated, including the occurrence and consequences of electrical faults at the level of the superconducting magnets, as well as their protection and instrumentation circuits. The purpose of this paper is to provide a first overview of the most common electrical faults and their frequency of occurrence in the first years of operation, and to perform a statistical analysis that can provide reference values for future productions of similar dimensions and nature. [ABSTRACT FROM AUTHOR]

Mainly used in ac grids, resistive-type superconducting fault current limiters may be still more interesting for dc systems due to their capability to reduce high short circuit currents appearing in case of dc cable fault. This limiter reduces the breaking capability, speed, and energy requirements of the required dc circuit breaker allowing the implementation of electromechanical breakers for fault current interruption. These breakers have lower breaking capability, on-load losses, and investment costs in comparison with hybrid circuit breakers based on power electronics. This paper presents a technical and economic analysis of a superconducting fault current limiter used in a radial three-terminal high voltage dc grid to protect a cable link. Based on simulation studies using an electromagnetic transient program, an effective system protection will be demonstrated with special attention to the continuity of power flow through healthy parts of the grid. [ABSTRACT FROM PUBLISHER]

Fast magnetic field alternation is indispensable for continuous magnetic refrigeration. An active magnetic regenerative refrigerator (AMRR) utilizes magnetocaloric effect of magnetic materials which occurs during magnetization and demagnetization processes. A conduction cooled high temperature superconducting (HTS) magnet can be one of the prospective candidates as an alternating magnetic field generator. This paper describes the development effort of the cryogen-free HTS magnet for the AMRR. The magnet consists of twelve double pancake GdBCO coils which are insulated with polyimide tape. A two-stage GM cryocooler was employed to cool down the magnet. The critical current of the magnet was measured at the operating temperature before alternating current (AC) operation. In order to remove heat produced by AC loss with small temperature difference, thermal links between the cryocooler and the magnet were carefully designed. This paper presents the test results, AC loss analysis of the HTS magnet in the AMRR system. Maximum central magnetic field of 3 T (150 A) was achieved with the maximum ramping rate of 1 T/s (50 A/s). The AC loss was measured as 11.2 W at the operating conditions and the generated heate was effectively removed by the cryocooler. The AC loss was predicted by the numerical simulation and the simulation results were compared with the experimental results. [ABSTRACT FROM PUBLISHER]

We propose a new inductive- and resistive- (LR) biased low-power single-flux quantum (SFQ) circuit that has a dynamic resetting mechanism of the bias current. Because the bias current returns to the initial state rapidly by switching of a Josephson junction in the bias circuit after circuit operation, the operating frequency of the LR-biased SFQ circuit can be improved. We simulated a Josephson transmission line (JTL) that employs the proposed biasing scheme and evaluated the bias current recovery time. Circuit simulation results show that the bias current recovery time of the proposed circuit is improved by 10–20% compared to that of the conventional LR-biased JTL. We have designed and measured a 10-stage JTL and an 8-bit concurrent-flow shift register (SR) with the proposed biasing scheme. We have experimentally demonstrated operation of the JTL with the bias margin of ±29.4% at the operating frequency of up to 70.4 GHz and operation of the 8-bit SR up to 12.3 GHz by the on-chip high-speed test. [ABSTRACT FROM AUTHOR]

We develop analytical expressions for the magnetic vector potential and the magnetic field of modulated double helical coils (MDHC). It is assumed that the coils are tightly wound and can be approximated by two infinite thin current sheets. From each coil parametric equation, the surface current density is derived by considering the turn-to-turn spacing. The field inside and outside each coil is then calculated by decomposing the surface current density into three contributions. By summation, the field of any MDHC can be obtained. As a validation, we evaluate the field of a superconducting double helical quadrupole. A good agreement is found between analytical and numerical results. From the field, the main coil parameters can be quickly estimated with a fair accuracy. This can be useful for the design an optimization of advanced magnets, both conventional and superconducting. [ABSTRACT FROM PUBLISHER]

Design activities on the helical-type fusion DEMO reactor, FFHR-d1, are progressing at NIFS. A 100 kA current-capacity is required for the helical coil conductors under the maximum magnetic field of \sim13 T. High-temperature superconducting conductor has been proposed as one of the conductor options for the FFHR-d1 magnet. In this study, a 30 kA class HTS conductor sample has been fabricated and tested. The sample had no current feeders and the current was induced by changing the background magnetic field generated by the 9 T split coils in the cryostat. Rogowski coils and Hall probes were used for the measurement of the transport current of the sample. The critical current of the sample was measured at various temperatures and bias magnetic fields. To verify the self-field effect of the sample, a numerical analysis was performed by considering the current and magnetic field distribution among the tapes self-consistently. The analysis result was compared with the experimental observation. [ABSTRACT FROM PUBLISHER]

The pressure head necessary for the forced convection of supercritical helium (SHe) across the ITER superconducting (SC) magnet system is generated by centrifugal-compressor type cold circulators. From the viewpoint of the cryogenic system, simulation results indicate that the main challenge of the ITER Central Solenoid (CS) operation is the peaking pressure head of SHe across the cold circulator induced during the rapid ramping of electrical current on the coils. Excess variation in pressure head will push the operation point of the rotating machine beyond the surge line in the compressor map which can trip the circulator and in the worst case result in damages. Therefore, in order to avoid the occurrence of a surge, it has been proposed to open adaptively a cryogenic valve, installed in parallel with the CS cooling channels, during the high pressure head instances. Such an action creates an additional flow channel which consequently suppresses the pressure head peak. The proposed strategy has been numerically benchmarked and tests have been performed in existing cryogenic facilities. In this paper, we will present the test results of pressure head mitigation across the cold circulator dedicated to the KSTAR CS and Poloidal Field (PF) coil cooling circuit with the main purpose of demonstrating the safe operation of the ITER CS circulator as well as cooling circuit during plasma shots. The tests were performed by progressively increasing the coil by-pass valve opening during identical PF/CS current shots and monitoring the tendency of the maximum pressure head variation across the cold circulator. Also, preliminary results of pressure head mitigation during real plasma experiments will be introduced. [ABSTRACT FROM PUBLISHER]

High strength and high electrical conductivity Cu–Nb tape was tested as the new type of stabilizing layer for YBCO-coated conductor. For electrical interconnection of stabilizing layer to coated conductor the soldering process was used and no degradation in critical current, Ic, of laminated coated conductor after soldering process was observed. The dependence of normalized transport critical current, Ic/Ic0, on the bending radius of coated conductors with and without Cu–Nb stabilizing layer was investigated using the bending test probe providing the uniform bend process at 77 K and under self-field conditions. The reversible and irreversible variations of Ic/I0 with inverse bending radius were found and the irreversible bending radius limit was observed to depend on the neutral axis shift. The generation of the cracks appears to be the primary reason for the Ic/Ic0 degradation that was supported by ScanHall technique investigations. [ABSTRACT FROM PUBLISHER]

ASIPP will supply for ITER all the current leads. There are three types of high temperature superconducting (HTS) current leads designed to carry 68 kA, 55 kA, or 10 kA to the ITER magnets. Different from the trial leads manufactured and tested in Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP), some critical technologies were qualified before the manufacturing of the ITER leads could commence, including: 1) welding, brazing, and soldering qualification; 2) fin type heat exchanger (HEX) with tight assembly tolerance; 3) low temperature superconducting (LTS) linker with cables soldered to the 5 K copper terminal; 4) instrumentation mock-up for the temperature and voltage test. In this paper, the outcome of these qualification activities will be reported together with the plans for the series production planning and development. [ABSTRACT FROM PUBLISHER]

Nonuniformity of critical current, Ic is one of the most important factors to be considered for the practical applications of high-temperature superconducting (HTS) REBCO coated conductors. To investigate the variation of Ic due to mechanical strain, local critical currents were measured at various tensile strain values from 0 to 1.2% for brass-laminated GdBCO tapes at 77 K, and analyzed using the Weibull distribution function. Measured local critical currents vary and decrease significantly at strain levels above about 0.8%. The Weibull function with three parameters turned out to be applicable for describing the Ic distribution of REBCO HTS wire for the entire strain range. The statistical minimum Ic calculated from the Weibull distribution function decreased with increased tensile strain. The degree of Ic variation was observed to drastically increase when the applied tensile strain exceeded the irreversible strain of about 0.8%. [ABSTRACT FROM PUBLISHER]

In this contribution, we develop a refined numerical model of pancake coils assembled from a coated conductor Roebel cable, which includes the angular dependence of the critical current density Jc on the magnetic field and the actual (three-dimensional) shape of the current lead used to inject the current. Previous works of ours indicate that this latter has an important influence on the measured value of the AC losses. For the simulation of the superconductor, we used two alternative models based on different descriptions of the superconductor’s properties and implemented in different mathematical schemes. For the simulation of the current lead we use a full three-dimensional finite-element model. The results of the simulation are compared with measurements and the main issues related to the modeling and the measurement of Roebel coils are discussed in detail. [ABSTRACT FROM PUBLISHER]

\REBa2\Cu3\Ox (REBCO, RE = rare earth) coated conductors are expected to show high performance for superconducting applications because of their high current density and high mechanical strength. Fujikura has developed REBCO coated conductor over 570 A/cm width at 77 K, self field with over 800 m length. In addition, we have succeeded in developing a 5 T cryocooled REBCO magnet with a stored energy of 426 kJ. The magnet is composed of 24 pancake coils with an inner diameter of 260 mm, and the total length of the REBCO coated conductors is approximately 7.2 km. We confirmed that the REBCO magnet could be excited up to 5 T for 720 min 9 months after the fabrication of the magnet. It is important to validate the long-term operation test results of the REBCO magnets with larger diameters in order to use these conductors in practical superconducting applications. On the other hand, we have fabricated and evaluated a model magnet before we fabricated a 426 kJ cryocooled magnet. The model magnet is composed of 6 REBCO pancake coils and 18 “dummy coils” with an inner diameter of 260 mm and an outer diameter of 515 mm. The model magnet is about the same size and shape as the 426 kJ cryocooled magnet. We have confirmed that the calculated critical current (Ic) of the top pancake coil of the model magnet was in good agreement with the measured coil Ic from 30 to 77 K under the conduction-cooled conditions. In addition, we have evaluated the thermal runaway behavior of the model magnet under the conduction-cooled conditions. As a result, we have confirmed that the model magnet with a 0.3-mm-thick copper stabilizer had sufficient time to ramp down without degradation at 361 A transport current after the detected normal transition. [ABSTRACT FROM PUBLISHER]

For economic reasons high-temperature superconductor (HTS) machines, such as HTS motors and generators, are designed to use an iron core to reduce the HTS tape length. In these situations, the HTS tapes are positioned in the iron core and transport the ac current within the ac leakage magnetic field. We investigated the influence of the iron core arrangement on ac loss characteristics. We modified the iron core of a transformer by removing a rectangular segment and then positioned an HTS tape in the rectangular recess created. The iron core was affected by the ac magnetic field generated by the ac coil, and the HTS tape transporting the ac current. We placed the HTS tapes in different rectangular positions and varied their shape. In all conditions, the ac transport current losses were greater than losses experienced when the HTS tapes were situated without the iron core, and the ac leakage magnetic fields produce ac magnetization losses. Therefore, how the HTS tape is arranged in the iron core affects the ac loss characteristics and merits further study. [ABSTRACT FROM PUBLISHER]

After the commercialization of REBCO-coated conductors, a number of REBCO coils have been fabricated targeted toward various magnet applications. One of the major technological problems is degradation in coil performance such as in the critical current, due to delamination of the REBCO-coated conductors in epoxy impregnated windings. A number of effective methods to prevent such degradation have been proposed by several groups including our laboratory. However, detailed mechanisms of those methods have not been definitively clarified and thus they have not been technologically categorized in REBCO coils technology. In this paper, we discuss these mechanisms, focusing on the effects of different mixture ratios of curing agent and epoxy prepolymer on the performance of epoxy-impregnated coils. Also, a direct interaction between the YBCO layer and epoxy at room temperature was investigated for short wire samples. The results showed that a REBCO coil impregnated in epoxy prepolymer has no degradation in critical current. The degradation of the coil was induced by the addition of the curing agent, and the critical current was decreased by the increase in the amount of the curing agent. The direct effect shows a decrease in the critical current with the increase of the impregnating duration. The optimum conditions with the impregnating duration were investigated to protect the wire from the direct interaction. [ABSTRACT FROM PUBLISHER]

We measure transport ac losses in planar one-layer four-turn parallel coated conductor arrays (1 \times 4) and in two-layer (2L) four-turn parallel coated conductor arrays (2 \times 4) with a frequency up to 1 kHz. The horizontal separation between the conductors, i.e., gh, and the vertical separation between the neighboring superconducting layers, i.e., gv, were varied to investigate the transport ac loss dependence on gh and gv. In 2L arrays, the tapes in the top layer sit either aligned with the tapes in the bottom layer or aligned with the gaps between the tapes in the bottom layer. We show that the losses differently scale in arrays with low turn numbers to the scaling expected with an infinite array of tapes. [ABSTRACT FROM PUBLISHER]

In this paper, we report a new synthesis route to produce boron powders characterized as being amorphous and having very fine particle size. This route has been developed to improve the performances of superconducting \MgB2 powders, which can be directly synthesized from this nanostructured boron precursor by following the ex-situ or the in-situ PIT method during manufacturing of tapes, wires, and cables. All the procedure steps are explained, and the chemical–physical characterization of the boron powder, using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques, is reported. Furthermore, a comparison with commercial boron is given. Preliminary results of the magnetic and electrical characterization, such as critical temperature TC and transport critical current density JC\, t, for the \MgB2 tape are reported and compared with those for the tape prepared with commercial boron. [ABSTRACT FROM PUBLISHER]

In this paper we extend the recently developed CtFD strategy for the analysis of the thermal-hydraulics of a meander flow type heat exchanger, validated against the Wendelstein7-X (W7-X) High Temperature Superconductor (HTS) current lead prototype experiment, to the case of a heat exchanger for a 68 kA HTS current lead. We aim to assess the optimized operative conditions and the influence of different geometrical configurations on the performance of the heat exchanger. [ABSTRACT FROM PUBLISHER]

This paper aims to study the feasibility of improving pulsed current output by using High temperature superconducting (HTS) air-core transformer. Based on the theoretical analysis, the simulations are done. Results of the simulations indicate that the HTS air-core pulse transformer can magnify the output current magnitude and accelerate the velocity of discharge. However, when a series of inductor modules use the same one HTS air-core transformer, the residual current may influence the discharging waveform. To eliminate residual current, self-coupling discharging model is proposed. The simulated and experimental results illustrate that a self-coupling model can eliminate the residual current effectively. The results of this analysis contribute to the research of superconducting inductor pulsed current output. [ABSTRACT FROM PUBLISHER]

This paper describes new kind of HTS (High Temperature Superconducting) element for current leads, which can transfer large electric current in the nuclear fusion system. Since the HTS tapes have no resistance and the generated Joule heat is also very small compared to the conventional current leads, cooling costs of the current leads can be reduced. For this reason, the various feasibility researches for HTS current leads have been promisingly progressed in the superconducting power applications. However, there is a limitation on the capability of current carrying for single HTS tape. In addition, the cross-sectional area of the current leads should be small enough to minimize the heat conducted through the HTS current leads. In order to improve the current carrying capacity of the current leads, multiple HTS tapes are required. In this paper, we proposed several structures of compact HTS current leads and compare them other 2 kA class current leads. We report on the calculated characteristics of stabilized HTS current leads and on the performance measured during critical current measurement tests. [ABSTRACT FROM PUBLISHER]

The GENI project for applying the 22.9 kV HTS cable and the SFCL to real power system has been progressed in South Korea since 2008. The HTS power devices were applied to the Icheon substation in the real Korean power grid in August 2011. This is the first demonstration of HTS power devices in South Korea. For a successful application, this paper proposes proper specifications of a current limiting resistor/reactor and an activating current for the 22.9 kV SFCL in the Korean power distribution system. These specifications are determined, considering the protection system of real Korean power system. [ABSTRACT FROM PUBLISHER]

Japan Atomic Energy Agency (JAEA) has fabricated and tested the four conductor samples composed of high performance Nb3Sn strands manufactured by the bronze-route process for the ITER Central Solenoid (CS) conductor. The current sharing temperature (Tcs) electrically assessed at 45.1 K and 10.85 T along the cycling loading at 48.8 kA and 10.85 T initially were 6.0 K and 6.1 K, and then 5.3 K and 5.5 K after 6000 cycles for the first SULTAN sample named JACS01, respectively. As results of second SULTAN sample named JACS02, the Tcs values initially were 7.2 K and 6.8 K, and then 6.6 K and 6.1 K after 10000 cycles for each conductor, respectively. The Tcs degradation was not saturated at the end of the test campaign. From the destructive observation, the large bending at the low transverse loading side in the high field zone was observed. The strand buckling and accumulating by slipping between the cable and the jacket are considered. [ABSTRACT FROM PUBLISHER]

Recently, many HTS-SMES systems have been designed and investigated in many countries. They usually consist of some superconducting element coils owing to effectively storing excessively high energy. If one of the superconducting element coils transition into a resistive state, the energy stored in the resistive superconducting element coil has to be immediately dispersed by a shunt resistor to prevent the superconducting conductor from burning. However, the electromagnetic behavior of the HTS-SMES with some resistive superconducting element coils has not yet been well investigated. Therefore, we have developed a simulation code to investigate the electromagnetic behavior of the HTS-SMES magnet after one or more superconducting element coils transitions into the resistive state. In the simulation, the magnetic field analysis and the electrical circuit analysis are coupled with the critical current calculation considering the B-J-\theta characteristics of HTS tape. By the electromagnetic simulation, it is indicated that a chain of quenches is caused by the quench of one element coil. [ABSTRACT FROM PUBLISHER]

The second generation (2G) HTS conductors, the YBaCuO Coated Conductors, show very exciting performances in terms of critical currents under very high fields whereas their mechanical properties, the key issues for very high field magnets, are outstanding for the IBAD (Ion Beam Assisted Deposition) route. Preliminary measurements have shown critical currents Ic above 500 A at 15 T and 4 K on commercial YBCO coated conductors. They are now available in reasonable length and manufacturing focus to provide reliable, consistent performance conductors. With these high critical current and tensile strength above 600 MPa, these conductors are very promising for making HTS superconducting coils able to generate very high field. But very few characterizations exist above 20 T. LNCMI is one of the few facilities in the world where such measurement can be performed. [ABSTRACT FROM PUBLISHER]

The Cable-In-Conduit Conductor (CICC) is the most promising one for large scale fusion magnets. Now it has been adopted as conductors for ITER magnets. Although the conductor has good mechanical strength against large electromagnetic force, the performance is not so good because the Nb3Sn strands are fragile and the critical current density is sensitive to strain. Because conductor is composed of hundreds or thousands of strands which are twisted and become tangled, the strands experience extra-bending during energizing magnets. It seems so difficult to analyse plastic deformation of the strands of whole conductor. Our approach to calculate it is unique in terms of using structural mechanics called “Beam Model” based on the measured strand traces inside the conduit. The calculated traces provide us the local curvatures of strands under electromagnetic force. This leads to the evaluate the conductor performance such as Ic degradation. [ABSTRACT FROM PUBLISHER]

In order to investigate superconducting properties such as long decay time constants, current imbalances and critical current degradations, we need detailed information about all strand locations in the cable-in-conduit conductor (CICC), and hence we develop a new estimation method to obtain all strand locations. It is very difficult to estimate all strand positions because all strands in the real CICC are squeezed into the conduit and are not regularly arranged but displaced. In order to estimate these strand displacements due to the compression, we introduce mechanical potential energy among strands, and hence we search the minimum energy locations which should be realized in the conductor. In order to calculate this process, we perturb all strands from the original locations and continue these processes by using a genetic algorithm until the potential energy is minimized. This analytical method is very useful to simulate all strand positions and allows us to investigate all the electromagnetic phenomena in the CICCs. [ABSTRACT FROM PUBLISHER]

A benchmarking experiment was conducted to compare strain measurement facilities at the National Institute of Standards and Technology (NIST) and the University of Twente. The critical current of a bronze-route Nb3Sn wire, which was fabricated for the International Thermonuclear Experimental Reactor (ITER), was measured as a function of axial strain and magnetic field in liquid helium at both institutes. NIST used a Walters' spring strain device and University of Twente used a bending beam (“Pacman”) apparatus. The ITER bronze-route wire investigated had a very high irreversible strain limit that allowed comparing data over a wide range of applied strain between -1% and +1%. Similarities of the data obtained by use of the two apparatuses were remarkable, despite the many differences in their design and techniques. [ABSTRACT FROM PUBLISHER]

Quantity of consumed electricity is increasing due to increase of population and industrial development. Consequently, fault current is increased during occurrences of faults. For restricting these fault currents, in this paper, recovery characteristics per types of faults was analyzed by applying reclosing motion to 3-phase transformer type superconducting fault current limiter. Established reclosing cycle (CO-t-cycle-CO-t-cycle) is 5-10-7-20-5 cycle. (C: Close, O: Open) Electricity burden of SFCL is different according to types of faults. So, according to turn ratio, a test was carried out with regard to fault current limit per types of faults and recovery characteristics. In single line-to-ground fault and in double line-to-ground fault, it could be confirmed that it limits electric current because fault current of fault phase provides impacts on coiling wire of different sound phase. And it was also confirmed that fault current limit rate is lowered during double line-to-ground fault instead of single line-to-ground fault. When it is triple line-to-ground fault, it was confirmed that size of fault current limit of T-phase is lower than R-phase and S-phase. In addition, it could be confirmed that size of fault current limit is lower the more transformer secondary stream turn ratio is smaller. Also, it was also confirmed that time of recovery of superconducting element became shorter in open cycle the more turn ratio per types of faults is smaller. And power consumption affecting superconducting element was related to recovery time. [ABSTRACT FROM PUBLISHER]

MRI magnets and other magnets that have a low current and high self-inductance are passively quench-protected with a system that includes sub-divided coils with resistors and diodes that are in parallel with sections of the coils. The primary purpose of coil sub-division is to protect the coil from the high voltages that can occur during a quench. In the event of a lead failure (conventional or superconducting) between the coil and its power supply or its persistent switch, the total current in the coil flows through the diodes and resistors in parallel with the coil. When a lead fails, the current decay time constant for the coil current can be quite long. It is desirable that the coil quench in a time that is short compared to the coil current decay time constant. Experience shows that the heating from the resistors and diodes will eventually quench the magnet. This paper presents methods for shortening the time between a lead failure or a persistent switch failure and the eventual magnet quench. [ABSTRACT FROM PUBLISHER]

Among superconducting fault-current limiters (FCLs), the inductive type has some distinctive merits such as large design flexibility due to the turn ratio, isolation between a current-limiting device and a power transmission line, and low heat losses. This paper highlights the future perspective for an inductive-type superconducting fault-current limiter (LSFCL) by using an autotransformer (AT) in closed- and open-core schemes. These are considered technically feasible and economically viable alternative for the LSFCL in terms of compactness, efficient limitation, and lower alternating-current losses, which prove to be a construction cost-effective means of fault-current management. In the hybrid scheme, a diode-bridge-type SFCL is integrated with an AT-based LSFCL. The above is accomplished by advanced numerical techniques and, hence, simulation studies in a sample distribution system to realize the significant efficiency improvement of the superconductor-based technology. [ABSTRACT FROM AUTHOR]

This paper proposes a reliability model for a superconducting fault current limiter (SFCL), which is a new alternative in limiting the fault current recently increasing in a network. An evaluation technique for distribution reliability that uses the improved failure rate of all protective devices in a network, depending on the location of the SFCL, is also proposed. As a result, it is expected that the SFCL makes the reliability of adjacent equipment on an existing network improve, and these changes are analyzed. In addition, in order to apply the effect of the intermittent output of renewable-energy sources, distribution reliability indices were redefined in this paper. Case studies verify that the SFCL is effective in reducing fault currents and improving distribution reliability. These effects are analyzed with respect to the location of the SFCL in a case study system. [ABSTRACT FROM AUTHOR]

A new method based on the principle of magnetic circuits is proposed and realized for continuous Ic examination of HTS tapes. The greatest advantages of the new method are that it first eliminates all the noise caused by mechanical fluctuations, and thus makes high speed and high stability measurement possible, and second has a natural ability to measure HTS tape with a magnetic substrate. The principle of the method is introduced with the help of Finite Element Analysis. An apparatus for examination of kilometer long tapes has been constructed, by which continuous Ic examination for a YBa2Cu3O7-x tape with and without a magnetic substrate and a Bi2Si2Ca2Cu3Ox multi-filamentary tape is reported. [ABSTRACT FROM AUTHOR]

We developed a non-destructive and contactless system for measuring the critical current (Ic) in YBa2Cu3O7-\delta (YBCO)-coated conductors by using a permanent magnet (Sm2Co17). This Ic measurement method is based on the repulsive force (Fr) between the magnet and the shielding current in high-temperature superconductor-coated conductors. We measured Fr using a high-resolution load sensor and found that accurate Fr could be determined without the effect of thick copper film on the YBCO thin film and Hastelloy tape of the substrate. We can determine Ic from Fr0, which is the maximum repulsive force determined from an extrapolated value of the Fr vs. L curve for L=0\ \ mm, described in our previous paper [1]. We show that the permanent magnet method can be used to determine the longitudinal Ic distribution and large-scale defects in YBCO-coated conductors. In addition, it turned out from this experiment that the permanent magnet method was effective to rapidly measure the longitudinal Ic distribution of long-scale coated conductors. [ABSTRACT FROM AUTHOR]

Superconducting fault current limiters (SFCLs) are expected to improve the reliability and stability of power systems. We have proposed new design of a transformer type SFCL whose primary and secondary superconducting coil has rewound structure. The fundamental characteristics of the proposed SFCL were investigated using a small model designed and made with BSCCO wire. This paper describes on the power system characteristics of the proposed SFCL with rewound structure. The basic experiments were carried out by use of the model SFCL in a laboratory scale power system (one-machine and infinite bus system). It was confirmed that the proposed SFCL successfully limited the fault current and suppressed the voltage drop of the generator and recovered quickly even in repetitive limiting operation. [ABSTRACT FROM AUTHOR]