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Comparative studies on the Ag-clad 27-filamentary Bi-2223 tapes deformed under different conditions have been carried out using ac susceptibility and critical current measurements. Hot pressing improves the grain alignment and grain connectivity, resulting in a noticeable improvement in the critical current density in the low field region. However, the irreversibility line for the cold pressed Ag/Bi-2223 tape is positioned at higher temperatures than that for the rolled tape which is in turn positioned at higher temperatures than that for the hot-pressed tape. These results indicate that the hot deformation is only beneficial to the improvement of weak links whereas the cold deformation induces more defects which act as pinning centres in these tapes, responsible for the improvement in flux pinning. [ABSTRACT FROM PUBLISHER]

Bi-2212/Ag tapes have been produced using a continuous dip coating and partial melt processing technique. The role of the annealing and melt processing temperatures on the microstructure and current-carrying properties of the tapes are reported. In particular, the effect of a pre-anneal heat treatment on the residual carbon content from the organic binder has been investigated, in order to improve critical currents. These results have been used to optimise the temperature profile of a multiple-zone tube furnace through which continuous melt processing of the tape is possible. Multiple metre lengths of superconducting tape have been produced and wound into coils. Critical currents of 8.3 A in statically processed tapes and 1.9 A in continuously processed tapes have been achieved at 77 K, zero field. [ABSTRACT FROM PUBLISHER]

The critical current density (J/sub c/) is very sensitive to the maximum temperature (T/sub m/) used to melt process Ag-sheathed Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ tapes. In this study we have found that the optimum T/sub m/ was 894-896/spl deg/C and that variations of /spl plusmn/2/spl deg/C strongly decreased J/sub c/. We found that the density of the oxide core and its Vickers hardness displayed a maximum in tapes that had been processed at the optimum T/sub m/. In addition, the room temperature electrical resistivity of the core was lowest for the tapes with the maximum J/sub c/ at 4.2 K. A formation of macropores was observed in tapes processed at T/sub m/ above the optimum one. MO imaging and SEM observation showed that the magnetic flux penetrates more easily into tape areas containing macropores. Together these observations show that T/sub m/ exerts a very powerful effect on the macroscopic density of the oxide core, this controlling the connectivity and the effective cross-section of the oxide core. Thus J/sub c/ depends on T/sub m/ primarily because the effective cross-section of the core depends on T/sub m/. [ABSTRACT FROM PUBLISHER]

Silver-sheathed powder-in-tube processed tapes and thick films of the Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub 8/spl plusmn//spl delta//-type (Bi-2212) superconductor have been annealed under high temperature, high oxygen fugacity (i.e.fO/sub 2/>0.1 MPa) conditions. At sufficiently high temperatures and oxygen fugacities, the Bi-2212 phase decomposes into a mixture of solid oxides: a Bi/sub 2/(Sr,Ca)/sub 2/Cu/sub 1/O/sub 8/spl plusmn//spl delta//-type (Bi-2201) phase, an alkaline-earth bismuthate Bi/sub 9/Sr/sub 1/1Ca/sub 5/O/sub y/-type (Bi-91_1_5) phase and CuO. Subsequent reformation of Bi-2212 in pure, flowing oxygen at 0.1 MPa and 860/spl deg/C has yielded plate-like grains with enhanced 00l texture (as discerned from X-ray pole figure analyses and electron microscopy). The values of oxygen fugacity leading to sub-solidus decomposition and reformation of Bi-2212 at 500 to 860/spl deg/C are given. XRD and SEM analyses, as well as preliminary critical current measurements of decomposed and reformed Bi-2212 tapes, are presented. [ABSTRACT FROM PUBLISHER]

The effect of the Sr/Ca ratio and Bi content on the microstructure and J/sub c/ of Ag-sheathed 2212 tapes was studied. Changing the Sr/Ca ratio changed the melting temperature of 2212 phase, the phase assemblage in the melt, and the nonsuperconducting phases in the fully processed tape. In tapes with Sr/Ca=2.75, the 2201 phase crystallizes from the melt before 2212 during cooling, and this 2201 remains in the microstructure. In tapes with Sr/Ca=1.3, there is more liquid left after cooling, and it converts to 2201 as the tape cools to room temperature. Fully processed tape with overall composition 2.1:2:1:2 had the most homogeneous microstructure and highest J/sub c/. [ABSTRACT FROM PUBLISHER]

Many applications of superconductors are limited by low values of the engineering critical current density (J/sub cc/). Significant improvements are possible through the merger of green tape and composite reaction texturing technologies. Tape casting and elastomer processing techniques have produced insulating (MgO and Al/sub 2/O/sub 3/), conducting (Ag) and superconducting (Bi-2212+MgO-fibre) tapes with uniform thickness ranging from 0.1-2 mm. Green tapes of the desired thickness can be laminated into multilayer structures and co-reacted; the superconducting layer occupying over 50% of the cross section allows the engineering of an artefact for optimal I/sub c/, and maximum J/sub c/c. The texture observed in the Bi-2212 layer is induced by specifically aligned MgO-fibres. As a necessary step in developing this technology, results are presented on (1) additions of 0-10 %wt Ag to Bi-2212 in order to modify its partial melt behaviour, (2) control of the shrinkage and densification of individual layers which is critical to uniformity and (3) chemical buffering of the Bi-2212 layer from insulating layers of doped MgO and Al/sub 2/O/sub 3/ during co-reaction. [ABSTRACT FROM PUBLISHER]

GE manufactured Nb/sub 3/Sn tape was examined to determine the influence of critical temperature, both conductor and coil current density (J/sub c/), and tape width on flux jump stability. The onset of flux jump instability was measured in 3 mm wide, copper stabilized tapes reacted to a range of critical currents (I/sub c/) above and below the normal I/sub c/ in production tape. These tapes were stacked in approximations of coil cross sections with and without Insulating interlayer glass cloth. Production tape, 3 mm wide, was found to be stable above 9 Kelvin (K) with normal quantities of interlayer glass when reacted to yield an I/sub c/ no greater than 482 amps at 5 Tesla (T) and 4.2 K. To evaluate low temperature operation in the range of 4-5 K, consistent with cryocooler advances, narrower width tapes were studied as decreasing tape width will decrease the flux jump stability temperature. Flux jump stability was measured in identically reacted tapes slit to 3.0, 2.5, 2.0 and 1.5 mm. The 1.5 mm tape was found to be stable above 6.5 K. Slitting edge damage in the narrow widths was found to be similar for all widths of tape. The I/sub c/ of the narrower tapes were predictably reduced. Decreasing coil current density also decreased the flux jump stability temperature. Nb/sub 3/Sn tape, 3 mm wide, cowound with copper into a solenoid was tested to evaluate lower temperature operation. The coil was stable during both ramping and operation near the short sample I/sub c/ of the tape at 4.2 K. [ABSTRACT FROM PUBLISHER]

One goal of our research is to be able to manufacture high temperature superconducting cables for power transmission. The key elements is the production of superconducting tapes using the oxide powder in tube process. If quality and critical current density of the tapes can be improved, the quality and capacity of the final cable will also be improved. In this work we have calcinated the powder used in the powder in tube process at different temperatures and the microstructure of ceramic phase has been studied after rolling and after two annealings. It is observed that the powder calcination temperature has a strong influence on the microstructure, that is the arrangement and growth of superconducting phases as well as the secondary phases. It is found that the amount of big secondary particles is lowest for calcination temperatures of 820-830/spl deg/. Better crystal growth and grain sintering during first and second annealing are also observed for these calcination temperatures. [ABSTRACT FROM PUBLISHER]

We have studied the effect of wire drawing and cold rolling on the texture development of precursor (Bi,Pb)2Sr2CaCu20x (2212) phase and its influence on the subsequent (Bi,Pb)2Sr2Ca2Cu30y (2223) phase texture in Ag-clad tapes. A mixture of (Bi,Pb)2Cu04 and SrCaCu03 powders having an overall 2223 composition was reacted to form the 2212 phase at different stages of deformation. X-ray diffraction peak height analysis was used to quantify the 2212 texture F2212= I(OOS)/[I(OO8)+I(115)] at various oxide filament thickness. Wires containing powder reacted to the 2212 phase prior to loading into a Ag tube had F2212≈0.3 after drawing. This texture increased to F2212=0.7 upon rolling. Two other composites reacted to the 2212 phase immediately after drawing, and after being drawn and partially rolled, had worse initial textures, but improved during rolling to FzZl2≈0.7. Samples reacted to 2212 after rolling was complete had F2212≈0.35. The results indicate that the 2212 texture reaches a maximum value of F2212≈0.7 and remains at that level upon subsequent rolling. Samples of filament thickness ≈80 μm were then reacted to form 2223. For the samples which contained 2212 that had received at least some mechanical deformation, the 2223 phase formed with a texture factor F2223 > 0.9, while the tape that contained 2212 formed after rolling developed a 2223 texture of only F2223≈0.75. The results show that there is a substantial texture enhancement upon reaction to 2223, which could be the result of either the 2223 formation mechanism or geometrically constrained grain growth. [ABSTRACT FROM PUBLISHER]

BSCCO tapes with dispersion hardened AgMg sheaths possess excellent mechanical properties but reach commonly only about 70-80% of the critical currents of Ag sheathed reference tapes. Investigating the temperature dependence of I/sub c/ and the (2223) phase content for two annealing steps on 19 filamentary Ag and AgMg sheathed tapes, characteristic differences with respect to the reaction kinetics and the resulting final phase content were found. A detailed characterization of the properties of the AgMg envelope, defining the boundary condition during the tape annealing process, gives first indications, that the oxygen exchange between filament and annealing atmosphere is modified with obviously significant influence on the phase formation kinetics and phase diagram shifts. [ABSTRACT FROM PUBLISHER]

AC losses in the transport regime were measured in Ag-sheathed (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ (Ag/2223) tapes at 77 K in the frequency range 35-180 Hz. The samples were multifilamentary, prepared by OPIT (oxide powder in tube) technique, and "concentric" prepared by the wire-in-tube technique, and they had different superconducting core geometries. Measured losses were confirmed to be hysteretic in nature in the examined frequency range. The experimental results are compared with the prediction of the elliptical and thin strip Norris model. [ABSTRACT FROM PUBLISHER]

Nb/sub 3/Sn superconductors have been fabricated using Nb/sub 6/Sn/sub 5/ intermediate compound powder synthesized by a melt diffusion process. The mixed powder of Nb/sub 6/Sn/sub 5/ and Nb was encased in a Ta tube, and then fabricated into a tape without intermediate annealing. A Cu sheath with a Ta barrier was also used for the fabrication. The Nb/sub 3/Sn tape shows a B/sub c1/ of 24.7 T at 4.2 K after the reaction at 900/spl deg/C. In addition the B/sub c2/ increased further by Ti doping. Moreover, the addition of 0.5-1.0 wt% Ge produces appreciable improvements in Tc and Jc at high magnetic fields. A Jc (Nb/sub 3/Sn) of 2.7/spl times/10/sup 4/ A/cm/sup 2/ has been obtained at 21 T and 4.2 K in the Ge-doped specimen. A small amount of Cu addition decreases the optimum reaction temperature to 800-850/spl deg/C. Present Nb/sub 3/Sn conductors seem to be useful for NMR high-field magnets as well as for refrigerator-cooled superconducting magnets. [ABSTRACT FROM PUBLISHER]

Silver sheathed Bi-2223 tapes have been investigated by transport and magnetization measurements in the temperature range between 4.2 K and 77 K for magnetic fields up to 12 T. The superconducting current through the tape can be explained by assuming a network of platelike grains coupled by weak links. At high temperatures the critical current is governed by flux creep of pancake vortices within the grains. At temperatures below 40 K this intragrain critical current exceeds the intergrain Josephson current leading to a weak link limitation in the tape. In this picture the differences between critical transport and magnetization currents can be explained by a reduction of the geometrical length scale of current loops. An improvement of the weak link current density is observed in multifilamentary wires and tapes with AgCu sheath material. [ABSTRACT FROM PUBLISHER]

The spatial current distribution in monofilamentary BSCCO-2223 tapes is evaluated numerically using the critical state model with a field dependent critical current density. The overall transport current density is the sum of the local currents which perceive different magnetic fields depending on their location within the tape. In self field a current peak in the center of the specimen occurs. This is caused by the field dependence of j/sub c/. If a monofilamentary tape is sliced longitudinally the self field effect leads to an enhancement of j/sub c/ in the slices that formed the tape edges, even though the microstructure of the monofilament itself is assumed homogeneous. Thus the fact that this enhanced current flow at the tape edges is found experimentally does not necessarily mean that the microstructure in the tape edges is better, but could be-at least in part-due to the self-field effect. In twisted multifilamentary tapes the current distribution is expected to be homogeneous since the filaments cross over the tape. The self field effect also leads to a reduction of the overall current density for use of stacks of tapes as current leads. [ABSTRACT FROM PUBLISHER]

Flux history and local inhomogeneities in j/sub c/ govern the current distribution in measured Ag-sheathed TlBaCaCuO-2212 and Bi(Pb)SrCaCuO-2223 tapes. The sausage effect and local grain density and coupling fluctuations result in inhomogeneity in j/sub c/ distribution. This is reflected in violation of axial symmetry across the tape as well as longitudinal translation symmetry along the tape. Hall probe mapping of self field component with or without presence of external field was used to achieve the data for inverse calculation of current distribution and its dynamics in response to time variation of flux. To reveal the asymmetry in j/sub c/ distribution across the tape width the method of gradient field scanning/reversing was applied. [ABSTRACT FROM PUBLISHER]

The magnetic self-flux distribution around high current mono- and multi-core BSCCO 2223 tapes with various filament configurations has been measured with a scanning micro-Hall probe. Using a simple model, the measured field component perpendicular to the tapes was deconvoluted to give an estimate of the way the transport current distributes itself across the width of the tape. From the changes in flux profile as the applied transport current is varied, the current distribution across the width of the tape can be inferred. In the untwisted tapes, the outer filaments tend to screen the inner ones and carry the bulk of the current; in a twisted sample, the current is shared more equally between filaments. [ABSTRACT FROM PUBLISHER]

The powder-in-tube (PIT) process has been widely used to fabricate long lengths of superconducting wires and tapes. However, it has been noted that the performance of long lengths of superconductor is variable and difficult to replace. To help pinpoint the possible sources of variation, a systematic study of the effect of processing variables, including deformation and heat treatment procedures, on the electrical properties of the Bi-2212 tapes at cryogenic temperatures was conducted. In addition, the effect of varying powder particle sizes was examined. For tapes fabricated by different thickness reduction schedules, significant variations in critical current density ( Jc) were observed. It is concluded that a combination of small roll diameter and small reduction-per-pass produces tapes with highest Jc. Moreover, the maximum Jc occurred in a narrow temperature range when melt processing was done in pure oxygen. Microstructural examination was used to correlate Jc and both the volume fractions of a nonsuperconducting second phase and the Bi-2212 grain orientation. [ABSTRACT FROM AUTHOR]

The microstructural variations in BSCCO Ag-clad tapes obtained by a conventional fabrication procedure were studied by SEM and microhardness tester. A method to improve grain alignment in the tape by treatment of the magnetic field with mechanical vibration was developed and investigated. [ABSTRACT FROM AUTHOR]

• Magnetization AC losses in iron based superconducting composites were studied. • Temperature was varied from 20 K to 42 K. • External magnetic field of frequencies 72 Hz and 144 Hz up to 70 mT was applied. • Parallel as well as perpendicular field orientation was examined. • Effect of eddy currents in Ag sheath were observed. Magnetization AC loss measurements of singe- and seven-core Ba122/Ag tapes have been done by calibration-free method in the range of temperature from 20 K to 42 K and field magnitudes up to 70 mT in RMS with two frequencies 72 Hz and 144 Hz. A strong effect of eddy current losses in highly conductive Ag sheath was observed for single-core sample, but negligible for seven-core tape with more resistive AgSn alloy outer sheath. For the estimation of eddy current loss component, pure Ag foil was measured in the same range of temperatures and used for analytical subtraction from the total losses of Ba122/Ag. In addition, loss measurement of singe-core sample with chemically etched away Ag sheath was also done. AC loss measurements in perpendicular as well as parallel field orientation have shown a strong effect of the filament size. [ABSTRACT FROM AUTHOR]

I have used the critical state model for investigating the magnetic moment of a flat type-II superconducting strip which carries a current such that the magnetic flux density B generated by this current depends solely on the coordinate along the width of the tape. To do so, I have also calculated the magnetic flux distribution in the film. The calculations clearly show that the magnetic moment of the material exposed to this current is increased as the thickness of the sample is decreased; a behavior similar to the thickness dependence of the critical current density. [ABSTRACT FROM AUTHOR]

With the high penetration of Renewable Energy Sources (RES) in power systems, the short-circuit levels have changed, creating the requirement for altering or upgrading the existing switchgear and protection schemes. In addition, the continuous increase in power (accounting both for generation and demand) has imposed, in some cases, the need for the reinforcement of existing power system assets such as feeders, transformers, and other substation equipment. To overcome these challenges, the development of superconducting devices with fault current limiting capabilities in power system applications has been proposed as a promising solution. This paper presents a power system fault analysis exercise in networks integrating Superconducting Cables (SCs). This studies utilized a validated model of SCs with second generation High Temperature Superconducting tapes (2G HTS tapes) and a parallel-connected copper stabilizer layer. The performance of the SCs during fault conditions has been tested in networks integrating both synchronous and converter-connected generation. During fault conditions, the utilization of the stabilizer layer provides an alternative path for transient fault currents, and therefore reduces heat generation and assists with the protection of the cable. The effect of the quenching phenomenon and the fault current limitation is analyzed from the perspective of both steady state and transient fault analysis. This paper also provides meaningful insights into SCs, with respect to fault current limiting features, and presents the challenges associated with the impact of SCs on power systems protection. [ABSTRACT FROM AUTHOR]

A critical problem for melt-processed silver-sheathed Bi-2212 tapes is gas release during heat treatment which deforms the sheath ("bubbling") and forms voids in the superconducting core. An overpressure furnace is used to study how the extent of bubbling changes with the total pressure (P/sub tot/). By processing in P/sub tot/ up to 9 atmospheres with constant oxygen partial pressure (pO/sub 2/=1 atm), bubbling in coils is eliminated. The critical current density increases with increasing P/sub tot/. Also, the phase assemblage in overpressure-processed tapes is unchanged compared to conventionally processed tapes. [ABSTRACT FROM PUBLISHER]

The properties of Ag-sheathed Bi2223 tapes depend strongly on the thermomechanical treatment processing parameters. We have examined the conversion of precursor powders to Bi2223 in heat-treated tapes as a function of ramp-to-temperature rate. Tapes containing precursor powders were ramped at rates from 50/spl deg/C/h to 800/spl deg/C/h to a final temperature of 835/spl deg/C, then held for 50 h, all in 20% O/sub 2/ and 80% N/sub 2/. The composition of the tapes was then determined by X-ray diffraction and by low-temperature magnetization measurements. The heat-treated tapes consisted almost entirely of a mixture of Bi2212 and Bi2223. The volume ratio of Bi2223 to Bi2212 in the tapes depended on the ramp rate in a complicated way; the volume ratio was largest (1.17) at 50/spl deg/C/h, the slowest ramp rate. [ABSTRACT FROM PUBLISHER]

• Even transverse voltage (ETV) appears at superconducting transition of the Nb–Ti tape near Hc2. • The features of the ETV change along the tape. • There is a strong dependence of the ETV on the excitation current. • When changing the geometry of the experiment from a perpendicular geometry (field directed normally) to the geometry when the field is in the plane of the tape, there is no significant change in the ETV. • The ETV is not described within the framework of the usual understanding of the resistivity appearance as the vortices movement. We have measured both longitudinal and transverse voltages with respect to current in flat samples of superconducting cold-worked and heat-treated Nb-50wt%Ti tapes. In the vicinity of the H c2 a transverse voltage is even with respect to the magnetic field inversion. We have found that transverse voltage varies significantly along the sample and depended on the magnitude of exciting current. Moreover, the behavior of the transverse voltage was qualitatively similar for two different orientations of applied field: in the plane of the tape and normal to the tape. The obtained data not only suggest that the main cause of the transverse voltage is material inhomogeneity, but also indicate that the transverse voltage is not described within the framework of the usual understanding of the resistivity appearance as the vortices movement. [ABSTRACT FROM AUTHOR]

Improvement of the critical current density (Jc) of superconducting wires/tapes is one of the key issues in the field of superconductivity applications. Here we report the fabrication of a silver-sheathed Ba1−xNaxFe2As2 (BaNa-122) superconducting tape by using a powder-in-tube technique and its superconducting properties, in particular transport Jc, as well as the tape-core texture. The optimally-doped BaNa-122 tape with Na concentration x = 0.4 exhibits the superconducting critical temperature (Tc) of 33.7 K and high transport Jc of 4 × 104 A/cm2 at 4.2 K in a magnetic field of 4 T. Patterns of x-ray diffraction for the superconducting core show that the degree of c-axis orientation is significantly enhanced through the tape fabrication process. The tendency of c-axis orientation is advantageous for achieving higher Jc, suggesting the high potential of BaNa-122 for superconducting wire/tape applications. [ABSTRACT FROM AUTHOR]

In this paper, through AC and DC overcurrent tests on second generation high temperature superconducting tape (2G HTS tape), we respectively summarize the typical types of quenching resistance and corresponding quenching degree, in which there are three types under AC overcurrent and two types under DC overcurrent. According to experimental results, a rule was found that, when 2G HTS tape quenches to normal state, the relationship between quenching resistance and joule heat generated from 2G HTS tape presents a fixed trend line, and the influence of liquid nitrogen can be ignored. Then, the characteristics and rules of quenching resistance found in experiments are well explained and confirmed by a detailed 3D finite element model of 2G HTS tape including electromagnetic field and thermal field. Finally, based on above works, our group proposes a new equivalent method to estimate the quenching resistance, where the results of AC and DC overcurrent experiments can be equivalent to each other within a certain range. Compared with FEM, the method has the following advantages: (i) The method is simple and easy to implement. (ii) This method combines precision and computational efficiency. (iii) With superconducting tape quenching to normal state, this method presents a good consistency with experimental results. [ABSTRACT FROM AUTHOR]

Ag-sheathed CaKFe4As4 superconducting tapes have been fabricated via the ex situ powder-in-tube method. X-ray diffraction analyses suggest that the CaKFe4As4 phase reacts strongly with the silver sheath at temperature above 500 °C. We therefore anneal the tape at 500 °C and obtain a transport critical current density Jc(4.2 K, 0 T) ∼ 2.7 × 104 A cm−2. The pinning potential derived from magnetoresistance measurements is one order of magnitude lower than that of the (Ba/Sr)1−xKxFe2As2 tapes. Combining with the scanning electron microscopy and magneto-optical imaging results, we suggest that bad connectivity between superconducting grains caused by the low sintering temperature is the main factor responsible for the low Jc. However, this system is still a promising candidate for superconducting wires and tapes if we find a compatible sheath material and further optimize the post-annealing process to achieve better grain connectivity. [ABSTRACT FROM AUTHOR]

Bi-2223 precursor powders are prepared by both oxalate co-precipitation (CP) and spray pyrolysis (SP) methods. The influence of fabrication methods on the superconducting properties of Bi-2223 tapes are systematically studied. Compared to the CP method, SP powder exhibits spherical particle before calcination and smaller particle size after calcinations with more uniform chemical composition, which leads to a lower reaction temperature during calcination process for Bi-2223 tapes. Meanwhile, the non-superconducting phases in SP powder are more uniformly distributed with smaller particle sizes. These features result in finer homogeneity of critical current in large-length of Bi-2223 tape, higher density of filaments and better texture after heat treatment. Therefore, the SP method could be considered as a better route to prepare precursor powder for large-length Bi-2223 tape fabrication. [ABSTRACT FROM AUTHOR]

The critical current behavior of REBa2Cu3O7−δ (REBCO, with RE = Yb, Y, Ho, Dy, Gd, Eu, GdYb, DyY, GdY, EuY, SmY, GdEu, GdSm) superconducting tapes has been systematically studied for the temperature range of 10–77 K, magnetic field range of 0–5 T and field orientation (angle between the field and tape) of 0°–180°. We report that the RE size dependencies of in-field critical current density (Jc) at low temperatures (below 40 K) are significantly different from those at 77 K. In a magnetic field of 1–3 T applied at 77 K, the Jc of REBCO films increases with the RE ionic radius (r). EuBCO film, with the largest r in this study, shows the highest Jc at 77 K in a magnetic field above 1 T, while YbBCO film, with the smallest r, has the lowest Jc at 77 K. At temperatures below 40 K, however, the trend of in-field Jc as a function of r reverses. There are crossovers among the functions of critical current density versus temperature for various RE ions and mixes. RE mixed films such as GdYBCO, EuYBCO, SmYBCO and GdEuBCO exhibit enhanced self-field critical current densities correlating with effective low field random pinning due to their suitable ion size variance. Strongly enhanced pinning by both random and correlated defects has been obtained in GdYbBCO films. Those pinning centers are especially effective at low temperatures. In a magnetic field of 5 T applied at 10 K, GdYbBCO gives the highest critical current density compared with other REBCO films, being 1.9 times greater than GdEuBCO film. This work provides a guideline regarding how to optimize RE ions in REBCO films for given application temperatures and magnetic fields. [ABSTRACT FROM AUTHOR]

High temperature superconducting (HTS) tape can be cut and stacked to generate large magnetic fields at cryogenic temperatures after inducing persistent currents in the superconducting layers. A field of 17.7 T was trapped between two stacks of HTS tape at 8 K with no external mechanical reinforcement. 17.6 T could be sustained when warming the stack up to 14 K. A new type of hybrid stack was used consisting of a 12 mm square insert stack embedded inside a larger 34.4 mm diameter stack made from different tape. The magnetic field generated is marginally higher than the previous trapped field record achieved by a bulk HTS magnet and 30% greater than previously achieved in a stack of HTS tapes. Such stacks are being considered for superconducting motors as rotor field poles where the cryogenic penalty is justified by the increased power to weight ratio. The sample reported can be considered the strongest permanent magnet ever created. [ABSTRACT FROM AUTHOR]

We fabricated (Ba,K)Fe2As2 superconducting wires and tapes using the powder-in-tube method and hot isostatic pressing (HIP). HIP wires and tapes showed a high value of transport critical current density (Jc) exceeding 100 kAcm−2 at T = 4.2 K and the self-field. Transport Jc in the HIP wire reached 38 kAcm−2 in a high magnetic field of 100 kOe. This value is almost twice larger than the previous highest value of Jc among round wires using iron-based superconductors. Enhancement of Jc in the wires and tapes was caused by improvement of the drawing process, which caused degradation of the core, formation of microcracks, weak links between grains, and random orientation of grains. Details of the effect of the improved fabrication processes on the Jc are discussed. [ABSTRACT FROM AUTHOR]

This paper experimentally analyzes the critical current degradation and AC (alternating current) losses of second-generation (2G) high-temperature superconductor (HTS) tape during the impregnation process. Two impregnation materials were utilized: Gallium-Indium-Tin (GaInSn), and an epoxy resin, Araldite. The critical current of the impregnation materials was measured after different thermal cycles and compared with the tape with no impregnation process. The experimental results show that the critical current of Yttrium Barium Copper Oxide (YBCO) short samples varies between differently impregnated materials. The resin, Araldite, degraded the critical current; however, the GaInSn showed no degradation. Two degradation patterns with Araldite were identified due to the impregnation process, and the corresponding causes were analyzed. We further measured the AC losses of tapes impregnated with liquid metal at different frequencies, up to 600 Hz. Based on the experimental results, GaInSn liquid metal should be the most suitable impregnation material in terms of critical current degradation. [ABSTRACT FROM AUTHOR]

Fluorescent microthermographic imaging, a method using rare-earth fluorescent coatings with temperature dependent light emission, was used for quench investigation in high temperature superconductors (HTS). A fluorophore was embedded in a polymer matrix and used as a coating on top of an HTS tape, while being excited with UV light and recorded with a high-speed camera. Simultaneously, the tape was pulsed with high amplitude, short duration DC current, and brought to quench with the help of a localised defect. The Joule heating during a quench influences the fluorescent light intensity emitted from the coating, and by recording the local variations in this intensity over time, the heating of the tape can be visualised and the developed temperatures can be calculated. In this paper, the fluorophore europium tris[3-(trifluoromethylhydroxymethylene)-(+)-camphorate] (EuTFC) provided sufficient temperature sensitivity and a usable temperature range from 77–260 K. With the help of 2500 image captures per second, the normal zone development was imaged in a 20 μm copper stabilised HTS tape held in a liquid nitrogen bath, and using a calibration curve, the temperatures reached during the quench have been calculated. [ABSTRACT FROM AUTHOR]