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Abstract: The effects of a ferromagnetic substrate on ac losses of a YBa2Cu3O7, YBCO, coated conductor in perpendicular ac magnetic fields were investigated by measuring the losses of a set of the specimens which were made by placing one Ni-5at.% W tape on one or both sides of a YBCO layer on a Hastelloy tape. For applied field amplitude, μ0H0, <∼5mT, the losses with the Ni-W tape(s) were higher than those of the YBCO tape, but for ∼5mT<μ0 H 0 <∼0.1T, the losses were reduced by putting the Ni-W tape(s) on the YBCO tape. For μ0 H 0 >∼0.1T, the losses became the same for all of the specimens. Also, the geometric portion χ 0 of the susceptibility χ was determined from the hysteresis loops for these specimens, and was found to decease with the addition of the magnetic substrate. These observations agreed very well with the theoretical calculations for the losses and χ 0 for a YBCO layer on a ferromagnetic substrate, by [Mawatari, arVir:0710:2151v1, (cond-mat.supr-con)]. [Copyright &y& Elsevier]

We studied the thermal and electromagnetic behavior of a conduction-cooled superconducting pulse coil. It was wound with a 4-strand parallel conductor composed of silver sheathed Bi2223 multifilamentary tapes and impregnated with an epoxy resin. We first investigated the temperature dependence of the thermal runaway current in dc operation. It was higher than the critical current by several tens amps at any temperature from 40 to 90 K. In order to study the mechanism of the thermal runaway, we carried out the numerical simulation of the coil behavior. We found out that the thermal runaway was caused when the heat generation at the winding end close to the cryocooler head where the flux-flow loss is the largest due to perpendicular magnetic field exceeded the cooling through thermal diffusion though the thermal runaway of the coil started at the other end of the winding. If the transport current is smaller than the thermal runaway current at the coil temperature just after applying current, the temperature distribution in the longitudinal direction of the coil varied into a monotonous gradient and the steady thermal flow was established. After that the coil temperature decreased to the balanced one. [ABSTRACT FROM AUTHOR]

We fabricated a cryocooler-cooled Bi2223 superconducting pulsed coil and experimentally studied the thermal runaway in dc or ac operation. We carried out numerical simulation of thermal properties of the coil in order to explain the thermal runaway of the coil. Firstly, we analyzed the total heat generation of flux-flow losses and ac losses inside the winding from the experimental results of the external field losses and the E - J characteristics for the Bi2223 strands. Secondly, we numerically simulated the thermal properties by using a 2-dimensional heat conduction equation with axial symmetry. The numerical simulation shows the relation between the initiation of thermal runaway and the temperature distribution with highly concentrated heat source in the winding. We have a semi-quantitative agreement between the numerical results and the experimental ones for the condition of the thermal runaway. [ABSTRACT FROM AUTHOR]

We studied the possible application of high-TC superconducting traction transformer to railway rolling stock, and designed an iron core type two-leg 4 MVA superconducting traction transformer for Shinkansen. This traction transformer has a primary winding, four secondary windings and a tertiary winding. The four secondary windings are independent of each other. Two secondary windings are arranged around each leg of the iron core and placed inside and outside the primary and tertiary windings. In this study, we fabricated a high-TC super-conducting coil whose form and dimension are the same as those of the inner secondary winding. This coil can be used as the inner secondary winding of the experimental high TC superconducting traction transformer that will be fabricated in the future. The inner secondary winding has 96 turns and a later with eight parallel Bi2223 superconducting tapes. Transposition among the superconducting tapes is performed 15 times every six turns. We measured the voltage-current and AC loss characteristics when it was cooled in saturated and sub-cooled liquid nitrogen. [ABSTRACT FROM AUTHOR]

Abstract: The uncertainty of AC loss measurements for multifilamentary superconducting wires by a pickup coil method is evaluated on the basis of the law of propagation of uncertainty. In this evaluation, the effects of measurement conditions, signal processing, and the division of the AC loss into its components (hysteresis loss and coupling loss) are taken into account as elements of uncertainty. The effect of the measurement conditions is evaluated using theoretical expressions of the two main components. Additionally, the effect of signal processing is considered in accordance with the actual processes of the AC loss measurement using experimental outputs. The main factors that contribute to the uncertainty in the propagation process are discussed. The estimated resultant uncertainties are compared to experimental ones for round robin tests of AC loss measurement of Nb–Ti multifilamentary wires exposed to an alternating transverse magnetic field. [Copyright &y& Elsevier]

Abstract: We are experimentally studying basic AC loss properties of IBAD/CVD-YBCO coated conductors with a copper layer for stabilizing, especially the temperature dependence of perpendicular field loss in alternating electromagnetic environments. We prepared two types of short specimens with and without a copper layer and measured AC losses by a saddle-shaped pickup coil in an alternating magnetic field perpendicular to the wide surfaces at liquid helium temperature. In the ranges of the amplitude up to 4T and the frequency up to 0.2Hz, the AC losses both of the two specimens are hardly dependent upon the frequency. The results show that hysteresis loss is a major component of the AC loss in the specimens and the effects of the copper layer can be negligible. We also measured AC losses for the specimens with the copper layer at liquid nitrogen temperature to estimate the dependence on measurement temperature. The results suggested that the AC loss vs. the amplitude of applied field can be scaled by a critical current at a zero magnetic field. [Copyright &y& Elsevier]

Abstract: We numerically calculate total AC losses in a single Bi-2223 tape carrying a transport current in an external magnetic field parallel or perpendicular to the tape face. We also carry out the calculations for two models of three-strand parallel conductor. One is without transposition, and the other is with optimum transposition so that the branch current in each strand becomes equal. It is confirmed the total AC losses fairly increase with the simultaneous application of transport current. It is also found that in the perpendicular field the total losses are scarcely dependent on transposition but on the number of strands in the smaller field amplitude. In the parallel field, the effect of the number of strands on the total AC losses is notable as well as transposition. [Copyright &y& Elsevier]

We fabricated a 1 T cryocooler-cooled oxide superconducting pulsed coil. It is a 16-layer solenoidal coil wound with an interlayer-transposed 4-strand parallel conductor composed of Bi2223 multifilamentary flat wires. The insulated strands were transposed only between layers to make all strands inductively equivalent. To suppress the temperature rise due to the ac loss, the aluminum nitride(AIN) plates were arranged between layers as heat drains. The pulsed coil was cooled down to 30 K by a single stage cryocooler. It can be operated continuously at 40 K in the 1 T triangular wave operation at 1 Hz. First we studied the temperature dependence of thermal runaway current of the coil under the application of direct transport current. The runaway current was higher than the critical current, which was defined as the current where the electric field of 10-4 V/m was generated on average over the whole length of the conductor. Next we studied the temperature variation of the coil in a sinusoidal operation of 1 Hz. The temperature increment was much more gradual than that in the dc operation. In this paper, we discuss the thermal properties of the cryocooler-cooled oxide superconducting pulsed coil, taking into account the heat generation of ac loss and flux-flow loss and the cooling capacity of a cryocooler. [ABSTRACT FROM AUTHOR]

The ac losses in three disk-shaped YBa[sub 2]Cu[sub 3]O[sub 7] (YBCO) films, which were deposited on SrTiO[sub 3] by the pulsed-laser-deposition technique and had thicknesses, d, of 0.2, 1.0, and 3.0 μm, were measured in perpendicular applied ac magnetic fields to ∼0.14 T at 10 Hz in liquid nitrogen. The losses at low fields were found to be a strong function of the film thickness. The measured losses were compared with the theoretically calculated losses. The ac losses calculated using a field-independent critical-current density, the Bean model [J. R. Clem and A. Sanchez, Phys. Rev. B 50, 9355 (1994)], agreed very well with the 0.2-μm-thick film, while the calculated losses agreed well with the measured ones when a field-dependent critical-current density, the Kim model [D. V. Shantsev, Y. M. Galperin, and T. H. Johansen, Phys. Rev. B 61, 9699 (2000)], was used for the films of thickness 1.0 and 3.0 μm. However, a surprising discrepancy was found in the values of B[sub c] and B[sub 0] for thinner YBCO films depending on whether they were determined by ac or dc measurements. B[sub c] is defined as B[sub c]=μ[sub 0]J[sub c](0)d/2, B[sub 0] is the characteristic field in the Kim-model critical-current density J[sub cK](B[sub a])=J[sub c](0)/(1+B[sub a]/B[sub 0]), and J[sub c](0) is the critical-current density at applied magnetic field B[sub a]=0. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: In the Japanese national project to develop superconducting power applications using Y-based coated conductors, the present focus is on various aspects of technological development of superconducting power transformers. Since Y-based multi-filament wire contributes to reduction in AC loss of superconducting transformer coils, a 5mm-wide long-length multi-filament, between the filaments of 3 and 5, has been developing by a laser scribing method. In the case of the project target, a 66kV/20 MVA power transformer coils require a Y-based multi-filament wire between the lengths of 200m and 300m. It also must withstand over-current of about seven times the rated current, which is generated when a power system fault occurs. In this paper, over-current characteristics of model coil using Y-based 3-filament wire were evaluated. [Copyright &y& Elsevier]

Abstract: We are developing elemental technology for 66kV/6.9kV 20 MVA-class YBCO power transformer. The YBCO transformer is considered to have a possibility to stabilize the power system by improving function of fault current limiting. Current limiting behavior functions over critical current flows. There is a possibility that superconducting characteristic may be damaged due to increase in temperature of YBCO tapes. Therefore, we have taken a measure to combine YBCO tape with CuNi tape or Cu Tape. We manufactured model coils using these conductors and conducted the AC over-current tests. The test current was two to seven times larger than the I c of conductor and it was damped with time from its maximum value according to the generation of conductor resistance. We verified the effectiveness of current limiting characteristics. In these tests, the I c of model coil did not degrade. We consider this conductor to be able to withstand AC over-current with the function of current limiting. [Copyright &y& Elsevier]

Abstract: We have been developing twisted Bi-2223 multifilamentary taped wires to suppress the AC losses in perpendicular-field configuration for industrial-production process. It is confirmed that the hysteretic losses in the filamentary region can be reduced by twisting in a same manner as in situ Nb3Sn multifilamentary ones, while the coupling loss remains in unsatisfactory situation for commercial frequency uses. As one of practical methods for further reduction of the coupling loss, we propose an advanced multifilamentary structure of the taped wires in which an insulation layer is arranged in the central region of the tape to effectively restrict the main part of the coupling current in the perpendicular-field configuration instead of an insulation barrier around each filament that may be not usually suitable to the practical production process. We have designed and fabricated prototype wires with the proposed structure, and measured the AC loss properties in the perpendicular-field configuration. The experimental results suggest that the central insulation barrier has a function to suppress the coupling loss remarkably. We also discuss improvement in the structural design for the further reduction of the AC losses. [Copyright &y& Elsevier]

Abstract: Establishment of processing technology for multifilamentary coated conductors (CCs) is a key issue for superconducting electric power applications from the viewpoint of AC loss reduction. On the other hand, CCs sometimes have local inhomogeneity in the superconducting layers, and that will cause a current blocking in a filament or inhomogeneity of critical current among filaments in a multifilamentary CC. Therefore, we need an assessment method for local electromagnetic behavior on AC loss properties of CCs. In this study, we developed a method for visualizing time-dependent AC loss distribution in CCs by using scanning Hall probe microscopy. We succeeded in visualizing local current density, electric field and loss density simultaneously with a spatial resolution of a few hundred micrometers. The measurement system has possible scanning area of 150×50mm2 and current capacity of 500A. This enables us to discuss the local electromagnetic behavior on a practical scale of CCs. We believe that this visualization method will be a very powerful tool to estimate the feasibility of processing technology for multifilamentary CCs. [ABSTRACT FROM AUTHOR]

Abstract: For high temperature superconductor (HTS) applications such as a power cable, a motor, and a transformer, a refrigerator enough to cool them below liquid nitrogen temperature is required to attain the HTS system stable operation. Since no refrigerator matched for the HTS application both in temperature and in cooling power is available up to now, a neon turbo-Brayton cycle refrigerator of 2kW at 70K was developed. Neon gas was used as the working fluid in the refrigerator. Although hydrogen and helium could be selected as a working fluid for the refrigerator, neon is better energy carrier since it has higher heat capacity and larger molecular weight than hydrogen and helium at a temperature around 70K in order to make a refrigerator smaller in size. Neon has an advantage in using a small turbo-expander with an impeller of 25mm in diameter. The turbine rotated at a maximum speed of 100,000rpm. The information for developing a suitable refrigerator for HTS applications was collected and a new type of neon refrigerator was proposed. [Copyright &y& Elsevier]

Abstract: Coated conductors (CCs) are prospective for electric power applications intended for not only better cost performance but also high critical current density (J c) under magnetic fields comparing with Bi2Sr2Ca2Cu3Oy (BSCCO) tapes. Furthermore, they also have a possibility to reduce AC losses by various methods of post-treatments since the CCs are of a laminated structure with the insulating buffer layers. Multifilamentation by narrowing the tape width is quite effective to reduce the AC losses and therefore this approach is valid for the standard process to fabricate practical CCs with an appropriate architecture. In this study, we developed a tape scribing technique applying a technique of YAG laser with/without chemical etching to control the filament width in YBa2Cu3O y (YBCO) CCs for the multifilament. The AC loss was reducible to one-twentieth by 20-multifilament structure in a short sample test, and to one-third by 3-multifilament structure in the coil using 28m long tapes in total. The authors measured the resistance between the filaments at 60–300K after post-treatment to investigate the effective bridged materials, which is essential for decoupling of the filaments. We improved the resistance value between the filaments at liquid nitrogen temperature up to the order of 10Ω/cm using the YAG laser with high-temperature oxygen anneals. Furthermore, the resistance over 106 Ω/cm was evident by the combination of laser scribing and chemical etching, which is much higher than the requirements of all the applications. [Copyright &y& Elsevier]

AC losses in the conduction-cooled low temperature superconducting (LTS) pulse coil with stored energy of 1 MJ are estimated. The 1 MJ coil is a superconducting pulse coil for 1 MW, 1 sec UPS-SMES. UPS-SMES is an uninterruptible power supply (UPS) with superconducting magnetic energy storage (SMES) for protection of production lines of an industrial plant or large-scale experimental devices such as a fusion device, from a momentary voltage drop and an instant power failure. The winding conductor for the 1 Mi coil is a NbTi/Cu Rutherford cable, which is extruded with aluminum. The 1 Mi coil was wound by a new twist winding method. A 1 MJ coil was fabricated and cooling and excitation tests were carried out. In this paper, two methods to estimate ac losses in conduction-cooled LTS coils are proposed. One method estimates ac losses in the coil under steady-state conditions. The other method estimates ac losses in the coil under transient-state conditions. For estimation of ac losses in the 1 Mi coil, measurement of temperature in the coil during tests and thermal analysis using the two-dimensional finite element method are compared. These procedures clarified that the 1 MJ coil has low losses. [ABSTRACT FROM AUTHOR]

Abstract: It is highly expected that superconducting transformers, which are characterized by incombustibility, light weight, and compactness, will be used practically for equipment in substations and office buildings sited in urban areas. In recent years, remarkable improvements in the performance of YBaCuO (YBCO) tape wire have been seen. This kind of tape wire has the property that its critical current is large in a highly magnetic field; and, its use is expected to reduce AC loss by applying slit processing on the tape wire, contributing to future cost reductions. In addition, the development of efficient, economical cryogenic units is also expected. The authors have developed a conceptual design for a 66kV/20MVA power transformer using YBCO tape wires, or an YBCO power transformer. As a result, we were able to identify the transformer’s optimal system structure including coil winding comprised of coils and tape wires; and, we confirmed that the devised transformer can made to be both compact and highly efficient. [Copyright &y& Elsevier]

We have been developing a lightweight and high-efficiency superconducting traction transformer for railway rolling stock. We designed and fabricated a prototype superconducting traction transformer of a floor-mount type for Shinkansen rolling stock. In this study, we present test results such as type test, system test and vibration test. We performed the type test in accordance with JIS, E5007. In this test, we measured the basic electrical characteristics. In the system test, we tested the transformer with a dynamic simulator for rolling stock, as a converter connected at secondary winding, and verified the operating characteristics. We performed vibration tests in accordance with JIS, E4031, vibrating the transformer on a shaking table with three-dimensional movement. As a result, we could verify that the transformer satisfied the requirement almost exactly as initially planned. [ABSTRACT FROM AUTHOR]

Abstract: The output limit of the available power of a prototype conduction-cooled low temperature superconducting (LTS) pulse coil is clarified for the optimization of the coil. The winding conductor of this coil is a NbTi/Cu Rutherford cable, which is extruded with aluminum. Dyneema® fiber reinforced plastics (DFRP) and Litz wires are used as the spacers of this coil. A prototype coil with a stored energy of 100kJ was successfully fabricated and tested, and the coil performed excellently. In this paper, the stability margin of this coil is clarified by thermal analysis, using a two-dimensional finite element method, taking into account the effects of both types of spacers, DFRP and Litz wires. Additionally, the maximum output power of the coil is estimated at about three times the rated output. [Copyright &y& Elsevier]

In order to reproduce the experimental results of AC losses in a Bi-2223 Ag-sheathed tape exposed to the external magnetic field with an arbitrary angle to the broadest face, we calculate the AC losses by means of the two-dimensional finite element method that directly analyzes the magnetic field distribution around the wire. It is assumed that the voltage–current characteristics are represented by the power-law model including the dependence of both the critical current density and n-value on an effective perpendicular component of applied magnetic field. The obtained numerical results have a good agreement with the experimental results in the large amplitude of applied magnetic field. [Copyright &y& Elsevier]

We fabricated and tested a cryocooler-cooled high temperature superconducting (HTS) single pancake coil wound with a Bi2223 tape in order to investigate thermal stability of the HTS coil. The inner diameter of the coil is ∅100 mm and the outer diameter is ∅257 mm. The coil is impregnated with epoxy resin and a conduction plate made of aluminum is fixed on the surface of the coil through an AlN plate for insulation. We measured thermal runaway currents at several temperatures. In this paper the thermal stability of the coil is discussed. [Copyright &y& Elsevier]

The influence of effective vacuum part is numerically evaluated on AC losses in superconducting wires calculated by means of a two-dimensional finite element method, which is formulated with a self-magnetic field due to an induced current as unknown. In the present method, the high-resistivity metal around the wires is needed for the sake of the simplicity in program coding. The superconducting wires carry an alternating transport current or are exposed to an external AC magnetic field. The AC losses are numerically calculated for square and circular effective vacuum parts with wide ranges of the sizes and the resistivity. Relative errors in the obtained results are discussed as compared with conventional analytical predictions. [Copyright &y& Elsevier]

We fabricated two high-T[sub c] superconducting coils that simulated the winding of a traction transformer for railway rolling stock. The multi-layer solenoid coil to simulate the primary winding of the transformer had five layers with a single Bi2223 superconducting tape. The closed solenoid coil to simulate the secondary winding of the transformer had one layer with eight parallel Bi2223 superconducting tapes. We measured the voltage-current, AC loss and current sharing characteristics of these coils cooled in saturated liquid nitrogen at 77 K. As a result, we concluded that the multi-layer solenoid coil is applicable to the primary winding and the closed solenoid coil is also applicable to the secondary winding. [ABSTRACT FROM AUTHOR]

AC losses of bundles of non-twisted superconducting tapes in an external magnetic field perpendicular to the wide faces of them are evaluated by means of both numerical simulation and theoretical consideration. First, the AC losses are numerically calculated in a slab, whose thickness is equal to the width of filamentary region in the tape. Next, in order to add the effects of magnetic interaction between tapes, the effective demagnetization factors of stacked tapes are estimated with a theoretical expression, in which it is assumed that the filamentary region is regarded as a uniform magnetic material in the form of an elliptic cylinder. By combining the AC loss properties of slab and the effective demagnetization factors of stacked tapes, it is finally found that the experimental results can be well reproduced in three kinds of Bi-2223 multifilamentary tapes. [Copyright &y& Elsevier]

Discusses the application of high temperature superconductor (HTS) to a fusion plasma systems in the National Institute for Fusion Science. HTS application in the large current feedthrough to a superconducting coil; Development of HTS current lead; Development of superconducting magnetic levitation coil.

Abstract: We have strategically promoted R&D activity for the development of elemental technologies in order to put into practical HTS power transformers applying YBa2Cu3O7 (YBCO) coated conductors, focused on AC loss reduction in HTS coils. This paper shows AC loss reduction in model coils of YBCO tapes divided into five filaments by laser ablation. At first experiment, magnetization loss of YBCO tape with five filaments and YBCO tape with non-divided were firstly measured using a pick-up coil technology. Then, AC loss measurement is performed using two types of model coils of YBCO tapes with five filaments and non-divided, by two different technologies: an electric technique (i.e. 4-probe) and a calorimetric technique (i.e. boil-off). The results of the experiment show that the AC loss in the model coil of YBCO tapes with five filaments was reduced to one-fifth when compared with model coil of YBCO tapes with non-divided. [Copyright &y& Elsevier]

Abstract: The nitrogen boil-off method, which is categorized as one of the calorimetric methods, has been developed as a practical method for measuring AC losses in high temperature superconducting (HTS) coils. The boil-off method offers direct and convenient measurement compared to the electric method. The measurement sensitivity of about 0.5W was confirmed by the improvement of sample vessel structure and the control of the heater power. This paper reports the results of a comparison of the AC losses in superconducting coils using YBCO tapes measured with the boil-off method and those obtained by the electric method and by analysis. [Copyright &y& Elsevier]

Background: The COVID-19 pandemic has spurred the growth of a global infodemic. In order to combat the COVID-19 infodemic, it is necessary to understand what kinds of misinformation are spreading. Furthermore, various local factors influence how the infodemic manifests in different countries. Therefore, understanding how and why infodemics differ between countries is a matter of interest for public health. This study aims to elucidate and compare the types of COVID-19 misinformation produced from the infodemic in the US and Japan., Methods: COVID-19 fact-checking articles were obtained from the two largest publishers of fact-checking articles in each language. 1,743 US articles and 148 Japanese articles in their respective languages were gathered, with articles published between 23 January 2020 and 4 November 2022. Articles were analyzed using the free text mining software KH Coder. Exploration of frequently-occurring words and groups of related words was carried out. Based on agglomeration plots and prior research, eight categories of misinformation were created. Lastly, coding rules were created for these eight categories, and a chi-squared test was performed to compare the two datasets., Results: Overall, the most frequent words in both languages were related to health-related terms, but the Japan dataset had more words referring to foreign countries. Among the eight categories, differences with chi-squared p ≤ 0.01 were found after Holm-Bonferroni p value adjustment for the proportions of misinformation regarding statistics (US 40.0% vs. JP 25.7%, ϕ 0.0792); origin of the virus and resultant discrimination (US 7.0% vs. JP 20.3%, ϕ 0.1311); and COVID-19 disease severity, treatment, or testing (US 32.6% vs. JP 45.9%, ϕ 0.0756)., Conclusions: Local contextual factors were found that likely influenced the infodemic in both countries; representations of these factors include societal polarization in the US and the HPV vaccine scare in Japan. It is possible that Japan's relative resistance to misinformation affects the kinds of misinformation consumed, directing attention away from conspiracy theories and towards health-related issues. However, more studies need to be done to verify whether misinformation resistance affects misinformation consumption patterns this way., (© 2024. The Author(s).)

This study explores the perceptions of the Undetectable = Untransmittable (U = U) campaign among gay men with HIV in Japan who are part of the HIV community on Twitter. We conducted detailed semistructured interviews with 12 participants using a modified grounded theory approach. The analysis resulted in 31 concepts, 5 subcategories, 9 categories, and 2 core categories. The relationship between categories and core categories was examined in conjunction with the transcriptions, yielding a comprehensive category map depicting the process of understanding U = U. The three main processes emerged: participants expressed "expectations for improvement," underwent stages of "understanding U = U," and encountered "dilemmas" in forming their opinions. There are two routes to "understanding U = U": Route 1 involved a frictionless understanding of U = U, and Route 2 involved difficulty in understanding the slogan. In both routes, participants experienced the dilemma of "but I still have HIV" and regarding its ease of use. These dilemmas and difficulties in understanding U = U affected their "expectations for improvement." Efforts to promote U = U in Japan must address challenges in public understanding and related dilemmas. This entails reformulating the U = U message in simpler terms, leveraging professional explanations, disseminating it to a broader audience, and incorporating ideas from individuals living with HIV to enhance the message., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)