Search

This paper presents a perspective on flux pumps. Flux pumps are a means of providing current to a coil or a magnet without direct electrical or physical contact. Typically, a coil would be charged directly using current leads, which would then be withdrawn if the magnets operated in the persistent mode (as with magnetic resonance imaging) or left in place if the field required maintenance or ramping. Flux pumps use the principle of magnetic induction. They present two distinct advantages. The first is that there is no direct connection to the external world and, therefore, no associated heat loss. The second is that, although high current can be developed in the magnet or the coil, these can be produced without the need for high-current power supplies, which are bulky and expensive. Flux pumps are especially appropriate for machines constructed from high temperature superconductors (HTSs). They facilitate the full use of the HTS's current carrying capability, cheaply and simply, enabling smaller, lighter, and more powerful magnets, motors, and generators. [ABSTRACT FROM AUTHOR]

We provide experimental evidence for a vortex migration phenomenon in YBa2Cu3O7-δ (YBCO) thin film caused by travelling magnetic wave. The experiment is carried out on a 2 in. diameter YBCO thin film with a circular-type magnetic flux pump. We found that the travelling wave helps the vortices migrate into the centre of the sample: after the zero-field cooling process, the increase of the flux density in the centre is four times larger than the amplitude of the travelling wave. The reason for this massive vortex migration is probably due to the magnetic stress variation caused by the travelling wave: the magnetic stress increases locally in the crest region while decreases locally in the trough region, which could help the vortices to move locally. A comparison shows that the magnetization by standing wave can be easily predicted by Bean's model while travelling wave causes vortex migration generally much larger than the prediction of Bean's model. It is possible that travelling magnetic wave can be an effective way to magnetize a type II superconductor in considering this unusual vortex dynamics. [ABSTRACT FROM AUTHOR]

Theoretical and experimental AC loss data on a superconducting pancake coil wound using second generation (2 G) conductors are presented. An anisotropic critical state model is used to calculate critical current and the AC losses of a superconducting pancake coil. In the coil there are two regions, the critical state region and the subcritical region. The model assumes that in the subcritical region the flux lines are parallel to the tape wide face. AC losses of the superconducting pancake coil are calculated using this model. Both calorimetric and electrical techniques were used to measure AC losses in the coil. The calorimetric method is based on measuring the boil-off rate of liquid nitrogen. The electric method used a compensation circuit to eliminate the inductive component to measure the loss voltage of the coil. The experimental results are consistent with the theoretical calculations thus validating the anisotropic critical state model for loss estimations in the superconducting pancake coil. [ABSTRACT FROM AUTHOR]

High-Tc superconducting (HTS) flux pumps are capable of injecting flux into closed HTS magnets without electrical contact. It is becoming a promising alternative of current source in powering HTS coils. This paper reviews the recent progress in flux pumps for HTS coil magnets. Different types of HTS flux pumps are introduced. The physics of these flux pumps are explained and comparisons are made. [ABSTRACT FROM PUBLISHER]

High-Tc Superconducting (HTS) magnets operating in persistent current mode suffer a current decay due to flux creep of superconductor and joint resistance. Flux pumps are able to inject direct current into superconducting circuit to compensate the current decay, without the thermal loss caused by current leads. In this work, we proposed a flux pumping mechanism for HTS coils, with an experimental verification and an analytical model. The basic principle we have used is that flux flow can be triggered when the superconductor carrying a direct current is subjected to a perpendicular AC magnetic field. Low frequency alternating current is induced in a loop of YBCO tape using an AC field. A portion of the tape which we refer to as the "bridge" shorts a superconducting coil. A high frequency AC field is applied perpendicular to the bridge tape when alternating current in the tape reaches one polarity. This triggers a net flux flow and results in a current increase in the coil. The proposed flux pump has clear physics and is easily controllable, which may make it promising in practical use. [ABSTRACT FROM AUTHOR]

COOMBS T., CURTIS J. & CROOKES P. (2013) What is the process of a comprehensive mental health nursing assessment? Results from a qualitative study. International Nursing Review 60, 96-102 Background: It is a truism that nursing care must be informed by assessment, otherwise how can one know what care is required or that it has been successfully delivered? Yet, little is known about the process of comprehensive mental health nursing assessment in practice. If the education of mental health nurses is to be effective, it is essential that the key content of, and the processes involved in carrying out a mental health nursing assessment in practice are able to be articulated to learners. Aim: To identify the processes of assessment that occur in mental health nursing practice based on interviews with mental health nurses working in clinical and management roles in clinical areas. Method: Interviews were undertaken with 18 nurses who worked in inpatient and community mental health settings either as clinicians or managers. The nurses ranged from new graduates to those with more than 20 years of experience. Findings and discussion: Clear processes were reported to be involved in undertaking a comprehensive mental health nursing assessment in practice, with three main themes emerging during analysis. First is the importance of engaging the patient; second is tell me what the problem is? with one subtheme reconcile inconsistencies; and finally, the ongoing nature of the assessment process. Conclusion: Common processes emerged when the nurses described their individual approaches to undertaking comprehensive mental health assessment. The results have important policy implications for the educational preparation of mental health nurses, their ongoing supervision and further research into contemporary mental health nursing practice. [ABSTRACT FROM AUTHOR]

Accessible summary Little is known of how a comprehensive mental health nursing assessment is undertaken in practice., Nurses describe the content of a comprehensive mental health nursing assessment in different ways., Different content may lead to different interventions., More work is required to ensure comprehensive mental health nursing assessments are undertaken in practice., Abstract Assessment is the foundation of mental health nursing practice, but little is known of how it is undertaken. This paper explores how mental health nurses describe the content of a comprehensive mental health nursing assessment. Eighteen nurses who worked in inpatient and community settings either as clinicians or managers, ranging from new graduates to nurses with greater than 20 years of experience, were interviewed and asked to describe the content of a comprehensive mental health nursing assessment. Transcribed interviews were analysed using a grounded theory methodology. The primary theme to emerge was one of variability. Most respondents hesitated and then identified different content areas that needed to be assessed as part of a comprehensive mental health nursing assessment. If the areas that are being assessed vary between nurses, then logically the types of interventions being offered will also vary. These results have implications for the education of nurses, their clinical practice, ongoing supervision and research into contemporary mental health nursing practice. [ABSTRACT FROM AUTHOR]

Superconductors have a bright future; they are able to carry very high current densities, switch rapidly in electronic circuits, detect extremely small perturbations in magnetic fields, and sustain very high magnetic fields. Of most interest to large-scale electrical engineering applications are the ability to carry large currents and to provide large magnetic fields. There are many projects that use the first property, and these have concentrated on power generation, transmission, and utilization; however, there are relatively few, which are currently exploiting the ability to sustain high magnetic fields. The main reason for this is that high field wound magnets can and have been made from both BSCCO and YBCO, but currently, their cost is much higher than the alternative provided by low- Tc materials such as Nb3Sn and NbTi. An alternative form of the material is the bulk form, which can be magnetized to high fields. This paper explains the mechanism, which allows superconductors to be magnetized without the need for high field magnets to perform magnetization. A finite-element model is presented, which is based on the E –J current law. Results from this model show how magnetization of the superconductor builds up cycle upon cycle when a traveling magnetic wave is induced above the superconductor. [ABSTRACT FROM AUTHOR]

High Temperature superconductors are able to carry very high current densities, and thereby sustain very high magnetic fields. There are many projects which use the first property and these have concentrated on power generation, transmission and utilization, however there are relatively few which are currently exploiting the ability to sustain high magnetic fields. There are two main reasons for this: high field wound magnets can and have been made from both BSCCO and YBCO but currently their cost is much higher than the alternative provided by low Tc materials such as Nb3Sn and NbTi. An alternative form of the material is the bulk form which can be magnetized to high fields and using flux pumping this can be done in situ. This paper explores some of the applications of bulk superconductors and describes methods of producing field patterns using the highly uniform magnetic fields required for MRI and accelerator magnets as the frame of reference. The patterns are not limited to uniform fields and it is entirely possible to produce a field varying sinusoidally in space such as would be required for a motor or a generator. The scheme described in this paper describes a dipole magnet such as is found in an accelerator magnet. The tunnel is 30\times 50\times 1000\ mm and we achieve a uniformity of better than 200 ppm over the 1000 mm length and better than 1 ppm over the central 500 mm region. The paper presents results for both the overall uniformity and the integrated uniformity which is 302 ppm over the 1000 mm length. [ABSTRACT FROM AUTHOR]

This paper proposes a practical and memory efficient method to model YBCO coated conductors by commercial finite element software. This method uses the H formulation to directly solve a magnetic field in a two-dimensional space. This model has been successfully used for bulk materials and thick wires, and is extended in this article to solve geometries with high aspect ratios such as coated conductors. The effect of mesh quality and order of element on the performance and accuracy of the model is discussed. A model using 2nd order single layer elements is chosen as the optimal setting for solving AC loss in coated conductors. Based on this setting, a series of simulations with the thickness of the tape varying from 1 μm (the actual thickness) to 120 μm have been performed to investigate the effect of artificially expanding tape thickness. The results obtained from our FEM model are compared with the classical analytical solutions. The discrepancies between the two are discussed and explained. The model proposed in this paper is able to give an accurate solution of AC loss for simple geometry (such as a single tape with expanded thickness) within just a few minutes. Even in the case of dealing with complex problems (such as a tape in its actual dimension or a stack of tapes under complicated magnetic conditions), the model would only require a few hours to solve the problems with excellent convergence properties. [ABSTRACT FROM AUTHOR]

A method is described for calorimetric ac-loss measurements of high-Tc superconductors (HTS) at 80 K. It is based on a technique used at 4.2 K for conventional superconducting wires that allows an easy loss measurement in parallel or perpendicular external field orientation. This paper focuses on ac loss measurement setup and calibration in a rotating magnetic field. This experimental setup is to demonstrate measuring loss using a temperature rise method under the influence of a rotating magnetic field. The slight temperature increase of the sample in an ac-field is used as a measure of losses. The aim is to simulate the loss in rotating machines using HTS. This is a unique technique to measure total ac loss in HTS at power frequencies. The sample is mounted on to a cold finger extended from a liquid nitrogen heat exchanger (HEX). The thermal insulation between the HEX and sample is provided by a material of low thermal conductivity, and low eddy current heating sample holder in vacuum vessel. A temperature sensor and noninductive heater have been incorporated in the sample holder allowing a rapid sample change. The main part of the data is obtained in the calorimetric measurement is used for calibration. The focus is on the accuracy and calibrations required to predict the actual ac losses in HTS. This setup has the advantage of being able to measure the total ac loss under the influence of a continuous moving field as experienced by any rotating machines. [ABSTRACT FROM AUTHOR]

Magnets made from bulk YBCO are as small and as compact as the rare earth magnets but potentially have magnetic flux densities orders of magnitude greater than those of the rare earths. In this paper a simple technique is proposed for magnetizing the superconductors. This technique involves repeatedly applying a small magnetic field which gets trapped in the superconductor and thus builds up and up. Thus a very small magnetic field such as one available from a rare earth magnet can be used to create a very large magnetic field. This technique which is applied using no moving parts is implemented by generating a traveling magnetic wave which moves across the superconductor. As it travels across the superconductor it trails flux lines behind it which get caught inside the superconductor. With each successive wave more flux lines get caught and the field builds up and up. The wave could be generated in many different ways but the preferred way is simply to heat a material whose permeability changes with temperature at its edge. As the heat travels across the material so the permeability changes and a magnetic wave is generated. It is in effect the first novel heat pump in a very long time and one which will enable the enormous potential available from these unique and highly versatile superconducting magnets to be fully realized. Within this paper we present results showing the superconductor being progressively magnetized by sequentially applied "heat" pulses. We also demonstrate that the sign of the magnetization is reversed if "cold" pulses are applied instead of heat pulses. These experimental results are supported by modeling. [ABSTRACT FROM AUTHOR]

Discharge from public community mental health services has proven difficult for mental health workers and managers. Mental illness can often be long term, with ongoing disability, requiring a need for corresponding long-term care. Community mental health services are now becoming recovery focused and are recognising the need for alternative management arrangements for individuals with long-term care needs. There are, however few tools to assist in the decision making about discharge or transfer of care between community mental health teams. This article describes a quality improvement project to develop a flag for mental health workers to prompt decisions regarding discharge and transfer using the Health of the Nation Outcome Scales (HoNOS). Relevant literature and HoNOS data collected as part of routine clinical practice were reviewed to develop the flag. The implementation process is described along with plans for future developments. [ABSTRACT FROM AUTHOR]

The apparatus described here is designed to measure the total ac loss in 2G tape subjected to a rotating magnetic field of up to 1 Tesla applied perpendicular to the tape axis and at speeds of up to 3600 rpm, while carrying a transport current. Both thermal and electrical measurement techniques are incorporated in the apparatus. The data collected from the apparatus will be used to assist the design of superconducting machines in which the superconductor is used for the stator as well as the rotor and where the minimization of AC losses is crucial to the success of the machine. The measurement of ac losses will give results that are difficult to predict from mathematical modeling. [ABSTRACT FROM AUTHOR]

This paper presents research into superconducting Micro-Bearings for MEMS systems. Advanced silicon processing techniques developed for the Very Large Scale Integration (VLSI) industry have been exploited in recent years to enable the production of micro-engineered moving mechanical systems. These devices commonly known as Micro-Electromechanical Systems (MEMS) have many potential advantages. In many respects the effect of scaling a machine from macro-sized to micro-sized are either neutral or beneficial. However in one important respect the scaling produces a severely detrimental effect. That respect is in the tribology and the subsequent wear on the high speed rotating machines. This leads to very short device lifetimes. This paper presents results obtained from a MEMS motor supported on superconducting bearings. The bearings are self-positioning, relying on, the Meissner effect to provide a levitation force which moves the rotor into position and flux pinning to provide stability thereafter. The rotor is driven by a simple electrostatic type motor in which photo resist is used to pattern the motor poles directly onto the rotor. [ABSTRACT FROM AUTHOR]

This paper explores the role of mental health nurses in medication adherence and their perspective of what influences patients' medication non-adherence. Forty-eight mental health nurses with active patient caseloads completed a comprehensive questionnaire assessing a number of variables related to medications, including whom they felt was primarily responsible for monitoring the side-effects of medication, their knowledge skills and confidence in dealing with medication adherence and their prior education and training in medication adherence strategies. Lack of patient insight was endorsed as the strongest influence on patient non-adherence. Over 84% of nurses indicated they did not have any prior education or training in medication adherence strategies. Implications of the findings for education and training and nurses' roles in supporting medication adherence are discussed. [ABSTRACT FROM AUTHOR]

Investigates the use of flywheels supported on superconducting magnetic bearings for energy storage. Need for high efficiency of flywheel devices; Retrievable energy of the production device; Basis of the experimental rig.

Superconducting journal bearings have been investigated for use in flywheel systems. We report on the zero-field cooled and field-cooled stiffness of these bearings. They are made up of radial magnet rings with alternating polarities, a pole pitch of 11 nun and a surface field of 0.1 T. Field-cooled stiffness of the journal bearings increased four thus over the zero-field-cooled stiffness. [ABSTRACT FROM AUTHOR]

Starting from an existing model by Clem et al., this paper has analyzed how the current density and magnetic field distribution of a stack of superconducting tapes with ac transport currents or applied fields will change in a full cycle. This paper assumes when the ac current or field starts to change in the other direction, a new penetrated region will begin to penetrate from the superconductor surface. If we assume Jc is constant in the critical region, this paper demonstrates that the Claassen formula (7) can be used to calculate the exact ac losses. If Jc depends on local Bz, we can use Eq. (9) to quickly predict the ac losses. This approach does not need to calculate a complete ac cycle. This saves considerably computation time while gives a result which is in close agreement with that calculated from a complete ac cycle. The calculation method can be applied for calculating a superconducting pancake coil if the coil radius is much larger than the tape width. [ABSTRACT FROM AUTHOR]

The article focuses on the study which aims to examine the effect meloxicam administration in cows before caesarean section the lying down behaviour of the said animals following the surgery.

The main obstacle for the application of the high-temperature superconducting (HTS) coated conductors (CCs) in AC energy applications is the relatively large AC loss. To tackle this, several forms of HTS cables for AC applications have been invented and investigated, such as the HTS Roebel cable, Cable on Round Conductor (CORC), and Twisted Stacked Tape Cable (TSTC). In this paper, the possibility of encapsulating Roebel cables into a single HTS CC is investigated, from which a novel conception of a Roebel tape is proposed. Compared with the existing HTS cables, HTS Roebel tapes are more compact, more capable at carrying large current with minimised AC losses, and easier to manufacture. A 3D finite element method (FEM) model of the Roebel tape is built to optimise the structure and verify the performance. The results show that, compared with normal ReBCO CCs, Roebel tapes with optimum patterns can reduce AC transport losses by 60% through field-cancelling and can reduce magnetisation losses by the factor of the filament number through patterning. With excellent loss reduction performance and high current capability, the Roebel tape shows great potential to become a revolutionary HTS cable for high-current power transmission and AC machine applications. [ABSTRACT FROM AUTHOR]

The crossed-magnetic-field effect on the demagnetization factor of stacked second generation (2G) high temperature superconducting tapes is presented. The superconducting sample was initially magnetized along the c-axis by the field cooling magnetization method and after achieving the magnetic relaxation of the sample, an extensive set of experimental measurements for different amplitudes of an applied ac magnetic field parallel to the ab-plane was performed. On the one hand, a striking reduction of the demagnetization factor compared with the reported values for superconducting bulks is reported. On the other hand, the demagnetization factor increases linearly with the amplitude of the ac transverse magnetic field confirming the universal linear behavior for the magnetic susceptibility predicted by Brandt [Phys. Rev. B 54, 4246 (1996)]. The study has been also pursued at different frequencies of the ac transverse magnetic field in order to determine the influence of this parameter on the demagnetization factor measurements. We report an even lower demagnetization factor as long as the frequency of the transverse magnetic field increases. Thus, the significant reduction on the demagnetization factor that we have found by using stacked 2G-superconducting tapes, with higher mechanical strength compared with the one of superconducting bulks, makes to this configuration a highly attractive candidate for the future development of more efficient high-power density rotating machines and strong magnet applications. [ABSTRACT FROM AUTHOR]

Clinicians have been found to hold predominantly negative attitudes toward routine outcome assessments (ROA). This study aims to assess changes in clinicians' attitudes to ROA, and in particular, the provision of feedback from such assessments following a training workshop. Ninety-six mental health workers attended a training workshop on ROA, which was supported by the use of a CD-ROM video resource. Participants completed a questionnaire before and after training that assessed their attitudes toward ROA and the provision of feedback from these assessments. Attitudes toward feedback were predominantly positive at baseline. Significantly more positive attitudes on general attitudes and specific attitudes related to the provision of feedback were found following training. Generating positive clinician attitudes is the first step toward improving the processes and effectiveness of ROA. Controlled trials with a follow up of clinicians' behaviour are needed to determine whether the changes found are maintained and reflected in practice. [ABSTRACT FROM AUTHOR]

A numerical method is proposed to analyse the electromagnetic behavior of systems including high-temperature superconductors (HTSC) in time-varying external fields. The E–J constitutive law together with an H-formulation is used to calculate the current distribution then the magnetisation hysteresis loop of the superconductor can be obtained. This numerical method is adapted to commercial finite element software to solve the partial differential equations time dependently and is able to give accurate results to many problems in complex geometries. [ABSTRACT FROM AUTHOR]

A superconducting fault current limiter (SFCL) in series with a downstream circuit breaker could provide a viable solution to controlling fault current levels in electrical distribution networks. In order to integrate the SFCL into power grids, we need a way to conveniently predict the performance of the SFCL in a given scenario. In this paper, short circuit analysis based on the electromagnetic transient program was used to investigate the operational behavior of the SFCL installed in an electrical distribution grid. System studies show that the SFCL can not only limit the fault current to an acceptable value, but also mitigate the voltage sag. The transient recovery voltage (TRV) could be remarkably damped and improved by the presence of the SFCL after the circuit breaker is opened to clear the fault. [ABSTRACT FROM AUTHOR]

Second generation YBCO tapes have extremely high (∼10000) geometric aspect ratios (width to thickness), which require huge computer resources and thus renders the simulation of fault current limiters (FCLs) based on them very difficult. In this paper we offer a solution to the aforementioned problem by assuming a linear scaling of the thermal and electrical properties with the geometrical size. The results obtained in proprietary software are in very good agreement with those from commercial FEM software. We also compare the limiting properties of YBCO and BSCCO, and find that in order to enable BSCCO to carry the same rated current as YBCO, one needs more than 40 times larger volume of BSCCO. In addition, YBCO limits the current quicker and much more efficiently than BSCCO. Finally, we study the influence of defects on the current limiting properties of HTS tapes and find that defects lead to stronger heating and more non-uniform current and temperature distributions, especially in BSCCO. [ABSTRACT FROM AUTHOR]

We present temperature-dependent modeling of high-temperature superconductors (HTS) to understand HTS electromagnetic phenomena where temperature fluctuation plays a nontrivial role. Thermal physics is introduced into the well-developed H-formulation model, and the effect of temperature-dependent parameters is considered. Based on the model, we perform extensive studies on two important HTS applications: quench propagation and pulse magnetization. A micrometer-scale quench model of HTS coil is developed, which can be used to estimate minimum quench energy and normal zone propagation velocity inside the coil. In addition, we study the influence of inhomogeneity of HTS bulk during pulse magnetization. We demonstrate how the inhomogeneous distribution of critical current inside the bulk results in varying degrees of heat dissipation and uniformity of final trapped field. The temperature-dependent model is proven to be a powerful tool to study the thermally coupled electromagnetic phenomena of HTS. [ABSTRACT FROM AUTHOR]

A comprehensive study of the quench properties of single laminated wires having a double-layered superconducting structure is presented. In particular, we have focused on the influence of the angle and intensity of an external magnetic field perpendicular to direction of the applied current on the minimum quench energy (MQE) and normal zone propagation velocity (NZPV) values. We conclude that strong changes on the NZPV are mainly determined by the intensity of the applied current, while the orientation and magnitude of the applied field have a less but not negligible impact on the resulting NZPV. The quench parameters are also reported for the case when the applied current is considered as a constant parameter in which case the MQE has been found to reach a maximum value when the in-field critical current is the largest. [ABSTRACT FROM AUTHOR]

This paper presents the modeling of second generation (2 G) high-temperature superconducting (HTS) pancake coils using finite element method. The axial symmetric model can be used to calculate current and magnetic field distribution inside the coil. The anisotropic characteristics of 2 G tapes are included in the model by direct interpolation. The model is validated by comparing to experimental results. We use the model to study critical currents of 2 G coils and find that 100 μV/m is too high a criterion to determine long-term operating current of the coils, because the innermost turns of a coil will, due to the effect of local magnetic field, reach their critical current much earlier than outer turns. Our modeling shows that an average voltage criterion of 20 μV/m over the coil corresponds to the point at which the innermost turns' electric field exceeds 100 μV/m. So 20 μV/m is suggested to be the critical current criterion of the HTS coil. The influence of background field on the coil critical current is also studied in the paper. [ABSTRACT FROM AUTHOR]

High temperature superconductor (HTS) is becoming more and more attractive for the application in high field magnets, which can be utilized in the magnetic resonance imaging (MRI) and rotating machines. To charge the HTS magnets and operate them in persistent current mode, a persistent current switch (PCS) is very necessary. This paper will focus on how to build a fast persistent current switch controlled by ac magnetic field. The PCS can present a large resistance rapidly compared with conventional PCS and recover to zero-resistance in a short recovery time. Impacting factors and strategy to control the proposed PCS are discussed. An experimental system is built and tests are carried out to verify the practicality of the proposed PCS. [ABSTRACT FROM AUTHOR]

Since many applications of YBCO tapes operate in external magnetic fields, it is necessary to investigate the magneto-angular dependence of critical current and n-values in coated conductors. In this paper, five commercial YBCO tapes with different microstructures produced by three different manufacturers are chosen. The selected samples have a width of 2.0, 4.0, 4.8, 6.0 or 12 mm, with copper, brass or stainless steel laminations. The critical current density dependence Jc(B, θ) and n-values characteristics n(B, θ) of the tapes are comprehensively measured under various magnetic fields and orientations. Afterwards, the obtained experimental data sets are successfully fitted using a novel multi-objective model which considers the material anisotropy. By using this approach, a fitting function Ic(B, θ) can always be obtained to accurately describe the experimental data, regardless of the fabrication and width differences of the superconducting tapes. Moreover, our experiment shows that when subject to different external magnetic fields, the angular dependence of n-values characteristics is directly correlated with the corresponding critical current profiles. Our results are helpful to predict the critical current of electromagnetically interacting 2G HTS wires, thereby improving the design and performance of the devices made from YBCO tapes. [ABSTRACT FROM AUTHOR]

The application of resistive-type superconducting fault current limiters (RSFCLs) in electrical networks is very attractive due to their relative compactness, light weight, and good performance. However, this technology still has drawbacks: asymmetrical quench, uncertain limiting velocity, passive action and incapability of enlarging capacity. Here, we present an active quenching technique which can potentially solve these problems. The quenching process is triggered using high-frequency (HF) AC fields, which are generated by two coupled copper coils attached on both sides of the YBCO sample. Our experiments show that this approach is effective in guaranteeing uniform quench and therefore is expected to be able to significantly extend the service life of the device. Moreover, the quench speed can be considerably increased by the HF field. We find that the performance of acceleration is positively correlated to the transport current, intensity and frequency of the AC field. In addition, a DC magnetic field is added around the sample holder simultaneously with the AC field, to study the field-angular-frequency dependence of the quench time t(BACfACBDC휃DC). Experimental results prove that the DC magnetic field can cooperate with the HF AC field to accelerate quench, which means better performance can be produced with lower costs with the two fields acting together. In all, this technique showed outstanding performance regarding quench acceleration and tape protection. We believe the HF-assisted quenching technology has a promising future in current-limiting devices and hope our findings could be helpful for its potential applications. [ABSTRACT FROM AUTHOR]

A fully high temperature superconducting motor has been built in the EPEC laboratory at the University of Cambridge, U.K. Two different pulsed field magnetization (PFM) strategies have been implemented for studying the magnetization of a cylindrical rotor designed by an asymmetric array of superconducting bulks. Asymmetric or uneven distribution of superconducting bulks could occur when the size of the superconducting bulks is compromised due to the curvature of the rotor and the design aims to cover the largest area as possible for the magnetic poles. It is certainly an unusual design which nevertheless deserves to be explored, as possible misalignments between the superconducting poles to be magnetized by PFM can be studied when an uneven arrangement of columns of superconducting bulks is implemented for along a cylindrical shaft. In the first of the PFM strategies, only six out of 15 columns of superconducting bulks have been effectively magnetized, and the performance of the resulting rotor has been compared with the case when the PFM strategy leads to the magnetization of up to 93% of the superconducting bulks. The advantages and disadvantages of each of the PFM strategies are discussed. [ABSTRACT FROM PUBLISHER]

Nowadays, superconducting high field magnets are used in numerous applications due to their superior properties. High temperature superconductors (HTS) are usually used for production of circular pancake or racetrack coils. However different geometries of HTS coils might be required for some specific applications. In this study, the HTS coil wound on a rectangular frame was fully characterized in homogeneous DC background field. The study contains measurements of critical current angular dependencies. The critical current of the entire coil and two selected strands under different magnitudes and orientations of external magnetic fields are measured. The critical regions of the coil in different angular regimes are determined. This study brings better understanding of the in- field performance of HTS coils wound on frames with right-angles. [ABSTRACT FROM AUTHOR]

Direct current carrying type II superconductors present a dynamic resistance when subjected to an oscillating magnetic field perpendicular to the current direction. If a superconductor is under a homogeneous field with high magnitude, the dynamic resistance value is nearly independent of transport current. Hoffmann and coworkers [Hoffmann et al., IEEE Trans. Appl. Supercond. 21, 1628 (2011)] discovered, however, flux pumping effect when a superconducting tape is under an inhomogeneous field orthogonal to the tape surface generated by rotating magnets. Following their work, we report the whole Voltage-Ampere (V-I) curves of an YBCO coated conductor under permanent magnets rotating with different frequencies and directions. We discovered that the two curves under opposite rotating directions differ from each other constantly when the transport current is less than the critical current, whereas the difference gradually reduces after the transport current exceeds the critical value. We also find that for different field frequencies, the difference between the two curves decreases faster with lower field frequency. The result indicates that the transport loss is dependent on the relative direction of the transport current and field travelling, which is distinct from traditional dynamic resistance model. The work may be instructive for the design of superconducting motors. [ABSTRACT FROM AUTHOR]

This paper presents the design and modeling of a second-generation (2G) high-temperature superconducting (HTS) magnet, which is suitable for Lorentz force electrical impedance tomography (LFEIT). The concept of constructing a superconducting magnet using the configuration of a Halbach array is proposed, which can achieve a favorable thin geometry for the LFEIT system, and is able to build a homogeneous magnetic field with high intensity. The modeling of this superconducting Halbach array magnet has been executed by COMSOL Multiphysics. \boldsymbolH-formulation together with \boldsymbolB-dependent critical current density and bulk approximation are used as the basic tools for modeling. Results reveal that this magnet can achieve over 1-T magnetic field in the cross section required. The optimization of HTS coils' location and different numbers of coils are carried out to balance the strength and homogeneity of magnetic field. [ABSTRACT FROM PUBLISHER]

A heat-shrink tube insulation for second-generation high-temperature superconducting (2G HTS) coils is studied experimentally in this paper. The insulation can be used to prevent the delamination of 2G HTS due to epoxy impregnation. According to the experiment results, the insulated coil shows no degradation before and after the epoxy impregnation. To validate the performance of 2G HTS coils with the heat-shrink insulation, we measured the transport loss, magnetization loss and total loss of a 2G HTS coil. The study demonstrates the feasibility of the heat-shrink tube insulation method for electrical applications. [ABSTRACT FROM PUBLISHER]

Pancake or racetrack coils wound with second generation high-temperature superconductors (2G HTSs) are important elements for numerous applications of HTS. The applications of these coils are primarily in rotating machines such as motors and generators where they must withstand external magnetic fields from various orientations. The characterization of 2G HTS coils is mostly focused on AC loss assessment, critical current and maximum magnetic field evaluation. In this study, racetrack coils will be placed in different orientations of external magnetic fields--Jc (Ic) versus angle measurements will be performed and interpreted. Full attention is paid to studies of anisotropy Jc versus angle curves for short samples of 2G HTS tapes. As will be shown, the shape of the Jc versus angle curves for tapes has a strong influence on the Jc (Ic) versus angle curves for coils. In this work, a unique and unpredicted behavior of the Jc versus angle curves for the 2G HTS racetrack coils was found. This will be analyzed and fully explained. [ABSTRACT FROM AUTHOR]

A finite element model for a YBCO pancake coil with a magnetic substrate is developed in this paper. An axial symmetrical H formulation and the E-J power law are used to construct the model, with the magnetic substrate considered by introducing an extra time-dependent term in the formula. A pancake coil is made and tested. The measurement of critical current and transport loss is compared to the model result, showing good consistency. The influence of magnetic substrate in the condition of AC and DC current is studied. The AC loss decreases without a magnetic substrate. It is observed that when the applied DC current approaches the critical current the coil turn loss profile changes completely in the presence of magnetic substrate due to the change of magnetic field distribution. [ABSTRACT FROM AUTHOR]

Superconductors are known for the ability to trap magnetic field. A thermally actuated magnetization (TAM) flux pump is a system that utilizes the thermal material to generate multiple small magnetic pulses resulting in a high magnetization accumulated in the superconductor. Ferrites are a good thermal material candidate for the future TAM flux pumps because the relative permeability of ferrite changes significantly with temperature, particularly around the Curie temperature. Several soft ferrites have been specially synthesized to reduce the cost and improve the efficiency of the TAM flux pump. Various ferrite compositions have been tested under a temperature variation ranging from 77K to 300K. The experimental results of the synthesized soft ferrites—Cu0.3Zn0.7Ti0.04Fe1.96O4, including the Curie temperature, magnetic relative permeability and the volume magnetization (emu/cm3), are presented in this paper. The results are compared with original thermal material, gadolinium, used in the TAM flux pump system. Cu0.3Zn0.7Ti0.04Fe1.96O4 holds superior characteristics and is believed to be a suitable material for next generation TAM flux pump. [ABSTRACT FROM PUBLISHER]

As a variation of the thermally actuated flux pump and the linear type magnetic flux pump (LTMFP), the circular type magnetic flux pump (CTMFP) device is proposed to magnetize a circular shape type-II superconducting thin film and bulk. The basic concept is the same as the thermally actuated flux pump: a circularly symmetric traveling magnetic field is generated below a circular shape superconductor to increase its trapping field. However, this traveling field is created by the three phase windings instead of heating gadolinium block. Apart from the LTMFP, the three phase windings are wound concentrically instead of linearly. The speed of the traveling field is controlled by the AC frequency and the magnitude of the field is controlled by the magnitudes of AC currents. In addition, a coil with DC current is wound around the three phase windings to provide a background field. The concept design is presented in this paper. The magnetic waveforms are analysed numerically by the COMSOL 3.5a software. The impedances of the three phase windings are calculated and a corresponding circuit design is presented. This rig can be used as an advanced tool to study the flux pump behavior of a circular shape superconductor. [ABSTRACT FROM PUBLISHER]

In order to design a High Temperature Superconducting (HTS) machine that is able to operate safely and reliably, studies on the characterization of Second Generation (2G) HTS tapes are of paramount importance. This paper presents an experimental setup to measure critical current of 2G HTS tapes in high DC magnetic fields (up to 5 Tesla) with an AC current ripple superimposed, as well as various temperatures ranging from 25 K to 77 K. The 2G tape measured is the SGS12050 coated conductor made by SuperPower. The critical current is measured by a flux vector with reference to the widest sample face from 0 to 90 degrees in 10 degree steps. Smaller steps are required close to 0^\circ. A Variable Temperature Insert (VTI) is utilized to control temperature change. [ABSTRACT FROM AUTHOR]

As we known, the high temperature (77 K) superconducting (HTS) motor is considered as a competitive electrical machine by more and more people. There have been various of designs for HTS motor in the world. However, most of them focus on HTS tapes rather than bulks. Therefore, in order to investigate possibility of HTS bulks on motor application, a HTS magnet synchronous motor which has 75 pieces of YBCO bulks surface mounted on the rotor has been designed and developed in Cambridge University. After pulsed field magnetization (PFM) process, the rotor can trap a 4 poles magnetic field of 375 mT. The magnetized rotor can provide a maximum torque of 49.5 Nm and a maximum power of 7.8 kW at 1500 rpm. [ABSTRACT FROM AUTHOR]

YBaCuO-coated conductors offer great potential in terms of performance and cost-saving for superconducting fault current limiter (SFCL). A resistive SFCL based on coated conductors can be made from several tapes connected in parallel or in series. Ideally, the current and voltage are shared uniformly by the tapes when quench occurs. However, due to the non-uniformity of property of the tapes and the relative positions of the tapes, the currents and the voltages of the tapes are different. In this paper, a numerical model is developed to investigate the current and voltage sharing problem for the resistive SFCL. This model is able to simulate the dynamic response of YBCO tapes in normal and quench conditions. Firstly, four tapes with different Jc's and n values in E\-J power law are connected in parallel to carry the fault current. The model demonstrates how the currents are distributed among the four tapes. These four tapes are then connected in series to withstand the line voltage. In this case, the model investigates the voltage sharing between the tapes. Several factors that would affect the process of quenches are discussed including the field dependency of Jc, the magnetic coupling between the tapes and the relative positions of the tapes. [ABSTRACT FROM AUTHOR]

A high temperature superconducting magnetic energy storage system (HT-SMES) is constructed using YBCO coated conductor and is integrated with a cryogenic system using sub-cooled LN2. A closed loop control algorithm, based on the digital signal processor (DSP) TMS320F2812, is proposed using the 2G HT-SMES to compensate dynamic voltage sag in power systems. A dynamic simulation experiment for compensation of instantaneous voltage sag is achieved. The experiment circuit is built using a signal conditioning circuit, a DSP controlling circuit, a power conversion circuit and a SMES unit. Analysis of the voltage waveforms before and after compensation validates that this SMES system is able to compensate instantaneous voltage sag. [ABSTRACT FROM AUTHOR]

This paper begins with introducing the winding techniques of two superconducting double-pancake coils wound using 2G coated conductors. These winding techniques are able to guarantee a good performance for the superconducting coils. Then the coil critical currents were measured and compared with a simulation model. The results were consistent. Finally the coil AC losses were measured using an experimental circuit including a compensation coil. The simulation results are close to the experiment results. [ABSTRACT FROM AUTHOR]