Flux Pump Research Articles

Miniaturized HTS linear flux pump with a charging capability of 120 A

Owing to the presence of joint resistance and flux creep, high-temperature superconducting (HTS) coils without a power supply inevitably suffer from current decay. A flux pump is a voltage supply that requires connections with smaller footprints and a lower heat load than traditional current leads. In this study, we explain the principle of the upper limit for the output current of the traveling wave flux pumps. Based on this principle, a miniaturized linear flux pump device was developed. With narrow and misaligned iron teeth, elaborate 3D geometry of the iron pieces, and optimized driving current waveform, the miniaturized flux pump can support more than 120 A output current with only a 10 mm wide HTS tape and a compact size of 4.6 × 4.6 × 3.4 cm. Our experimental results show that the critical current of the HTS tape has a significant effect on the flux pump output. An HTS tape with a larger critical current supports a higher maximum transport current, whereas an HTS tape with a smaller critical current requires less applied current for positive output. Finally, excitation tests on HTS coils were performed. Charge/active discharge and field supplement experiments were done on a maglev HTS racetrack coil of 0.4 H, where charging/field supplement capability of the miniaturized flux pump were demonstrated up to 46.8 A (close to the critical current of the coil). It has also been proved that the flux pump can work together with an external power supply with persistent current switch. The miniaturized flux pump can also independently charge an HTS coil of 60 μH to 91.6 A, which is the critical current of the coil at a low voltage criterion.

Effective circuit modelling and experimental realization of an ultra-compact self-rectifier flux pump

This paper presents experimental and modelling results of an ultra-compact self-rectifier flux pump (FP) energizing a superconducting coil. The device fits inside a volume of mm and generates up to 320 A dc through the coil and a peak output voltage up to 60 mV. We also develop and present a full electromagnetic effective circuit model of the FP and compare its predictions to the experimental results. We show that our model can reproduce accurately the charging of the load coil and that it reproduces the systematic dependence of the maximum load coil current on the input current waveform. The experiments and modelling together show also the importance of dc-flux offsets in the transformer core on the final achievable current through the coil. The miniaturization possible for this class of FP and their minimal heat-leak into the cryogenic environment from thermal conduction make them attractive for applications with demanding size, weight and power limitations. Our effective circuit model is a useful tool in the understanding, design and optimization of such FPs which will accelerate their progression from research devices to their application.

Feedback-controlled flux modulation for high-temperature superconducting magnets in persistent current mode

High-temperature superconducting (HTS) magnets have found wide applications in high-field settings owing to their high current capabilities. Typically, these magnets are powered by high-current power supplies via current leads, which can complicate insulation between cryogenic and room temperature environments. However, new developments in flux pumps for HTS magnets have enabled charging of kA levels of current without power supplies. By combining flux pumps with HTS persistent current operation, it is possible to achieve accurate flux modulation and eliminate the need for power supplies and current leads. In this study, we report on a novel feedback-controlled flux modulation for HTS magnets in persistent current operations. This flux modulation is based on a flux pump mechanism that generates a DC voltage across the charging superconductor by applying a current higher than its critical current. With closed-loop feedback control, our flux modulation can achieve precise injection and reduction of HTS magnet current in increments of 0.5 A. This technology can lead to stable magnetic fields in HTS magnet designs. We anticipate that this work will enable future magnets to operate in a stable persistent current mode within a closed cryogenic chamber, significantly reducing the footprint and power demand of HTS magnets and opening up new opportunities for their applications.

Stator optimization for HTS rotating permanent magnets based flux pump

Stator optimization for HTS rotating permanent magnets based flux pump

Achieving High Ion Flux and Uphill Pumping in Nanofluidic Membranes Reconstructed from Layered Double Hydroxide Nanosheets

Achieving High Ion Flux and Uphill Pumping in Nanofluidic Membranes Reconstructed from Layered Double Hydroxide Nanosheets

Critical current asymmetry in HTS switches using iron-core electromagnets

Iron-core electromagnets are widely used as applied-field switches in high-temperature superconducting (HTS) flux pumps. It was recently reported that the critical current () of the HTS wire is suppressed by up to 45% in the air gap of the iron core. Here, it is reported that the self-field of a single tape (unifilar) is suppressed from 357 A to 195 A while in the air gap of an iron core, agreeing closely with the previous study. This is extended by showing that the response to a perpendicular magnetic field is asymmetric, with a peak of 249 A found to be at 0.16 T of applied magnetic field. This effect can be eliminated using an anti-parallel current configuration (bifilar), which is shown experimentally to recover close to the no-core self-field of 357 A with no observed asymmetry. The results of both types of switch configurations are closely replicated in finite-element modelling using COMSOL Multiphysics®. This is caused by the asymmetric interaction between the self-induced magnetic field of the HTS switch element and the magnetic circuit of the iron-core electromagnet.

A Noninductive Bifilar Coil to Design Compact Flux Pumps for HTS Magnets

High-temperature superconducting (HTS) flux pump is a promising way of energizing superconducting magnets without direct electrical contacts. It can remove the resistive heating and heat leakage from the current leads at room temperature. It is well known that applying the current over the critical current of the superconductor will force the superconducting layer to enter into the flux flow regime. This flux flow resistivity generates a dc voltage across the length of the HTS tape. This phenomenon is well understood; however, it is difficult to generate a high dc charging voltage without a high current. In this article, we demonstrate a novel flux pumping technique by using a noninductive bifilar bridge wound in parallel to the HTS coil. This configuration can generate large dc voltages using relatively small currents. It results in effectively pumping dc currents equal to the critical current for large HTS magnets.

The Combined Effects of the Membrane and Flow Channel Development on the Performance and Energy Footprint of Oil/Water Emulsion Filtration.

Membrane filtration is a promising technology for oil/water emulsion filtration due to its excellent removal efficiency of microdroplets of oil in water. However, its performance is highly limited due to the fouling-prone nature of oil droplets on hydrophobic membranes. Membrane filtration typically suffers from a low flux and high pumping energy. This study reports a combined approach to tackling the membrane fouling challenge in oil/water emulsion filtration via a membrane and a flow channel development. Two polysulfone (PSF)-based lab-made membranes, namely PSF- PSF-Nonsolvent induced phase separation (NIPS) and PSF-Vapor-induced phase separation (VIPS), were selected, and the flow channel was modified into a wavy path. They were assessed for the filtration of a synthetic oil/water emulsion. The results showed that the combined membrane and flow channel developments enhanced the clean water permeability with a combined increment of 105%, of which 34% was attributed to the increased effective filtration area due to the wavy flow channel. When evaluated for the filtration of an oil/water emulsion, a 355% permeability increment was achieved from 43 for the PSF-NIPS in the straight flow channel to 198 L m-2 h-1 bar-1 for the PSF-VIPS in the wavy flow channel. This remarkable performance increment was achieved thanks to the antifouling attribute of the developed membrane and enhanced local mixing by the wavy flow channel to limit the membrane fouling. The increase in the filtration performance was translated into up to 78.4% (0.00133 vs. 0.00615 kWh m-3) lower in pumping energy. The overall findings demonstrate a significant improvement by adopting multi-pronged approaches in tackling the challenge of membrane fouling for oil/water emulsion filtration, suggesting the potential of this approach to be applied for other feeds.

Contactless superconducting field exciter with active current control using hybrid magnet for high-temperature superconducting rotating machine

Rotary-type high-temperature superconducting (HTS) flux pumps using permanent magnets (PMs) are effective contactless superconducting excitation devices used for generating excitation in the field winding of HTS rotating machines. Although contactless superconducting excitation devices overcome the disadvantages of conventional contact-type excitation systems, those based on PMs are not the ideal solution because current supply to the field winding is allowed only when the HTS rotating machine is rotating in the same direction: a rapid discharge occurs when the rotation direction is reversed. They do not meet the practical operational requirements of rotating machines, viz., initial start, load fluctuation, and direction change, and alternatives to actively control excitation of field winding are essential. In this study, novel functions to improve the application feasibility in various HTS rotating machine operation modes have been proposed. Based on a numerical analysis, a prototype contactless superconducting active excitation device (CSAED) comprising PMs, alternating current (AC) and direct current (DC) electromagnets was developed using the hybrid magnet concept. The operational characteristics of active control functions in the CSAED were experimentally analysed for stationary, forward, reverse, and compensation operations of the HTS rotating machine and the qualitative effectiveness for active control of the charged current was verified. The first novel function CSAED using AC electromagnet was successfully demonstrated in initial current excitation by generating the alternating magnetic field without physical rotation for a small-scale HTS magnet. However, upgrading of the AC electromagnet is required to apply for large-scale load magnet due to small value in saturation current of the CSAED. The second novel function of CSAED using DC electromagnet worked well in current-adjustment and current-conservation modes by controlling the magnetic field density using the hybrid magnet. By controlling the current of DC electromagnets without any change in the rotation speed, the saturation current was adjusted within the ranges from 61.4 A to 1.7 A, which are 86.6 and 2.4 % of critical current for load HTS magnet, respectively. In the reverse rotation, the current discharging time of CSAED using activation of DC electromagnet increased by 2474 % compared to without energizing the DC electromagnet.

Analytical approximations for the self-field distribution of a superconducting tape between iron cores

Magnetic switches apply AC magnetic fields to DC current-carrying high temperature superconducting (HTS) tapes to generate DC voltages and are commonly used in the persistent current switches (PCSs) and flux pumps to charge HTS-coated conductor magnets. Normally, they are made of copper field coils and iron cores with narrow air gaps for the HTS tape to pass through. However, the perpendicular components of the self-field of the HTS tape in the air gap can be enhanced by the iron cores and cause a critical current reduction of up to 40% to the tape. If ignored, this reduction, rather than the magnets themselves, will limit the current carrying capability of the HTS magnets. To tackle this problem, we present analytical approximations to calculate the self-field distribution of a superconducting tape between iron cores. The approximate solutions are based on the method of images in electromagnetics to simplify the derivation and are then verified by the experiments and 3D finite element method models using the T–A formulation. The solutions are universal and can be applied to almost all the magnetic switches currently in use. A case study of typical magnetic switches shows that the solutions can be used to determine the critical current reduction quickly and accurately, analyse the influence of different parameters, and simplify the design process of magnetic switches. The results can significantly benefit the design and optimisation of PCSs and flux pumps for HTS magnet charging systems in the future.

Evaluation of ellagic acid and gallic acid as efflux pump inhibitors in strains of Staphylococcus aureus.

ABSTRACTThe Gram-positive bacterium Staphylococcus aureus is responsible for a number of infections and has been described to exhibit resistance to antibacterial drugs through different resistance mechanisms. Among these, active efflux has been shown to be one of the main mechanisms of bacterial resistance associated with S. aureus. In this sense, the aim of the present study was to evaluate the ability of ellagic acid and gallic acid to reverse resistance by inhibiting the efflux pumps present in S. aureus strains IS-58 and K2068, which express the TetK and MepA flux pumps, respectively. In addition, the toxicity of both compounds was verified in Drosophila melanogaster. Broth microdilution assays were performed to obtain the minimum inhibitory concentration (MIC) values of ellagic acid and gallic acid, whereas efflux pump inhibition was tested using a subinhibitory concentration of standard efflux pump inhibitors, gallic acid and ellagic acid (MIC/8), where the ability of these compounds to decrease the MIC of ethidium bromide (EtBr) and antibiotics was verified. Toxicity was evaluated by mortality and negative geotaxis assays in D. melanogaster. Ellagic acid and gallic acid showed no direct antibacterial activity on S. aureus strains carrying the efflux pumps TetK and MepA. However, when we looked at the results for the TetK pump, we saw that when the two acids were associated with the antibiotic tetracycline, a potentiation of the antibacterial effect occurred; this behavior was also observed for the antibiotic ciprofloxacin in the MepA strain. For the efflux pump inhibition results, only the compound gallic acid showed potentiating effect on antibacterial activity when associated with the substrate EtBr for the IS-58 strain carrying the TetK efflux pump. Ellagic acid and gallic acid showed no toxicity on the model arthropod D. melanogaster. These results indicate the possible use of gallic acid as an adjuvant in antibiotic therapy against multidrug-resistant bacteria.

Flux Pumping of Multiple Double-Loop Superconducting Structures for a Planar Magnetic Field Source

Flux Pumping of Multiple Double-Loop Superconducting Structures for a Planar Magnetic Field Source

A Kilo-Amp Linear-Motor Type Flux Pump

A kilo-amp linear-motor type flux pump with the maximum output DC current exceeding 1610 A had been designed and manufactured. We had optimized the large-current flux pump based from the previous design, and shortened the travelling wavelength of the flux pump, and simulated its magnetic density distribution with COMSOL Multiphysics, and obtained the present design parameters after analysis. We had placed 12 superconducting single loops side by side in the air gaps on both sides of the flux pump, and had used the flux pump to charge them. We had applied different magnetic flux density in the air gap, the maximum DC output current of the flux pump was measured at 1619 A in the liquid nitrogen at 77 K. We have carried out theoretical analysis on the direction of the pumped current on both sides of the flux pump, while had changed the polarities of the DC windings to make sure that the current directions on both sides are the same. Comparing with the traditional superconducting power supply of the same output current level, this flux pump had not only eliminated the current leads, but also reduces the cost, size and energy consumption of the power source by at least one order. Finally, we designed the prototype of the kilo-amp linear-motor type flux pump to measure the critical current of the superconducting cables.

The Performance Test of an Updated Linear-Motor Flux Pump With Single-Sided DC Winding

In order to further optimize the size of the linear-motor type flux pump, an updated linear-motor type motor flux pump device with single side DC winding was designed and fabricated. Compared with the previous generation of linear-motor type flux pump with traveling wave length of 21 mm, the volume of this generation of linear-motor type flux pump with traveling wave length of 15 mm is reduced by nearly 30% and the pumping current capacity is increased by more than 30%, which generated the same DC biased AC travelling magnetic wave in the airgap, and pumped DC current into the high temperature superconducting (HTS) closed-loop in a non-contacting manner, based on the macroscopic magnetic coupling effect. In this work, we tested the performances of this updated flux pump device. We pumped current into two parallel superconducting stators and a YBCO double pancake coils. The pumping current of two parallel superconducting stators reached 219 A, while pumped current in YBCO double cake coil (DPC) reached 73 A, mainly due to the limit of the small critical current of the HTS DPC. The experimental results show that using one-sided DC coil can achieve effective bias effect, which further verified the rationality of explanation based on the macroscopic magnetic coupling effect. These results are helpful to optimize the HTS flux pump device and further understand the working mechanism of the flux pump.

A Novel Switch Design for Compact HTS Flux Pump

High temperature superconducting (HTS) magnets are becoming more and more attractive for many commercial applications. HTS magnets, however, need an external power supply to operate in persistent current mode. One way to charge an HTS magnet is using a conventional power supply. This, however, is not the most efficient way to charge an HTS magnet due to losses from the current leads. Flux pumping is an alternative method to charge an HTS magnet. Over the years different types of flux pumps have been proposed specific to different applications. Transformer-rectifier flux pump is one of the many types of flux pumps that have been researched widely. The design of switches plays a central role in a transformer-rectifier flux pump. In this paper, we propose a novel switch design for a half-wave transformer-rectifier flux pump. The switch proposed in this study will be used in compact and mobile HTS Magnetic Resonance Imaging (MRI) instruments.

Conduction-Coolled HTS Magnets Closed-Loop System Excited by a Rotating Magnets Flux Pump

High-temperature superconducting flux pumps usually need to work in a liquid nitrogen immersion environment, which limits their practical high-field magnet applications. In this paper, China's first conduction-coolled high-temperature superconducting flux pump with a rotating magnet structure is developed, and a non-insulated (NI) high-temperature superconducting coil with considerable inductance has been successfully excited. The vacuum dynamic sealing technology is used to isolate the rotating motor and drive leads from the low-temperature dewar, and ultimately minimize the thermal load of the flux pump, making future applications in MRI/NMR and superconducting motors/generators possible. Comprehensive measurement and analysis of parameters such as excitation current, excitation rate, magnetic field stability, and power consumption. Under the cooling conditions of the G-M cryogenic cooler in the temperature range of 30 K to 50 K, the feasibility and reliability of using the mechanical flux pump as the power source to excite the high-temperature superconducting magnet is verified.

An Active Controllable Demagnetization of Closed-Loop HTS Magnet and its Distributed 2.5D H-Model

Closed-loop high temperature superconducting (HTS) magnets have great potential to be used in many fields due to their abilities to be operated in persistent current mode. However, in emergency rundown, they are required to get demagnetized actively and controllably. In this paper, an active controllable demagnetization of closed-loop HTS magnet by flux pump with thermal switches is proposed and investigated. The Joule heat dissipated and the transport current in the magnet during demagnetization is calculated numerically. Besides, in order to improve the calculation speed, a distributed 2.5D H-model of the magnet is suggested, in which the computing tasks are divided into two coupled parts: a 3D model and a 2D axisymmetric model, and are deployed on two different computing nodes. Experiments are carried out to verify the rationalities of the introduced demagnetization method and the distributed 2.5D H-model. The results shows that the proposed demagnetization method can realize active-controlled demagnetization of a closed-loop HTS magnet rapidly without generating too much heat, and, compared with H formulation, the suggested model can effectively reduce the calculation time.

Improving the Central Magnetic Field of an HTS Magnet Using Multiple Flux Pumps

This paper investigated the method of using multiple linear-motor flux pumps to increase the central magnetic field of an HTS magnet composed of six stacking insulated YBCO double pancake coils. In this work, we compared two different excitation methods based on linear-motor flux pumps, i.e., in series excitation and in segmented excitations, to investigate their exciting performances on this HTS magnet. Experiments showed that in the series excitation, the maximum operation current of the HTS magnet was limited by the YBCO coil of the smallest critical current. On the other hand, in the segmented excitations, both the maximum operation current of each YBCO coil and the central magnetic field of the HTS magnet were increased effectively. Moreover, in the segmented excitation, we revealed the interaction between excitation current of one YBCO coil, to the induced currents of other YBCO coils, due to their mutual inductances and different charging sequences. In addition, we found that the charging sequences had an influence on the maximum central magnetic field of the HTS magnet, due to the different vertical field on different YBCO coils, which was consistent with the simulation results. The results of this work showed that using multiple linear-motor flux pumps for excitation can effectively increase the magnetic field of an HTS magnet.

A statistical model for the design of rotary HTS flux pumps based on deep-learning neuron network

Rotory high temperature superconducting (HTS) flux pumps can consistently generate a DC voltage by rotating magnets over superconducting tapes, and thus energize the circuit if a closed loop is formed. The voltage output is a crucial factor to reflect the performance of such an HTS flux pump, which is determined by a set of design specifications, and some of them have been investigated extensively in the current literature. However, no work has been done yet to study the HTS dynamo output voltage by efficiently integrating all the design parameters together. In this paper, a well-trained deep-learning neuron network (DNN) with back-propagation algorithms has been put forward and validated. The proposed DNN is capable of quantifying the output voltage of an HTS dynamo instantly with an overall accuracy of approximately 98% with respect to the simulated values with all design parameters explicitly specified. The model possesses a powerful ability to characterize the output behavior of HTS dynamos by considering multiple design parameters, e.g., airgap, superconductor tape width, operating frequency, remanent flux density, rotor radius, and permanent magnet width, which have covered all the typical design considerations. The output characteristics of an HTS dynamo against each of the design parameters have been successfully demonstrated using this model. Compared to conventional time-consuming finite element method (FEM) based numerical models, the proposed DNN model has the advantages of automatic learning, fast computation, as well as strong programmability. Therefore the DNN model can greatly facilitate the design and optimization process for HTS dynamos. An executable application has been developed accordingly based on the DNN model, which is believed to provide a useful tool for learners and designers of HTS dynamos.

Thermal Behavior Modelling of a Fast AC Field Controlled HTS Switch

When a type II superconductor carrying a direct current is subjected to a perpendicular AC magnetic field, a DC voltage can be observed, commonly referred to as “dynamic resistance effect”. This dc voltage appears in a very short time when AC field is applied and disappears quickly when AC field is removed. These advantages make the type II superconductors to be a fast AC-field-actuated HTS switch, which plays an important role in many potential high-temperature superconducting (HTS) applications, especially for HTS flux pumps or HTS magnetic energy storage systems. However, the temperature in the superconductor varies due to this dc voltage and may result in quench for the superconductor. Therefore, it is important to investigate the thermal behavior of an AC-field-actuated HTS switch. In this paper, we build and experimentally verified a 2D electromagnetic-thermal coupled model to investigate the electromagnetic-thermal characteristics of HTS switches in different working conditions. This model can estimate the dynamic voltage rise and the temperature rise of the superconductor. This work is indicative for designing an AC-field-actuated HTS switch in terms of increasing the dc voltage, and enhancing the safety and stability.