Superconducting Magnet Research Articles

Yu-Shiba-Rusinov bound states studied by tuning the electron density at the Fermi energy

Magnetic atoms can break the Cooper pairs of superconductors, leading to the formation of Yu-Shiba-Rusinov (YSR) bound states inside superconducting gaps. Theory predicts that the YSR bound states can be controlled by tuning the electron density at the Fermi energy, but it has not been studied deeply. In this work, we studied the nature of YSR bound states in response to the potential scattering U by tuning the electron density at the Fermi energy. By comparing two systems, Mn-phthalocyanine molecules on Pb(111) and Co atoms on PbSe/Pb(111), we demonstrate that the sign of U can be unambiguously determined by varying the electron density at the Fermi energy. We also show that U competes with the exchange interaction JS in the formation of YSR bound states. Our work provides insights into the interactions between magnetic atoms and superconductors at a fundamental level.

Topological magnetic order and superconductivity in EuRbFe4As4

We study single crystals of the magnetic superconductor EuRbFe$_4$As$_4$ by magnetization, electron spin resonance (ESR), angle-resolved photoemission spectroscopy (ARPES) and electrical resistance in pulsed magnetic fields up to 630 kOe. The superconducting state below 36.5 K is almost isotropic and only weakly affected by the development of Eu$^{2+}$ magnetic order at 15 K. On the other hand, for the external magnetic field applied along the c-axis the temperature dependence of the ESR linewidth reveals a Berezinskii-Kosterlitz-Thouless topological transition below 15 K. This indicates that Eu$^{2+}$-planes are a good realization of a two-dimensional XY-magnet, which reflects the decoupling of the Eu$^{2+}$ magnetic moments from superconducting FeAs-layers.

Study of Superconducting Magnetization Effects and 3D Electromagnetic Analysis of the Nb$_3$Sn cos$\theta$ Short Model for FCC

The Falcon Dipole (Future Accelerator post-LHC Cos-theta Optimized Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn Dipole) is a single aperture Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn cos-theta dipole short model in the framework of the Future Circular Collider (FCC) project. The Italian Institute of Nuclear Physics (INFN), in collaboration with CERN, is in charge of designing and constructing the magnet, which is a crucial step towards the construction of High Field Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn magnets suitable for a post LHC collider. This paper recalls the electromagnetic design, the field quality and performances of the Falcon Dipole. The coil ends design has been implemented in a 3D FEM to study the peak field distribution on the magnet and influence on field quality. A special focus is given to the 2D analysis to study the effect of superconductor magnetization on field quality from the injection to the final energy and then to investigate the effectiveness of compensation methods.

Rotating magnetization method for inspection of local defect in HTS conductor

High temperature superconducting (HTS) magnet used for a accelerator for high energy physics or a large-scale magnetic confinement system for nuclear fusion requires large current capacity HTS conductor in order to dump the stored magnetic energy quickly to protect the coil when quench has been occurred. To realize the HTS conductor, superimposed or stacked HTS tapes conductors are invented. However, local degradation of the critical current has been observed in the production of HTS conductors. Therefore, to confirm the soundness of the HTS conductor, it is necessary to establish the non-destructive detection method for the observation of degraded HTS tapes. In this study, we have investigated to inspect the degradation position in stacked HTS tapes by adopting rotating magnetization measurement method. This measurement method is measuring magnetization signal by rotating and transporting stacked HTS tapes in a static magnetic field. As a result, intentionally introduced buckling defect positions were detected by this measurement method.

Upper Limit Estimation of Resistive Heating Made by No-Insulation HTS Magnet Having Defects

Seoul National University and Hanmi Techwin Inc. have launched a program for the development of a large bore, low field, and low-cost high temperature superconductor (HTS) magnet for industrial applications. HTS coils exhibit defect-irrelevant behaviors when wound using no-insulation (NI) technique, i.e., wound without turn-to-turn insulation. Incorporation of defect-irrelevant winding (DIW) technique would be favorable to constructions of HTS magnets as it may drive the cost of production down and curtail construction time if used appropriately. An HTS magnet having a center magnetic field of 2 T and cold bore size of 230 mm has been designed, and charging simulation was performed using a turn distributed circuit model. Defect-irrelevant behaviors are examined stochastically, considering random occurrences of defective turns. Using the turn distributed circuit model indicates that the magnitudes of defects have limited effects on resistive heatings in both steady state and transient operations. The upper bounds of excess heat contributed by defective turns are numerically formulated using characteristic resistances and operating currents.

Hot-Spot Modeling of REBCO NI Pancake Coil: Analytical and Experimental Approaches.

The No-Insulation (NI) winding provides intrinsic bypassing current paths that enable self-protection from overheating. The self-protection of the NI coil is one of the most promising protection techniques for the high field high-temperature superconductor (HTS) magnet applications. Since the additional paths are valid for an HTS magnet with a thinner matrix, the self-protection mechanism is applicable even for the higher current density magnet with reduced matrix thickness inside the HTS tape. However, reducing the matrix can cause damage to the magnet by producing excessive heat during the quench. This research introduces a new modeling method to investigate the hot-spot characteristics in the REBCO NI pancake coil. The model is also validated with a sample NI HTS coil experiment result. Radial direction Normal Zone Propagation (NZP) velocity of the sample coil is estimated based on the suggested model. The calculated radial direction NZP velocity is applied to calculate the center field drop of the NI HTS coil, and the result is well-matched with the experiment result. We also introduce one example of the model applications. The maximum current density that will not exceed a given reference temperature in the adiabatic cooling condition is estimated using the model.

Design and Construction of a High Field Cable Test Facility at Fermilab

Fermi National Accelerator Laboratory, together with Lawrence Berkeley National Laboratory, is building a new High Field Vertical Magnet Test Facility (HFVMTF) to be situated in the Magnet Test Facility at Fermilab. The HFVMTF is jointly funded by the US DOE Offices of Science, High Energy Physics, and Fusion Energy Sciences, and will serve as a superconducting cable test facility for both communities. The background magnetic field for test samples is 15 T and will be produced by a magnet provided by LBNL operating at 1.9 K in superfluid helium. The samples will be placed in the background magnetic field, cooled to between 4.5 K and a user-specified upper limit, and will be powered with a superconducting transformer at up to 100 kA. Additionally, this facility will be used to test high-field superconducting magnet models and demonstrators, including hybrid magnets, produced by the US Magnet Development Program. Currently, the various tasks of the project are at different stages of execution, from conceptual to ready-for-construction designs. This paper describes the parameters and design status of the pit construction, cryostat, heat exchanger, lambda plate, power system, and quench protection and monitoring systems of the facility.

Development of a Cryogen-Free Compact 3 T Superconducting Magnet for an Electromagnetic Property Measurement System

A cryogen-free portable 3 T high-temperature superconducting magnet for an electromagnetic property measurement system has been developed to serve as a user facility at the Korea Basic Science Institute. The metallic insulation method was adopted to reduce the charging delay without sacrificing the self-protecting feature. A genetic-algorithm-aided optimized design was carried out to minimize the superconducting tape consumption while satisfying several design constraints. After the design, the compact high-temperature superconducting magnet composed of eight double-pancake coil modules was wound with high-temperature superconducting tape and stainless steel tape, and integrated with a two-stage cryo-cooler. The 3 T magnet was successfully cooled to approximately 20 K with a cryo-cooler and reached the target field of 3 T without any problems. Long-term measurements and a range of other tests were also implemented to verity the performance of the magnet. Test results demonstrated the feasibility of a cryogen-free portable high-temperature superconducting magnet system for electromagnetic property measurement experiments.

Neon-Helium Hybrid Cooling System for a 10 MW Class Superconducting Wind Power Generator

In this paper, we describe a cooling system for a high temperature superconducting (HTS) magnet of 10 MW class superconducting wind power generator (SWPG). To cool the HTS magnet below 35 K, a novel neon-helium hybrid cooling system is proposed. Neon cools the heat exchanger based on the thermosiphon principle and a cryogenic blower forcibly circulates helium gas between the heat exchanger, attached to a rotating neon vessel, and the HTS magnets. This cooling system has two advantages: applicability to large rotating HTS magnets and high reliability by removing a cryogenic or a high-pressure rotating coupling. To verify the performance of this cooling system, a lab-scale performance evaluation system(PES) is designed. The PES will be proved by cooling the generated heat and penetrated heat of the HTS magnets during operation. This paper describes the detail design process and the preliminary test results of the fabricated cooling system.

A Two-Dimension Force Model Between High-Temperature Superconducting Bulk YBaCuO and Halbach-Type Permanent Magnet Guideway

With the merits of self-levitation, self-stabilization, zero magnetic drag, environment-friendliness, and low energy consumption, high-temperature superconducting (HTS) maglev is regarded as one of the main technology modes for the future rail transit. For the researches on the lateral-vertical coupled dynamics of the HTS maglev, there is still a lack of lateral-vertical coupled force model that can characterize the macroscopic force between high-temperature superconductor and permanent magnet guideway (PMG). In this article, a scanning experiment of levitation force and guidance force in a selected area on the vertical plane was carried out, and the law of levitation force and guidance force changing with coordinates was studied as well. Moreover, the finite element method was used to calculate the magnetic field distribution of the Halbach-type PMG, meanwhile, the Lorentz force formula was utilized to analyze the influence law of PMG's magnetic field on the levitation force and guidance force. On the basis of this research, a 2-D force model that neglects the hysteretic between high-temperature superconductor and PMG was established. By comparing the simulation results of the model with the measured data of the experiment, it is found that both of them are in good agreement, which verifies the reliability of the proposed model. The 2-D force model is very helpful to the future research and calculation of the dynamics of the HTS maglev.

Fusion startup plans reactor with small but powerful superconducting magnets

Fusion startup plans reactor with small but powerful superconducting magnets

A Study on Cooling System of HTS Quadrupole Magnets for Heavy Ion Accelerator

Quadrupole magnets located at the front end of an in-flight fragment (IF) separator in a heavy ion accelerator have large heat loads due to neutron radiation. Thus, high-temperature superconducting (HTS) magnets are used instead of low-temperature superconducting (LTS) magnets because of their high cooling efficiency and thermal stability. The cooling system of the HTS magnet uses circulation of cold helium gas. The circulating helium gas is provided from the distribution box, where helium gas lines are divided into 7 pairs of small helium lines corresponding to 7 HTS magnets. To cool down the 7 HTS magnets with different heat loads, the mass flow rate of each magnet should be individually controlled by monitoring the temperature of the magnets. This paper describes the cooling system for the 7 HTS magnets considering the heat load of each magnet and the thermohydraulic characteristics of the cooling system, including a heat exchanger, a cryogenic blower, control valves, etc. The helium mass flow rates for each magnet and the temperature at the outlet of the magnet are determined so that the magnets operate below 45 K. The optimal helium mass flow rates for each magnet were determined by analyzing the correlation between the magnet outlet temperature and flow rate.

Evaluation of the Structural Dynamics of a 2G HTS Magnet System Considering Electromagnetic and Thermal Stress

Magnetically levitated (maglev) trains with superconducting technology has been developed rapidly in recent decades due to such promising features as high cruising speed. The second-generation high-temperature superconducting (2G HTS) magnets used on maglev trains are state-of-the-art among different types of magnets, like permanent magnets, electromagnets, or low-temperature superconducting magnets. A series of works have been done by the group on the development of the 2G HTS maglev, including optimal design, manufacturing, and testing of the ground propulsion system and on-board 2G HTS magnet system. In this work, as a continuation of the development progress, the structural dynamics of the on-board 2G HTS magnet system are evaluated. Since the HTS magnets are operated in a cryogenic environment featuring large current inflows, consideration of both the electromagnetic and thermal stresses on the maglev's structural dynamics is necessary. Modal analysis, harmonic response, random vibration, and shock response are conducted, based on standard IEC 61373. Fatigue assessment is also provided.

Discharge Behaviour and Modelling of a 1.5T REBCO Magnet With Quench Tolerant Coils Impregnated with Conductive Epoxy.

We have designed and built a small, conduction cooled, 1.5 T high-temperature superconductor (HTS) magnet. The magnet coils have been wet-wound with a novel conductive epoxy resin system to achieve a derivative of the no-insulation coil winding method. The epoxy is filled with copper powder to reliably set the turn-to-turn contact resistivity and diamond powder to accurately space the coil turns apart, as well as match the filled epoxy thermal contraction rate to that of the HTS. The magnet is designed to act as a test bed to measure sudden discharge rates and hence validate models of coil behaviour using the filled epoxy system we have developed. A lumped-element electrical model was used to predict the coil contact resistivity needed to bring the magnetic field of the 1.5 T magnet down to a near-zero level within 0.5 s. The conductive epoxy blend was tuned to give a contact resistivity of 1 × 10-6 Ω m2, based on previous measurements of coil contact resistivity at 77 K. Once the magnet was wound and tested at 40 K, we found the magnet's sudden discharge time constant was 500 ms rather than 69 ms as was predicted from the 77 K measurements. The discrepancy was traced to the temperature dependence of the contact resistivity. With further testing of the individual coils this was accounted for and the model adjusted. The predicted discharge time was 2 s, in good agreement with the measured sudden discharge time of the magnet.

Intelliquench: An Adaptive Machine Learning System for Detection of Superconducting Magnet Quenches

In superconducting magnets, the irreversible transition of a portion of the conductor to resistive state is called a “quench.” Having large stored energy, magnets can be damaged by quenches due to localized heating, high voltage, or large force transients. Unfortunately, current quench protection systems can only detect a quench after it happens, and mitigating risks in Low Temperature Superconducting (LTS) accelerator magnets often requires fast response (down to ms). Additionally, protection of High Temperature Superconducting (HTS) magnets is still suffering from prohibitively slow quench detection. In this study, we lay the groundwork for a quench prediction system using an auto-encoder fully-connected deep neural network. After dynamically trained with data features extracted from acoustic sensors around the magnet, the system detects anomalous events seconds before the quench in most of our data. While the exact nature of the events is under investigation, we show that the system can “forecast” a quench before it happens under magnet training conditions through a randomized experiment. This opens up the way of integrated data processing, potentially leading to faster and better diagnostics and detection of magnet quenches.

Numerical Simulation of Dynamic Electromagnetic Characteristics of Superconducting Electrodynamic Suspension (EDS) Train

Dynamic electromagnetic characteristics is significant for the design and operation of superconducting (SC) electrodynamic suspension (EDS) train. This paper established a three-dimensional transient numerical model in COMSOL. The current density excitation comes from the homogenized model of the superconducting magnet. In order to decrease the computing time, periodic boundary is introduced taking the place of finitely long route. Mapping operator is adopted to ensure the continuity of physical quantities in the case of geometric discontinuity in the process of motion. Induced current and magnetic force at different operation velocity and different structure are simulated. In general, this model could be applied to simulate long term operation. It is also suited for the simulation of propulsion systems for EDS systems. In addition, this model provides electromagnetic environment intuitively that would be helpful for the stability analysis and design of onboard SC magnets during long term operation.

Static magnetic field induces abnormality of glucose metabolism in rats’ brain and results in anxiety-like behavior

In this study, fifty-four male Wistar rats were randomly divided into four groups according to the static magnetic field (SMF) intensity, namely, control, low-intensity, moderate-intensity, and high-intensity groups. The rats' whole body was exposed to a superconducting magnet exposure source. The exposure SMF intensity for the low-intensity, moderate-intensity, and high-intensity groups was 50 m T, 100 m T, and 200 m T, respectively, and the exposure time was 1 h/day for consecutive 15 days. After different exposure times, glucose metabolism in rats' brain was evaluated by micro-positron emission tomography (micro-PET), and the expression of hexokinase 1(HK1) and 6-phosphate fructokinase-1(PFK1) was detected by western blot. The exploration and locomotion abilities of the rats were evaluated by conducting open field test (OFT). Furthermore, pathological changes of rats' brain were observed under a microscope by using hematoxylin–eosin staining. PET results showed that moderate-intensity SMFs could cause fluctuant changes in glucose metabolism in rats' brain and the abnormalities were SMF intensity dependent. The expression of the two rate-limiting enzymes HK1 and PFK1 in glucose metabolism in brain significantly decreased after SMF exposure. The OFT showed that the total distance, surrounding distance, activity time, and climbing and standing times significantly decreased after SMF exposure. The main pathological changes in the brain were pyknosis, edema of neurons, and slight widening of the perivascular space, which occurred after 15 times of exposure. This study indicated that SMF exposure could lead to abnormal glucose metabolism in the brain and might result in anxiety-like behaviors.

Thermal-hydraulic analysis of Cable-In-Conduit Superconductor: A CFD approach

Superconducting (SC) magnets with Cable in Conduit Superconductor (CICSC) winding, cooled by helium at 4 K temperature are employed for many applications which require high magnetic field and high current densities. The construction of CICSC aims to maintain superconductivity state by optimization of various parameters, i.e., thermal stability, ratio of normal conductor to superconductor material, mechanical strength, low hydraulic impedance, current density, magnetic field, etc. The cryogenic thermal stability of the CICSC is of prime importance for the safe, stable and reliable operation of SC magnets. The prediction of thermal and hydraulic behaviour of CICSC in large SC magnets is difficult due to the complex geometry, variation of fluid properties, various heat in-flux incidences over the long length of CICSC and a complex heat transport phenomenon. Here we present a CFD approach for the thermal hydraulic analysis of a typical CICSC applying the porous media analogy and discuss the suitability for a wider range of operational scenario at higher Reynolds number and for various geometries.

WITHDRAWN: Design and analysis of ML-VSC based SMES with improved power quality features

Now a days there is high demand of power. In the process of supplying the required amount of power, the power system become complex and transient stability has become a major challenging. In order to progress transient stability there are various measures identical as discrete control of excitation systems, ML-VSC (Multi Level Voltage Source Converter) based SMES (Super Conducting Magnetic Energy Storage System) etc., in that ML-VSC based Super Conducting Magnetic Energy Storage System has acknowledged much responsiveness in the power system application. As the inertia is little, if some distraction at load side will disturb frequency of a system and it will create electromechanical oscillations. The SMES controller which is using as a fast acting storage system, it be capable of supervise the electromechanical oscillations immediately and helps in plummeting the frequency deviancies underneath the limits. This paper is apprehensive by way of the control of ML-VSC based SMES for effective assistance of active and reactive power of a power system. Super Conducting Magnetic Energy Storage System is a device comprises of a superconducting coil, wherein ac power is converted into dc by ac-dc power conversion system and it will be stored in superconducting coil as magnetic energy, it can be charged and discharged very rapidly during the ac-dc conversion because of its high storage efficiency and fast response. Here, the ML (Multilevel inverter) provides more than two voltage levels due to this the harmonic contents are reduced and desired output voltage waveform can be obtained. The time domain parameters of the SMES are controlled by PID controller with the help of PID controller technique.

High temperature superconducting material based energy storage for solar-wind hybrid generating systems for fluctuating power management

The green energy infrastructure plays an important part in existing world of power scarcity. Owing to their dependence on environmental factors, renewable energy technologies continue to fluctuate. Using the energy storage device will solve the problem. The technical and economical requirements of the energy storage process can be met with the use of hybrid combinations. This paper proposes a hybrid energy management system based on the Super conductive magnetic material and the lead acid battery to provide power stabilization in the grid-connected unstable microgrid. Here, second-generation High Temperature Superconducting (HTS) material is used as Super Conducting Magnet Energy Storage (HTSMES) which exhibits a high irreversibility field and critical current density within an active magnetic field. The proposed system may be a good solution to minimize the impact of the Point of Common Coupling (PCC) power variability during fault condition. To improve the efficiency and flexibility of the proposed system, the two hybrid power sources are connected via dual input single output zeta converter. The HTSMES is used to minimize the difference in active power during fault and to give the reactive current to handle the fault. Grid connected microgrid with HTSMES-battery was simulated using the MATLAB Simulink platform and tested using an energy management algorithm with and without the presence of fault. The system proposed is demonstrated with detailed simulation results.