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Defining what a successful SUPER-conductor for a magnet is, isn’t easy. It is often underestimated to what extend the type of magnet and its application are strongly determining the conductor requirements. Whether it is a one-off magnet where cost is not an issue, a quasi-commercial small series, or a long-term commercial production of magnets, is crucially influencing the conductor choice. The technical and economic considerations for a single high-end magnet in a satellite or for an insert in a high-field facility are very different from those for a few hundred or thousands of magnets for particle accelerators or ultimately the long-term series production of MRI magnets.
In textbooks, we find long tables with superconducting materials ever discovered, but when it comes to those for practical use in magnets, only a few remain. Yet another hurdle we encounter when attempting to use these NbTi, Nb3Sn, MgB2, BSCCO and ReBCO wires in high-current multi-strand cables and often mechanically reinforced conductors. They have to survive the enormous Lorentz force and thermal-electro-magnetic infestation present in large-scale magnets and guarantee degradation free and reliable operation for some 20 to 30 years.
The requirements for successful SUPER-conductors will be reviewed and a few striking examples, where naive initial designs had to be corrected, will be presented. Long-term research and development to learn, understand and improve not only bare transport properties of conductors but also their thermal-mechanical behavior are required for magnets to be successful.
We focusing on investigating the protection of meter-class REBCO no-insulation (NI) coils applied in next generation high-field magnetic resonance imaging scanners. In order to address the issue of controllable contact resistance, we proposed a method is based on an external variable resistance, which is paralleled with an NI coil to realize the controllable contact resistance. It can maintain the temperature increase of the coil in the safety range during a charging and discharging by the efficient leading-out the electromagnetic energy. To certify the feasibility of this method, in this study, a numerical analysis was conducted of a partial element equivalent circuit along with a thermal analysis of a simple equivalent circuit model to investigate the effective range of variable resistor to realize the protection method for the meter-class NI coil. Based on the results, we discussed the feasibility of the inhibitory effect of variable resistor on the temperature increase of meter-class NI coil and the energy dissipation rate during a sudden discharging.
Cryogenic bypass diodes have been installed in all superconducting dipole magnets (1232) and all main superconducting quadrupole magnets (392) of the Large Hadron Collider (LHC) at CERN, and operated during the physics runs since 2009. The by-pass diodes are a fundamental ingredient of the quench protection system for those main dipoles and quadrupoles magnets. Diodes are located inside the magnet cryostats, operating in superfluid helium and exposed to ionizing radiation. The connection between the superconducting magnet and the bypass diode is made through a mechanically clamping system and copper bus bars. Since their first installation, all LHC diodes have undergone at least one full thermal cycle (from 1.9 K to room temperature and back to superfluid helium temperature).
The evolution of electrical parameters as well as improvements and modifications made over a period of 10 years are reviewed under a critical eye.
The maximum estimated dose accumulated for one single diode is today of the order of 500 Gy. A test setup has been developed to qualify diodes for higher neutron fluences and integrated doses than they were initially. The setup was installed at CERN in a radiation test facility and diodes irradiated at cryogenic temperatures over 2018. The qualification process has allowed to identify three candidates that could be used for the new High-Luminosity LHC circuits. This paper will also report on the behaviour and performance of the diodes that have been measured.
With CERN preparing for LHC’s High Luminosity era, the long-term strategy for cold diodes will be presented, based on the overall results and experience gathered so far.
In general, superconducting magnets operate at high currents, and excessive joule heating due to high currents can damage the magnet when quench occurs. Therefore, a quench protection system that can reduce the magnet current quickly is required when the normal zone occurs in the magnet. For this reason, several quench protection methods are being developed to rapidly reduce the current. In this paper, we present a new quench protection method that rapidly reduces current in a superconducting magnet by injecting current into a magnetically coupled secondary coil. The proposed system is magnetically coupled without direct connection to the magnet and is used in conjunction with a protection method using a conventional dump resistor to help reduce the current quickly. The performance of this system was verified using a small scale high temperature superconducting test coil.
The quenching of superconducting magnets is one of the key issues affecting the safe and stable operation of superconducting devices. The effect of Magnetic flux jump and electro-magnetic stress leads to local critical current drop, continuous accumulation of heat of joint resistance, failure of refrigeration equipment or other auxiliary equipment, etc. These effects may cause quenching of the superconducting magnet. When the superconducting magnet is quenching, it will cause the point of overheating. When the quenching is continued, the locali-zation will continue to heat up. Therefore, the establishment of the automatic quench protec-tion system and the correction of the quenching judgment are important for the long-term sta-ble operation of the superconducting device. In poor electromagnetic environment, quench detection based on electrometric method is easily interfered by noise and severely disrupted quench signal may cause wrong quench determination and malfunction of quench pro-tection, thereby resulting in unnecessary loss. Because of the noise cannot be completely eliminated, in order to effectively judge the quench and reduce the malfunction of the annihilation detec-tion, a real-time least squares method is proposed.
The overcurrent experiment shows that the real-time least squares method can effectively judge the point of quench.
Recently, a new quench protection system using capacitor and switches has been announced to rapidly extract energy from high temperature superconducting (HTS) magnets. When a quench occurs, the quench protection system activates four MOSFET switches in sequence, and the energy stored in the magnet is extracted through an external resistor through a capacitor. In previous studies, the system was implemented for the protection of small-scale magnets, and the feasibility of the system was experimentally verified. The experimental results show that the energy extraction of the magnet is faster than the quench protection system using a conventional dump resistor. However, since proposed system is sensitive to capacitance, inductance, and four resistors, it is necessary to optimize design variables for various magnet systems. However, since the system is sensitive to capacitance, inductance, and four resistances, it is necessary to analyze and optimize the design parameters for various magnet systems. In this paper, the effect of each design variable on the protection performance is analyzed and a method for optimal design is presented. We also evaluated the performance by applying a design optimized for the scale-up test coil.
Quench protection is critical for superconducting systems, especially those containing enough energy to damage the system during quench. We propose a new quench protection approach for multi-coil low temperature superconducting (LTS) systems that minimizes the number of protection components that must be activated during quench. In this approach, the electrically (and probably also inductively) coupled coils are electrically connected in these possible ways: all in parallel; several parallel-connected groups, with each group consisting of several series connected coils; several series-connected groups, with each group consisting of several coils in parallel. If one of the parallel-connected coils or groups quenches, current in this coil or group decreases while current in the other parallel-connected coils or groups tries to increase to keep total current flow in the circuit the same, and this tendency will be affected by the nature of the inductive coupling among the coils. If during this event the non-quenching parallel coils or groups remain superconducting (i.e., their current is below critical current and there are no mechanical or thermal events that may cause these coils to quench), then the quench is limited to only the quenched coil or group. In some cases, the equipment may continue operation after quench, although at a somewhat reduced capacity. The proposed approach is potentially more advantageous for superconducting systems that consist of many similar coils with relatively weak inductive coupling.
Previously, we verified the feasibility of using a Raman-based distributed temperature sensor (RmDTS) system to measure a no insulated (NI) high temperature superconducting (HTS) coil temperature variation during an overcurrent induced quench event. In addition, to reduce the temperature response time of the RmDTS, we further optimized the whole measurement system. However, the combination method between optical fibers and HTS coil in these works is immobilizing spiral optical fibers on the turn-by-turn surface of HTS coil by using epoxy which could be harmful for the structures of HTS coils. Therefore, an ideal combination structure that encapsulating optical fibers in HTS tapes along the length direction was proposed. Before winding HTS coils, the electrical properties of these optical fiber encapsulated HTS tapes (OFE-HTS tapes) should be studied in advanced. In this study, we have compare the vibration of the critical current values, resistive values at room temperature, anti-impulse current characteristics of normal HTS tapes and OFE-HTS ones. The foundational study can really promote the RmDTS application for quench detection. More detailed experimentation and comparison results will be presented and discussed in this paper.
When a quench occurs in a high field no-insulation (NI) high temperature superconductor (HTS) magnet that consists of a stack of double-pancake (DP) coils, a large amount of current is often induced in an NI DP coil that is electromagnetically coupled with neighbor DP coils. Depending on the strength of external magnetic field, the large induced current leads to an excessive magnetic stress and occasionally damages the magnet. In this paper, we propose a new quench protection concept to reduce the amount of induced current in an NI HTS magnet. The key idea is to use resistive copper within the magnet windings in order to absorb a portion of electromagnetic energy that is initially stored in the magnet before the quench. We tentatively name these resistive coils or plates as a “magnetic dam”, as they may slow down the electromagnetic quench propagation speed among the NI DP coils, which may be beneficial to avoid the mechanical damage by the large over-current.
This work was supported by Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-IT1801-09.
HTS coils wound with insulated wires are actually quenched, even though HTS wires have a high quench margin and can be easily damaged, if the quench protection system does not work properly, especially in the case that current density of the magnet wires is high, It should be noted that the training effects as in LTS magnets have not been observed in HTS magnets and that damaged HTS magnets cannot be reused. Therefore, protection of HTS magnets from quench damage is important for their repeated use. The most probable cause of quench damage of HTS magnet is over-heating at the highest temperature spot (hot-spot) in the magnet wire during the quench protection sequence. Therefore, to avoid damage, it is necessary to reduce heat generation in the hot-spot. In a previous work, the authors proposed a quench protection method to reduce hot-spot temperature and increase quench detection voltage to protect an HTS magnet composed of multiple pancake sub-coils from quench damages. In the method, a current of a quenching sub-pancake coil is transferred to the other sub-coils of the magnet forming auxiliary resistive shunt loop (ARSL) by resistively shorting the other sub-coils. In this work quench behaviors of the pancake sub-coils of a model magnet was investigated by simulation experiment using small scale test pancake coils wound of YBCO wire. Current patterns of the sub-pancake coils of a model magnet at a quench event were calculated for the case that ARSL method was applied. In the experiment, the same patterns of currents calculated for the model magnet were applied to the quenching test coils by a controllable current supply. Experimental results show effectiveness of the proposed method.
This work is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).
The superconducting wires have been developed for high field magnet, transformers, motors and so on. The quench detection and protection system are essential for safety operations of the HTS facilities. The high voltage signal conditioner (HVSC) method is generally used for the quench detection and protection, however, especially for high voltage operation magnet such as international thermonuclear experimental reactor (ITER) magnet (56 kV, DC), it is difficult to apply to HVSC method due to the risks in terms of high voltage sparks. As well as, the power supply for HVSC should be isolated since the super high field magnet such as ITER magnets, which is supplied by 15 MA, generate about 10 T (tesla) strong magnet. To solve these problems, insulation resistance of power supply should be larger than 500 MΩ; a lower resistance can affect the common-mode voltage of the differential amplifier in the HVSC system. From these reasons, our research team, the wireless power transmitter (WPT) system has been considered as one of reasonable options to solve insulation resistance obstacles since WPT system can transfer power through any non-metallic media between antenna (Tx) and receiver (Rx) coils. Now, the one wireless power system generally supplies operating power for one differential amplifier in the HVSC. Practically, numerous differential amplifiers would be installed in the high field magnet to detect and protect magnet system. From this reason, in this study, authors described the conceptual design and fundamental performances of quench detection system for super high field magnet using wireless power technology. Especially, the thermal distribuitons of antenna and receiver will be evaluated. As well as, the number of wireless power supply including insulation resistance can be reduced by multi resonance receiver under the 100 kHz with 3kW RF generator.
The Large-scale Superconductor Test Facility (LSTF) serves as an important part of superconducting magnet load testing for fusion research which concerns about the nuclear energy producing. During the testing process, quench protection (QP) is indispensable for protecting the load from being overheated damaged. In this paper, a compatible and flexible QP framework is put forward to meet the different QP requirements including transferring time, protection voltage, the temperature raise, current decay speed and so on. The QP framework can provide the solution of changing the power units parameter on account of specific testing superconducting magnet. Firstly, the LSTF is introduced and the QP process in the system is comprehensively analyzed by discussing the power units’ actions and circuits currents’ flowing. Then the power units of QP system are studied by elaborating the power parameters adjustments in corresponding to different loads, especially the counter-pulse capacitor unit and the fast discharge resistor system. Finally, the testing process of central solenoid coil used for the China Fusion Engineering Test Reactor is described to illustrate the operation of the QP framework.
Electromagnetic forming (EMF) processes of sheet metal are used to manufacture several components in modern industry. The EMF process is a highly nonlinear phenomenon and its understanding is a complex task due to the coupling of the electrical, magnetic, thermal and mechanical problems. The generated electromagnetic forces in this process are directly correlated to the resulting deformed workpiece geometry and strongly dependent on EMF system parameters as capacitance, initial capacitor energy, tool geometry, and its electrical conductivity, inductance, and mechanical properties. This study focuses on performing a parametric sensitivity analysis by numerical simulations of free bulging of circular sheet metal aiming a high and adequate force distribution from the EMF system. The numerical method solves the electromagnetic problem using an in-house script implemented in Matlab and then the mechanical problem is solved using the ABAQUS/Explicit Finite Element software. In the presented method, the EMF process is treated as fully coupled electric-magnetic and uncoupled with the mechanical problem, solving electrical circuits, identifying their parameters, and presenting calculations method for the magnetic flux density, the self and mutual inductances, and the electromagnetic force distribution regarding coil geometry to the initial time instant. The electromagnetic force calculated with Matlab is employed in a user subroutine of ABAQUS/Explicit to predict the movement of the workpiece. The research methodology involves a parametric sensitivity analysis considering the following design variables parameters of EMF devices: system capacitance, energy pulse, and tool coil geometry. Finally, conclusions and design principles for the free bulging of sheet metal by EMF are outlined.
Rare earth barium copper oxide (REBCO) coated conductor has been promising conductor for the design of high field magnets due to its high strength, high critical current and high critical field. However, high temperature superconducting (HTS) magnets are challenging to protect due to slow normal zone propagation velocity (NZPV). No-insulation (NI) winding technology has been demonstrated to produce compact, reliable, stiff and strong magnets. This technology is not devoid of its own challenges either. The charging delay due to radial bypass path in NI coil is an actively researched area. To verify that such magnets are truly self-protecting and to understand other unique behaviors of NI magnets, they are modeled using “lumped circuit model” where each “sub-coil” is modeled as a single inductor with resistances in series (quench resistance, Rq) and parallel (characteristic resistance, Rc). The results obtained using this method and lessons learned are presented in this article: (1) During fast electromagnet quench propagation of NI magnets, overcurrents (currents greater than designed operating current) are produced which can overstress the magnets. (2) Variation of Rc with temperature and magnetic field can influence the magnet voltage. (3) In asymmetric quench of nested NI magnets, the axial centering force can be large and need to be considered. (4) Screening current and its effect in field homogeneity and magnet stress is also an important challenge unique to NI magnets. Despite the challenges, the work presented here shows that it is possible to construct high field magnets using NI REBCO technology after careful consideration of these challenges and lessons learned which will be beneficial for advancing the area of HTS magnet development.
As part of the design justification of the ITER magnet system and in preparation of the commissioning activities, the heat deposition on the ITER cold structures has been computed in order to generate input loads for subsequent thermo-hydraulic analyses, which are essential for the assessment of the temperature margins of the superconducting cables. The Finite Element model of a 40 degree sector of the ITER magnet system presented in  has been updated, including Poloidal Field (PF) coils clamps and Correction Coils (CC) supports. A new inductive plasma scenario (DINA-2017) as well as the Toroidal Field (TF) coils fast discharge have been simulated with the electromagnetic code CARIDDI. The results are in line with the old computations. In addition to these events, the effects of the voltage ripple generated on the TF coils by the power supply have been analyzed and the induced eddy currents assessed.
 F. Cau et al., “Joule Losses in the ITER Cold Structures During Plasma Transients”, IEEE Transactions on Applied Superconductivity, vol. 26, no. 4, Apr. 2016.
In order to control and reduce the vibration of magnetically controlled reactors(MCRs) with gaps core structure, accurate stress computation should be carried out. Previously, researchers proposed a finite element model for reactors core stress calculation considering Maxwell stress theory and magnetostriction effect. Giant magnetostrictive materials are used to be filed into the gaps to reduce the electromagnetic force in iron cores between gaps. However, they did not compute MCRs core stress considering the hardness of the gap filler under service condition.
Under the MCRs service condition of AC and DC excitations, the main factors which have influence on stress distribution in gaps area include magnetostriction effect of silicon steel, electromagnetic force effect of iron cores between gaps and the hardness of the gap filler. The magnetostrictive stress and electromagnetic stress have been studied, but the influence of gaps filler hardness on the total vibration of MCRs has not been analyzed. This paper presents an electromagneto-mechanical coupled model for MCRs to analyze their stress distribution under service condition. Firstly, magnetostriction and magnetization properties for oriented electrical steel sheet along the rolling direction (RD) and the transverse direction (TD) under AC and DC excitations are tested. Then, based on the measured constitutive relations, an electromagneto-mechanical coupled model for MCRs considering electromagnetic force effect, magnetostriction effect and the hardness of inserted materials is presented and the stresses in different directions in gaps area are calculated. Finally, an MCR prototype is made and the core vibrations in gaps area under different AC and DC excitations are tested to prove the validity of the proposed model. From the calculated and experimental results, it can be seen that the vibration in the outer edge of cores is more serious than that in the center of cores.
ABSTRACT: The large range of length scales presents within superconducting magnet and its heterogeneity, a straightforward numerical simulation of a magnet, considering all details of the microstructures would cost enormous time, so incorporation of the multiscale approaches into computational models can facilitate the numerical analysis. Additionally, the superconducting magnet with high transport current and intense magnetic field are often exposed to large Lorentz forces, which lead to the unavoidable deformation in superconducting coils, the deformation will further disturb the quality of the magnetic field. In this work, the stress/strain and magnetic field of a 4T NbTi/Cu racetrack superconducting magnet were numerical analyzed, a multiscale model from the NbTi filament scale to the coil scale was developed to obtain the homogenized and the orthotropic material properties of the superconducting coil based on the representative volume element (RVE) and rule of mixture of composite methods, these material properties are employed to solve for stress/strain and magnetic field development by using three-dimensional finite element method (FEM), and taking into account the effect from magneto-mechanical coupling of superconducting coils. The study shows that the numerical predictions based on multiscale approach for the superconducting coils on the strain are in better agreement with the previous experimental data than those based on a single-scale approach, and shows the magneto-mechanical coupling behavior of the superconducting coils is remarkable especially in intense magnetic field and large transport current. The FEM based on multiscale model was demonstrated as an acceptable method to estimate the required material properties of the superconducting coils for the magneto-mechanical analysis of a superconducting magnet.
Key words: multiscale model, magneto-mechanical coupling, FEM, superconducting magnet.
Computational modeling of superconducting magnets allows for predicting and understanding magnet behavior. The commercial software ANSYS is a widely used finite element software for mechanical, thermal, and electromagnetic modeling of superconducting magnets. ANSYS also allows its user to create custom elements by programming the elements’ properties and its finite element matrices. These user elements can capture additional material properties and physics that current ANSYS elements do not. Once compiled, they are then compatible with all other aspects of the software, including geometry generation, meshing, solving, and post-processing. Additionally, these elements can also be used with the multiphysics solver. We have developed two 3D user elements, one thermal and one electromagnetic with circuit coupling. In addition to the basic capabilities of ANSYS, they capture quench propagation, interfilament coupling currents, current sharing, and temperature and field dependent material properties. Two-dimensional user elements have previously been developed; however, modeling superconducting magnets in 3D allows for better representation of end effects, and other non-symmetric physics. Using the ANSYS multi-field solver, these two elements are shown to simulate coupled transient electromagnetic, thermal, and circuit effects for Nb3Sn undulators and other magnets built and tested at Lawrence Berkeley National Laboratory, particularly within the MDP. The effects of quench, interfilament coupling currents, and structural eddy currents are studied and compared to magnet test data while steps towards parallelization are also explored.
FEM simulations are a standard step in the design of accelerator magnets. It is custom for accelerator applications to characterize the field quality in terms of field expansion coefficients. Expansion coefficients are usually calculated by means of a Fourier transform of the local FEM solution evaluated at points on a circle (2D) or cylinder (3D case). The accuracy of the coefficients calculated this way depends strongly on the FEM mesh configuration and simple refinement of the mesh does not always improve accuracy. The accuracy of the expansion coefficients calculation can be improved by using the data on the magnetization of elements in the magnet yoke, obtained in the solution, instead of using directly the local solution. Since currents and the yoke magnetization are the only sources of the field, with these data the field expansion coefficients can be calculated at any remote point. We derive closed forms for calculating expansion coefficients and implemented these results in the ANSYS® add-on. Results for a case study are presented, which demonstrate that expansion coefficients can be calculated with good accuracy even for a rather coarse mesh.
Kai Zhang, Sebastian Hellmann, Marco Calvi
Paul Scherrer Institut, Villigen, CH
Lawrence Berkeley National Laboratory, Berkeley, CA
Abstract – In this work, we will introduce the feasibility of using A-V formula in ANSYS to simulate the magnetization process of HTS bulk materials. The iterative algorithm method (IAM) based on ANSYS APDL is firstly developed to simulate the magnetization current issues in a ReBCO bulk disk based on Bean model. Specifically, we confirm it is feasible to simulate the development of trapped current density in the ReBCO bulk during the process of ramping and damping the external magnetic field. Using IAM, we can update the magnetic field-dependent critical current density for each element in the ReBCO bulk after each load step of electromagnetic analysis. It is also feasible to take the mechanical strain effects into consideration if we update the strain-related critical current density after each load step of electromagnetic-mechanical coupled analysis. Finally, a systematic study of HTS magnetization current issues is performed to test the newly developed ANSYS user defined element (UDE) in which E-J power law is defined. The flux creep effects of the ReBCO bulk during Field Cooling Magnetization (FCM) are investigated when using different n-values. The simulation results of using ANSYS IAM and UDE are compared with the simulation results of using COMSOL.
Characterizing the magnetic properties of industrial magnetic materials has great significance on the development of transformers, motors and other electrical equipment. Recently, high-frequency and high-power density electrical equipment has attracted more attention. As the frequency is getting higher and higher, the losses of the magnetic core are much higher than that in the power frequency situation. Nanocrystalline and amorphous alloys lead to a significant reduction in the core loss which gives the opportunity to develop high-efficiency devices in high-frequency applications under frequencies from 20 Hz to 20 kHz. For better using of these materials, it is very necessary to have a deep understanding of these materials’ loss behavior under rotational magnetization condition. In this paper, a new magnetizing structure for nanocrystalline alloys rotational core loss measurement is designed and optimized by the 3D-FEM method. The optimization goal is to achieve both the best homogeneity and the highest testing frequency. As the affecting factors are very complex and the 3D-FEM calculation is very time consuming, improved SVM and PSO algorithms are combined in the optimization process. The improvement of PSO is one of the significant parts of this paper. PSO is a kind of swarm intelligence algorithm. It is simple and easy to implement. But it also has the problem of low search accuracy and is easy to fall into local extrema. In this paper, an improved PSO called the velocity-controlled PSO (VCPSO), based on the analysis of the particles’ distribution has been developed and used in the optimization process. As the 3D FEM calculation is very complex, support vector machine (SVM) is used to establish a regression model between the designed parameters of the RSST during the optimizing process. The results well detailed discussed in the full paper.
The High-Luminosity LHC Accelerator Upgrade Project (HL-LHC AUP) is approaching the production phase of the US-contributed Q1 and Q3 Interaction Region Quadrupoles (MQXFA). The structures for the MQXFA prototypes were design and inspected by the US-LARP (LHC Accelerator Research Program), AUP developed criteria, which will be used for the pre-series structures. As the first two full-length prototypes with 4.2 m magnetic length, MQXFAP1 and MQXFAP2, were designed and assembled at Lawrence Berkeley National Laboratory (LBNL), and tested at Brookhaven National Laboratory (BNL). The end aluminum short shell of MQXFAP2 was fractured along the shell length during the test, and tests were stopped. Analytical and Finite Element analysis were performed in light of the graded procedure defined in the Structure Design Criteria to investigate the fracture failure for MQXFAP2.
In this paper, we report the fracture analysis of the current shell design, including the elasto-plastic simulations with sub-model technique, crack propagation simulations, and calculations with Linear Elastic Fracture Mechanics (LEFM). Test material properties are also presented. The results of this analysis explain why the end shell of MQXFAP2 failed, and suggest fillets on the end shell notches to meet the margin specified in the Structural Design Criteria.
In the frame of the HL-LHC upgrade, assemblies of two 5.5 m long 11 T Nb3Sn dipoles (MBH) are expected to replace 8.3 T NbTi LHC main dipoles (MB). Double and single aperture models, each 2 m long, were built and cold tested in operational conditions. The models have design features that are verified during these tests to provide feedback for the technology development of 5.5 m full-size magnets. With the last model magnets tested, using the final conductor, conductor insulation and assembly processes, the performance is evaluated and the readiness for series production is confirmed. In this paper, the test results of the latest model magnets in terms of training behaviour and memory, conductor limits, endurance, quench protection and other cold powering tests are presented. Additionally the results of cold endurance tests, thermal cycles and powering cycles, are discussed in view of the operational requirements in the LHC.
The HL-LHC Project at CERN requires the installation of 11 T Nb3Sn dipole magnets to upgrade the collimation system. Given the high operating field and current density, the quench protection of these magnets is particularly challenging. The baseline protection scheme of the 11 T dipoles is based on the quench heaters technique.
Dedicated quench tests were carried out at CERN on short samples of the 11 T dipole magnets, in which the quench heaters were fired either individually or simultaneously. The aim of these tests was to measure the quench energy and quench location in the coils, in response to heat depositions of different amplitude. The tests were carried out at transport currents in the range from 11.85 and 12.85 kA; the applied heat flux densities were increased stepwise between 5.9 and 12 W/m until a quench was detected.
Two different modeling approaches were developed to analyze the test results. The first model is based on a simplified 1-D representation of the magnet components along a line crossing radially the middle plane of one quadrant of the magnet cross section. To improve the description of heat exchange with superfluid helium, this model was also applied to analyze dedicated tests carried out in the cryogenic facility of CERN.
The second model represents in detail all magnet components in the 2-D cross section of one dipole quadrant. The model allows one to identify the parts of the magnet which are more thermally solicited in the quench tests, and therefore the most probable quench initiation locations.
The paper presents a detailed description of the models, their validation by comparison with the experimental results, and their application to analyze the details of the quench propagation in the magnet cross section.
In the CERN Large Magnet Facility (LMF), the series production of the Nb3Sn-based 11 T dipole magnets is currently ongoing. Results from magnet tests and observations regarding the conductor irreversible stress limitations have shown that a uniform and well-defined pre-load is crucial. The collaring force in the assembly is adjusted by the thickness of a longitudinal shim derived from the measured coil’s azimuthal excess. One of the key features to define the collaring force is given by the control of the coil dimensions. The results from two measurement setups are presented using Coordinate Measurement Machines (CMM) featuring ±34 μm and ±5 μm accuracy. The analysis accuracy is modelled taking into account the 11 T coil branch geometry and measurement setup characteristics.
In the framework of the HiLumi project, the present LHC low-β superconducting quadrupoles will be substituted with more performing ones, named MQXF. MQXF will have high peak-field on the conductor (~12 T), therefore the Nb3Sn technology is needed in order to reach the target performance.
One of the main technological challenges for the Nb3Sn magnets is the coil fabrication: due to the brittleness of Nb3Sn, coils needs to be impregnated with epoxy resin in order to improve mechanical properties, and avoid conductor damaging. Quench heaters are necessary for quench protection, and they need to be impregnated with the coil as well, in order to be close enough to the coil itself and to reach the required efficiency. Quench heaters are insulated from the coil by a 145 μm layer S 2 Glass® and Epoxy resin, and a 50 μm layer of Kapton®.
The test of the first MQXF prototype (4 m long) has been interrupted due to a heater-to-coil short circuit. Therefore, the electrical testing procedures have been improved, and a deep analysis of the heater-to-coil insulation has been performed.
In this paper, we report the results of the heater-to-coil insulation analysis, showing the simulations of the peak voltages expected in the magnet, modelling of the insulation during quench and electrical test conditions, including failure analysis, and the experiments performed on coil sections, short coils and models, long coils and prototypes made in order to prove the robustness of the insulation. Alternatives to the present fabrication solution are also presented, showing advantages and disadvantages. The results of this analysis are of general interest for all the Nb3Sn coils impregnated together with quench heaters.
The CERN Large Magnet Facility (LMF) is currently producing 5.5 m long 11 T dipole and 7.2 m long MQXFB quadrupole coils for the HL-LHC project. Both coil types are fabricated with Nb3Sn conductor and therefore produced based on the so-called wind and react process. These coils require a vacuum impregnation process to form the final electrical insulation.
The paper will present the impregnation process applied at CERN, together with the one used in the US for the MQXFA coils, within the Accelerator Upgrade Program (AUP) framework. The impregnation process and its reproducibility are shown, ongoing developments to further improve quality control are proposed. Furthermore, the LMF impregnation infrastructure and recent applied upgrades are described, aiming for a reliable process workflow based on a modular hardware with an improved interchangeability.
The United States High Luminosity Large Hadron Collider Accelerator Upgrade Project (US-HL-LHC AUP) is designing and fabricating 11 Q1/Q3 cold masses for the interaction regions of the LHC. Each cold mass contains two 4.2 m quadrupole magnets. The Nb3Sn quadrupole magnets operate in superfluid He at 1.9 K with a nominal field gradient of 132.6 T/m. The design and fabrication of the through and local buses for the cold masses is carried out at Applied Physics and Superconducting Technology Division at Fermilab (FNAL). The bus-bars consist of two superconductive NbTi cables soldered together and wrapped in Kapton.
This paper reports the characterization of the bus-bar thermo-electric properties to validate the bus design and assure quench protection. Calculations have been performed to estimate the quench integral, the quench propagation velocity and the maximum voltage developed in the bus. The bus design was validated testing the cable together with a short Nb3Sn magnet in the vertical test facility of Applied Physics and Superconducting Technology Division at FNAL.
The test demonstrated that the bus design is sound; no spontaneous quench took place up to 17870 A current value. Temperature margins were measured to be higher than the required 5 K for the High-Luminosity Q1/Q3 triplet bus at nominal operating current. Protection studies revealed that the bus can be adequately protected using 100 mV voltage threshold value for the entire current range the magnet will operate in the LHC tunnel. Results of quench propagation velocity and quench integral measurements as a function of temperature and current are also presented in this paper.
Abstract— A future Electron Ion Collider (EIC) may require high gradient superconducting quadrupole magnets for final focusing of the hadron beam in the interaction region. Due to the closeness to the beam collision point and the narrow 25mr crossing angle these high gradient magnets will reside in close proximity to electron beam magnets, thereby requiring a very compact support structure in comparison with typical accelerator magnet support structures, for the high Lorentz forces that are generated with excitation. This paper reports on the design of a proof of principle support structure for a 132 T/m, 120mm aperture superconducting magnet, utilizing the (HQ) coil design developed for the LHC Accelerator Research Program (LARP). In addition to the design work a 15cm long mechanical model based on the design is being built and loaded to the required level of coil precompression at room temperature, and then cooled to 77K to also confirm the level of coil precompression at cryogenic conditions. Future work will include construction and testing of a proof of principle magnet based on the design in an accelerated time frame, utilizing previously tested LARP HQ coils.
Index Terms—EIC, LARP, Hi-Lumi, LHC, Nb3Sn, superconducting magnets
IMP is developing a Nb3Sn superconducting magnet system for a 45 GHz electron cyclotron resonance (ECR) ion source. To achieve this complicated and difficult Nb3Sn magnet, a prototype with identical cross section but half length of the magnet is proposed. Recently a single sextupole coil about 0.5 m long has been fabricated and tested. The coil has a bore size of 200 mm and was wound by using a Nb3Sn wire with 1.3 mm diameter. In order to test the coil efficiently, a mirror structure is utilized. And the Bladder & key technology is employed to exert the required preload on the coil. This paper describes the magnetic field design of the sextupole mirror structure, presents the fabrication of the sextupole coil and reports the test results.
Circular Electron Positron Collider (CEPC) with a circumference about 100 km, a beam energy up to 120 GeV is proposed to be constructed in China. Most magnets for CEPC accelerator are conventional magnets, except some superconducting magnets are required in the interaction region of CEPC collider ring. High gradient final focus doublet quadrupoles QD0 and QF1 are required on both sides of the collision points in the interaction region of CEPC collider ring to achieve high luminosity. QD0 and QF1 are both double aperture superconducting quadrupoles with a central field gradient of 136 T/m and 110 T/m, respectively. The field crosstalk between the two apertures in the quadrupoles should be solved. Since the final focus superconducting quadrupoles are operated inside the field of the Detector solenoid magnet with a central field of 3.0 T, strong superconducting anti-solenoid is need to cancel the Detector solenoid field and minimize the effect of the solenoid field on the beam. In this paper, the layout and magnetic design of CEPC final focus superconducting magnets are described, and the R&D status of prototypes superconducting magnets is presented.
Due to the small size and low power consumption, compact superconducting cyclotron are suitable to be installed in hospital for cancer therapy, which becomes a research hotspot in recent years. China Institute of Atomic Energy has been developing a 230MeV compact superconducting cyclotron CYCIAE-230 to meet the demands of proton therapy in China. Accelerator physics design requires a strict control of the average field error and first harmonic in the main field. A processing method of inclined 45o continous cutting on the two pole edges is proposed to shim the field in CYCIAE-230. For a spiral sector magnet, the 45o continous cutting generates an asymmetrical magnetic field on both sides, and the field change is not proportional to the milling depth, which makes the establishment of the shimming algorithm much more complicated. In this paper, a Mathematica model of the linear equation for field shimming calculation is established. The field change caused by the local cutting is calculated numerically by the integral equation method to describe the nonlinear relation of the complex shape cutted parts. And then the shimming process is built with multi-iterative simulation based on the least squares method. The finite element model is built to confirm the field change brought by the inclined 45o cutting value, which is added to the iterative calculation for cutting value correction and expecting the shimming effect. The new shimming algorithm is applied for the field measurement, amending and processing of CYCIAE-230, which achieve significant results to reduce the shimming times and further the fabrication period. The process of the shimming algorithm and the corresponding shimming effect of CYCIAE-230 will be presented as well.
A 230 MeV superconducting cyclotron CYCIAE-230 is being constructed by the China Institute of Atomic Energy. The technology of magnetic field measurement and amending processing is the primary task to realize the isochronous acceleration of cyclotron. The CYCIAE-230 has higher magnetic field, higher field gradient and dense rotation orbits. Therefore, the isochronous field and resonance crossing amended simultaneously. The first harmonics is also shimmed at the same process to achieve about 80% of the extraction efficiency by using resonance and precession extraction. The precision of field measurement, amending and processing is much higher and the algorithm is much more difficult. In addition, the compact structure of the magnet has very narrow installation space, which makes mapper design more difficult. In this paper, we will introduce:
1.The asymmetric field amending method for spiral sectors of SC cyclotron based on 45 degree chamfering on the pole edge is proposed and implemented for the first time. This method can effectively shim the isochronous field and first harmonics, reduce the magnetic saturation surround the pole edge, and facilitate the installation of main components such as central region and RF cavity.
2.During the processing, the asymmetric amending on both sides of the spiral sectors is creatively introduced to adjust the local tune value, so as to avoid the beam staying near harmful resonance and realize the effective control of the beam quality in the cyclotron.
3.A automated magnetic field measurement device, with both searching coil and hall probe has been developed. A series of optimum design and implementation of mechanical parts and EMC have effectively improved the positioning accuracy, greatly reduced the interference signal, and achieved the relative field measurement accuracy of 5×10-5.
After four times of field measurements, amending and processing, the results show that the phase shift, tune value and first harmonics have achieved excellent results. Detailed process will also be given in this paper. Such results will benefit greatly the overall performance of CYCIAE-230.
Proton beam with an average power of 5MW-10MW have important applications in particle physics towards the intensity frontier, as well as in the advanced energy, and material science. The fixed field alternating gradient (FFAG) accelerator combines the advantages of existing accelerators, which has a higher limitation of beam energy than high power cyclotron and has a higher beam-to-grid efficiency than existing high power linac and synchrotron, thus is considered as a good candidate for high power proton machine.
By utilizing the strong focusing and large acceptance features of FFAG in the theoretical framework of the fixed field and fixed frequency of isochronous cyclotron, a 2GeV/6MW continue wave FFAG design has been proposed in China Institute of Atomic Energy (CIAE). Due to the beam loss of high power proton beams, the resulting high radiation will deposit a large amount of radiation dose and head load on the SC magnet. As the high temperature superconductors (HTS) have a much larger thermal margin due to high critical temperature (> 90 K) and high upper critical field (> 100 T) than the traditional low temperature superconductors, and have been also considered have the lower overall construction costs and power consumption than the conventional magnet, currently the HTS magnet is the favorable solution for the 2GeV FFAG magnet design. In this paper, the lattice design along with the requirements on the F-D-F magnet of the 2GeV FFAG design is briefly introduced first. Then, the design of the F-D-F magnet is outlined. And the details of the HTS coil design utilizing ReBCO conductor and operating at ~40 K is also included.
This paper presents a 3D mechanical analysis study of the mechanical behaviour of the complete magnet structure of the Block-coil Dipole option for the future Circular Collider. The analysis includes three steps: (i) pre-loading with bladders and keys, (ii) cooling down from room to operating temperature, (iii) ener-gization at operating temperature. The main objective of the 3D optimization is to contain the large elec-tromagnetic forces, both in the straight section and in the coil ends. The optimization must guarantee that the stress level in the coil and in each component of the structure remains lower than the allowable values at each loading step. The magnet design in the straight section has been optimized and validated previous-ly using a 2D model. A 3D model is then required to optimize the coil ends and the longitudinal sup-port.This study was performed in the framework of the EuroCircol project.
Superconducting accelerator dipole magnets, based on Nb3Sn technology, with a nominal operation field of 16 T in a 50 mm aperture are being considered for the Future Circular Collider (FCC) with a center-of-mass energy of 100 TeV and a circumference in the range of 100 km, or an energy upgrade of the LHC (HE-LHC) to 27 TeV. To demonstrate the feasibility of such magnets, a twin-aperture 16T Nb3Sn dipole demonstrator based on a 4-layer cos-theta coil with 50 mm aperture and cold iron yoke is developed in the frame of the EuroCirCol program. The main design challenges for 16 T magnets include large Lorentz forces at this field level while maintaining accelerator requirements. To counteract the electromagnetic forces, an innovative mechanical structure based on the bladder-and-key concept, incorporating asymmetric coils and both aluminum and stainless steel skins, has been developed at INFN and further studied in collaboration with the University of Patras. This paper describes the design concept of the 16 T twin-aperture dipole magnet and the fully 2D & 3D parametric multi-physics finite & boundary element model (FEM & BEM), including the end regions. The design optimization is described and the optimized assembly parameters are presented.
*Work is supported by CERN, under contract No. FCC-GOV-CC-0141.
The Italian Institute for Nuclear Physics (INFN), in collaboration with CERN, is going to build the short model in Nb3Sn of the main bending dipole for the Future Circular Collider (FCC). The magnet will be developed on the basis of the baseline design presented in the FCC Conceptual Design Report (CDR) in the end of 2018. The magnet is based on cosine-theta design, with an internal aperture diameter of 50 mm and a “Bladder & Key” configuration for the mechanics.
The main purpose of the model construction is to demonstrate the feasibility of a magnet dipole with field quality characteristic suitable for collider and magnetic field above the LHC frontier.
The mechanical structure, which is a critical aspect of the magnet design, especially for the brittleness of the Nb3Sn cables, will have to demonstrate the effectiveness to reach the highest performance achievable in terms of bore magnetic field.
Here we present both the electromagnetic and mechanical design study of the model.
The forecast hadronic synchrotron studied in the FCC-hh program aims to reach 100 TeV center-of-mass collision energy using 16 T bending dipole magnets along a 100 km long ring. Gaining such magnetic field occupying a reasonable volume requires new technologies to be tested and validated on demonstrators. In collaboration with CERN, CEA is developing F2D2, the FCC Flared-end Dipole Demonstrator based on the block-coil option proposed in the EuroCirCol study. This single aperture 1.4 m long magnet is designed to reach at least 15 T with 14% margin at 1.9 K using two different Nb3Sn cables. The energy density per unit length is 1.4 MJ/m, about 3 times the energy density per unit length of the LHC dipoles. The combination of the high energy density and the graded coils makes the quench protection of this magnet one of the most challenging. A study considering the state-of-the-art of active quench protection technologies such as heaters and CLIQ is here presented, completed with multi-physics models to accurately describe the quench evolution, the hotspot temperature and the voltages between and at the end of the coils.
As part of an international collaboration, CERN has recently published a Conceptual Design Review of the Future Circular Collider (FCC), a proposed particle accelerator to succeed the LHC. Under the options considered, a proto-proton accelerator with collision energies up to 100 TeV, would require approximately 4’500 Nb3Sn superconducting dipole magnets operating at 16 T fields, installed in a new tunnel of about 100 km circumference. A proposed variant, as a possible first step towards the FCC, is the incorporation of these magnets in the existing LHC tunnel infrastructure. This will provide a proton-proton collider with about twice the collision energy of the LHC, the so-called High Energy LHC (HE-LHC). The 16 T dipoles, which are considerably larger and heavier than the 8.33 T LHC dipoles, require compact cryostats to keep the overall dimensions comparable with the size of the LHC tunnel.
In this paper, we report on the design and integration work on the baseline 16T cosine-theta design dipole magnets within their cryostats. We present here, possible design options departing from the well-established solution of the LHC cryostats, including mechanical and thermal design considerations on the cryostat. We also explore the electromagnetic and mechanical coupling between the magnet and the vacuum vessel, in the case of a stray field in the cryostat space, as would be required to reduce the volume of the cold mass.
We report the design for a hybrid block-coil dipole using advanced cable-in-conduit windings. The dipole is designed for use in the arcs of an energy-doubling lattice in the LHC tunnel.
The block coil design facilitates configuration of hybrid sub-windings of Bi-2212, Nb3Sn, and NbTi, each operating to the same fraction of critical current.
The cryogenics utilizes supercritical helium, operating in the window 4.5-5.5 K.
A novel method is provided for the support structure that provides robust support and stress management, and provides for the three sub-windings to be separately wound and heat-treated and then assembled and preloaded to complete the dipole.
Aiming to develop a combined superconducting magnet for a fourth-generation ECR source operating at 45 GHz at the Institute of Modern Physics (IMP) in Lanzhou of China, a significant gain in performance can be achieved by using Nb3Sn to allow solenoids and sextupole coils to reach a high field of 12 T. In consideration of special design of the sextupole-in-solenoid shape, the supporting structures with pre-tensioned aluminum cylinders named Bladder are used to bear the large loading and maintain the configuration during the magnet assembly and operation in cryogenic and electromagnetic environment. A dipolar structure based on an aluminum shell and home-made bladders were designed in this work. The mechanical characteristics of the dipolar support structure were explored numerically and experimentally. A 3D finite element modeling was developed to analyze the deformation and stresses in the structures during its assembly, cool-down and warm-up for simulating the practical operation conditions. The measurements on the strains profiles in the aluminum shell in the dipolar support structure also has been conducted using low-temperature resistance strain gauges combined with a half-bridge compensation method for temperature. Our results show that the pre-stresses induced in the support structures during the two stages of gas loading in the bladder and shrinkage during cool-down process reach the level for efficiently hustling the 12T superconducting ECR magnet. The numerical analysis is in good agreement with the measurements. Additionally, the mechanical behavior of the bladders during gas loading and cool-down is obviously dependent with the friction property between contact surfaces, which gives the main concerns in the design and optimization such special support structures under cryogenic environment.
Key words: Superconducting magnet, dipolar support structure, bladder, cryogenic environment, mechanical analysis
The first 100-m iron-based superconductor (IBS) tape was produced by Institute of Electrical Engineering, Chinese Academy of Sciences (IEE-CAS) using the powder-in-tube technique in 2016. Since then, the development of IBS tape provides an opportunity to propel the practical IBS application. In this study, the world first IBS racetrack coil was made using a 100-m 7-filamentary Ba1-xKxFe2As2 (Ba122) tape at the Institute of High Energy Physics, Chinese Academy of Sciences (IHEP-CAS). The IBS tape was winded in parallel with stainless steel tape before heat reaction and impregnated with epoxy resin after reaction. The performance of the IBS coil was tested at 4.2 K and 0 - 7.5 T background field provided by an Nb3Sn Common-Coil dipole magnet named LPF1.2. The racetrack coil quenched at 7.5 T with operating current of 45.9 A, which is about 64% of the quench current at self-field. And the quench was caused by heat from one joint. The details of fabrication process and performance test results were presented in this paper.
The Institute of High Energy Physics (IHEP, China) has been engaged in the development of shell-based dipole magnet with common-coil configuration for the pre-study of Super proton-proton Collider (SppC) project. The first subscale magnet LPF1, with two Nb3Sn coils and four NbTi coils, reached a bore field of 10.2 T at 4.2 K. Then a higher safety margin model has been proposed as LPF2, which has six Nb3Sn coils and two NbTi coils to reach a 12-T main field in both apertures with an operating current of 5300 A. The shell and yoke are reused from LPF1, as well as the two Nb3Sn coils and two inner NbTi coils of LPF1. The pre-loaded method of LPF2 is much alike that in LPF1: using Bladder & Key technology to overcome the Lorenz force in horizontal and vertical direction and pre-tightening six aluminum rod to pre-load the coil packs in the axial direction. While, the strain gauges are applied both at the surface of the aluminum shell and the inner surface of the innermost coils to monitor the pre-loading effect. The main design parameters, stress analysis, assembly procedure and strain measurement results during the assembly and test at 4.2 K will be presented.
MQXF is the Nb3Sn Low-β Quadrupole magnet that the HL-LHC project is planning to install in the LHC interaction regions in 2026 to increase the LHC integrated luminosity by about a factor of ten. The magnet will be fabricated in two different lengths: 4.2 m for MQXFA, built in the US by the Accelerator Upgrade Project (AUP), and 7.15 m for MQXFB, fabricated by CERN. In order to qualify the magnet design and characterize its performance with different conductors, cable geometries and pre-load configuration, five short model magnets, called MQXFS, were fabricated, assembled and tested. The last model, MQXFS6, used a new PIT superconductor, featuring a bundle barrier surrounding the filaments. The coil and the support structure were equipped with strain gauges and optical fibers to monitor strain during assembly, cool-down and excitation. We describe in this paper the mechanical performance of MQXFS6, analysed through experimental data and numerical models, and we compare it with the one of the previous short model magnets.
Abstract: Based on the Agreement of Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) and Ministry of Science and Technology of China during the Thirteen Five-Years Plan (so called 13∙5 plan), A dedicated test complex of superconducting magnet for China Fusion Engineering Test Reactor (CFETR) will be constructed in Hefei, China. A pair of high temperature superconducting (HTS) current leads rated at 100 kA for the CFETR magnet test complex is being designed at ASIPP. Because magnetic energy stored in the toroidal field magnet is 134 Giga Joules which are 3 times higher than the ITER case, HTS current leads must work in high voltage and nominal current without performance degradation during the magnet quench. In order to verify the safety and reliability of HTS current lead, this paper will numerically simulate the time of loss of flow accident (LOFA) from 50 K helium stoppage to the current sharing temperature starting and the burnout time from the current sharing temperature starting to the hotspot temperature of 200 K or the max. voltage of 100 mV along HTS module. The load line of static magnetic field is presented to predict the maximum current carrying capacity of HTS module. The inhomogeneous current distribution as a function of magnetic field with/without external applied field of 30 mT for the 90 HTS stacks is calculated by ANSYS iteration to estimate the current margin. The analysis results indicate the LOFA time is more than 500 s and the full current burnout time of 30 s is better than the requirement of the toroidal field magnet fast discharge time constant of 20 s, the HTS module heat load is less than 15W.
Index Terms—HTS, Current lead, Safety, CFETR
Acknowledgment: This work was supported by the Research of CFETR Integration Engineering Design Project (Grant No. 2017YFE0300500).
Engineering design of China Fusion Engineering Test Reactor (CFETR) Central Solenoid (CS) coil had been started in Institute of Plasma Physics, Chinese Academy of Sciences. The highest field of CS coil is 17.2T when the running current is 60KA. CS magnet system mainly consists of 8 Nb3Sn coils compressed with 8 sets of preload structure. The functions of the preload structure are to apply an enough axial compression to the CS coils and to have a mechanical rigidity against the repulsive force between 8 Nb3Sn coils. This paper describes structural design of CFETR CS magnet system. A global finite element model was created based on the design geometry data to investigate the mechanical property of CFETR CS preload structure and support structure under the different operating conditions. A local finite element model based on structure design was created to calculate the stress on the conductor jacket and turn insulation.
Key words: CFETR, Central Solenoid, structural design, FEA, Magnet
The Central Solenoid Model Coil (CSMC) project of CFETR that began in 2014 is devoted to develop and verify the manufacturing and testing technology of the large-scale superconducting magnet. The main manufacturing processes for the coil are verified by the mockup coil’s fabrication. For now, the winding for the Nb3Sn inner and outer coils are finished and preparing for its heat treatment, and the vacuum pressure impregnation for the NbTi middle coil is being done. This paper introduces the main manufacturing progress of the CFETR CSMC.
In order to further study fusion, China National Integration Design Group designed and developed a new superconducting magnet tokamak device, China Fusion Engineering Test Reactor (CFETR). As one of the most important components of the CFETR, the CS coil will be constructed to create, form and maintain a stable operation of the plasma. The latest CFETR CS magnet system design requirements are as follows：
1) To produce a 12-T peak field in the core of the magnet.
2) The maximum magnetic field on the NbTi module is lower than 6 T.
3) The maximum magnetic field change rate is 1.5 T/s, and the operating current is 47.65 kA.
4) The unit length of one Nb3Sn conductor is shorter than 1 km.
These requirements will bring a series of problems and challenges such as stability margin and mechanical safety to the design work of CS magnets. In recent years, with the development of HTS wires (especially ReBCO tapes), HTS has become an important choice for designing CS magnets in the future. Among the HTS wires, only Bi2212, Bi2223 and ReBCO are considered suitable for large-scale applications. Compared to the former two, ReBCO tapes not only has higher current transfer capability, but also No complicated heat treatment process is required after the strip is wound. Therefore, ReBCO will be one of the important alternatives for the design of CS magnet for fusion device in the future.
In this paper, we first calculate the equivalent material properties of the TSTC based on ReBCO. Then, according to the latest CFETR CS magnet design requirements, a hybrid CS magnet model based on ReBCO, Nb3Sn and NbTi was designed and analyzed. The results will provide reference for the design of high field strength and large current magnets in future fusion devices.
Abstract:The China Fusion Engineering Test Reactor (CFETR) Central Solenoid Model Coil (CSMC) is being designed and fabricated by the Institute of Plasma Physics Chinese Academy of Sciences. In order to validate structure strength and reliability of the CS Model Coil, model analysis and seismic response analysis have been carried out. Firstly, the paper established the CFETR CSMC model by using the CATIA software. Then the natural frequencies and modes of the CSMC are obtained by modal analysis. On this basis, the single-point seismic response spectrum of the CSMC is analyzed. From the results of analysis, it is concluded that the destructive effect of the horizontal seismic wave is bigger than that of the vertical seismic wave for the CSMC. Finally, El Centro, a 7.1 magnitude seismic wave, is selected to conduct the time-history analysis of the CSMC. The results reflect the maximum displacement of the CSMC coil under seismic action occurs at about 1.9 s, and the maximum displacement is 7.10 mm, 4.14 mm and 0.04 mm, respectively. During the whole earthquake, the maximum shear stress of the CSMC coil part is 2.06 MPa, which is lower than the allowable shear stress of the insulation layer of 60MPa. The maximum displacement of the whole model coil under earthquake is 10.37 mm and the maximum equivalent stress is 138.0 MPa. Our analysis results show that the design of the CSMC meets the design criteria.
Keywords: CFETR CSMC; Seismic spectrum analysis; Time history analysis
The design of the China Fusion Engineering Test Reactor (CFETR) has been updated since the end of 2018, the major and minor radius are enlarged to 7.2 m and 2.2 m. The CFETR magnet system consists of 16 TF coils, a eight-module CS coil, 6 PF coil and 18 CC coils. It is decided recently that a TF coil will be designed and fabricated from 2019 through 2024 by the Institute of Plasma Physics Chinese Academy of Sciences, which will produce a toroidal field of 6.5 T and a peak field above 14 T. A new circle-in-square Nb3Sn CICC conductor is being designed and the CFETR TF coil will be made of the CICC conductor without radial plates. For the preliminary design, the mechanical analysis shows that the von-Mises stress on the coil case of the inner leg and the shear stress on the ground insulation are over the limit, the reason is that the self-supporting strength of the present winding pack is not strong enough. Therefore, the design of the CFETR TF coil will be optimized by modifying the conductor design, the cross-section configuration of the winding pack and the coil case dimensions. Then the electromagnetic and mechanical analyses will be performed in order to verify the feasibility of the optimization design. The pretension, cool-down and Lorentz load will be applied for the 3-D analysis, and the orthotropic smeared material properties of the winding pack calculated with the finite element method will be used. In addition, 2-D analysis of the TF cross-section will also be performed.
The CSMC are major components of CFETR to generate the magnetic field for Simulating the Central Solenoid coil manufacturing process.Several trials were performed to qualify and optimize the heat treatment procedure of the Central Solenoid coil. In the trials, gas replacement, temperature controlling, protective gas flow controlling, coil fixture, and assembling procedure were performed to resolve some technical issues and to demonstrate the fabrication procedure. Major requirements are: the radius increase of the conductor must be less than 4.3mm in the reaction heat-treatment when the residual stress relax; the temperature ramp rate limited to 5℃/hr; the temperature uniformity need to be satisfied ± 5℃ at the same time in whole of the furnace; The gas ,which is exhaust from the furnace and conductor ,its’ impurity content must be less than 10ppm;
The central solenoid (CS) of JT-60SA has four electrically independent modules, and one module is 52-layer coil combined 6 octa-pancake coils and a quad-pancake coil vertically. The CS module is supplied with current through the room temperature busbar and current feeder of the superconductor. The maximum voltage between the CS module terminals is designed to be 10 kV, the voltage between the layers under ideal conditions is then about 0.38 kV because the CS module has 52 layers. But, in operating condition, there is a possibility that the voltage between the conductors is higher than 0.38 kV due to the voltage fluctuations of the power supply and the inhomogeneous voltage distribution in the CS induced by the resonance phenomenon. Hence, it is important to investigate the voltage behavior between the conductors in the CS module.
In the previous works, the circuit simulation model was created which includes CS module (the 52-layer pancake coil), the room-temperature busbar, superconducting current feeder and the structures (ground insulation) supporting TF coil. And the influence of resonance phenomenon on voltage distribution was investigated. In this works, based on the results of the previous works, we created the circuit simulation model of the entire CS (4 modules) and estimated the voltage distribution affected by resonance phenomenon. As a result, it can be concluded that the influence of resonance phenomenon on JT-60SA CS modules is negligible small under the operating conditions. These results therefore represent important information for the safe operation of the JT-60SA.
The construction of a full-superconducting tokamak referred as JT-60 Super Advanced (JT-60SA) is in progress under the JA-EU broader approach projects. The magnet system of JT-60SA consists of 18 toroidal field (TF) coils, 4 modules of central solenoid (CS) and 6 equilibrium field (EF) coils.
CS modules are manufactured one by one, then 4 modules are stacked. Finally, the pre-compression are conducted as a final process of CS manufacturing.
There are two methods for pre-compression, one is shrink fitting method, and the other is mechanical compress method. The shrink fitting method is simple method for pre-compression because it is not needed additional jig. However it is difficult to control compress load because the height and the amount of shrinkage by compress load of CS module is not completely uniform. In addition, if compress load become reduced, re-compress will be required after starting operation, but re-compress is impossible with the shrink fitting method.
Mechanical compress process was selected for pre-compression of JT-60SA CS to avoid above problems. Nine sets of hydraulic jacks and compress jigs, and stainless steel shims were used for pre-compress process to subject compress load by mechanically. Compress load of each sector can be controlled independently with this method. And re-compress after starting operation can be conducted. It means hydraulic jacks and compress jigs can be inserted from manhole of cryostat.
Pre-compression of CS module was successfully performed using mechanical compress process. The compress load of each sectors measured by strain gauges on tie plates was more than requirement of 4.2 MN/sector.
In this paper, procedure and result of pre-compression with mechanical compress process will be described.
In recent years, axial flux hybrid-excited permanent magnet machines with high power density, high efficiency and compact structure have the potential application prospect in the electrical vehicles. Besides, due to the rare earth resource crisis, the less-rare-earth permanent magnet machines have been taken much attention. In this paper, an axial flux partitioned stator hybrid-excited less-rare-earth permanent magnet synchronous machine (APHLPSM) which combines the structure of hybrid excitation and hybrid permanent magnet is proposed. The stator of the machine is divided into two parts, which are the armature stator and the excitation stator and the rotor locates between the two stators. The armature stator includes the armature teeth and the excitation teeth, by adopting the DC field windings wound on the excitation teeth as the auxiliary excitation source, the flux-regulation capability of the machine can be achieved. The design of the stator partition alleviates the space conflict in stator-PM machines and eases the difficulty of the current control in conventional axial flux double-stator machines. The excitation stator contains three-layer PMs, where two types of PMs of ferrite and NdFeB are reasonably combined, which not only guarantees the required power but also reduces the cost.
In the first part of the paper, the power volume equation is deduced，and the initial design parameters are given. Based on the finite element method (FEM), the electromagnetic performances, including air-gap flux density, back-EMF, cogging torque, and torque, are investigated. Then, the influence of the key structure parameters of the NdFeB and ferrite PMs on the electromagnetic performances are discussed, and the flux-regulation of the AFPHSM machine is also studied in the different DC excitation conditions. Moreover, a multi-objective optimization method is applied to optimize the APHLPSM machine, where the electromagnetic performances and the flux-regulation capabilities are considered. Finally, the optimization design results will be compared with that of the initial design to validate the effectiveness of the multi-objective optimization method. It will also verify the validity of the novel AFPHSM machine.
In case of Surface-mounted Permanent Magnet Synchronous Motor(SPMSM), PMs are attached to the surface of laminated core. They are connected by adhesion and magnetic force. However, in order to withstand rotation of the motor, thousands of revolutions per minute, rotor-teeth between PMs are essential to hold them strongly in position.
The rotor-teeth are also ferromagnetic material, they would be additional paths of magnetic flux in q-axis. These paths affect to flow of magnetic flux around airgap, and it could bring about leakage. Output performance get worse in this process, but also it reduces a risk of irreversible demagnetization on edge of PMs. Because load, magnetic field intensity, on PM decreases. And thicker rotor-teeth grip PMs stably more. So, it could be shown as trade-off relation. There are many variables which have influence on this phenomenon as motor composition like number of poles and slots, PM shape, airgap length, magnetic flux density, current and so on. Especially, thickness of rotor-teeth is one of them as well.
In this paper, relations between variables and effects are determined by means of analytical method. Considering variables mentioned, magnetic equivalent circuit could be offered. Both analytical method and numerical method based on a finite element analysis(FEA) are used with respect to several SPMSM models, in order to estimate that the proposed method is valid or not. Then the finding data by proposed method are compared with them of numerical method and verify that the technique is reasonable. So, we can predict the various characteristics analytically fast including performance variation and irreversible demagnetization prevention function. Also, mises stress and displacement ratio are interpreted in accordance with stability of PMs. Finally, a proper way to design optimized rotor-teeth depending of types of motor is suggested.
Recently, much research has been conducted on non-rare-earth magnet motors due to limited reserves and high prices of rare-earth materials. Among them, a magnetic flux concentrating motor using a ferrite magnet is being commercialized in many parts. However, it is disadvantageous to high-speed operation due to the structure of the rotor. In this paper, we propose a hybrid structure of a magnetic flux concentrating and an axial motor to solve this problem and named it FC-AFPM motor. In the axial direction motor, the axes for generating torque and centrifugal force are separated from each other to ensure mechanical stability. FC-AFPM can increase the power density by using ferrite magnets, and is excellent in mechanical stability and suitable for high-speed high-torque applications. Double-sided and Single-sided FC-AFPM motor were designed and evaluated, and the validity of the proposed new structure was verified.
This work was supported by the Energy Efficiency & Resources of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Trade, Industry & Energy (No. 20172010105920
As the price of rare earth permanent magnet (PM) is very high, developing of high performance electrical machines with non rare earth PM is have received extensive attention, and synchronous reluctance machine (SynRM) has show good performance when comparing with other electrical machines. The torque ability of SynRM is proportional to its saliency ration which is determined by the rotor topology and rotor material. In this paper, a new SynRM with the aid of grain oriented steel is adopted. the main magnetic structure of new SynRM is similar to that of traditional SynRM. In this SynRM the main core are made by the traditional non oriented silicon steel and the grain oriented steel is used to fill in the part of magnetic barrier in each layer. the rolling direction of grain oriented steels filled in the new SynRM is parallel to the direction of d-axis of the rotor core, thus the main magnetic flux flows can be increased along the rolling direction of the filled material and the d-axis reluctance can be decreased greatly. On the other hand the magnetic reluctance of the new SynRM along the q-axis direction is kept the same since the magnetic permeability of the grain orient steel vertical to the rolling direction is very low and there is some air gap existed. Therefore the saliency ratio can be increased and thus the torque can be increased. In this paper, a new SynRM is designed and optimized for the electric vehicle application, its main parameters and performance have been compared with a traditional SynRM based on the finite element method (FEM). Compared with the traditional SynRM, the torque of new SynRM has been improved about 7% with only very low material cost required.
Post-assembly magnetization is usually used in manufacturing process of high-speed permanent magnet(PM) rotors. This paper reports the optimization and test of a saddle-shaped post-assembly magnetizing coil for a 300kW 2-pole high-speed permanent magnet (PM) rotor. The required magnetizing space is 85 mm in diameter and 200 mm in length. A saddle-shaped coil structure is proposed, which effectively improves the coupling performance between the coil and the rotor, and reduces the magnetic field energy by 61% in comparison with the existing triple-coil structure. During the magnetizing process, eddy currents are produced in the coil and rotor reinforced structure and permanent magnet block. The influence of eddy currents on the magnetizing magnetic field and the electromagnetic force acting on the coil structure is analyzed. By optimizing the coil structure and pulse width, the effect of eddy current on the magnetizing magnetic field is reduced to less than 1%, and the power supply energy required for the magnetizing coil is optimized to the minimum. The saddle-shaped coil was fabricated and tested and has generated transverse magnetizing field of 6 T / 25 ms in the required space. The 300 kW 2-pole high-speed PM rotor has been successfully magnetized after assembly. The measured residual magnetic flux density agreed well with the theoretical calculation.
Weihua Huang, Junchen Zhao, Jin Wang*, Libing Zhou
State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Schoole of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
With the increasing demand for electric vehicles, electric power steering (EPS) system is in the spotlight. The EPS system has high requirements for the driving motors, such as high torque density, high reliability and low torque ripple. Permanent magnet synchronous machines (PMSM) are suitable for EPS applications because they offer many advantages like high torque density and efficiency. Irreversible demagnetization of the faults permanent magnets (PM) is troublesome in permanent magnet synchronous motors since they may greatly reduce the performance. Demagnetization fault of PMSM is also one of the key factors affecting the reliability of EPS system.
This paper presents a study on demagnetization analysis method and design optimization of PMSM for EPS system. A demagnetization analysis method based on 2D and 3D finite element analysis (FEA) for PMSM of EPS system is proposed. Based on the computation of the distribution of magnetic flux density on the surface of PM, the demagnetization risk is evaluated. EPS systems are strict to cost while PM is the most expensive material, so it is necessary to restrain irreversible demagnetization under the condition of minimizing the amount of PM. Therefore, in terms of design optimization, the thickness of PM in magnetization direction is mainly optimized. The simulation results clearly show that the optimized PMSM design can meet the requirements of EPS system, which is also verified by experimental results.
This work is partly supported by the National Key Research and Development Program of China (Grant No. 2018YFB0606000)
The corresponding author is Jin Wang.
The vibration occurring in an electric motor can be largely divided into mechanical vibration due to nonaligned bearings and shafts, and electromagnetic vibration by the electromagnetic force. For existing industrial electric motors, the mechanical vibration associated with the life of the motor was the most important concern. However, in recent years, electric motors—such as the ones used for electric cars and hybrid cars—have high-torque density by using the rare-earth permanent magnet. Thus, the relative importance of electromagnetic noise and vibration is increasing. Electromagnetic vibration and noise affect people emotionally, so it has become very important to reduce vibration when designing a motor.
There are two types of noise due to the electromagnetic field of the motor. The first is the structure-born noise, which is transmitted through the bearings of the motor to the mechanical path, and the torque riffle is the source. Second, the radial-force of the motor is the source of the air-born noise propagated to the air by the stator or housing of the motor.
In a three-phase motor, the torque ripple is produced by making the sixth harmonic of the electrical frequency as the primary wave. The magnitude of torque ripple also depends on the number of pole-slot combinations, the shape of the rotor / stator, and the magnitude of current applied. In order to analyze the radial force, which is the source of air-borne noise, an analysis of time and space harmonic of radial force density is required.
In this paper, NVH characteristics of 8p12s, 10p12s IPMSM are compared and analyzed quantitatively and qualitatively. The NVH test also measured and compared the noise and vibration levels and frequencies of each motor.
In order to cope with environmental pollution caused by the recent increase in electric power consumption, 'Minimum Energy Performance Standards(MEPS)' is being implemented in developed countries. MEPS is a policy to regulate the efficiency of the motor, which is a large part of the industrial power consumption, and it is a policy to prohibit the use of low efficiency induction motors. Research has been conducted to improve the efficiency of induction motor in order to cope with this policy. However, since it is adjacent to the saturation state, researches to replace it with a synchronous reluctance motor have been actively carried out. A synchronous reluctance motor is an electric motor using reluctance torque generated by using a rotor difference of inductance and is considered to be a suitable motor to replace an induction motor due to its simple structure and manufacturing convenience. This research was conducted to achieve IE5 level of IE4 class SynRM. The output characteristics of SynRM are determined according to the rotor difference of inductance and arc type barrier is applied to maximize the difference of inductance. In addition, the shape of the arc type barrier was mathematically identified and the rotor design parameters were reduced. Whereas induction motors can be directly driven, SynRM is required to be driven by a controller composed of inverters. In order to achieve IE5 efficiency, we analyzed the efficiency distribution of existing IE4 class motors through Co-analysis and studied IE5 class SynRM design by deriving improvement model. Additional studies have also investigated the output characteristics for Pma-SynRM by inserting permanent magnets inside the rotor. Finally, to confirm the validity of this study, we conducted the fabrication and testing and confirmed that the analysis results and the test results converged.
Permanent magnet (PM) motors, which have various advantages such as the wide operation range and high power density, are widely developed in various industrial fields such as automobile, aerospace, home appliance, defense industry and so on. The study and development of the slot-less PM motor is actively underway as the servo and driving motor, because it does not have teeth and their corresponding slots so that it has a variety of electromagnetic and structural advantages compared to the slotted motor : No cogging torque, Smooth motor running even at low speed, Less vibrations and audible noise, and Compact design and so on. This paper presents the study of the design and analysis of BLDC slot-less PM motor with the magnetic and electric loading using Response Surface Method(RSM).
[Body & Conclusion]
In the defense industry, the slot-less PM motor is widely developed and studied for the driving motor of guided weapon. The guided weapon is necessary a high output density and efficiency motor to improve its mobility and effectively strike a fast moving target. Especially, it should have the low rotor inertia in order to have the rapid response for forward and reverse rotation. In this paper, the electromagnetic characteristics of the BLDC slot-less PM motor are analyzed by Finite Elements Analysis (FEA). And the optimal design of BLDC slot-less PM motor is conducted with RSM and 3-Dimensional FEA (3-D FEA) to meet the requirements of a driving motor of guided weapon: the high torque constant and low rotor inertia. In conclusion, BLDC slot-less PM motor is designed with the optimal design using RSM and FEA. The achievement of the objective functions of the design for the driving motor of guided weapon is verified by FEA and the experimental tests with the prototype. Therefore, this paper provides the effective design method and process of BLDC slot-less PM motor.
The recent next-generation railway vehicles are aiming at energy saving and weight lightening and IPMSM(Interior Permanent Magnet Synchronous Motor) with a more improved efficiency and weight to output ratio than induction motor when rare-earth permanent magnet with high energy density is applied to synchronous motor have been developed a lot. Interior permanent magnet synchronous motor, used in this study is a high-capacity traction motor for railway vehicles and has a totally-enclosed structure to prevent dust, foreign materials, etc during operation as it is placed at the bottom of railway vehicles. This totally-enclosed structure is vulnerable to temperature because the cycle of heat is not good. The high-capacity traction motor for railway vehicles requires a high weight to output ratio and to increase the weight to output ratio, rare-earth neodymium permanent magnet with high energy density should be used, but are characterized by high-temperature demagnetization. Also, high current may flow due to failure in power converter and it may produce a big reverse magnetic field and be demagnetized by the reverse magnetic field. Demagnetization characteristics caused by such high- temperature demagnetization and reverse magnetization are characterized by permanent demagnetization as a new demagnetization curve called as recoil line is generated. This study proposes how to interpret demagnetization characteristics and carries out demagnetization analysis to obtain the reliability of rotor. It sets up an analysis scenario to drive electric motor based on demagnetization characteristics by considering recoil line and predicts the demagnetization of permanent magnet. And it examines the effects of output based on predicted demagnetization characteristics. It manufactures a model verified through analysis as test product and designs interior permanent magnet synchronous motor to obtain the reliability of rotor based on demagnetization characteristics proposed in this study through performance test and saturation temperature teste.
It is necessary to develop a motor with high output density, high efficiency, and high control accuracy in various industries like automobiles, robots and defense industry. Among the various types of motors, Slotless permanent magnet (PM) motors having relatively structural and electromagnetic advantages over slotted motors have been continuously developed for the precise control as a driving and servo motor. However, since the slotless motor has no tooth and corresponding slots, it requires a complex winding method, applied the skew, to maintain the structure of windings so that it makes the production process complicated and requires a lot of time and money. In this paper, design method of coreless PM motor with non-magnetic tooth-slot structures using 3D printing technology, which can replace the conventional slotless motor, is proposed.
[Body & Conclusion]
This paper proposes design method of coreless PM motor with non-magnetic tooth-slot structures using 3D printing technology. The electromagnetic characteristics of coreless motor which consists of the rotor of PM and teeth-slot structure of non-magnetic material(PC: Polycarbonates) are analyzed by finite elements analysis(FEA). Coreless PM motor with 3D printing technology and the commercial slotless motor which has the skewed-winding are designed and compare the electromagnetic output characteristics each other. The coreless motor, designed with the design method proposed in this paper can improve the difficulties of the fabrication and also have advantages of the electromagnetic output characteristics that conventional slotless motor has such as no cogging torque and high precise control with compact size. In addition, it can improve the electromagnetic output characteristics by applying the overhang of the permanent magnet of the rotor unlike the conventional slotless motor. In conclusion, the effective design method of coreless PM motor using 3-D printing which provides the reliability and convenience of the design and fabrication by getting out of the winding methods of the conventional slot-less motor is proposed.
This paper presents a comparison of cylindrical and plane air gap magnetic couplings in which the tile permanent magnet polarizations can be either radial or tangential or axial.The expressions of the torque transmitted between the two rotors of each coupling are determined by using the finite element method . For this system, a Halbach permanent magnet (PM) array structure is applied as a high torque density design method for a mangetic coupling. In addition, the high torque density magnetic coupling designing requires computation of the PM size by irreversible demagnetisation considering the tempera-ture environment, magnetic coupling position, and magnetic optimum design process. Finally, the validity and superiority of the optimized design are confirmed by manufacturing the prototype model and performing the experiment.
Recently, a new types of high efficiency motors are increasingly receiving attention because of the minimum energy performance standards (MEPS). A permanent magnet assistant synchronous motor (PMA SynRM) has high efficiency since it does not have copper loss of rotor in comparison with induction motor. Therefore, PMA SynRM receive attention as the new type of high efficiency motor. PMA SynRM with the asymmetric rotor can improve the torque by shifting the current phase angle of the magnetic torque and the reluctance torque. In addition, using the asymmetric rotor can reduce cogging torque and torque ripple. Therefore, research on the asymmetric PMA SynRM is actively underway. However research on the analysis method of asymmetric PMA SynRM is insufficient.
This paper establishes an analysis method of permanent magnet assistant synchronous motor (PMA SynRM) with asymmetric barrier. In a general motor analysis method, the inductance is calculated using the dq-axis vector diagram. In addition, the characteristics of the motor are analyzed by separating the magnetic torque and the reluctance torque. However, in an asymmetric motor, the magnetic neutral plane (MNP) is shifted because the magnetic permeance is asymmetric. Therefore, it is difficult to analysis the characteristic of the asymmetric motor because it involves errors applying the general analysis method. In this paper, the magnetic property of the asymmetric motor is analyzed and the analysis method of asymmetric motor is proposed. To verify the proposed analysis method, PMA SynRM is designed as a conventional model. Furthermore, the magnetic torque and reluctance torque are separated through the proposed analysis method. The validity of the proposed analysis method is verified through finite element analysis (FEA) and manufacture of the conventional model.
Compared to three-phase motors, multi-phase motors have higher torque density, smaller torque ripple, and higher reliability. In addition, multi-phase motors can be operated with other healthy phases, even if one phase fails. Therefore, with the increase in industrial applications that require fault-tolerance and continuous operation, such as EVs, military, and aerospace, multi-phase motors have received much attention. Similar to the three-phase IPMSM, faults of the six-phase IPMSM can be classified as: mechanical, magnetic, and electrical faults. An example of a mechanical fault is rotor eccentricity and bearing damage, an example of a magnetic fault is demagnetization, and an example of an electric fault is a turn-to-turn fault in an open-circuit phase. An inter-turn fault causes excessive current flow, which not only accelerates the breakdown of insulation but also can cause demagnetization. Therefore, if the inter-turn fault is detected in advance, the repair cost of the motor is reduced.
In this paper, the performance of the inter-turn fault diagnosis of a six-phase interior permanent magnet synchronous motor (IPMSM) was analyzed through d-axis current using finite element analysis (FEA). The high-frequency injection method was used to perform fault diagnosis with a current response before and after a fault. To obtain the response of the current versus the applied voltage, the voltage equation of the six-phase IPMSM was obtained for the occurrence of the inter-turn fault. In addition, the dq-axis current responses in the healthy and faulty conditions were derived from the voltage equations. Furthermore, since the response of the current is a function of the magnitude and frequency of the voltage, the performance of the fault diagnosis was determined from the magnitude and frequency of the applied voltage. To verify this, the inter-turn fault diagnosis performance was analyzed through FEA and the control simulation tool. As a result, we proposed a voltage and frequency to maximize the inter-turn fault diagnosis performance of the six-phase IPMSM.
In this paper, the influence of the change of eddy current loss of the IPMSMG (interior permanent magnet synchronous motor generator) for automotive ISG according to magnet lamination direction on the Demagnetization characteristics and vibration was studied. Reduction of the eddy current loss reduces the heat generation in the magnet and affects the demagnetization characteristics and vibration characteristics of the magnet. Therefore, in this paper, we propose a magnet structure that maximizes the reduction of eddy current loss, increases the reliability of the demagnetization, and has the low vibration characteristics that automotive motors should have. In this paper, the operation points of ISG model are divided into three regions: motoring 3000 rpm, power generation area 4000 rpm, and 16500 rpm. Since the demagnetization characteristics and the eddy current loss depend on the lamination type of the magnets inserted into the rotor, the vertical Segmented magnet model and the horizontal Segmented magnet model are analyzed. We compare the demagnetization characteristics according to the magnet division method by applying various drive current ranges where irreversible demagnetization can be occurred. In order to analyze the effect of eddy current loss and demagnetization according to direction of magnet division on vibration, vibration characteristics are analyzed through co-simulation of electromagnetic and mechanical properties. In this study, electromagnetic analysis is performed using ANSYS Electromagnetic Suite 19.0, and the magnet division model is considered through 3D simulation. In order to compare more precise characteristics of the demagnetization, the temperature distribution of the device in the analysis program using the J-H Curve and the thermal coefficient of the permanent magnet is calculated. In addition, we analyze the effect of electromagnetic characteristics due to the magnet division on vibration by using WORKBENCH 19.0 and analyze the magnet heat distribution using CFD thermal analysis program. In order to verify the reliability of the simulation data presented in this paper, we will prove by carrying out an experiment.
This paper presents the optimal design method of cage-bars in a single-phase line-start permanent magnet synchronous motor considering the starting torque and magnetic saturation. This method consists of two procedures. First, the basic design of cage-bars is made by analytic method of a single-phase induction motor. In this case, the equivalent magnetic circuit method is used but this method cannot consider nonlinear characteristic as magnetic saturation and leakage flux. Second, for considering the nonlinear characteristics, the optimal design of cage-bars is performed by the response surface method (RSM).
1. Procedure for Design of LSPMSM
The design process of LSPMSM is as follow. First, using the stator with winding and air-gap volume in conventional single-phase induction motor, the outside diameter of rotor can be determined. Next, the basic cage-bars design to maximize the starting torque is performed. After the basic cage-bars design is determined, the shape and the position of permanent magnet are determined. And the barrier is designed to minimize leakage of magnetic flux.
2. Optimal Rotor Design
The basic design of rotor is only considered to the starting torque. Because the LSPMSM adjust the magnetic flux path such as barriers at steady state, the LSPMSM need to consider the optimal design including the magnetic saturation and the leakage flux, which cannot be considered by analytic method. These two components are concerned with efficiency as well as starting torque.
The parameters of the cage-bars design are performed by setting up the limited flux value of possible points of the magnetic saturation and the leakage flux. Using RSM, the design of rotor calculates the optimal value.
The prototype of optimized model is not manufactured. So, to verify optimized model, the FEM result and experiment result of original model are compared. Through the FEM, it was confirmed that the start time was faster than the existing model.
Through the design process, the optimized model has higher starting torque and higher efficiency.
In semiconductor photolithography equipment, high productivity and nanometer precision of the motion stages are combined to enable shrink in chip dimensions at reasonable cost. High-force density linear and planar motors drive the stages which carry the reticle mask and the wafer with acceleration levels of multiple tens to hundreds of m/s2. Superconducting actuation might be a next step to increase productivity of semiconductor equipment.
Motion stages offer a new challenge to superconducting motors and their design. The dynamic motion profiles induce significant AC losses, requiring dedicated thermal design of the coils. The combination with precision pose challenges to the dynamics of the superconducting structural mechanics, as well as to the precision with which the superconducting coils are manufactured and assembled. Finally, the usage of superconducting magnets for actuation of a production machine poses specific challenges to reliability and recovery times.
The contribution will offer a glimpse on the expected loads on the superconducting coils and the specific challenges for a semiconductor motion stage application.
This paper proposes a design and optimization of ferrite assisted synchronous reluctance machine. SRM(Synchronous Reluctance Motor) could be applied in electrical vehicle traction due to its salient advantage. SRM is cheaper than traditional PMSM(Permanent Magnet Synchronous Motor) because it needs no permanent magnet or some ferrite(in Permanent Magnet Assisted Synchronous Machine), which means it has lower cost. Moreover, benefiting from the simple structure of rotor, SRM can be easily manufactured and has better robustness. Also, SRM has good performance in high efficiency and wide speed range. However, SRM has some shorts in average torque, torque ripple and Power Factor, so it is necessary to optimize the topology and improve its performance.
Compared with traditional Induction Machine and Permanent Magnetic Synchronous Machine, the structure of PMASRM(Permanent Magnet Assisted Synchronous Reluctance Motor) has good performance in EVs traction. But its disadvantage is apparent in torque ripple and torque density. It should be essential to optimize its pole/slot ratio and structure of rotor. This paper is going to compare two different kinds of topologies and optimize the structure to obtain better operating performance. The two topologies differ mainly in the types of flux barrier, one of type is angular and the other is curve. The optimization is about to be imposed in the structures considering multiple factors in order to compare the performance on the different topologies.
Two different structures of the rotor are shown in the following figure. The first one is angular flux barrier, the other one is curve flux barrier.
Generally, when designing an electric device, the harmonic components in the electric angle of the MMF do not generate the average torque, so only the fundamental component in the electric angle is considered. Also, the back EMF and the torque ripple include only the harmonic components based on the electric angle. Therefore, the conventional MMF wave equation considers only the harmonic components based on the electric angle.
Conventional equations are not problematic in obtaining electromagnetic characteristics such as back EMF, torque, and torque ripple generated by electric machines. However, the distribution of radial force density, which is the cause of electromagnetic vibration of electric machines, also generates sub harmonics in addition to the fundamental component of electric angle depending on the combination of poles and slots. Therefore, in order to consider the electromagnetic vibration characteristics, the harmonic components of the MMF waveform based on the machine angle, not the electrical angle, should be considered.
For example, consider the stator MMF of the 8 pole 9 slot motor. Using the conventional equation, the spatial harmonic component of the air gap MMF waveform generated by a single-phase winding can be obtained only in the 1st, 3rd, 5th and 7th components of the electrical angle shown in black. This means that only the 4th, 12th, 20th, and 28th harmonic components of the mechanical angle can be calculated, and it is difficult to calculate the remaining sub harmonics, so that the electromagnetic vibration of the electric machine cannot be accurately predicted.
In this paper, we propose a generalized three-phase stator three-phase winding equation that can accurately calculate the spatial distribution of stator MMF for all combinations of poles and slots.
To verify the equation proposed, the magnetic flux density of the 8p9s and the 8p48s models was calculated by FEM and the proposed equation.
An important index in determining the performance of a permanent magnet synchronous motor (PMSM) is the maximization of using the permanent magnet (PM) inserted in its rotor. Thus, a process that verifies the demagnetization of PM is generally included in a design process of PMSM. However, the magnetization, which is also one of the important indexes in the design process, has not been much considered. It is due to the fact that most of the mass produced motors are categorized as surface permanent magnet synchronous motors (SPMSMs) and interior permanent magnet synchronous motors (IPMSMs) and the whole magnetization of these motors can be performed using properly designed magnetization yokes without any major trouble.
The spoke type PMSM is a shape that maximizes the surface area of PM vertically inserted in a rotor core. Also, studies on SPMSM have been actively performed because of increasing more power density than that of IPMSM. However, it plays disadvantage to the magnetization performance in a rotor structure for improving motor performances. Consequently, the whole magnetization could not possibly be performed depending on models of the spoke type PMSM and it requires a new process that has not been considered in the conventional design process of PMSM. Thus, a new design process of the spoke type PMSM that considers the magnetization performance is proposed in this study. First, types of magnetization methods and its advantages and disadvantages were analyzed. Then, a cause that decreases the magnetization performance in the magnetization method based on yokes for the mass production of PMSM was analyzed. In addition, the major factors that affect the magnetization performance in the spoke type PMSM structure were investigated, and a new design process considering the magnetization of the spoke type PMSM was proposed. Finally, a model of the spoke type PMSM was designed, fabricated, and evaluated using the proposed design process.
The Axial Flux Permanent Magnet Synchronous Motor (AFPMSM), manufacturing 3 Dimensions are limited in few ways. 3D modeling is less mass-produced with high cost of unit production because stator must roll up the amorphous electrical steel plate or be molded. The study shows AFPMSM with 3D printing technique cannot be materialized in existing motor. Under the same conditions of motor design like size, amount of permanent magnet (PM), and winding used in power density of RFPMSM and new AFPMSMS. AFPMSMS includes comparative analysis of torque density between existing model produced by Soft Magnet Composite (SMC) core with molding techniques and model that contain stator shoe produced by 3D Printing technique.
The Direct Drive Type motor for front-load washer was selected in this paper. Specifications of AFPMSM were determined in size, number of poles and slots, and amount of PM usage based on the existing RFPMSM. To increase precision, the study of axial direction Dummy analysis to consider the magnetic flux leakage in the axial direction to carry out when setting up 3D finite element method. A stator core and double-sided PM rotor type which can increase the torque density efficiently by using more PM at the same size of selected among the types of AFPMSM. The shapes could bring a high torque density because of the difficulties of stacking the stator, the free shape form of 3D Printing was suitable for this study. Specifications Design of AFPMSM with parameter analysis was made stator core shape, which is applied with 3D printing technique. Firstly, existing AFPMSM was comparative analysis with AFPMSM that stack a shoe on stator teeth with 3D Printing technique. Finally, new AFPMSM were combined of high directional electric steel plate and SMC core for better performance, and the feasibility of the study was verified through prototype test.
In this paper, the demagnetization and vibration characteristics of a 48V 5kW BLDC ISG motor generator are analyzed according to the magnet segments. Particularly, permanent magnet is divided into 3segments and 7segments as a comparison model. According to the operation characteristics of the ISG, the driving area was divided into three areas: motoring 3000rpm, power generation area 4000rpm, and 16500rpm. In general, electrical equipments of the vehicle are very sensitive to vibration characteristics and ISG is attached to the engine part of the vehicle, so specifications are given to minimize vibration. In addition, the high output ISG has a very high driving current, which causes a risk of irreversible demagnetization. And We apply various driving current ranges that can generate irreversible demagnetization. In addition, the characteristics of demagnetization and eddy current depends on the lamination type of the inserted magnet in the rotor, so this is mainly compared and analyzed. We analyze how does the stacking of magnets in the fractional slot winding method affects the eddy current loss reduction. and then Modal analysis and harmonic analysis are performed for vibration characteristics analysis and resonance frequency is found. The demagnetization phenomenon and vibration of laminated magnets are analyzed by 3D simulation. In order to analyze the effect of the irreversible demagnetization of the laminated magnets on vibration, we used mechanical Co-simulation technique. In this research, analysis was carried out using ANSYS EM and WORKBENCH. Based on the results, the optimization design was performed. In order to verify the results of this analysis, various types of magnets were made and a comparison test was conducted using various types of magnets. so we are willing to show program analysis data and experimental data.
Permanent magnet synchronous machines (PMSM) with fractional-slot concentrated winding (FSCW) configuration are featured with short end windings, low mutual coupling between phase windings, high self-inductance, high slot fill-factor, reduced losses and easy and cheap manufacturing process, which makes them best choices for many applications. Based on these merits, a novel type of FSCW topology is presented. This paper investigate the method to form this topology with method of slot vector star map and slot number phase diagram, and try to find the combination of slots and poles which is available to this topology. Recent study has found that the feasible combinations of slots and poles are an even multiple of number of slots and poles of the unit machine that can use FSCW originally. And when the new topology is applied, the number of the unit machine will be halved. It means FSCW stator with even number of unit machine can apply either the original FSCW or the new topology of FSCW. In this research, a 20-pole, 24-slot PMSM is chosen to analyse the characteristics of this topology of FSCW. Conductor phasor superposition method is adopted to analysis the MMF harmonics since FSCW leads to high harmonic content, and 2D finite element analysis (FEA) is adopted to deal with the machine performances like torque ripple, harmonic losses especially permanent magnets eddy current loss and radial electromagnetic force. All the results are dealt and compared with the original FSCW under the same situation. Research has found PMSM with the new topology of FSCW configuration has lower torque ripple and lower noise under the same electric and magnetic load. Other features are currently under study.
Torque motors for servo valves were created about 50 years ago, and they are used in several military and aerospace applications. Servo valves, which are now widely used in the general industrial and simulator fields, are still the beginning of fusion devices located at the top of hydraulic devices can do. A common torque motor uses a feedback spring for the rotor's alignment. This is a drawback that a separate mechanism is required like feedback spring. This study deals with the design and characteristics analysis of LART (limited angle rotary torque) motor, which satisfies the movement of limited angle when DC current is applied and returns to the initial position when the current is cut off through the magnetic circuit and motor shape design. LART motors using permanent magnets have a high energy density, low weight, and high efficiency. The LART motor in this study has a constant rotation range and it can be applied to a system that regulates the supply amount of fuel, oil, etc., by controlling the movement of the main control valve (MCV). Due to the characteristics of the system, when a specific DC current is applied, the desired rotation angle should be set to maintain the stationary state. When the power supply is interrupted, it should return to its initial position. In addition, ideal control is possible when there is a linear change in the torque value and the rotation range generated according to the magnitude of the current. In order to satisfy these characteristics, this paper study focuses on the design of the rotor, stator structure, the winding method based on the finite element analysis. The validity and reliability of the design method are verified using the manufactured LART motor.
Under the construction schedule of the next generation of Circular Electron-Positron Collider building in China, the cryogenic conception design of the detector magnet is completed, and some related preliminary research works have come out good results as well. A network of LHe tubes in the thermosiphon circulating mode, which is attached to the extemal coil wall, is used to cool the coil. The thermosiphon loop has been simulated with different working media, tube lengths and diameters, heatloads. The results can help to design the thermosiphon properly for different working condition of the solenoid.
The 3rd generation synchrotron light source will use a lot of insertion device, such as SC wiggler and SC undulator, to generate synchrotron radiation photon. The cryostat of 3W1 SC wiggler magnets have been finished assembling and cryogenic testing, the test results show that in the normal operating mode (no power failures, unexpected quenches etc.) the cryostat work with close to zero liquid helium consumption. The cryostat of SC undulator have been finished mechanical design and will start assembling at October2019. Advanced development of the cryostat of the CEPC final focus superconducting magnets have been started at September 2018 and will finish the design and construction at December 2019.
The high temperature superconducting (HTS) magnets cooled by solid nitrogen (SN2) are of great merits of lower thermal temperature gradient, better thermal uniformity and thermal stability. However, the existing cooling system cannot provide a long-term stable low-temperature circumstance for HTS magnets due to significant heat load, since they are not specially designed for the SN2. Meantime, due to the large density and thickness of the stainless steel, which is the main constituent constructing the cryostat, the whole system is too weight to realize the compact and light-weight design of the HTS magnets. To overcome these shortcomings, we utilized two radiation shields, which are cooled by liquid nitrogen and first stage of cryocooler, to reduce the heat load of SN2 cooling system as well as to improve the working time of SN2 in this study. And we have introduced a pluggable cryocooler to reduce the whole weight of the SN2 cryostat. Afterwards, we have investigated the performance of the presented cooling system in conjunction with HTS magnets, the theoretical calculation shows that the 20 liters of SN2 can work more than 6 hours from 30K to 40K without any operating and thermal problems. The results of this work could provide a diagram for the future design and construction of high efficiency SN2 cooling system for HTS magnets.
Key words: Solid nitrogen; Cooling system; HTS magnets; Heat load
The cryogenic system plays a vital role in the development of superconductivity. In a sense, superconductivity would be in more widespread use now if it were not for the problems associated with the cryocoolers needed to cool the superconducting devices or facilities. For a variety of high-Tc superconducting applications such as transformers, fault current limiters, motors, generators, power cables and synchronous compensators, the technology itself is relatively mature. However, the problems associated with the used cryocoolers have hampered the advancement of their practical applications. An ideal cryocooler for the applications should have the following features: low maintenance, high reliability, long operation life, high capacity and high thermodynamic efficiency.
In the authors’ laboratory, a long-life, high-capacity and high-efficiency cryogenic system based on the Stirling-type pulse tube cryocooler (SPTC) is being developing. The pulse tube cryocooler (PTC) without any moving component at the cold end has the intrinsic merits of long life at the coldhead, and the SPTC driven by the linear compressor also achieves the high reliability at the warm end. The developing SPTC is inherited from a series of ones developed for aerospace applications and thus keeps the merits of high reliability and long life. Its mean-time-to-failure (MTTF) can reach 10 years, which is over ten times the average MTTF of most existing cryocoolers for the similar applications. Another formidable challenge for the aimed applications is often from the required huge cooling powers. The developing high-capacity SPTC can achieve 1.1 kW of cooling powers at 77 K for each unit. And multiple units can also be combined together to provide more than 20 kW at 77 K. Another advantage of the cryogenic system is that it can vary freely between 20 K and 90 K. The SPTC has also achieved the high efficiency with a relative COP of 20% of Carnot at 77 K.
The application background and design approaches will be described and the performance characteristics of the developed cryogenic system presented and discussed.
A conduction-cooled HTS magnet is designed and tested to produce AC magnetic field of maximum 4 T for an adiabatic demagnetization refrigerator (ADR). The magnet equipped with extensive copper thermal drains is conductively cooled by a GM cryocooler to approximately 5 K and stably generates alternating magnetic field between 0 and 4 T at 0.2 T/s. The fastest ramping rate that dictates the cycle frequency of continuous ADR, is to be determined by the AC loss of the magnet assembly. The thermal loss to destabilize the AC operation of the magnet is carefully estimated and confirmed by using two different methods for cross-checking; electrical and caloric (direct temperature rise measurement) ones. The novel scheme of in situ quench detection technique is employed to eliminate an electrical inductive pick-up noise of the auxiliary metal components as well as HTS so that the non-inductive voltage signal is reliably utilized for judging the quench event of the conduction-cooled magnet. This paper addresses fast-ramping characteristic issues of HTS magnet operation for continuous ADR. The analysis of the detailed pre-quench signal prior to full quench is an essential procedure that can determine the maximum performance of ADR. The developed conduction-cooled magnet shall be indispensable for running the integrated continuous ADR operating between 5 K and 2 K.
The design of a large purpose built cryogen-free magnet is reviewed. The system has been manufactured for the Fundamental Neutron Physics Beamline (FNPBL) at the Spallation Neutron Source (SNS), Oak Ridge, Tennessee.
The magnet system will house a custom spectrometer and be used to measure a, the electron-neutrino correlation parameter, and b, the Fierz interference term in neutron beta decay.
The cryostat is cylindrical, nominally 7.5m along its axis and 1.43 m in diameter. It houses a complex set of niobium-titanium superconducting windings which provide a varying magnetic field profile along a 320mm diameter gold-plated UHV bore. The bore tube extends along the full length of the cryostat and has orthogonal ports connected to the neutron beamline. A vacuum of <3.10-10 mbar is achieved.
The stray field generated by the magnet windings surrounding the UHV bore is compensated by a series of negatively wound co-axial windings which have approximately twice the diameter of the internal positive windings. The cryostat system will be housed in a passive steel shield to further compensate the stray field.
The magnet windings operate nominally at 4K and are cooled by four Gifford McMahon two-stage cryocoolers, each delivering 1.5W cooling power at their second stage. No liquid cryogens are used for normal operation of the system. The cryostat design allows the magnet system to be operated in both horizontal and vertical orientations.
High temperature superconducting (HTS) taped stacks have broad application in magnetic levitation because of uniform induced current distribution, good heat dissipation and preferable mechanical properties. Configuration of the stack has a great influence on the uniformity and strength of the trapped magnetic field. In this paper, 3D modeling and experiments of HTS taped stacks with different stacking configurations are carried out under field cooling conditions, and the influence of three different configuration samples on the profile and uniformity of trapped field was compared. The first sample consisted of the superconducting tapes is arranged in a straight line; the second sample is the knitted tape stack (KTS); the third is inclined stacks with an angle. 3D modeling simulation is promoted by using the E-J constitutive law together with a T-A formulation to calculate the electromagnetic properties of the taped stacks. Finally, the simulation result is roughly consistent with the experimental result. Result shows that the location of the trapped field of the stacks in the straight arrangement matches the location of the tape arrangement. In the cross-shaped sample, it has been found that the maximum trapped magnetic field values appear in the regions where the superconducting tapes overlap each other, and the minimum values appear in the overlapping edges of the tapes. Compared to the other two samples, the inclined stack sample has a greater attraction for capturing a uniform magnetic field over a larger area.
Keywords: HTS tape stacks, 3D modeling and analysis, T-A formulation
Abstract-Stacks of commercial high temperature superconducting (HTS) tape can be magnetized to act as strong magnets for magnetic levitation. Based on our laboratory's high temperature superconducting magnetic levitation platform, in this paper, commercial superconducting tapes are used for stacking to replace the superconducting bulks. We stacked new model round bulk with a diameter of 24-mm and square bulk with a side length of 24-mm, and we have performed theoretical and experimental studies with these stacks. The samples were magnetized using a Nd-Fe-B magnet in a temperature range of 77k to 20k. The axial levitation force was measured between field cooled HTS stacks and permanent magnet in our laboratory device. We also tested the magnetic levitation force of bulk samples of the similar shapes and compared it to stacks.
Index Terms-HTS tape, bulk superconductors, stack of tapes, trapped field, magnetic bearings, magnetic levitation
The top seed method and the interior seed method are com-bined for the purpose of improving the electromagnetism of the superconductor by removing defects such as processing and cracks in the YBaCuO crystal. The top seed melt growth process is widely used as a process for growing superconducting bulk.When measuring the magnetic levitation force on the upper surface of YBCO superconductor, the YBCO superconductor fabricated by Top + Interior seeding process was observed at 66.787N. In the case of the YBCO superconductor fabricated with the Interior seeding process, it was observed at an average of 37.387N. In the YBCO superconductor fabricated using the Top + Interior seeding method, the growth surface of the superconducting bulk upper seed and the part where the growth surface of the seed touches from the center are generated, so from the measurement result of the YBCO superconductor fabricated by the Interior seeding processIt is also confirmed that it is high. The Top + Interior seeding process proves to be a very effective way to complement the disadvantages of the Interior seeding process displayed on the top surface of the YBCO superconducting bulk.This research was supported by the Korean Electric Power Corporation [Grant number:R16XA01].
Dynamic behavior with the hysteresis of the levitation force of a magnet-superconductor system is investigated with application of an alternating magnet field. The effect of a resonance swinging and break-off of the samples from the levitation level is found. Subharmonic resonance associated with the nonlinear of levitation dynamics is shown to the system. The critical amplitude vs. the field frequency to the superconductor is discussed. Levitation is stable most when the sample is exposed to a low-frequency field. In this case a large amplitude of the alternating field is needed to break-off of the sample.
The levitation properties of permanent magnet-superconductor systems have been studied for a long time. Recently it has been demonstrated extensive possibilities of application of stacks, slabs and windings from HTSC tapes for levitation systems.
In this work a design of a superconducting passive magnetic levitation bearing on the base of HTSC flexible tapes is proposed and implemented. The bearing consists of a cylindrical stator with a superconducting winding and a concentrical rotor. The rotor consists of a set of permanent magnets located around the stator in three layers. Different configurations of superconducting windings with different numbers of pancakes and different numbers of tape layers in one pancake are implemented. The values of the horizontal and vertical components of the levitation force are measured. A comparison is made of the obtained dependences with the values of the levitation force of stacks of HTSC tapes with different numbers of tapes over the line of magnets, similar to a rotor.
The magnetic gear can prevent the noise, vibration, and damage due to the noncontact drive.
Many papers have been published with regard to the design of magnetic gears. However, most design methods in the study only considered magnetic properties. The structure of the magnetic gear has two voids, and permanent magnets are located on the inner and outer rotor. And, a fixed-pole is located between the inner and outer permanent magnets to modulate the magnetic flux.
In this study, design and fabrication are performed considering only the electromagnetic performance of the magnetic gear. However, there are significant differences between the FEA results and experimental results in terms of the efficiency characteristics. In order to analyze the errors of the analysis and measurement results, the stress analysis was performed from the results of electromagnetic force characteristics analysis of the manufactured magnetic gears. As a result, it can be confirmed that the stress distribution of the fixed core is out of the yield stress. For this reason, it can be seen that the deformation of the fixed iron core occurs and the loss due to friction is greatly increased.
In this paper proposes a method for the design and analysis of coaxial magnetic gears considering the mechanical stress as well as the electromagnetic performance. Considering the magnetic and mechanical properties of magnetic gears, the design area to increase permanent magnet usage to within 10% compared to the existing model and satisfy the maximum pull-out torque of the same level was derived. Then, the optimum design model in which the yield stress does not occur is presented through the stress analysis of each model. The production of the magnetic gear, electromagnetic and mechanical analysis, and the design method will be explained in detail in the final paper.
At temperatures near absolute zero, the materials used in the superconducting magnetic suspension device are chemically inactive and the electrical losses are very low, which makes the device have a high accuracy in measuring angular velocity and angular displacement. In order to determine the accuracy of the device, it is necessary to carry out the drift test for the device. One of the commonly used methods for drift test is the torque feedback method. However, this method requires that the device be able to rotate 90 degree. In this paper, in order to meet this requirements of the drift test, four special lateral suspension coils were designed, which were evenly distributed along the equator of the spherical rotor. When the device was deflected by 90 ° for the drift test, circumferential support forces can be provided by the four lateral suspension coils. Levitation characteristics of the lateral suspension coils were analyzed by using 3-D magnetic field finite element analysis method. Due to the special structure, a tooling was designed for winding the lateral suspension coils. The results will be helpful for the drift test of the superconducting magnetic suspension device next step.
Magnetic gear which is capable of non-contact transfer torque has replaced mechanical gear and has advantages of high-efficiency and improved reliability. Common electrical devices, such as motors and generators, have a single air gap. However, there are two air gaps in the magnetic gear, and a laminated structure called a pole piece is arranged between the two gaps at regular intervals in the circumferential direction. This structural feature causes difficulty in mechanical earth of the pole piece. In this paper, two methods of supporting the pole piece are presented.
Model 1 was made of non-magnetic metal as the material of the pole piece supporter and Model 2 was made of epoxy. Model 1 was easy to fabricate and mechanically robust, but it was confirmed that eddy current loss occurred in metal pole piece supporter. The higher the rotation speed, the higher the loss exponentially and the lower the output and efficiency. On the other hand, Model 2 had no eddy current loss, but was not mechanically robust, and was damaged during the experiment due to circumferential torque and vibration acting on the pole piece.
This paper presents information on the advantages and disadvantages of the pole piece supporter according to the materials. Through the result, it is possible to consider materials suitable for the pole piece supporter according to the torque and rotation speed of the magnetic gear. Each model was designed with 3D-FEM to improve analytical reliability. An opinion is also presented on the torsional stiffness of the pole piece, which was mentioned as one of the causes of the decline of analytical reliability in previous studies.
Specific design and experiment contents are disclosed through the full paper.
This research was supported by Korea Electric Power Corporation. (Grant number: R19XO01-34)
Because typical electrical devices cannot be driven without a power converter, the use of gears is essential. Various studies have focused on magnetic gears without mechanical losses. In certain linear motion systems, such as wave energy power generators, using linear gears is inevitable. The most important aspect of gears in linear systems is manufacturing feasibility. Recently, research on linear magnetic gears has focused on tubular structures. However, tubular magnetic gears have the disadvantages of being difficult and expensive to manufacture. Alternatively, similar performance can be achieved by simplifying the tubular structure to a linear one. There are unfortunately few researches on simplified linear magnetic gears to date, and this is therefore very important.
In this paper, we performed an electromagnetic analysis of simplified linear magnetic gears (LMGs) according to the characteristics of their flux-modulation poles (FMPs). The performance of LMGs varies greatly depending on the characteristics of their FMP. Therefore, we proposed the optimal type of LMG by comparing the characteristics of the FMPs of three types of LMGs: non-laminated core, laminated core, and soft magnetic composite (SMC) core. Generally, non-laminated cores yield low efficiency because of core losses and eddy current losses, but their stiffness is vastly superior. Laminated cores have low stiffness but high efficiency because of their low electromagnetic losses. SMCs offer several advantages, including low core losses, low eddy current losses, 3-D isotropic ferromagnetic behavior, flexible machine design, and relatively good recyclability. By comparing these characteristics, we show the superiority of simplified LMG fabrication and its performance and then propose the best type of FMP by comparing their electromagnetic characteristics. The final focus of our electromagnetic analysis is determining the feasibility of constructing a simplified linear magnetic gear, along with its manufacturing cost, electromagnetic characteristics, and safety during operation. All results are validated through FE analysis and experimental results. Therefore, the final manuscript will cover more details about analysis process.
A magnetic bearing uses eddy current sensors or Hall sensors to detect rotor displacement, which results in the problems such as large volume, increased cost and reduced reliability. Therefore, the research on self-sensing methods of rotor displacement for magnetic bearings has theoretical and application value. State estimation method and parameter estimation method have problems such as complicated structure and over-dependence on precise mathematical models. The neural network method does not depend on the mathematical model and parameters of the magnetic bearings, but it is easy to fall into the local optimum and its convergence speed is slow. In this paper, a self-sensing method of rotor displacement for six-pole double-stator hybrid magnetic bearing (HMB) based on improved particle swarm optimization (PSO) least square support vector machine (LS-SVM) is proposed, which can accurately predict the rotor displacement of HMB.
The structure and working principle of the six-pole HMB are introduced, and mathematical model is deduced. Based on the regression principle of LS-SVM, the prediction model between currents in control coils and rotor displacements is established, and the performance parameters of LS-SVM are optimized by improved PSO. In the process of optimization, the mean square error between the predicted value and the measured value is taken as the evaluation criterion to compare the prediction ability of the improved PSO with the standard PSO. The comparison results show that the performance of the prediction model based on the improved PSO LS-SVM is obviously better than that of the standard PSO. The simulation system for self-sensing modeling of rotor displacement for the six-pole double-stator HMB is constructed. The simulation results show that the method is feasible. Simulation experiments on floating and anti-interference are carried out, and the simulation results verify the feasibility of the method.
Besides the advantages of the conventional magnetic bearings such as high speed and high precision, AC magnetic bearings also have strengths such as small size and low cost because of the use of mature technology of inverter driving. Therefore, AC magnetic bearing has potential application prospects in industrial manufacturing, aeronautics and astronautics, wind power generation and other fields. However, the installation error of displacement sensors or the influence of the rotor non-uniform material and non-uniform heating will cause the working position of the rotor to deviate from the given reference position, resulting in the change of the stiffness of the magnetic bearing at different positions, which will reduce the rotation accuracy of the rotor and limit the further increase of rotor speed. In this paper, the influence of variable stiffness on the six-pole AC hybrid magnetic bearing is analyzed, and parameter optimization design is proposed.
Firstly, the structure of six-pole AC hybrid magnetic bearing is introduced and the formula of radial suspension force is derived by using the equivalent magnetic circuit method. Secondly, the variable stiffness coefficient is deduced according to the eccentric displacement , and the influence of the variable stiffness coefficient on the parameters design of magnetic bearing is analyzed. Thirdly, the parameter optimization design of six-pole AC hybrid magnetic bearing is carried out with reference to the characteristic of variable stiffness coefficient. Finally, simulations and experiments are carried out, the displacement waveforms of the rotor including floating, stable suspension and under external disturbance are tested. The simulation and experimental results show that the static and dynamic characteristics of the magnetic bearing are excellent. In other words, the parameter optimization design of the six-pole AC hybrid magnetic bearing which considers variable stiffness is feasible.
With the development of energy saving and advanced equipment in the modern industry, the requirement of high-speed and high-power density motor are developing. Compared with the conventional bearings, magnetic bearings have the advantages of no friction, no lubrication and sealing, high speed, high precision, long service life. Thus, Magnetic bearings have been widely used in high-speed turbines, compressors, and high-speed motorized spindle, flywheel energy storage system, and so on. At present, the three-pole magnetic bearing driven by three-phase power inverter is a common magnetic bearing. The three-phase power inverter has the advantages of mature technology and low price, which can greatly reduce the cost of the magnetic bearing. However, the three-pole magnetic bearing has the disadvantage of low bearing capacity, low space utilization and so on.
Therefore, a six-pole radial-axial active magnetic bearing (AMB) driven by an inverter is proposed, which axial biased flux and radial biased flux are both provided by the axial biased current. Firstly, the configuration, working principle and mathematical model of the six-pole radial-axial AMB are analyzed in detail. Secondly, the working principle of the six pole radial-axial AMB is verified by finite element analysis (FEA). Thirdly, the advantages and disadvantages of linear active disturbance rejection control (LADRC) and nonlinear active disturbance rejection control (NLADRC) are analyzed, and decoupling control of six-pole radial-axial active magnetic bearings by the linear/nonlinear active disturbance rejection switching control (SADRC). When the disturbance is large or the output state estimation error is large, the LADRC is used in the system, otherwise, the NLADRC is used in the system. Finally, related experiments based on the prototype are also conducted to verify the superior performance of the SADRC. The results show that the decoupling control effect of the SADRC is better than that of LADRC and NLADRC.
Comparing with traditional bearings, magnetic bearings have the advantages of no friction, no lubrication, high speed, high precision, long life, etc.. Therefore, magnetic bearings have broad application prospects in the fields of flywheel energy storage, wind-generated electricity, high-speed machine tool and so on. The six-pole hybrid magnetic bearing is driven by a three-phase inverter, thus the volume of the magnetic bearing is reduced and the overall cost of the magnetic bearing is cut. However, there are still many shortcomings in the hybrid magnetic bearing for the practical application. For example, the iron core material is utilized inexpediently, and the coil turn number is designed unreasonably, which affects the current stiffness of magnetic bearings.
In order to overcome the problems above, the optimal design of six-pole hybrid magnetic bearings is proposed in this paper. Firstly, on the basis of introducing the structure and working principle of six-pole hybrid magnetic bearings, the mathematical models of radial suspension forces of six-pole magnetic bearings are derived. Secondly, according to the requirements of the test prototype, the main parameters (such as air gap length, stator pole shoe thickness, stator magnetic pole area and coil turn number) of the six-pole magnetic bearing are designed and optimized, and the radial suspension forces are analyzed by using the finite element software. Finally, the static floating and disturbance experiments of the six-pole hybrid magnetic bearing are carried out. The theoretical research and experiments show that the magnetic circuit structure of the six-pole hybrid magnetic bearing is reasonable, and the static suspension force and the maximum suspension force can both meet the performance requirements.
It is crucial to calculate the levitation force in the designation of superconducting magnetic bearing (SMB). Due to the external disturbances or the time-variable load, it is necessary to study the dynamic levitation behavior in order to ensure the stable levitation of SMB. In this paper, we investigate the dynamic behaviors of the axial levitation force for the radial-type SMB. By adopting the Power-law E-J relation of the superconductor, the simplified H-formulation finite element model of the radial-type SMB is established to calculate the axial levitation force in the PDE module of software COMSOL. The experimental measurements of the levitation force are carried out in both the field cooling and zero-field cooling condition so as to validate the model. Then, the dynamic model is built with the aid of ODE module, which can describe the dynamic response of the PM rotor along the z-axis easily. The dynamic behaviors of the radial-type SMB are discussed when the PM rotor suffer from the external disturbances including the axial constant load with different initial velocity and the sinusoidal time-variable load. The study is useful to predict the influences of the external disturbances on the dynamic levitation behaviors in the practical applications of the radial-type SMB.
We are studying magnetic bearings combining multiple cubic superconducting bulks. Calculate the placement by optimum calculation so that the fluctuation of the trapped magnetic flux distribution is minimized according to the cubic bulk arrangement and decide the optimum arrangement for the magnetic bearing.
In this experiment, eight magnetic cubic blocks were arranged in a square to construct a magnetic bearing surface. A verification experiment was carried out with a model in which the rotating floating body as a permanent magnet was sandwiched between upper and lower bearing surfaces, with the magnetic bearing surface as one side.
This research report summarizes the influence on rotational test etc. based on the index of optimal placement.
Recently, magnetic levitation techniques have been developed for various fields such as energy storage flywheels and magnetically levitated vehicles. Thus, there are many reports about levitation techniques using high critical temperature (Tc) superconducting magnetic bearings (SMBs) composed of superconducting (SC) bulk and permanent magnet (PM). In this paper, new SMBs composed of SC bulk, SC coil and PM are discussed.
SC BEARING AND EXPERIMENTAL METHOD
In this paper, we propose a SC bearing composed of SC bulk, SC coil and PM. The levitation is performed using pinning force between SC bulk and PM. A neodymium (NdFeB) PM with a diameter of 27 mm and a thickness of 3.4 mm is used. The SC bulk (Dy1Ba2Cu3OX, Jc=3 ×108 A/m2 at 77 K and 1.0 T) measures 44 mm in diameter and 7.5 mm in thickness. The yttrium type SC coil (Ic=150A) measures 35mm in inner diameter, 38mm in outer diameter and 5mm in thickness with four turns. The SC bulk and the SC coil are field-cooled using liquid nitrogen.
EXPERIMENTAL RESULTS AND DISCUSSIONS
In the experiments, the SC bearing with SC coil is compared with the SC bearing without SC coil. The distance between SC bulk and PM is changed at 7mm, 8mm and 9mm. At each distance, impulse responses for the SC bearing without SC coil are performed. The result shows that the displacement amplitude for each distance decreases gradually as the time increases.
Impulse responses for the SC bearing with SC coil are performed. The displacement amplitude for each distance decreases rapidly. It is found that the damping for the SC bearing with SC coil is larger than that for the SC bearing without coil.
The SC coil is effective on the damping for the SC bearings. From the experimental results, both stiffness and damping coefficient for the SC bearing with SC coil are improved compared with the SC bearing without SC coil.
Studies on coaxial magnetic gears (CMG) have been actively conducted. CMGs can replace mechanical gears as they can perform noncontact power transfer, thereby minimizing loss and damage from friction.
However, the permanent magnet eddy current loss among the electromagnetic field loss of the magnetic gear is pointed out as the biggest problem in the high speed drive. Among other losses, iron loss can be greatly reduced by stacking electrical steel sheets, while permanent magnets have many technical problems to be stacked like electric steel sheets. The biggest cause of permanent magnet eddy current loss is electrical conductivity of rare earth magnets. In this paper, we applied the ferrite permanent magnet and the NdFeB permanent magnet to the magnetic gears in order to compare the characteristics of the magnetic gear according to the electric conductivity of the permanent magnet. Ferrite and NdFeB were used to design magnetic gears that exhibited the same torque, and then the characteristics of each magnetic gear at the same drive speed were compared. Since the ferrite is not electrically conductive, the ferrite-applied magnetic gear does not exhibit permanent magnet eddy current loss. However, we observed mechanical and electric problems due to its size. Also, the efficiency of the two magnetic gears was reversed on a specific speed.
In this paper, we provide information on mechanical and electromagnetic losses of magnetic gears, and it is possible to examine suitable application fields of magnetic gears according to permanent magnet materials. Each model was compared with the mechanical and electromagnetic characteristics of the two models through FEM design and prototype production. Specific design and experiment contents are disclosed through the full paper.
Acknowledgement: This research was supported by Korea Electric Power Corporation. (Grant number: R19XO01-34)
A HTS linear synchronous motor (LSM) that uses YBCO-coated conductor as the secondary excitation system and double layer concentrated windings as the primary was recently demonstrated in our laboratory. Two YBCO-coated conductor racetrack coils were wound on a fiberglass frame via the epoxy impregnation technique and injected dc currents to provide a high stationary magnetic field for LSM. Thirty-nine copper racetrack coils manufactured modularly were assemblled into double layer concentrated winding to act as the primary of a 15-m long test line. Prior to assembling the whole system, we tested the current versus voltage curve of the connected YBCO coils with a four-proble setup, and the short circuit test and steady state test were processed on home-made electromagnetic force testing system to investagte the starting characteristics and back electromotive force of HTS LSM. Using a frequency converter to regulate the three-phase currents of stator, the secondary system could take a back-and-forth movement along the stator at electromagnetic clearances of ~50 mm. Dynamic measurements were carried out to observe the transient thrust and thrust fluctuation against the input current of the YBCO coils, clearance as well as the amplitude and frequency of the primary current. Moreover, we also established a finite-element model using which the transient thrust and thrust fluctuation at various speeds (up to 613 km/h) of the prototype were computed and found to be comparable with the measured dataset. This work has advanced the study of YBCO-coated conductor linear motor from the static measurements to the dynamic operation, taking a step forward to the application of such promising linear traction system of EDS train.
Recently non-insulation (NI) HTS coils using coated conductors (CCs) draw extensive attention because of their self-protecting capability. Closed-loop coils are also promising in the application of electrodynamic-suspension (EDS) Maglev train with superconducting magnets since the heat load of the on-board magnet can be significantly reduced, typically >50%. Therefore, closed-loop NI-HTS coils are proposed to be employed in our prototype EDS-Maglev system.
Several key points on the coil design/optimization are considered and supposed to be presented: (1) Topological structure. Each on-board magnet has at least one pair of N-S poles. Each pole is composed of several, typically 4-8, double-pancake coils with a race-track shape. The optimization target is to use the least number of joints between and inside these coils and poles, especially bridge-type joints which usually are with high resistances. (2) Turn-to-turn contact resistance, which is mainly determined by the material of stabilizer layer and the contact pressure. These two factors are ex-situ studied experimentally with short CC tapes and verified in a practical coil; (3) The normal-state resistance of the PCS, which is determined by its operation temperature, the tape length and also by the material of stabilizer layer. Actually this factor has a similar influence on the charging speed as the turn-to-turn contact resistance. Therefore “how large it should be” is analyzed in the same circuit model. And then we achieve it according to our experimental study on temperature and material of stabilizer layer. (4) The decay rate. Our target is less than 1%/day. This is important for the daily operation of a real maglev train and mainly determined by the joint resistance as well as the topological structure (inductance, joint number and type), if not considering the influence of external AC magnetic field. (5) The bobbin structure. With an optimized structure, the turn-to-turn contact pressure can be controlled with an acceptable precision. Also the coils are hoped to be bonded to the bobbin with practical insulation and thermal conductance simultaneously.
Recently, we investigated High Temperature Superconductor (HTS)-ElectroMagnet (EM) interaction characteristics with experiments and computer simulations. In this investigation, new type of EMs with different geometries were designed and built for comparative analysis. We also set up a three dimensional force measurement system to evaluate the levitation and guidance forces with different EM geometries and configurations. The magnetic field distribution at different EM configurations and different excitation conditions was simulated with a commercial FEA software. The simulation results were verified by the experimental ones. The goal of this study is to explore the practical applications of a HTS-EM levitation transportation system. In principle, EM rails are able to adopt a Segmented Instant Excitation (SIE) mode to realize a minimum levitation power loss as well as sufficient levitation and guidance forces for the train. In this presentation, we report the details of this study and confirm the feasibility of a HTS-EM levitation transportation system.
In this paper we present a quadratic approximation method for the limit value of magnetic stiffness in a high temperature superconducting levitation system. The levitation configuration discussed is that of a cylindrical permanent magnet (PM) placed above a coaxial high temperature superconductor (HTS). The magnetic levitation force between the PM and the HTS is obtained on the basis of Kim’s critical model and Ampère circulation theorem. The central issue of magnetic stiffness associated with the hysteresis of levitation force is discussed. To a given levitation gap between the PM and the HTS, the approximate values of magnetic stiffness are obtained corresponding to different displacement increments from 0.1mm to 3mm. In the first approximation the least squares method is used to curve fitting force-displacement table. Secondly, the limit value of magnetic stiffness is gained at the zero displacement increment in the polynomial fitting curve of these approximate values. The results show that the limit value of magnetic stiffness is dependent on the levitation gap and the movement direction of the levitated object, which is believed to be responsible for the penetration history of shielding currents distribution in HTS and magnetic field gradients. Some displacement increments, such as 0.5mm or 1mm, are usually used in superconducting levitation experiments. The difference between experimental data of magnetic stiffness and the limit ones is also investigated.
A new type of electromagnetic guideway for high temperature superconducting maglev was proposed in this paper. The guideway unit is a fan shaped electromagnet that can generate magnetic field for providing enough levitation and guidance forces. A simple multi-object optimization method was used in order to determine the relative optimal geometrical parameters, so that the electromagnet can have a relative higher energy transfer efficiency. The design model was built in COMSOL Multiphysics and an experimental prototype was made to verify the design feasibility. The levitation and guidance forces were measured by a high precision force-measuring platform. The levitation performances of guideway unit along with different variables were analyzed and compared with the simulation results. Afterward, a simple maglev system was built to test the driving stability in the guideway direction. This system consist an electromagnetic guideway and a train body dewar. The guideway can be assembled in two forms: single track and double track. The comparison between the both forms was discussed and analyzed.
Superconducting permanent magnet such as bulk, stack tapes and ring-shape magnet has been proved to be a potential candidate for superconducting motors. In real applications, especially the superconducting electrodynamic-suspension(EDS) levitation system, vibrations in all directions during high speed operation are unavoidable. This paper focuses on the demagnetization process of superconducting permanent magnets under different kind of vibrations. Firstly, test samples, including stack tape, ring-shape magnet, are fabricated by laser cutting and epoxy packaging technique. Modification of commercial vibration platform is done to represent the vibration condition of EDS levitation system. The central magnetic field is chosen as the key parameter to evaluate the demagnetization performance of test samples. Both experimental and numerical methods are used to explore the demagnetization mechanism during vibration. Results obtained in this paper will be crucial for the design of excitation system as well as the cooling system in the EDS levitation system.
The “Divertor Tokamak Test” is an experimental machine currently under construction in Italy, at the Frascati research center of ENEA. The main goal of this project is to explore various divertor solutions for defining the best way to manage power and particles exhaust, in view of the realization of the EU-DEMO machine. The DTT magnet system is fully superconducting and it is based on NbTi and Nb3Sn Cable-in-Conduit Conductors. It consists of 18 Toroidal Field (TF) coils plus 6 Poloidal Field (PF) and 6 Central Solenoid (CS) stacked module coils, all independently fed. The magnet system design was already presented in its previous versions, but as analyses and technical choices have further progressed, in this work the up-to-date design solutions are presented and discussed. An overview of the technical needs leading to the present conceptual design is given, having particular care of discussing the aspects that mainly impact on the procurement and construction phases which are on-going.
The “Divertor Tokamak Test” is an experimental machine currently under construction in Italy, at the Frascati research center of ENEA. The main goal of this project is to explore various divertor solutions for defining the best way to manage power and particles exhaust, in view of the realization of the EU-DEMO machine. The DTT machine is relatively compact, and the magnet system works at high fields, this combination being quite challenging from the mechanical point of view. In particular, the loads acting on the Inner and Outer Inter-coil structures, on the Poloidal Field coils supports and on the gravity supports of the whole magnet system, are quite demanding. An overview of the design solutions adopted for all the inter-coils structures and supports is presented in this work, focusing particularly on their industrial feasibility.
Research and engineering design work of superconducting magnet system of CFETR (China Fusion Engineering Test Reactor) is in progress and supported by China government. The major radius and minor radius of CFETR is designed as 7.2 m and 2.2 m, respectively.
For one hands, such big size will bring big challenges to the magnet system because it will be difficult to get high enough volt seconds and magnetic field in plasma center. For another hands, high voltage seconds generated by central solenoid coils and high magnetic field provided by toroidal field coils are required to get high performance plasma with current of 10-14 MA. Therefore, to generate high enough magnetic field of 6.5 T field at R= 7.2m, the peak field at TF coils will reach to 14.3 T. The big challenge will be the enough stability margin and enough temperature margin of the high-Jc NB3Sn CIC (cable-in conduit) conductor.
Besides, China government support new funding ($600 Million) to design and manufacture a TF prototype coil since from 2019. Although the engineering design work goes smoothly in now stage, it is still big challenge to get high enough stability margin of the TF coil under the condition of peak field of 14.3 T. Besides, the peak stress of the TF coil will be about 700MPa. The new design of high Jc Nb3Sn conductor and structure of TF prototype coil will be detailed introduced.
In addition, the eight CS coils with HTS insert coil which can reach to peak filed of 17 T are investigated which can provide a high voltage second of 480V•s in the plasma region. The poloidal field coils are far away from plasma, so the big overturning moment generated by PF coils is a big challenge for snowflake plasma equilibrium configuration. It hopes that the presentation can not only be good reference for other DEMO projects, but also a good bridge for the broad international cooperation for fusion research work.
Design of CFETR TF Prototype Coil
Wu Yu, Shi Yi, Lu kun, Liu Xiaogang, Qin jinggang, Liu Xufeng, Hao Qiangwang, Li Junjun, Hu Yanlan, Xiao Yezhen, Shen Guang, Han Houxiang, Wei Jin, Fang Chao, Yin Dapeng, Li Jiangang.
China Fusion Engineering Test Reactor （hereinafter referred to as “CFETR”）, based on ITER technology and bridged between ITER and DEMO, has been supported by China government to start technologies R&D and engineering design. Superconducting coil is treated as important device for fusion reactor. The field of CFETR at plasma core is 6.5T, maximum field of TF coil is about 14.5T. TF coil is winded by high-performance Nb3Sn wires and CICC conductors. Coil weight is about 550T with height about 22m and width about 15m. Design and manufacturing technologies of TF coil need to be developed and validated. TF coil design consists of mechanical & electro-magnetic design and analysis, conductor design and analysis, coil AC loss analysis, thermal-hydraulic analysis and coil cooling, quench detection and coil protection, coil winding, case manufacture, and coil assembling. Engineering design has been carried out at ASIPP. Duration for design and manufacture will be 5 years.
Key words: CFETR, TF coil, CICC.
In DEMO fusion reactor the confinement of the plasma is achieved through the magnetic field generated by superconducting coils. The DEMO magnet system includes 16 Toroidal Field (TF) coils, 6 Poloidal Field (PF) coils and 5 modules for the Central Solenoid (CS) magnet. For the TF coils, four winding pack options are presented: one solution reproduces the ITER concept with radial plates, whereas the other three designs explore different winding approaches (pancakes vs. layers) without radial plates, and manufacturing techniques (react & wind vs. wind & react Nb3Sn), with the aim of improving the effectiveness of the conductors and propose cost effective solutions for the magnet system.
For the CS modules two designs have been proposed: the first is based on a pancake wound W&R Nb3Sn conductor, like in ITER. The second concept is based on a hybrid design with layer-wound sub-coils using HTS conductors in the high field section. Compared to the first option, the hybrid configuration allows keeping the same flux with reduced size or increasing the flux keeping the same size. Two different designs are also presented for the PF coils, following the concept that one solution is similar to the ITER one, whereas the second explore alternative concepts, such as the design of PF 1 and PF6 wound with Nb3Sn Cable-in-Conduit Conductors.
In order to validate the designs, thermal-hydraulic and mechanical analyses are carried out for all WPs, as well as experimental tests on full size and sub-size prototypes. Results are encouraging, with some critical aspects that shall be solved in future designs.
Finally, preliminary studies of the auxiliary systems (fast discharge units, feeders and cryogenic system), aiming to optimize the power consumption and the space allocation, are presented.
ReBCO-CORC wires, long dreamed about practical high current density thin conductors, are now reality and feature diameters in the 2 to 4 mm range. They are multi-purpose, but at CERN specifically developed for application in high-field magnets. CERN is interested to further aid the development of such conductors for possible implementation in the next generation of accelerator magnets and high-field insert coils. Therefore, a series of demonstrator coils are planned to develop and mature the technology. Here we report on two CORC based demonstrator coils currently in development.
The first is a solenoid to be used either standalone or as an insert. It aims to demonstrate the high performance of CORC wires in magnets, as well as to find critical parameters in the design and handling of both wire and magnet. The solenoid comprises two layers of 3.3 mm diameter CORC wire of each 17 turns wound on a former of 60 mm diameter. The 53 µH coil, with critical current of 9.7 kA in self-field and 4.2 K, can generate 4.5 T central field. As insert in a background of 10 T, it yields an additional 2.5 T central field. Test results at 77 K in self-field are reported followed by a test at 4.5 K during summer of 2019.
The second demonstrator magnet is a compact multi-layer racetrack coil of 190 mm long, 54 mm wide and with 20 mm head radius. It is wound with CORC wire embedding cutting-edge ReBCO tape comprising 25 µm substrate thickness. The reduction of substrate thickness from 30 to 25 µm yields a thinner and more flexible CORC wire, which is a hard requirement for this magnet. The manufacturing technology of this unique coil is reported along with its test results. More exciting new developments can be expected in the near future.
Advanced Conductor Technologies has been developing high-temperature superconducting Conductor on Round Core (CORC®) cables and wires wound from ReBa2Cu3O7-x coated conductors for use in high-field magnets. Initial development is aimed at CORC® cable performance goals of operating currents exceeding 5-10 kA and engineering current densities (Je) of over 600 A/mm2 at 4.2 K in a background field of 20 T. Thinner CORC® wires result in an even more flexible magnet conductor, bendable to radii of less than 25 mm, while operating at comparable currents and current densities as CORC® cables.
CORC® cables and wires have matured into practical magnet conductors with their initial performance goals close to being met. The next step in their development is underway, which is their incorporation into high-field demonstration magnets. Here we outline the latest results of high-field insert magnet development using CORC® cables and wires. Several magnet programs will be discussed, including those focused on the development of high-field solenoids and accelerator magnet inserts for canted-cosine theta (CCT) and Common Coil magnets to reach a total field of 20 T when operating the CORC® insert within a low-temperature superconducting outsert magnet. Progress in each of these magnet programs will be outlined. We will focus on the design and performance test of a CORC® insert solenoid that is being developed to operate in a 14 T background field, while generating a field of 2 – 3 T at an operating current of 5 kA, resulting in a total field of 16 – 17 T. The 80 mm bore CORC® insert magnet leaves room for an additional CORC® insert that would increase the total field to 20 T.
A pancake coil was prepared with a length of 15-strand ReBCO 2G Roebel cable and studied in detail at different operating temperatures between 4.2K and 77K, cooled with either liquid cryogens or flowing liquid helium gas. The coil was impregnated with epoxy and the transient cooling was predominantly by conduction from current contacts. Critical current measurements were carried out with a transport current up to 1kA in an external axial field up to 10T. Quench measurements were carried out foloowing point-like disturbances initiated by a localised miniature heater embedded inside the coil. The different heat dissipation at the current contacts were dynamically compensated with collocated axillary heaters to ensure the isothermal condition of the coil for the successive quench episodes. Minimum quench energy (MQE) were obtained at different temperatures, fields and current load relative to the critical current. The present work is a substantive follow up of previous studies at 77K in liquid nitrogen where it has been established that the coil retained the critical current of the superconducting strand/cable and its quench behaviour was unaffected by the lateral cooling by the cryogen.
The National High Magnetic Field Laboratory (NHMFL) is in the fortunate situation to put substantial effort into advancing all three high field magnet relevant types of high temperature superconductor (HTS) technologies, REBCO, Bi-2223, and Bi-2212, as a part of its commitment to develop all-superconducting high field magnets. Here we are presenting our work on Bi-2212 coil technology, which experienced a strong boost after significant progress was made in the heat-treatment process of the wire . Bi-2212 wire has distinctive advantages compared with the other HTS conductors, as it can be made as round or aspected wire, it can be twisted, is multifilament, it can be easily cabled, it has low magnetization, and has isotropic electromagnetic properties. Operating conditions at highest fields, however, are extremely demanding on the coil mechanics and have yet to be fully explored in in HTS coils in general. Several test coils have been built and tested to evaluate various coil reinforcement schemes. In a collaboration with Lawrence Berkeley National Laboratory (LBNL), we heat treated several of Bi-2212 racetrack and CCT coils. This presentation will provide an overview and update of our on-going Bi-2212 coil R&D effort.
Acknowledgement: This work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1644779 and DMR-1839796, and the State of Florida, and is amplified by the U.S. Magnet Development Program (MDP).
 D. C. Larbalestier et al., “Isotropic round-wire multifilament cuprate superconductor for generation of magnetic fields above 30 T,” Nature Materials volume 13, pages 375–381 (2014)
Two subscale coils of Bi-2212 wire have been made and tested in a DOE STTR collaboration between Cryomagnetics and the Applied Superconductivity Center at Florida State University. The coils are used to test the feasibility of using small-diameter wire in a solenoid configuration where single strand wire performance is crucial. If successful, the implementation of small-diameter wire into high field Bi-2212 HTS solenoids will allow for high J_E operation with moderate currents, making feasible the use of more modest control equipment, power supplies, and current leads. Furthermore, lower operating currents may allow series-connected design configurations with LTS background magnets, allowing for better, simpler, and more effective quench protection methods. A 25-Tesla magnet design, consisting of an 8-Tesla Bi-2212 coil with a 17-Tesla LTS coil, is underway at Cryomagnetics, and considerations of critical current, hoop stress, and quench protection will all be fully addressed.
Superconducting Nb3Sn accelerator magnet technology start to reach maturity and the 11 T dipole magnets based on that technology are prepared to be installed in the LHC. Performing detailed diagnostics on Nb3Sn model magnets has been vital for giving feedback on the design and fabrication of the magnets and for the conductor performance in that particular configuration. In the last few years, tens of Nb3Sn magnets have been tested in the SM18 test facility at CERN, including flat racetrack models, cosƟ dipoles, cosƟ quadrupoles, and block-coil dipoles. The large and different type of instrumentation of the model magnets allowed precise measurements of superconducting-normal transition, voltage measurements on quenching segments, mechanical transients, vibration spectra measurement with different methods. Diagnostics are completed by using quench patterns following ramp rate studies, temperature dependencies, and current cycles.
The methods to interpret and conclude on the performance of relatively large size magnets, with a relatively small amount of instrumentation are discussed using the instrumentation and diagnostic tools.
Fluctuation of critical current along the length of conductor is commonly observed in the 2nd generation of high-temperature superconductor tapes. In difference to low-temperature wires it seems that an elimination of this adverse feature is not a simple task. Then it would be sensible to incorporate its description in the standard tape characterization. We report on our effort to develop the procedure allowing to predict for such a tape the “overall critical current” at which the transition to resistive state takes place.
We started by analyzing the case of statistical Ic fluctuations defined by Gaussian and Weibull distributions. It was found that from the parameters describing these distributions (the mean and standard deviation in case of Gaussian distribution, the scale and the shape in case of Weibull distribution) one can nicely compute the current-voltage curve expected for the whole length of tape used in a superconducting device. This allows to establish the overall critical current even when the contribution to the total voltage comes only from a small portions of conductor. Main problem in application of this approach is that the data of industrially produced tapes usually do not fit perfectly any of these two distributions and then the predictions could fail. Significant difference is caused by weak points with Ic dropping outside the low end of statistical distribution. At currents well below the typical Ic value found in short sample testing, such locations are converted to hot spots with dissipation causing a catastrophic increase of temperature leading to a local damage.
Distinguishing between “statistical” and “unstatistical” Ic fluctuations is necessary because these two cases lead to very different behavior. For the tapes with fluctuations reliably described by a statistical model it makes sense to predict the overall critical current. In case of the tape with weak points the overall voltage is not representative and the dissipation at the weakest point defines the limitation for the current that could pass the whole device.
The use of silicon carbide varistors for quench protection of superconducting magnets has previously been reported , where the varistor unit is external to the magnet in a room temperature environment. Here it has been demonstrated that, in comparison to similar linear resistors, the varistor has beneficial effects in both limiting the magnitude of clamping voltages as well as limiting the temperature of hotspots in superconducting elements, through an accelerated discharge time.
This piece of work now considers how silicon carbide varistors may be applied to superconducting magnets, whereby the dump resistor is located inside the cryogenic system. Typical electrical characterises of the varistors at room and cryogenic conditions are presented and the benefits of using silicon carbide varistors as a replacement to traditional metallic resistors, commonly used in these applications, is then discussed. These benefits include a device with a higher failure energy (for a comparable footprint size) as well as having a preferred short circuit failure mode.
Winding REBCO conductors on round cores (CORC) has innovatively transformed REBCO thin tapes to round cables which allow high temperature superconductor to meet low-inductance requirement and offer symmetrical electromagnetic and mechanical properties for large-scale high field accelerator magnets. HTS conductors, however, are known for slow quench propagation and large minimum quench energy, and very few quench studies have been conducted on the CORC cables. Its dynamic current sharing is largely unknown due to complex layer structure and layer-to-layer contacts. We plan to perform quench simulations of the CORC cables to achieve better understanding about transient current sharing during quenching. H formulation and T-phi formulation will be employed to model critical state magnetization in layers and A-V formulations will be used to characterize layer-to-layer current sharing behaviors and resulted Joule losses. Heaters will be imbedded into various locations inside the cable volume or on the cable outside surface. Current redistribution and normal zone propagation mechanism will be studied in addition to voltage and temperature signals. These studies will help find effective quench detection and protection for the HTS-cable based accelerator magnets.
The authors would like to thank K. Amm, R. Gupta, D. Hazelton, D. van der Laan, J. Weiss for helpful discussions and general support.
Hybrid electric aircraft requires high power density for power transmission, which makes the ReBCO conductor-on-round-core (CORC) cable a powerful candidate for the transmission line used in the hybrid-electric aircraft. However, quenching remains one of the biggest challenges in the development of CORC cable, for it can significantly influence the thermal stability and safety of the CORC cable. The quench behaviour of CORC cable is quite different with single tapes due to the influence of terminal joint resistance and inductance, which has to be elucidated in detail.
This work presents the results of a numerical and experimental investigation on the quench behaviours of two typical CORC cable models with multi-layer structure. Each layer of the first cable (Cable A) was consisted of only one ReBCO tape and was wound into 3 layers, while the second cable (Cable B) was a two-layer CORC cable with three ReBCO tapes in each layer. A heater was induced on the central area of the cables to generate pulses. Hotspot induced quenches were studied by calculating the current redistribution among tapes, voltage of each tape, minimum quench energy (MQE) and normal zone propagation. Influences of the inductances and terminal joint resistances on the thermal stabilities were analysed and discussed. Quench detection and protection measures were proposed.
Numerous high current conductor designs based on High Temperature Superconducting (HTS) materials for fusion magnets have been recently proposed worldwide.
One of the most promising is the Twisted-Slotted-Core Cable-in-Conduit-Conductor comprised of an aluminum core with twisted slots in which REBCO tapes are stacked and with an external metal jacket. The coolant flows in a central hole and in lateral gaps between the stacks and the slots.
A thermal-hydraulic/electric 1D multi-region conductor model is under development to properly address the quench propagation in HTS conductors accounting for their design peculiarities.
Indeed, quench propagation in HTS materials is a well-known issue due to the low normal zone propagation velocity compared to low temperature superconductors (LTS). Since no quench tests have been carried out on HTS conductors, reliable thermal, hydraulic and electric modeling of quench propagation in such conductors is of paramount importance to assess their performance.
The direct applicability of well-known modeling tools for quench analysis in LTS conductors is questionable, due to very different materials, e.g. low and anisotropic thermal conductivity of the HTS tapes with respect to isotropic high thermal conductivity of LTS strands, as well as the different geometry, e.g. a bulky core with few twisted HTS stack compared to the ~ 1000 (<~1 mm outer diameter) LTS strands, employed in the HTS conductor design.
In order to properly calibrate the electric model free parameters, e.g., the electrical resistances between the HTS stacks and the slotted core are measured at 77 K.
After the calibration, the model is validated against electrical tests carried out on the HTS conductor equipped with superconductive stacks.
Finally, the 1D multi-region model is applied to the analysis of the quench propagation in the HTS conductor, accounting for the coolant flow in the lateral gaps and in the central hole as well as for the heat conduction in the solids and the current distribution in the current-carrying elements.
Stacks of high temperature superconducting (HTS) tapes magnetized by pulsed fields have been demonstrated a way for the development of the HTS magnet capable of trapping high field. A novel structure of the flux pump was proposed to magnetize the HTS magnet stacks of RE (RE= rare earth) Ba-Cu-O annular plates in this paper. Prototypes of the flux pump constructed of two types of the solenoidal coil with or without the iron core and pulsed triangular waveform current source were tested in the HTS magnet excitation system at 77 K (LN2 bath). The experiment and simulation analysis of the HTS magnet magnetized by two different structures of the flux pump was reported. There is good qualitative agreement between simulation and experiment. It can be noted that the induced magnetic field of the HTS magnet excited by flux pump with iron core in comparison to flux pump without iron core has considerable efficiency of generating high magnetic field.
We have shown that a persistent current can be induced in HTS coils with the form of double pancakes or single solenoids by the technique of joint-less winding with 2G REBCO tapes. However, the inevitable gap located at the center of the joint-less coil caused very poor magnetic field homogeneity, which was shown by the magnetic field mapping from the previous experimental work. In this paper, to improve the performance of the coil, we proposed another HTS coil wound by the same joint-less technology but arranged differently. A conventional joint-less coil usually has two coil parts arranged coaxially, but the proposed one will have two coil parts arranged concentrically. By this arrangement, we could improve the magnetic field homogeneity by removing the unfavorable gap near the magnet center. We tried to induce the persistent current in the fabricated coil system in the operating temperature of 20 K reached by the conducting cooling system with a GM cryocooler. After maintaining the persistent current mode for 15 hours, we carried out the magnetic field mapping to analyze the harmonics of the central field under the 10-mm DSV. The analyses data will be used for the future design work of the passive shimming.
The critical current degradation of YBCO coils have been observed in a large number of experiments, which have been explained that the thermal expansion mismatch between the YBCO tapes and resins lead to damage of the conductor. The no-insulation coil can avoid the performance degradation, but it has a poorer mechanical strength without any reinforcement. A new impregnation method by ice was introduced to the YBCO coils. This method can perfectly solve the critical current degradation of YBCO coils, and the coils also have higher mechanical strength and higher thermal stability. The impregnation process is easy and the YBCO tapes can be recycled.
The 25 T all superconducting magnet designed as a combination of 14 T low temperature superconductor (LTS) background field magnet and 11 T YBCO insert coil has been developed at Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The electromechanical properties of YBCO coated conductors and magnetic field intensity and orientation dependence of the critical current were investigated to support the design of the insert coil. The insert coil with No-Insulation (NI) winding technique has the inner and outer diameters of 16 mm and 56 mm, respectively, and consists of ten single pancakes wound with about 240 m of YBCO conductors produced by Shanghai Superconducting Technologies Co., Ltd (SSTC). The preliminary tests were carried out at 77 K and 4.2 K in self-field. The results show that the performance of insert coil did not degrade during the manufacturing process, and it can generate a maximum central field of 15.6 T at 4.2 K, self-field. The YBCO insert coil will be tested in the 14 T LTS background field magnet in the next step to evaluate the performance in the ultrahigh magnetic fields. The latest design, construction, and preliminary test results of the YBCO insert coil will be fully introduced in this paper.
The advent of REBCO tape has led to the development of tape-wound coils by a number of organizations. The 32 T magnet at the NHMFL uses two coils made of double-pancakes of REBCO installed within five LTS coils. It reached full field in December 2017. This is the highest field produced by an all-superconducting magnet to date. Since the 1970s it has been known that screening currents exist in tape-wound magnets which impact field distribution, helium consumption and stress. In recent years several groups have been computing screening currents and ac losses in REBCO tape in a variety of applications. However, there has been little published about coils of this size, particularly the stress state. This problem is very challenging due to the need to analyze 20,000 REBCO turns which are not bonded together. The T-A formulation of Maxwell’s equations employing a homogenization technique enables efficient estimation of the current distribution while structural calculations employing contact element allows estimation of stresses. Computational results are compared with test results.
In this article, we presented a design and experimental results of a Bi2223 superconducting magnet cooling by a free-piston stirling cryocooler. Depending on mechanics, thermal and electromagnetic multi-field couple analyzes results, we winding the coils with the type pancake type. We optimized the magnetic field by iron flange at the end of coils to avoid the vertical field effect of the Bi2223. And the coils are suspended from the room temperature vacuum vessel by six G10 suspension links. It is cooling by a stirling cryocooler with the cooling power 14W@77k,Now we finished the magnet and test it with the highest magnetic field 1T with the temperature 62K with PCS in it, the test results will be reported.
Compared to low temperature superconducting materials (LTS), Bi-2212 is more promising due to excellent current-carrying capability in ultrahigh magnetic field. In order to verify the long-line performance and small-scale superconducting magnet technology, a 2 T Wind & React Bi-2212 solenoid insert coil has been designed and fabricated at Institute of Plasma Physics, Chinese Academy of Science (ASIPP). The inner and outer diameters of the insert coil are 20mm and 32mm with 50mm height respectively. The No-Insulation (NI) winding technology is used to coil manufacture. The coil were reacted under 30 bar pressure followed the heat treatment process ordered by Northwest Institute for Non-ferrous Metal Research in China (NIN). It will generate a maximum central field of 16 T in a cold bore of 70 mm background field magnet at 4.2K. This study confirmed that present performance of the Bi-2212 round wire had satisfied the required high-field condition. This effort can also provide experience for superconducting magnet further design and experiment. This paper mainly presents the design, fabrication and pre-experiment of the insert coil, including wire specifications and heat treatment R&D, coil structure, no-insulation winding test and assessment.
High temperature superconductor Bi2Sr2CaCu2O8+δ (Bi-2212) exhibits high irreversibility ﬁeld Hc2 of nearly 100 T, and high critical current density under high field with the Jc of over 6800 Amm-2 under 4.2 K, 15 T. Therefore, it shows great potential in the fabrication of low temperature, high field magnet. In our institute, Bi-2212 multifilamentary round wires with length over 200 m have been successfully prepared. With our optimized high pressure sintering technique, the current capacity of obtained wires has been obviously improved. The maximum engineering critical current density of 1300 A/mm2 has been obtained under 4.2 K, 5 T and over 800A/mm2 at 12T. With these wires, we have developed a Bi-2212 high temperature superconducting magnet through the winding and reacting method. The magnet inner diameter and outer diameter are 18mm and 45 mm, respectively, and its height is 80mm. It was made from 1.0mm diameter Bi-2212 wire with the length of 110 m. The wire was insulated with TiO2 paste. After the heat treatment at 5 MPa, the critical current of the magnet reach 340 A at 4.2 K and self field. The central field is calculated to be 5 T.
Screening currents (SC) induced by varying magnetic fields may not only affect the field quality but also cause overstressing of REBCO coated conductor coils, making it a critical issue for NMR and other high-field magnets. We present in this paper results of an experimental and analytical study, performed with small REBCO pancake coils, on SC-overstressing of REBCO coil. Because SC is presumed to increase with REBCO tape width, we have studied test coils of two widths. The terminals of each coil, φ240 mm, were joined with a resistance sufficiently low to maintain the induced current constant enough during data taking. We use a 5-T/300-mm room-temperature bore magnet to not only supply an external field, but also induce up to 1000-A current to each coil at 4.2 K. Our experiment and analysis have demonstrated, and quantified, that the greater the REBCO tape width, the severer the SC-overstressing in REBCO coil will be.
Acknowledgement: Research reported in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health under award number 5R01GM114834-13
As a novel structure of second-generation high-temperature superconducting (2G HTS) tapes, narrow-stacked HTS wire with 1 mm width was proposed to reduce AC loss. Its fabricated processes are to cut the HTS tapes into 1 mm wide ones mechanically and stack them into one wire through the soldering furnace. In our previous work, compared with the traditional 5 mm wide HTS conductor, the remarkable AC loss reduction effect by narrowing the HTS tapes has been confirmed to be about 80%. Thus, the narrow-stacked wire is suitable to help the 2G HTS electrical device overcome the energy dissipation caused by AC loss. However, the effect of different HTS tapes stacking number on AC loss is not clarified in the narrow-stacked wires yet. To meet the requirement of the practical HTS applications, we evaluate AC loss of the narrow-stacked wires with different tapes stacking structure. Moreover, an HTS coil is wound with the narrow-stacked wire composed of two HTS narrow tapes and one same wide copper tape. The related AC loss analysis is carried out for further understanding the influence of tapes stacking.
The HTS windings in magnets can provide large current excitation in a limited space. However, under high level excitation condition, especially in the case of fast adjusting process, AC loss will occur and lead to reduction of thermal stability. The H-formulation method is widely used and basically meets the requirements of AC loss calculation for thousand-turns coil group. However, for magnets with iron core, the nonlinear saturation characteristic in ferromagnetic domains makes it difficult to calculate AC loss accurately and efficiently with traditional methods. Based on H-formulation method, we provide an improved modeling process of AC loss calculation in COMSOL Multiphysics. A sample magnet is simulated with the method and the AC loss calculation results are compared with experimental measurement results. The results show that AC loss of HTS magnets with iron core can be calculated accurately and efficiently with the improved method.
CORC is one of the candidates for high magnetic field and large currents. We are interested in applying CORC to HTS power transformers that require not only large currents but also very low AC losses. We measured and calculated the magnetization losses of short straight CORC samples made of striated YBCO CC. The effect of the striation is certain for reducing the magnetization loss, but the effect is not directly dependent on the number of the striations and the applied field amplitude. For considering the effect in an HTS coil design, we defined striation effect factors from the measured data, and the factor used to revise the coil loss. To compare the patterns of the loss distributions in RACC and CORC coil, we also calculated the magnetization losses of an RACC coil. The RACC consists of 4 YBCO CC with the width of 4mm and the RACC coil had 22 turns in two layers.
Dynamic resistance refers to the emergence of a DC electrical resistance in a superconductor carrying a DC transport current that is exposed to an oscillating AC magnetic field1,2. This phenomenon arises due to the interaction between the transport current and moving fluxons in the superconductor. Quantitatively predicting the magnitude of this effect is important when designing and utilising superconducting components for power system applications, in order to appropriately manage the associated AC losses. Examples of such superconducting components include: rotor coils for high power-density motors/generators and HTS flux pumps.
Here we present 2D numerical calculations of the dynamic resistance which occurs in parallel-connected stacks of ReBCO tapes. These calculations are performed using an H-formulation finite-element model¬3. The Jc(B,θ) dependence of the tape is described by interpolating experimental data obtained across the full range of field orientation for a wide range of field amplitudes. The modelling allows investigation of parallel connected tapes in a way that is problematic experimentally due to contact resistance variability in short length stacks.
Our results indicate that the outer tapes act to shield the inner regions of the stack, with this effect becoming less pronounced as the transport current approaches the stack critical current. Current is redistributed between the tapes such that dynamic resistance is zero at applied field amplitudes less than a threshold field. Above this threshold field dynamic resistance appears simultaneously in all tapes.
1. Mikitik G P and Brandt E H 2001 Phys. Rev. B 64, 092502
2. Oomen M P, Rieger J, Leghissa M, ten Haken B and ten Kate H H J 1999 Supercond. Sci. Technol. 12, 382
3. Mark D Ainslie et al 2018 Supercond. Sci. Technol. 31, 074003
AC loss is an unavoidable problem for a conduction-cooled HTS SMES magnet during dynamic operation, which may cause a temperature raise and affect the reliable operation of the magnet. In this paper, the 3D-model calculation method of 10MJ- annular magnet is analyzed. And then, the “Dimensionality Reduction-Inversion” method based on H-equation and homogenization modeling method is proposed, which realizes the fast calculation of AC loss of annular magnet. The accuracy and error source of the method are analyzed, which provides ideas for the calculation of AC loss of 3D superconducting magnets. In order to verify the accuracy of the "Dimension Reduction-Inversion" method, we built a small-scale annular magnet experiment platform, and measured the AC loss at 77K temperature, comparing the experimental results with the simulation results.
Our research group have proposed the introduction of transposed parallel conductors which are generally used in conventional electric power machines and devices in order to realize a large current capacity, uniform current sharing and low AC loss. In previous studies, the additional AC loss due to the formation of the parallel conductors composed of two REBa2Cu3Oy (REBCO) superconducting tapes was investigated by pickup-coil method. In this study, three-strand parallel conductors were measured and compared with theoretical predictions. The objective of this study is to clarify the additional AC loss properties of three-strand parallel conductors composed of REBCO tapes and to prove the validity of the theoretical expressions via experiment.
The theoretical expressions of the AC loss assumed that the voltage-current characteristics are expressed by the n-value model. The samples of REBCO superconducting tapes were provided by Sumitomo Electric Industries, Ltd. The total thickness, width, critical current and n-value are 178 μm, 2.1 mm, 100 A and 25-30 at 77.3 K, respectively. The three insulated REBCO strands were co-wound into one-layer solenoidal coil. They were soldered at both ends. Three kinds of sample coils were prepared: non-transposed sample, once transposed sample and twice transposed sample.
The non-transposed sample was already measured and compared with the theoretical predictions. The observed AC loss roughly corresponded with the theoretical predictions. Furthermore, the current distribution of three-strand will be investigated using Rogowski coils.
This research was partially supported by the Japan Science and Technology: Advanced Low Carbon Technology Research and Development Program and the Japan Society for the Promotion of Scienve: Grant-in-Aid-for Scientific Research (JP18H03783 and JP17H06931).
AC loss is an intractable and inevitable issue on high temperature superconducting (HTS) coils and magnets. The HTS coils used in HTS applications will suffer from distorted currents when operate in malfunction. Based on this, AC loss of the double-layer racetrack coil (DRC) carrying harmonic contents in phase or out of phase has been measured with laminated silicon steel sheets (SSS) or not. To a first approximation, the experimental data agree with the simulated results and give corresponding explanations. The influence of different harmonic currents on AC loss has been analyzed and has found that the 3rd harmonic in phase increases the loss at most and reaches up to 9.3% compared to that of the fundamental waveform. Two methods are proposed to reduce AC loss of the DRC around SSS. It is significant and straightforward that the reduction ratio of AC loss can attain 20.7% and 18.0% respectively by enlarging L and d 5 mm.
Index Terms—Double racetrack coil, silicon steel sheets, distorted currents, AC loss.
We will describe the first persistent-mode medium magnetic field (400 MHz, 9.39 T) NMR magnet which uses superconducting joints between high-temperature superconductors (HTSs). As an ultimate goal, we aim to develop a high-resolution 1.3 GHz (30.5 T) NMR magnet operated in the persistent-mode . The 1.3 GHz NMR magnet requires superconducting joints between HTSs and those between an HTS and a low-temperature superconductor (LTS). Towards this goal, we have been developing persistent-mode HTS inner coils to be operated in a 400 MHz (9.39 T) NMR magnet, and here we present the first prototype of an inner coil wound with a single piece REBCO conductor . The coil and a newly developed REBCO persistent current switch (PCS) are connected with intermediate grown superconducting (iGS) joints which can transport very high currents in external magnetic fields. To evaluate the performance of the joints with an ultimately stable and homogeneous magnetic field in a real magnet system, the coil is operated in the persistent-mode, generating 0.1 T, in a 9.3 T background magnetic field of a persistent-mode LTS outer coil. A magnetic field drift rate of this 400 MHz LTS/REBCO NMR magnet is <1 ppb/h, sufficient to obtain high-resolution NMR spectra. The 1H NMR spectrum line shape gives a half height width of 1 ppb, demonstrating that the superconducting joints perfectly functions in a high-resolution NMR system. As the next development steps, we will develop a REBCO inner coil with many joints and a Bi-2223 inner coil, which coils will also be tested in the 400 MHz LTS/HTS NMR magnet in the persistent-mode.
 Maeda et al, submitted to IEEE TAS
 Yanagisawa et al, Presented at ASC2018, 4LPo1E-05
This work is supported by the JST-Mirai Program Grant Number JPMJMI17A2.
High magnetic field uniformity is important for various applications, including NMR, MRI and quantum computing. A novel scheme has been developed to significantly improve magnetic field uniformity in a good field region, defined by (Bmax-Bmin)/Bmin, to levels well below 1X10-6 limit achievable in modern NMR and MRI magnets with shimming. This novel scheme can achieve theoretical field uniformity of 1x10-11 in a good-field-region as proven by semi-analytic calculations. The proposed scheme has a main coil that generates a high- uniformity main field, correction coils and permanent magnet arrays a two-step correction procedure to successively reduce field errors. The main coil is a discretized wire-wound spherical coil with optimized winding pitch between adjacent conductors. Assuming conservative manufacturing tolerances a field uniformity of parts per million (1X10-6) is feasible without shimming ofthe main coil. The two-step correction procedure uses a novel field decomposition technique, based on 3D cylindrical multipole description of measured magnetic field along two orthogonal axes, which allows identification and systematic correction of field errors. The first correction step uses correction coils of appropriate multipole order and with high field uniformity to correct the main field error by one or two orders of magnitude. Persistent mode superconducting magnets are needed for the main coil and correction coils to achieve sufficient temporal stability. In the second step further improvements in field uniformity are achieved using permanent magnet arrays that constitute crude Halbach arrays of given multipole order. State-of-the-art NMR field mappers with accuracy of 1X10-9 can be used for shimming of magnets with flux densities in the Tesla range. Additionally, another variation of this novel scheme is presented that enables shimming of parts per billion with peak field levels of mTesla and below.
A portable nuclear magnetic resonance (NMR) superconducting magnet with conduction-cooled cryostat system was under development with central field strength 7 T. The designed diameter of spherical volume (DSV) of the magnet is 0.05 m and the peak-peak homogeneity is 8 ppm. After shimming, the field homogeneity will be improved to 0.1 ppm over a DSV 0.01 m. The magnet is actively-shielded with a 5 Gauss line 0.65 m at the longitudinal direction and 0.40 m at the radial direction. The magnet coils have a diameter 0.27 m and length 0.36 m. The fabricated magnet will have a standard warm bore diameter 0.054 m.
The magnet design was based on NbTi superconducting wire, which consumes wire length 16.6 km and wire volume 0.005 m3. There are 12 magnet coils in total including 5 primary coils, 4 compensating coils and 3 shielding coils and superconducting wires with several gauges were applied to reduce the integral wire usage. The operating current for the target field strength is 110.59 A, accompanying a maximum hoop stress 122 MPa. The current margin and temperature margin for the magnet are 78.1% and 1.49 K at 4.2 K, respectively. The coil inductance is 14.8 H and the magnetic energy is 90.6 MJ.
Four bobbins were designed for the magnet coils support and another one between the compensating coils and shielding coils was used for shim coils attachment. The cold heads of cryocooler were mounted on the metal bobbins, which cooled the magnet coils temperature much lower than critical temperature.
The conduction-cooled NMR magnet largely reduced the dependence of superconducting magnet on liquid helium, which not only well copes with the scarcity of liquid helium market in the future, but also reduce the overall cost of the magnet system in a long run.
In this paper, we propose a new concept of “multi-bore” NMR (nuclear magnetic resonance) magnet, where multiple high temperature superconductor (HTS) NNR magnets are closely positioned to form a magnet array. A key benefit of the multi-bore NMR system over its single-bore counterpart may be that it shares some common parts, especially cryogenic system and current lead, thus the overall multi-bore NMR system could be substantially more compact than the same number of single-bore NMR systems. However, due to the close positioning of multiple HTS NMR magnets, the electromagnetic interference among neighbor magnets may be significant, which leads to challenges in: (1) obtaining NMR quality field uniformity; (2) keeping sustainable electromagnetic force and stress; and (3) safe quench protection. This paper presents our initial design of a 4-by-4 multi-bore NMR magnet array. Then, a set of ferro-shims is designed to obtain a target field uniformity for all magnet components. The unbalanced Lorentz force on each magnet is also calculated with a first-cut design of the support structure. Finally, a post-quench analysis is performed with mutual inductances among magnets taken into consideration.
Keywords: Array of magnets, field uniformity, HTS magnet, multi-bore NMR
Category: D01 - Magnets for NMR
This work was supported by the Korea Basic Science Institute (KBSI) grant D39611. It was also partly supported by the National Research Foundation of Korea as a part of Mid-Career Research Program (No. 2018R1A2B3009249).
In this paper, a new design method using a stacked multilayer ferromagnetic shim is proposed and experimentally verified. Because of large harmonic errors caused by the screening-current induced magnetic field (SCF) and absence of superconducting active shim coils, ferromagnetic shimming is one of the most important technologies to develop the homogeneous high temperature superconducting (HTS) NMR magnets. In conventional designs of ferromagnetic shim, it has been important to optimize the thickness of hundreds of shim elements. Since the optimal thickness combination can be very complex, 0.025 mm (1 mil) to 0.5 mm (20 mils) thick, a method to reduce manufacturing errors should be considered from the design stage. Even if the shim of the complex combination is well fabricated, the performance may not be perfect, so that the shimming is iterative process. In order to reduce the manufacturing errors of the shim layer and flatten the contact section when stacking, each shim set is designed with shim elements of the same thickness. In this paper, the design method to reach 1 ppm with ferromagnetic shim alone and the process of installing multilayer shim are explained. The newly designed shim has been fabricated and verified by the shimming test of a 400 MHz all-ReBCO NMR magnet, which is supposed to have the final homogeneity level of sub-ppm, including room-temperature (RT) shims.
In the ultra-high field NMR (nuclear magnetic resonance) and MRI (magnetic resonance imaging) application with using high-temperature superconducting (HTS) materials, the elaborate analysis of multiple coaxial solenoid coils is essential for the magnet design. The inductance and force were calculated by some authors using analytical and semi-analytical expressions based on double integrations or elliptical integrals of the first and second kinds, Heuman’s Lambda function. In this study, we present new and fast procedures for calculating inductance and force exerted between coaxial coils. The combination of Biot-Savart law and Numerical method are used to calculate magnetic field at the interesting area, the inductance is the flux linkage surface integral over the cross section and the force is the Lorentz force volume integral over the solenoid in the cylindrical coordinate system. The derived inductance and force formula based on double integral can be implemented respectively by MATLAB programming with no concern of singularity. Compared with the traditional method, in the MIT 1-GHz NMR magnet design, the inductance and force calculation results respectively differ by less than 8 ‰ and 1 ‰ when the coil distance is 0.26mm. With the increase of the distance, the minimum differences are 7.0×10-3 ‰ and 4.8×10-3 ‰. The suggested method calculation time is 2 times faster in the meantime. The presented approach is more general for calculating the inductance and force of coaxial coils and more applicable to get highly accurate results caused by a relatively simple procedure and shows low computational time.
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2017R1A2B3012208) and Research reported in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health under award number R21GM129688.
Level 2 Posters 1
A joint method for enlarging the length of a superconducting coil should be developed in order to cope with the power demand of industrial society. There are many kinds of joint methods are proposed to enlarge the length of a superconducting coil with high electrical reliability. Among them, a stop joint box method is known as the most promising method to enlarge the length of a superconducting coil because the pressure of a superconducting coil system keep constant with a stop joint box method. However, electrical breakdown could occur because of the vulnerable dielectric characteristics at surface between epoxy resin and polypropylene laminated paper (PPLP) in the stop joint box method. It is well known that the dielectric characteristics of surface between two solid insulation materials are inferior to those of a liquid or a solid insulation material. Therefore, creepage discharge characteristics of surface between epoxy resin and PPLP should be performed according to surface roughness. In this study, experiments on dielectric characteristics of a stop joint box method are performed according to pressure and roughness. It is found that the dielectric characteristics of a stop joint box method are dependent on the roughness of solid materials.
With the rise of power level of high power device like magnetic power supply systems of fusion device, the section size of smoothing and current-limiting reactor becomes larger and larger. To keep the linearity of inductance, the structure of air-core with vacuum pressure impregnation (VPI) casting is widely used. In this paper, a numerical method based on equivalent model is adopted to study the transient voltage process of air-core coil under the overvoltage excitation, focusing on the effect of dielectric constant, thickness of insulating medium, number of coil layers on the resonance frequency and voltage distribution of various layers. To verify the numerical analysis results from MATBLE and ATP-EMTP, multi-group and various coils prototype like single layer with resin, single layer without resin and so on are fabricated and tested, which demonstrated the accuracy of proposed analysis method. In addition, the research results can provide a reference of the insulation design and fabrication of large current coils with large section.
Two types of new organic resins are under development at KEK for the magnet insulation materials. One is Cynate ester resins which will be used in warm magnet insulation instead of usual epoxy resins. One of its typical (possible) characteristics is its radiation hardness. We have already developed a new type of the insulation resin based on Bismaleimide-Triazine （BT) resin. BT resin was widely used for high intensity accelerators because of its one order of magnitude higher radiation hardness than normal epoxy resins. Especially, most magnets of J-PARC, Japanese high intensity proton accelerator complex, were assembled with the BT resin. However some thermal characteristics of the BT resin is somewhat too keen with its curing temperature to be handled by easy manner. Then we found some possibility to realize the easy-manner handling characteristics in Cynate ester resins. Some parts of the R&D works are now under progress at KEK and at several chemical collaborating companies in Japan. We will be able to report the latest status of this R&D works at MT26.
Another trial is under progress with resins which are hardened by Ultra Violet light. Then the resin is called as "UV-resin". This UV resin can be very smooth liquid in normal room temperature. However the resin will be hardened quickly under the irradiation of UV-light, which can be found in natural light from the sun and from light source assembled with UV-light LED, etc. Thus their very important characteristics is its rapidness to be hardened. Some UV-resin will be hardened within several second from smooth liquid by the irradiation of UV-LED light. This phenomenon will help us to assemble warm magnet coils with very much complicated shape. Possible problems are its mechanical strength and radiation hardness. At present R&D of the UV-resin has just started and we will be able to report some progress at MT26.
The insulation system is a key component of Nb3Sn superconducting accelerator magnets under construction for the LHC High Luminosity upgrade (HL-LHC). It needs to ensure the magnet operation at 1.9 K and to guarantee the functionality during the complete service life of the magnet in the accelerator under high mechanical stress and irradiation dose up to 35 MGy. A first set of experimental tests have been performed at room and cryogenic temperature to confirm the stress-strain behaviour, the mechanical strength and the failure mechanisms of the cable insulation system used for the HL-LHC Nb3Sn accelerator magnets. CERN is performing tensile and inter laminar shear strength (ILSS) tests and a non-standardized combined compressive shear test, which is more representative for magnets operational conditions. The tested samples consists of the same raw insulation material and follow similar specific manufacturing procedures as the ones of the 11 T Nb3Sn dipole and the MQXF Nb3Sn quadrupole magnets. In order to represent the different design criteria of these magnets, the sensitivity to the mechanical behaviour of the CTD-101K resin impregnated samples to a varying S2-glass yarn density, sizing and fibre volume fraction was investigated with different types of samples as well as the effect of mica used in the insulation system.
A study on the cryogenic dielectric characteristics for developing a high voltage superconducting magnet system such as a superconducting fault current limiter, a superconducting transformer, and a superconducting cable has been performed. A high voltage superconducting magnet system uses liquid nitrogen as an insulating medium as well as a cooling medium by immersing a superconducting magnet into liquid nitrogen and uses gaseous nitrogen as an insulating medium by pressurizing. In many cases, electrical breakdown occurs frequently where a current lead and an enclosure meet due to the vulnerable dielectric characteristics of gaseous nitrogen compared with those of liquid nitrogen. In this study, the dielectric characteristics of gaseous nitrogen according to the work function of materials is performed and a new method for enhancing the dielectric characteristics of a high voltage superconducting magnet system is proposed. As a result, it is found that the probability of electrical breakdown at the dielectric weak point of a high voltage superconducting magnet system could be enhanced by adopting the proposed method.
The construction of high-performing magnets has to take into account the mechanical properties of the employed materials, and insulation adhesion to the conductor is one of the key factors. ICAS, the Italian Consortium for Applied Superconductivity, after an R&D phase, set up a new production line to process copper conductors in order to prepare, apply and cure a cyanate ester based primer, CTD-450, developed by Composite Technology Development, to improve the adhesion of fiberglass epoxy resin insulation to copper. With this new semi-automatic line, a total of about 1.5 km of conductors were treated successfully in a complete temperature and moisture controlled clean environment. In order to mitigate the risk of contamination prior to curing, the whole workshop was constantly kept in overpressure and the whole line was designed to employ only non-contaminating materials. This paper offers an overview of ICAS' technical capabilities and what was learned in terms of key parameters and quality controls.
Abstract-High-temperature superconductors motors driven by power electronics or its startup requires an insulation system which prevents pulse voltage in Liquid Nitrogen.Materials like polyimide(PI) or fiber reinforced plastic materials are usually used in insulation system because of its high performance.Due to driven by power electrics,repetitive square wave voltage(RSWV) will be more appropriate than sinusoidal wave.So this paper presents characteristic of partial discharge(PD) of coil used Kapton under RSWV in liquid nitrogen(LN2).RSWV which has different parameters such as rise/fall time,frequency and duty cycle will significantly influence PD characteristics.Therefore,each condition will be measured by five same samples and same parameters of RSWV except rise time.The results,experimental site and more details will be introduced.
Index Term-insulation partial discharge repetitive square wave voltage liquid nitrogen
PITHIA is an advanced simulation tool, in-house developed by FEAC Engineering P.C., with currently three available modules for electromagnetic, cathodic protection and fluid-structure interaction problems (either 2D or 3D), which can effectively treat large-scale problems as well. This paper describes PITHIA’s electromagnetic module, focusing on applications such as superconducting accelerator magnets. Its capability in solving large-scale linear and non-linear magnetostatic problems to create digital twins of superconducting magnets is being further developed and validated, in the frame of the “KR3870/KT/IT/018L know how & consultancy agreement" with CERN amongst others. The software’s capabilities are characterized by accurate field calculations and modelling of arbitrarily complex coil geometry. The electromagnetic module of PITHIA is based on a coupled FEM/BEM scalar potential formulation that exploits both the advantage of BEM to treat infinite domains and the advantage of FEM to treat nonlinear problems. The numerical results of different types of accelerator magnets simulated with PITHIA are presented in this paper and compared with corresponding results obtained by other commercial simulation software in terms of accuracy and efficiency.
Several investigations have shown that ReBCO coils wound without turn-to-turn insulation are self-quench protecting due to the current bypass through layers. However, some of the obstacles that this type of magnets face are charging and discharging delays, directly related to the generation of eddy currents increased by the low contact resistance between turns. The inter-tape contact resistance plays a key role to address the disadvantages that no insulation brings to magnet performance and benefit from the current sharing feature. In this work we propose an electric-circuit model to describe the inter-tape contact resistance and its impact on the current sharing between tapes for REBCO cables and magnets. With the developed model, we present the ideal contact resistance that can suppress the inter-tape eddy currents and enhance the current sharing between tapes. We also report quench experiments on short REBCO tapes to validate the model. Our model is expected to provide insight into the current sharing and target values for inter-tape contact resistance in REBCO cables and magnets for various applications.
Electrical equipment is tending to miniaturization and high frequency in modern industry development. High frequency transformer (HFT) has a broad application prospects whose volume obeys the law of inverse-squares of the operating frequency. Magnetic properties of its core materials under actual conditions need to be studied.
The soft magnetic ferrites, amorphous and nanocrystalline alloys are usually used to the core of HFT. High running frequency can also lead to the increase of power loss in the magnetic cores and windings, which will cause the temperature rise. Magnetic properties of the core materials measured in laboratory at room temperature cannot meet the requirement of performance analysis and loss evaluation of HFT. Therefore, it is necessary to do further research on the magnetic properties and loss properties of high frequency core materials at different temperatures.
In this paper, a testing system for ring sample is designed considering the influence of temperature. Magnetic properties of the ferrite (N87), nanocrystalline (1k107B) and amorphous alloys (1k101) are measured in the range of 25 °C to 120 °C from 1 kHz to 20 kHz. The saturation flux density, coercive force, remanence, permeability and loss properties of the above materials at different temperatures are analyzed and the change regularities are summarized. The temperature dependencies of three materials under different conditions are compared by using the coefficient of loss variation. At the specific flux density, the loss variation with temperature of 1k101 is the least, 1k107B is the slightly worse than 1k101, and the loss variation with temperature dependence of ferrite is the largest. With the increase of frequency, the loss variation of 1k107B with temperature decreases and their temperature stability is better than the other two materials. Meanwhile, the conductivity of material at different temperatures is measured and analyzed by using van der Pauw method. The overall performances of core materials are summarized in combination with the experimental phenomena and three materials are evaluated objectively.
The superconducting magnetic bearing (SMB) has great application potential in flywheel energy storage system (FESS), because of the merits of wear-free, low-drag torque, self-stable, unlubricated and vacuum-compatible operation. A fully high-Tc superconducting (HTS) FESS with a 300 kW power has been established in Japan, 2015. The next generation MW-class FESS needs a larger weight and higher-speed rotor, therefore, the fully high-Tc SMB composed of the HTS coils and HTS bulks is the best choice. This fully SMB should have a flywheel rotor of over a ton-class weight with thousands-of-round-class per minute. Accordingly, both the mechanical and thermal stabilities of stator of HTS coils and rotor of HTS bulks are critical issues in engineering application. In the present work, a two-dimensional (2-D) finite-element model of the fully SMB based on H-formulation and a nonlinear constitutive relationship was built and calculated by finite-element method. The dynamic, electromagnetic and thermal characteristics in the rotor of HTS bulk and stator of HTS coated conductor coils were calculated and discussed systematically, when the rotor of HTS bulks operates under different speeds from hundreds to thousands of rpm. An overall picture were build to show the mechanical, electromagnetic and thermal stabilities of this SMB, especially the heat loss and speed degradation in superconductors. Based on this prognostic work, several operable rules are provided for the design and operation of SMB.
This work was supported in part by the National Natural Science Foundation of China under Grants 51475389, 51722706 and 51707164, in part by China Postdoctoral Science Foundation under Grant 2017M623055, and in part by the Sichuan Youth Science & Technology Foundation under Grant 2016JQ0003.
Toroidal magnets are widely exploited in industry and scientific research, involving a vast spectrum of applications, such as thermonuclear fusion, particle detectors, SMES systems and medical devices. Toroidal configurations may involve different number of coils of different planar and three-dimensional geometries; to properly analyse these systems, it is crucial to determine the magnetic field generated by various configurations.
The multipole expansion theory in the complex plane is widely adopted to describe the magnetic field of particle accelerator magnets with straight axis. The main advantage of this analytical description is the possibility of identifying multipolar field components of the magnetic system and use them to predict the interaction of a charged particle beam with the field itself. In this case, the correlation between current distribution and field harmonics is well known.
The multipole expansion theory can also be applied to the analysis of toroidal configurations, by solving the Laplace equation for the magnetic scalar potential in toroidal coordinates. In this case however, the correlation between the current distribution and the field harmonics cannot easily be identified.
This paper proposes a methodology for the determination of the field harmonics in toroidal coordinates. The starting point of the model is the calculation of the magnetic scalar potential, based on a hybrid analytical-numerical approach, which was validated versus well-established software for electromagnetic calculations.
The developed algorithm was applied to explore the correlation between the shape and number of coils disposed along the torus and the multipolar components generated by the magnetic system. A specific focus on non-planar configurations and corrector coils is presented, reporting the effect on the field harmonics of various geometric solutions.
High temperature superconducting (HTS) materials are nowadays considered as possible candidates for high field magnets, e.g. for fusion and high-energy physics, and for AC or DC power applications. The development of HTS conductors requires extensive information about the impact of the main characteristics of the cable architecture on the electrical performances of the superconducting tapes or wires. In particular, for a proper conductor design, it is important to characterize the bending behavior of the tape.
In this work, a detailed finite element (FE) model is used to investigate the thermo-electro-mechanical behavior of a commercial (Re)BCO tape from Superpower. A measurement procedure to determine the critical current of the tape when wound helically around cylindrical mandrels of different diameters is simulated. This tape configuration can be found in conductor on round core (CORC®) cables as well as in many types of conductors for power applications.
As a first step, the cooldown to cryogenic operating conditions is fully analyzed, thus computing the strain field corresponding to the first critical current measurements performed on the straight sample. After that, the heating up to room temperature, the helical winding and the following new cooldown is modeled to obtain the final strain map in the tape. This complete analysis is repeated for different mandrel diameters and helix pitches. The numerical results are finally compared to the outcomes of experimental tests performed at 77 K.
The combination of thermal contraction effects and bending/twisting loads due to helical winding is simulated with a fully coupled approach and temperature dependent mechanical properties for HTS tapes. The experimental and numerical results presented in the paper give a better insight to the distribution of 3D thermo-mechanical strain components inside the tapes and their impact on the conductor electrical performance.
Recently, there have been a number of studies using empirical machine learning approaches to extract useful insights on the structure-property relationships of superconductor material. Especially, these approaches are bringing extreme benefits when superconductivity data often come from costly and arduously experimental work. However, this assessment cannot be based solely on an open “black box” machine learning model, which is not fully interpretable, because it can be counter-intuitive to understand why the model gives a particular response to a set of data inputs for superconductivity characteristic analyses e.g. critical temperature, critical current density, and critical fields. This paper aims to present an alternative approach for predicting the superconducting transition temperature Tc from SuperCon database obtained by Japan’s National Institute for Materials Science. We address an explainable and reliable machine-learning framework called Bayesian neural network using superconductor’s chemical elements and formula to predict Tc. In such a context, the importance of the paper in focus is twofold. First, to improve the interpretability, we use a generative statistical model to capture the mutual correlation of superconductor compounds. Finally, Bayesian optimization is utilized to search for the optimal parameters of Bayesian neural network for an improved performance of the prediction model.
Transcranial magnetic stimulation(TMS), as a new medical technology with great development prospect, has been shown to be effective in treating a variety of mental illnesses. The stimulation intensity and focality of the transcranial magnetic coil are often used to measure its biological effects. In order to improve its performance, a magnetic core can be added to the existing coil to enhance the local magnetic permeability. However, the eddy current loss in the core generated by the high-frequency alternating magnetic field cannot be ignored. Thus, this paper proposes a design scheme of transcranial magnetic stimulation thin core coil based on multi-objective optimization. Firstly, the core material suitable for high frequency alternating magnetic field is selected to improve the overall performance. Secondly, several groups of core placements and geometric sizes, which are used as decision variables, are designed using the exhaustive method. Then the corresponding induced electric field intensity, focality as well as the core coil heat can be calculated using the finite element method. Taking reducing the heat of the core and improving the intensity of the induced electric field as well as the focality of the coil as multiple optimization objectives, the final optimization model can be established after normalizing the above-mentioned objectives. At last, the optimal core placement and the geometric size can be obtained accordingly. In the case study, the stimulation effects are analyzed and compared. Under the same power output condition, results show that the proposed core coil can increase the intensity by 80% and the focality by 20% compared with the figure of eight coil. Compared with the existing core coil, it can reduce the heat by 50% with better intensity and focality.
A 9 T NbTi superconducting magnet with large bore is designed and will be fabricated for EMPS (Electro-Magnetic Property measurement System) whose sample space is 50 mm in diameter. To satisfy the large sample space of the system, winding bore of the magnet should be larger than 100 mm in diameter. Since the winding diameter is larger than that of conventional 9 T class NbTi superconducting magnets, wire selection and magnet design are very important and difficult in this research. Optimal design with genetic algorithm considering critical current, magnetic stress, thermal stability and field uniformity is carried out to develop 9 T large bore NbTi EMPS magnet. The design algorithm calculates the structure and dimensions of the magnet to minimize the total volume with satisfying the constraints related to the stability of the magnet. The magnet is composed of series connected three coaxial NbTi coils, of which the wire diameters are different. To evaluate thermal stability of the magnet, quench analysis is also implemented considering the two boundaries among adjacent three coaxial NbTi coils. The maximum hot spot temperature of the magnet is calculated based on the quench analysis model and the fabrication of the 9 T large bore NbTi magnet will be performed after design optimization.
ENEA is currently working on the design of an experimental fusion reactor named DTT (Divertor Test Tokamak).
DTT magnetic system will be realized using superconductor materials thus implying the need for specific protection strategies. In particular, in case of magnet quench, detection and protection devices are needed and they represent a significant cost. The design of quench protection circuits should take into account reliability requirements and also possible protection circuit failures.
To the aim of design purposes, it is fundamental to evaluate all possible failure scenarios in order to identify the most critical conditions. Failure scenarios analysis is a typical problem involving the detection of an extreme condition which is suitable to be solved using parametric optimization algorithms.
From the point of view of magnetic couplings, the quench protection system may be thought as composed of two subsystems: 1) the Central Solenoid (CS), Poloidal Field coils (PF) and Plasma; 2) Toroidal Field coils (TF).
Both the magnetic subsystems include the possibility of timely Fast Discharge Units (FDU) in order to discharge the energy stored into the superconducting coil in case of quench detection. Each unit includes proper breaker circuit with discharge resistor banks in parallel. When the quench is detected, the current carried out by the circuit breaker is commutated into the discharge resistor, and the superconducting coil energy is dissipated with the circuit time constant. Therefore, these resistor banks are designed to fulfill the requirements in terms of discharge time constants. After the mentioned discharge time constants, failure occur in superconductors.
Voltages and currents in each single coil and each single FDU component, both in design and quench conditions, are estimated developing a suitable electrical model and implementing it in the ANSYS software.
In order to protect superconducting magnets, quenches must be detected on time. Unfortunately, conventional simulation predictions are not accurate enough, because they often overestimate the quench detection thresholds. These false triggers lead to frequent and unneccessary shutdowns, which considerably reduce the availability of the entire system and become even more critical for the newly developed magnets based on the Nb$_3$Sn technology. While multiphysical three-dimensional (3D) simulations are computationally expensive, two-dimensional (2D) simulations of the magnet's cross-section lack accuracy. To increase quench prediction quality while keeping the computational effort low, quasi-3D simulation methods can be employed. Here, the cross-section of the magnet is discretized with linear finite elements, while the transversal direction is resolved with polynomial spectral elements. This hybrid approach achieves significantly smaller system of equations than in the standard 3D approach and provides a higher accuracy than in the 2D case. This work deals with the transient simulation of the heat propagation in a dipole magnet. Different spectral basis functions are investigated and the method is validated against a benchmark model.
Quench detection of high-temperature superconducting (HTS) magnet is carried out using various signals like voltage, current and temperate from the magnet. Normally, the detection point is set to a fixed value, and when the measured value exceeded detection point, it is detected as a quench. The problem of this method is that the detection system may malfunction in a sequence that the user has not set before or high disturbance situation. In this study, various signals from normal operating state of HTS magnet are learned to the detection system using clustering which is one of the unsupervised learning methods. The learned data are clustered into a set of patterns that are classified through a K-means algorithm. Signals that are over the clustered range are detected as a quench. Quench detection is simulated using MATLAB and is analyzed the results with respect to the learning parameters.
This paper presents a summary of protection studies being performed within the scope of the High-Luminosity Large Hadron Collider (HL-LHC) upgrade with the STEAM (Simulation of Transient Effects in Accelerator Magnets) simulation framework.
The HL-LHC upgrade features new technologies that are to be introduced into the Large Hadron Collider (LHC). This includes challenging Nb3Sn-based magnets with current densities that exceed those of the NbTi-based magnets presently used in the LHC, as well as new protection strategies such as the Coupling-Loss-Induced-Quench (CLIQ) device. Therefore, it is important to study the impact of these new technologies on the transient behaviour and protection aspects of the HL-LHC upgrade. These studies feature quench simulations of the various HL-LHC circuits where both the protection of the magnets and the busbars are considered. In addition, less common simulations types are done, such as studies of the impact of spurious quench heater and CLIQ firing on the beam, and the impact of fast losses arising from asynchronous beam dumps on the voltage-to-ground in the affected magnets.
The STEAM framework provides numerical tools for the efficient and accurate modelling of accelerator magnets, busbars and circuits. Beyond accurately modelling individual system components, STEAM also emphasizes the systems-engineering point of view, under which failures in one component (magnets, busbars, circuits, controls, etc.) cause system-wide repercussions that are studied with a cooperative simulation approach. These studies are relevant for the understanding of protection aspects and the preparation for the HL-LHC upgrade. Moreover, they will serve as references for performance evaluation of the upgraded machine.
Quench protection system aims to protect superconducting magnets in Large Superconducting Fusion Device (LSFD) from long time and severe conducting current. A 100kA super-high pulse current with very short pulse width produced by LC commutation circuit, flows reversely into the Vacuum Circuit Breaker (VCB) to force the magnets current cross zero, which ensures the reliable turn-off of VCB to protect the superconducting magnets. However, the large current change rate of the pulse current and the stray inductance of external circuit will generate extremely high overvoltage on the both end of VCB, which may result in the turn-off failed and shortened life of VCB. As the result, a snubber circuit consisted of snubber capacitor and snubber resistor is applied to mitigate the overvoltage of VCB.
In this paper, the producing reason of overvoltage of VCB is analyzed firstly. Then, the calculation and the theoretical analysis of transient process are given to illustrate the overall work principle of snubber circuit. And a series of simulations by using Matlab is presented to verify the correctness of the above analysis. In addition, in order to consider the performance and cost of the snubber circuit at the same time, the genetic algorithm is proposed to obtain the optimal parameters of the snubber circuit. At last, both simulation and theoretical analysis indicate that this set of parameters can greatly mitigate the overvoltage of VCB at a relatively lower cost.
The International Thermonuclear Experimental Reactor (ITER) is an international project aimed to build a fusion reactor using a magnetic confinement (Tokamak) for the high-energy plasma. This magnetic confinement it created by a set of various very large superconducting coils, mainly round poloidal field (PF) coils (upto 24 m wide) and D-shaped toroidal field (TF) coils (as high as 16m). The ITER machine utilises 18 TF coils in total, which are composed of a 100 tons winding pack (WP) enclosed in a 200 tons coil case (CC), each. F4E commissioned the insertion of the WP into the CC and subsequent closure welding to SIMIC. Before inserting the WP in the CC, the WP is cold tested at 80K. This cold testing process including all necessary equipment has been subcontracted from SIMIC to NOELL.
This document presents the design and manufacture of the cold testing equipment as well as status of execution and first results of the TF WP cold testing.
The International Tokamak Experimental Reactor relies in magnetic confinement of hot plasma. The main driver for the confinement is played by the Toroidal Field Coils (TFC). These magnets are composed by a winding pack, made of Nb3Sn superconductors, and a surrounding stainless steel structure or coil case (TFCC) which is closed by welding once the WP is inserted in the TFCC. The closure GTAW weld of the TFCC includes about 70m of weld ranging from 40 to 120mm.
Due to the tight tolerances that have to be respected on the final TFC, a mechanical quasi-static Finite Element Model (FEM) has been developed using ANSYS® software by Enginsoft and SIMIC, under the workframe of an F4E contract, to predict the welding distortion by simulating different welding scenarios and to confirm the definition of the required extra-material in the TFCC.
The FEM model was firstly benchmarked with validation coupons, then verified and fine-tuned with four 1:1 scaled TF coil case cross section mock ups. Finally, a full TF coil FEM model was developed in order to predict the deformation of the TFCC during the welding process.
The first TF coil was welded during the first half of 2019.
In this paper, a comparison between the deformation predicted by FEM and direct dimensional measurements of the distortions taken during the welding process of the TFC is presented. From the observation of the real deformed TFC shape, a new tuning of the model is proposed in order to improve the FEM model and reproduce with higher fidelity the welding distortions.
The ITER magnetic system includes the Toroidal Field (TF) Coils. To cope with the fatigue exercised on the TF Coils, and with the deformation resulting from the powerful magnetic fields, 3 Pre-Compression Rings (PCRs) will be placed on top of them and 3 below them. An extra set of 3 will be manufactured as spare and installed below the ITER machine in case there is a need in the future to replace the lower set.
In December 2016, F4E signed the contract with the French company CNIM for the procurement of 3 PCRs (with the option to produce 6 additional PCRs). 3 optional PCRs had been released in November 2018 so that CNIM is due to produce 6 PCRs and deliver them from May to November 2019.
This highly innovative process, proposed by CNIM and chosen by F4E, is based on a pultrusion technique that involves the manufacture of profiles of epoxy S2-glass. Each PCR is a manufacture by winding the flat pultruted profile (2mm thick and about 2800 m long) and utilizing an adhesive tape (0,12 mm thick) between layer to freeze the geometry. Finally, the PCR is machined to reach the required geometry tolerances. Each PCR will have a diameter of approximately 5 m, a cross-section of nearly 300 mm x 300 mm and will weigh approximately 3 T. The PCRs will finally be proof tested at 600MPa in hoop stress which corresponds to 1.5 time the operational hoop stress.
An extensive qualification phase has been released to prove that both materials and manufacturing technology can procure PCRs according to requirements.
This paper will describe the manufacturing processes, the results of the qualification phase and the status of the production.
The Pre Compression Ring (PCR) system is a key component of ITER magnetic system that radially constraints the Toroidal Field (TF) coils against the out of plane magnetic forces. Due to its peculiar characteristics (one of a kind component, unidirectional S2 fiberglass in epoxy matrix) an experimental campaign has been planned on both reduced and full scale specimens. The tests purpose is the validation of the manufacturing technique verifying the compliance with the structural requirements. The Pre Compression Ring Test Facility (PCRTF) aims at reproducing the loading condition whom the PCR is subjected to in the tokamak assembly with a safety margin. For this purpose a detailed non linear 3D FEM model was developed permitting the simulation of the tests to be performed of the full scale PCR and on two different reduced PCR sub-assemblies. The analyses permitted to assess not only the stress field inside the specimens themeselves but also the stress, displacements and global forces for the modules of the testing rig. This led to a fine optimization of the PCRTF components also investigation several off-design scenarios that may occur during the assembly and the operation of the facility.
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization
The electrical performance degradation of Nb3Sn cables in the Cable-in-Conduit Conductors design has been well documented in literature. The Nb3Sn composite strands exhibit a critical current density that strongly depends on the strain state of the superconducting filaments. During the machine operation, the conductors are submitted to several electromagnetic and thermal cycles affecting the Nb3Sn mechanical state and consequently the capacity of the conductors to transport current. Different studies based on both a macroscopic and a microscopic approach have been performed so far to identify the mechanisms determining the conductors’ behavior. Nevertheless, no theory permitting to predict the electrical performance of cyclically loaded conductors has been developed yet. Therefore, a solid electromechanical model able to tackle the analysis of CICC and other fusion cables when they undergo thousands of cyclic loadings would be very useful.
In this paper an advanced mechanical model to study the mechanical behavior of ITER TF CICC based on the new version of the MULTIFIL finite element code is presented. The thermal loadings simulations in MULTIFIL code have been upgraded to solve the non-homogenous strain distribution problem presented in a previous work. The model was adapted to take into account the Lorentz force cumulative effect of the other petals on the one under analysis. Moreover, new material constitutive laws have been implemented in the code.
An assessment of the electromagnetic behavior based on the mechanical analysis was also performed to make a preliminary comparison between the trend of the simulated results and the trend of the experimental ones obtained in the tests of the TFIO1 sample in the SULTAN facility.
Modelling by analytical approach the coupling losses of CICCs used in tokamaks remains a challenge to be reliable at all frequencies. This is usually done using either CPU consuming numerical approaches or heuristic models such as MPAS now used for ITER.
A recently developed analytical model COLISEUM (COupling Losses analytIcal Staged cablEs Unified Model) applies at various scales going from strands to two-stage cables and is able to predict AC losses upon geometrical and electrical parameters of a cable. A previous analysis identified the impact of these parameters on the behavior of a multiplet of strands, in order to give our model a solid base starting from the most academic step of the simulation. COLISEUM and MPAS are based on different assumptions and confronted to cross validate and strengthen themselves.
In the present work we confront COLISEUM with results from purely numerical model (JACKPOT, U. Twente). Previous crosscheck performed showed a moderate mismatch that we tried to understand by starting over from basic CICC stages (low level multiplets). We will in particular put the emphasis on conductances definitions in every models (i.e. MPAS, COLISEUM, JACKPOT) and the way to ensure their crossed consistency.
The analysis using COLISEUM and MPAS is confronted to experimental measurements of AC losses performed at CEA Cadarache in the JOSEFA facility using magnetization method. Two main objectives: compare the construction (assumptions, limitations, etc.) and reduce the number of free parameters in both models. New settings were implemented in JOSEFA enabling to generate sinusoidal field variations, giving access to more refined signal interpretations.
Contribution of the above results to COLISEUM and MPAS enhancement and complementarity of analytical, experimental and numerical part of the work will be discussed to consolidate our models. Recommandation will be given regarding extension of the model to three stage description.
The cryogenic circuit used to cool a large superconducting magnet such as a tokamak system must be designed while considering the cooling conductance due to the many branches.The KSTAR PF1~2 upper and low magnet have ten and eight cooling channels parallel respectively. The pressure drop of the magnets is adjusted by cryogenic valve and is maintained by a supercritical helium circulator. The flow rate should be uniform among the cooling channels or magnets but the flow unbalance is observed in the real system. To investigate of the unbalance effects, the simple model of PF1~2 upper and low magnets is developed using Supermagnet code. The maximum temperaure is studied in details depending on the unbalance ratio.
Typical tokamak fusion device uses CS (Central Solenoid) coil to initiate plasma heating by ramping up the coil with steadily increasing current which induces the plasma inside the vacuum vessel. For the case of the KSTAR (Korea Superconducting Tokamak Advanced Research) which uses superconductor for all of its magnets, this operation brings various AC losses to the magnets including hysteresis loss, coupling current loss, and eddy current loss. Thus it is important to analyze AC losses of the superconducting magnet for its reliable operation in two main perspectives: short term quench prevention and long term steady-operation. With 10 years of operation, KSTAR has provided many invaluable data in superconducting magnet operation regarding AC loss issues. This paper focuses on the AC loss of the KSATR PF (Poloidal Field) coil based on the long term operation data. Among the components of the PF coils, PF1L coil contributes to CS coil operation from which it experiences the highest field, and consequently the largest loss. First, numerical approach will be taken to analyze quantitatively each AC loss. Then the losses will be compared with the total loss measured by the calorimetric method. Finally, the results will be interpreted in qualitative manner to investigate the possible relation between the AC loss and the magnet’s performance in persistent operation.
This study was supported by Korean Ministry of Science and ICT under the Korea Superconducting Tokamak Advanced Research (KSTAR) Project. A part of the study was also supported by the National Research Foundation of Korea as a part of Mid-Career Research Program (No. 2018R1A2B3009249).
Conceptual design of the K-DEMO magnet system has been under way. From the up-to-date design activities, the TF magnets use two different types of cable-in-conduit conductors (CICCs) where high field region uses quite an amount of superconducting wires, but in relatively low field region, substantial amount of superconducting wires should be replaced by copper wires. The stored magnetic energy is estimated to be over 49 GJ. Eighteen TF magnets are series-connected and charged by a power supply, where the design current is 65.52 kA. Protection circuits for the K-DEMO TF magnets should be designed with a fail-free concept after interlock signals are received. The design activities to minimize the system failures are carried out to guarantee the reliable and stable operation
China Fusion Engineering Test Reactor (CFETR) is the next device in the roadmap for the realization of fusion energy in China, which aims to bridge the gaps between the fusion experimental reactor ITER and the demonstration reactor (DEMO). CFETR will be operated in two phases: Steady-state operation and self-sufficiency will be the two key issues for Phase I with a modest fusion power of up to 200 MW. Phase II aims for DEMO validation with a fusion power over 1 GW. For saving the cost of construction and meeting both Phase I and Phase II target with achievable technical solutions, a new design has been made by choosing a larger machine with R =6.6m,/a=1.8m, BT= 6-7T. Over 1GW fusion power can be achieved technically and it is easy to transfer from Phase I to Phase II with the same machine.
The Toroidal Field (TF) coil is a crucial system in the tokamak, which provides the main magnetic field to confine the plasma. One TF coil will be constructed next 5 years in the support of Chinese government. The quench of TF coils can be induced by many factors, for example, thermal disturbance, mechanical disturbance, vacuum destruction and so on. For the safety operation of superconducting magnet, the quench detection and quench protection system is very important for the TF coil system of CFETR. In order to give the design reference of quench detection and protection system, the assumed quench phenomenon of TF coil is analyzed. The evolution of the voltage of the normal zone, hot spot temperature and mass flow rate of cooling channel of the TF coil are simulated.
The KSTAR magnet system has stably operated since the first plasma in 2008. Scientifically important results have been achieved such as long-pulse plasma operation up to approximately 80 seconds, ion temperature more than 100 million degrees, the world-longest ELM suppression, and so on. During more than 20,000 shots, the CS magnet has experienced temperature rise especially due to AC losses as well as electro-magnetic loads. In this paper, the operational characteristics are analyzed with accumulated data such as coil voltages, temperatures, pressures, flow rates, and so on. Based on these results, conductor performance and stability issues are discussed.
The pressure drop in Cable-in-Conduit Conductors cooled by a flow of liquid or supercritical helium is one of the key parameters for the design of the large superconducting magnet systems, which determines the heat removal capability and the thermal stability. In this paper, a new model for predicting pressure drop in Cable-in-Conduit conductors is derived based on an analogy between the bundle of strands in the cable and a porous medium. The new prediction model indicate that the pressure drop in Cable-in-Conduit conductors is affected by the structure of cable and the physical properties of the liquid, such as void fraction, tortuosity, hydraulic diameter, density and viscosity of liquid helium. In order to verify the validity of the pressure drop model developed in this paper, the predictions are compared with the experimental data, the results show that the predictions are in good agreement with the experimental data, this verifies the validity of the present pressure drop model for Cable-in-Conduit conductors. In addition, the effects of the cable structure parameters on pressure drop are simulated, which explains why the Katheder correlation can be used to predict the pressure drop of Cable-in-Conduit conductors at large Reynolds numbers.
To perform fast beam switching during spot scanning procedure, the kicker system is adopted in HUST-PTF (Huazhong University of Science and Technology Proton Therapy Facility). The rise and fall time is about 100us, and the maximum repetition rate is 250Hz. A high dynamic performance power supply is required to implement the kicker function. Utmost care should be taken to avoid Electro-magnetic disturbances to surrounding equipments caused by high voltage slopes and voltage overshoot. This paper introduces the optimal design and presents the test results of the power supply. A trade-off between voltage slope reduction, overshoots and dynamic performance has been made. The results show that the power supply meets the design specification.
A superconducting multi-coil magnet system has been designed, analyzed and optimized, serving as demonstrator for a high filed Magnetic Resonance Imaging (MRI). The designed superconducting magnet inductance is 3500H. The operating current is 230A. The stored energy is as high as 93MJ. The superconducting material is NiTi/Cu. The normal excitation and demagnetization are completed by the power supply, after the excitation, the power supply is disconnected. This paper presents the design and research of the two different kinds of magnet power supplies which are all adjusted for the project, the one is three-phase bridge phase-controlled rectifier which is simpler and the other is based on high-frequency which is of high power density, reduced weight, and low noise without compromising efficiency and reliability. Besides, the design of the quench detection systems for solenoid model coil was also described in this paper.
The pulsed magnets power supplies systems to affect injection and extraction of the electron beam have been realized for the Taiwan Photon Source (TPS) and Taiwan Light Source (TLS). The control systems of these pulsed magnets power supplies have been achieved as the well operation interfaces. To accomplish higher reliability operation, the advanced real-time diagnostic toolkit of pulsed magnets power supplies has to be developed. The SoC (System-on-Chip) embedded waveform acquisition system has been designed, implemented and applied for inspecting the pulsed magnets power supplies during routine operation. This waveform acquisition system not only owns 125 MS/s sample rate, 50 MHz bandwidth and 14 bits resolution, but also supports the EPICS software framework for complete system integration. The acquired current transformer waveform has been extracted immediately specific characteristics for examining the status easily, and these values have been archived for long time observation. This paper reports the design, implementation and real-time data analysis of SoC embedded waveform acquisition system for pulsed magnets power supplies systems.
High-Tc superconducting (HTS) dynamos are simple devices that provide an effective alternative to current leads for driving DC currents in superconducting coils. The simple geometry of these devices consists of some arrangement of superconducting stators and exciter magnets. With recent advances in our ability to model such systems, we investigate the relationship between width of the superconducting stator and the exciting magnet. This is of interest as previous studies have shown that a non-trivial optimum exists, as the extreme cases yield poor performance. With validation against experiment, we show that this optimum is caused by the trade-off between spatial field gradient and the total flux magnitude from the exciter magnet. Simulations also allow us to inspect the local flow of critical and over-critical currents in the stator that give rise to the relationships presented.
HTS flux pump is a contactless charging method for a superconducting magnet, which can reduce the cryogenic losses associated with current leads. Rotating type flux pump is a simple and practical flux pump, which has great application in charging HTS magnets. For the rotating flux pump, the design of rotor has great impact on the performance of flux pump. In this study, we will change the rotor design of the rotating type flux pump. Different design will be compared and analysed. Based on the study, we will investigate the effective methods to improve the performance of HTS flux pump.
Flux pumps are capable of injecting flux into an HTS circuit without electrical contact. They are ideal alternatives to traditional current sources and current leads to power HTS magnets. These devices make it possible for HTS magnets to be smaller, lighter, and more accessible.
In recent years, our group in Cambridge has developed a transformer-rectifier HTS flux pump switched by dynamic resistance, which demonstrates superior performance. Despite the achievements, many works could be done to improve performance. This paper aims to analyze the power loss and efficiency of the flux pump and further reduce the loss. The analytical solution will be proposed and verified by comprehensive experiments.
Recent progress in material science has proved that high temperature superconductors have a great potential to trap significant magnetic flux due to the characteristics of flux pinning, which makes them particularly attractive for a variety of engineering applications. However, using traditional methods to magnetise a superconductor, the applied field needs to be at least as high as the expected magnetic field, which needs high current power supply equipment and leads to a huge expenditure. This research focuses on a Thermally Actuated Flux Pumping Method (TAFPM) which is a novel technique to magnetise the superconductor which only requires a magnetic field with strength as low as that of permanent magnets and theoretically a flux density of more than 20 T can be obtained. Finally，with this thermally actuated magnetisation flux pumping technique, we can make lighter, more efficient and cheaper superconducting power devices, which will make a big contribution to the technical innovation of a variety of engineering applications, ranging from public transportation, through medical equipment, to high energy physics.
Based on the YBCO high temperature superconducting bulk, This research uses the Thermally Actuated Flux Pumping Method to generate a travelling magnetic wave in order to magnetise the superconductor, by measuring the trapped field and AC loss in the high temperature superconducting, optimising the Thermomagnetic Material (TM) and the travelling magnetic wave, finally making the Thermally Actuated Flux Pumping system more efficient and stable. Based on the critical state model, this research also analyses the critical current density JC and flux pinning force FP, investigating the micromechanism of the flux creep effect for 2G high temperature superconductors, revealing the physics underlying the flux pumping effect based on the travelling magnetic wave, finally providing the theoretical support and technical assurance to realise the steady strong magnetic field for high temperature superconductors.
Recently, several high temperature superconductor (HTS) companies, such as SuperPower, SuperOx, Shanghai Superconductor Technology (SST), and THEVA, succeeded in improving current-carrying performance of their REBCO products under high magnetic field at low temperature. However, except HTS coils made of SuperPower REBCO tape, there are insufficient reports regarding thermal, electrical and mechanical behaviors of HTS coils wound with other REBCO tapes such extreme conditions. Therefore, in this study, two sets of two metal-as-insulation (MI) REBCO double-pancake (DP) coils which have inner joint between top and bottom pancake were fabricated: 1) a set A with two DP coils wound with 140 µm thickness THEVA tape for one pancake and with a 75 µm thickness SuperPower tape for the other pancake, the aim being to use the THEVA tape to use its different a-b plane orientation with regards to the tape surface to accommodate the bending magnetic flux line at the extremity of the assembly ; and 2) a set B of two DP coils wound with a 75 µm thickness SST tape. When winding the DP coils, a sapphire plate was inserted between the single pancakes as a cooling channel inside the DP coils. After each MI DP coil was tested in a bath of LN2 at 77 K, the DP coils were mounted on a support structure for assembly as MI HTS magnet set A and B. The thermal, electrical and mechanical characteristics of the HTS magnet sets were examined with various ramping conditions under various background magnetic fields at 4.2 K. From these results, current-carrying performance, critical current uniformity, thermal and mechanical stabilities of the MI magnet under back ground fields in range of 0-20 T will be discussed with regards to technical specifications of each company’s REBCO tape.
ACKNOWLEDGMENTS: The authors acknowledge the support of the LNCMI-CNRS, member of the European Magnetic Field Laboratory (EMFL), and of the French National Research Agency (ANR) through the contracts ANR-10-LABX-51-01 (Labex LANEF) and ANR-14-CE05-0005 (NOUGAT project)
As a novel high-temperature superconducting (HTS) conductor structure composed of the stacked 1-mm wide REBCO tapes, Narrow-Staked (NS) wire has been demonstrated to have a significant reduction effect of AC loss and screening current induced field (SCIF) in the insulated HTS coils. Thus, NS wire is a promising HTS conductor design for the practical magnet applications. Meanwhile, due to the enhanced engineering current density, thermal stability, and self-protecting features compared with the traditional insulted HTS coil, no-insulation (NI) coil has been a widely used technology for HTS magnets. Although NS wire was proved as an improvement for insulated HTS magnet, the NS wire effects on NI coil is not confirmed due to the special characteristics of the NI coil. In this paper, a NI pancake coil sample was wound with the fabricated NS wire. To evaluate the performance of NI coil wound with NS wire, the charge-discharge and sudden discharge tests were undergone at the liquid nitrogen temperature. Besides, the characteristic resistance was also analyzed for the NI coil sample. This paper result will provide a useful reference for NS wire application on NI HTS magnets.
Comparing with conventional insulated high temperature superconducting (HTS) coil, the no-insulation (NI) one has advantages of high stability, self-protection and fast quench recovery. However, the unstable and non-uniform magnetic field appear in NI coil during exciting owing to too low transverse resistivity among turns. This paper proposed a method for increasing stability and decreasing screen current by enhancing transverse resistivity among turns of no-insulated HTS coil which was fabricated by co-winding REBCO and stainless steel (SS) tapes. The latter tape functioned as increasing mechanical strength and protection of NI HTS coil. In order to enhance the transverse resistivity, the SS tape was thermally and chemically treated. Two NI HTS coils co-wound with treated and non-treated SS tapes were designed and fabricated. Both of them are analyzed and tested, the results show that the NI HTS coil with co-wound by treated SS tape has lower screening current and coupling losses as well as higher temporal stability than that one co-wound by non-treated SS tape.
Key words: non-insulation coil; temporal stability; transverse resistivity, treatment
When high temperature superconducting (HTS) devices run in the power system, the superconducting tapes may quench due to power system fault. Therefore, quench characteristic is one of the most important characteristics of superconducting tapes. In this paper, in order to obtain the quench characteristics of YBCO coated conductor, we have established an over-current experiment system based on waveform controllable power supply. The voltage and current of YBCO coated conductor sample are measured under over-current with various amplitudes. The variation of quench and recovery performance for YBCO coated conductor samples is discussed. In order to verify the validity of the experiment data, we used the thermal-electrical analogy method to build a computational model. During the over-current process, the transient resistance of YBCO coated conductor sample is greatly influenced by over-current current amplitude and its rate of change. When the over-current current is relatively large, the YBCO coated conductor sample has a recovery process after impact process. The work in this paper may contribute references to design and protection of superconducting fault current limiter (SFCL).
NI (no-insulation) winding method have been widely used to develop high field superconducting magnets using REBCO wires due to excellent mechanical and electromagnetic stability. When REBCO magnets are operated in a bath of cryogens such as liquid helium and liquid nitrogen, sufficient cooling is achieved by pool boiling of the cryogen. However, conduction-cooled REBCO magnets must ensure sufficient thermal paths from cryocoolers to the magnets. When the NI REBCO magnets are not impregnated by epoxy, radial heat transfer, which is perpendicular to the wire surface, is limited due to the dry contacts between the REBCO wires. To solve this problem, thin metal conduction plates, attached by epoxy to the wound surface of the coil, are usually used to enhance radial thermal conductance as additional thermal path. In the case of REBCO magnets with large mechanical stress, vacuum impregnation is applied using epoxy with thermal contraction similar to the magnet to avoid well-known delamination problem of REBCO wires.
In this study, two kinds of REBCO DPCs (Double Pancake Coil) were fabricated: 1) DPC with conduction plates which are attached to the wound surface of the coil by epoxy; 2) Vacuum impregnated DPC with conduction plates. The coils were installed in a conduction cooling test apparatus to compare the thermal characteristics during charging and discharging operations. In addition, AC loss, eddy current loss and leak-current loss were quantified by analyzing the measured temperature variations. The results will be used to develop mechanically robust and thermally stable REBCO magnets of maglev trains and large wind power generators.
This research was supported by "Core technology development of subsonic capsule train" of the Korea Railroad Research Institute (Grant number: PK1901A1) and by Korea Electric Power Corporation (Grant number: R18XA03).
We have been studied the no-insulation (NI) technique and co-winding method with various metallic tapes. The improved thermal stability of NI test coils by bypassing the transport current into the transverse direction was experimentally confirmed and reported. However, there are the problems of the transient stability and the reduction of critical current of NI HTS coils due to the thermal and mechanical stress according to electromagnetic force and cooling process. In addition, in NI HTS coils, we could not expect an effect of NI winding technique when a normal transition occurs at the outermost part of the coils. Therefore, in this study, we propose to install the metallic protection rings composed of two or more rings with different electrical and mechanical properties on the outermost turn of NI coils to improve the thermal, mechanical and electrical stabilities. This protection rings are mechanically and electrically connected to NI coils in parallel. The current bypassing characteristics in the transverse direction and normal zone propagation property in NI test coil with/without copper protection ring was investigated experimentally. The current bypassing from the outermost part of NI test coil to the copper protection ring was observed and the local temperature rising at outer part of test coil due to thermal disturbance was suppressed. The detail experimental results by copper protection ring will be presented.
The no-insulation coil is expected as a technology that can realize both high current density and high thermal stability which are originally trade-off relationship in REBCO coil application. And this technique has been mainly studied for application to small diameter inner coil of NMR magnet exceeding 30T. In this case, the coil is cooled by 4.2 K liquid helium. On the other hand, we have been developing a REBCO coil system aimed at application to high-magnetic-field whole-body MRI and medical cyclotron for cancer therapy. For this application as well, a no-insulation coil is considered as a technology satisfying both high current density and high thermal stability. The REBCO coil which we aim for development has a diameter of about 1 m, the generated magnetic field is about 10 T, and conduction cooling around 30 K is assumed. Therefore, since the size, operating temperature and magnetic field are different compared with those of the NMR coil, there is a possibility that the electromagnetic, thermal and mechanical behavior when adopting the no-insulation coil winding may be quite different. In this presentation, we report on the behavior when local normal transition occurred in multi-stacked no-insulation REBCO pancake coils by numerical analysis considering coil size, operating temperature and magnetic field as parameters. For numerical analysis, we conducted a coupled analysis of current distribution analysis based on PEEC (Partial Element Equivalent Circuit) model and thermal analysis by two-dimensional finite element method.
The part of this work was supported by Grant-in-Aid for Scientific Research (S) Grant Number 18H05244, the Ministry of Education, Science, Sports and Culture.
We have tested an intermediate-size HTS stainless steel double pancake coil (132 turns per coil) and discovered dynamic effects during sudden discharge on millisecond scale. Two main approaches have been compared: soft and hard breaks. The soft break is when the power supply is turned off suddenly but the shunt resistors (168 milliohm) is still connected. The hard break uses a high voltage contactor to suddenly open the circuit so that the DPC leads are completely open. The hard break is dangerous to traditionally insulated low temperature magnets, but the SS-insulated HTS DPC retained integrity over >80 power cycles. Voltage decay curves for the soft and hard breaks are studied on short and long timescales. On long timescales, we observe the expected exponential decay and measure the time constant to calculate contact resistance. On short timescales, we observe highly dynamic effects: a hyper-exponential decay suggesting that the inductance or contact resistance is changing with time, likely an indication of the RL circuit forming.
The authors would like to thank Y. Wang, E. Burkhardt, K. Holland, K. Schrock, and S. Chandrasekaran for their assistance and support at Michigan State University and thank K. Amm and P. Wanderer for general support at BNL. This work was supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661. Magdelena Allen was funded by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internships Program (SULI), and thanks Honghai Song for his mentorship at BNL.
Brushless dc motor (BLDC) has high output and high efficiency characteristics. It is possible to reduce the size and weight of the device and is used throughout the society. Among them, vibration and noise reduction are becoming important issues as they are used in household appliances and automobiles adjacent to people.Vibration and noise are caused by electrical causes such as spatial harmonics and magnetic saturation. Mechanical causes are caused by cogging torque and mechanical assembly.In a BLDC motor using a permanent magnet, the ferromagnetic material near the magnetized teeth is subjected to force when the teeth are magnetized by permanent magnets. In other words, the rotor located at the upper part moves by the tangential force and stops at the position where the rotor and the tooth that are shifted coincide with each other. The generated force at this time is called the cogging torque.Cogging torque induces torque ripple during operation of the motor, adversely affecting noise and vibration.In this paper, the design optimization of the stator shape of the surface permanent magnet type (SPM type) outer ring type BLDC motor was carried out for cogging torque and magnetic saturation reduction.Typically, there are skew, tapered, notch, etc. in a manner for cogging torque reduction and magnetic saturation relaxation. Among them, the application of the notch shape is easy and cost-effective.Therefore, the notch shape is applied considering cost reduction and fabrication, and the notch shape of the stator increases the magnetoresistance and magnetic flux density by increasing the length of the gap and the volume of the gap.Therefore, as the magnetic flux density is reduced, the cogging torque and the magnetic saturation decrease. To verify this, electromagnetic analysis is performed using FEM software ANSYS Electromagnetic.In order to analyze the effect of cogging torque reduction and magnetic saturation on vibration, electromagnetic characteristics analysis and vibration characteristics analysis are performed in conjunction with ANSYS Workbench.
Currently, the ISG is commercialized and under active research in the 48V hybrid system. However, in a typical vehicle using a 12V system, the starter motor and generator are operated separately. In this paper, we report the development of a general advanced integrated starter-generator(AISG) for vehicles using 12V power supplies. The specifications of the power source are lower than that of conventional integrated starter-generator(ISG). It is not easy to implement in a 12-V battery system of a typical car without using a separate power conversion device, such as a converter. combining a starter motor and an alternator into one integrated system has many advantages. The first one is improving the fuel economy by stopping the engine during deceleration, unlike existing starter motors. The reason is that the conventional starter motor uses a DC motor, which is much lower in efficiency than a permanent magnet (PM) motor. Second, the torque of the motor can be reduced, and the price can be reduced. Rare earths account for approximately 40% to 50% of the price of PM motors. The AISG system in this study reduces the torque burden by using a torque increase mechanism instead of reducing rare-earth use. The motor used in the AISG is a permanent magnet-assisted-wound field synchronous motor(PMA-WFSM) that includes a brush and slip ring. A permanent magnet inside the rotor core of a PMA-WFSM increases the air gap flux density and relaxes the magnetic flux saturation of the core. As a result, the torque of the electric motor can be increased and a coordinated operation with the planetary gears leads to higher performance. The effect of increasing the torque by including permanent magnets in the design was validated using finite element method (FEM) analysis. In addition, analysis of the mechanisms was performed vis-à-vis the various mechanical structures.
Brushless DC motor (BLDC) have wide operating range and can high power density and high torque. Therefore, BLDC is used in various fields such as vehicle, aviation, home appliances. However, there is a problem that a torque ripple occurs in a phase commutation section in which a current flows. In order to overcome such problems, various studies have been conducted to improve the power characteristics of the BLDC motor.
In this paper, a study on power density and efficiency improvement of permanent magnet brushless DC motor (BLDC). In general, there is a way to improve the power characteristic of the motor by increasing the main flux of the permanent magnet. Applying the halbach magnet array structure not only increase the magnetic flux, but also reduces the coreloss of the motor. Also, the inner rotor type motor has a simple radiating structure for the reducing thermal loss generated in the teeth of the motor. Therefore, it is superior in terms of reduction of thermal loss compared to the outer rotor type motor. On the other hand, outer rotor type motor has motor magnet usage than inner rotor type motor. Therefore, outer rotor type motor can improve torque and efficiency compared to inner rotor type motor for the same size. In order to verify this, the inner rotor type motor and the outer rotor type motor with the same size and power were designed. Also, the electronic and thermal characteristic of the two motors were analyzed through the finite element analysis (FEA).
Flux-modulated permanent magnet (FMPM) motors have attracted widespread attention in many applications due to the superiority of low-speed large-torque, such as the electric vehicles. In the type of motors, the flux modulation effect is the key to obtain the excellent torque performances, which realize the electric gear operation by forming the matching between the magnetic fields with high PM pole-pairs and low winding one. So in previous studies, the flux modulation effect of the FMPM motor has been the main research subject, where the performance improvements are often realized by the single design of PMs, or modulator, or winding. It reveals that the highly efficient utilization of modulation effect is an effective path to deeply explore and develop the performance potential of the FMPM motors. It is worth noting that, in motor energy conversion, the motor flux is often modulated by one time, which is inferred that the increase design of modulation times may be another effective way to improve the modulation effect utilization. In this paper, a concept of multi-flux-modulation (MFM) is proposed, and a multi-flux-modulation flux-modulated permanent magnet (MFM-FMPM) motor is designed and investigated. It contains a stator, middle PM rotor, and inner PM rotor. And the halbach-array is applied in the inner rotor to increase the PMs utilization. The key of the MFM-FMPM motor is that the MFM can be divided into three modulation combinations. One of the magnetic fields generated by the PMs in the inner rotor is modulated by the modulator in the middle rotor. Simultaneously, the other two magnetic fields generated by the PMs in the middle rotor are modulated by the stator and the modulators on the inner rotor respectively. The main harmonics in the three magnetic fields are utilized by the armature windings on the stator. With the unique MFM effect, the performances of the motor are significantly improved. Finally, the prototype is manufactured to verify the effectiveness of the MFM design and the MFM-FMPM motor.
Flux-modulated permanent magnet (FMPM) motors have attracted considerable attention due to the predominant torque performance in low speed condition. Recently, the flux modulation principle is always to be developed in diverse PM motors. Intensive study results demonstrate that the harmonics in motor airgap are abundant, and they are essentially the deliverer during the process of the motor energy conversion, which is more important for the FMPM motors. Yet, it is noted that all the harmonics are not exactly playing a driving role for energy conversion. Actually, some of the working harmonics show the negative effects in motor operation. Hence, it can be inferred that analyzing the influence of harmonics on performance objectives and distinguishing its functional effects are necessary and meaningful for achieving high performance FMPM motors. In this paper, the concept of positive and negative harmonics is proposed. The harmonics having the same speed and direction with the Pw-th harmonic (Pw is the number of pole pairs of armature windings) are considered as the positive harmonics, while the opposite case is regarded as the negative harmonics. It is noted that the positive harmonic is beneficial to the improvement of motor performances, and the negative one has the opposite effect. In other words, the more positive harmonics in the FMPM motor, the better performance can be obtained. For extensive investigation, a dual-stator flux-modulated PM (DS-FMPM) motor is selected to analyze the influence of the positive harmonics on the motor performances, the harmonic characteristics of which can be changed by adjusting the relative position between the inner and outer stators. In this paper, three representative cases of the relative positions is studied, where the main magnetic field distribution are in parallel, in series and in hybrid. The electromagnetic performance and the positive airgap harmonics of the three cases are analyzed and compared in detail. Finally, the prototype machine is built to confirm the effectiveness of the design of positive airgap harmonics and the studied DS-FMPM motor.
Brushless direct current (BLDC) motors have the advantage of power density and low maintenance cost compared to DC motors. DC motors are increasingly being replaced with BLDC motors due to low cost of driving devices and the development of control technology. In particular, outer rotor type BLDC motors have higher power density than inner rotor type BLDC motors since permanent magnets (PMs) can be used more in the former. In this type of BLDC motors, housing-integrated rotor core structure can reduce the radial size by decreasing the thickness of the rotor core due to its three-dimensional (3D) flux path. And BLDC motors with this 3D structure requires 3D analysis for an accurate prediction of their electromagnetic characteristic. Meanwhile, overhang structure is commonly used in ferrite magnets to enhance the effective air-gap magnetic flux; this 3D structure also requires 3D analysis. However, 3D analysis is time consuming, and hence, inefficient for motor design. Therefore, in this paper, we proposes semi-3D analysis techniques using two-dimensional (2D) finite element analysis (FEA), considering the 3D structures of PM overhang and housing-integrated rotor core. First, the PM overhang structure was corrected to a 2D analysis model by equating the amount of magnetic energy to the volume of the PM. In addition, to take 3D flux path of a housing-integrated rotor core structure into account, this structure was corrected to a 2D analysis model by the cross-sectional area in a tangential direction from the definition of the magnetic flux density. Finally, semi-3D analysis techniques taking into account the 3D structures of BLDC motors were performed using 2D FEA and validated by experiments. Detailed discussions and results will be presented in the final paper.
A bearingless permanent magnet slice motor(BPMSM) has compact structure and high efficiency, which can realize the rotor magnetic suspension at five degrees of freedom. Bearingless pumps have been established in applications that demand high temperature and corrosion. The extreme environment, especially the high temperature environment, will cause the PM demagnetization fault and so on. As one of the most common faults of permanent magnet motor, permanent magnet losses will cause the motor to be unable to operate normally. Therefore, a permanent magnet flux observer is proposed to ensure the stable operation of the motor.
Firstly, the mathematical model of torque and suspension forces of the BPMSM are deduced. Secondly, the temperature field distribution of the BPMSM is simulated by finite element method, and the temperature rise of the motor is calculated, and the variation law of residual magnetic field of permanent magnet rotor at different temperatures is analyzed. Thirdly, the permanent magnet flux observer is constructed, and the appropriate feedback gain is designed to improve the robustness of the observer. The correctness of the mathematical model and control algorithm are verified by Matlab/Simulink. Finally, the proposed strategy is applied to a 4kW prototype. The experimental results show that the robustness of the system is effectively improved, as well as the dynamic and static performance.
A novel axial-radial flux permanent magnet machine (ARFPMM) is proposed to improve the performance of PM machine. The ARFPMM is capable to reach higher torque density and lower cogging torque than traditional axial and radial PM machine when designed properly. To reach higher performance, T-type SMC core, reluctance rotor, and PM rotor are applied. The T-type stator core is made of soft magnetic composite (SMC) which allows 3-D flux path and plays an important role in both axial and radial flux path simultaneously. As a part of radial flux path, reluctance rotor makes full use of the radial space and produces synchronous reluctance torque. The PM rotor exists as a part of axial flux path and produces PM synchronous torque. 3-D FEM simulation costs significant time for computation. An effective method of decoupling axial and radial flux path is adopted. A 2-D FEM model is built to investigate the influence of two reluctance rotors with different structure. Comparison study is carried out between the two reluctance rotors on average torque and torque ripple. The optimum current phase angle is confirmed for the optimum reluctance rotor. Bidirectional PM skewing technique is applied to reduce the cogging torque. The influence of PM skewing mode, magnet pole-arc ratio, skew angle, and position angle is analyzed and the regularity is confirmed. Based on the analysis above, a response surface methodology (RSM) model is established, and genetic algorithm (GA) is adopt to optimize the cogging torque. A 3-D FEM model is built to verify the validity of RSM and GA. The result shows that the cogging torque is reduced by 90% compared with the initial design. The optimization results show that the ARFPMM can increase output torque by making full use of the axial and radial space. In terms of cogging torque, an optimum combination of magnet pole-arc ratio, skew angle, and position angle can be found using RSM and GA, while the other performance remain nearly invariable.
The vibration occurring in an electric motor can be largely divided into mechanical vibration due to nonaligned bearings and shafts, and electromagnetic vibration by the electromagnetic force. For existing industrial electric motors, the mechanical vibration associated with the life of the motor was the most important concern. However, in recent years, electric motors—such as the ones used for electric cars and hybrid cars—have high-torque density by using the rare-earth permanent magnet. Thus, the relative importance of electromagnetic noise and vibration is increasing. Electromagnetic vibration and noise affect people emotionally, so it has become very important to reduce vibration when designing a motor.
The electromagnetic vibration can be predicted by analyzing radial force as a vibration source when designing the electromagnetic field of an electric motor. Thus, analyzing the spatial and time harmonics of the radial force enables us to find the harmonic that most influences the vibration. In this study, the optimum design of a 8pole 12-slot IPMSM for vibration reduction was performed. The optimum design was created by analyzing the radial force and finding the design variables that affect vibration. Additionally, to verify the validity of the design results, the results were compared using an electromagnetic-vibro coupled analysis.
In this study, an analysis was made to identify the shape parameters that affect the magnetic flux density of rotor and slot relative permeance in a permanent magnet motor. Using these parameters, optimal design was performed to minimize the vibration velocity in a 8pole 12slot IPMSM initial model. As a result, vibration velocity was reduced by 5.5%. In addition, electromagnetic field-vibration interaction analysis was performed, and thus the results of the optimum design were verified.
Spoke type Permanent magnet synchronous motors (PMSM), which are superior to other PMSM in terms of output density by maximizing the surface area of permanent magnet (PM), have recently been actively studied. However, spoke type PMSM are magnetically separated by connecting each pole of the rotor core to a magnetically saturated rib or bridge. Therefore, there is a rotor structure in which magnetic potential difference may occur between neighboring poles. The magnetic potential difference between the rotor poles of such a spoke type PMSM induces leakage flux in the direction of the rotor axis. Since the leakage flux in the rotor axial direction has a component in the z-axis direction, this can be taken into consideration only through 3D analysis. This makes it difficult to analyze the performance of spoke type PMSM. Several studies have been conducted on the 3d leakage magnetic flux of the spoke type PMSM. However, in the previous studies only the axial leakage magnetic flux between the poles of the rotor was taken into consideration, and the linkage magnetic path between the rotor pole and the stator shoe via the axial direction was neglected. In this paper, we have further investigated the correction coefficient of spoke type PMSM which further improve the accuracy of 3d leakage paths as well as 3d linkage ones.
Nowadays, hybrid electric vehicles (HEVs) have been employed and developed extensively for promoting the rapid development of resource-conserving and environment-friendly society. Due to the multi-mode operations of the HEVs, the high integrated electric drive system with the motors which features the high torque density, high efficiency, and wide speed range are becoming the main trend in the HEVs. In this paper, a partitioned-rotor and staggered-stator hybrid excited flux switching permanent magnet（PS-HEFSPM）motor is proposed for hybrid vehicles, in which the air-gap field can be easily controlled.
The PS-HEFSPM motor consists of 12-stator and 10-rotor poles, in which the NdFeB permanent magnets and the DC field windings both serve as magnetic excitation sources. The partitioned rotor consists of two parts of inner and outer portion, which are connected together by an end disc to realize the same operating speed. The adoption of this unique partitioned rotor configuration effectively obtains the high torque density and avoids the stator flux leakage. Furthermore, the staggered stator of the proposed motor includes two salient pole parts staggered at a certain angle on the circumference, as well as the 12-rectangular magnetic bridges which connect the two salient pole parts in radial direction. The merits of this new stator structure are forming series magnetic circuit which runs through two rotors smoothly and creating space for the field windings which are wound around each rectangular magnetic bridge to fulfill the flux-adjusting function by controlling and changing the polarity and amplitude of the field current.
Firstly, the operation principle of the PS-HEFSPM motor is introduced and the initial design parameters are given. Then, in order to improve the flux regulation capability of the motor, the leading parameters are optimized by multi-objective optimization method. Moreover, the basic electromagnetic performances including back-EMF, torque, as well as torque–speed and power–speed characteristics are analyzed by 2D-FEA. Thereafter, it shows that after the targeted optimization design, the flux regulation capability reaches a high level, which meet the application requirements.
This study shows the novel rotor shape of the spoke-type PMSM for a washing machine to improve power and widen operating range by changes of inductance in the rotor and air gap. Applying a new shape to the rotor results in an inductance change in some areas of the rotor in which low magnetic flux density existing, which in turn changes the magnetoresistance in the air gap. As the inductance changes, the inductance of the rotor d-axis decreases and the q-axis inductance increases to improve the reluctance torque. We investigated to maximize the reluctance torque and air-gap magnetic flux density with a novel rotor shape. In other words, low magnetic flux density area which help rarely torque increase was subtracted. In addition, it also can extend operating range as the saliency is maximized. The Finite Elements Method analysis results show that the back-electromotive force decreases as the saliency increases. As a result, the maximum speed range of the designed motor can be widen and it is applicable to the motor requiring high speed range. For instance, washing machine needs high speed motor in dehydrating mode to remove moisture from clothes.
It is contrast to the common technologies that increasing coil turn for power improvement results in increasing back-electromotive force. Accordingly, it was confirmed that average torque improves as some area of rotor where magnetic flux density is low, was removed. A prototype has been manufactured and is now being under experiment. The results of power improvement and operating range widened will be compared and verified.
Our group has been conducting various studies of high-temperature superconducting induction/synchronous motor (HTS-ISM) for next generation transportation equipment. The HTS-ISM has various advantages, such as co-existence of synchronous and slip rotation modes, high efficiency for variable speed control, high torque density. For the HTS-ISM with copper stator winding, the torque density and efficiency are limited, because of limited current density and large copper losses. In order to achieve higher torque and efficiency, the fully HTS-ISM with superconducting stator winding should be developed.
In this paper, different stator winding structures of a 50kW fully HTS-ISM are studied and compared. Since the distributed winding is difficult to be realized, due to the limitation of bending diameter and mechanical strength of HTS tapes, the conventional concentrated winding and proposed toroidal winding are compared. Firstly, the current transport property of the HTS tape based on the different flux density is measured. Finite Element Analysis (FEA) simulations with different winding structures are performed. The results show the toroidal winding can achieve higher torque and lower torque ripples. Moreover, because of the magnetic mirror image effect, the perpendicular component of flux density HTS tape for toroidal winding is much lower than that of conventional concentrated winding. It demonstrates that the toroidal winding can improve the current transport property of HTS tapes. The detailed results will be shown and discussed.
This work has been supported by Japan Science and Technology Agency under the program of Advanced Low Carbon Technology Research and Development Program (JST-ALCA) in Japan.
Due to the high thrust density and operational speed, superconducting linear synchronous motor is considered a favorable propulsion system for high-speed ground transportation. Korea Railroad Research Institute (KRRI) has researched on high-Tc superconducting linear synchronous motor (HTS LSM) to develop new high-speed transportation of which speed is over 500 km/h. As a feasibility study for HTS LSM, we developed a small-scale prototype HTS LSM and evaluated its operational performances. The design scheme of prototype was focused mainly on testing the thrust performance of HTS LSM. The HTS electromagnet consists of 2-pole HTS coil, which was developed with GdBCO tape in single cryostat vessel. To enhance self-quench protection, the HTS coils were fabricated with non-insulated windings. The rating magneto-motive force of each HTS coil was designed to be 320 kAt at the operating temperature of 20 K. And the prototype was designed to generate about 3 kN in the maximum thrust at the given operating condition. We confirmed these performances by carrying out static operational tests. This paper describes design process, fabrication and evaluation results of the prototype HTS LSM.
Axial flux permanent magnet machines (AFPM) are being increasingly used in a great of industrial applications e.g. the electrical vehicle and wind generators, due to its very compact structure and high torque density. The single stator and single rotor configuration is the basic structure of axial flux machine. For AFPM the fractional slot concentrated winding and surface mounted PM structure is normal adopted. To increase the speed adjust range of AFPM, a new mechanical flux weakening adjuster is proposed in this paper. In additional to the traditional stator core and rotor core, the proposed new mechanical flux weakening adjuster is located on the outside of the stator core. The mechanical flux weakening adjuster can be rotated with a determined degrees, and the main magnetic flux can be adjusted. The operation principle of proposed AFPM is similar to the traditional AFPM and the only difference is the adopted mechanical flux weakening ability. Compared with the traditional flux weakening method, the inductance can be regulated as well during the main magnetic flux adjusts process in this new AFPM. As a example, when the d-axis current equals zero method is used in this machine, then the more torque can be achieved when it operates in the high speed range. In this paper, the operational principle has been explained and the power equation has been deduced for the initial dimension design. The main dimension of the machine will be optimized to achieve higher output torque and wider constant power adjust range. The main parameters and performance will be calculated by using the finite element method (FEM).
Superconducting tape-based stacks used as trapped magnetic flux magnets in electrical machines are subject to an AC-demagnetizing field. This study provides analysis of trapped flux and demagnetization of several stacks’ architectures for electrical machines applications. This work is an application-driven enhancement of a previous study on stacks architecture in regards of trapped flux profile and uniformity for applications requiring uniform magnetic field over a large area [1,2].
The trapped field and demagnetization of several stacks’ architectures made of SuperOx tapes were investigated. Using the same magnetizing field and the same number of tapes, rearranging the architecture of stacks was found to have an effect on the current density distribution, the trapped flux and the demagnetization. The electromagnetic time-dependent finite element model has been used; the latter implements the power law that takes into account field dependency of the superconductor critical current density and the power law exponent, n, at liquid nitrogen temperature interpolated from experimental characterization data.
Experimental measurements on some of the modeled architectures have been carried out to check the viability of the numerical models.
 T. B. Mitchell-Williams, A. Patel, A. Baskys, S. C. Hopkins, A. Kario, W. Goldacker, B. A. Glowacki, Towards Uniform Trapped Field Magnets Using a Stack of Roebel Cable Offcuts IEEE Transactions on Applied Superconductivity, 26 (3) 6800404 (April 2016)
 T B Mitchell-Williams, A Baskys, S C Hopkins, V Kalitka, A Molodyk, B A Glowacki and A Patel, Uniform trapped fields produced by stacks of HTS coated conductor tape, Superconductor Science and Technology, 29 (8) 085008 (16 June 2016)
This research is financially supported partially by the European Union’s Horizon 2020 research innovation programme under grant agreement No. 7231119 (ASuMED “Advanced Superconducting Motor Experimental Demonstrator”) and also by EPSRC grant No. EP/P000738/1 entitled “Development of superconducting composite permanent magnets for synchronous motors: an enabling technology for future electric aircraft”.
Flux reversal permanent magnet machine (FRPMM) is a special kind of permanent magnet machine with the permanent magnet (PM) installed on the stator side and there is no winding or PMs on the rotor side. Claw pole machine (CPM) is a special kind of transverse flux machine (TFM), with the adopted claw pole teeth, the torque ability and power factor of CPM can be even higher than those of TFM. Combing above two machines, this paper proposes a novel flux reversal claw pole machine (FRCPM) with soft magnetic composite (SMC) cores, the proposed FRCPM has both the advantages of flux reversal permanent magnet machine (FRPMM) and claw pole machine (CPM). Specifically, with the permanent magnets (PMs) are surface mounted on the surface of stator claw pole teeth with a determined pattern, the FRCPM can operate based on flux reversal principle. As the adopted winding is global ring winding and 3D magnetic flux stator core structure is similar to the CPM’s, the FRCPM is operated based on magnetic flux characteristic of the CPM as well. Therefore, the FRCPM can be operated under relatively high rotate speed since there is no winding or PMs on rotor, and the weak PMs, ring winding and SMC stator cores are encapsulated together as a whole part. Moreover the adopted 3D magnetic flux path can bring FRCPM with relatively high torque ability, and the adopted SMC cores can bring FRCPM with low core loss at the high speed operation. The operation principle of FRCPM is explained, the power equation is deduced for obtaining the initial design, and the main dimensions are optimized to ensure the developed FRCPM can have good performance. The main electromagnetic parameters and performance of FRCPM are obtained based on using the 3D finite element method (FEM).
The objective of this paper is an analysis method for traction motor which targeting to electric bus and trailer. The type of the studied motor is IPMSM(Interior Permanent Magnet synchronous motor) which has delta type magnet topology of the rotor. It is possible to maximize reluctance torque and output characteristics by arranging the permanent magnet arrangement of the rotor in delta shaped.
Conventionally the two main methods for analyzing electrical machines include magnetic equivalent circuit(MEC) and finite element method(FEM). Whereas FEM is a very accurate yet computationally expensive method, the MEC method has the advantage of faster calculation speed and more feature variables can be considered. Therefore, it can be combined with optimal design algorithms. However, its main disadvantage is the poor accuracy of characteristics analysis as there are many considerations when using MEC method.
Because IPMSM operates in magnetic saturation region, the magnetic saturation characteristics of the iron core are nonlinear and the change in operating current is significant. In addition, because it is a method of expressing a motor with a few lumped constant circuit, there are many errors and more circuit constant or correction factors should be used to solve them. For the above reasons, it is difficult to analysis the motor using the conventional MEC method. To compensate for the inaccuracy of the conventional MEC method without taking into account the magnetic saturation, this paper will show an active MEC analysis method which actively changes according to saturation conditions. It will be implemented as an active function to segment the magnetic equivalent circuit in the rotor’s saturated area into variable resistance, so that it is actively set up according to the load. This will allow to increase accuracy and reduce costs and time. Method will be verified by comparison with FEM and conventional MEC method.
Low-speed and high-torque permanent magnet motors (LSHT-PMM) are widely used in many industrial fields. Due to the inherent characteristics, the outer diameter of the LSHT-PMM is large. Therefore, in order to make full use of the internal space of the motor, a double stator structure is proposed in this paper. In order to reduce the amount of permanent magnets (PMs) and reduce the cost, a PM and reluctance hybrid rotor is proposed. The proposed hybrid rotor structure is a combination of a magnetic barrier reluctance rotor and a permanent magnet rotor which are embedded on the inner and outer sides of the magnetic isolation ring respectively. The proposed rotor not only has the advantages of a PM assisted reluctance rotor, but also makes the design method more flexible due to the structures of PM and magnetic barrier reluctance relatively independent. In this paper, the electromagnetic design method of the proposed LSHT-PMM is studied in detail. Firstly, in order to determine the stator design, the different winding connection modes, slot-pole combination and winding distribution of the inner and outer stators are compared and analyzed. Secondly, in order to design the novel rotor, the influence of the relative position between the magnetic barrier and the PM, the shape of PM, the width and the number of the magnetic barrier rotor on the electromagnetic performance of the proposed LSHT-PMM are studied based on the field-circuit coupling method. Finally, the correctness and rationality of the designed motor are verified by the simulation and experiment. This work is supported by the National Natural Science Foundation of China under Grant 51877139.
Our group has been developing a High Temperature Superconducting Induction/Synchronous Motor (HTS-ISM) for highly efficient transportation equipment. So far, the 20 kW class prototype, which consists of BSCCO rotor and copper stator, has already been developed and shown its excellent characteristics based on experiment and analysis. Furthermore, the 50 kW class model, in which both the rotor and the stator are made of BSCCO superconducting tapes, has been fabricated, and various characteristics have been evaluated.
In order to realize a practical HTS-ISM drive system, not only the HTS-ISM but also peripheral devices such as an inverter and a refrigerator must be investigated. Furthermore, the cooling characteristics during drive condition is really important.
In this paper, we have developed a multidisciplinary analysis method which couples the nonlinear voltage equation, the motion equation and the thermal equivalent circuit. We performed a multidisciplinary analysis for starting and variable speed controllability of a 50 kW class fully HTS-ISM. We consider the standby mode temperature (stationary mode) at 110 K and drive temperature (operation mode) at 80 K. We showed that the nonlinear resistance of HTS stator winding should be considered in the voltage equation to express exact performance of the HTS-ISM. We also clarified there exists optimal waiting time before motor operation when the cryocooler is in higher temperature stand-by mode. These results would be very important for the achievement of highly efficient HTS-ISM system for transportation equipment.
This work has been supported by Japan Science and Technology Agency under the program of Advanced Low Carbon Technology Research and Development Program (JST-ALCA) in Japan.
Transformer is important in power system. No-load loss and apparent power of amorphous alloy transformer core change obviously with temperature. Moreover, the inner temperature varies in large scale. At present, little research has been done on no-load loss of amorphous alloy cores with temperature change. Therefore, it is very important to study the no-load loss at different temperatures.
In this paper, three amorphous alloy cores of different strips are designed and manufactured based on measuring platform and scaled-down transformer core model. Measurements were carried out in the same temperature control box within range of 10-110℃. Measurements were made every 10℃from 10 ℃. When the inner box temperature reached set temperature and it was maintained stable for 10 minutes, measurements were then made after internal temperatures of amorphous alloy cores were in consistence with externals. The no-load loss and apparent power were measured respectively within 0.05T-1.4T magnetic density, meanwhile, the induced voltage and excitation current waveform were recorded.
Temperature changes may have certain effects on loss characteristics of the three types of amorphous alloy core models. When magnetic density is not saturated, as core temperature increased, the active power loss decreases by 6%-10%, and the apparent power will be reduced by about 5%. Within standard-operating magnetic density, as core temperature increases, the active power loss of core decreases by 4%-5%, while the apparent power increases by 4%-7%. When the magnetic density is supersaturated and the temperature rises, the active power loss is basically unchanged, at this point, an irregular state emerged. However, the apparent power will increase by more than 50%. Hence, the temperature change has evident effects on apparent power of amorphous alloy cores under supersaturated magnetic density.
Fully turboelectric propulsion systems with lightweight and high power density are one of the solutions to realize future electric aircrafts. Our research group started to develop 10 MW fully superconducting synchronous generators and 2 MW motors. In this system, we designed so that the generators supply electric power at the voltage of 6.9 kV, however, the motors operate at the low voltage of a few kV. Therefore, a 6.9 kV-10 MVA step-down transformers with lightweight are required for this system. In our previous studies, a 66/6.9 kV-20 MVA superconducting transformer with REBCO superconducting tapes was developed. The low AC loss was realized by using multifilamentary REBCO tapes which were made by laser-scribing technique and parallel conductors in which REBCO tapes were stacked and transposed. The target of this study is to realize superconducting transformers with a power density over 20 kW/kg. Firstly, the structure of the superconducting transformer was assumed as an inner iron double concentric windings type. When one-turn voltage is 23 V/turn, the three-phase superconducting transformer becomes the most lightweight design of around 200 kg. Next, the optimum transposition patterns for parallel conductors which were applied to the windings were investigated to realize uniform current distribution among the tapes and low AC loss. The AC loss was calculated by using JMAG (electric instrument analysis software of JSOL). The detailed properties and design specifications of superconducting transformers will be reported in this conference.
This research was partially supported by the New Energy and Industrial
Technology Development Organization (NEDO), the Japan Science and
Technology Agency (JST): Advanced Low Carbon Technology Research and
Development Program (JPMJAL1405) and the Japan Society for the Promotion
of Science (JSPS): Grant-in-Aid-for Scientific Research (JP18H03783 and
Insulation materials have different electrical characteristics according to temperature and voltage frequency. These characteristics are very significant factors for the insulation design of high voltage power apparatus. Since there are not always consistent overvoltages, it is necessary to ensure the dielectric strength against various overvoltages. In particular, high voltage power transformers can be exposed to overvoltages of very high frequency components caused by external switching operations and lightning strokes, which can lead to dielectric breakdown. In addition, in order to develop a superconducting power transformer, the insulation characteristics of material for these overvoltages should be reliable in a cryogenic environment. However, researches on non-standard impulse overvoltages are limited. In this paper, lightning and switching impulse dielectric breakdown experiments were performed to analyze the effect of overvoltage frequency on dielectric strength. In order to make different oscillation frequencies of the impulse overvoltages, the front time was set differently by adjusting resistors of impulse generator. Nomex paper used as conductor insulation for power transformer were tested in liquid nitrogen using two electrode types. Uniform electric field electrodes are composed of two same cylinder shaped materials. Turn to turn electrodes were composed of varying the number of Nomex paper layers. The difference of dielectric breakdown characteristics between lightning and switching impulse was analyzed by varying the front time and oscillation frequency. From the experiments, we have confirmed that the insulation properties of dielectric material are different depending on the type of front time, oscillation frequency and overvoltage source.
Residual ﬂux of the power transformer will accelerate the magnetization saturation of transformer core and generate high transient inrush current. Generally, the peak value of inrush current generated by residual flux in the core can reach 6-8 times of the rated current, which endangers the mechanical stability and insulation strength of the power transformer windings and destroys the normal operation of the power system. Therefore, the study of residual ﬂux in the power transformer has considerable signiﬁcance, especially when the residual ﬂux cannot be directly measured. The point-on-wave control methodology is proposed to control switching for the re-energization of a transformer. However, this method does not accurately measure the residual ﬂux, and the switch-on instant is difﬁcult to control. Another method uses the fluxgate sensors to measure the residual flux in real time, but this method is costly and has errors brought by the additional fluxgate sensors.
To overcome the shortcomings of the existing methods, this paper proposes a method for analyzing and detecting the residual ﬂux, based on the nonlinear magnetizing characteristics of the core. A model of single power transformer core is built to simulate transients in MAGNET software. By analyzing the transient current of the measured coil under applying positive and negative DC voltage to the measuring coil of the toroidal transformer, the direction of residual ﬂux can be determined and the relationship between residual ﬂux density and the magnetizing transient current can be obtained. Finally, the experimental results show that the proposed method can effectively determine the direction and accurately measure magnitude of the residual ﬂux. According to the measured magnitude and direction of the residual ﬂux, the demagnetization data of the toroidal transformer is set to effectively weaken the residual ﬂux and reduce the inrush incurrent.
Conductor on Round Core (CORC®) cables with scalability, flexibility, strong mechanical strength and high current density are of large potential for different power applications. In this paper, CORC® Cables are proposed to be the secondary winding for superconducting fault current limiting transformer (SFCLT). In order to evaluate the working performance of CORC® cable in SFCLT, firstly, a 60cm-long CORC® short sample is fabricated, fundamental parameters including self-field critical current and room temperature resistance are measured by experiments. Then, so as to represent the real working condition, both rated current tests and overcurrent tests are carried out to the CORC cable, respectively. In rated current test, AC loss and current uniformity are used as key parameters to evaluate the performance, discussions are investigated by both experimental and numerical method. Meanwhile, in overcurrent tests, the recovery-under-load (RUL) capability is used an important evaluation parameter. Because the RUL capability shows the uninterruptible power ability of the power system with SFCLT. Conclusions obtained in this paper can verify the feasibility of this technique and also provide useful information for future SFCLT applications.
Abstract: Based on the finite element method (FEM), a simulation model of a single-phase HTS transformer was established according to a developed HTS transformer, and the simulation results are in good agreement with the experimental data. On this basis, a 120kVA/6kV single-phase HTS transformer was designed, the primary windings were solenoid coils consisted of 8 helically wound layers, and the secondary windings were consisted of 13 double pancakes connected in parallel with 9 layers. The current distribution in windings, magnetic field and stress analysis under rated working condition and in fault were simulated. The results are important to the design of HTS transformer.
Keywords: HTS transformer, wingding, current distribution, magnetic field, stress
Traction transformers are key components for the Chinese high speed train system, and it is hoped that a superconducting version will replace oil-based conventional transformers in this application. Since 2018 Beijing Jiaotong University has been leading a six partner project, funded by the Chinese Ministry of Science and Technology (MOST), to develop a 6.5 MVA HTS traction transformer. The transformer consists of four single-phase 25 kV/1.9 kV HTS windings, operating at 65 K, each of which drive a motor. The rated currents for each of the HV (high voltage) and LV (low voltage) windings are 63 A and 846 A, respectively. The HTS transformer should demonstrate improved performance, achieving 99% efficiency and 3 tonne total system weight. Minimization of AC loss in the HTS windings is critical to achieve both efficiency and weight targets; the weight of the cooling system scales directly with AC loss.
Despite this improved performance, the cost of the HTS windings is critical for commercialization of the HTS traction transformer technology. Wire costs can be minimized without significantly increasing AC loss by using hybrid windings: the end-part of the windings is wound with high-cost and high-performance wire/Roebel cable; the central part of the windings is wound with low-cost and low-performance wire/Roebel cable.
We report H-formulation 2D axisymmetric FEM AC loss simulation results on hybrid structure HTS windings with both HV and LV windings wound with REBCO coated conductors. The simulation uses measured Jc(B) curves at 65 K for each conductor. The HV windings utilize 4 mm coated conductors and LV windings utilize 8/5 Roebel cables assembled using Roebel strands from 12 mm conductors. Both windings have a hybrid structure in order to reduce the wire cost. Flux diverters are placed at the end of the windings to reduce AC loss. AC loss values in the HTS transformers with the hybrid structure are compared with HTS transformers with non-hybrid structures and the feasibility of the hybrid winding structure is discussed.
When a large power transformer is switched on, the residual flux in the iron core may cause inrush current, which may cause the transformer to no longer be put into operation, thus affecting the continuity of power supply in the power grid. However, the traditional methods can only estimate the residual flux. It is impossible to effectively weaken the residual ﬂux. Therefore, the study of residual ﬂux in the closed magnetic core of a power transformer has considerable signiﬁcance.
This paper describes a novel method for analyzing and detecting the residual flux, based on externally applying multiple positive and reverse excitation. This method can accurately measure the residual flux of iron core without damaging the transformer itself and can be extended to the residual flux analysis of three-phase transformer.
A model of single phase transformer core is built to simulate transients in COMSOL software .Under the same residual flux, different current responses will be generated when the external positive and reverse excitation is applied. Under different residual flux, different current responses will also be generated when the same external excitation is applied, the experimental results show that the proposed method can effectively determine the direction and accurately measure magnitude of the residual flux. Moreover, according to the measured magnitude and direction of the residual ﬂux, the demagnetization data of the transformer is set to effectively weaken the residual flux.
Measurements of residual flux for a simple laboratory setup verified that the simulation gave reasonable values.
This paper is a the fault current limiting characteristics of superconducting fault current limiter due to three phase ground fault in power system.
In this system, two superconducting elements are connected to a-phase and c-phase respectively, and a transformer type superconducting fault current limiter is proposed to limit the fault current in case of a ground faults.
In order to measure the fault current limiting characteristics of the proposed superconducting fault current limiter, b and c phases were connected and short - circuit simulations were carried out using the quench characteristics of the superconducting elements.
we compared and analyzed the peak current and the instantaneous power load characteristics with the integrated three phase superconducting fault current limiter.
The distributed power generation has increased due to the development of the electric power industry and the active generation of renewable energy. This causes a large increase in the fault current when fault occurs, which exceeds the capacity of the existing protective device. Thus it creates a risk of shutdown failure. The superconducting fault current limiter (SFCL) has been demonstrated by previous studies that one of the effective methods to limit the fault current. Installation of the SFCL is expensive, but it is more reasonable than replacement of existing protective equipment.
In addition, the superconducting fault current limiters studied in many cases are often designed as single phase, and when applied to three phases, three single phase superconducting fault current limiters are installed. In this case, at least three superconducting modules are required.
In this paper, the double quenching SFCL using E-I three-phase transformer core is proposed. The proposed superconducting fault current limiter is designed as three phases and has a similar fault current limiting effect to that of existing superconducting fault current limiters by using a small number of superconducting modules compared to existing ones. The primary side of the three-phase transformer is connected in series with the power system, and the secondary side is connected to the superconducting module. In the fault case, the single-quenching or double-quenching operation is performed depending on the magnitude of the fault current. In this paper, the operation characteristics of the proposed double quenching SFCL using E-I three-phase transformer core are analyzed through the experiments.
A Wireless Power Transmission (WPT) system for a railway vehicle has been investigated to reduce the greenhouse gas emissions in a diesel vehicle. However, the WPT system is required to transmit the electric power of several hundred kW in a short time while the railway vehicle is stopping at a station. Since there are power converters and control devices under the floor of the railway vehicle, the coil space for the WPT system is limited. Therefore, when high power is transmitted to the coils installed in a limited space, eddy current loss generates in the coils and rails, and a long time coil operation becomes difficult due to the coil heat generation. Therefore, it is required to reduce the losses in the coil and the rails and lower the operating frequency. Since a copper coil using Litz wire has low current density, it is difficult to increase the number of turns of the coil in the limited space. Since the quality factor of the copper coil decreases with decreasing the operating frequency, it is difficult to suppress the coil heat generation by decreasing the operating frequency. Therefore, we investigated an HTS coil structure suitable for high-power transmission in a short-time in a WPT system. A high-quality factor was obtained in the WPT system using the HTS coils even at the frequency region around 1 kHz. It was found that the reduction of the current load factor was particularly important for the high-power transmission in a short time because the AC loss in the HTS coil strongly depended on the current load factor. Considering this point, we were able to realize the high-power transmission in a short-time at the low-frequency region around 1 kHz in the WPT system with the HTS coils composed of parallel conductor with wide tapes.
45 T is the highest continuous magnetic field available to the scientific user community, and this now since practically 20 years. We address the question of how to access the next level, defined as 60 T, with a hybrid magnet. The outsert, wound from low-temperature superconductors (LTS) will generate the highest field possible: 18 - 20 T in a 1 m bore. For the inner part, two approaches are investigated: a high-power resistive magnet or a combination of a resistive insert magnet and a “midsert” magnet employing high temperature superconductors (HTS). First rough estimates suggest equal field contributions of 20 T from the LTS outsert, HTS midsert and the resistive insert. We have then investigated of how to optimize dimensions and field contributions from the three subsystems under the primary constraint of actual feasibility and investment cost. Additional constraints are: a) current density and stress levels of the outsert conductor including its reinforcement, b) conductor and coil winding options and their maturity confidence for the midsert and c) stress level, power density, and available power for the insert. For insert and outsert a large basis of experience exists, from which reasonable extrapolations can be made with sufficient certainty. This is not the case for the HTS coil, where important decisions have to be justified, such as conductor type and its reinforcement, nature of insulation and winding techniques. Conductor cost reduces in our optimization routine the HTS contribution to a minimum; however, progress in HTS magnet technology and projected cost reductions are impressive and included in our estimations. The results of our detailed magnet design and optimization calculations indicate that it is feasible to build a 60 T hybrid magnet of rather compact dimensions with a maximum total magnet height of 1.3 m and an outer diameter of only 1.8 m. Distinct, feasible developments of the HTS and LTS conductors and resistive magnet technology have been defined. We propose a novel method, the fast ramp-down of the resistive insert, to safely protect the HTS midsert by quenching it globally and instantaneously.
Index Terms— Very high field magnets, Hybrid magnet, Large bore LTS and HTS magnets, Resistive magnets.
A 100 T pulsed magnet of triple coils was developed in WHMFC in 2018, the outer coil was powered by a 100MJ/100MW pulsed generator, and the middle and inner coils are energized by capacitor banks. The inner and middle coils are made of CuNb wire, and copper wire for the outer coil, the outline size of the magnet is 800 mm in O.D. and 1200mm high. The magnet failed at about 83 T during test, however, the magnet does not blow up and still remain intact after failure. All the current of the positive and negative ends for the three coils were measured, the experimental results show that the current of the positive end does not equal that the negative end for both middle coil and outer coil, and the difference between positive and negative ends of middle coil equals that the difference of both ends of the outer coil. This means electrical breakdown happens between the middle coil and outer one in lateral direction. It was found that indeed there was a breakdown path between the outmost layer of middle coil and the inner-most layer of outer coil after the magnet being disassembled and cut open. Moreover, many places of the windings of middle coils were burned and some part of windings fractured, and windings even penetrated into the reinforcement in some place. The magnet broke in a relative low field, and the stress may not be the primary reason. The reasons for the magnet failure are complicated, it may be the overvoltage, or defective conductor and structural instability like buckling, and all this will be discussed in this paper.
The Dresden High Magnetic Field Laboratory (HLD) is a pulsed-field user facility which provides external and in-house researchers with the possibility to perform a broad range of experiments in pulsed magnetic fields . Being a member of the European Magnetic Field Laboratory (EMFL), HLD receives more than 100 scientific proposals annually.
The Dresden High Magnetic Field Laboratory operates ten experimental chambers equipped with a variety of pulsed magnets energized by two independent, modular capacitor banks with maximum stored energies of 50 and 14 MJ at 24 kV maximum operational voltage. The pulsed magnets at the HLD are subject of permanent improvements in terms of peak field, reliability, noise level, cooling time, and longevity. Detailed analysis of the magnet performance and failure scenarios are provided in this work for various pulsed magnets operating between 65 and 95 T. Furthermore, we present a triple-coil pulsed magnet design for magnetic-field experiments beyond 95 T.
We acknowledge the support of the HLD at HZDR, a member of the European Magnetic Field Laboratory (EMFL), the DFG via SFB 1143, and the BMBF via DAAD (project-id 57457940).
Ultra-high field pulsed magnets must simultaneously satisfy a number of often competing electrical, electromagnetic, structural, thermal, and economic constraints. To produce the highest field possible, nondestructive pulsed magnets are designed to operate at the limits of mechanical strength and electrical capacity of conductors. In this presentation, we will introduce a coupled multi-engineering finite element method (FEM) implemented in COMSOL TM Multiphysics package for detailed and accurate calculations of the mechanical, thermal and electromagnetic performances in entire longitudinal cross-section of the pulsed magnet. These transient FEM simulations are performed for entire pulse length and take into account the temperature and magnetic field dependencies of electrical conductivity and mechanical properties of all the materials to provide better accuracy. Application Programming Interface (API) feature of COMSOL was used to automate repetitive modeling steps to significantly reduce the necessary time to create FEM models for a pulsed magnet which may consists up to thousands of turns and insulation/reinforcement layers. Computational results for our signature 100T non-destructive pulsed magnet will be presented.
Material is a key issue for the high field magnet development. For DC resistive magnets, copper alloys with high strength and high electrical conductivity from room temperature up to 200 °C are required.
Steady high field resistive magnets developed worldwide used mainly two technologies: the Bitter and the polyhelix one. Each technology encounters material limits.
In the case of Bitter, magnets are made of thin plates (from 0.2 to 1 mm) up to 1000 mm in diameter. High performance Copper alloys with a high content of Silver (classically 18 wt.%, with a yield strength ranging between 800 to 1000 MPa and a minimum of conductivity at room temperature of 50 MS.m-1) have been industrialized by one company up to 250 mm in diameter. For the need of larger diameters, copper plates with a possible addition of a low content of Silver are proposed by different companies. They give a lower yield strength (between 400 to 450 MPa) and a higher conductivity around 58 MS.m-1. This could be a limitation when optimizing Hybrid magnets where the external superconducting windings increase the forces on the outer most Bitter as compared to stand alone resistive magnets.
For the polyhelix technology a similar limitation is existing: the forged and heat treated tubes needed for the helix magnets exhibit decreasing physical properties with increasing diameters. To overcome this problem, the LNCMI has started a R&D program in 2012 to consolidate an alternative way of production. The Cold Spray technology, classically used for repairing purposes or layer deposition, was adapted for the production of thick tubes of copper alloys. We present the results obtained on a material point of view as well as the field production that was obtained using these new products.
Copper-based conductive wires with both a high strength and a high electrical conductivity could find applications in aerospace and power engineering as well as in niche scientific applications such as materials for the production of high-field pulsed magnets. Indeed, in order to produce non-destructive fields, the coils must be wound of wires with a very high mechanical strength to resist Lorentz forces. LNCMI-Toulouse produces some of the most intense non-destructive pulsed magnetic fields in the world with a European record of 98.8 Tesla and aims at reaching more than 100 Tesla.
For several years, LNCMI and CIRIMAT have been exploring the design and preparation of novel copper-based nanocomposite wires, including the present silver nanowire-copper wires.
Silver nanowires were synthetized and mixed with a commercial micrometric copper powder. Samples containing 1, 5 and 10 vol.% silver were prepared. Copper and silver-copper cylinders (diameter 8 mm, length 33 mm) prepared by spark plasma sintering the corresponding powders serve as precursors to wire-drawing. The diameter of the cylinders is reduced by wire-drawing at room temperature, in several passes, thus producing progressively finer wires (diameter in the range 1-0.2 mm).
The copper grains show a lamellar microstructure with ultrafine grains (200-700 nm for a 0.5 mm diameter wire) elongated over several micrometers. The silver nanowires are dispersed along the grain boundaries of copper.
The electrical resistivity and tensile strength were measured at 293 K and 77 K. The tensile strength for the composite wires is more than twice the value measured for the corresponding pure copper wires. Interestingly, the wires containing only 1 vol.% silver offer the best combination of high strength (1100 ± 100 MPa at 77 K) and low electrical resistivity (0.50 µΩ.cm).
Thus, the present 1 vol.% silver-copper composite wires compare favorably with silver-copper alloy wires containing about 20 times more silver.
A design study started in 2014 at CERN for a Future Circular Collider. A new 100 km ring-tunnel for the collider magnets is foreseen as well as new particle detectors to probe electron-positron (ee), electron-hadron (eh) and hadron-hadron collisions (hh). A conceptual design report is due in 2019 for all FCC collider and detector options. Baseline designs for the various Detector magnets were developed.
For FCC-ee detectors two variants were defined: (1) a 7.6 m bore and 7.9 m long classical 2 T / 600 MJ superconducting solenoid surrounding the calorimeter; and (2) a very challenging 4 m bore, 6 m long, ultra-thin and radiation transparent 2 T / 170 MJ superconducting solenoid surrounding the tracker only.
In the case of the FCC-eh, the detector solenoid is combined with a dipole magnet for guiding the electron beam in and out the collision point. This detector comprises a 3.5 T / 230 MJ, 2.6 m free bore and 9.2 m long superconducting solenoid.
Demanding is the FCC-hh detector featuring a 14 GJ magnet system of three series connected solenoids, comprising a 4 T superconducting main solenoid with 10 m free bore, 20 m long, in line with two 3.2 T superconducting forward solenoids with 5.1 m free bore, 4 m long.
A quite challenging family of detector magnets has been proposed that need further engineering in the years to come. However, the conductor technology is essentially the same in all solenoids, using Ni doped and structurally reinforced pure Al stabilized NbTi/Cu strands based Rutherford cables, conduction cooled solenoid windings, almost entirely comprising high yield strength Al alloy. A survey of the various magnets is presented and the engineering challenges highlighted, in particular focusing on superconductor requirements and structural aspects.
The magnet system of the Muon to electron (Mu2e) experiment at Fermilab consists of three solenoid magnets: the Production Solenoid (PS), the Transport Solenoid (TS), and the Detector Solenoid (DS). The S-shaped TS contains 52 coils grouped into modules, which are typically 2 coils shrink fitted into Al shells. These modules are further grouped into units made of 1-3 modules. As part of the acceptance process for these units, the magnetic center of all coils and critical dimensions of the Al shells are measured. The magnetic model is updated with these as-built values to ensure the magnetic requirements for the experiment are met. In addition, units are tested to 120% of nominal current at liquid helium temperatures to study quench performance and splice resistance. Results from the first units will be presented.
The ALPHA-g experiment at CERN aims to be the first-ever to precisely weigh antimatter under Earth’s gravity, by “dropping” antihydrogen atoms with a magnet system. The anti-atoms are initially confined inside a vertical octupole and between two end cap coils. The currents in the coils are then gradually decreased to release the anti-atoms. The up -down balance of the escapes depends on gravity and the relative strength of the coils. By observing the escapes at different coil balances, the weight of antihydrogen is determined.
Achieving our first target of 1% precision in weight requires controlling the measurement field to an unprecedented 10 ppm precision. A sophisticated dual-cryostat magnet system is constructed for this purpose. An inner wet cryostat contains five octupoles, 22 coils and two solenoids (2 m overall height, 48 mm I.D.), and an outer dry cryostat contains a human-sized, shielded solenoid (2 m height, 600 mm I.D.). The centre of the system is used for gravity measurement, while other parts are used to confine, manipulate, transfer and cool the anti-atoms and their constituents. The octupoles and mirror coils are made to high precision at BNL by CNC wire-laying with active correction. The location, geometry and wire stock of each winding and its associated leads and splices are carefully designed using simulation to minimise field error. Wire placement inaccuracy and mechanical deformation of the windings are taken into account. Persistence effect is studied and mitigated by minimising the amount of superconductor, constructing an up-down symmetric magnet system, and using a special high-filament count NbTi cable. Higher-order corrector windings are constructed around the measurement region to provide additional field-shaping flexibility. A DCCT-based, bi-polar PID current control system is used to power the windings with < 10 ppm current precision. An environmental field-cancelling system is planned.
The MADMAX (MAgnetized Disc and Mirror AXion) project is a dark matter experiment that aims at finding axion particles with masses in the range of 100 µeV. In order to achieve this goal, the chosen approach is to use a detector comprised of many magnetized dielectric discs put in parallel in front of a mirror. The relevant level of magnetic induction needed to increase the probability of detecting axions is expressed by physics laws as the square field integral over the disc surface, and fixed at a Figure Of Merit of 100 T²m² over an axial length of 2 meters. In the framework of an innovation partnership with the Max Plank Institute, CEA proposed a conceptual design for a large NbTi dipole creating a field of 9 T in a warm bore of 1.3 m in diameter. This paper will give an overview of the magnet main features. First, the technical specifications, constraints and strategic choices are introduced. Then, the overall design approach is described including magnetic, mechanics, cryogenic, conductor and quench studies. Finally, technological aspects, development plan and cost optimization will be discussed.
Searching for axion like particles is one of the top priorities in particle physics. Using helioscopes is a promising technology to detect solar axions. The conceptual design of the state-of-the-art facility, the International Axion Observatory (IAXO), has resulted in a 22 m-long / 660 MJ stored energy, toroidal magnet system comprising 8 racetrack coils. In order to ensure readiness of the technology required for IAXO, a smaller scale but fully functional 10 m-long twin bore demonstrator called BabyIAXO is prepared for construction in the early 2020s. Similar to IAXO, the two magnet bores have to point to the Sun and thus to rotate $360^\circ$ horizontally and $\pm25^\circ$ vertically. The 50 MJ detector magnet of BabyIAXO is based on a common-coil layout, comprising two flat racetrack coils of 10 m length spaced by 0.8 m. Using Al-stabilized Rutherford cable with 8 NbTi strands of 1.4 mm diameter, the system can operate at 9.8 kA nominal current with 2 K temperature margin, while producing 2.0 T in the center of detection bores and 3.2 T peak field. The magnet operates in persistent mode by using a thermally activated switch made of NbTi/CuNi matrix wire. The current leads are ‘over-current’ designed in order to reduce associated heat loads during short charging and long idle periods at full current. Uniquely, a group of two 1-stage GM and three 2-stage PT cryocoolers is used for precooling and maintaining 4.5 K in the coils. In addition, two cryocirculators are used to transfer efficiently the available cooling capacity to cold mass, thermal shield and current leads. While using completely ‘dry’ cooling conditions, this cryogenic setup ensures cooling down the 15 t cold mass in 18 days. The relevance of design, construction and operational experience gained with BabyIAXO for a fully fletched IAXO system is further discussed.
The Precision Experiment on Neutron Lifetime Operating with Proton Extraction (PENeLOPE) will use a large superconducting multipole magnet to trap ultracold neutrons. To achieve this, a large volume of 750$~$L needs to be enclosed within a steep magnetic-field gradient of at least 2$~$T, requiring a unique multipole arrangement with a high current density of 316$~$A/mm$^2$ and thin support structures. Additionally, it needs to be able to ramp within 100$~$s, so ultracold neutrons can be filled into the trap, stored, and then detected.
The goal is to measure the beta-decay lifetime of free neutrons with unprecedented precision and accuracy. The novel combination of counting neutrons surviving the trapping period and detecting protons from neutron decay in situ should be able to resolve the discrepancies between previous neutron-lifetime experiments.
This presentation will cover the design of the magnet and show results of first tests at Technical University of Munich.
This work is supported by Deutsche Forschungsgemeinschaft (DFG), the Excellence Cluster "Origin and Structure of the Universe" and the Maier-Leibnitz-Laboratorium, Garching.
The design for a new approach to cable-in-conduit (SuperCIC) for use in the high-field windings of tokamaks. Two layers of high-field superconductor wires are cabled onto a thin-wall perforated center tube. An overwrap is applied and the cable is inserted as a loose fit into a sheath tube. The sheath tube is drawn down onto the cable to compress the wires onto the center tube and immobilize them. The SuperCIC is then co-wound with a high-strength armor extrusion, which is kerf-cut so that the co-winding onto a coil mandrel can be made without deformation within the armor or the CIC. Windings can be layer-wound so that the wires used in the SuperCIC for each successive layer are appropriate to the magnetic field seen by that layer (NbTi, Nb3Sn, Bi-2212). Demountable splices interconnect layers and can be configured as a split-shell toroid that accommodates assembly onto an intact plasma chamber. Optimized simulations show that a tokamak with field at plasma of 12 T could be made with winding current density ~150 A/mm2, sufficient for optimizing the fusion power density in a compact spherical tokamak.