Superconducting Magnetic Bearing Research Articles

Analysis of a passive vibration damper for high-speed superconducting magnetic bearings

Superconducting magnetic bearings (SMB) based on a combination of high temperature superconductors and permanent magnets enable the realization of self-stabilized high-speed devices with significantly reduced friction. However, external vibration might couple in the bearing resulting in large amplitude oscillations due to a resonance case. A dedicated eddy current damper (ECD) might be used to eliminate these oscillations for a stable operation. The influence of such damping elements was studied for a frictionless SMB twisting system designed to speed up the conventional ring spinning process. Therefore, conductive copper rings with different thicknesses were implemented at different positions into the bearing setup as ECD. Afterward, the SMB setup was analyzed during acceleration using an array of laser distance sensors to record the displacement of the levitating permanent magnet ring in radial and axial direction, respectively. Simultaneously, a numerical model was developed to investigate the influence of the ECDs on the dynamic and static behavior of the SMB in more detail. It was shown that the simulated damping coefficients are in good agreement with the measured values, which allows further optimization of the ECD with the developed numerical model.

3D modeling and measurement of HTS tape stacks in linear superconducting magnetic bearings

Superconducting magnetic bearings (SMBs) are among the possible new technologies to be incorporated in maglev vehicles. Stacks of high-temperature superconductor (HTS) tapes can be used as an alternative to bulks, because stacks offer better mechanical properties, a better thermal conductivity and a simpler production process. Numerical modeling has been employed as a cost-effective, fast and reliable tool for improving the performance of SMBs. Several scenarios can be simulated with fast and relatively simple 2D models; however, in some cases using 3D models is inevitable. In this study, we use a full 3D model to solve the problem of magnetization of the tape stacks and obtaining the hysteresis force loop between a permanent magnet and the tape stacks. For this purpose, we employ an energy minimization-based method called minimum electromagnetic entropy production in 3D, combined with a homogenization technique and the Jc(B,θ) dependence of the HTS tape as input. The modeling results agree very well with the experiment both in the zero-field cooled and field-cooled conditions. The presented approach offers significant computational advantages, delivering faster and more efficient results compared to previously proposed 3D methods.

<i>In Situ</i> Measurement of Twist Propagation and Yarn Tension with Superconducting Magnetic Bearing Twisting Element for Ring Spinning Process

The twisting of yarn in one of the most widely used conventional ring spinning processes is based on the ring/traveler system. The existing limitation of productivity in the ring spinning process lies on the prevailing force relation between ring, traveler and yarn as well as the frictional heat between traveler and ring, principally in the ring traveler system. Recently, a frictional free twisting element based on a superconducting magnetic bearing (SMB) was developed to increase the productivity of ring spinning drastically, which was patented by ITM and Leibniz IFW Dresden. This SMB consists of a circular superconductor and a permanent magnet (PM) ring. In the superconducting state, the PM ring levitates and can freely rotate even up to an angular speed of 50.000 rpm. It is connected with the spindle via the yarn through a guide attached to the PM ring to impart yarn twist. Through the rotation of the PM ring, the twist propagates to the nip point of the delivery rollers. The twist propagation rate depends on different parameters, e.g., spindle speed, balloon geometry, and friction between yarn and yarn guides. A change in the level of twist affects the process, yarn tension, yarn breakage rate, and yarn properties. Hence, it is important to investigate the twist distribution to derive effective measures for improving the twist propagation especially at higher angular spindle speeds and thus eliminate weak points to increase process stability and yarn quality. The aim of these measurements is to analyze the twist distribution along the yarn path to understand the causes of yarn breakages. In this study, the yarn path was traced at different regions by in-situ measuring the helix angle of twisted yarn using a high-speed camera. From the recorded images, the number of twists per unit length was determined using the image processing software ‘Image J’. Thus, the measurement method allows a new insight into the problem of yarn breakages originating from twist propagation in order to take optimized measures at higher angular spindle speeds.

Stiffness and loss characteristics of superconducting magnetic bearings using layered HTS tapes and a permanent magnet

This paper discusses some mechanical results from experiments on Superconducting Magnetic Bearings (SMBs) consisting of HTS tapes wound in a ring and a permanent magnet as could be applied to larger rotating machines and ultra-low temperature submerged motors. The wound-ring superconductors are made of 12 mm-width HTS tapes. The authors estimated the spring constant, k, after measuring the thrust force, as 3.85 × 103 N/m, for three-layered wound HTS tapes, and 2.44 × 103 N/m, for the single-wound HTS tape, respectively. The rotating losses for speeds of 500–4500 rpm in the constructed SMB system were also estimated and they were less than 10 W in the constructed measurement system.

Modeling, simulation, and implementation of a superconducting magnetic bearing twisting system in a high‐speed ring spinning process

AbstractThe implementation of a Superconducting Magnetic Bearing (SMB) system is a promising solution for the problem of friction exhibited in the twisting elements of the conventional ring‐spinning process. This research focuses on the development of a dynamical model with six degrees of freedom of the Permanent Magnet (PM) ring used in an SMB system for a high‐speed ring spinning process. The modeling takes into account the magnetic forces and torques that enable the magnetic levitation of the PM ring. Experimental tests allow the identification of unknown parameters of the model and the validation is done through simulations.

Simulation on modified multi-surface levitation structure of superconducting magnetic bearing for flywheel energy storage system by H-formulation and Taguchi method

Improving the performance of superconducting magnetic bearing (SMB) is very essential problem to heighten the energy storage capacity of flywheel energy storage devices which are built of components such as superconductor bulks, permanent magnets, flywheel, cooling system and so on. In this paper, three surfaces levitation-superconducting magnetic bearing (TSL-SMB) was simulated in two-dimensional axisymmetric system using H-formulation and Taguchi method. The system was worked by field cooling (FC) method. Taguchi-based L32(21×49) mixed orthogonal array was used to formulate the simulation plans for TSL-SMB, and effects of geometric parameters on levitation force in TSL-SMB was considered using Analysis of Variance (ANOVA). In the optimized TSL-SMB structure, there was no good difference whether the effect of concentric ring PMs with opposite polarization was included or not. Therefore, four surfaces levitation-superconducting magnetic bearing (FSL-SMB) as advanced multi-surface levitation system was presented to improve the performance of SMB. The simulation results in the FSL-SMB system showed that the gap between the stator and the rotor and levitation force per permanent magnet volume might be increased more than those of TSL-SMB system in the condition of same load capacity, this will contribute to improve the load capacity of SMB.

A Linear Motor Launcher System Integrating a Multisurface Superconducting Magnetic Bearing

In this study, a linear motor launcher system equipped with superconducting magnetic bearings has been constructed and tested under various conditions. The guide rail of the launcher features permanent magnets that support superconducting levitation and interaction between square prism-shaped bulk superconductors on various surfaces. This results in increased stiffness of a single superconductor along any given axis and comprehensive support of lateral forces. The study investigates the use of a superconducting magnetic bearing in a linear launcher system as a novel approach to a multi-surface levitation structure. The experimental system integrates the high-temperature superconductor (HTS) bulk material-based carriage system and an open cryostat structure. The carriage system levitates on the permanent magnet (PM) rail by moving it using an integrated DC linear motor. The study examines the levitation force relationship and performance of the system under different selected speeds and acceleration profiles. The design of the system allows for an adjustable slope of the permanent magnet rail, demonstrating the potential for use as a linear launcher pad. Additionally, the proposed system has the potential for application in larger systems, such as maglev vehicles.

The impact of magnetic field periodicity on the hysteresis loss in superconducting magnetic bearings

Since the discovery of high-temperature superconductors (HTS), superconducting magnetic bearings (SMB) have attracted much attention for practical applications such as flywheel energy storage systems, electrical machines, gyroscopes, etc., because of their ability to provide passive stable levitation under high-load conditions. Despite providing contactless linear and rotational motion, SMBs gradually decelerate by AC losses mainly generated by magnetic field inhomogeneity. The main component of AC losses at low rotational speeds is hysteresis loss, which is said to be independent of rotational speed, intrinsic to HTS, and proportional to the cube of magnetic field inhomogeneity. Although the state-of-the-art analytical expression of hysteresis loss in SMBs captures the general physics of the loss mechanism, it ignores the periodicity of the magnetic field in one complete rotation of the bearing. In this paper, the analytical expression of hysteresis loss is modified, taking into account the impact of magnetic field periodicity and the distribution of loss over the bearing surface. The new expression is tested by performing spin-down experiments with magnets of different levels of inhomogeneity in an actual SMB environment. The impact of magnetic field inhomogeneity on the dynamic behaviour of the bearing is also investigated. The results show consistency between modified analytical calculations and experimental data.

Vibration Characteristics of a Continuously Rotating Superconducting Magnetic Bearing and Potential Influence to TES and SQUID

We measured the vibration of a prototype superconducting magnetic bearing (SMB) operating at liquid nitrogen temperature. This prototype system was designed as a breadboard model for LiteBIRD low-frequency telescope (LFT) polarization modulator unit. We set an upper limit of the vibration amplitude at $36~\mathrm{\mu m}$ at the rotational synchronous frequency. During the rotation, the amplitude of the magnetic field produced varies. From this setup, we compute the static and AC amplitude of the magnetic fields produced by the SMB magnet at the location of the LFT focal plane as $0.24~\mathrm{G}$ and $3\times10^{-5}$$~\mathrm{G}$, respectively. From the AC amplitude, we compute TES critical temperature variation of $7\times10^{-8}$$~\mathrm{K}$ and fractional change of the SQUID flux is $\delta \Phi/\Phi_0|_{ac}=3.1\times10^{-5}$. The mechanical vibration can be also estimated to be $3.6\times 10^{-2}$$~\mathrm{N}$ at the rotation mechanism location.

Basic Study On Four Types of Superconducting Magnetic Bearings (SMBs) Using High T c Superconductor Bulks and Superconducting Coils

Superconducting magnetic bearings (SMBs) are usually composed of superconductors and permanent magnets (PMs). These SMBs are based on pinning forces between superconductors and PMs. In this paper, SMB-I composed of disk-shaped superconductor and SMB-II composed of doughnut-shaped superconductor are studied. To compare SMB-I with SMB-II, impulse responses in the vertical and horizontal directions are performed. Moreover, new types of SMB-III and SMB-IV are proposed. These SMB-III and SMB-IV are composed of superconductor and superconducting coils. To compare SMB-III with SMB-IV, impulse responses in the vertical and horizontal directions are studied. Then, natural damped vibration curves for impulse responses are observed. The damping coefficient for SMB-IV is larger than other SMB-I, SMB-II and SMB-III.

Suspension-Type of Flywheel Energy Storage System Using High Tc Superconducting Magnetic Bearing (SMB)

In this paper, a new superconducting flywheel energy storage system is proposed, whose concept is different from other systems. The superconducting flywheel energy storage system is composed of a radial-type superconducting magnetic bearing (SMB), an induction motor, and some positioning actuators. The SMB is composed of a superconducting stator and a flywheel rotor. The flywheel rotor is suspended by the superconducting stator, whose one end is fixed to a stable and heavy base. Free-run experiments in the case of the unfixed stator are performed. The natural rotation decay curve, displacement at the upper position of the rotor and displacement at a lower position of the rotor are measured. Moreover, free-run experiments in the case of the fixed stator are performed, and the same dynamic characteristics of the unfixed stator are measured. Especially, impulse responses for the rotor in the case of an unfixed stator are very different from those in the case of a fixed stator. The experimental results discuss some important characteristics of the superconducting flywheel energy storage system, whose rotor is suspended by the superconducting stator.

Evaluation of the effect of gravity on the rotational loss of superconducting magnetic bearings for space applications

We study the relationship between the levitation gap change and losses in a superconducting magnetic bearing (SMB) system. We develop a polarization modulator bearing for a cosmic microwave background (CMB) polarization experiment. The heat generated by the polarization modulator needs to be kept very low. Therefore, it is essential to model the effect of the levitation gap change of a rotor due to gravity on the rotational loss. We have constructed a prototype small experimental platform of an axial-flux SMB with an array of high-temperature superconductors, YBCO, and a permanent magnet ring. In this system, the weight of the rotor can be set. We measured the effect of the change in the levitation gap of the rotor due to gravity on the loss. When the levitation force was 5.5 N and 16.0 N, the losses generated in the rotor were 9.1 × 10−3 W and 1.6 × 10−2 W, respectively. It was confirmed that the loss increases with the increase in the levitation force of the SMB.

Stabilization of a Magnetic Repulsive Levitation Flywheel System Using a High-Efficiency Superconducting Magnetic Bearing

In this study, we developed a superconducting magnetic bearing using a permanent repulsive magnet. A repulsive magnetic levitation system with a permanent magnet can generate a strong levitation force in the absence of a power supply. However, it is unstable, except in the direction of repulsion. In contrast, superconducting magnetic bearings can generate a restoring force in all directions by utilizing the magnetic flux pinning property of the superconductors. Therefore, we constructed a superconducting magnetic bearing (SMB), which is stable along all axes without control, and has a strong axial levitation force, by combining a repulsive-type magnetic levitation system and a superconducting magnetic levitation system. We also reduced the amount of HTS used for the SMB and proposed an efficient method of using HTS. Furthermore, a driving test of the flywheel incorporating the SMB was conducted to verify the characteristics of the SMB. The experiment confirmed that the flywheel could overcome the resonance and drive the flywheel. In the drive experiment, the flywheel was driven up to 10,000 rpm.

Influence of cooling temperature on load-carrying performance of a radial HTS magnetic bearing

High temperature superconducting (HTS) magnetic bearing can operate in the harsh environment of low temperature and negative pressure with low loss and self-stability. Therefore, it has been gradually applied in flywheel energy storage, cryogenic liquid pump, cold compressor and some other cryogenic rotating machinery. The load-carrying performance of HTS magnetic bearing is affected by the cooling temperature of HTS directly. In this paper, the linear model is used to modify the temperature dependence to evaluate the influence of cooling temperature on load-carrying performance quantitatively, and the results are analyzed and displayed from the aspects of maximum levitation force, levitation stiffness and hysteresis effect. The research results of this paper have practical significance for the design and safe operation of HTS levitation system.

A Review of Superconducting Magnetic Bearings and Their Application

Magnetic bearings are being researched for high-speed applications, such as flywheel energy storage devices, to eliminate friction losses. As per Earnshaw's theorem, stable levitation cannot be achieved for a static passive magnetic bearing system. Fully passive stable levitation can be achieved with the help of superconducting magnetic bearings (SMB). This article provides an in-depth review of the modeling, analysis, and development of SMB. The different SMB configurations are highlighted, together with essential methodologies for estimating and improving their performance. The advancements in mathematical models used and the optimization of bearing characteristics are thoroughly discussed. Further, key developments in the application of SMB in flywheel energy storage systems are also reviewed.

Analysis and testing of a superconducting maglev submersible cryogenic liquid pump

This paper studies a superconducting maglev submersible cryogenic liquid pump (CLP) using superconducting magnetic bearing (SMB). A new structure is proposed for the self-stability of high-temperature superconducting magnetic levitation, and the compact structure of disk motor-pump. The rotor of the axial-flux disk motor is connected with a centrifugal impeller to form an impeller-rotor of the proposed superconducting CLP. Supported by a SMB system, the impeller-rotor rotates frictionlessly with self-stabilisation as a suspension rotor. The SMB system includes a radial-type SMB, an auxiliary permanent magnet bearing, and an electromagnetic bearing composed of the stator and the rotor of disk motor. Theoretical calculations and experimental measurements are performed to examine the axial and radial levitation force behaviours of the SMB system. Then, a kinetic model of the suspension rotor is established and analysed to assure force balance and stable levitation. Finally, a prototype pump is fabricated and an experimental setup for liquid nitrogen transmission is constructed for validation purposes. The experimental tests on the pump head and the flow rate are carried out, which demonstrate the effectiveness of the proposed superconducting maglev submersible CLP.

Modelling the Energy Losses of a Superconducting Magnetic Bearing due to the Change of the Levitation Height Under Gravity

This paper describes the losses of the rotor of the prototype superconducting magnetic bearing (SMB) that is employed for a polarization modulator of a Cosmic Microwave Background polarization experiment. The stator is composed of 20 segmented YBCO bulks, and these multiple superconductors produce the inhomogeneous magnetic field particularly due to the gravitational displacement of the rotor magnet position from the initial field cooling. This inhomogeneity causes the power dissipation to the spinning rotor. We estimated the power dissipation originating from this inhomogeneous magnetic field by using a numerical approach. The superconductors were modelled as electrically conducting components in the numerical simulation to avoid the complexity in modelling superconductivity. The results show about 4 mW dissipated at the rotor.

Scalable superconductive magnetic bearing based on non-closed CC tapes windings

A new type of scalable high-temperature superconducting magnetic bearing is proposed. The bearing is based on the multilayer open windings made of coated conductor-tapes (CC-tapes). To demonstrate the possibility of manufacturing such a bearing construction we have built a working prototype and studied its characteristics. The manufactured model of bearing includes a stator, consisting of three multilayer rings (CC-tapes pancake coils) of 12 mm CC-tape and a composite rotor consisting of three rings of permanent magnets, each composed of 16 NdFeB 10 × 10 mm permanent magnets. We showed a contactless levitation of rotor relative to stator, as well as rotation of rotor and we measured load curves, namely the dependence of the rotor displacement on restoring force for axial and radial loads. Numerical simulation of bearing load characteristics has been carried out by the finite element method in the Comsol Multiphysics software. The calculation results are in a good agreement with the experimental data.

A cryogenic continuously rotating half-wave plate mechanism for the POLARBEAR-2b cosmic microwave background receiver

We present the design and laboratory evaluation of a cryogenic continuously rotating half-wave plate (CHWP) for the POLARBEAR-2b (PB-2b) cosmic microwave background receiver, the second installment of the Simons Array. PB-2b will observe at 5200 m elevation in the Atacama Desert of Chile in two frequency bands centered at 90 GHz and 150 GHz. In order to suppress atmospheric 1/f noise and mitigate systematic effects that arise when differencing orthogonal detectors, PB-2b modulates linear sky polarization using a CHWP rotating at 2 Hz. The CHWP has a 440 mm clear aperture diameter and is cooled to ≈50 K in the PB-2b receiver cryostat. It consists of a low-friction superconducting magnetic bearing and a low-torque synchronous electromagnetic motor, which together dissipate <2 W. During cooldown, a grip-and-release mechanism centers the rotor to <0.5 mm, and during continuous rotation, an incremental optical encoder measures the rotor angle with a noise level of 0.1 μrad/Hz. We discuss the experimental requirements for the PB-2b CHWP, the designs of its various subsystems, and the results of its evaluation in the laboratory. The presented CHWP has been deployed to Chile and is expected to see first light on PB-2b in 2020 or 2021.

Analysis of the high-speed rotary motion of a superconducting magnetic bearing during ring spinning

Ring spinning is the leading textile technology for the production of short staple yarn, which runs commercially up to a maximum speed of 25 000 rpm. Higher speeds result in yarn damage mainly due to frictional heat. To eliminate this limitation, a friction-free superconducting magnetic bearing (SMB) was introduced as alternative high-speed yarn twist element consisting of a cryostat with an array of superconductors and a levitating permanent magnet ring with a yarn guide. Whereas stable spinning was possible until 30 000 rpm, it turned out that the new SMB twist element is more susceptible to external disturbances resulting in oscillating movements of the magnet. Therefore, a measurement system with an array of 5 synchronized optical laser triangulation sensors and one tachometer was implemented to analyse this motion in detail during spinning with high speeds. To test the system, the spinning speed was varied between 10 000 rpm and 21 000 rpm for different yarn qualities. In general, the magnetic ring oscillates around its centre position with the rotation frequency and a peak amplitude between 10 μm and 14 μm, which might be due to a small imbalance of the magnet. At the same time, the small tilt of the ring remained fixed with respect to the machine for all speeds. In addition, larger oscillation amplitudes of up to 300 μm are observed at 18 Hz for selected spinning parameters arising most probably from resonance effects with machine vibrations.