The mechanical properties of Y-Ba-Cu-O and Gd-Ba-Cu-O/Ag bulk superconductor magnets

Single-grain RE-Ba-Cu-O bulk high temperature superconductors [or (RE)BCO, where RE = rare earth element or yttrium] have demonstrated significant potential for practical applications due to their ability to trap magnetic fields in excess of 17 T, which is an order of magnitude greater than what can be achieved with conventional iron-based permanent magnets. One of the major obstacles to the use of (RE)BCO trapped field magnets is their poor mechanical properties, as bulk samples typically contain a large number of defects, such as pores and micro-cracks. Furthermore, significant electromagnetic stresses develop in bulk superconductors during magnetisation as a result of the Lorentz force, leading frequently to sample failure above around 10 T. Therefore, it is clear that the mechanical properties of bulk (RE)BCO need to be studied comprehensively and improved upon to realise the full potential of this technologically important material. This study first investigated the mechanical strength of YBCO single grains at room temperature by utilising three-point bend and Brazilian tests. This was followed by measurement of the mechanical deformation of GdBCO/Ag single grains in situ, i.e. during high-field magnetisation, to determine the strains and stresses experienced by the samples as a trapped field was established inside them at 64 K. Two techniques for improving the mechanical reliability of (RE)BCO bulk superconductors were subsequently developed. Firstly, samples of YBCO were melt-processed with artificial holes to reduce the defect population and to improve the intrinsic strength of the resultant single grains. As a result, the YBCO sample with artificial holes was able to survive significantly higher magnetisation fields and achieved a surface trapped field of 8.8 T at 30 K without any external reinforcement, which was not possible with the standard YBCO sample. Secondly, a composite structure was proposed, which involved reinforcing GdBCO/Ag single grains with stainless-steel sheets and shrink-fit stainless-steel rings. This preparation technique is also expected to improve the thermal stability of the overall structure. The first composite stack achieved 16.8 T and 17.6 T at 26 K and 22.5 K, respectively, in sequential magnetisation cycles, demonstrating the effectiveness of this reinforcement approach

Theoretical and Experimental Investigations of a Permanent Magnet Excited Transverse Flux Machine with a Segmented Stator for In-Wheel Motor Applications

A three-phase transverse flux permanent magnet (PM) motor with flux concentrating (FC-) topology that has a segmented stator is studied in this dissertation. The phases of the stator have been placed around the rotational axis of the machine instead of placing them in a classical way over each other along the axial direction. Through this phase arrangement, the electrical and mechanical shifts between the phases are considered to ensure proper operation of the transverse flux machine (TFM) without the need of extra components such as a start-up capacitor or a special designed power supply. The segmented stator construction has required that the conventional ring coils to be replaced by a type of concentric winding that take a saddle shape enabling parallel magnetic circuits to take place. This has initiated studying the effect of the distances located between the phases on all over the performances of the machine. In order to select an initial construction for the stator, a preliminary assessment study of some conventional PM-TFMs having ring coils are carried out, through which they are re-designed as outer rotor motors and compared based on the level of electromagnetic torque and the inductance profile. As the main application of the design is to achieve a compact construction for an outer rotor, low noise and speed too for possible future in-wheel applications, the most interesting issue in this study is how to bring all the phases of the machine around the shaft in one layer without losing the torque productivity as when the phases are placed under each other in the conventional way. Therefore, the designed machine is set in further theoretical evaluation studies via finite element method (FEM) with the conventional layered TFM, and it shows that the TFM with segmented windings has a better torque density as its correspondence in the conventional layered structure. This result is in favor to the segmented structure, in particular, about 31% of the PMs number in the segmented structure (i.e., total number of PMs located between the phases) will not have an active role in the torque production. A detailed mathematical theory has been analytically developed and investigated to show the validity and limitation of the design. The study has incorporated how the segmentation of each phase and placement of the two parts opposite to each other can improve the mechanical balance of the TFM and hence quite rotation. The approach has been shown for two- and three-phase PM-TFMs. Moreover, illustration for applying the same principle of segmented stator to surface PM topology of TFMs is analytical verified and shown via FEM. Possible constructions with segmented stators are developed in a periodical table format to give the machine designer a shortcut for a possible construction with the selected number of magnets, number of segments per phase and the desired space between the phases. Since the noise is a well-known problem of TFMs, due to the ripple in the electromagnetic torque waveform and the natural magnetic normal forces, the normal and axial forces in PM-TFM with segmented stator have been investigated too, where introducing more segments per phase will reduce their effects. In order to validate the theoretical investigation, a low-scaled test machine is designed, constructed and a complete test bench has been built to experimentally test the machine. The experimental investigations have included generator and motor operation modes as well as measuring the ratings, performances of the machine and the starting methods. The test machine has reached via the conducted tests an average torque of about 2.1 Nm with an efficiency of 53% and it has a great development potential to be improved via shaping of stator poles, the room available for the windings, fill factor and more optimization possibilities. Based on the theoretical and experimental investigations, the operation of the segmented winding design of PM-TFM proves itself to work and to have a future for compact motors in industrial operation, or as in-wheel outer rotor motor for mobile platforms. For higher power applications, a machine with such type of stator should be designed with big diameters that will allow the utility of more PMs as well as more segments per phase, where both are involved in the torque production, i.e., more torque density for the segmented TFM

Investigation of self switching flux pump for high temperature superconducting magnets

The rapid development of second-generation (2G) high-temperature superconducting (HTS) coated conductors (CCs) has made it possible to manufacture 2G HTS coils with enormous potential for a wide range of applications, including magnetic resonance imaging (MRI) magnets, electrical propulsion systems (HTS machines), magnetic levitation trains, and energy storage (SMES). While these coils can be operated using either DC or AC current, challenges such as properly magnetizing an HTS coil under DC conditions and reducing losses under AC conditions still need to be addressed before their widespread use in scientific and industrial settings. Typically, high-current power supplies power these coils through current leads, which can complicate insulation between cryogenic and room temperature environments. Fortunately, HTS flux pumps provide an alternative method of energizing superconducting magnets without the need for direct electrical contacts, reducing resistive heating and heat leakage from current leads at room temperature. Recent developments in flux pumps for HTS magnets have made it possible to charge kA levels of current without the need for thick current leads. This thesis aims to provide a comprehensive investigation of charging an HTS magnet to operate it in a persistent current mode, and presents a novel perspective on controlling the magnetic field in HTS magnets via flux pumping. First a two-dimensional (2D) model of a single turn high-temperature superconducting (HTS) coil was developed using a well-established H-formulation, which was iteratively refined to eliminate numerical errors from the solution. The resulting model provides insights into the self-rectifying flux pumping mechanism, which was subsequently validated experimentally. The 2D model also enables the estimation of the over-critical current voltage (also known as the flux flow voltage) across the HTS tape, which acts as a stable voltage source for injecting current into the HTS magnet. This results in the quantization of the bridge voltage, enabling precise flux injection into a fully superconducting circuit. A higher stable dc voltage can be achieved across the terminals of the HTS magnet using a bifilar coil as a bridge (bridge – the HTS tape short-circuits the terminals of the magnet and the secondary coil), the results are verified experimentally. The influence of the HTS tape and bifilar coil acting as a bridge across the HTS magnet is investigated. The results show that the bifilar bridge gives higher stable dc voltage to charge the HTS magnet to its critical current values and leads to the compact geometry making it suitable for adoption to complex geometries like rotor magnets in HTS machines. HTS flux pumps can charge the magnet and compensate for any current decay, enabling quasi-persistent operation of HTS magnets. To operate an HTS magnet in the persistent current mode, a jointless HTS magnet is constructed that offers zero joint resistance, allowing it to operate in persistent current mode. However, when used in applications like rotors of fully superconducting machines, it continuously experiences a background magnetic field in the form of magnetomotive force coming from the stator. The external alternating field can cause a gradual decay of the magnetic field. Therefore, this work presents a closed-loop feedback control for field modulation in HTS magnets to operate in persistent current mode. This method eliminates the need for continuous flux pumping and allows for the injection and reduction of current in increments of 0.5 A. This flux modulation can enable a stable magnetic field for HTS magnets. Finally, the thesis investigates critical aspects of the flux pumping in HTS magnets operating at 30 K, marking an advancement in the field of HTS magnet technology as previous flux pumps have only been reported to operate at higher temperatures. These results provide insight into achieving a stable magnetic field in HTS magnets via flux pumping and outline the methods to compensate for current decay in HTS magnets operating in the persistent current mode – opening new pathways to high-field, low-cost HTS magnets.The rapid development of second-generation (2G) high-temperature superconducting (HTS) coated conductors (CCs) has made it possible to manufacture 2G HTS coils with enormous potential for a wide range of applications, including magnetic resonance imaging (MRI) magnets, electrical propulsion systems (HTS machines), magnetic levitation trains, and energy storage (SMES). While these coils can be operated using either DC or AC current, challenges such as properly magnetizing an HTS coil under DC conditions and reducing losses under AC conditions still need to be addressed before their widespread use in scientific and industrial settings. Typically, high-current power supplies power these coils through current leads, which can complicate insulation between cryogenic and room temperature environments. Fortunately, HTS flux pumps provide an alternative method of energizing superconducting magnets without the need for direct electrical contacts, reducing resistive heating and heat leakage from current leads at room temperature. Recent developments in flux pumps for HTS magnets have made it possible to charge kA levels of current without the need for thick current leads. This thesis aims to provide a comprehensive investigation of charging an HTS magnet to operate it in a persistent current mode, and presents a novel perspective on controlling the magnetic field in HTS magnets via flux pumping. First a two-dimensional (2D) model of a single turn high-temperature superconducting (HTS) coil was developed using a well-established H-formulation, which was iteratively refined to eliminate numerical errors from the solution. The resulting model provides insights into the self-rectifying flux pumping mechanism, which was subsequently validated experimentally. The 2D model also enables the estimation of the over-critical current voltage (also known as the flux flow voltage) across the HTS tape, which acts as a stable voltage source for injecting current into the HTS magnet. This results in the quantization of the bridge voltage, enabling precise flux injection into a fully superconducting circuit. A higher stable dc voltage can be achieved across the terminals of the HTS magnet using a bifilar coil as a bridge (bridge – the HTS tape short-circuits the terminals of the magnet and the secondary coil), the results are verified experimentally. The influence of the HTS tape and bifilar coil acting as a bridge across the HTS magnet is investigated. The results show that the bifilar bridge gives higher stable dc voltage to charge the HTS magnet to its critical current values and leads to the compact geometry making it suitable for adoption to complex geometries like rotor magnets in HTS machines. HTS flux pumps can charge the magnet and compensate for any current decay, enabling quasi-persistent operation of HTS magnets. To operate an HTS magnet in the persistent current mode, a jointless HTS magnet is constructed that offers zero joint resistance, allowing it to operate in persistent current mode. However, when used in applications like rotors of fully superconducting machines, it continuously experiences a background magnetic field in the form of magnetomotive force coming from the stator. The external alternating field can cause a gradual decay of the magnetic field. Therefore, this work presents a closed-loop feedback control for field modulation in HTS magnets to operate in persistent current mode. This method eliminates the need for continuous flux pumping and allows for the injection and reduction of current in increments of 0.5 A. This flux modulation can enable a stable magnetic field for HTS magnets. Finally, the thesis investigates critical aspects of the flux pumping in HTS magnets operating at 30 K, marking an advancement in the field of HTS magnet technology as previous flux pumps have only been reported to operate at higher temperatures. These results provide insight into achieving a stable magnetic field in HTS magnets via flux pumping and outline the methods to compensate for current decay in HTS magnets operating in the persistent current mode – opening new pathways to high-field, low-cost HTS magnets

Investigation of diamagnetic bearings and electrical machine materials for flywheel energy storage applications

Recent trends in energy production have led to a renewed interest in improving grid level energy storage solutions. Flywheel energy storage is an attractive option for grid level storage, however, it suffers from high parasitic loss. This study investigates the extent to which passive diamagnetic bearings, a form of electromagnetic bearing, can help reduce this parasitic loss. Such bearings require three main components: a weight compensation mechanism (lifter-floater), a stabilizing mechanism and an electrical machine. This study makes use of a new radial modification of an existing linear multi-plattered diamagnetic bearing. Here a prototype is built and analytical expressions derived for each of the three main components. These expressions provide a method of estimating displacements, fields, forces, energy and stiffness in the radial diamagnetic bearing. The built prototype solution is found to lift a 30 [g] mass using six diamagnetic platters for stabilization (between ring magnets) with a disc lifter and spherical floater for weight compensation. The relationship between mass and number of platters was found to be linear, suggesting that, up to a point, increases in mass are likely possible and indicating that significant potential exists for these bearings where high stiffness is not needed – for instance in flywheel energy storage. The study examines methods of reducing bearing (parasitic) losses and demonstrates that losses occur in three main forms during idling: air-friction losses, electrical machine losses, stabilizing machine losses. Low speed (158 [rpm]) air-friction losses are found to be the dominant loss at 0.1 [W/m3]. The focus of this study, however, is on loss contributions resulting from the bearing’s electrical machine and stabilizing machine. Stabilizing machine losses are found to be very low at: 1 × 10−6 [W/m3] – this leaves electrical machine losses as the dominant loss. Such electrical machine losses are analysed and divided into eddy current loss and hysteresis loss. Two components of hysteresis loss are remanent field related cogging loss and remagetization loss. Eddy current losses in silicon steel laminations in an electrical machine are quite high, especially at high speeds, with losses in the order of 1 × 105 [W/m3]. Noting the further high cost of producing single unit quantities of custom lamination-based electrical machine prototypes, this high loss prompts a look at potentially lower cost ferrite materials for building these machines. A commercial sample of soft magnetite ferrite is shown to have equivalent eddy current losses of roughly 1 × 10−13 [W/m3]. The study notes that micro-structured magnetite has significant hysteresis loss. Such loss is in the order of 1 × 10−3 [W/m3] when referring to both remanence related cogging and remagnetization. This study, thus, extends its examination of loss to nano-structured magnetite. Magnetite nano-particles have shown superparamagnetic (no hysteresis) behaviour that promises the elimination of hysteresis losses. A co-precipitation route to the synthesis of these nano-particles is examined. A detailed examination involving a series of 31 experiments is shown to demonstrate only two pathways providing close-to-superparamagnetic behaviour. After characterization by Scanning Electron Microscope (SEM), X-Ray Diffractometer (XRD), Superconducting Quantum Interference Device (SQUID) and crude colorimetry, the lowest coercivity and remanence found in any given sample falls at −0.17 [Oe] (below error) and 0.00165 [emu/g] respectively. These critical points can be used to estimate hysteresis related power loss, however, to produce bulk ferrite a method of sintering or bonding synthesized powder is needed. A microwave sintering solution promises to preserve nano-structure when taking synthesized powders to bulk material. A set of proof-of-concept experiments provide the ground work for proposing a future microwave sintering approach to such bulk material production. The study uses critical points measured by way of SEM, XRD, SQUID characterization (e.g. remanence and coercivity) to implement a modified Jiles-Atherton model for hysteresis curve fitting. The critical points and curve fitting model allow estimation of power loss resulting from remanent related cogging and remagnetization effects in nano-structured magnetite. Such nano-structured magnetite is shown to exhibit hysteresis losses in the order of 1 × 10−4 [W/m3] from remagnetization and 1 × 10−7[W/m3] from remanence related cogging drag. These losses are lower than those of micro-structured samples, suggesting that nano-structured materials have a significant positive effect in reducing electrical machine losses for the proposed radial multi-plattered diamagnetic bearing solution. The lower parasitic loss in these bearings suggests excellent compatibility with flywheel energy storage applications

Critical Metals in Strategic Energy Technologies - Assessing Rare Metals as Supply-Chain Bottlenecks in Low-Carbon Energy Technologies

Due to the rapid growth in demand for certain materials, compounded by political risks associated with the geographical concentration of the supply of them, a shortage of these materials could be a potential bottleneck to the deployment of low-carbon energy technologies. In order to assess whether such shortages could jeopardise the objectives of the EU’s Strategic Energy Technology Plan (SET-Plan), an improved understanding of these risks is vital. In particular, this report examines the use of metals in the six low-carbon energy technologies of SET-Plan, namely: nuclear, solar, wind, bioenergy, carbon capture and storage (CCS) and electricity grids. The study looks at the average annual demand for each metal for the deployment of the technologies in Europe between 2020 and 2030. The demand of each metal is compared to the respective global production volume in 2010. This ratio (expressed as a percentage) allows comparing the relative stress that the deployment of the six technologies in Europe is expected to create on the global supplies for these different metals. The study identifies 14 metals for which the deployment of the six technologies will require 1% or more (and in some cases, much more) of current world supply per annum between 2020 and 2030. These 14 significant metals, in order of decreasing demand, are tellurium, indium, tin, hafnium, silver, dysprosium, gallium, neodymium, cadmium, nickel, molybdenum, vanadium, niobium and selenium. The metals are examined further in terms of the risks of meeting the anticipated demand by analysing in detail the likelihood of rapid future global demand growth, limitations to expanding supply in the short to medium term, and the concentration of supply and political risks associated with key suppliers. The report pinpoints 5 of the 14 metals to be at high risk, namely: the rare earth metals neodymium and dysprosium, and the by-products (from base metals) indium, tellurium and gallium. The report explores a set of potential mitigation strategies, ranging from expanding European output, increasing recycling and reuse to reducing waste and finding substitutes for these metals in their main applications. A number of recommendations are provided which include: • ensuring that materials used in significant quantities are included in the Raw Materials Yearbook proposed by the Raw Materials Initiative ad hoc Working Group, • the publication of regular studies on supply and demand for critical metals, • efforts to ensure reliable supply of ore concentrates at competitive prices, • promoting R&D and demonstration projects on new lower cost separation processes, particularly those from by-product or tailings containing rare earths, • collaborating with other countries/regions with a shared agenda of risk reduction, • raising awareness and engaging in an active dialogue with zinc, copper and aluminium refiners over by-product recovery, • creating incentives to encourage by-product recovery in zinc, copper and aluminium refining in Europe, • promoting the further development of recycling technologies and increasing end-of-life collection, • measures for the implementation of the revised WEEE Directive, and • investing broadly in alternative technologies. It is also recommended that a similar study should be carried out to identify the metal requirements and associated bottlenecks in other green technologies, such as electric vehicles, low-carbon lighting, electricity storage and fuel cells and hydrogen.JRC.F.7-Energy systems evaluatio

Design and development for the Rearsection of the KATRIN experiment

Die Rearsection stellt verschiedene Werkzeuge zur Kalibration und Überwachung des Quellbereichs des KATRIN Experiments zur Verfügung. Diese Arbeit stellt die wichtigsten Design- und Entwicklungsschritte an der Rearsection dar. Dazu gehören beispielsweise die Optimierung des elektromagnetischen Designs der integrierten Elektronenkanone wie auch verschiedene Testexperimente zur Finalisierung der "Rear Wall" des KATRIN Experiments

Energy: A continuing bibliography with indexes

This bibliography lists 1546 reports, articles, and other documents introduced into the NASA scientific and technical information system from April 1, 1981 through June 30, 1981