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A model of the evolution of the onshore wind turbine blade mass installed in Denmark is proposed described by a Weibull distribution and the age of the blades is estimated from decommissioning data to t = 29 years when half of the blade mass of an installation year has been decommissioned. This is considerable longer than the 20 year design life time of onshore turbines, which is often assumed to be an estimate of the End-of-Life of turbine blades. Thus blade waste predictions using the simple assumption may predict that installed blade masses are entering recycling processes about 9 years sooner that what is observed in Denmark. The blade mass for decommissioning in Denmark is estimate to peak at 2000 ton/year and 5000 ton/year in 2028 and 2045 using the Weibull model.

Prior to processing magnetic NdFeB material for recycling, it must be demagnetized. Here, we demonstrate a simple low-cost method. Large blocks of NdFeB permanent magnets of dimension 10 cm $\times 7$ cm $\times 2$ cm and with easy axis along the shortest dimension are shown to demagnetize when heated on a planar induction heating device. The initial magnetization of the magnets is reduced by a factor of 10 within a period of 30 min, in which the surface temperature of the magnet reaches 225 °C. This method simplifies the demagnetization process of the permanent magnets in wind turbine generators as part of the rapidly increasing demand for improved recycling capabilities of permanent magnets.

An increasingly unstable supply of 3He in the past decade along with growing demands for detectors from the large-scale neutron facilities have led to a higher focus on developing neutron detectors not relying on 3He. In this study a superconducting transition edge sensor (TES) based on a stack of thin films is combined with a neutron absorbing layer of 10B4C to build a sensitive and robust neutron detector. The difference in lattice structure causes tensile strain in the thin, stacked, structure, which results in changes in the superconducting parameters. The strain was measured along with its effect on the superconducting transition and thereby the sensitivity of the detector. A decrease in Tc of a few percent and in the range of 0.3 to 2.2 K was found from two different samples with varying boron coverage for a calculated strain of < 0.07%. A change in sensitivity due to strain was found to be from -58% to -15%, depending on deposition coverage and the deposition process. Effects on the superconducting properties were found to be within a range that can be compensated by design and setup considerations and these are therefore not expected to pose problems for the future detectors build on this principle.

We report on the testing of a 1 m long and 0.5 m wide racetrack coil wound from 4.5 km of MgB2 tape-shaped superconductors with a copper strip soldered to the nickel matrix. The cross-section of the coil corresponds to what is needed for the field windings of a 10 MW direct drive wind turbine generator pole, but where the straight section has been shortened. Ten double pancake sub-coils were wet-wound, with epoxy as the only electrical insulation, and assembled. The entire coil was cooled down to 14 K, and the direct current was ramped up. Voltage measurements were made over the double pancake coils. For eight of the ten double pancake coils, excessive voltages appeared at currents much lower than the design current. These voltages may either be attributed to the wire quality or to the winding process. A quench was observed at 149 A, which is in reasonable agreement with the predicted load line of the coil obtained by scaling wire transport measurements at 1 T and 20 K with hysteretic magnetization measurements in the range 1-5 T and 5-20 K. publishedVersion

The current work addresses a mass/cost-optimization procedure for galvanic anode cathodic protection systems based on both cathodic protection (CP) standards and numerical simulation. An approach is developed for optimizing the number and dimensions of the galvanic anodes, distributing the optimized anodes on the support structure, and finally evaluating the protective potential on the structure during the lifetime by using finite element (FE) software. An algorithm based on sequential quadratic programming is used for optimizing the number and dimensions of the anodes. Both simplified and detailed models are suggested for calculating the protective potential on the structure. The simplified model is selected based on its advantages in terms of calculation time and compatibility with DNV standard data. A time-dependent FE model is used to take into account the electrical isolation degradation of the structure coating as well as the mass reduction of the anodes during the CP lifetime. The performance of the proposed optimization process is examined on a mono bucket inspired (with some simplifications) by the Dogger Bank metrological mast in England. The optimized designs for different coating and anode types are compared and the best designs in terms of both cost and protective potential during the lifetime are suggested. The achieved results show that the proposed optimization procedure can reduce the cost of the CP system around 70% compared to the original non-optimized CP design of the Dogger Bank metrological mast. Furthermore, evaluating the time-evolution performance of the CP systems can reduce their lifetime uncertainty.

A Hydrogen Decrepitation Press-Less Process (HD-PLP) recycling method for recycling of anisotropic NdFeB magnets is demonstrated. The method combines hydrogen decrepitation (HD) disintegration of the initial magnet, powder sieving and the Press-Less Process (PLP), where hydride powder is sintered in a graphite mold. Coercivities up to 534 kA/m were obtained in porous samples based on powder size d < 100 μm. Adding a ball milling step resulted in full density isotropic magnets for d > 100 μm. The coercivity reached Hci = 957 kA/m being 86 % of the original N48M material without addition of rare earth elements.

Superconducting synchronous generators (SCSGs) are drawing more attention in large direct-drive wind turbine applications. Despite low weight and compactness, the short circuit torque of an SCSG may be too high for wind turbine constructions due to a large magnetic air gap of an SCSG. This paper aims at assessing the effects of armature winding segmentation on reducing the short circuit torque of 10-MW SCSGs. A concept of armature winding segmentation with multiple power electronic converters is presented. Four SCSG designs using different topologies are examined. Results show that armature winding segmentation effectively reduce the short circuit torque in all the four SCSG designs when one segment is shorted at the terminal.

In this feasibility study, we use finite element method simulations to compare superconductors (SC) coils and permanent magnets (PM) assemblies as main field source for a small-scale magnetic resonance imaging scanner. The motivation behind this investigation is that for certain tissues, e.g., knee ligament, diagnosis can be performed with equipment operating with relatively weak magnetic fields. It is then interesting to assess whether the relaxed field requirement enables alternative technologies, which present some advantages over the well-established helium-cooled low-temperature superconductors. As prototypical magnetic systems, we consider the Helmholtz coil and the Halbach cylinder for the SC and PM cases, respectively. Each possibility is simulated over a wide range of combinations of the fundamental design parameters. We estimate field strength, field homogeneity, and total cost over the service life of the device. From these figures of merit, we evaluate the optimal combinations of design parameters. Finally, we compare the SC and PM systems and we establish the range of field requirement values for which one alternative is more suitable than the other one. The result of the present investigation provides the starting point for more detailed studies where more specific design considerations are taken into account.

Superconducting (SC) synchronous generators are proposed as a promising candidate for 10-20-MW direct-drive wind turbines because they can have low weights and small sizes. A common way of designing an SC machine is to use SC wires with high current-carrying capability in the dc field winding and the ac armature winding is made with copper conductors. In such generators, the dc field winding is exposed to ac magnetic field ripples due to space harmonics from the armature. In generator design phases, the ac loss caused by these ripple fields needs to be evaluated to avoid local overheating and an excessive cooling budget. To determine the applicability of different design solutions in terms of ac losses, this paper estimates the ac loss level of 10-MW wind generator designs employing a MgB 2 SC field winding. The effects on ac losses are compared between nonmagnetic and ferromagnetic teeth with different numbers of slots per pole per phase. The necessity of an electromagnetic shield is then discussed based on the obtained loss levels. The results show that the total ac loss is so small that ferromagnetic teeth can be applied in the generator design without using an electromagnetic shield.

Here, we present a detailed characterization of the critical current density of YBa ${}_2$ Cu ${}_3$ O ${}_{7-x}$ two level undercut-profile substrate (2LUPS)-based samples made at the Technical University of Denmark using Hastelloy substrate. The CC architecture was produced at Bruker HTS by means of alternating beam assisted deposition and pulsed laser deposition. The magnetization of different samples having all the same size, but with various numbers of filaments, including a non-filamentary reference sample have been measured in applied magnetic fields up to 16 T and at temperatures ranging from $T = 2$ K to 77 K. A simple multiple rooftop model is proposed to estimate the critical current density of the filaments and it has been observed that filaments of 0.25 mm and 0.5 mm width are providing similar critical current densities in the order of $J_c \approx 2.3\,\text{MA}/\text{cm}^2$ at $T = 4.2$ K and $B = 10$ T as well as the reference samples without filaments. This result indicates that the filaments have been fabricated with no degradation of the superconductor and that the filaments are decoupled with non-superconducting material. Finally, the lift factor of the critical current $I_c$ with respect to $T = 77$ K and self field of the 2LUPS samples is estimated. This is reaching 10 at $T = 4.2$ K and $B = 10$ T.

This paper investigates the influence of system-level innovations on the fatigue life of jacket substructures for offshore wind turbines. The innovations consist of active control strategies as individual pitch control and individual flap control. Further the effect of a magnetic pseudo direct-drive generator (PDD) mounted upfront the rotor is investigated. Fully-coupled aeroelastic simulations are performed for 10 MW and 20 MW wind turbines, with the selected innovations, supported by jacket structures under specific met-ocean conditions at 50 m of water depth. Fatigue limit states at the jacket’ welded joints are evaluated based on S-N curves and Miner’s rule according to DNV-RP-C203 guideline. Results show the potential of advanced control systems to reduce stresses at jacket members. Few design challenges characterize PDD models, as increased tower base torsional loads and excitation of global bending modes may be critical for jacket’s members. Altogether, this study indicates the benefit of an integrated-iterative design approach for jacket substructures, where system-level parameters are iterated along with the jacket design parameters using fully-coupled models.

The magnetic phase diagram of the quaternary borocarbide ${\mathrm{TbNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ is investigated by direct means and by studying magnetically induced modifications of the crystal structure. Detailed superconducting quantum interference device measurements reveal a complex phase diagram with five distinct magnetic phases. The phase boundaries are mapped out comprehensively. Synchrotron hard x-ray measurements in applied magnetic fields are employed to probe the magnetoelastic distortions throughout the phase diagram. The determination of the wave vectors of these field-induced lattice deformations suggests a range of commensurate spin-slip-type magnetic structures at low temperatures with wave vectors of the form $(q,0,0)$ with $q=6/11$ and $5/9$. The proposed magnetic structures yield values of magnetization well in-line with observations. The scattering intensity due to the magnetoelastic deformations exhibits a drastic jump at the phase boundary at 1.3 T and low temperatures.

The European Academy of Wind Energy (eawe), representing universities and institutes with a significant wind energy programme in 14 countries, has discussed the long-term research challenges in wind energy. In contrast to research agendas addressing short- to medium-term research activities, this eawe document takes a longer-term perspective, addressing the scientific knowledge base that is required to develop wind energy beyond the applications of today and tomorrow. In other words, this long-term research agenda is driven by problems and curiosity, addressing basic research and fundamental knowledge in 11 research areas, ranging from physics and design to environmental and societal aspects. Because of the very nature of this initiative, this document does not intend to be permanent or complete. It shows the vision of the experts of the eawe, but other views may be possible. We sincerely hope that it will spur an even more intensive discussion worldwide within the wind energy community.

The two level undercut-profile substrate (2LUPS) has been introduced as a concept for subdividing rare-earth-Ba 2Cu3O7 coated conductors (CC) into narrow filaments that effectively reduces the ac losses and improves field stability for dc magnets. The 2LUPS consists of two levels of plateaus connected by a wall with an undercut-profile, which enables a physical separation of the superconducting layer between the plateaus without reducing the effective width of the superconducting layer. In this study, we report for the first time the results of fabrication and characterization of a filamentary CC produced in an industrial setup by SuperPower Inc. using ion beam assisted deposition and metal organic chemical vapor deposition (IBAD-MOCVD) on a 2LUPS realized at the Technical University of Denmark, whereas previous studies discussed the fabrication using alternating beam assisted deposition and pulsed laser deposition (ABAD-PLD). We also present Hall probe scanning measurements performed using a standard THEVA TAPESTAR XL machine that is routinely employed for industrial critical current characterization of long length CCs. From these results is it clear that additional analysis of the measured field profiles are required when characterizing filamentary 2LUPS CC using a standard TAPESTAR setting. Using a model representation of the 2LUPS we calculated the expected magnetization response by means of finite element methods simulations and we find a good agreement with the experimentally observed magnetic profiles.

Adding impurities or defects destroys crystalline order. Occasionally, however, extraordinary behaviour emerges that cannot be explained by perturbing the ordered state. One example is the Kondo effect, where magnetic impurities in metals drastically alter the temperature dependence of resistivity. In Type-II superconductors, disorder generally works to pin vortices, giving zero resistivity below a critical current jc. However, peaks have been observed in the temperature and field dependences of jc. This peak effect is difficult to explain in terms of an ordered Abrikosov vortex lattice. Here we test the widespread paradigm that an order-disorder transition of the vortex ensemble drives the peak effect. Using neutron scattering to probe the vortex order in superconducting vanadium, we uncover an order-disorder transition from a quasi-long-range-ordered phase to a vortex glass. The peak effect, however, is found to lie at higher fields and temperatures, in a region where thermal fluctuations of individual vortices become significant., The disordering of the vortex lattice in a type-II superconductor is widely perceived to underpin unusual peaks in the temperature and field dependence of critical current. By contrast, here Toft-Petersen et al. find an order-disorder transition in a superconducting vanadium sample that is unconnected with peaks observed in critical current.

A method for comparing the Levelized Cost of Energy (LCoE) of different superconducting drive trains is introduced. The properties of a 10 MW MgB$_{2}$ superconducting direct drive generator are presented in terms weight scaled to a turbine with a rotor diameter up of 280 m and the cost break down of the nacelle components. The partial load efficiency of the generator is evaluated for a constant cooling power of 0, 50 kW and 100 kW and the annual energy production is used to determine the impact on Levelized Cost of Energy. Copyright IEEE Comparison of Levelized Cost of Energy of superconducting direct drive generators for a 10 MW offshore wind turbine

Field windings made of MgB2 wires or tapes are considered for their potential to reduce volume, weight and cost of large offshore wind turbine generators. To gain experience of how to use this relatively new material in full-scale generators, tests of different winding methodologies and techniques are needed. In this paper, we describe in detail the steps used to wind a racetrack coil with a length of 1 m and a width of 0.5 m out of 4.5 km of MgB2 superconducting tape. The width corresponds to a full-scale pole of a 10 MW generator, whereas the length of the straight section is shorter than the corresponding full-scale pole. The coil was built up of 10 double pancake coils. Each double pancake coil was wet-wound using a semi-automatic winding process, where Stycast 2850 was applied directly to the MgB2 tape without any other dedicated electrical insulation. The strengths and weaknesses of the winding process are discussed and compared to the dry-winding method. This is the author's version of an article that has been published in this journal. Changes were made to this version by the publisher prior to publication. © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

This paper reviews the trends in wind turbine generator systems. After discussing some important requirements and basic relations, it describes the currently used systems: the constant speed system with squirrel-cage induction generator, and the three variable speed systems with doubly fed induction generator (DFIG), with gearbox and fully rated converter, and direct drive (DD). Then, possible future generator systems are reviewed. Hydraulic transmissions are significantly lighter than gearboxes and enable continuously variable transmission, but their efficiency is lower. A brushless DFIG is a medium speed generator without brushes and with improved low-voltage ride-through characteristics compared with the DFIG. Magnetic pseudo DDs are smaller and lighter than DD generators, but need a sufficiently low and stable magnet price to be successful. In addition, superconducting generators can be smaller and lighter than normal DD generators, but both cost and reliability need experimental demonstration. In power electronics, there is a trend toward reliable modular multilevel topologies.

This paper aims at assessing the potential of partially superconducting generators for 10 MW direct-drive wind turbines by investigating their performance for a very wide range of excitation currents. Performance indicators such as shear stress and efficiency and other generator characteristics are compared for 12 different generator topologies. To be sufficiently attractive, superconducting generators must have significant advantages over permanent magnet direct-drive generators, which typically have shear stresses of the order of 53 kPa and efficiencies of 96%. Therefore, we investigate what excitation is required to obtain a doubled shear stress and an efficiency of 98%. To achieve this, the different topologies require a range of excitation from 200 to 550 kAt (ampere-turns) with a low armature current density of 2 A/mm $^2$ . The more iron that is used in the core of these topologies, the easier they achieve this performance. By examining the maximum magnetic flux density at the location of the superconducting field winding, feasible superconductors can be chosen according to their engineering current density capabilities. It is found that high- and low-temperature superconductors can meet the performance criteria for many of the topologies. MgB $_2$ superconductors are feasible for the fully iron-cored topology with salient poles but need cooling down to 10 K.

The Pressless Process (PLP) was adopted to manufacture NdFeB sintered magnets, where the investigations on carbon and oxygen residues from heptane milling liquid media and graphite crucibles used for sintering were quantified to evaluate the influence on the magnetic characteristics. The carbon and oxygen content in the magnets produced from wet ball milling of strip cast flakes was found to be of the order 10 4 ppm and 4·10 4 ppm respectively, which resulted in soft magnetic behavior. However using jet milling the carbon and oxygen concentration were decreased by an order of magnitude resulting in coercivity of up to 829 kA/m. Thus the influence of the carbon from the graphite crucibles is small.

This paper addresses the effect of nano-TiC addition on sintered Nd-Fe-B permanent magnets. TiC nanoparticles were added to sintered Nd-Fe-B magnets with a specific aim to improve the Curie temperature and thermal stability. A standard powder metallurgy route was adopted to prepare the magnets. It was found that introducing nano-TiC prior to jet milling was effective as the nanoparticles dispersed in the final alloy, concentcalcrating in the neodymium-rich phase of the magnets. Magnets with optimal properties were obtained with the addition of 1 wt% TiC nanoparticles. The hysteresis loop for such magnets showed an improved shape and VSM analysis a coercivity value of 1188 kA/m, a remanence value of 0.96 T and a maximum energy product of 132 kJ/m3. The maximum working point and the Curie temperature of the developed magnets were 373 K and 623 K respectively.

This paper aims at finding feasible electromagnetic designs of superconducting synchronous generators (SCSGs) for a 10-MW direct-drive wind turbine. Since a lower levelized cost of energy (LCoE) increases the feasibility of SCSGs in this application, 12 generator topologies are compared regarding their LCoE in a simplified form of levelized equipment cost of energy (LCoE$_{\text{eq}}$). MgB$_2$ wires are employed in the field winding. Based on the current unit cost and critical current density capability of the MgB $_2$ wire at 20 K, the topologies with more iron have a much lower LCoE$_{\text{eq}}$ than the topologies with more nonmagnetic cores. The fully iron-cored topology with salient poles has the lowest LCoE $_{\text{eq}}$. Then a scenario study shows that the difference of LCoE$_{\text{eq}}$ between the topologies will become much smaller when the unit cost of the MgB$_2$ wire drops to a quarter and the current density capability of the MgB $_2$ wire increases to four times. Then the topologies with more nonmagnetic cores will become comparable to those with more iron. Aiming at a lower LCoE $_{\text{eq}}$ to increase the feasibility of SCSGs for large wind turbines, those topologies having the most iron in the core are the most promising for both now and the long term. If low weight is required, the topologies with more nonmagnetic cores should be considered.

We have numerically proved that the dependence of AC susceptibility χ of a E ( J ) power law superconducting thin disc on many parameters can be reduced to one penetration parameter h , with E the electric field and J the current density. Based on this result, we propose a way of measuring the critical current density J c of superconducting thin films by AC susceptibility. Compared with the normally used method based on the peak of the imaginary part, our method uses a much larger range of the AC susceptibility curve, thus allowing determination of the temperature ( T ) dependence of J c from a normally applied χ ( T ) measurement. A fitting equation J c = 1.9 H a ∣ χ ′∣ 0.69 / d , −0.4 χ ′ H a is the amplitude of the applied AC field, χ ′ is the real part of the normalized susceptibility and d is the thickness of the film. The method is valid for the cases where the film is fully penetrated. We also discuss how the finite London penetration depth affects the susceptibility when the film is screened. Measurements with varying T , H a and DC background field H dc are performed to support the arguments.

In this work we present a simulation of a synchronous generator with superconducting rotor windings. As many other electrical rotating machines, superconducting generators are exposed to ripple fields that could be produced from a wide variety of sources: short circuit, load change, mechanical torque fluctuations, etc. Unlike regular conductors, superconductors, experience high losses when exposed to AC fields. Thus, calculation of such losses is relevant for machine design to avoid quenches and increase performance. Superconducting coated conductors are well known to exhibit nonlinear resistivity, thus making the computation of heating losses a cumbersome task. Furthermore, the high aspect ratio of the superconducting materials involved adds a penalty in the time required to perform simulations.The chosen strategy for simulation is as follows: A mechanical torque signal together with an electric load is used to drive the finite element model of a synchronous generator where the current distribution in the rotor windings is assumed uniform. Then, a second finite element model for the superconducting material is linked to calculate the actual current distribution in the windings of the rotor. Finally, heating losses are computed as a response to the electric load. The model is used to evaluate the transient response of the generator.

We present the results of transport measurements of AC losses in a racetrack shaped superconducting coil made from coated conductor tape. The outer dimensions of the coil are approximately 24 cm × 12 cm and it has 57 turns. The coil is impregnated with epoxy resin and fiberglass tape is used to insulate the individual turns and to improve the mechanical properties of the epoxy when exposed to thermal cycling. The coil is manufactured as a part of the field winding of a small synchronous generator; therefore stainless steel frames are installed on the inner and outer side of the winding to reinforce it. The AC loss is measured versus the transport current I a with the coil immersed in liquid nitrogen. Measurements at frequencies 21 Hz, 36 Hz and 72 Hz are compared. The AC losses follow I a 2 dependence at low current amplitudes and I a 3 at high amplitudes. After cutting the inner steel frame the low amplitude losses are decreased, their frequency dependence is reduced but their dependence on the current remains unchanged.

This paper describes Superwind HTS machine laboratory setup which is a small scale HTS machine designed and build as a part of the efforts to identify and tackle some of the challenges the HTS machine design may face. One of the challenges of HTS machines is a Torque Transfer Element (TTE) which is in this design integral part of the cryostat. The discussion of the requirements for the TTE supported with a simple case study comparing a shaft and a cylinder as candidates for TTE are presented. The discussion resulted with a cylinder as a TTE design rated for a 250Nm and with more then 10 times lower heat conduction compared to a shaft. The HTS machine was successfully cooled to 77K and tests have been performed. The IV curves of the HTS field winding employing 6 HTS coils indicate that two of the coils had been damaged. The maximal value of the torque during experiments of 78Nm was recorded. Loaded with 33%, the TTE performed well and showed suffcient margin for future experiments.

In situ synchrotron x-ray diffraction is used to study the phase and texture formation of ceria based films and superconductor films deposited by the chemical solution method on technical substrates. Combined analysis using in situ synchrotron x-ray diffraction, thermogravimetry/differential thermal analysis and Fourier transform infra-red (FTIR) spectroscopy allows to study the details on the decomposition and crystallization processes of ceria based in form of bulk and film. The success of this work demonstrates the possibility of studying chemical reaction pathway and texture evolution of oxides starting from solution precursors using non destructive method.

The alternating-current losses in superconducting multifilament BiSCCO-2223 tapes and a 3.15-m single-phase test cable were measured at 77 K using an electrical transport method. The cable had an inner diameter of 42 mm; it was composed of a single layer of 31 multifilament tapes and had a critical current of Ic = 4.1 kA. The measured losses of the tapes were found to be in good agreement with the Norris ellipse (NE) model. The losses of the cable were, for high currents, found to be bounded by the monoblock and independent NE models.

The feasibility of installing a direct drive superconducting generator in the 5 MW reference offshore wind turbine of the National Renewable Energy Laboratory (NREL) has been examined. The engineering current densities Je obtained in a series of race track coils have been combined with magnetization measurements to estimate the properties of suitable field coils for a synchronous generator, which is more light weight than the conventional used combination of a gear box and a fast rotating generator. An analytical model and finite element simulations have been used to estimate the active mass of generators with varying number of poles. A 24 pole machine with an outer diameter of 4.2 m and active length and mass of 1.2 m and 34 tons is suggested possible, if a Je = 300 A/mm2 can be obtained in B = 4 T pointing to an operation temperature around 40 K.

article i nfo The phase and texture formation of La doped CeO2 (CLO) films deposited by the chemical solution method are studied by in situ synchrotron x-ray diffraction. It is found that the CLO crystallites forms excellent in-plane texture as soon as the phase appears at 860 °C, indicating that interfacial nucleation dominates at the beginning of the amorphous-crystallization transition. Grain growth is almost complete after at 900 °C for 15 min. Analysis of the isothermal process of crystallization at 900 °C by the Johnson-Mehl-Avrami- Kolmogorov equation shows that grain development is mainly controlled by diffusion. The success of this work demonstrates the possibility of studying crystallization behaviors of solution derived films using a non- destructive method, which has the potential of being applicable to most types of thin film samples.

This work presents a method to simulate the electromagnetic properties of superconductors with high aspect ratio such as the commercially available second generation superconducting YBCO tapes. The method is based on a multiscale representation for both thickness and width of the superconducting domains. A couple of test cases were successfully simulated and further investigations were made by means of structured (mapped) meshes. Here, large aspect ratio elements were used to simulate thin material layers with a reduced number of elements. Hence, more complex geometries can be studied at considerable lower computational time. Several test cases were simulated including transport current, externally applied magnetic field and a combination of both. The results are in good agreement with recently published numerical simulations. The computational time to solve the present multiscale approach in 2D is estimated as two orders of magnitude faster than other 2D methods.

An optimized buffer layer architecture prepared by a metal organic deposition method on biaxially textured metallic substrate is proposed and developed successfully. The major achievement of this work is to choose a Ce0.9La0.1O2 layer as cap layer that possesses an excellent lattice match with the superconductor layer, and to employ 200 nm thick Gd2Zr2O7 film as barrier layer. The effect of thermal cycling on the texture and morphology of the crystallized films and NiW substrate is discussed in detail. The texture quality and the epitaxial relationship between the buffer layer stack and the metallic substrate were studied by synchrotron x-ray diffraction. Well textured, smooth and crack-free Ce0.9La0.1O2/Gd2Zr2O7 buffer layer stacks are obtained, demonstrating the possibility of producing a high quality buffer layer stack by a low cost chemical solution deposition route.

Engineering of materials with specific physical properties has recently focused on the effect of nano-sized 'guest domains' in a 'host matrix' that enable tuning of electrical, mechanical, photo-optical or thermal properties. A low thermal conductivity is a prerequisite for obtaining effective thermoelectric materials, and the challenge is to limit the conduction of heat by phonons, without simultaneously reducing the charge transport. This is named the 'phonon glass-electron crystal' concept and may be realized in host-guest systems. The guest entities are believed to have independent oscillations, so-called rattler modes, which scatter the acoustic phonons and reduce the thermal conductivity. We have investigated the phonon dispersion relation in the phonon glass-electron crystal material Ba(8)Ga(16)Ge(30) using neutron triple-axis spectroscopy. The results disclose unambiguously the theoretically predicted avoided crossing of the rattler modes and the acoustic-phonon branches. The observed phonon lifetimes are longer than expected, and a new explanation for the low kappa(L) is provided.

The drivetrain of a 10 MW wind turbine has been designed as a direct drive transmission with a superconducting generator mounted in front of the hub and connected to the main frame through a King-pin stiff assembly by DNV-GL. The aeroelastic design loads of such an arrangement are evaluated based on the thrust and bending moments at the main bearing, both for ultimate design and in fatigue. It is found that the initial superconductor generator weight of 363 tons must be reduced by 25% in order not to result in higher extreme loads on main and yaw bearing than the reference10 MW geared reference drive train. Aweight reduction of 50% is needed in order to maintain main bearing fatigue damage equivalent to the reference drive train. Thus a target mass of front mounted superconducting direct drive generators is found to be between 183-272 tons.

We have studied the kinetics of the formation of from a stoichiometric mixture of Mg and 2B in Fe tubes using in-situ synchrotron powder diffraction at photon energies between E = 76-100 keV. Reaction with the sheath was studied in Fe tubes holding only Mg or B. We here demonstrate the use of a Pb absorber ring or aperture to damp the signals from the sheath material and thereby increase the quality of the diffraction pattern from the superconductor considerably. The new method has revealed a slow reaction between Mg and B when the temperature is below the melting point of Mg and a dramatic increase in the reaction kinetics as the Mg is melted. The reaction is complete on a timescale of the order 15-20 minutes after the Mg is melted.

To reduce the cost of energy of offshore wind energy conversion, large individual wind turbines of 10 MW or higher power levels are drawing more attention and expected to be desirable. Conventional wind generator systems would be rather large and costly if scaled up to 10 MW. Direct drive superconducting generators have been proposed to reduce the generator size, because the electrical machines with superconducting windings are capable of achieving a higher torque density. However, a superconducting machine is likely to produce an excessive torque during a short circuit because of its small reactance. An electromagnetic (EM) shield between the rotor and the stator as well as iron or non-magnetic composite (NMC) armature teeth affects the sub-transient reactance of a superconducting machine so that they play a role in the short-circuit performance of a superconducting wind generator. This paper presents a 10 MW superconducting generator design and studies the effects of material, thickness and position of an EM shield and the effects of NMC and iron armature teeth on the torque and the field current density during a three-phase short circuit at the generator terminal. One result shows that the short circuit torque is not able to be effectively reduced by varying the EM shield and the armature tooth material. The other result shows that the field current density is likely to exceed its critical value during a short circuit although the EM shield material and the armature tooth material take some effect.

Bulk samples of MgxB2 with starting composition of 0.5≤x≤1.3 were prepared using a solid-state reaction route. Their structure and critical current density (Jc) were investigated. The experimental results show that the starting composition MgxB2, as well as the sintering temperature, has a significant influence on Jc and Hirr. The lattice parameter a increases with x and c shows a maximum value around x = 0.9. All the samples possess a Jc value about 106 A/cm2 in self-field for x > 0.5. However, at high magnetic field the Mg-deficient samples exhibit higher Jc values. The highest irreversibility field of Hirr = 5.2 T at 20 K was reached for x = 0.8 with sintering temperature of 800 ℃, which is 0.8 T higher than that of the stoichiometric MgB2 sample. It is suggested that the formation of MgB4 nanoparticles is responsible for the increase of Hirr and Jc.

Bismuth substituted yttrium iron garnet (Bi–YIG) thin films (300 nm ) are prepared on (1 1 1) gadolinium gallium garnet (GGG) substrates by laser ablation. The films have high specific Faraday rotation up to 26°/μm and saturation field of 120 mT . They are used for magneto-optical (MO) imaging of superconductive YBa 2 Cu 3 O 6+ x (YBCO) thin films. It is found that although the observed intensities are lower than observed with thick films, the thinness of the films makes the background corrections possible at higher magnifications than is possible with standard LPE films. It was also found that zig-zag patterns disturbing MO-imaging using thick films are completely nonexistent.

MgB 2 samples doped with TiO 2 nanoparticles were prepared and the effect of TiO 2 addition on the superconducting transition temperature ( T c ), irreversibility field ( H irr ) and critical current density ( J c ) were investigated. It is found that the hexagonal lattice parameters a and c decrease with TiO 2 doping. T c decreases gradually from 38.2 to 37.8 K as the TiO 2 content increases from 0 to 15 wt%. The H irr increases at 20 K from 4.3 to 4.9 T as the TiO 2 content increases from 0 to 10 wt%, and at the same temperature J c increases from 450 to 4250 A/cm 2 at 4.2 T.

A series of polycrystalline samples of Mg 1− x (Zn 0.5 Al 0.5 ) x B 2 (0⩽ x ⩽0.8) were prepared by solid state reaction method and their structure, superconducting transition temperature ( T c ) and transport properties were investigated by means of X-ray diffraction (XRD), ac susceptibility, magnetization and resistivity. The double doping leads to decreases in both the lattice parameters a and c , and the T c decreases with increasing dopant content. A systematical comparison with Al doped- and Li, Al double doped MgB 2 of structure, superconducting transition and critical current density ( J c ) is made. It is suggested that the chemical pressure effect plays a more important role influencing the normal state transport and T c than the change of carrier concentration, and the introduction of disorder into the Mg layers shows little influence improving the irreversibility field and J c .

A series of polycrystalline samples of Mg 1− x (Al 0.5 Li 0.5 ) x B 2 (0⩽ x ⩽0.6) were prepared by a solid state reaction method and their structure, superconducting transition temperature and magneto-transport properties were investigated by means of X-ray diffraction (XRD), ac-susceptibility and resistance in varied magnetic fields. The double doping leads to decreases in both the lattice parameters a and c . The superconducting transition temperature ( T c ) decreases with double doping, but the T c is systematically higher than that of the single Al-doped samples. It is suggested that the hole band filling has little effect on T c at high doping level, while the disorder induced by doping plays an important role in suppressing T c . A systematic comparison with Al-doped MgB 2 of the structure, superconducting transition and irreversibility field is made.

Large wind turbines of 10 MW or higher power levels are desirable for reducing the cost of energy of offshore wind power conversion. Conventional wind generator systems will be costly if scaled up to 10 MW due to rather large size and weight. Direct drive superconducting generators have been proposed to address the problem with generator size, because the electrical machines with superconducting windings are capable of achieving a higher torque density of an electrical machine. However, the topology to be adopted for superconducting wind generators has not yet been settled, since the high magnetic field excitation allows for lightweight non-magnetic composite materials for machine cores instead of iron. A topology would probably not be a good option for an offshore wind turbine generator if it demands a far more expensive active material cost than others, even if it has other advantages such as light weight or small iron losses. This paper is to provide a preliminary quantitative comparison of 10 MW superconducting MgB2 generator topologies from the perspective of active material. The results show that iron-cored topologies have a cheaper active material and their sizes are relatively smaller than the others.

The microstructural dynamics of Bi-2223 tapes are investigated in situ during annealing in 8% O2 by means of 100 keV x-ray diffraction. A green mono- and a green multi-filamentary tape are annealed at 829.5 °C. During ramp-up (Ca,Sr)2PbO4 decomposes above 750 °C, resulting in an incorporation of Pb in Bi-2212. The associated grain growth of Bi-2212 is the main cause of the strain relief and the c-axis grain alignment of the Bi containing phases. Above 825 °C the Bi-2212 partly dissociates into (Ca,Sr)14Cu24Ox and a liquid phase. The linewidth of Bi-2212 is constant during the transformation to Bi-2223, indicating no strain or finite-size broadening. The most probable transformation mechanism is found to be nucleation and growth with a fast decomposition of the individual Bi-2212 grain, followed by a growth of Bi-2223 from the Bi-2212 melt reacting with (Ca,Sr)14Cu24Ox. The multi-filamentary tape transforms faster and exhibits a much better degree of c-axis alignment. Results are compared to similar studies in air. During a final annealing of a fully converted tape no change is found in the average concentration, stoichiometry and grain misalignment. A post-annealing experiment at 650 °C on quenched tapes shows a reaction over 3 weeks, whereby randomly oriented 3222 grains are formed and Bi-2223 is depleted of Pb. Simultaneously, the critical current decreases by a factor of 2.

We have investigated the temperature dependence of the H parallel to c flux line lattice structural phase transition from square to hexagonal symmetry, in the tetragonal superconductor LuNi2B2C ( T(c) = 16.6 K). At temperatures below 10 K the transition onset field, H2(T), is only weakly temperature dependent. Above 10 K, H2(T) rises sharply, bending away from the upper critical field. This contradicts theoretical predictions of H2(T) merging with the upper critical field and suggests that just below the H(c2)(T) curve the flux line lattice might be hexagonal.