1,721,064 research outputs found
Strain Effects of Absorbing Layer on Superconducting Properties of a High-Flux Neutron Detector
No full textAn 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
Increasing the Feasibility of Superconducting Generators for 10 MW Direct-Drive Wind Turbines
No full textIn recent years, superconducting synchronous generators (SCSGs) have been proposed as an alternative to permanent magnet synchronous generators (PMSGs). They are expected to reduce the top head mass and the nacelle size for such large wind turbines. In 2012, the INNWIND.EU project initiated this research to investigate SCSGs for 10-20MWdirect-drive offshore wind turbines. However, the feasibility of SCSGs was limited by a few critical issues, such as high costs, AC losses in the superconducting winding and excessive short circuit torque. Furthermore, SCSG designs proposed in the literature were various but all less competitive than PMSGs
Possible magnetism in vortex cores of superconducting TmNi<sub>2</sub>B<sub>2</sub>C studied by small angle neutron scattering
Get PDFThe borocarbide intermetallics RNi2B2C (R = Y, Ce-Lu) were discovered in 1994 and attracted a large attention because superconductivity and magnetic ordering are coexisting in R = Dy, Ho, Er and Tm. Early reports concluded that these compounds should be considered as anisotropic BCS superconductors with a phonon-mediated moderately strong coupling between the conduction electrons causing the creation of Cooper pairs. The magnetism is of the indirect Ruderman-Kittel-Kasuya-Yosida(RKKY) type where the conduction electrons are polarized by the local magnetic moment of the rare-earth ions and thereby mediates a coupling between the ions, which orders into a spin density wave at sufficiently low temperatures. Thus an intricate interplay between the magnetism and the superconducting state is expected and has indeed been observed. The compound TmNi2B2C has previously been studied by Small Angle Neutron Scattering(SANS) with the applied field along the crystalline c-axis and a very rich phase diagram in terms of flux line lattices(FLL) with different symmetries have been found. One of the FLL transitions is coincident with a magnetic phase transition between two spin density waves. In this thesis additional SANS studies of the FLL phases in TmNi2B2C are reported and an interpretation of the phase diagram in the paramagnetic region is presented. It is suggested that the observed square FLL is stable in between two transition lines determined by two different length scales. The lower transition field is reached when the distance between the flux lines becomes comparable to the non-locality radius resulting from non-local electrodynamics, whereas the upper transition field is determined from the crossover from intermediate to high flux line density where the vortex cores start to overlap and the superconducting order parameter is suppressed in between the flux lines. A detailed examination of the intensity of the neutron diffraction spots caused by scattering on the flux line lattice in TmNi2B2C is presented and analyzed on the basis of the form factor of an isolated flux line. This analysis can not provide a good explanation for the observed scattering and it is suggested that the scattering from the Tm ions must be considered. One can argue that the moments of the Tm ions are modulated by the flux line lattice, because the RKKY interaction between the Tm ions might be different inside the vortex cores than outside in the superconducting phase. A calculation of the neutron scattering cross section of such a magnetic flux line lattice has been performed and compared to the SANS data. This offers a qualitative explanation of some of the observations, but future work is needed to make a more quantitative comparison
Variation of Extreme and Fatigue Design Loads on the Main Bearing of a Front Mounted Direct Drive System
Get PDFThe 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
Comparison of MgB<sub>2</sub> and Coated Conductor Based 5 MW Superconducting Wind Turbine Generator
No full textDirect drive superconducting generators might become attractive in large offshore wind turbines, because the drive train must provide a torque scaling with the radius of the rotor blades as R3 due to limitation of the tip speed of the blades. We have previously found that a coated conductor based generator can technically compete with a gear box drive train equivalent to the 5 MW NREL reference turbine [1]. However the price of the coated conductor results in a generator price exceeding the expected price of the entire turbine. MgB2 conductors can be seen as a low cost alternative to the coated conductors, but the operation temperature in range of T = 15-20 K and the engineering current density Je is smaller. We have found that a 16 pole synchronous generator with active diameter D = 4.2 m and length L = 1.5 m based on a MgB2 wire with Je = 70 A/mm2 in approximately 4 Tesla field would result in a wire usage in the order of 330 km. This has the potential to decrease the price of the superconductor wires in the generator by a factor of 10 compared to the coated conductors, but the cryogenics will be a challenge and is discussed. Finally we will use turbine load simulations to discuss the torque events that such a 5 MW generator would experience if installed in the NREL turbine
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