To fabricate 10-16 Tesla high-field accelerator magnets, the high-Jc Nb 3 Sn superconductor is one of the most practical choices. However, it is a brittle material and is strain-sensitive. To reduce ...the potential Jc degradation of the conductor, it is crucial to accurately evaluate the stress of the coils owing to the large Lorentz force during magnet excitation. In the traditional stress analysis of magnets, the coils are usually regarded as homogenized structures using isotropic material coefficients; however, most superconducting (SC) coils have hierarchical and complicated structures. To obtain a more accurate estimation, it is necessary to consider the detailed internal structure of the coils during stress analysis. In this study, the homogenization method was applied to multi-scale stress analysis of a high-field accelerator SC magnet. The effective material coefficients of Nb 3 Sn coils were calculated using this method. Stress analysis of the magnet was performed using the effective material coefficients and isotropic material coefficients for comparison. Compared with the result obtained using isotropic material coefficients, the Von-Mises stress of the coil using effective material coefficients is larger at different load steps. The stress level of most Nb 3 Sn filaments in the strand was higher than that of the coil. The maximum stress of the Nb 3 Sn filaments appeared in the strand contact regions. In addition, there was a significant difference in the average stress of all materials in the strand. These findings will help develop more accurate analysis and simulation models for high-field SC magnets.
Abstract
High magnetic fields play a critical role in the development of modern science and technology, breeding many significant scientific discoveries and boosting the generation of new ...technologies. In the last few years, China has undertaken a great deal of work on the application of ultra-high-field (UHF) superconducting magnet technology, such as for the Synergetic Extreme Condition User Facility in Beijing, the UHF nuclear magnetic resonance/magnetic resonance imaging, nuclear fusion energy, particle accelerator, and so on. This paper reports the research status of UHF superconducting magnets in China from different perspectives, including design options, technical features, experimental progress, opportunities, and challenges.
The probability of wind-induced failure accidents in three-axle trucks under pulsating strong crosswinds and the corresponding critical safe speed are investigated in this study. Reliability theory ...and random fuzzy methods are utilized to establish the membership function of the failure probability in the series system (FPSS) composed of rollover, side-slip, and rotation failure accidents. The Kaman spectrum is used to realistically simulate the fluctuating wind time history curves of different average speeds. Four factors affecting the six-component force coefficient of the three-axle truck and the crosswind load are considered: fluctuating average wind speed, wind direction (angle), truck driving speed, and road adhesion coefficient. A three-axle truck nonlinear model is established accordingly. The model is used to obtain the dynamic response of the three-axle truck under strong crosswind conditions as per the time-varying curves of the vertical load of the truck, the time-varying curves of the lateral displacement of the center of mass, and the time-varying curves of the heading angle. An advanced Monte Carlo simulation algorithm based on importance sampling is used to determine the probability of a three-axle truck with FPSS under strong crosswinds; the given acceptable probability of failure (accident) is used to obtain the critical safety speed. The sensitivity analysis of random variables reveals that the possibility of three truck failures of the three-axle truck in strong crosswinds is, from largest to smallest, rollover, side-slip, and rotation. This research may provide useful guidance for exploring the probability of wind-induced accidents and the critical safety speeds of vehicles, as well as useful general information for road transportation management departments.
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DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
This paper proposes a method for visibility detection based on the recognition of the preceding vehicle's taillight signals using in-vehicle camera and millimeter-wave (mm-W) radar. First, we design ...two methods of vehicle identification. One is to use Haar-like features and an AdaBoost algorithm to train the vehicle classifier, which is mainly used to identify vehicles without turning on the taillights. The other is to identify vehicles with taillights on by means of taillight segmentation. The two identification methods are combined with a Discriminative Scale Space Tracker (DSST) to track the vehicle in the image acquired by vehicle camera and to measure anthropic visibility with mm-W radar. In addition, we drove a test vehicle on a foggy highway and collected experimental data through in-vehicle camera and mm-W radar. The experimenter observed the movement of the vehicle in front until it disappeared from the field of vision and recorded the distance of the vehicle in front measured by radar at that time as human visibility, which was also used as the ground truth to verify the accuracy of the proposed visibility detection method. The experimental results show that the visibility measured by the proposed algorithm is essentially consistent with the visibility obtained by human eyes, that is, the visibility of vehicles with no taillights, clearance lamp, emergency flasher, or fog lamp tends to rise, with an average accuracy of 88%, 91%, 90%, and 95%, respectively. In contrast to the traditional visibility measurement, this method mainly measures the maximum distance that the driver can observe when the front vehicle is not turned on or different taillights are turned on.
Iron-based superconductor (IBS) is expected to be the next generation high temperature superconductor with their potential good properties for the high-field application. This study focus on ...exploration of the characteristics of IBS coils at high field and development of the IBS coil fabrication technology. A series of diameter 35 mm IBS coils including single pancake (SPC) and double pancakes (DPC) were designed and winded with the 7-filamentary Ba1-xKxFe2As2 (Ba122) tape which was produced by the Institute of Electrical Engineering, Chinese Academy of Sciences (IEE-CAS). The IBS coils were divided into 3 groups according to the different fabrication processes. The tests of the IBS coils were firstly carried out at 4.2 K and 10 T background field. The highest quench current of the coils at 10 T is 69.4 A, which is about 90% of the critical current of the short sample at 10 T. Then, two SPCs were selected and tested at 4.2 K at 24 T <xref ref-type="bibr" rid="ref1">1 . The highest quench current of the coils at 24 T is 25.6 A, which is about 39% of the quench current at self-field. The test results were presented and analyzed with respect to the different fabrication processes.
An Nb 3 Sn/NbTi subscale dipole magnet named LPF1 with graded coil design and common-coil configuration has been designed, assembled, and tested at the Institute of High Energy Physics, Beijing, ...China. Compared to the previously proposed FECD1, LPF1 is designed with a longer outer NbTi racetrack coil to reduce the peak field in the coil end. The computed bore field and peak coil field of LPF1 is 12.0 T and 12.1 T, if it works at 6100 A with a safety margin of 17% at 4.2 K. The horizontal and vertical directions of the coil packs are preloaded by using bladder and key technology while the axial direction of the coil packs is preloaded by pretightening four aluminum rods. Before assembly, we tested the electron-beam welded bladders in a subscale shell-support structure and verified the strain measurement system. During assembly, we preloaded the coil packs gradually by referring to the measured shell strain after inserting stainless steel keys and removing the bladders. After assembly, we started to test the subscale dipole magnet vertically at 4.2 K. LPF1 reached a bore field of 10.2 T after 13 training quenches and then it reached a stable quench current without detraining. This paper presents the updated design parameters, the stress analysis, the magnet assembly, and test of LPF1.
The A15-type superconductors (Nb 3 Sn, Nb 3 Al) have been used to fabricate the 10 -15-T high-field superconducting magnets. Due to the strain sensitivity of this type of conductors, minimization of ...the strain in conductors is an important issue to realize the highest critical current density during operation. It is also known that the superconductors in epoxy-impregnated coils exhibit much less critical current degradation than wire samples when subjected to transverse compressive stress, due to the stress buffer effect of the epoxy and insulation materials among strands. This paper presents analytical and numerical investigation of the stress and strain distributions in A15-type superconducting coils, which are usually wound with copper-stabilized Rutherford cable and are epoxy impregnated. Analytical formulas have been derived to calculate the strain in superconductors from the average strain in coils. In addition, a FEM simulation model has been built to get a clear view of the strain distribution between superconductors and the surrounding insulation materials.
We carried out the three-dimensional (3-D) mechanical design of a 2-m-long 20 T common-coil dipole magnet and provided solutions for coil stress management. Instead of using flared ends to make space ...for the beam pipe, the prototype magnet is designed with a coil configuration which consists of four Nb 3 Sn and six Bi-2212 flat racetrack coils. The designed peak coil field is 20.4 T at the operating current of 14 700 A. The operating margin is 11% on the load line at 4.2 K. The magnitude of the calculated Lorentz force for 1/8 model is around 1562, 405, and 206 t for the horizontal, vertical, and axial directions, respectively. The special coil configuration and such significant magnetic force bring unprecedented challenges in applying preload to coils and optimizing the coil stress and the stress in the other components. By using an extended aluminum shell and a split yoke assembly, we minimized the coil end effects and applied a uniform and large enough preload to the coil straight section and the coil ends. This paper presents the stress analysis and the optimized 3-D mechanical design of the magnet.
High temperature superconducting insert technique is necessary for high field accelerator magnet, and ReBCO insert coil is one of the options. A no-insulation (NI) ReBCO racetrack double pancake coil ...was wound and tested in a bath of liquid nitrogen at 77 K for the research on NI winding method. This paper reported an experimental study of the NI ReBCO racetrack double pancake coil. The experimental results presented the central magnetic field at different phases and the partial voltages inside the coil. As a comparison, an insulated ReBCO racetrack double pancake coil was tested as well. Two coils were investigated by the typical behavior of critical current, partial voltages, and n value. In addition, the experimental results were compared with the theoretical calculation to clarify the NI winding characteristic as well.
The High-Luminosity Large Hadron Collider upgrade (LHC) project aims to increase the peak luminosity of the LHC to 5 ×10 34 cm - 2 s - 1 , and a total integrated luminosity of 3000 fb - 1 from 2020 ...to 2030 by upgrading the low-beta insertion system for the ATLAS and CMS experiments. The aperture of the insertion magnets including the focusing/defocusing quadrupoles and separation dipoles will be doubled to achieve a smaller β*. This paper presents the latest design updates of the separation dipole D1 magnet, including the study of the different cable types to vary the main field; the modifications of the iron shape for the new design options to minimize the iron saturation effect on field quality; and the optimization of the coil ends to reduce the peak field and higher order harmonic field integrals in the ends.
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