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The Superconducting Conductor Testing Facility, which is developed to evaluate the reliability of engineering technology and safe operation in a fusion reactor operation environment, is under construction by the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). Since the Nb3Sn layer coil of this test facility adopts the manufacturing process of the wind & react, the high-strength glass fiber used as the inter-turn insulation material will carbonize after high-temperature heat treatment at 665℃, thereby reducing the mechanical and electrical properties of the winding. The surface decarburization and modification process of high-strength glass fiber was developed to improve the properties of glass fiber after heat treatment. It is verified that the developed glass fiber tape treatment process can meet manufacturing process requirements of layered Nb3Sn superconducting magnets through the coil winding radial pressure test and VPI sample performance test. This processing technology has been successfully applied in the manufacturing of experimental magnets, providing technical support for the insulation manufacturing of a large Nb3Sn layer coil. [ABSTRACT FROM AUTHOR]

We have successfully developed cryogen-free dilution refrigerators with medium cooling power that can be applied to quantum experiments. Breakthroughs have been made in some key technologies and components of heat switches and dilution units. Our prototype has been running continuously and stably for more than 100 hours below 10 mK, with a minimum temperature of 7.6 mK and a cooling power of 450 μW at 100 mK. At the same time, we have also made progress in the application of dilution refrigerators, such as quantum computing, low-temperature detector, and magnet integration. These indicators and test results indicate good prospects for application in physics, astronomy, and quantum information. [ABSTRACT FROM AUTHOR]

High fracture toughness at cryogenic temperature and radiation hardness can be conflicting requirements for the resins for the impregnation of superconducting magnet coils. The fracture toughness of different epoxy-resin systems at room temperature (RT) and at 77 K was measured, and their toughness was compared with that determined for a polyurethane, polycarbonate (PC) and poly(methyl methacrylate) (PMMA). Among the epoxy resins tested in this study, the MY750 system has the highest 77 K fracture toughness of KIC = 4.6 MPa√m, which is comparable to the KIC of PMMA, which also exhibits linear elastic behaviour and unstable crack propagation. The polyurethane system tested has a much higher 77 K toughness than the epoxy resins, approaching the toughness of PC, which is known as one of the toughest polymer materials. CTD101K is the least performing in terms of fracture toughness. Despite this, it is used for the impregnation of large Nb3Sn coils for its good processing capabilities and relatively high radiation resistance. In this study, the fracture toughness of CTD101K was improved by adding the polyglycol flexibiliser Araldite DY040 as a fourth component. The different epoxy-resin systems were exposed to proton and gamma doses up to 38 MGy, and it was found that adding the DY040 flexibiliser to the CTD101K system did not significantly change the irradiation-induced ageing behaviour. The viscosity evolution of the uncured resin mix is not significantly changed when adding the DY040 flexibiliser, and at the processing temperature of 60 °C, the viscosity remains below 200 cP for more than 24 h. Therefore, the new resin referred to as POLAB Mix is now used for the impregnation of superconducting magnet coils. [ABSTRACT FROM AUTHOR]

Compressive magnetic radial stress is favored, over tensile one, for a high field magnet, mainly because it lowers the overall peak magnetic stress within the windings of the magnet. It is of particular importance for a no-insulation (NI) high temperature superconducting (HTS) magnet, because the compressive radial stress leads to good turn-to-turn contact that is essential for current sharing in the NI HTS coils and consequent self-protecting behaviors. Depending on key magnet design parameters such as target center field, background magnetic field, inner and outer winding diameter, and overband radial build, we have shown that electromechanical conditions for a high field superconducting magnet to have compressive radial stress may be analytically pinpointed. With our suggested method, we can identify 3 different patterns of radial turn-to-turn contact behavior in the dry wound coils: (1) fully separated; (2) fully contacted; and (3) mixed (i.e., partially separated and contacted). After that, we suggest an analytical method to calculate stress distributions in dry wound coils by using the electromechanical condition for fully compressive radial stress. Finally, by performing the finite element analysis with examples, we verified that our analytical method shows a good agreement with the numerical one. The results may provide insight for magnet engineers to better overview the electromechanical behaviors of their high field HTS magnets at the early design stage. [ABSTRACT FROM AUTHOR]

A 5T semi-open split superconducting magnet has been recently developed at the Advanced Energy Science and Technology Guangdong Laboratory, China, in pursuit of a versatile high magnetic field test facility for measuring the field-dependent and mechanical behaviors of superconductors. It is a better candidate to generate transverse fields in a larger working region (Ø80 mm × H800 mm) and enables non-contact deformation measurements with digital image correlation (DIC). In our previous work, the simulation of the strain and the magnetic field distribution of the coil and support structure had been reported in detail; and the strain measurements for the key points were also carried out using traditional low-temperature strain gauges. However, the distributed strain of the large-scale superconducting magnet is important for exploring the whole stability. And single-point strain gauges often have difficulty measuring global strains for these complex structures. In addition, for resistance-based strain gauges, obtaining accurate strain is even more challenging due to electromagnetic interference. Therefore, in this paper, using the semi-open magnet structure, the distributed strain measurement method based on the Optical Frequency Domain Reflectometry (OFDR) principle under cryogenic and intense field is mainly validated. The global profile of the magnet system strain was monitored throughout the entire operating process, including cool-down, excitation, and warm-up. The distributed fiber strain measurements agree well with traditional single-point resistance measurements. Interesting insights into the global strain characteristics of semi-open split superconducting structures were obtained, such as the catastrophe data and asymmetrical information. The successful application of distributed fiber strain measurements provides a critical distributed detection method in superconducting magnet technology. [ABSTRACT FROM AUTHOR]

A HTS (High temperature superconductor) current lead, which provides an electrical connection between a power supply and a superconducting magnet, needs to be designed to minimize the heat leakage transferred to the cold end to save the cooling power of the superconducting magnet system. Since the heat leakage of the HTS current lead can be reduced not only through the material properties of the metal lead but also through structural analysis, we will introduce study results of the shape design method of a metal lead. We performed a numerical analysis based on a segment algorithm using the general solution of temperature distribution and heat leakage to mathematically express the design method. The results of the simulation revealed that the heat leakage at the cold end of the vapor cooled HTS current lead is determined by conduction, Joule heating and vapor cooling, thus demonstrating that liquid helium consumption can be reduced by adjusting the perimeter and hydraulic diameter of the metal lead. Based on these results, we performed a numerical analysis of the temperature distribution and heat leakage on a metal lead with an axially varying cross-sectional area. After the design, the metal lead was manufactured with the proposed method and applied to a 5 T class superconducting magnet system to evaluate the performance of the system. We compared the evaluation results to the simulation results to verify the feasibility of the proposed numerical analysis method. The study confirmed that the proposed metal lead design method can be applied to the superconducting magnet system to save cooling power.

We have designed a 30-T superconducting magnet for important experimental facilities in condensed matter physics research. The critical current of rare-earth barium copper oxide (REBCO) tapes directly or indirectly affects the electromagnetic margin, central magnetic field, hysteresis losses, field homogeneity, and screening current–induced stresses (SCIS) of the magnet. Given the poor critical current consistency of REBCO tapes at 4.2 K and their complex field-dependence, the arrangement of double-pancake (DP) coils is crucial in superconducting magnets. Based on measurements of over 100 REBCO tapes at 4.2 K and under an 8-T perpendicular field, we studied the arrangement of DP coils with different critical currents to assess their impact on the electromagnetic margin, central magnetic field, hysteresis losses, field homogeneity, and SCIS of the 30-T superconducting magnet. The results indicate that, depending on the magnet's requirements for different performance aspects, DP coils wound with higher critical currents should be positioned in locations with lower sensitivity to critical current. This approach serves to reduce the operating factor, screening current–induced field (SCIF), peak hoop SCIS, and losses, respectively. These findings provide valuable insights into the design of ultra-high-field REBCO superconducting magnets and arrangement of DP coils. [ABSTRACT FROM AUTHOR]

Rectifier diodes play a vital role in the operational aspects of a superconducting magnet, and their selection and characterization are crucial for optimal performance and reliability. These diodes are placed within the magnet cryostat, which subjects them to liquid helium (4.2 K) or cryogenic temperatures. The behavior of power diodes can change significantly at cryogenic temperatures. Hence, it is essential to verify their performance before they are installed onto a superconducting magnet system. Thus, a test bench was developed to determine the V–I characteristics of power diodes at low temperatures. In this paper, the two power diodes were tested at 300 K, 77 K, and 4.2 K. The forward voltage was found to increase and have a modest reduction in the on-resistance with the decreases in temperature. The diodes withstood low temperatures down to 4.2 K. The observed forward voltage for the power diode was 4.78 V at 4.2 K, which is around 6–7 times higher than that at room temperature. [ABSTRACT FROM AUTHOR]

The relatively fragile low-temperature stability of cryogen-free superconducting magnetic resonance imaging (MRI) magnets requires the careful management of exogenous heat sources. A strongly shielded gradient magnetic field is important for the optimal operation of cryogen-free MRI systems. In this study, we present an enhanced shielding method incorporating a regionalized stray field constraining strategy. By optimizing the constraint parameters, we could develop engineering-feasible gradient coil schemes without increasing system complexity but with the stray field intensity reduced by half. In real measurement in an integrated MRI system, the developed gradient assembly demonstrated good performance and supported to output images of excellent quality. Our findings suggested that the proposed method could potentially form a useful design paradigm for cryogen-free MRI magnets. [ABSTRACT FROM AUTHOR]

Numerous experiments have shown that the loads applied to Nb3Sn strands and cables can reduce their critical current. Experiments, performed on uniaxially loaded strands, allowed to define clear laws to describe the evolution of the critical surface as a function of the applied current, field, temperature and strain. It is, however, still unclear how these laws can be applied to superconducting magnets. The present paper proposes a methodology to estimate the critical current and temperature margin reduction on superconducting magnets due to stress on the superconducting material. The methodology is tested on the MQXF magnets, a quadrupole developed for the High Luminosity LHC project, and successfully validated by comparing computed strain with data from strain gauge measurements. Results suggested that, because of the stresses arising in winding during assembly, cool-down and powering, the current limit of the magnet is lower than the expected short sample limit, and that the most critical region does not coincide with the peak field location.

High fracture toughness at cryogenic temperature and radiation hardness can be conflicting requirements for the resins for the impregnation of superconducting magnet coils. The fracture toughness of different epoxy-resin systems at room temperature (RT) and at 77 K was measured, and their toughness was compared with that determined for a polyurethane, polycarbonate (PC) and poly(methyl methacrylate) (PMMA). Among the epoxy resins tested in this study, the MY750 system has the highest 77 K fracture toughness of KIC = 4.6 MPa√m, which is comparable to the KIC of PMMA, which also exhibits linear elastic behaviour and unstable crack propagation. The polyurethane system tested has a much higher 77 K toughness than the epoxy resins, approaching the toughness of PC, which is known as one of the toughest polymer materials. CTD101K is the least performing in terms of fracture toughness. Despite this, it is used for the impregnation of large Nb3Sn coils for its good processing capabilities and relatively high radiation resistance. In this study, the fracture toughness of CTD101K was improved by adding the polyglycol flexibiliser Araldite DY040 as a fourth component. The different epoxy-resin systems were exposed to proton and gamma doses up to 38 MGy, and it was found that adding the DY040 flexibiliser to the CTD101K system did not significantly change the irradiation-induced ageing behaviour. The viscosity evolution of the uncured resin mix is not significantly changed when adding the DY040 flexibiliser, and at the processing temperature of 60 °C, the viscosity remains below 200 cP for more than 24 h. Therefore, the new resin referred to as POLAB Mix is now used for the impregnation of superconducting magnet coils.

The main devices for generating synchrotron radiation at the SKIF synchrotron light facility under construction will be superconducting wigglers and undulators created at the Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences. This report presents the rationale for the choice of operating parameters, the main characteristics and design features of these devices, and their current development status. [ABSTRACT FROM AUTHOR]

High-temperature superconductors have great potential for various engineering applications such as a flywheel energy storage system. The levitation force of bulk YBCO superconductors can be drastically increased by increasing the strength of the external field. Therefore, a 6T conduction-cooled superconducting magnet has been developed for levitation force measurement application. Firstly, to protect the magnet from mechanical damage, reliable stress analysis inside the coil is paramount before the magnet is built and tested. Therefore, a 1/4 two-dimensional (2D) axisymmetric model of the magnet was established, and the mechanical stress in the whole process of winding, cooling down and energizing of the magnet was calculated. Then, the charging, discharging, and preliminary levitation force performance tests were performed to validate the operating stability of the magnet. According to the simulation results, the peak stresses of all coil models are within the allowable value and the winding maintains excellent mechanical stability in the superconducting magnet. The test results show that the superconducting magnet can be charged to its desired current of 150 A without quenching and maintain stable operation during the charging and discharging process. What is more, the superconducting magnet can meet the requirements for the levitation force measurement of both low magnetic field and high magnetic field. [ABSTRACT FROM AUTHOR]

The Superconducting Conductor Testing Facility, which is developed to evaluate the reliability of engineering technology and safe operation in fusion reactor operation environment, is under engineering design by ASIPP. In case of an emergency shut-down like in succession of a quench, the voltage across the coil may rise to about 2.5 kV. The facility has to be reliably insulated. In this study, we present the preliminary design of the insulation system of the Superconducting Conductor Testing Facility, which includes turn and ground insulation. Since the magnet of the facility adopts the manufacturing process of “Wind&React”, the turn insulation material should withstand a heat treatment with temperature up to 650 °C. The insulation system is composed of S-glass fiber reinforced tape and vacuum-pressure impregnated in a DGEBF epoxy system. The mechanical properties are being subjected to investigations with respect to the design requirements and operating conditions. The test results are analyzed to verify the feasibility of the insulation system design. [ABSTRACT FROM AUTHOR]

A compact gantry delivering 70-220 MeV protons with fixed field in the superconducting magnets could reduce the cost and improve the adoption of proton therapy. While a number of magnet and cryogenics designs have been proposed, the combined capital and operating costs of state-of-the-art superconducting materials have not been analyzed. In response, we develop a thermoeconomic model of a multi-stage, conduction cooled gantry lattice and analyze the cryocooler operating cost, cryocooler capital cost and conductor capital cost for Nb-Ti, Nb3Sn, REBCO and Bi-2223 over a continuous range of magnet temperatures, and a differential evolution algorithm is used to identify the optimal combination of thermal intercept temperatures. Although Nb3Sn yields the lowest Net Present Value (NPV) of $111.7k at a magnet temperature of 9.4 K, the optimized Bi-2223 design at 12.8 K approaches the realm of commercial feasibility by offering improved thermal stability and forgoing the need for costly conductor heat treatment and magnet quench training. Furthermore, it was found that Nb3Sn was more cost effective than Nb-Ti and that REBCO was not economically viable for the parameters of this investigation. The thermoeconomic model developed herein can optimize conductor choices, magnet temperatures and thermal staging which has value for any conduction-cooled superconducting magnet.

[Introduction] Magnetically confined fusion is an effective way to solve the energy problem. To direct to quasi-steady state discharges and their relevant physics, the superconducting magnet (especially the high field HTS magnet) had become the first choice for tokamak design in the future. [Method] This reserch was devoted to introduce the recent experimental progress and future research schemes of EAST, and summarized the latest progress of CFETR, especially the research on superconducting magnet. [Result] EAST device, the world's first full superconducting tokamak, has achieved a new pulse length world record (1056 seconds) for high temperature tokamak plasma by the end of 2021. [Conclusion] The designs of CFETR, which aim to bridge the gaps between the fusion experiment ITER and the demonstration reactor (DEMO), have been carried out within CFETR National design team.

A topology optimization method based on sensitivity analysis is proposed for designing superconducting systems operating under critical current densities. The topology changes in the structure of the superconducting materials are achieved by creating air holes in the superconducting material and superconducting dots in the vacant space. The positions of the air holes and superconducting dots are determined via hole and dot sensitivity analyses. The hole and dot sensitivity expressions are derived based on the continuum sensitivity of the superconducting system. The proposed design optimization method can not only achieve fast convergence based on the sensitivity-based approach, but also alter the topology through the introduction of holes and dots and obtain a high-quality optimal solution. The level set method is used to express the topology and shape changes of the superconductors. The topology changes due to the air holes and superconducting dots are represented by adding a zero-level set to the newly formed material interface. The proposed method is validated through numerical examples involving the design of superconducting magnets. The results demonstrate that the hole and dot sensitivity analysis accurately predicts the optimal locations for air holes and superconducting dots to improve the system performance. Additionally, the design examples show that the holes and dots created near material boundaries accelerate shape optimization while minimizing the risk of the divergence. [ABSTRACT FROM AUTHOR]

An experiment to investigate the two-phase closed loop thermosyphon (TPCLT) to cooling the compact superconducting magnet has been performed. This study is motivated mainly by our development of cryogenic cooling for a superconducting cyclotron magnet system. In the two-phase closed loop thermosyphon system, the cooling of the cold mass (27 kg copper block) from room temperature to 4 K is achieved in three stages by refilling subsequently the loop with Nitrogen (80 K), Neon (30 K) and Helium (4 K) based on the different boiling point of each of the gases. The cooldown process and efficiency were analyzed and compared with directly conductor cooling method. The results show that the TPCLT cooling method can reduce the liquid helium and shorten the cooling time, so it has a potential to achieve lower energy consumption and higher efficiency for cooling compact a superconducting magnet (the weight large than 100 kg) in practical applications. [ABSTRACT FROM AUTHOR]

Multifilamentary Bi2Sr2CaCu2Ox (Bi-2212) wire made by the powder-in-tube technique is the only high temperature superconductor made in the round shape preferred by magnet builders. The critical current density (J C ) of Bi-2212 round wire was improved significantly by the development of overpressure heat treatment in the past few years. Bi-2212 wire is commercially available in multiple architectures and kilometer-long pieces and a very promising conductor for very high field NMR and accelerator magnets. We studied the effects of precursor powder and heat treatment conditions on the superconducting properties and microstructure of recent Bi-2212 wires. Short samples of recent wire with optimized overpressure processing showed J C (4.2 K, 15 T) = 6640 A/mm2 and J C (4.2 K, 30 T) = 4670 A/mm2, which correspond to engineering critical current densities J E (4.2 K, 15 T) = 1320 A/mm2 and J E (4.2 K, 30 T) = 930 A/mm2.

The superconducting ECR source magnet for the Facility for Rare Isotope Beams at Michigan State University was designed and built by the Superconducting Magnet Group at Lawrence Berkeley National Laboratory (LBNL). The 28-GHz NbTi ion source magnet features a sextupole-in-solenoids configuration, which is comparable to the VENUS ECR magnet operated at LBNL. A shell-based support structure using bladders and keys has been incorporated into the design to allow for adjustments of the preload and reversibility of the magnet assembly process. The magnet has been assembled and successfully tested to operational currents at LBNL. This paper describes the basic design of the magnet and the passive quench protection system. The test results are also presented, including the quench behavior of the magnet, the training performance, and the magnetic measurement results.

The high luminosity large hadron collider (LHC) upgrade requires new quadrupoles, MQXF, to replace the present LHC inner triplet magnets. The MQXFA magnet is the first prototype that has a 150-mm aperture and uses Nb3Sn superconducting technology in a 4.2-m magnetic length structure. The support structure design of the MQXFA magnet is based on the bladder-and-key technology, where a relatively low pre-stress at room temperature is increased to the final preload targets during the cool-down by the differential thermal contraction of the various components. The magnet support structure components experience different load levels from pre-load to cool-down and excitation. Consequently, a few parts experience high stresses that may cause localized plastic deformations or internal fracture development. The concept presented in this paper for the failure assessment of support structures integrates nonlinear finite-element (FE) analysis with detailed sub-models and fracture mechanics into an advanced engineering tool. The nonlinear FE solutions enable estimations of the structural response to the given loads, and the advanced fracture analysis with failure assessment diagram assesses the structure safety index of results obtained from the FE model. The paper describes how the MQXFA end-shell segments are being optimized based on the failure analyses.

The heart of the present-day MRI scanners is a superconducting magnet that produces a highly homogeneous field at the centre. A multi-coil actively shielded superconducting magnet is designed, having dry winding i.e. free from any epoxy, for a whole-body 1.5 T MRI scanner. The magnet produces a homogeneity of ± 3.3 ppm in a 45-cm field of view. The multi-coil magnet would experience the stresses from the various sources during operation. The winding pre-tension; the thermal strains, due to cooling; and the Lorentz forces that contribute to the overall operational stress are considered to calculate various parameters of the dry wound magnet. The winding pretension has been determined after a thorough analysis of the hoop stress and the radial displacement of various components of the winding pack at various winding prestress ranging from 30 to 80 MPa. The role of the slip plane and the material (SS 304L and AA5083) of the bobbin in determining the operational stress in the dry magnet has been studied. The operational stresses have been analysed in minimizing the radial gaps between the coil and the bobbin. The role of the number of over-binding layers and their winding pretension has been studied for the multi-coil 1.5 T MRI magnet. [ABSTRACT FROM AUTHOR]

A rapid-cycling superconducting magnet is currently under development for the next-generation heavy-ion therapy. The non-oriented electrical steel (NOES) sheet, M470-50A5, is adopted as the cold iron yoke in the superconducting magnet to enhance the field and minimize the AC losses. In this paper, we measure the magnetic properties, magnetic permeability and hysteresis loss of a 0.5-mm thick NOES sheet at 4.2 K, 77 K and room temperature with a toroidal test specimen. The magnetic permeability as well as the hysteresis loops are investigated with a very low frequency until 3 T. To provide the magnetization for the magnet design, we modify the Jiles–Atherton (J–A) model so that the modified J–A model can predict not only the magnetization loops but also the magnetic permeability until a high magnetic field region. [ABSTRACT FROM AUTHOR]

Superconducting undulators generally depend on a liquid helium cryostat. If the cryostat can liquefy the boil-off helium completely, a large helium refrigerator can be avoided, and a large amount of electrical energy can be saved. However, many studies are limited by the excessively high heat load. In this work, systematic thermal analysis and optimization are carried out to minimize the total heat load so that it can be covered by the cooling capacity. Based on the analysis, one single thermal shield is set in the cryostat, and thermal interruptions are widely adopted together. Moreover, the cooling capacity matches the heat load well, and the excess cooling capacity is increased significantly. In the experiment, the cryostat was tested with no magnet, a small magnet and a full-scale magnet respectively so that the heat load could be analyzed step by step. Finally, zero liquid helium consumption was achieved with the full-scale superconducting magnet, which reached a current of 450 A. The excess cooling capacity accounts for approximately 40 % of the total cooling capacity, which is as high as approximately 2.0 W. This study can serve as a reference for the research of superconducting undulator and other magnet cryostats. • Zero liquid helium consumption is realized with a 1.5 m superconducting undulator. • Various heat load parts are analyzed, measured and investigated clearly. • Thermal interruptions play an important role in heat insulation of the cryostat. • The mechanical structure is simplified by one single thermal shield. • The cryostat can provide a large temperature margin for the superconducting magnet. [ABSTRACT FROM AUTHOR]

• The superconducting coil shapes for the Czochralsky technique magnet were optimized. • A uniform magnetic field was generated by two curve shape coils. • The conventional and optimized shapes were compared; the two curve shape coils will significantly reduce the magnet's cost and size. • Mechanical analysis was performed, and it was found that the stress in the coils was less than the permissible limit. Solar cells, electronics, and the semiconductor industry all need high-quality silicon crystals. The Czochralsky technique has been widely used to make a high-quality single silicon crystal from the silicon melt. However, this technique needs a strong magnetic field to stabilize the melt and control the temperature. In this paper, two coils with a curved shape have been optimized and simulated to produce a transverse magnetic field for the Czochralsky technique grower. The coils face each other and have an opening angle of 150°, and a NbTi superconducting wire was used to wind the coils with 5110 turns. The current was 106 A and flowing in the same direction. The finding results indicated that the magnetic field at the silicon melt center is 0.4 T, and the peak field in coils is 2.95 T. The optimized curve shape coils were compared with conventional coils (circle shape coils). The comparison indicated that the curve shape coils produced a highly uniform magnetic field, required less current, and significantly reduced the outer diameter of the superconducting magnet. In addition, heat generation by the current leads was calculated. In the case of the curve-shaped coils, less heat leakage has been achieved; as a result, the cooling capacity, magnet size, weight, and cost will be reduced. Furthermore, mechanical analysis was performed, and the results showed that the stress in the coils is within the permissible range for NbTi at 4.2 K. [ABSTRACT FROM AUTHOR]

• MD simulation and cryogenic experiments established comprehensive study. • The validity of the method is verified by the establishment of MD models. • The relationship between structure and properties in MD model is revealed. Epoxy resin (EP) plays a crucial role in safeguarding superconducting magnets. One of the major concerns related to its usage is its inherent susceptibility to cracking under cryogenic temperatures and the strong electromagnetic forces experienced during the operation of superconducting magnets. In this study, we utilize molecular dynamics (MD)simulation and cryogenic experiments to conduct a comprehensive investigation aimed at gaining a profound understanding of the cryogenic toughening mechanism in hyperbranched polymers-toughened (HBPs) EPs. Five different crosslinking models of EP composites were established by MD simulations. The performance parameters obtained from the MD simulation calculations are highly consistent with the experimental results, which included the glass transition temperature, coefficient of thermal expansion, mechanical properties, free volume and atomic mean square displacement. Moreover, the relationship between structural changes and properties of the MD models was investigated. This research method provides a new avenue of exploration for superconducting magnet encapsulation resin materials. [ABSTRACT FROM AUTHOR]

• The reliability of high-power switches in Fast Discharge Unit (FDU) is very important for the safety operation of superconducting magnets. In this paper, the reliability and test number of FDU switches are discussed. • The FDU configuration characteristics of different types of superconducting magnets are introduced, and some explanation and calculation on reliability are provided. • The reliability interval estimation after a certain test number is discussed by using the binomial distribution theory. • The reliability conformance test based on the claimed reliability is discussed to derive the test number. High-power switches, as the important active part of Fast Discharge Unit (FDU) in Tokamak, are designed to interrupt the circuit current and transfer the quench energy for protecting expensive superconducting magnets. Hence, their reliability has always been highly underlined. In this paper, the reliability and test number of FDU switches are discussed, mainly including three issues. First, the FDU configuration characteristics of different types of superconducting magnets are introduced, and explanations and calculations on reliability are provided. Second, the reliability interval estimation after a certain test number is discussed by using the binomial distribution theory. Three, the compliance test based on the claimed reliability is studied, and two types of test plans are discussed and compared to derive the test number. The discussion in this paper focuses on the FDU switches and provides valuable guidance for their reliability test and assessment. [ABSTRACT FROM AUTHOR]

To fabricate 10–16 Tesla high-field accelerator magnets, the high-Jc Nb3Sn 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 Nb3Sn 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 Nb3Sn filaments in the strand was higher than that of the coil. The maximum stress of the Nb3Sn 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.

The LHC accelerator research program (LARP), in collaboration with CERN and under the scope of the high luminosity upgrade of the Large Hadron Collider, is in the prototyping stage in the development of a 150 mm aperture high-field Nb3Sn quadrupole magnet called MQXF. This magnet is mechanically supported using a shell-based support structure, which has been extensively demonstrated on several R&D models within LARP, as well as in the more recent short (1.2 m magnetic length) MQXF model program. The MQXFA magnets are each 4.2 m magnetic length, and the first mechanical long model, MQXFA1M (using aluminum surrogate coils), and MQXFAP1 prototype magnet (the first prototype with Nb3Sn coils) have been assembled at the LBNL. In this paper, we summarize the tooling and the assembly processes, and discuss the mechanical performance of these first two assemblies, comparing strain gauge data with finite element model analysis, as well as the near-term plans for the long MQXF magnet program.

Poly(bithiophene) was synthesized in a nematic liquid crystal under a magnetic field. The polymers prepared by electrochemical polymerization exhibited an aligned schlieren texture parallel to the magnetic field direction. As a function of linear polarized electrochromism, the poly(bithiophene) thus obtained shows linear dichroism with color change via electrochromism. [ABSTRACT FROM AUTHOR]

A new quench detection and diagnostic system is required for the reliable operation of high-field superconducting magnets for fusion which is fabricated with high-temperature superconductor (HTS) cables. The conventional voltage-based diagnostic methods have a limitation in detecting local temperature changes in large-scale HTS magnets. To address the limitation, an acoustic-based diagnostic method using torsional waves applied by piezoelectric transducers is proposed. In addition, from the sensor data collected by the piezoelectric transducers, a new monitoring index that can measure the temperature change is extracted via chirplet transform (CT), which is one of the time–frequency analyses. The proposed quench detection method using torsional wave guiding is implemented in a vacuum pressure-impregnated, insulated, partial dislocation, extruded, and roll-formed (VIPER) cable, and the performance of the new index, time–frequency-based phase delay, is validated. This work proves that the propagation characteristics of torsional acoustic waves depend on the strength and location of the heat and that the change can be monitored via the proposed time–frequency-based phase delay. The preliminary development and results of a new quench detection method are discussed to validate future use in complex environments such as fusion power plants. [ABSTRACT FROM AUTHOR]

The article presents a new family of low voltage dc switching energy extraction (EES) systems designed for protection of superconducting magnet circuits at CERN, which is appropriate also in other applications. During normal operation, superconducting magnet circuits can store large amounts of energy in their magnetic fields. In the case of a resistive transition (known as “quench”), this energy may be dangerous as it can lead to high temperatures and voltages, eventually damaging the superconducting magnet coils. To prevent this, the magnetic energy must be extracted and dissipated outside the superconducting windings. For this purpose, dedicated energy absorbers are introduced in the circuit by means of opening of dc switches. For the protection of future superconducting magnet circuits at CERN, direct current switching systems (DCSS) with rated currents of 2000 and 600 A have been developed and qualified. Each DCSS is unpolarized and redundant, i.e., composed of two identical direct current switch (DCS) connected in series. Two methods for the current commutation toward the energy absorber element have been investigated, the first one based on IGBT and the second one based on thyristors. A high-power, inductive-dynamic drive provides the ultrafast opening of the vacuum interrupter in the DCS. [ABSTRACT FROM AUTHOR]

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We present magnetic, mechanical and thermal modeling results for a 3 Tesla actively shielded whole body MRI (Magnetic Resonance Imaging) magnet consisting of coils with a square cross section of their windings. The magnet design was a segmented coil type optimized to minimize conductor length while hitting the standard field quality and DSV (Diameter of Spherical Volume) specifications as well as a standard, compact size 3 T system. It had an overall magnet length and conductor length which can lead to conduction cooled designs comparable to NbTi helium bath cooled 3 T MRI magnets. The design had a magnetic field homogeneity better than 10 ppm (part-per-million) within a DSV (Diameter of Spherical Volume) of 48 cm and the total magnet winding length of 1.37 m. A new class of MgB2 strand especially designed for MRI applications was considered as a possible candidate for winding such magnets. This work represents the first magnetic, mechanical and thermal design for a whole-body 3 T MgB2 short (1.37 m length) MRI magnet based on the performance parameters of existing MgB2 wire. 3 Tesla MRI magnet can operate at 20 K at 67% of its critical current. [ABSTRACT FROM AUTHOR]

High-temperature superconductors have great potential for various engineering applications such as a flywheel energy storage system. The levitation force of bulk YBCO superconductors can be drastically increased by increasing the strength of the external field. Therefore, a 6T conduction-cooled superconducting magnet has been developed for levitation force measurement application. Firstly, to protect the magnet from mechanical damage, reliable stress analysis inside the coil is paramount before the magnet is built and tested. Therefore, a 1/4 two-dimensional (2D) axisymmetric model of the magnet was established, and the mechanical stress in the whole process of winding, cooling down and energizing of the magnet was calculated. Then, the charging, discharging, and preliminary levitation force performance tests were performed to validate the operating stability of the magnet. According to the simulation results, the peak stresses of all coil models are within the allowable value and the winding maintains excellent mechanical stability in the superconducting magnet. The test results show that the superconducting magnet can be charged to its desired current of 150 A without quenching and maintain stable operation during the charging and discharging process. What is more, the superconducting magnet can meet the requirements for the levitation force measurement of both low magnetic field and high magnetic field.