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Conventional power supplies for superconducting magnets rely on dissipative power electronic converters and current leads, which are a thermal path connecting room temperature to cryogenic superconductors, as well as an additional source of joule dissipation, thereby imposing a significant heat load on the cooling system. Flux pumps offer a contactless, low-voltage, and high-current alternative to power electronics exciters and current leads solutions. However, as flux pumps physical mechanism is complex and counterintuitive, their engineering process and development of viable and executive designs have proved to present major challenges. This Ph.D. project focused on numerical modeling, investigation, and engineering analysis of flux pumps. The research aimed to address gaps in scientific research surrounding the technology and its potential disruptive impact on enabling contactless and efficient energization of superconducting magnets. First, a numerical model was developed and validated against experimental results to unveil the intricacies related to voltage rectification in traveling field flux pumps. The model embeds artificial intelligence methods to address the relationship between critical current and n-value of HTS tapes concerning temperature and magnetic field. A new complete equivalent circuit was derived and exploited for fast system-oriented analysis of flux pumps. The numerical model was further exploited to develop an application-oriented optimal design procedure for traveling field flux pumps, which was tested to design and characterize a HTS dynamo and a linear flux pump for real applications. The study found that the performance of the flux pumps is highly dependent on the rated current and its total resistance and discussed the influence of these two load parameters on the viability of flux pumps. Overall, this Ph.D. project aimed to overcome the empirical approach with which flux pumps have been designed and analyzed for decades and applied a s

High-temperature superconductors (HTS) have the potential to enable magnetic fields beyond the current limits of low-temperature superconductors in applications like accelerator magnets. However, the design of HTS-based magnets requires computationally demanding transient multi-physics simulations with highly non-linear material properties. To reduce the solution time, we propose using Parareal (PR) for parallel-in-time magneto-thermal simulation of magnets based on HTS, particularly, no-insulation coils without turn-to-turn insulation. We propose extending the classical PR method to automatically find a time partitioning using a first coarse adaptive propagator. The proposed PR method is shown to reduce the computing time when fine engineering tolerances are required despite the highly nonlinear character of the problem. The full software stack used is open-source., Comment: Pre-submission version (preprint). Presented at and submitted to the proceedings of "The 15th International Conference on Scientific Computing in Electrical Engineering" (SCEE 2024), March 4-8, 2024, Darmstadt, Germany

It is expected to build a sustainable social system that uses “hydrogen” as a fuel to generate electricity without emitting CO2. To realize this, technology for storing a large amount of hydrogen is indispensable, and storage as liquid hydrogen is ideal. However, the efficiency of the cooling device in the temperature range around 20 K required for long-term storage with liquid hydrogen is low, and the equipment is huge and expensive, so it has not been established as a widely used technology. Magnetic refrigeration is expected to be a highly efficient refrigerator in the temperature range of around 20 K because it can realize an ideal refrigeration cycle. However, in magnetic refrigeration, it is necessary to give a magnetic field change to the magneto caloric material (MCM). Further, in order to perform cooling with a large capacity and extremely low temperature by magnetic refrigeration, the magnetic field strength of a permanent magnet is insufficient, and it is indispensable to use a superconducting coil capable of generating a strong magnetic field with low power consumption. This study aims to develop a static magnetic refrigeration system using multiple high-temperature superconducting coils. By utilizing the energy storage characteristics of the superconducting coil, we are considering a magnetic refrigeration system that can repeatedly generate magnetic field changes to save energy without the need for large amounts of energy to be taken in and out of the outside. We report on the technical feasibility of a static magnetic refrigeration system using HTS coils. The power consumption including the AC loss of two superconducting coils, which is the basic configuration of the static magnetic refrigeration system, is calculated, and the efficiency is estimated as a ratio to the assumed refrigeration capacity of the MCM., source:N. Hirano, Y. Onodera, T. Mito, Y. Ueno and A. Kawagoe, "Development of Static Magnetic Refrigeration System Using Multiple High-Temperature Superconducting Coils," in IEEE Transactions on Applied Superconductivity, vol. 32, no. 6, pp. 1-5, Sept. 2022, Art no. 0500105, doi: 10.1109/TASC.2022.3152456., source:https://doi.org/10.1109/TASC.2022.3152456

As a high-efficiency cooling technology for high-temperature superconducting coils, we have begun research and development to examine the feasibility of a cooling assist technology that maintains a cryogenic state by combining the magnetic force generated by the superconducting coil with magnetic refrigeration technology. Magnetic refrigeration requires the magneto caloric material to change the magnetic field. In many cases, the magnetic field change is obtained by moving the magnetic source, but moving the superconducting coil is not a good idea. Although it is possible to generate a change in the magnetic field by turning on and off the power supply of the high-temperature superconducting coil, it is unlikely to be established as a system that assists cooling of the superconducting coil because the coil generates heat due to AC loss. Therefore, it was considered that the magnetic field change can be obtained if the magnetic force generated from the superconducting coil can be controlled by the magnetic shield. As a verification of the principle, it was clarified experimentally that a magnetic field change can be obtained by repeatedly inserting and removing the magnetic shield into and from the gap between the magnetic field generation source and the magneto caloric material, and the temperature change can be extracted by the magneto caloric effect. In the experiment, the temperature change obtained when a magnetic shield was inserted into the air gap was measured by a simple test device using an iron-based magneto caloric material having high magneto caloric effect performance at room temperature and a permanent magnet. The principle verification confirmation test was performed using several types of magnetic shielding materials such as Permalloy bulks and the electrical steel sheets. In addition, numerical analysis is performed on the magnetic shielding effect, and the shielding effect is improved by increasing the thickness of the shielding material and the po, source:N. Hirano, S. Nagai, Y. Okazaki, T. Okamura, Y. Onodera and T. Mito, "Feasibility Study of High-Efficiency Cooling of High-Temperature Superconducting Coils by Magnetic Refrigeration," in IEEE Transactions on Applied Superconductivity, vol. 31, no. 5, pp. 1-4, Aug. 2021, Art no. 0600104, doi: 10.1109/TASC.2021.3055994., source:https://doi.org/10.1109/TASC.2021.3055994, identifier:0000-0002-1565-8353

Conceptual design studies for the Large-Helical-Device-type helical reactor, i.e., FFHR-d1, are being conducted in the National Institute for Fusion Science. Three different cooling schemes and conductor types have been proposed for the superconducting magnet system. A multiscale structural analysis is used to assess the mechanical characteristics of the magnet structure, taking into account the types of cooling schemes and superconductors. Multiscale analysis evaluates both the stress distribution in the coil support structure and local stress in the constituents of the superconductors without rebuilding a finite-element model of the support structure. Concerning a segmented fabrication of the helical coils using a high-temperature superconductor, the feasibility of segment installation is confirmed using a three-dimensional printing model, which identifies the maximum segment length and the necessary gap in the coil casing to install a segment., source:H. Tamura, N. Yanagi, K. Takahata, A. Sagara, S. Ito and H. Hashizume, "Multiscale Stress Analysis and 3D Fitting Structure of Superconducting Coils for the Helical Fusion Reactor," in IEEE Transactions on Applied Superconductivity, vol. 26, no. 3, pp. 1-5, April 2016, Art no. 4202405, doi: 10.1109/TASC.2016.2531008., source:https://doi.org/10.1109/TASC.2016.2531008, identifier:0000-0003-4210-9859

We report the fabrication of small (Ba,A)Fe2As2 (A: Na, K) coils using 10 m-class long round wires, fabricated by the powder-in-tube method. Coils are sintered using the hot-isostatic-press technique after glass-fiber insulations are installed. Critical current (Ic) of the whole coil using (Ba,Na)Fe2As2 and (Ba,K)Fe2As2 are 60 A and 66 A under the self-field, and the generated magnetic fields at the center of the coil reach 2.6 kOe and 2.5 kOe, respectively. Furthermore, the largest transport critical current density (Jc) and Ic in (Ba,Na)Fe2As2 wires picked up from the coil reach 54 kA cm−2 and 51.8 A at T = 4.2 K under a magnetic field of 100 kOe, respectively. This value exceeds transport Jc of all previous iron-based superconducting round wires. Texturing of grains in the core of the wire due to the improvement of the wire drawing process plays a key role for the enhancement of Jc.

The invention provides an assembly comprising a cryostat (6, 7, 8, 9) and a flat coil layer (3) of superconducting coils (2) for use with a magnetic levitation and/or acceleration motor system (1) of a lithographic apparatus. The cryostat comprises two insulation coverings (8, 9). The coil layer is arranged between the two coverings. The coverings each comprise an inner plate (10) configured to be cryocooled and an outer plate (11) parallel to the inner plate, and an insulation system with a vacuum layer (13) between the inner and outer plate. The insulation system of said covering comprises a layer of circular bodies (101), the central axes of these bodies extending perpendicular to the inner and outer plate, and is configured to provide a layer of point contacts between two layers of circular bodies or between a layer of circular bodies and the inner and/or outer plate.

Quench detection capability is essential for reliable operation and protection of superconducting magnets, coils, cables, and machinery. We propose a quench detection technique based on sensing local temperature variations in the bulk of a superconducting winding by monitoring its transient acoustic response. Our approach is primarily aimed at coils and devices built with high-temperature superconductor materials where quench detection using standard voltage-based techniques may be inefficient due to the slow velocity of quench propagation. The acoustic sensing technique is non-invasive, fast, and capable of detecting temperature variations of less than 1 K in the interior of the superconductor cable stack in a 77 K cryogenic environment. We show results of finite element modeling and experiments conducted on a model superconductor stack demonstrating viability of the technique for practical quench detection, discuss sensitivity limits of the technique, and its various applications.

Saturated-core fault current limiters (FCLs) are devices that have many applications and potential for use within power networks. At a commercial scale, these devices require high H-field magnets to saturate the steel core, which can typically only be achieved through the use of superconducting coils. Here, we present several challenges that arise in the application of superconducting coils in FCLs and discuss how to address these issues through a case study MgB2-based coil. It is found that significant ac magnetic fields, Lorentz forces, and Joule heating in components occur during normal and fault operations; however, these issues can be mitigated when properly addressed.

We have proposed a new method for detecting unusual local conditions in a high-temperature superconducting coil. In this method, two kinds of pick up coils for measuring electric fields and magnetic fields are used to obtain Poynting's vectors around the coil. This is a noncontact method using pick-up coils around the vessel for cooling the coil. The method has the following benefits: safe detection, easy handling, high sensitivity, and high usability. The purpose of this paper is to clarify the relation of measured signals to the conditions of the windings. When a temperature rise has been produced locally in the Bi-2223 solenoidal coil, Poynting's vectors around the coil and the temperature of windings were measured. It was found that the measured signals rapidly decrease as the temperature of the winding achieved a critical level, making this a reliable method to estimate the conditions in the windings.

Superconducting Magnetic Energy Storage (SMES) systems have theoretically been considered for model applications in a potentially compact and practical form for domestic sustainable power. Using two different models, we have compared two different types of superconducting solenoids for this purpose. The optimal performance of helically wound solenoids of NbTi (or MgB2) wires are compared with that of pancake solenoids of the YBCO tape. The maximum energy storage of the coils has been obtained for various parameters and dimensions by optimizing core radius, coil length, and magnetic field strength. Helical solenoids made from NbTi wires are shown to somewhat outperform pancake coils made of YBCO-coated conductors. However, this consideration is, respectively, made at operation temperatures of 4.2 and 77 K. The viability of such compact SMES for "domestic" (or some "exotic") sustainable energy systems is discussed.

This report results from a contract tasking Institute of Electrical Engineering as follows: The Grantee will investigate experimental studies of superconducting coils wound with the second generation of superconductors (11 G), which have YBCO superconducting layer deposited on a metallic substrate The behavior of coils carrying AC (alternating) currents with frequencies of the order of 100 Hz will be studied Short sample experiments and those with test coils using AC tolerant (filamentary) conductor under development and experiments with saddle type winding will also be performed., The original document contains color images.

Conductor insulation is one of the key components needed to make Ag-alloy clad Bi2Sr2CaCu2O8+x (Bi-2212/Ag) superconducting round wire (RW) successful for high field magnet applications as dielectric standoff and high winding current densities (Jw) directly depend on it. In this study, a TiO2/polymer insulation coating developed by nGimat LLC was applied to test samples and a high field test coil. The insulation was investigated by differential thermal analysis (DTA), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), dielectric properties measurement, and transport critical current (Ic) properties measurement. About 29% of the insulation by weight is polymer. When the Bi-2212/Ag wire is full heat treated, this decomposes with slow heating to 400{\deg}C in pure O2. After the full reaction, we found that the TiO2 did not degrade the critical current properties, adhered well to the conductor, and provided a breakdown voltage of >100 V, which allowed the test coil to survive quenching in 31.2 T background field, while providing a 2.6 T field increment. For Bi-2212/Ag RW with a typical diameter of 1.0-1.5 mm, this ~15 um thick insulation allows a very high coil packing factor of ~0.74, whereas earlier alumino-silicate braid insulation only allows packing factors of 0.38-0.48., Comment: Submitted to Superconductor Science and Technology

In recent years, many HTS superconducting magnetic energy storage (HTS-SMES) systems are investigated and designed. They usually consist of some superconducting element coils due to storing excessively high energy. If one of them was quenched, the storage energy of the superconducting element coil quenched has to be immediately dispersed to protect the HTS-SMES system. As the result, the current of the other element coils, which do not reach to quench, increases since the magnetic coupling between the quenched element coil and the others are excessively strong. The increase of the current may cause the quench of the other element coils. If the energy dispersion of the element coil quenched was failed, the other superconducting element coil would be quenched in series. Therefore, it is necessary to investigate the behavior of the HTS-SMES after quenching one or more element coils. To protect a chain of quenches, it is also important to investigate the time constant of the coils. We have developed a simulation code to investigate the behavior of the HTS-SMES. By the quench simulation, it is indicated that a chain of quenches is caused by a quench of one element coil.

In recent years, many HTS superconducting magnetic energy storage (HTS-SMES) systems are investigated and designed. They usually consist of some superconducting element coils due to storing excessively high energy. If one of them was quenched, the storage energy of the superconducting element coil quenched has to be immediately dispersed to protect the HTS-SMES system. As the result, the current of the other element coils, which do not reach to quench, increases since the magnetic coupling between the quenched element coil and the others are excessively strong. The increase of the current may cause the quench of the other element coils. If the energy dispersion of the element coil quenched was failed, the other superconducting element coil would be quenched in series. Therefore, it is necessary to investigate the behavior of the HTS-SMES after quenching one or more element coils. To protect a chain of quenches, it is also important to investigate the time constant of the coils. We have developed a simulation code to investigate the behavior of the HTS-SMES. By the quench simulation, it is indicated that a chain of quenches is caused by a quench of one element coil.

A literature review of the state of the art of HTS AC losses and power devices determined that the subject of low AC loss HTS tapes required additional work and input and that these could be applied to HTS transformers to obtain a device with lowered AC loss compared to using straight filament tape. A procedure for manufacturing short lengths of twisted filament tape, with novel matrix alloys, and physically distinct filaments was developed. Two alloys were used for the matrix material and the range of twist pitches was from 4 to 20 mm. Tapes samples with twist pitches of 10 and 8 mm were produced with Ic's of 40 A. The AC losses were measured at power fi-equencies in fields up to 0.04 T using a pick-up loop and a lock-in amplifier technique. Control samples of HTS tapes with straight filaments were found to have an AC loss which was predicted very well by the estabhshed equations in the literature. Some twisted filament samples had an AC loss signature that showed a significant lowering of the losses in the range of 0.01 to 0.03 T. No straight filament samples, however, were found to have lowered losses, including those with novel matrix alloys. Suitable materials for use at liquid nitrogen temperatures that can electrically insulate HTS tapes were investigated. It was found that many commonly available materials can be used in liquid nitrogen, however, the application method and adhesives must be considered. A range of pancakes and coils were manufactured using those insulation materials found most suitable. A suitable construction technique was investigated to manufacture robust potted pancake and solenoid coils and these coils were found to give negligible degradation in the Ic after thermo-mechanical testing.

The extensive research effort in the development of high-Tc superconducting (HTSC) class-II (Bi,Pb)2Sr2Ca2Cu3Ox+10(Bi(Pb)-2223) coils, and magnets, through processing optimization, and characterization of silver, and silver-alloy composite tapes, has been conducted at the Center for Superconducting and Electronic Materials (part of the Institute of Materials Technology and Manufacturing), Department of Materials Engineering, University of Wollongong. Studies leading up to the production of Bi(Pb)-2223 class-II coils, and magnets include the following investigations in materials processing, and science of Bi(Pb)-2223 composite tapes:- The processing of Bi(Pb)-2223 short, and long length composite tapes (from the standard procedure of PIT, to the conventional method of CTFF, and the novel format of WIT , or wire-in-tube), and the characterization on their physical, chemical, electrical, and magnetic properties by means of measurements - implemented techniques include; Vickers microhardness tests (HyT), particle size analysis (PSA), Xray diffraction (XRD), differential thermal and thermo-gravimetric analysis (DTA/TG), scanning electron microscopy with energy-dispersive spectrometry (SEM/EDS), electrical transport, ac-susceptibility, and the SQUID (superconducting quantum interference device) magnetometry. The effect of powder packing density, using the conventional method of powder-intube (PIT) by various means, on the transport critical current density, Jc, mechanical properties, and high-Tc phase (2223) formation of Bi(Pb)-2223 single filamentary (SF) superconducting tapes - higher initial packing density of PIT monocore short tapes has been found to give higher Jc values, as well as higher rate of 2223 formation, while lower initial packing density samples gave better mechanical performance. Critical strains for bend tests showed a dependence on the core thickness, and silver/oxide volume ratio. The effect of sintering periods on the microstructure, phase developmen

The general problem of shielding the occupants of manned space vehicles from various radiations likely to be encountered in space flight is discussed, and various published papers on the subject are briefly reviewed. The review indicates the importance of the problem and the interest that would attach to a radical solution. One possibility is shielding by the permanent magnetic field of a superconducting coil. A detailed analysis is made of the shielding that could be provided by such a coil and a preliminary estimate of the weight of such a device is made paying particular attention to the weight of the structure required to support the coil. A comparison is made of the weights calculated in this way with the weight of the spherical H2O shield which would give comparable protection. (Author)

In 1991, the superconducting magnet test facility had been constructed in National Institute for Fusion Science. The facility consists of a helium liquefier/refrigerator with the cooling capacity of 600 W at 4.5 K, large cryostats, a mechanical testing machine, DC power supplies with the maximum current of 75 kA and a distributed control system. So far, the development of the superconducting coils for the Large Helical Device had been conducted and many collaborative works have been carried out. However, the test facility with higher bias filed is needed to develop superconducting coils for fusion reactors and the cooling system, which can supply coolant of various temperature to test samples, is required to apply HTS to large-scale conductors. Therefore, the test facility will be upgraded to promote the development of superconducting coils for fusion reactors. The maximum bias field will be upgraded from 9 T to 15 T to investigate the performance of superconductors under the higher bias field and the existing helium liquefier/refrigerator will be replaced with a variable temperature one to test those under various temperature environment. Consequently, it is expected to progress the development of the superconductors for fusion reactors and the development of large-scale HTS conductors., source:https://doi.org/10.1585/pfr.10.3405020

An investigation into AC superconducting coils is performed with a permanent magnet generator for a wind power turbine of 15 MW. Two reference models are sized: on the one hand, a DTU and NREL 15 MW wind turbine model is taken as a reference to set the mechanical speed according to the output power and the mechanical constraints of the blades; and on the other hand, a 10 MW AC superconducting PM design by Dong Liu is taken as a reference to set the geometry and slot-pole combination, and resized the machine to 15 MW. Both reference models are fractional slot concentrated windings. The aim is to study the effects of multi-phase symmetric windings on the AC HTS coils and the overall performance of a superconducting PM machine. Thus: 1) A comparison is made between 3-phase and 12-phase windings with the same machine geometry. 2) A design of a 24-phase winding is made to endorse the findings and comprehend the multi-phase symmetric windings and their advantages. 3) The AC superconducting losses are assessed for the different winding layouts with the same current and turns per coil, focusing on the behaviour of the magnetic fields into the HTS coils. The analysis found that multi-phase symmetric windings enhance the machine's magnetic behaviour by making it smoother and eliminating the space sub-harmonics. Furthermore, reducing the flux densities' rippling behaviour in the airgap and the iron causes a reduction in hysteresis and dynamic losses. Also, the better winding factor of multi-phase windings improves the output power, making the machine even more compact. Moreover, to achieve an excellent multi-phase symmetric winding layout, the phasors must be unique. However, it is observed that using symmetric multi-phase windings cannot improve the AC losses and power factor. On the first hand, the hysteretic superconducting losses for HTS tape coils depend on the magnetic flux line's incident angle. On the other hand, the power factor strongly depends on the magnetic energy, https://doi.org/10.36227/techrxiv.15123966 In this paper, an AC superconducting multi-phase symmetric-winding machine is designed for a wind power generator to improve its performance and reduce losses, where four handpicked topological designs were explored and compared. In particular, it is found that using high-phase order of unique phasors further improves the performance. The iron losses are reduced, and the rippling behaviour is reduced due to the smoother airgap magnetic flux density. Furthermore, a higher LCM is achieved due to a better slot-pole combination for fractional slot concentrated windings without having space sub-harmonics. Nonetheless, it is shown that creating a smooth air gap magnetic flux density does not improve the AC hysteretic superconducting losses; thus, further analysis with another approach must be done. Moreover, it is found that the Meisner effect is present in the machine and is inversely proportional to the AC hysteretic superconducting losses. Finally, it shows that a 13-phase AC-superconducting machine can achieve a theoretical limit approaching 101.7017 Nm/kg for the torque-to-weight (TTW) ratio, outperforming a classic winding layouts., European Wind Energy Masters (EWEM)

An advanced ISO-FLUX equilibrium control scheme is developed and implemented in the JT-60SA equilibrium controller. For future fusion reactor, the VDE control by the active superconducting coils is essential due to the absence of in-vessel coils and stabilization plates, and the presence of large gap between plasmas and vacuum vessels with the tritium breeding blanket. Under the circumstances, the equilibrium controller should achieve plasma position/shape control and plasma current control by superconducting coils within limited power supply voltages, where plasma current control affects plasma position/shape control, and vice versa. The newly developed ISO-FLUX control scheme enhances the controllability under the above hybrid control of position/shape and plasma current circumstances. Furthermore, the new scheme also provides good controllability under large eddy currents conditions, which will also be expected in future superconducting tokamaks, such as JT-60SA, ITER, and DEMO due to its large inductance and high target plasma current. The JT-60SA equilibrium controller with the developed scheme is well verified by a magnetohydrodynamic equilibrium control simulator 'MECS' and ready for the integrated commissioning of JT-60SA.

The fast thermal and electromagnetic transients that occur in a superconducting magnet in case of a quench have the potential of generating large mechanical stresses both in the superconducting coils and in the magnet structure. While the investigation of such quench loads should generally be conducted to ensure a safe operation of the system, its importance is greatly enlarged in the case of high-field magnets based on strain sensitive superconductors. For these, a rigorous analysis of the magnet mechanics during a quench becomes critical. The scope of this work is hence to bring, for the first time, a detailed understanding of the three-dimensional mechanical behavior of a Nb3Sn accelerator magnet during a quench discharge. The study relies on the use of finite element models, where various multi-domain simulations are employed together to solve the coupled physics of the problem. Our analysis elaborates on the case study of the new MQXF quadrupole magnet, currently being developed for the high-luminosity upgrade of the LHC. Notably, we could find a very good agreement between the results of the simulation and experimental data from full-scale magnet tests. The validated model confirms the appearance of new peak stresses in the superconducting coils. An increase in the most relevant transverse coil stresses of 20–40 MPa with respect to the values after magnet cool-down has been found for the examined case., Peer Reviewed, "Article signat per 13 autors/es: J Ferradas Troitino, H Bajas, L Bianchi, B Castaldo, P Ferracin, M Guinchard, S Izquierdo, J V Lorenzo, F Mangiarotti, J C Perez, E Takala, G Vallone and C Senatore", Postprint (published version)

A mirror machine with a minimum B field for MHD stability is an option for a steady-state compact fusion neutron source design. A previous calculation of an idealized quadrupolar mirror field in Ref Agren and Moiseenko (2017) is extended to a magnetic field which smoothly evolves to expander regions beyond the mirror throats. In a minimum B field, the projection of a flux surface on planes perpendicular to the magnetic axis evolves from a circular shape at the mid-plane to a highly elliptical shape as the mirror ratio is increased. Magnetic shaping is made to find the minimal ellipticity. The ellipticity depends sensitively on the gyro center magnetic drift in the confinement region, and the optimal result approaches a state where the magnetic drift is made as small as possible, which corresponds to the SFLM (Straight Field Line Mirror) field. In such a magnetic field, in combination with a weak radial electric field, each guiding center is forced to move close to its mean magnetic surface, thereby suppressing neoclassical transport effects. Biased end plates, placed at the end tank outside the confinement region, is a tool to control the radial electric field. The biased end plates could also assist to more precisely determine the positioning of drift surfaces in the confinement region. The reproduction of the optimized magnetic field with superconducting coils is a challenge due to the strong gradients in B. This is solved by a special arrangement with compact 3D superconducting coils, and the reproduction of the magnetic field is demonstrated with a mirror ratio of 4. Mirror ratios exceeding 10 may be reachable with finite effects included. Analytical expressions in closed form are derived.

The residual magnetic field was measured to investigate its source for the Large Helical Device, the superconducting magnet system of which consists of two Helical Coils (HCs), two Inner Vertical (IV) coils, two Inner Shaping (IS) coils, and two Outer Vertical (OV) coils. NbTi cable-in-conduit conductors were adopted for the IV, IS, and OV coils. Firstly, Hall probes were installed at five periodic positions on the mid-plane of the inner cylinder of the cryostat. Since the residual field was changed by around 0.1 mT at all the positions during the warm-up of the superconducting coils, a major part of the residual field had to be induced by magnetization of the coils. In the next campaign (cool-down, plasma experiment, and warm-up), the Hall probes were moved to the five different vertical positions in order to measure the distribution of the residual field. Calculation of the residual field has been carried out under the assumption that NbTi filaments in each conductor are magnetized in the same direction as the field at the center of the conductor during excitation. From comparison between the measured and calculated values, we conclude that the residual field from the coils that had been excited to high currents should be reduced by around 35%, due to the self-field in strands in the conductor. The best fitted critical current densities of the IV and IS coils are 1.31 and 2.81 × 1010 A/m2, respectively, which are consistent with the field dependence obtained from the magnetization curve of each strand., source:https://doi.org/10.1016/j.cryogenics.2023.103673, identifier:0000-0003-1454-8117

Magnetic refrigeration technology is expected to be a highly efficient process at a temperature of around 20 K, which is the hydrogen liquefaction temperature. In magnetic refrigeration, a magnetic field change is applied to a magnetocaloric material (MCM) to obtain a magnetocaloric effect. In addition, since the greater the magnetic field change, the better the cooling characteristics, the magnetic field strength of permanent magnets is insufficient, and the use of superconducting coils that can generate strong magnetic fields with low power consumption is essential. We are researching and developing a static magnetic refrigeration system (SMRS) that does not have moving parts to obtain magnetic field changes, and generates them by altering the energizing current to the coil. The key to devising this system is an AC loss of the superconducting coil. In this study, we measured the AC loss under energization conditions of multiple palm-sized REBCO coils at liquid nitrogen temperature, and calculated the efficiency of the SMRS by improving the accuracy of the analysis method for evaluating the AC loss, based on the results. We report the results and discuss the technical feasibility of SMRS., source:N. Hirano, Y. Onodera, T. Mito, Y. Motoki and A. Kawagoe, "Basic Research on a Magnetic Refrigeration System for Cooling to Liquid Hydrogen Temperature," in IEEE Transactions on Applied Superconductivity, vol. 33, no. 5, pp. 1-5, Aug. 2023, Art no. 4702605, doi: 10.1109/TASC.2023.3263786., source:http://doi.org/10.1109/TASC.2023.3263786, identifier:0000-0002-1565-8353

Conductive surfaces in linear motors, performing high-dynamic motion, generate significant losses and parasitic forces due to eddy currents. While finite-element-analysis (FEA) models can estimate these effects accurately, their long computing time makes them unfavorable for the parametric analysis of the motor. Therefore, a computationally faster and accurate tool using semianalytical techniques is developed for these linear motors. This tool is applied to a superconducting linear motor where eddy-current losses within the cryostat are critical to the performance. The modeling tool is applied to two benchmark models of such a motor. Using benchmark 1, the developed tool is validated with FEA. The tool shows a major improvement in computation time when compared to FEA, with a relative error in instantaneous loss and force below 3%. For these reasons, the developed tool is suitable for the parametric analysis of the motor. In another study, a superconducting motor with essential conductive structures - cryostat wall, radiation shield, and cooling platform - is considered for parametric analysis. Results show that eddy-current losses increase when using a higher number of turns for the superconducting coils on account of a larger volume of the conductor and higher armature reaction.

The mass of stars is enough to confine a plasma to fuse light atoms, but this is not possible to engineer on Earth. Fortunately, nuclear engineering can rely on the magnetic confinement of a plasma using superconducting coils so long as the Tritium Breeding Ratio (TBR) is optimized. This paper will investigate some of the materials which can increase the rate at which Tritium is produced within the breeding blanket layer of Submersion Tokamak reactors, a design that uses magnetic confinement of a plasma in the shape of a torus to execute nuclear fusion. Using the Paramak Python module to model several geometries and OpenMC to run a simulation, it can be observed how neutron multipliers, enrichment, and the neutron energy spectrum affect TBR. This experiment will mainly observe different material choices that have been considered and their TBR based on their cross sections, dose rate, thermal properties and safety. By altering the neutron energy spectrum to account for DD and DT plasma, the difference in these compounds' Tritium breeding efficacy is noted. Neutron energy spectra are an important factor in optimising the TBR levels as the neutrons generated by the fusion reactions in the plasma interact with the breeder material in the blanket and produce tritium through the reaction with Lithium. Since Tritium is a rare isotope of hydrogen that is used as fuel in fusion reactions and has a short half-life, it is essential to produce tritium within the fusion reactor itself. Without the tritium breeding capability, it would not be feasible to generate energy via fusion. A TBR greater than unity indicates that the reactor can generate more tritium than it consumes, ensuring self-sufficiency in the tritium inventory. Since Tritium is the most reliable and efficient fuel for these reactors, optimising the TBR is of paramount importance in the long road to commercialization of nuclear fusion., Comment: 8 pages, 5 figures

The magnetic components produced by nonaxisymmetric superconducting coils in the Large Helical Device produce a complicated magnetic structure in the plasma periphery, which strongly depend on the configuration of electric currents in the magnetic coils. A tangentially viewing charge-coupled device camera has observed line emission of doubly ionized carbon CIII. The dependence of the 3-D distribution of the CIII emission on magnetic configurations will be discussed., source:M. Shoji and T. Watanabe, "Visible Images Induced by the Three-Dimensionally Complicated Structure of the Plasma Periphery in the Large Helical Device," in IEEE Transactions on Plasma Science, vol. 36, no. 4, pp. 1374-1375, Aug. 2008, doi: 10.1109/TPS.2008.927340., source:https://doi.org/10.1109/TPS.2008.927340

In a cold test of the JT-60SA CS1 module, which is composed of six octa-pancake coils and one quad-pancake coil wound with Nb3Sn CIC conductors, the measurement of self-magnetic fields generated by the CS1 module was conducted. As a result, the decay of the self-magnetic field was observed after the CS1 module was degaussed. The time constant of the decay was from 90 s to 269 s. The measurement results indicate that loop currents with long time constants occurred in the CS1 module due to coil energization. The loop currents with long time constants, which are also called ‘supercurrents’, are irregular coupling currents that are an unexpected phenomenon from the conductor design.Loop currents with long time constants in CIC conductors have only been observed in large superconducting coils so far. To verify an occurrence of loop currents with long time constants in a CIC conductor without coil winding configuration, self-magnetic fields were measured using a short straight CIC conductor where a multi-strand cable was connected electrically at the conductor ends. As a result, loop currents with long time constants ranging from 57 s to 105 s occurred in the short straight CIC conductor, the length of which is approximately 1 m. The measurement results indicate that the conductor length is not always related to loop currents with long time constants. The occurrence of loop currents with long time constants in the CIC conductor depends on the presence of current paths at the conductor ends., source:Tetsuhiro Obana, Kazuya Takahata, Shinji Hamaguchi, Hirotaka Chikaraishi, Suguru Takada, Akifumi Iwamoto, Shinsaku Imagawa, Toshiyuki Mito, Haruyuki Murakami, Kyohei Natsume, Kaname Kizu, Investigation of long time constants of magnetic fields generated by the JT-60SA CS1 module, Fusion Engineering and Design, Volume 137, 2018, Pages 274-282, ISSN 0920-3796, https://doi.org/10.1016/j.fusengdes.2018.10.005., source:https://doi.org/10.1016/j.fusengdes.2018.10.005

The fundamental research of HTS coil cooling assist technology by magnetic refrigeration has been studied. Using magnetic refrigeration technology, we are focusing on numerical analysis to see if the cooling efficiency around 20 K of high-temperature superconducting coils can be enhanced. The feature of the proposed cooling method is that it utilizes the leakage magnetic field from the HTS coil. Magnetic refrigeration technology needs to apply a change of magnetic field to a certain type of magnetic material, and the configuration of applying a change of magnetic field to the material in the cryostat is the point of the proposed cooling assist method. We confirm a system that uses a magnetic refrigerator in combination with a refrigerant circulation cooling system by utilizing the leakage magnetic field generated when using a superconducting coil and producing a magneto caloric effect has higher refrigeration performance than the refrigerant circulation cooling system alone., source:Naoki Hirano et al 2020 J. Phys.: Conf. Ser. 1559 012090, source:https://doi.org/10.1088/1742-6596/1559/1/012090

This article describes the DEMO cryostat, the vacuum vessel, and the tokamak building as well as the system configurations to integrate the main in-vessel components and auxiliary systems developed during the Pre-Conceptual Design Phase. The vacuum vessel is the primary component for radiation shielding and containment of tritium and other radioactive material. Various systems required to operate the plasma are integrated in its ports. The vessel together with the external magnetic coils is located inside the even larger cryostat that has the primary function to provide a vacuum to enable the operation of the superconducting coils in cryogenic condition. The cryostat is surrounded by a thick concrete structure: the bioshield. It protects the external areas from neutron and gamma radiation emitted from the tokamak. The tokamak building layout is aligned with the VV ports implementing floors and separate rooms, so-called port cells, that can be sealed to provide a secondary confinement when a port is opened during in-vessel maintenance. The ports of the torus-shaped VV have to allow for the replacement of in-vessel components but also incorporate plasma limiters and auxiliary heating and diagnostic systems. The divertor is replaced through horizontal ports at the lower level, the breeding blanket (BB) through upper vertical ports. The pipe work of these in-vessel components is also routed through these ports. To facilitate the vertical replacement of the BB, it is divided into large vertical segments. Their mechanical support during operation relies on vertically clamping them inside the vacuum vessel by a combination of obstructed thermal expansion and radial pre-compression due to the ferromagnetic force acting on the breeding blanket structural material in the toroidal magnetic field.