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Superconducting electron cyclotron resonance ion sources (ECRISs) using NbTi coils and optimized for 28 GHz resonant heating have been successfully operated for almost two decades. Moving to higher heating frequencies requires increased magnetic fields, but traditional racetrack-and-solenoid ECRIS structures are at their limit using NbTi. Rather than moving to a superconductor untested in this field, the Mixed Axial and Radial field System (MARS) being developed at Lawrence Berkeley National Laboratory employs a novel closed-loop-coil design that more efficiently utilizes conductor fields and will allow the use of NbTi in a next-generation, 45 GHz ECRIS. This article presents the design of the shell-based support structure central to the MARS-D magnet design, as well as structural analysis of its components and optimization of pre-load parameters that will guarantee its successful operation.

In a typical Nb3Sn cable for fusion applications, the knowledge of the strain state of Nb3Sn filaments is important to predict and interpret the conductor performance in operation. Amongst the relevant strain sources, the predominant is the thermal strain that arises during the cool-down of the conductor to operating temperature, due to the different expansion of Nb3Sn and copper in the cable and the stainless steel conduit. This work addresses the characterization of Nb3Sn thermal strain in the React & Wind prototype (RW2) developed by EPFL-SPC for the toroidal field coil and the central solenoid of the EUROfusion DEMO fusion reactor. AC susceptibility measurements were performed on the RW2 prototype to assess the thermal strain distribution in the cable cross-section, before and after undergoing electromagnetic and thermal cyclic loading. The results of the analysis have shown that RW2 exhibits a significantly lower absolute mean strain value (about −0.3%), compared to many Wind & React ITER conductor samples investigated with the same method. In addition, the analysis highlighted that the assessed thermal strain distribution does not vary significantly before and after the electromagnetic and thermal cycles, confirming the small performance degradation in the RW2 conductor that has been recently reported. [ABSTRACT FROM AUTHOR]

The Center Solenoid Model Coil (CSMC) is a pre-research project of CFETR, and its task is to design and manufacture the CS superconducting model coil to gain wider experience in solving the related technical problems existing in design and construction of CFETR CS coils. The expected achievement is to charge the CSMC up to the operation current of 47.65 kA and the maximum magnetic field to 12 T with a swift rump rate of 1.5 T/s without quench. Quench detection by voltage measurements is likely to be the fastest available technical solution to avoid coil's damage caused by quench, but the voltage detection is a real challenge due to large noise induced by the power supply in alternating current operation. The pick-up sensors, comprising the co-wound wire (CWW) and the co-wound tape (CWT), are used in the CSMC quench detection system for noise compensation and suppression. To accurately compensate all related induced voltage in the multi-pulse coil system, the foremost task is to estimate the static inductance matrix between the CSMC and its pick-up sensors. In this paper, a numerical model is developed for inductance calculation and analysis. Moreover, several numerical simulations with this design model to evaluate the maximum inductive noises and quench detection signals by CWW and CWT have been conducted for the case of the worst test scenarios. [ABSTRACT FROM AUTHOR]

The “Divertor Tokamak Test” (DTT) facility is an experimental fusion reactor being built in Frascati (IT) in the framework of the European Fusion Roadmap. The DTT Central Solenoid comprises six independently energized modules, wound from Nb3Sn Cable-In-Conduit Conductors (CICC). The future addition of a High Temperature Superconductor (HTS) insert would enhance the CS performance, in terms of magnetic flux density and magnetic field produced in the machine and would represent a fundamental technology demonstration toward high-field fusion. Along with the LTS cables, the Central Solenoid complex aims to reach 18 Wb at the pre-magnetization phase, being 16.54 Wb with the LTS CS only. Each LTS module is internally divided into three sub-modules: High Field (HF), Medium Field (MF) and Low Field (LF), each with a dedicated CICC cable optimized for the intense electromagnetic loads during the plasma scenarios. The LTS cables adopt a 316LN steel jacket and a fiberglass-reinforced resin insulation layer. The conceptual design presented here concerns an HTS insert, to be possibly placed inside the CS bore in the machine, employing a Round-In-Square (RIS) configuration of the conductor with either aluminum alloy or steel jackets. The study carried out for the design of the HTS insert and its pre-compression structure, the main electromagnetic and structural analyses and the design solution are presented in this work. [ABSTRACT FROM AUTHOR]

As part of the European Strategy for Particle Physics there is an ongoing development towards a Future Circular Collider (FCC-ee) where electron-positron collisions could be used to study the entire electro-weak sector in a low background environment. Particle detectors are used to study these collisions and a strong magnetic field is required to measure the particles’ momenta. Currently, two detector concepts are being studied: the Innovative Detector for Electron-positron Accelerators (IDEA) and the CLIC-Like Detector (CLD). Both these detectors include a superconducting solenoid magnet with a central field of $2 \,\mathrm{T}$ of which the designs are presented here. The IDEA magnet has an stored magnetic energy density of 14 kJ/kg and in CLD this is 12 kJ/kg. Taking into account their respective free-bore diameters of $4.2 \,\mathrm{m}$ for IDEA and $7.2 \,\mathrm{m}$ for CLD this results in very challenging designs for which the mechanical and quench studies are presented. Their results are promising, but extensive R&D on these magnets would be needed in the future to reach the goals set out in the Conceptual Design Report (CDR). [ABSTRACT FROM AUTHOR]

The ITER Central Solenoid (CS) consists of a stack of six independent coil packs called modules. It features a total height of 18 m and a diameter of over 4 m. The modules are in an advanced stage of fabrication and testing by the US ITER Project Office (USIPO) and its subcontractor General Atomics (GA). A qualification module mockup at one to one scale but of reduced height was wound and Vacuum Pressure Impregnated (VPI) by GA to validate final manufacturing, using tooling and processes fully representative of a series module. The module was submitted to a thermal cycle down to the temperature of 4.5 K at which the coils will be cooled by supercritical helium. During plasma operation, the CS modules are subjected to a complex combination of static and dynamic forces. The understanding of the mechanical behaviour of the CS module coils is of paramount importance to analyse and predict the overall response of the CS stack. To this purpose, an extensive programme of investigation of the module mockup has been defined and applied. This allowed assessing, through examination and testing of a large number of VPI conductor array samples extracted from the mockup, the soundness of the coil through advanced non-destructive examination techniques including X-ray microtomography, dimensional metrology measurements and micro-optical observations. Moreover, additional testing of physical and mechanical properties carried out at room and cryogenic temperature allowed the behaviour of the conductor stacks to be assessed. The paper summarises the results of these investigations and their interpretation through mechanical analyses based on the individual properties of the coil constituents. [ABSTRACT FROM AUTHOR]

The electron cooling technology is applied in the spectrometer ring (SRing) to improve the luminosity of ion beam for the High Intensity heavy-ion Accelerator Facility (HIAF). The electron cooler consists of a gun section, two 90-degree toroids, a cooling section and a collector section. There are four kinds of main coils used to provide longitudinal magnetic fields along the path of the electron beam. In this paper, we present the modeling and analyzing of the electron cooler magnets by three-dimension software. The optimizing of the magnetic field of cooling section is completed to achieve the required effective cooling length. The magnetic fields along the electron beam path and ion beam path are calculated and the beam trajectory of typical ion is also simulated to offer data for correcting the orbit. [ABSTRACT FROM AUTHOR]

In this work, we experimentally investigate the current carrying capacity of single REBCO tapes and stacks made 5 12 mm REBCO tapes with a 25 μm copper stabilizer in liquid helium in comparison with those made of bare tapes with no stabilizer at current ramp rates up to 55 kA/s. The motivation for the research was checking the usability of REBCO stacks as basic sub-elements for high current superconducting cables operating in fast cycling modes at 4.2 K. An original experimental technique was employed to induce the extremely high ramp rates. During the tests, one or 5-folded stacks curled into rings 95 mm dia with different types of joints were charged in the external magnetic field generated by an outer solenoid at ramp rates up to 1.6 T/s. The curled REBCO stacks were either soft-soldered over their entire length or contained local joints only. The maximum screening current induced in the samples during the outer solenoid charging Imax was registered. Our experiments showed that the current carrying capacity of the REBCO tapes and stacks was strongly affected by the absence or presence of the copper stabilizer as well as the type of the joint. The reasons for the Imax limitation for the copper stabilized and bare samples are also briefly discussed. [ABSTRACT FROM AUTHOR]

The Fermilab Mu2e experiment has been developed to search for evidence of charged lepton flavor violation through the direct conversion of muons into electrons. The transport solenoid is an s-shaped magnet that guides the muons from the source to the stopping target. It consists of 52 superconducting coils arranged in 27 coil modules. A full-size prototype coil module, with all the features of a typical module of the full assembly, was successfully manufactured by a collaboration between INFN-Genoa and Fermilab. The prototype contains two coils that can be powered independently. To validate the design, the magnet went through an extensive test campaign. Warm tests included magnetic measurements with a vibrating stretched wire and electrical and dimensional checks. The cold performance was evaluated by a series of power tests and temperature dependence and minimum quench energy studies.

Bi-2212 is one of the most hopeful superconducting material by virtue of its excellent irreversible field and isotropic electromagnetic characteristic. We developed Bi-2212 insert coil for the sake of testing the uniform performance of the round wire (RW). Some important explorations were made including the preliminary test of coil insulation, sealing and heat treatment. In the end, the insert coil achieved a critical performance of 130 A at 12 T and 4.2 K. The experiment results indicated that Bi-2212 RW had met the future application. [ABSTRACT FROM AUTHOR]

2G high-temperature superconducting (HTS) wires and YBCO-coated conductors perform better carrying current capability, which is potentially applied to the manufacture of HTS magnets. This article presents the experimental results of the pumping current for YBCO coils using a pulse-type magnetic flux pump in the conduction-cooling system and liquid nitrogen bath (LN2) cryogenic environment. The optimization of the flux pump used in the conduction-cooling system is that a constantan heater was added to keep the temperature of the pumping bridge at a certain value. The excitation effects of the YBCO coil at different temperatures were investigated in the conduction-cooling system. A fast increase of pumping current in the YBCO coil occurs when the temperature of the YBCO sheet (i.e., pumping bridge) is in the range of 50–80 K. The relationships among the saturated pumping current and input voltage, working frequency, numbers of magnetic poles were also studied. Using the seven-pole configuration, the saturated current can reach 155 A when the frequency is 20 Hz and the voltage is 6 V. The excitation characteristics of the flux pump in the LN2 cooling system show the possibility of the pulse-type magnetic flux pump for the practical application of HTS magnets. [ABSTRACT FROM AUTHOR]

The “Divertor Tokamak Test facility” (DTT) is an experimental fusion reactor being built in Frascati (IT) in the framework of the European Fusion Roadmap. The DTT Central Solenoid operates in a pulsed regime to generate the magnetic flux needed to induce the plasma current and is therefore subjected to burdensome load conditions. In DTT, this magnet will consist of a stack of six layer-wound independently energized modules, wound with Nb3Sn Cable-in-Conduit Conductors. Different layout solutions have been studied to improve the performance of the CS in terms of magnetic flux density and structural integrity. The design presented is the result of the “Design Explorer” algorithm that has been specifically developed for this purpose. This code investigates all possible configurations to find the optimum conductor geometry and winding solution by considering measurable physical quantities to maximize the magnetic flux density while maintaining mechanical stresses at an acceptable level. This manuscript includes the electromagnetic calculation related to the heterogeneous plasma scenarios of the machine, the static structural and the fatigue life assessment and the full set of in-depth analyses performed for the qualification of the main components of the CS structure. [ABSTRACT FROM AUTHOR]

High Temperature Superconductors (HTS) are promising materials for future fusion magnets. One of HTS conductors' main issues is the quench protection: the quench develops much slower than in LTS, delaying the quench detection by voltage monitoring and causing a massive temperature increase before detection. The Swiss Plasma Center (SPC), with the support of EUROFusion, has upgraded the SULTAN facility to test large current conductors during the whole quench evolution. The 100 kA superconducting transformer has been replaced by an 18 kA direct power supply, which allows sustaining the operating current in the sample during a quench. Five HTS conductors have been manufactured at SPC: they are sub-size of the HTS high-current cables designed by the group for an HTS high current high field cable proposed for EU-DEMO Central Solenoid (CS) hybrid magnet. Every conductor has a specific feature. The aim is to compare the quench behavior of the five conductors “parametrically”. The commissioning of the upgraded facility and the preliminary results of the measurements are presented in this work. [ABSTRACT FROM AUTHOR]

In the framework of the HL-LHC project, the present LHC low-β superconducting quadrupoles will be substituted with higher performance Nb3Sn magnets (MQXF) with 11.4 T coil peak field. MQXF coils are impregnated with epoxy resin to reduce risk of stress concentration on the brittle conductor. The magnet quench protection is provided by CLIQ and quench heaters to ensure a redundant system. Quench heaters are impregnated with the coils in order to have suitable thermal contact with them, and to prevent the hot spot temperature from exceeding 350K during normal operation in case of a quench. Quench heaters are insulated from the coil by S-2 Glass and polyimide. The test of the first MQXF prototype (4 m long) MQXFAP1 was stopped by a coil-to-ground short circuit triggered by a heater-to-coil short. This issue triggered a root analysis of the causes of this short. Here we prove that the use of a non-conforming cloth in coil impregnation, further weakened by non-conforming high voltage test, has triggered the shorts. Moreover, we present an analysis of the heater-to-coil insulation strength, showing the role of blistering phenomena and how they are triggered by a combination of magnet powering and heater firing. [ABSTRACT FROM AUTHOR]

The Deep Underground Neutrino Experiment (DUNE) at Fermilab is one the most challenging next-generation experiments in the field of neutrino physics. It will feature two detectors for a detailed study of neutrino oscillations using an unprecedentedly intense neutrino beam. The two detectors are a Near Detector located on the Fermilab site, 574 m away from the neutrino generation, and a Far Detector in South Dakota, 1300 km away. The Near Detector consists of three subdetectors, based on different technologies in order to achieve the best understanding of the neutrino beam. One key element of the Near Detector is a High Pressure Argon TPC surrounded by a calorimeter. This detector will need a 0.5 Tesla magnetic field transverse to the neutrino beam direction, with a 7 m diameter, 8 m long warm bore. A thin superconducting solenoid with a partial yoke, needed in order to minimise the amount of material along the path particles take crossing the different elements of the Near Detector is proposed. In this paper we present a detailed magnetic analysis and a preliminary study of the cooling, the cable and the mechanics for this magnet. [ABSTRACT FROM AUTHOR]

The ITER Central Solenoid (CS) will be manufactured by assembling a stack of six modules, which are under fabrication by the US ITER organization and its subcontractors. The tests of the first CS Module have been performed at the premises of the General Atomics (GA) facility in Poway (US), in order to check compliance to the ITER requirements. Among other tests, the magnet was submitted to exponential dumps of the transport current from different initial values (10, 15, 20, 22.5, 25, 35, 40 kA) down to 0 kA. These tests are aimed at conducting DC breaker commissioning of the test facility and were used to measure the AC losses in the coil during electrodynamic transients. This paper presents the results of these measurements, along with a comparison with analytical computations of the losses in the magnet. [ABSTRACT FROM AUTHOR]

In the current energy scenario, due to the increment in power generation from renewable sources, the importance of electrical storage systems has increased significantly, and as a consequence, the study of the improvement of its efficiency and the design of new storage systems also increased. Superconducting material permits the design of Superconducting Magnetic Energy Storage (SMES). The main problem of SMEs is the low energy density they have, what make the optimization of design to be one of the keys for inclusion of this elements in the power grid and other specific applications as, for instance, flux pumps. As the only basic forms for SMES, and with the objective of its mathematical optimization, this work (i) evaluates the mathematical equations for a real solenoidal winding, and (ii) develops the equivalent equations for a toroidal winding, from the electromagnetic laws. Then, (iii) a practical structure formed by short solenoids connected in series along a circular axis (quasi-toroidal structure) is studied. Due to the large number of equations involved in this case, the finite-element method in used here. Finally (iv), in order to validate the results without building the complete solenoid (impossible at the time), one of the magnetic coupling between two solenoids in the quasi-toroidal winding was developed according with the theoretical method, and experimentally tested. The study was carried out by programming different dimensions in order to make conclusions for a further development of an optimization algorithm. These conclusions are presented. This work is the first stage for the optimized design of a SMES, and presents the complete equations of the real toroidal winding as the base of the outline dimensions of a practical quasi-toroidal SMES. [ABSTRACT FROM AUTHOR]

The ITER Central Solenoid (CS) modules are under fabrication by the US ITER organization and its subcontractors. US ITER will supply seven modules to the ITER Organization (IO), six of which will be assembled in a stack that forms the ITER Central Solenoid, the last one being spare. The first module, namely CSM 1 was manufactured by General Atomics (GA) and went through Factory Acceptance Tests (FAT) including high voltage testing, Paschen testing and then cold test at 4.5 K and up to 40.0 kA in order to demonstrate compliance with coil performance requirements. The paper focuses on the results of the first CS Module thermal hydraulic characterization without current (and field). Pressure drops, transit time, and thermal coupling between pancakes are presented. Analysis results and tests are also compared. [ABSTRACT FROM AUTHOR]

The last acceleration stage of the deuteron beam of the LIPAc linear accelerator is provided by eight superconducting cavities in a cryomodule (SRF Linac). Each cavity needs a magnet package, which consists of a solenoid for beam focusing and two vertical and horizontal dipole correctors for beam steering. The superconducting coils are fed by vapour cooled current leads. The beam position monitor is part of the magnet helium vessel. The series fabrication of eight sets of magnets and current leads has been performed by Elytt Energy, under CIEMAT follow-up. This paper describes the final design used for production, the main challenges addressed during fabrication, together with the quality control procedure, acceptance tests and qualification criteria to validate both the magnets and current leads. Currently some activities are being performed in the magnet helium vessels for improvement of surfaces for handling inside the clean room and reducing the risk of presence of particulate contaminations in the beam tube. [ABSTRACT FROM AUTHOR]

In the scope of the Future Circular electron positron Collider study (FCC-ee), the IDEA detector is developed. It comprises a superconducting solenoid with free bore of 4 m, 6 m long and a central magnetic field of 2 T. The positioning of the magnet between the inner tracker and the electronic calorimeter heavily constrains the magnet design, as it is required to have the lowest possible radiation length, so minimum thickness and lowest density material. With respect to the classical solution of a solenoid enclosing the calorimeters, a cost reduction of about 50% is expected due to size reduction. An optimization of the different components of the magnet system has been carried out, resulting in the development of a new composite high-strength conductor that can be used to build a 30 mm thin solenoid. The quench analysis of the solenoid will be presented as it is of critical importance given the high energy density in the magnet of 21 kJ/kg. A cryostat made of concentric aluminium shells would account for about 50% of the radiation length of the magnet and most of this material is used in the outer vacuum shell of the cryostat to prevent buckling. In order to further reduce the radiation length, two fundamentally different approaches are being analysed. The first method focuses on reducing drastically the outer shell thickness. This leads to use honeycomb composites, reinforcing bars and corrugated shells for the outer shell of the cryostat. The second approach consists of supporting very thin cryostat shells directly on the solenoid cold mass using proper support. This can be achieved by replacing the thick walls and MLI insulation by a material that can sustain 1 atm while having low radiation length and low thermal conductivity. Cryogel Z has shown promising properties and its suitability for this project is being analysed. This novel approach has never been used so far for superconducting magnets. [ABSTRACT FROM AUTHOR]

The construction of a magnet system for the tokamak device of JT-60 super-advanced (JT-60SA) was completed in March 2020. The manufacturing of central solenoid (CS) had been finished in March 2019. The circularity of 4.0 mm is a requirement for CS manufacturing from the point of view of plasma control. The high accurate manufacturing method and jigs had been developed, and the circularity of CS achieves 1.44 mm, which meets the requirement of 4.0 mm. The clearance between the CS and the TF coils is very small, only 14 mm in design. In case the CS touches the TF coils and is subjected to load during operation, the CS can be damaged. Thus the surface dimensions of the CS and the TF coils have been measured before the installation of CS to confirm if the clearance is sufficiently large to avoid the CS crashing into the TF coils. The CS was successfully installed to the tokamak center without any damages in December 2019 as the final step of the magnet assembly of JT-60SA. In this paper, the manufacturing results and the installation of the CS are described. [ABSTRACT FROM AUTHOR]

The central solenoid model coil (CSMC) for China Fusion Engineering Test Reactor (CFETR) is being developed in the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The maximum magnetic field is 12 T in the bore of the Nb3Sn coils. It has a 1.5 T/s changing rate under 47.65 kA operating current. It was designed as a hybrid superconducting magnet with Nb3Sn and NbTi coils to reduce cost. The detailed structure of the CSMC has been designed, it mainly including Nb3Sn coils, NbTi coils, preload structure, coil buffer zone, joints, supports, feederthroughs, helium pipes and pipe supports. The preload structure consisting of 15 preload beams, 30 preload rods and support plates. And a 75 MN preload force will be applied on the preload structure at room temperature. This paper describes the final design of the Central Solenoid Model Coil. And the mechanical analysis results show that the final design is reasonable and feasible. [ABSTRACT FROM AUTHOR]

The future compact fusion reactors, will feature very high, >16 tesla, magnetic fields, which can be only created by magnet coils wound with the second generation (2G) superconducting wire. The 2G wires are currently manufactured with a thin (1-2 μm) YBCO layer deposited on a ∼100 μm thick metal substrate. The substrate makes up a considerable portion of the cross-section, thus reducing the engineering current density. It also prevents effective inter-filament current sharing, and the wide tape geometry is responsible for high magnetization loss. We report on the recent progress in the development of a new type of high-temperature superconducting cable architecture for the central solenoid of a high-field fusion reactor. The new architecture combines two recent innovations: (i) Reduction of AC loss by bundling narrow, 1-2 mm, exfoliated YBCO filaments into a cable, (ii) continuous winding and parallel slicing technologies, which eliminate labor-intensive and expensive handling of narrow filaments, critical for the central solenoid, which operates under pulsed load. [ABSTRACT FROM AUTHOR]

The Central Solenoid (CS) model coil, which is used to develop and verify the larger-scale superconducting magnet technology of China Fusion Engineering Test Reactor (CFETR), has been designed and is currently being manufactured at ASIPP. In case of an emergency shut-down like in succession of a quench, the voltage across the coil may rise to about 2.1 kV. Therefore, the coil has to be provided with a reliable electrical insulation. The electrical insulation systems of the CS model coil consist of turn, layer, and ground insulation. The insulation electrical performance tests are required to carry out at different stages of the manufacturing process to verify the insulation performance of the model coil. This paper gives the description of the insulation system, the applied and proposed test procedures. The test process of the electrical qualification test on mock-up coil is introduced. The test results are analyzed to verify the feasibility of insulation system design and manufacturing. [ABSTRACT FROM AUTHOR]

A central solenoid model coil (CSMC) is being developed to verify the large-scalar superconducting coil manufacture technology for China Fusion Engineering Test Reactor (CFETR) in Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The turn insulation wrapping of the Nb3Sn pancake coil is conducted after the coil heat treatment. The turn releasing technology is necessary to be developed and verified to insure there is no damage to Nb3Sn conductor during the turn insulation wrapping of the Nb3Sn pancake coil. This paper introduces the design, analysis and verification for the safe stretch distance, the design and debugging of the special equipment, and the process experiment with the 4 × 4 mockup coil. [ABSTRACT FROM AUTHOR]

Bifilar coil is one of the most applicable structures used for resistive-type superconducting fault current limiter. However, the turn-to-turn (longitudinal) insulation of the bifilar coil under lightning and switching impulse is rather different from the conventional pancake coil. The longitudinal insulation is characterized as the distributed circuit of the coil under high-frequency excitation, and the capacitance, inductance, and resistance parameters are solved by finite element model. The influence of those resistance, inductance and capacitance (RLC) parameters on the accuracy of the model is analyzed, and two samples of one bifilar pancake coil and two series connected bifilar coils are fabricated for high-frequency impulse voltage testing. The experimental results are consistent with the simulation results. The initial voltage distribution and impulse response of two samples are calculated under standard lightning impulse. In the initial voltage distribution calculation, the interturn channels of one bifilar coil and two series-connected bifilar coils are subjected to a maximum voltage of 1 and 0.5 times the lightning impulse voltage. [ABSTRACT FROM AUTHOR]

The quench protection in high-temperature superconducting (HTS) magnets is a well-known issue. Therefore, it is fundamental to have reliable models available for the analysis of the quench propagation in such magnets. The quench propagation in an ENEA HTS cable-in-conduit conductor, developed for fusion applications with the particular reference to an insert for the central solenoid of the Italian Divertor Tokamak Test (DTT) facility, is analyzed here with a new 1-D multiregional thermal-hydraulic and electric model, based on dedicated preliminary analyses and experimental and numerical characterization of the conductor. It is shown that large temperature differences arise in the conductor cross section during the quench propagation. The model is then applied to parametrically assess the effects of delay and fast current-discharge times on the conductor peak temperature, to avoid damaging the HTS. The parametric study shows that both the delay and current discharge time should stay below 0.5 s, to keep the peak temperature below 150 K. [ABSTRACT FROM AUTHOR]

The longitudinal insulation analysis method is developed for the solenoid type windings. The distributed lumped model is proposed to calculate the response under high-frequency transient impulse for the solenoid type superconducting fault current limiter (SFCL). Various simulation results according to the proposed model are consistent with the experimental results, which indicates that the developed model is effective for describing such kind of “noninductive” type solenoid windings. Therefore, the longitudinal insulation of the 20 kV/400 A SFCL has been analyzed by this method. The initial voltage distribution and the standard lightning impulse response for different turn-to-turn distances of the superconducting windings are calculated. According to the simulation results, the most severe impact is at the time when the lightning impulse wave is applied to SFCL, and the first and last turns of the winding endure a very high voltage drop at this moment. Considering the insulation margin and size, the turn-to-turn distance of 4.5 mm is taken as the longitudinal insulation distance of the SFCL. [ABSTRACT FROM AUTHOR]

In this article, a general scheme of a 40-kV/2-kA resistive type dc superconducting fault current limiter (SFCL) is suggested, which could be utilized to suppress the surge current caused by short-circuit faults in voltage-source-converter HVdc (VSC-HVdc) power grids. This dc SFCL is designed and fabricated with 6 coil modules in parallel and 4 in series. In order to investigate the current-limiting performance of the dc SFCL under the rapidly rising fault current, the SFCL is tested on the platform with a pulsed dc impact generator. Besides the property of current limitation, the current capacity, insulation and quench recovery performance of such SFCL are also tested. Results indicate that the critical current of SFCL is larger than 2050 A at 69 K, and the dc withstand voltage is larger than 74 kV in 2 h. During the 9-kV dc impact test, the short-circuit current could be limited to 8842 A, and the quench recovery time is less than 200 ms. [ABSTRACT FROM AUTHOR]

Screening currents are a major drawback in the context of rare-earth-barium- copper-oxide (ReBCO) magnets because their parasitic effects on the generated field are exacerbated by the particular shape of the conductors. Previously, we have developed numerical tools for the computation of screening currents and their effects in the cases of systems featuring two-dimensional (2-D) symmetries, axial or longitudinal. Nevertheless, 2-D models are not always adequate for every three-dimensional (3-D) shape or alternative winding configuration such as layer-wound ones. Therefore, a quasi 3-D model has been implemented in the in-house CAST3M finite-element code, using the current function T formulation. We developed CAST3M operators to take into account the superconducting behavior of the material and the anisotropic dependence of the current density on the magnetic induction. Simple scenarios, especially one solved with analytical formulations, have been defined to benchmark codes; CASTEM was successfully benchmarked against them. Finally, we compared the generation of screening currents within a small solenoid depending on the type of winding, made either of layers or pancakes. We also compared these results with a simple 2-D model made of nested turns. [ABSTRACT FROM AUTHOR]

Application of high-temperature superconducting devices become promising in power networks, and transportation, including ship, train, and electric aircraft propulsion systems, with the advantages of light weight, compact size, and high efficiency, compared to conventional devices. In reality, electric networks—either in grid or transportation propulsion system—are polluted with harmonics due to the widespread use of power electronic devices and nonlinear loads. It is essential to explore the dependency of harmonic ac losses of different coil configurations carrying nonsinusoidal current. We modeled and compared harmonic ac loss behaviors in three coil configurations, single pancake coil (SPC), double pancake coil (DPC), and solenoid coil (SNC), where SPC and SNC are wound by identical wire length and DPC has twice conductor number compared to SPC. The research work has been carried out by means of H-formulation finite element method in a 2-D axisymmetric modeling environment of COMSOL Multiphysics. We explored and reported ac losses in these three coil structures carrying nonsinusoidal current with the third and the fifth harmonic orders, respectively, under different total harmonic distortion (THD) and fundamental current levels. It has been concluded that ac loss in these coils first decreases with the increase of the third harmonic content, when THD of the third harmonic <0.2; and increase with the increase of the third harmonic when THD >0.2. AC loss in coils monotonically increases with the increase of the fifth harmonic, drastically. We found that ac loss in SPC carrying the third harmonic and the fifth harmonic at different THD are more than 3.8 times of that in DPC; ac loss in SPC carrying either third or fifth harmonics at different THD are around 4.5 times of that in SNC. [ABSTRACT FROM AUTHOR]

The experimental muon source (EMuS) project foreseen for muon science and neutrino physics is utilizing a superconducting solenoid for muon and pion capture, and is proposed at the China Spallation Neutron Source (CSNS). For the optimal particles collection efficiencies, an adiabatic magnetic field from 5 to 2.2 T along the central axis of the solenoid is generated by the solenoid. The superconducting solenoid is composed of four windings and an iron yoke. The iron yoke is arranged for flux returning and magnetic field shielding. Two conductor options for the windings, the aluminum stabilized NbTi Rutherford cable and the NbTi monolith wire are compared from the mechanical structure and radiation performance. The results of the mechanical analysis from ANSYS show that the excitation stress is suitable. But the results of the radiation analysis from FLUKA Monte-Carlo show that the recovery of the Residual Resistivity Ratios (RRRs) is necessary for the stabilizers of the superconductor. The recovery cycle of the aluminum stabilizer and the monolith wire solenoids are three months and one year, respectively. However, the RRR of copper for the monolith wire solenoid will be less than 50, after 12 years continuous running, which is shorter than the EMuS lifetime of 30 years. Therefore, the aluminum stabilized NbTi Rutherford cables are chosen to fabricate the windings. [ABSTRACT FROM AUTHOR]

A novel design of the superconducting dipole magnet, which superposes two concentric and oppositely titled solenoids with respect to the bore axis, is briefly described. A dipole magnet prototype of 2 T is designed and constructed based on this conception. The prototype magnet consists of four layers tilted solenoids by using a 7-strands NbTi superconducting cable. Its operating current is up to 3 kA. The dipole magnet has the bore diameter of 50 mm and the length of 0.5 m. The detailed magnetic field design by the software of OPERA is presented. The fabrication and test of the magnet prototype are also reported in detail. It finally reaches 71% of the design current when quenched with the central dipole field of 1.42 T. [ABSTRACT FROM AUTHOR]

This paper presents a numerical model for evaluating the inductance and critical current characteristics in solenoid-type superconducting magnetic energy storage (SMES) magnets. The inductance submodel covers the estimations of self and mutual inductances among the single-pancake coils, double-pancake coils, and solenoidal magnets. The critical current submodel reveals the transient critical current characteristics such as the minimum critical current and initial quenching position inside one specific magnet. As a case study, numerical calculation and experimental verification of a small-scale ReBCO magnet are investigated. Being verified by both the simulations and experiments, the proposed SMES model can be expected to evaluate the energy storage property prior to practical magnet fabrication. [ABSTRACT FROM AUTHOR]

A proper understanding of the degradation of the transport properties of cable-in-conduit conductors (CICCs) due to a changing strain distribution or to crack formation in the filaments is essential to determine the operational limits of the conductors and to optimize their design. Based on the electrical and strain properties of the superconducting strand, the performance of short samples of the CICC can be analyzed, such as the ones tested in the SULTAN facility, or the full-size CICC used in real magnets. Mathematical fitting expressions are proposed to implement strand properties into the cable model. In combination with the strain maps generated by the mechanical model MULTIFIL, these expressions are introduced in the electromagnetic code JackPot to predict the current sharing temperature of the CICC of the international thermonuclear experimental reactor (ITER) Central Solenoid. A comparison is made with SULTAN short samples tests as well. [ABSTRACT FROM AUTHOR]

In this paper, a novel active shimming method is proposed to minimize the shim coil–magnet and the shim coil–shim coil magnetic couplings simultaneously. In standard superconducting shim coil designs, each shim coil is usually designed individually to correct specific field harmonic components of the inhomogeneous field without considering the magnetic couplings among the shim coils and the main magnet. In particular, a strong interaction among the zonal shim coils and the main magnet can lead to a series of problems, like the drift of main field, instability of field homogeneity, and even destruction of coils. In this paper, magnetic decoupling techniques for reducing magnetic interactions among the zonal shim coils and the main magnet are developed. To complete a set of independent shim coils design, a nonlinear optimization model considering the field deviation and magnetic coupling is established. To improve the efficiency and solution quality of the involved optimization problem, the nonlinear model is first converted to a linear one by using the McCormick envelopes scheme. Through linear programming (LP), the optimal topology and preliminary positions of the shim coils are determined. To further optimize the position and turn numbers of the shim coil, a nonlinear programming (NLP) is then implemented to achieve desired field uniformity. In order to verify the feasibility and effectiveness of the proposed method, a simulation design of two sets of shim coils, Z2 and Z4, for a practical 9.4T magnet for whole-body magnetic resonance imaging (MRI) is presented. Compared with coils designed by conventional methods, magnetic coupling between the zonal shim coils and the main magnet had been effectively reduced. And also, magnetic coupling between the zonal shim coils had also been minimized as much as possible, which consequently improve the stability and safety of the MRI magnet system. [ABSTRACT FROM AUTHOR]

For reaching very high magnetic fields in fully superconducting magnets, beyond 16 T for particle accelerators dipoles and beyond 23 T for solenoids, the use of high-temperature superconductors (HTS) is unavoidable. Due to the high minimum quench energy in HTS these coils are much more difficult to protect against quenches using conventional methods, such as quench heaters or coupling loss induced quench (CLIQ). Although it is possible to use a dump resistor on a short HTS magnet, extracting the energy externally, this does not provide a solution for longer magnets or magnets operated in a string, because the extraction voltage becomes unacceptably high. Here, a method named E3SPreSSO (External Energy Extraction Symbiotic Protection System for Series Operation) is proposed that allows for fast energy extraction in HTS magnets. The E3SPreSSO comprises of units with a near-zero self-inductance superconducting circuit, connected in series with the main magnet. When the protection is triggered, these devices are turned resistive, using quench heaters, overcurrent or CLIQ, causing them to absorb the energy of the system. The units can be located outside the main magnet and do not generate magnetic field. Therefore, it is possible to use relatively cost-efficient and robust Nb–Ti or possibly MgB $_2$ (at higher temperatures). This paper introduces the concept and provides an analytical method weighing the different options for designing the E3SPreSSO units themselves. [ABSTRACT FROM AUTHOR]

The central solenoid (CS) model coil (CSMC), which has a high stored energy, is developed to validate the CS manufacturing methods for the China Fusion Engineering Test Reactor (CFETR). The designed operation current of the model coil is 47.65 kA. The maximum rate of the magnetic field is 1.5 T/s. The stored energy of the model coil is 407.6 MJ. A set of verification test of the model coil will be conducted after manufacture, so a CSMC power supply, which generates the current for coil operation, and a quench protection, which could quickly release the stored energy, are required. The main circuit topology of power supply was designed according to the requirements of the testing current waveform. The current control was adopted, which controlled the actual output current provided by the power supply system to track any specified current reference of the model coil within acceptable precision. The design of the quench protection system for model coil was also described in this paper. [ABSTRACT FROM AUTHOR]

The central solenoid model coil (CSMC) for China Fusion Engineering Test Reactor (CFETR) is being developed in ASIPP (Institute of Plasma Physics, Chinese Academy of Sciences). It is a hybrid superconducting magnet of 12 T maximum magnetic field and 1.5 T/s changing rate, which is composed of Nb3Sn coils and NbTi coils in high and low magnetic fields, respectively. The coil continuous winding and forming is one of the keymanufacture technologies for CSMC. This paper describes the developing status of the coil winding and forming processes. Based on the short sample bending trials, the winding design and optimization have been completed. At present, the winding production line has been constructed and is subjected for debugging. The forming tools for joggles and leads are being tested. Several technical issues during trials have been solved, e.g., the vertical plastic deformation of the coil and the keystoning of bent conductor. As a result, the continuous winding and forming trial for quad-pancake (QP) of Nb3Sn inner coil has been conducted successfully, and presented here. [ABSTRACT FROM AUTHOR]

Currently, the use of high-temperature superconducting (HTS) cables in the high-field sections of central solenoid (CS) of DEMO is one of the most appealing applications of the HTS cables in fusion magnets. Due to the pulsed operation of such coils minimization of the ac loss is necessary for the CS conductors. For the stacked-tape HTS cable layout proposed at the Swiss Plasma Center (SPC), the main contributions in the total ac loss-- hysteresis loss in stacks, intra- and inter-strand coupling losses-- have been studied. The electrical network model is used for the coupling losses, based on which the scaling laws for the ac energy loss are proposed. On the basis of the developed numerical tools, the assessment of the ac loss for the next HTS cable prototypes at SPC is also reported. More than 50% reduction of the total ac loss is expected compared with the first TF cable prototypes tested in the European DIPOle (EDIPO). [ABSTRACT FROM AUTHOR]

In the Korea Superconducting Tokamak Advanced Research (KSTAR), quench detection system using central difference averaging (CDA) and mutual inductance compensation (MIK) for central solenoid (CS) magnet has been studied. Similar to the cowound voltage taps, it is expected that this method can provide the good capability of rejecting inductive voltage noise. Accordingly, CDA and MIK method could be considered as a promising way. For this method to be an effective way, the inductive voltages should be accurately estimated, and then the measured CDA voltages are compared with the estimated ones. In previous studies, CS and poloidal field (PF) coils were modeled as the ideal solenoids to calculate mutual inductances between them. However, the nonlinearity of inductances due to Incoloy-908 jackets of PF1-PF5 coils that are ferromagnetic materials still needs to be compensated for more accurate estimation of inductive voltages. In this paper, the inductive voltages were estimated by considering the ferromagnetic effect of Incoloy-908 jackets to compensate the error voltages. Based on this study, the effect of Incoloy-908 on accuracy and reliability of CDA and MIK quench detection scheme was analyzed and discussed. [ABSTRACT FROM AUTHOR]

The goal of the Mu2e experiment at Fermilab is to search for charged-lepton flavor violation by looking for neutrinoless muon to electron conversion in the field of the nucleus. The Mu2e experimental apparatus utilizes a complex magnetic field in the muon generation andmomentum and charge selection process. Precise knowledge of the magnetic field is crucial. It is planned to map the solenoid field with calibrated three-dimensional (3-D) Hall probes up to 10-5 accuracy. This article describes a new design of a Hall probe calibration system that will be used to calibrate 3-D Hall probes to better than 10-5 accuracy for the Mu2e solenoid field mapping system. [ABSTRACT FROM AUTHOR]

The intersection regions and the beam injection channel of a high-energy collider require magnets that must act strongly upon one beam yet not at all on a closely neighboring beam. Designs are presented for three examples: a septum dipole that serves as a forward spectrometer centered on an ion beam after collision, which must clear an electron beam leaving the IP; a final-focus quadrupole that must provide high-gradient focusing of electrons with large aperture but pass a close-lying ion beam; and a highgradient quadrupole that must operate in the background field of a spectrometer solenoid. All designs use to advantage a new superconducting cable-in-conduit that provides for compact winding, robust end geometry, and in-cable flow of liquid helium. [ABSTRACT FROM AUTHOR]

The finite element model of KSTAR central solenoid (CS) magnet has been developedwith new smeared orthotropic material properties of CS coils and the effective coefficient of thermal expansion of the magnet structures. The accuracy of structural analysis for assembly and cool-down processes is higher than in previous studies. Electromagnetic analysis was performed to evaluate Lorentz forces of poloidal field (PF) coils during a long pulse discharge. The analyzed structural behavior of the CS magnet was clearly consistent with the measured data and calculated Electromagnetic (EM) forces during the plasma operation. The current of PF4 coil had a significant effect on axial compression and the minimum preloading was maintained at 2.0 MN in the end of plasma. EquivalentEMforce can easily predict the axial compression of CS magnet without complicated structural analysis. The study on the structural behavior of CS magnet is expected to provide the optimal combination of PF coil current limits for large plasma current and long pulse discharges. [ABSTRACT FROM AUTHOR]

The ITER magnet system is made up of four main subsystems: 18 toroidal field (TF) coils, a six-module central solenoid coil, 6 poloidal field (PF) coils, and 18 correction coils (CCs). The Feeder system with its main busbar and correction coil busbar represents one of the main magnet components as well. All coils and busbars with different dimensions used cable-in-conduit conductors (CICCs). China needs to provide six different types of conductors. The ITER CICCs consist of a cable made of Nb3Sn or Nb-Ti strands inserted in a stainless steel tube (called jacket or conduit). Depending on the coil type, the jacket material is either made of a low carbon AISI 316LN (for TF coil) or AISI 316L grade stainless steels (for PF and CC coils, etc). Mechanical properties of base material need to be tested at room and/or cryogenic temperature under predefinedmechanical deformation and heat treatment conditions. This paper concerns mechanical tests on the jacket materials, including static tensile tests, fatigue crack growth rate, and fracture toughness tests. [ABSTRACT FROM AUTHOR]

The concept design of the China Fusion Engineering Test Reactor (CFETR) was started in 2012 in two stages. For CFETR-Phase I, the major radius is 5.7 m, the minor radius is 1.6 m, and the magnetic field at the plasma region, BT, is 4-5 T. There were 16 toroidal field coils and six central solenoid coils designed by a Nb3 Sn cable-in-conduit conductor (CICC) with the maximum operation current of 64 and 50 kA, respectively. Three types of plasma equilibrium configuration (ITER-like single null, super-X, and snowflake) were designed. The maximum flux provided by the central solenoid is set at 180 V s. However, to get much higher operation parameters such as steady-state operation, particle and heat exhaust, disruption mitigation and avoidance, ELM control, and material damage by high heat flux and neutron, the superconducting magnet system of CFETR-phase II has been updated based on the larger machine with R = 6.7 m-7.0 m, a = 2.0 m, and BT = 6.5-7 T. Such a new design makes over 1-GW fusion power and better plasma performance possible. Hybrid TF coils are designed by a high-performance Nb3Sn conductor, since the maximum magnetic field can reach to 14-15 T. Besides, in order to save the space for the blanket system and get higher flux, a high-temperature superconducting Bi-2212 magnet with better current-carrying performance under high field is supposed to be employed for the CS coils of CFETR-phase II. The Bi-2212 CICC sample has been tested at 4.2 K with a critical current of 26.6 kA under its self-field. [ABSTRACT FROM AUTHOR]

Comprehensive studies of the transport and the magnetic properties of MgB2 wires were carried out at temperatures 4.2-20 K and magnetic field up to 8 T. Cryomagnetic system with MgB2 coil was designed and constructed based on the received data. Cryomagnetic system is designed to create a permanentmagnetic field of up to 5 T in the warm bore of 40 mm in diameter. The operating current of the system is 100 A. The magnetic field is created by a system of three concentric solenoids. The inner coil is composed of 10 double pancakes wound with the second generation HTS tape produced by SuperOx. Middle coil is made of multifilament MgB2 wire with a diameter of 1 mm produced by Columbus Superconductors. Middle coil has height of 120 mm, an inner diameter of 80 mm, and an outer diameter of 88 mm. The inner and middle coils are connected in series, what allows both sections to operate at temperature range from 4.2 to 20 K. The external coil of background field is wound of NbTi. It is powered by a separate pair of current leads. The solenoids are cooled by cryocooler though copper bar. The present report describes the design and the manufacture of the cryomagnetic system. [ABSTRACT FROM AUTHOR]

Previous studies indicated that the use of hightemperature superconductors (HTS) in the highest field allows us achieving the required magnetic flux in the central solenoid (CS) of the European DEMO at a reduced outer diameter, which would enable a reduced overall size and cost of DEMO. The proposed winding pack design of the CS1 module is based on ten layerwound subcoils using an HTS, react and wind Nb3 Sn, and NbTi conductors in the high, medium, and low field sections, respectively. The design utilizes a stainless steel and a superconductor grading leading to different overall current densities in each of the ten subcoils. Both, the hoop stress and the vertical loads are taken into consideration for determination of the required stainless steel cross-section in the winding pack. The stainless steel grading has been found to have an even more pronounced effect on the overall subcoil current densities than the superconductor grading. A preliminary estimation of the space required for the precompression structure is also reported. [ABSTRACT FROM AUTHOR]