NbTi Coils Research Articles

Design and Fabrication of NbTi Coils for a Superconducting Wavelength Shifter

Design and Fabrication of NbTi Coils for a Superconducting Wavelength Shifter

Quench Protection Study of a 14 T Conduction-Cooled Magnet Built With Nb3Sn and NbTi Superconducting Coils for PPMS

A 14 T conduction-cooled superconducting magnet with a clear cold bore of 50 mm in diameter is designed and fabricated for a physical property measurement system. The magnet is built with six Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils and five NbTi coils arranged coaxially. To reliably protect the 14 T magnet, a passive quench protection scheme is developed, including a novel coil subdivision method and heater network design. The novel coil subdivision method mixes a NbTi coil and an Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coil into the same subdivision to reduce the hot-spot temperature of the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coil. Different heaters parameters are compared and analyzed to obtain a lower hot-spot temperature. In addition, an efficient way of raising the ratio of copper to superconductor in the superconducting wires is used to reduce the hot-spot temperature of the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils in the low magnetic field region. An in-house quench simulation code in MATLAB, including a finite difference method for the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils in the low magnetic field region and a quench ellipsoid propagation model for the other coils, has been developed. This article describes the details of the passive quench protection scheme and presents the quench simulation results.

Shell-Based Support Structure for the 45 GHz ECR Ion Source MARS-D

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.

Completion and Installation of the ITER Lower Poloidal Field Coils PF5 &amp; 6

The poloidal magnetic field of ITER is provided by 6 Niobium–Titanium (NbTi) coils mainly for plasma shaping and position control. The fabrication of the two lower coils PF6 from China ASIPP and PF5 from European F4E has been completed and the coils installed in the bottom of the Tokamak pit in 2021. This paper presents the challenge of the manufacturing process, which involves manufacturing of several dozens of superconducting double pancakes, requiring bending, insulating and welding steps to keep accuracy of a few mm on dimensions up to 25m. The reproducibility and reliability of the manufacturing processes to manage magnet winding/insulation and cryogenic skills are essential for final quality and schedule robustness. After having successfully completed final thermal cycles for site acceptance in Cadarache, the PF6 and PF5 have been delivered simultaneously and handed over to IO. This paper demonstrates the assembly scenario of the two coils, including assembly tools for transportation, preparation for lifting, lifting tooling design, temporary supports design in cryostat and alignment of positioning on supports from assembly hall to the tokamak pit. The coils are sensitive components and preservation steps are needed to protect them in the pit during other assembly operations. In future, the two coils will sit in pit for several years until mounted onto the TF coils through the support then connected to feeders at the coil terminals. PF6, PF5 will firstly rest on temporary supports, and later shift up by jacks and conical guides to align onto TFC. The alignment & shimming processes and tightening will be presented to show the practical functionality and avoidance of interferences with the other components of the ITER tokamak which achieving high accuracy to avoid error fields.

Conceptual Design of a C-Shaped 6.4 T Superconducting Dipole Magnet

Sirius is a 4th generation light source with a sub-nm.rad horizontal emittance currently under commissioning at CNPEM, Brazil. The Sirius beamlines will mainly use insertion devices as the source of synchrotron light, and some of the beamlines will use the currently installed central dipole magnets (permanent magnets) of 3.2 T. However, there is a demand for a high-energy X-ray tomography beamline that requires photons with a critical energy higher than 39 keV, which is not achieved with the current dipoles. In this sense, a dipole magnet with a magnetic field higher than 6 T would be of great interest. A conceptual design for a superconducting dipole magnet of 6.4 T, based on conduction-cooled NbTi coils and holmium poles, has been proposed and will be presented, emphasizing the first ideas of the electromagnetic, mechanical, cryogenic and quench protection designs.

Electrical Quality Assurance for the NbTi Coils of the HL-LHC High Order Corrector Magnets

The INFN-LASA laboratory (Milano, Italy) is involved in the High-Luminosity LHC program for the design, construction, and test of 54 superconducting high-order corrector magnets. One of the challenging project stages was the transition from the construction of laboratory prototypes to the series production, awarded to industries, with the demanding requirement of maintaining high-quality production standards. Common and custom quality assurance (QA) methods were adopted for the analysis of the electrical characteristics of the coils. This paper discusses in detail the principle of the methods, their expected sensitivity, and the final observed effectiveness on the 510 produced coils. In some cases, the methods led to early defect detection thus avoiding possible severe damages during the final cold test that have already occurred for a prototype magnet not subject to the QA procedures described in this paper.

Design of a Curved Superconducting Combined Function Bending Magnet Demonstrator for Hadron Therapy

Curved superconducting bending magnets have clear potential for compact hadron therapy gantries and medical synchrotrons. A combined function superconducting bending magnet design based on collared cos-theta coils is proposed for a new compact and cost-effective hadron therapy gantry initiative. This 3 T magnet, based on the technologies extensively developed for the LHC project, includes several gantry-specific features that shall be developed and validated with a demonstrator magnet. The main development areas include fabrication of epoxy-impregnated cos-theta Nb-Ti coils with 2.2 m radius of curvature along with the assembly of the surrounding curved cold mass. This paper presents the magnetic and mechanical design optimization of the proposed demonstrator magnet, the results of the numerical modelling of the transient losses during operation as well as the magnet quench protection analysis.

Optimized Design of a 170-GHz Gyrotron Magnet With Thermally Insulated Structures

An electron cyclotron is used to heat plasma by driving current in a fusion system. This system requires a strong and accurate magnetic field distribution for the interaction between the electron beam and the radio frequency wave energy [1]. A superconducting magnet is designed for a 170 GHz gyrotron system here. The magnet is composed of conduction cooled NbTi coils, a GM cryocooler with thermal links, supporters, and a cryostat. The magnet was designed using an optimization method that considered the normal stresses generated by electromagnetic forces, the critical current margin, the axial field profile, and field uniformity and losses under AC operation. A quench analysis was also carried out to ensure the safe operation of the gyrotron magnet. The inner bore of the designed superconducting coil is 200 mm to obtain a proper resonance region. A bobbin and structures for thermal insulation were also designed considering the heat transfer and cooling capacities of the cryocooler. The gyrotron magnet will be manufactured using an automatic winding machine based on these design results.

Development of a 7 T NbTi solenoidal magnet with 72 mm aperture

A close-packed coil with a 72 mm aperture is developed using the formvar-insulated NbTi wire made from the WST company. The micrometer-level inter-turn spaces are filled with CTD-101 K utilizing a vacuum pressure impregnation method with a controllable flow speed of the epoxy resin. The cryogenic excitation results indicate that the coil inter-turn spaces are well filled, so that it can generate a 7.35 T central magnetic field at an operation current of 176 A with no coil quench. The maximum loadline of the coil is proved to be 98.96%. The maximum hoop-stress is approximately 64.1 MPa at the center of the inner most coil layer. The VPI method is applicable to the close-packed coils (tcoil ≤ 28 mm) wound from the formvar-insulated NbTi wire.Differ from the fiberglass-insulated Nb3Sn wire, the formvar insulated NbTi provide a relative smooth wire surface, which does not absorb the epoxy resin. This significantly increases the difficulties of vacuum pressure impregnation (VPI) for a thick close-packed NbTi coil. With the purpose of understanding the applicable of current VPI procedure on formvar insulated NbTi coils, a close-packed solenoidal magnet wound from the formvar insulated NbTi is wound, vacuum pressure impregnated and cryogenic measured at the Institute of Plasma Physics (ASIPP), Chinese Academy of Sciences (CAS). The design aperture of the magnet is 72 mm, with coil thickness of 28.75 mm and coil height of 180.5 mm, the magnet is expected to generate a 7.04 T central magnetic field with an operation current of 170 A at 4.2 K. The excitation results show that the central magnetic field of the NbTi coil impregnated with current VPI procedure is able to reach 7.35 T with no quench under an operation current of 176 A. The loadline is close to 98.96% of the NbTi wire.

CFETR Nb3Sn coil in heat treatment deformation analysis and fixture designing

According to the research, it is found that the Hybrid Magnet coils, JT-60SA, ITER and CSMC coils are fixed by coils during heat treatment in order to prevent the coils deforming due to the release of residual stress. Since the penultimate process step of CFETR CSMC Nb3Sn coil manufacturing process is the final assembly of the coil, the theoretical value of the initial unilateral gap between Nb3Sn inner and outer coils is 27.4mm, and the theoretical value of the initial unilateral gap between Nb3Sn outer coil and NbTi coil is 50mm. This gap will be reduced in each process of coil manufacturing process. In order to successfully assemble the coil, it is of great significance to analyze and develop a set of tooling to reduce coil deformation in heat treatment process.

Electromagnetic Design and Mechanical Analysis of a 13-T Superconducting Magnet for Neutron Scattering Sample Experiments

A 13-T superconducting magnet for neutron scattering experiments was being developed at the High Magnetic Field Laboratory, Chinese Academy of Sciences, which will provide a high magnetic field environment to research condensed matter physics. It is made up of 6 Nb3Sn coils and 8 NbTi coils to provide a 13-T central magnetic field with 0.5% field inhomogeneity in the sample region of O10 mm×10 mm cylinder. Due to the horizontal opening angle of 320° and the vertical opening angle of ±8°, there is a very limited space for the support structure, which is expected to withstand an electromagnetic force of approximately 200 tons; as a result, the design of the support structure is crucial in order to avoid any harmful plastic deformation. In this paper, the electromagnetic solution, structure design, and mechanical analysis are mainly presented.

Quench Analysis of 5.8 T Conduction-Cooled Superconducting Magnet

A 5.8 T conduction-cooled superconducting magnet has been developed in the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP). The magnet has a warm bore diameter of 190 mm. It consists of four concentric closely compacted NbTi coils with an asymmetrical arrangement. A two-stage Gifford-McMahon cryocooler used to cool down the magnet from room temperature to 4.2 K. The magnet operated in the driving model with total energy 0.63 MJ and the temperature margin only 1 K at operating current 114.5 A, the maximum field up to 7.7 T. A quench protection circuit was designed to avoid damage during the quenching process. The protection circuit has adopted coil subdivision method. A 3D thermal, electromagnetic and electrical circuit coupled model was established to simulate the quenching process. The coupled model was solved by commercial finite element method (FEM) program. Using this model, the hot spot temperature of the coils, the variation of the current, and the voltage can be attained. The effect of a different number of coil subdivision on the quenching process has been studied.

Design of a 15 T hybrid superconducting magnet

In the framework of the program to fabricate a high-field superconducting magnet of the order of 19 T @4.2 K with a 150 mm free bore, a 15 T hybrid solenoidal superconducting magnet with a 78 mm bore was developed and preliminary tested. The purpose of the program is to upgrade the material test facilities in the Institute of Plasma Physics Chinese Academy of Science (ASIPP) and further extend their measurement functionality. This paper presents the design of the 15 T hybrid magnet and its preliminary test results. The magnet comprises two high-performance Nb3Sn coils, one ITER Nb3Sn coil and one NbTi coil respectively for the high-, medium- and low field section. The axial length of the homogeneity within a 99 % magnetic field region is designed to more than 40 mm, and the ratio between the peak and central magnetic field is expected to be less than 1.025. The Nb3Sn coils were reacted separately, after which all coils including the NbTi coil were impregnated with CTD-101 K individually. Then, the impregnated sub-coils were assembled into a concentric-coaxial configuration and electrically connected in series. The hybrid magnet was inserted to a liquid helium bath for the excitation test, it finally reaches 97.8 % of the design current with a 14.84 T central magnetic field.

Final Design of the CFETR Central Solenoid Model Coil

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 Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn 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 Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and NbTi coils to reduce cost. The detailed structure of the CSMC has been designed, it mainly including Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils, NbTi coils, preload structure, coil buffer zone, joints, supports, feeder throughs, 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.

Technology challenges of 14 T whole-body superconducting MRI magnets —A target of high-field superconducting magnet technology for large scale applications in next decade

This paper presents a brief review of the development trend of superconducting magnets in large scale applications towards high magnetic fields, depending on and pushing the Nb&lt;sub&gt;3&lt;/sub&gt;Sn wire technics' continuous improvement. The focus is on analysis of the technology challenges of 14 T whole-body superconducting magnets. Using the Bonze Nb&lt;sub&gt;3&lt;/sub&gt;Sn wires and on the base of a combination design of Nb&lt;sub&gt;3&lt;/sub&gt;Sn and NbTi coils, an electromagnetic conception design of a 14 T whole-body MRI magnet is presented, and the thermal stability and quench protection are analyzed by simulations. The critical issues on stress, joints as well as shimming of 14 T whole-body superconducting magnets are also discussed. According to the results, this paper believes: 1) Nb&lt;sub&gt;3&lt;/sub&gt;Sn wires are of the first important issue for 14 T whole-body superconducting magnets—the Bonze Nb&lt;sub&gt;3&lt;/sub&gt;Sn wire is of the best choice but the performance specifications of the current products need to be improved further to match the requirements; 2) quench protection of 14 T whole-body superconducting magnets is one of the most complicated technics that covers design of the copper to superconductor (Cu/SC) ratio, coordination of the operating current and coil inductances, subdivisions of passive protection circuits and quench triggering control of active protection, as well as the stray field limitation during the transient process.

R&amp;D Activities of Joint Manufacture for CFETR CSMC

The Central Solenoid Model Coil (CSMC) project was launched in the Institute of Plasma Physics Chinese Academy of Sciences for the China Fusion Engineering Test Reactor (CFETR). The CFETR CSMC is designed to generate 12 T peak magnetic field when the running current is 47.65 kA. The CSMC is composed of two Nb3Sn coils in the internal high field and three NbTi coils in the external low field. Electrical joints are one of the key technologies for the CSMC, because the superconducting coils are electrically connected into a single circuit by the joints. Lap type joints have been designed for the CSMC for its proven reliability and easy assembly. It is a great challenge to develop special equipment and technologies for the joint manufacture, including vacuum brazed terminal sleeve assembly, jacket removal, chrome coating removal for Nb3Sn cable, nickel coating removal and silver plating for NbTi cable, compact termination, etc. This paper mainly focuses on the research and development activities of the joint manufacture and the solution of the technical issues. The techniques and equipment can provide a basis for the electrical joint manufacture for the CSMC and other large-scale superconducting magnets.

Design and analysis of the 16T superconducting magnet for CFETR strand test facilities

Abstract A 16 T superconducting magnet is being designed with the aim of testing the Nb3Sn superconducting strands and high temperature superconductors. The superconducting magnet will produce a magnetic field of 16 T at the magnet center with magnetic field homogeneity better than 0.5 % at 180 A for a diameter spherical volume of 50 mm. The combination of the Nb3Sn and NbTi coils were used to manufacture the superconducting magnet. The superconducting magnet consists of four inner Nb3Sn coils and two NbTi coils. All coils are connected in a series with a power supply. This paper presents the magnet design, electromagnetic and mechanical behavior analysis of the superconducting magnet.

Manufacture and Test of a Prototype Nb3Sn-NbTi Joint Sample for the CFETR Central Solenoid Model Coil

The project of the Central Solenoid Model Coil (CSMC) was launched in the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) to develop the manufacturing technology of large-scale superconducting magnet for the China Fusion Engineering Testing Reactor (CFETR). The maximum magnetic field of the CFETR CSMC will be 12 T when the running current is 47.65 kA, and the maximum field change rate will be 1.5 T/s. The CSMC consists of two coaxial Nb3Sn coils in the internal high field and a stack of three NbTi coils in the external low field. All the coils are electrically connected in a single circuit by joints. To verify the electrical performance of the joint, a prototype Nb3Sn-NbTi joint sample has been designed and manufactured in ASIPP. The sample is composed of two different conductor legs, the tested joint of praying hands structure to be placed in the high field region, and two upper terminals to be connected to the transformer of the test facility. The prototype sample has been tested in the SULTAN facility at Villigen (Switzerland). In this paper, the sample design, the techniques used for the manufacturing steps of the different conductor legs, and the joint assembly are described in detail. The test results show dc resistance below 5 nΩ criterion, and ac losses below 30 J/cycle with the amplitude of 0.2 T and frequencies in the range of 0.03–1 Hz.

Design and Quench Protection Analysis of a 9 T NbTi Superconducting Magnet for a Large-Bore EMPS

A 9 T NbTi superconducting magnet with a large bore is designed and will be fabricated for an EMPS (electro-magnetic property measurement system) whose sample space is 50 mm in diameter. To match the large sample space of the system, the winding bore of the magnet should exceed 89 mm in diameter. Because the winding diameter is much larger than a conventional 9 T class NbTi superconducting magnets, wire selection and magnet design are very important and difficult in this research. An optimal design process with a genetic algorithm considering the critical current, magnetic stress, thermal stability and field uniformity is carried out to develop the 9 T large bore NbTi EMPS magnet. The design algorithm calculates the structure and dimensions of the magnet to minimize the total volume while satisfying the constraints related to the stability of the magnet [Jang et al. (2018)]. To evaluate the thermal stability of the magnet with a protection circuit, a quench analysis is also implemented considering the two boundaries among three adjacent coaxial NbTi coils. The maximum hot spot temperature of the magnet is calculated based on the quench analysis model via a numerical analysis and an electrical circuit simulation. After the optimized design is created, fabrication of the 9 T large bore NbTi magnet will be conducted for its application to the large bore EMPS.

Mechanical Design and Stress Analysis of LPF2: A 12-T Hybrid Common-Coil Dipole Magnet

The Institute of High Energy Physics (IHEP, China) has been engaged in the development of shell-based dipole magnets with a common-coil configuration for the pre-study of the Super proton-proton Collider (SPPC) project. The first subscale magnet LPF1, with two Nb3Sn coils and four NbTi coils, reached a bore field of 10.2 T at 4.2 K. Subsequently a higher safety margin model has been proposed as LPF2, which has six Nb3Sn coils and two NbTi coils to reach a 12-T main field in both apertures with an operating current of 5300 A. The shell and yoke are reused from LPF1, as well as the two Nb3Sn coils and two inner NbTi coils of LPF1. The pre-loaded method of LPF2 is much alike that in LPF1: using the Bladder & Key technology to overcome the Lorentz forces in horizontal and vertical directions and pre-tightening six aluminum rods to pre-load the coil packs in the axial direction. In addition, the strain gauges are positioned at the surface of the aluminum shell to monitor the pre-loading effect. The main design parameters and stress analyses results will be presented.