Meifen Wang

20-T Dipole Magnet With Common-Coil Configuration: Main Characteristics and Challenges

The Institute of High Energy Physics (Beijing, China) is pursuing R&D of high-field accelerator magnet technology for the recently proposed CEPC-SPPC project, which will need thousands of 20-T level accelerator magnets in 20 years. A long-term plan has been made aiming to realize the 20-T magnets in 15 years. The conceptual design study has been ongoing from 2014 based on the current Jc level of superconductors. As both Nb3Sn and high-temperature superconductor superconducting materials are strain sensitive, the common-coil configuration has been chosen as the first option for the design study of the 20-T dipoles, to simplify the coil structure, raise the bending radius, and lower the strain level in superconducting coils. The magnetic analysis, mechanical analysis, and preliminary design study of the straight section and the coil ends have been completed for a 20-T common-coil dipole magnet. The main characteristics and challenges of this design concept will be presented in this paper.

Magnetic Design Study of the High-Field Common-Coil Dipole Magnet for High-Energy Accelerators

The Institute of High Energy Physics (IHEP, Beijing, China) is proposing a two-stage particle collider: CEPC-SppC. The first stage is a circular electron-positron collider (CEPC), expected to carry out high-precision studies on Higgs bosons. Upon completion of the CEPC experiment, it will be upgraded to a super proton-proton collider (SppC), aiming at the discovery of physics beyond the standard model. The circumference of the accelerator for CEPC and SppC will be 50 ~ 70 km. The required dipole held strength is 20 T for SppC. As the start of a long-term R&D plan for high-held accelerator magnet technology at IHEP, a 15-T short sample held Nb3Sn dipole is planned to be developed within the next five years. The common-coil configuration is adopted to provide space for two apertures with a maximum diameter of 60 mm. The 10-4 level held uniformity will be reached at a reference radius of 15 mm. Magnetic analytical modeling and FEM cross section study of this high-held common-coil dipole has been done and will be presented here. A preliminary cross section study of the 20-T common-coil dipole will also be introduced; the design is based on the current Jc level of Nb3Sn and HTS superconductors.

Physical Design of High Gradient Superconducting Magnetic Separation Magnet for Kaolin

This paper describes the physical design of a 5.5 T central field, 300 mm room temperature bore, High Gradient Superconducting Magnetic Separation (HGMS) magnet for kaolin. The magnet has been designed and is under construction at the Institute of High Energy Physics (IHEP), Chinese Academy of Sciences. The first part of the paper introduces the size of the superconducting coil. The inner diameter of the coil is 400 mm, the height is 815 mm, and the current is 150 A. The central and maximum magnetic fields are 5.5 T and 5.6 T, respectively. By adding an iron shield the magnetic field is limited to 50 G in a radial distance of 1.0 m and an axial distance of 1.2 m. The second part analyzes the coil stress in process of winding, cool-down and charging. The winding pre-stresses applied on the coil and the bandage are 70 MPa and 100 MPa, respectively. The maximum hoop stress of the coil is limited to less than 150 MPa and at the same time the coil does not take off from the bobbin.

2-D Mechanical Design Study of a 20-T Two-in-One Common-Coil Dipole Magnet for High-Energy Accelerators

A two-stage particle collider, i.e., CEPC-SppC, is proposed by the Institute of High Energy Physics (Beijing, China). The circular electron-positron collider (CEPC) will be upgraded to a super proton-proton collider (SppC) after the first-stage experiment. According to the requirement of SppC, the field strength of the main dipoles is 20 T, and 10-4 level field uniformity should be reached within two thirds of the aperture. The outer diameter is restricted to be 900 mm. The magnetic design study of a 20-T two-in-one common-coil dipole magnet has been done and previously presented. This paper mainly focuses on the corresponding mechanical design study by establishing a two-dimensional finite-element model with a shell-based structure. The water-pressurized bladder is adopted to apply the preload on coils with the pressure of 80 MPa. The peak coil stress is minimized to reduce the critical current degradation of superconductors. An appropriate aluminum shell thickness is selected to overcome the significant Lorentz force under the restriction of the main dipoles outer diameter.

Development of an Eddy-Current Separation Equipment With High Gradient Superconducting Magnet

A high gradient magnetic separator (HGMS) used for recovery of waste electric and electronic equipment has been designed and fabricated in the Institute of High Energy Physics of China. It has a warm bore of 200 mm diameter and consists of two superconducting solenoid coils made of epoxy-impregnated NbTi/Cu superconductors. The designed center field is 5 T, and the field gradient more than 36 T/m. The magnet suffered several trainings to reach its designed current of 153 A and stably operated during many charging and discharging. In this paper, the detailed development of this magnet is presented.

Tests of 3 T Superconducting Electromagnetic Iron Separator

A 3 T central field Superconducting Electromagnetic Iron Separator (SEIS) has been designed, fabricated and tested at Institute of High Energy Physics (IHEP) of China. The SEIS system is deliberately designed to separate small pieces of hazardous ferromagnetic materials, such as detonators, from coal to achieve high purity and good yield. The SEIS system mainly consists of a NbTi superconducting magnet, a LHe recondensation type cryostat with two GM cryocoolers (31 W/40 K, 1 W/4.2 K), a pair of binary current leads (CL). The 1 ton cold mass was located in the cryostat of the system with 630 mm room temperature bore. The system is powered with a 250 A/50 V power supply, and has charging time and discharging time of 15 minutes and 20 minutes, respectively. It took 10 days for SEIS magnet to cool down from 300 K to 4.2 K and 6 days to accumulate LHe at designed level 360 mm. The SEIS magnet suffered no quench to reach its designed current, and operated stably during many experiments afterwards. The experiment research of the SEIS system is detailedly presented in this paper.

Design of Cylindrical Transverse Gradient Coil for 1.5 T MRI System

Magnetic resonance imaging (MRI) requires the gradient coils to produce magnetic field gradients, to encode three-dimensional information. In this work, a parametric method to the design of cylindrical transverse gradient coils for high-resolution magnetic resonance imaging (MRI) is proposed. The cylindrical transverse gradient coil was separated to several turns of curves, each turn is considered as a curve butted by two quasi-elliptic arcs. The parameterized curve is optimized with the simulated annealing algorithm. A cylindrical transverse gradient coil with high level of linearity is designed for 1.5 T MRI system. The cylindrical transverse gradient coil can build a high-quality transverse gradient magnetic field in a large spherical zone, concentric with the main magnet of the MRI system.

Development of a 6-T Conduction-Cooled Superconducting Magnet

A 6-T conduction-cooled superconducting (SC) magnet was successfully developed with the Institute of High Energy Physics of China. The magnet mainly consists of a NbTi solenoid coil, a cryostat with two thermal shields, a Gifford-McMahon cryocooler (35 W/50 K, 1.5 W/4.2 K), and a pair of binary current leads. The coil has an inner diameter of 110 mm, an outer diameter of 200 mm, and a height of 216 mm. The total 55-kg cold mass was located in the cryostat with a 50-mm room temperature bore. In order to minimize the heat load to an SC coil, two thermal shields were adopted in this system. The outer thermal shield and the inner thermal shield were thermally attached to the first stage and the second stage of the cryocooler, respectively. In addition, thermal contact resistance was carefully considered to minimize the temperature difference between the coil and the second stage of the cryocooler. It took 30 h for the magnet to cool down from 300 to 4 K level. The temperature of the second stage was stable below 3 K, which corresponded to about 0.2-W total heat loads. The magnet suffered no quench to reach its designed current of 148 A and stably operated during many charging and discharging processes. The detailed development of this magnet is presented in this paper.

Investigation of Adopting Shrink-Fit Multilayered Aluminum Shell in High-Field Common-Coil Accelerator Dipole Magnet

This paper presents the shrink-fit multilayered aluminum shell (SMAS) used for withstanding large Lorentz force in a 20-T shell-based common-coil accelerator dipole magnet. Finite element analysis (FEA) is carried out to optimize the required shell thickness when a single layer aluminum shell is used to support the 20-T dipole magnet. Also, FEA is carried out to study the performance of a three-layer SMAS used in the same dipole magnet. The analyzed results indicate that the three-layer SMAS with thickness of 75 mm can help us to reduce the peak shell stress significantly compared to a 75-mm-thick single layer aluminum shell when they provide the same preload to the coils. Some preliminary experiments have been carried out which prove that the initial stress distribution in the SMAS can be well controlled after the assembly. Hopefully, the outer diameter of the twin-aperture 20-T common-coil dipole magnet can be restricted to 900 mm if we use a three-layer SMAS as the support structure.

Electromagnetic Design Study of a 20-T Cos-Theta 2-in-1 Dipole Magnet for High-Energy Accelerators

High-field superconducting magnets are the key components of the high-energy particle accelerators. The Institute of High Energy Physics, Beijing, China, has been working on the related R&D since 2014. In parallel with the baseline R&D roadmap with common coil configuration, preliminary electromagnetic design of a 20-T 2-in-1 dipole magnet with cos-theta configuration has been carried out as an option for the model magnet R&D in future. Totally six layers of coils are required for each aperture of this dipole with the high temperature superconductor for the inner two layers and the low temperature superconductor for the outer four layers. Graded coil design is selected to increase the efficiency of the conductor utilization. For each aperture, the clear bore diameter is 50 mm. Asymmetric coil configuration has been adopted to obtain a good geometrical field quality. After optimization, the field uniformity of 10−4 within 2/3 of the aperture is achieved. The coil ends of the dipole magnet have also been designed and optimized. The detailed magnetic analysis and the main characteristics of this magnet are presented.