Qingjin Xu

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.

R&D steps of a 12-T common coil dipole magnet for SPPC pre-study

IHEP (the Institute of High Energy Physics, Beijing, China) has started the RD the final step is fabricating the 12-T common-coil dipole magnet with HTS (YBCO) and Nb3Sn superconductors to test the field optimization method of the HTS and Nb3Sn coils. The characteristics of these R&D steps will be introduced in the paper.

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.

The BESIII detector magnet

Publisher Summary BESIII (Beijing Spectrometer III) is a detector designed to run in the autumn 2007 at a 1 ╳ 10 33 cm -2 s -1 luminosity @1.89 GeV at BEPCII (Beijing Electron–Positron Collider II) at IHEP Beijing. It has a 1 T superconducting solenoid magnet with the inner winding diameter of 2962 mm, winding length of 3532 mm, and a 600 tonne flux return yoke. The indirectly cooled, pure aluminum stabilized single layer coil is internally wounded with a 4 kA superconductor. The magnet design is described. The NbTi/Cu superconductor has been delivered and the critical current test of a short sample of the superconductor has been performed. An inner winding machine is under construction.

Electromagnetic design of a 12 T twin-aperture dipole magnet

A 12 T twin-aperture subscale magnet is under development at the Institute of High Energy Physics (IHEP, Beijing, China), as the R&D of high-field accelerator magnet technology for SPPC (Super Proton–Proton Collider) pre-study. Four NbTi coils and two Nb3Sn coils will be fabricated firstly, to provide a 12 T dipole field in two apertures with the load line ratio of 20% at 4.2 K. After that, the HTS (ReBCO and Bi-2212) coils will be inserted between the Nb3Sn coils to realize a higher dipole field. The ReBCO coils with the block-type configuration will be inserted between the Nb3Sn coils with common-coil configuration (Combined Common-coil and Block type configuration, CCB), to make the broad plane of the tape parallel with the magnetic flux and maximize current-carrying capacity. The electromagnetic design, mechanical design and quench protection design have been completed. The fabrication is ongoing. The magnet will be assembled and tested in 2017.

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.

The Development of HTS Solenoid Lens for Electron Microscope

The electron microscope has higher resolving power than a light microscope and can reveal the structure of smaller objects. This paper describes the development of the lens of an electron microscope with high-temperature superconducting (HTS) solenoid. The lens consists of double Bi-2223 HTS pancake coils and a ferromagnetic container. The cryogen-free HTS coils are refrigerated by a cryocooler and operated at the temperature of 43 K. The diameter of the warm bore is 10 mm, and the peak central magnetic field is about 2 T.