Development of superconducting model dipole magnets beyond 12 T with a combined common-coil configuration

Abstract

The superconducting magnet group at IHEP (the Institute of High Energy Physics, Chinese Academy of Sciences, China) has been engaging in the R&D of high field accelerator magnets since 2014 for the pre-study of the next-generation high energy particle accelerators like CEPC-SPPC (Circular Electron Positron Collider-Super Proton Proton Collider), FCC (Future Circular Collider) and etc. A superconducting model dipole magnet named LPF1 was firstly fabricated with NbTi and Nb3Sn combined common-coil configuration in 2017 and tested in 2018, a main field of 10.23 T was reached within two 10-mm apertures. The magnet was reassembled with higher pre-stress in 2019 to investigate the influence of pre-stress loading level on the performance of common-coil dipole magnets. The main field of this upgraded magnet named LPF1-S was increased to 10.71 T within two 12-mm apertures. By improving the key process technologies in Rutherford cable fabrication, coil winding, Nb3Sn & NbTi splices soldering and coil impregnation, the recently fabricated model dipole magnet named LPF1-U got a 12.47-T main field in two 14-mm apertures in 2021. To fully take advantage of Nb3Sn and NbTi superconductors in different field regions, LPF1-U was still designed and developed with a combined coil configuration with Nb3Sn for the inner two coils and NbTi for the outer four coils. Besides, graded coil topology and different coil LSS (length of straight section) settings were adopted in the optimization of LPF1-U layouts. Bladder and key technology was used for the support structure and fiber optic sensors based on the FBG (Fiber Bragg Grating) were utilized to monitor the stress distribution and variation in the structures and coils through the whole process from magnet assembly to cool-down and excitation. During the performance test, a relatively large number of trainings were carried out and LPF1-U became more stable after thermal cycle. A peak field of 12.7 T in coils (12.47 T main field in apertures) corresponds to the operating current of 6865 A and the load line ratio of 90 % was finally attained. It is worth mentioning that LPF1-U is the first hybrid - Nb3Sn, NbTi- common coil dipole magnet which has achieved a main field of more than 12 T in two apertures. The design, fabrication and performance analysis of LPF series dipole magnets are presented in this paper.

Impregnation damage monitoring for the canted-cosine-theta magnets using time-domain reflectometry

“…where Γ After is the value after tape removal. Initially, Γ values before and after tape removal can be employed to calculate the characteristic impedance using equation (5). As the length of the tape increases, the ∆Γ also increases, consequently leading to a higher variation in impedance values.…”

“…Unlike the mock-up plate, the CCT Sub5 experiences conductor movement, impacting the spacing between the conductor and ribs. There are successive changes in capacitance, characteristic impedance, and TDR results based on equations (1), ( 2) and (5). Based on the correlation between rib spacing and impedance in figure 2(d), the conductor demonstrates movements ranging from 5 µm to 15 µm.…”

“…upgrades to transform its existing Large Hadron Collider (LHC) into the High Luminosity LHC [4]. In China, the Institute of High Energy Physics is currently working on the development of a 20 T dipole magnet utilizing Nb 3 Sn conductor and high-temperature superconductor [5].…”