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ISSN: 2772-8307
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cited:15
Development of a novel joint-less double aperture REBCO magnet with an innovative excitation circuit for stable magnetic field generation
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Article Number:Article 100139
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Abstract
Corresponding email:huangdaxing@mail.iee.ac.cn; guhw@mail.iee.ac.cn; dingfazhu@mail.iee.ac.cn
Second-generation high-temperature superconducting (2G-HTS) magnets operating in persistent current mode (PCM) effectively address the challenge of magnetic field stability. This paper introduces a novel joint-less double aperture (JDA) REBa2Cu3O7−δ (REBCO, RE: rare earth) magnet, designed to overcome the limitations posed by joint resistance in traditional 2G-HTS magnets. A single slit REBCO tape is innovatively wound into double-pancake (DP) coils on both sides and placed in spaced apertures within the magnet. This closed-loop design generates two stable magnetic fields while effectively preventing tape twisting between the DP coils. Furthermore, a new portable excitation circuit is proposed for the JDA REBCO magnet, utilizing pulsed magnetic fields generated by the copper coil, which eliminates the need for current leads, electrodes, and persistent current switches (PCSs), significantly reducing system complexity. Initially, a traditional PCS was used to charge the JDA REBCO magnet to 40 A at 77 K, generating a magnetic field of 60.6 mT at the center of one of the DP coil apertures. The magnet was then successfully excited using a pulse circuit after about 200 cycles. A comparative analysis with the PCS results showed that the current induced by the pulse circuit was approximately 40 A. The stability of the magnetic field within one DP coil of the JDA REBCO magnet was monitored for 107 h, with a magnetic field drift rate of approximately 0.86 ppm/h. The closed-loop advantage of the JDA REBCO magnet, combined with the portable pulsed excitation circuit, demonstrates the promising potential for applications in double aperture magnetic resonance imaging (MRI) equipment, particle accelerators, and other advanced technologies.
cited:42
Quench behaviors of parallel-wound no-insulation high temperature superconductor coils
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Article Number:Article 100140
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Abstract
Corresponding email:yawei.wang@sjtu.edu.cn
No-insulation (NI) high-temperature superconducting (HTS) coil wound with parallel-stacked tapes emerges as a prospective choice for high-field fusion magnets owing to lower inductance and faster ramping rate. The parallel stacked-tape structure leads to new current redistribution among stacked tapes in each turn during local quenches, which also considerably changes the current redistribution behavior through inter-turn contacts. Therefore, quench behaviors of parallel-wound no-insulation (PWNI) coil should differ from its counterpart wound with single tape, which are still unknown. This study is to illustrate quench behaviors of PWNI HTS coils induced by local hot spot. A multi-physics model integrating an equivalent circuit network, a FEM heat transfer module, and a FEM T-A model is developed to analyze the electromagnetic and thermal characteristics of PWNI HTS coils during quench. Results show that the transport currents are mainly redistributed among parallel-stacked tapes through terminal resistances when a local hot spot happens on one tape, while being less dependent on turn-to-turn electrical contacts. It leads to a coupling current within PWNI coils that is not present in NI coils wound with single tape (single-wound no-insulation (SWNI) coil), resulting in a highly non-uniform transport current distribution among parallel-wound tapes. The reduced terminal joint resistances further enhance the coupling current, potentially leading to an extra overcurrent quench risk in PWNI coils. Moreover, the current redistribution between parallel-stacked tapes inhibits the turn-to-turn current redistribution in the PWNI coil, thus significantly reducing its magnetic field degradation under a high heat disturbance, which can be almost less than half of the SWNI counterpart in this study. These results offer important theoretical guidance to safety operation and robustness improvement of high-field HTS magnets wound by PWNI technique.
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