Electromagnetic modeling, loss analysis, and stress evaluation of parallel-wound no-insulation high-temperature superconducting magnets
Yong Chen, Qiuliang Wang, Kangshuai Wang, Benzhe Zhou, Hongzhuo Zeng, Shixian Liu, Xiaoyu Ji, Lei Wang, Jianhua Liu
Abstract
The parallel-wound technique is an effective method for reducing charging delay and enhancing electromagnetic margin of no-insulation high-temperature superconducting (NI HTS) coils, as demonstrated by both experiments and numerical simulations. From an engineering standpoint, the parallel-wound design also mitigates the constraint of individual conductor length, which is a significant limitation in large-scale coils requiring a single continuous conductor of the same specifications. However, traditional electromagnetic modeling of parallel-wound no-insulation (PWNI) HTS coils relies on equivalent circuit models, and a combined finite element model is required to capture the screening current characteristics of HTS coated conductors. The mutual invocation between circuit models and finite element models increases the technical demands on simulation engineers and complicates the analysis of electromagnetic interactions with other physical fields. To address these challenges, we first propose an axisymmetric distributed equivalent circuit model for PWNI HTS double pancake (DP) coils. The equivalent circuit model is then integrated directly into the finite element framework of T - A formulation, resulting in a streamlined electromagnetic finite element model. The validity of this model is confirmed through the charging and discharging experiments with a dual-wound NI HTS coil. Utilizing this model, we further investigate the effects of joint resistance and turn-to-turn contact resistivity on the electromagnetic characteristics of PWNI HTS coils. Additionally, the excitation loss and stress of multiple PWNI HTS DP coils in a 35 T all-superconducting high field magnet are also analyzed. The results indicate that both the lower turn-to-turn contact resistivity and joint resistance may lead to significant non-uniform currents within the coil. The joint resistance has a significant impact on the critical current of PWNI HTS coils, and the optimization of energization methodology increased the critical current of the experimental coil by 12 A. Enhancing the equivalent radial resistance between bundled turns proves more effective for reducing charging delay of PWNI coil than increasing that within bundled turns. Multiple PWNI coils in high field magnet exhibit elevated losses relative to single-tape equivalents due to coupling currents, particularly during the initial excitation. However, their peak strain accumulation is marginally lower than that of single-wound configuration.