Abstract Body

The emergence of high-temperature superconductor (HTS) and the technologies for HTS wire production make it possible to generate high fields with HTS coils [1], [2]. They greatly contribute the performances of high-field superconducting applications: MRI, NMR, fusion reactor and so on [3]. A rare-earth barium copper oxide (REBCO) has a good prospect to ultrahigh field generation. To avoid burning-out from a normal-state transition followed by hotspots on HTS coils, the no-insulation (NI) winding technique was proposed by Hahn in 2011 [4]. The NI HTS coils enable currents to flow into adjacent turns at local hotspots, avoiding from normal-state transition regions. Some key technological innovations on HTS magnet applications have emerged for these decades.

Researches and developments have been ongoing for practical applications of compact fusion reactors. Some of HTS coils on recent compact reactors benefit from the research findings described above in terms of the realization of high thermal stability and high magnetic field. In addition, a multi-bundled REBCO tape structure and a metal-as-insulation (MI) technique are adopted on HTS coils on a few compact fusion reactors including the Smallest Possible ARC (SPARC). MI REBCO coils has large turn-to-turn contact resistances due to high-resistive metal insulators between REBCO tapes [5]. It reduces an excitation delay time during charging operation, which is a major problem in large-bore coils, while maintaining a thermal stability. Meanwhile, REBCO coils wound with multi-bundled REBCO tapes have small inductances than those wound with a single REBCO tape [6]. It is effective in not only decreasing an excitation delay time but enhancing a robustness of normal-state transition to local critical-current degradations.

The current behaviors and thermal stabilities of several-tape-bundled NI REBCO coils have been numerically investigated before [7]. Whereas, on several fusion reactors, the number of REBCO tapes bundled on the HTS coils is in the dozens, far more REBCO tapes than the investigation case. We requires a deeper investigation for the current and thermal behaviors of many-tape-bundled NI REBCO coils.

In this presentation, we will reoport the behaviors of many-tape-bundled NI REBCO coil at local normal-state transition using the partial element equivalent circuit (PEEC) method. Especially, the thermal stabilities are investigated in the term of the current behaviors through a sudden discharging, over-current, and local critical-current degradation tests.

References

[1] Wu M K, Ashburn J R, Torng C J, Hor P H, Meng R L, Gao L, Huang Z J, Wang Y Q and Chu C W 1987 Superconductivity at 93 K in a new mixed-phase Yb-Ba-Cu-O compound system at ambient pressure Phys. Rev. Lett. 58 pp 908–910
[2] 2023. [Online]. Available:https://www.fujikura.co.jp/eng/products/newbusiness/superconductors/01/2050255_12808.html
[3] Yokoyama S, Lee J, Imura T, Matsuda T, Eguchi R, Inoue T, Nagahiro T, Tanabe H, Sato S, Daikoku A, Nakamura T, Shirai Y, Miyagi D and Tsuda M 2017 Research and Development of the High Stable Magnetic Field ReBCO Coil System Fundamental Technology for MRI IEEE Trans. Appl. Supercond. 27 4400604
[4] Hahn S, Park D K, Bascunan J and Iwasa Y 2011 HTS Pancake Coils Without Turn-to-Turn Insulation IEEE Trans. Appl. Supercond. 21 pp 1592-1595
[5] Lécrevisse T and Iwasa Y 2016 A (RE)BCO Pancake Winding With Metal-as-Insulation IEEE Trans. Appl. Supercond. 26 4700405
[6] Geng J and Zhan M 2019 A parallel co-wound no-insulation REBCO pancake coil for improving charging delaysSupercond. Sci. Technol. 32 084002
[7] Kodaka K and Noguchi S 2022 Current Behaviors of NI REBCO Pancake Coil Wound With Multi-Bundled Conductors During Charging and Against Local Normal-State Transition IEEE Trans. Appl. Supercond. 32 4603105