Over the last decade substantial progress has been made in no-insulation (NI) high temperature superconductor (HTS) magnet technology [1]. Owing to the intrinsic “turn-to-turn current sharing” characteristics, NI HTS coils are essentially immune to electric burn-out upon a quench. Yet, they often experienced excessive magnetic stress and consequent mechanical damage mainly due to the large electromagnetic induction among nested coils during quench. In addition, recent experiment of an REBCO insert that generated a record high DC field of 45.5 T with a 31.1 T resistive background magnet revealed the unique “one-side-edge” mechanical damage of REBCO tapes in selected pancake coils, which is nowadays understood as a consequence of screening current induced stress [2]. This paper reports recent progress in no-insulation HTS magnet technology. First, selected milestone achievements are introduced in various applications, not limited to high field laboratory magnets. Then key technical challenges, especially relevant to >30 T ultra-high field applications, are followed and potential solutions are discussed such as “thermal eraser” and “magnetic dam”.

[1] S. Hahn, K. Kim, K. Kim, X. Hu, T. Painter, I. Dixon, S. Kim, K. R Bhattarai, S. Noguchi, J. Jaroszynski, D. C. Larbalestier, “45.5-tesla direct-current magnetic field generated with a high-temperature superconducting magnet”, Nature, 570: 496-499 (2019).
[2] X. Hu, M. Small, K. Kim, K. Kim, K. Bhattarai, A. Polyanskii, K. Radcliff, J. Jaroszynski, U. Bong, J. H. Park, S. Hahn, and D. Larbalestier, “Analyses of the plastic deformation of coated conductors deconstructed from ultra-high field test coils,” Supercond. Sci. Technol., 33: 095012 (2020).

Acknowledgement
work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2018R1A2B3009249) and the Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-IT1801-09. It was also supported by the National High Magnetic Field Laboratory (which is supported by the National Science Foundation under NSF/DMR-1157490), and by the State of Florida.

Keywords: high magnetic field, high temperature superconductor, no-insulation, superconducting magnet