Performance of Epoxy-Impregnated Intra-Layer No-Insulation (LNI) REBCO Coils at 77 K

Taisuke Yoshida, Yu Suetomi, Keisuke Takahashi, Tomoaki Takao, Yoshinori Yanagisawa, Hideaki Maeda, Hiroshi Ueda

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


The intra-layer no-insulation (LNI) method is effective for protecting a layer-wound REBCO coil from a quench. However, a recently reported hoop stress modification (both increase and decrease) due to screening currents is a potential problem causing conductor degradation during charging. Epoxy impregnation can suppress the hoop stress modification and in this work, we develop prototypes of epoxy-impregnated LNI-REBCO coils to be charged at 77 K. Degradation of the coil performance due to cooling down can be prevented by mechanically isolating each layer. The coil shows a reasonably short field delay and current bypassing behavior, which are major technical benefits of the LNI-REBCO coil. A structural analysis with screening current-induced electromagnetic forces qualitatively suggests that the epoxy-impregnated LNI-REBCO coil can support a compressive hoop stress which causes conductor degradation due to buckling. The tensile hoop stress, however, is still very high at the upper and lower ends of each layer, causing fracture of a superconducting layer; i.e., additional reinforcement is required.

Original languageEnglish
Article number9376923
JournalIEEE Transactions on Applied Superconductivity
Issue number5
Publication statusPublished - Aug 2021


  • Intra-layer no-insulation (LNI) REBCO coil
  • epoxy impregnation
  • screening current
  • self-protection
  • stress modification

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Electrical and Electronic Engineering


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