TY - JOUR
T1 - Performance of Epoxy-Impregnated Intra-Layer No-Insulation (LNI) REBCO Coils at 77 K
AU - Yoshida, Taisuke
AU - Suetomi, Yu
AU - Takahashi, Keisuke
AU - Takao, Tomoaki
AU - Yanagisawa, Yoshinori
AU - Maeda, Hideaki
AU - Ueda, Hiroshi
N1 - Funding Information:
Manuscript received December 1, 2020; revised February 5, 2021; accepted March 1, 2021. Date of publication March 12, 2021; date of current version April 16, 2021. This work was supported by the JST-Mirai Program, under Grant JPMJMI17A2 and Grant-in-Aid for JSPS Fellows under Grant 19J11812. (Corresponding author: Y. Yanagisawa.) Taisuke Yoshida and Keisuke Takahashi are with NMR Science and Development Division, RIKEN SPring-8 Center, Yokohama 230-0045, Japan and also with Sophia University, Tokyo 102-8554, Japan (e-mail: tsmtttt36@gmail.com; keisuke.takahashi@riken.jp).
Publisher Copyright:
© 2002-2011 IEEE.
PY - 2021/8
Y1 - 2021/8
N2 - 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.
AB - 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.
KW - Intra-layer no-insulation (LNI) REBCO coil
KW - epoxy impregnation
KW - screening current
KW - self-protection
KW - stress modification
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U2 - 10.1109/TASC.2021.3065875
DO - 10.1109/TASC.2021.3065875
M3 - Article
AN - SCOPUS:85102704136
SN - 1051-8223
VL - 31
JO - IEEE Transactions on Applied Superconductivity
JF - IEEE Transactions on Applied Superconductivity
IS - 5
M1 - 9376923
ER -