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Theoretical and Experimental Analysis of Nb₃Sn Strand Buckling in Large Scale CIC Conductor

Hidetoshi KUDOH, Tsuyoshi YAGAI, Kei HAMANO, Kazuki YOSHIDA, Shinji HAMAGUCHI¹⁾, Kyohei NATSUME¹⁾ and Tetsuhiro OBANA¹⁾

Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan

1)

National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan

(Received 12 December 2013 / Accepted 12 March 2014 / Published 10 June 2014)

Abstract

The assessment of the performance of toroidal field (TF) coil of ITER has been progressing. Unpredictable strand buckling was observed by the destructive investigation of the conductor. The buckling direction was perpendicular to the Lorentz force (LF), and the mechanism of it was due to the thermal shrinkage caused by the difference of thermal contraction between strand material and conduit. Our previous work utilized a 2-dimensional string model and demonstrated that the observed 2 mm stand bending could have led to strand bending if the total amount of slide at the contact cross over was assumed to be 53 μm. To verify this estimation, we fabricated a device for the measurement of friction force between strands under constriction force comparable to the LF several hundred kN/m. Our results for Cr-coated 0.89 mm diameter strand surrounded by bare Cu strand indicate that thermal contraction stress applied to strand of 45 N would be sufficient to overcome the static friction force when the contraction force reduced to tenth of maximum LF. The mechanism of slide motion could be divided into two processes: separation of the inner wall of the conduit and the separation from other strands due to a gradual reduction of LF.

Copyright (c) 2014 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

cable-in-conduit conductor, Nb₃Sn strand, buckling, thermal contraction, static friction

DOI: 10.1585/pfr.9.3405063

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References

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This paper may be cited as follows:

Hidetoshi KUDOH, Tsuyoshi YAGAI, Kei HAMANO, Kazuki YOSHIDA, Shinji HAMAGUCHI, Kyohei NATSUME and Tetsuhiro OBANA, Plasma Fusion Res. 9, 3405063 (2014).