6. Discussion

compressing a CS cable which was fabricated in CASIPP to validate the analytical model. When the CS cable specimen is compressed along axial direction, it extends transversely with high resolution. The transverse extension can be measured by using a laser sensor. The experimental setup is schematically illustrated in the inset of Figure 14. One can find that the theoretical model shows perfect consistency

presented theoretical model. The green triangle symbols denote the experimental results.

Relationship between the axial strain ε<sup>0</sup> and the transverse strain εT. The colored lines are obtained by using the

Nuclear Fusion - One Noble Goal and a Variety of Scientific and Technological Challenges

In Figure 14, we can get that the CS conductors with baseline and LTP (long twist pitch) shows a Tcs degradation after EM cycles, while for the samples with

A comparison of the experimental results and theoretical results based on the presented model [18].

with the experiment.

Figure 14.

Figure 15.

98

In the past half-century, the structure of CICC conductor was under continuous optimization and improvement. The CICC conductors have so many advantages such as good self-support, high operational stability, high current carrying capacity, low AC loss, etc., and they are widely used in the superconducting magnets. The nuclear fusion device CFTER built by China has also chosen the CICC conductors. However, there still have some problems to be solved: (1) there is a necessity for theoretical model to explain the degradation of critical current caused by mechanical deformation for the Nb3Sn strand; (2) accurate description of the mechanical response of complex strand structures in the coupling fields remains a challenging problem; (3) the untwisting behavior during the cable penetration is still not suppressed completely. One needs a more effective model to optimize the manufacturing process; and (4) the long-term stability and real-time monitoring of superconducting magnets are also a challenge for the engineers. Based on this, the equivalent mechanical parameters of CICC conductors and their mechanical behavior under coupled fields will be further studied. The authors hope that these models can provide a valuable reference for the related researchers.

## Acknowledgements

This work is supported by the Funds of the National Natural Science Foundation of China (Nos. 11622217, 11802291, and 11872196), the National Key Project of Scientific Instrument and Equipment Development (11327802), and National Program for Special Support of Top-Notch Young Professionals. This work is also supported by the Fundamental Research Funds for the Central Universities (lzujbky-2017-ot18 and lzujbky-2017-k18).

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