The effect of strain and filament fracture on the transport properties of ITER cable-in-conduit conductors

Dedicated experimental and modeling research studies on the performance of superconducting cable-in-conduit conductor (CICC) have been massively performed and are still ongoing in order to determine the operational limits of the conductors and to optimize their design. Strand strain distribution and crack formation in the filaments after cabling and compaction, and under cooling down and electromagnetic load have been considered as the main cause for the degradation of the CICC’s transport properties. In combination with the strain maps generated by the mechanical model MULTIFIL and the electromagnetic code JackPot with the basic electrical and strain properties of the superconducting strand, the current sharing temperature (Tcs) of the CICC of the ITER Central Solenoid has been simulated and analyzed. A quantitative analysis of the Tcs degradation due to strain variation and filament fracture, respectively, is still missing. Here, the approach of analyzing the performance of CICC (e.g., the short samples tested in the SULTAN facility, or the full-size CICC used in real magnets) has been presented. Consequently, the effect of filament fracture on the cable Tcs has been investigated and turns out to be limited. Instead, the dominant mechanism behind the degradation of the transport properties of ITER type Nb3Sn CICCs is shown to be the broadening and shift in the strain distribution of the superconducting filaments.