Spring model for mechanical-electrical properties of CICC in cryogenic-electromagnetic environments

Tests on short samples and subsize conductors have been extensively conducted to demonstrate the undesired degradation of Nb3Sn CICC. The spring rod is taken as a more accurate description for strand helix, compared to rectilinear beam in most of previous models. The proposed model simulates mechanical behaviors of the homogenized strand over cable range under operating loads. Improved hydrostatic pressure model is employed for initial transverse load transmission and a second-order reaction force is considered for further continuous contact. The average integral formulation is used to calculate transport electric field and critical current degradation. The spring model gives a distribution of the strand deformation in one characteristic length and the strain regime in whole cable cross-section. The simulated transport voltage-current curve at cable level is compared to the experimental one and found a good agreement. The proposed model also evaluates the effects of void fraction, n value and characteristic length. A certain extent of performance promotion for CICC independent with AC loss and cycling loading is suggested to increase the subsequent twist pitch length and reduce the void fraction in a reasonable range. It is also found that increasing the twist angle with respect to the cable axis properly is helpful for reducing the degradation.