Statistical analysis of the current-sharing temperature evolution in Nb3Sn cable-in-conduit-conductors for ITER

During the test of ITER conductors at nominal conditions, a degradation of the current sharing temperature has been observed after electromagnetic cyclic loading. Rather than focusing on the microscopic phenomena at the origin of the degradation, the degradation process has been studied from a statistical point of view, analysing the whole dataset of ITER conductors: average degradations have been calculated after various cycle numbers. Possible correlation with the strand critical current has also been analysed. In order to model the evolution of has been correlated with the reliability against cracks formation; the reliability is in turn defined according to a two parameters Weibull distribution. The validity of this approach has been tested with the so-called "Weibull plot". The Weibull exponents were calculated for several ITER conductors and were found to be lower than one, indicating that the failure rate, which may be regarded as the formation rate of fractures in the filaments composing the strands, is decreasing with the number of cycles.