Transverse stress effects in ITER conductors

The International Thermonuclear Experimental Reactor (ITER) Central Solenoid and Toroidal Field Model Coils (CSMC, TFMC) and the CSMC Insert Coils using Nb₃₃Sn had unexpectedly low current-sharing temperatures and cable "n-values." This paper argues that the anomalous effects can be explained by the high longitudinal strain due to transverse Lorentz loads. Simulated results of earlier experiments with A15 monoliths indicate that the transverse stress "multiplier" is actually a longitudinal strain multiplier due to transverse loading. Irreversible cyclic degradation effects in the cables with the lowest thermal contraction mismatches are explained by showing that a modest precompression is required to prevent tensile cracking of a significant number of individual filaments. Examination of filament breakage due to bending shows the possibility of a well-defined threshold for irreversible damage.