The Finite Element Simulation And Superconducting Performance Prediction Of CICC Conductors In The Extreme Conditions

Nowadays, the fusion energy is considered to be the most promising and cleaningenergy. ITER （International Thermonuclear Experimental Reactor Project） was establishedfor solving the scientific and engineering problem in large-scale fusion. Since the coils inITER are operated at high field with large currents, CICC which consist of thousands ofstrands within a conduit are used. The Nb₃Sn superconducting material has been widelyused in toroidal field （TF） and central solenoid （CS） superconducting coils due to itshighly current capacity. However, the performances are extremely sensitive on the strainstate. So it is quite necessary to quantitatively clarify the mechanical behavior underdifferent loading conditions. One of the typical loading conditions is cooling from heattreatment temperature to the operating cryogenic temperature the Nb₃Sn component isunder a thermal compression state due to the different thermal contractions for differentmaterials. The other typical loading condition is carrying a large current in a highmagnetic field, the strand will bending under a large transverse Lorentz force.One aim of this paper is to predict the critical current performance of Nb₃Sn strand.First，a model for an bronze-routed strand is built. The residual strain is calculated basedon the thermal-structure analysis，which shows a great agreement with both the theoryresolution and experimental value. Then the same finite element model is used for therunning strain calculations. An equivalent magnetic load is applied to the strand, and themechanical responses are discussed. In order to characterize the function of the loadingconditions such as magnetic field，temperature, load pitch，a series of analysis are carriedout. At the same time, the influence of thickness for Ta layer and twist pitch are alsostudied. The results indicates that a weaker magnetic field, lower temperature, smallerload pitch, thicker Ta layer and longer twist pitch are helpful for preventing thedegradation of strand from an excessive bending load.For the strand in CICC, the deformation is more complex than a single strand eventhough they are carried a same current at a same magnetic field. A45strand cable is performed for the equivalent magnetic force analysis. An explicit time integral methodbased on LS-DYNA is used for the need of convergence in a complex three-dimensionalcontact analysis. A mechanical response is also investigated with a varied magnetic load.Furthermore, the importance of the CICC spiral structure, cabling form for the accurateprediction of CICC mechanical response and the electrical behavior are emphasizedcompared to the theory resolution. Meanwhile, the influence of the cabling form and localfracture for the critical current performance are obtained. The results show that the criticalcurrent density including local fracture is degraded more than that local fracture excluded.The proposed method based on the procedural modeling and finite element analysis canreflect the multi-scale architectural feature and the multi-physics conditions to a greatextent. It is an attempt for accurate assessment for the performance of CICC on thecomplex multi-physical conditions. Then optimizations of the strand and conductor can becarried out on the basis of key parameters which influence the critical electricalperformance.