Calculation model of coupling loss time constant for Nb3Sn conductor under cyclic electromagnetic load

Abstract:

On ITER (International Thermal Nuclear Experimental Reactor) superconducting fusion device, the Nb₃Sn composite strands have been applied to CICC (cable-in-conduit conductor) to meet the impact of the magnet field above 12 T. The strain of Nb₃Sn-based conductor due to Lorentz forces leads to the change of critical current and coupling loss time constant. However, the study on critical performance degradation of CICC is still inadequate. Moreover, the most important is that the influence exploration of the contact properties with strain on coupling loss time constant is also insufficient. In order to calculate coupling loss accurately and quickly, a new calculation model of coupling loss time constant was put forward in this paper, which is expressed with a linear equation using some parameters that is the cabling sequence ratio, the contact resistance and the void fraction with strain main from electromagnetic force. In this model, not only the computation expression of cabling sequence ratio is given, but also the contact resistance and the void fraction is obtained with strain (from electromagnetic load cycle). Compared with numerical calculation using Gandalf and traditional method, the error of coupling loss calculated with the combination of the cabling sequence ratio, the contact resistance and the void fraction with strain is small, which is close to the engineering measured value.