Electromagnetic behaviors of superconducting Nb3Sn wire under a time-dependent current injection

We build a 3D model to analyze the electromagnetic behaviors of Nb3Sn filamentary strand exposed to a time-varying current injection, under the consideration of n value and strain effect. Electromagnetic behaviors, performance degradation and AC loss are investigated. Results show that the filament bundles prevent a further field penetration from the outer shell into the interior matrix. Different current/field profiles occur in the strand and outside. Compared to the critical current, the average transport current keeps a high value with little change over a broader strain range, and has a larger magnitude by several orders of magnitude. Increasing the strain results in a suppression of the current transport capacity, and part of the current is expelled into the metal matrix causing larger AC loss. The larger twist pitch implies a longer current circuit and more magnetic flux enclosed, thus increasing the loss. More details are presented in the paper.