Thermal Stress Analysis and Optimal Design of Large-Scale Nb3Sn Composite Superconducting Coils

Abstract

Since each material in the Nb 3 Sn superconducting wire has a different coefficient of thermal expansion, the Nb 3 Sn superconducting coil will generate a certain amount of thermal strain during the process from high-temperature treatments and molding to low-temperature operation. When it is exposed to a transport current, it will also be subjected to Lorentz force under the action of the self-field, thus generating a large mechanical deformation. Since Nb 3 Sn superconducting materials have high strain sensitivity and the strain generated in the superconducting wire affects the stability of the superconducting magnets, it is of scientific importance to calculate the mechanical behavior of superconducting magnets under thermal stress and electromagnetic body force. In this paper, based on the bidirectional homogenization method, finite element software is used to first analyze the variations of stress-strain of each material with the number of turns and layers under thermal stress in Nb 3 Sn coils. Secondly, by changing the number of Nb 3 Sn core wires, the size of Nb 3 Sn core wires and the diameter of the copper base in the superconducting wires, the stress and strain of each material with the copper excess ratio were analyzed. When the number of core wires is larger, the size of the core wires is larger or the diameter of the copper base is smaller. Thus, it provides a tool to optimize the design of superconducting coils structure in terms of mechanical properties. Finally, we consider the developments of stress and strain of each material in the superconducting coil under the combined effect of thermal stress and electromagnetic force.