Stress Analysis of Terminals From the Distribution of Screening Currents for the 40 T All-Superconducting Magnet Project

Stresses created by screening currents in high field superconducting magnets constructed of rare-earth barium-copper-oxide (REBCO) tapes have been shown to be a major issue that has led to reduced performance of some REBCO coils. Some superconducting alloys suffer more than REBCO when it comes to the degradation due to stress. It is becoming more commonplace to include the effects of screening currents in the design of REBCO coils. A 2D T-A electromagnetics model coupled with a structural COMSOL finite element model have been implemented to analyze strain from screening currents in the design of the 40 T all-superconducting magnet and associated test coils at the National High Magnetic Field Laboratory. The T-A model considering transport current parallel to the plane was verified with the H-formulation. This model has been expanded to a 3-D structural model to investigate the strain in the REBCO terminals, which interface REBCO pancake-wound coils with the coil leads. The effects of non-uniformly distributed magnetic field from the coil are considered and coupled with the screening current in the terminal. The stress and strain of multi-tape terminals caused by the screening currents are investigated and discussed. The calculated axial strain is less than 0.3%, which is within the limit of the yield strain for REBCO coated conductors. The developed model can be used to simulation more complex geometry with different directions of transport current and background field.