Modelling the mechanics of 32 T REBCO superconductor magnet using numerical simulation

Abstract

High temperature REBCO superconducting tapes are very promising for high-field magnets. Under high magnetic fields there are high electro-mechanical forces, and thus concern for mechanical damage. Due to large screening currents and composite structure of the tape, the mechanical design of these magnets are not straightforward. In addition, many present designs use insulated winding. In this work we develop a novel two-dimensional axisymmetric finite element tool programmed in MATLAB that assumes the displacement field within linear elastic range. The stack of pancakes and a large number of REBCO tape turns are approximated as an anisotropic bulk hollow cylinder. Our results agree with uni-axial stress experiments in literature, validating the bulk approximation. Here, we study the following configuration. The current is first ramp up to below the critical current and we calculate the screening currents and the forces that they cause using the MEMEP model. As a case study 32 T REBCO superconductor magnet is simulated numerically. We have done complete mechanical analysis of the magnet by including the axial and shear mechanical quantities for each pancake unlike previous work where only radial and circumferential quantities are focused. Effect on mechanical quantities without screening current is also calculated and compared. It is shown that including screening current induced field strongly affect the mechanical quantities, specially the shear stress. The latter might be the critical quantity for certain magnet configurations. Additionally, in order to overcome high stresses, a stiff over banding of different material is considered and numerically modelled which significantly reduces the mechanical stresses. The FE based model developed is efficient to calculate the mechanical behaviour of any general superconductor magnet and its devices.