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. With high magnetic field application there are high electro-mechanical forces, and thus
concern for mechanical damage. Due to the presence of large screening currents and composite
structure of the tape, the mechanical design of these magnets are not straight forward. In addition,
many contemporary 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 an-isotropic 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. This electromagnetic model can now take insulated
magnets into account. 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.