Numerical modelling and analysis of current induced stresses in REBCO coil stacks

This study reports the effect of the radial, axial, and hoop electromagnetic stresses caused by the large current density and the self-field (screening current-induced magnetic field) on REBCO superconducting coil stacks. A two-dimensional numerical model is used to study the stress distribution of a superconducting coil stack under current. The electromagnetically homogenized coil stack is assumed to be composed of four equally spaced coils with rectangular cross-section. Initially, the verification of the model is done by comparing the analytical calculations (which were in good agreement) of stress distributions of a superconducting slab exposed to a variable magnetic field and in a superconducting strip exposed to a variable current. Then, the two-dimensional model is used to obtain the components of stress that occurred in the coil stack under sinusoidal varying currents. The stress component distributions are calculated at different time intervals, currents, frequencies, and coil distances. Besides, one-dimensional stress distributions are plotted to show how the stress distributions change while the current increases. The upper and lower coils have much higher magnetic stress than the inner coils. Results obtained from the one-dimensional stress distribution calculations show that the stress occurring in the radial direction is lower than the stress in the z-direction in the coil stack. The stress distributions do not show a significant change as the frequency of the applied current changes. The stresses in both the radial and axial directions decrease as the distance between coils increases. All results are presented, and the possible reasons are explained.