Electromagnetoelastic Buckling on Three-Coil Superconducting Partial Torus

Numerical analyses and experiments on electromagnetoelastic buckling of superconducting toroidal field coils in a magnetic fusion reactor are presented. Magnetic attractive forces from neighboring coils lead to the electromagnetoelastic buckling when the coil current reaches the critical buckling current. The critical buckling currents of several types of toroidal field coils can be calculated by the numerical method developed here. The method is based upon the finite element method and the principle of stationary potential energy is applied to potential energy given by a sum of strain energy and magnetic energy. In order to confirm the buckling phenomenon and provide a check on the numerical method, the buckling experiments on a three-coil superconducting partial torus were carried out in liquid helium and the critical buckling currents were measured. The torus consisted of model coils made by winding a NbTi wire in D-shape and potting it in epoxy. On the other hand, elastic moduli of the model coil at liquid helium temperature are required for the numerical analysis. Those values were obtained from three point bend tests in liquid helium and from application of the theory for an orthotropic thin plate.