Structural analysis and measurement of the mechanical behaviour of the POLO coil under static and dynamic loads

The superconducting POLO coil (Ø 3 m) was designed as prototype poloidal field coil for application in a tokamak. It was tested at the TOSKA facility of FZK from March 1994 until March 1995. Different mechanical load cases were investigated by calculation and measurement to confirm that the orthotropic material data of the POLO winding were derived with sufficient accuracy. Besides static also transient deformations taking place within some milliseconds were measured and analysed by means of dynamic finite element calculations. The following load cases were investigated: (a) static excitation of the coil; (b) twisting of the coil by half-coil discharges (fast discharge of one half of the coil while the other half is shorted, *τ_min =5 ms); (c) bending of the coil by discharging it dose to a co-axial short circuit ring (the eddy currents induced in the ring cause dynamic forces of attraction between coil and ring). The good agreement of the measured and calculated deformations, displacements, and strains demonstrates the high standard of the tools for computation and measurement at helium temperatures. The arisen tensile and shear stresses in the winding show that the mechanical requirements for poloidal field coils were achieved according to the technical specification of the POLO coil