Numerical analysis of eddy current problems involving saddle-shaped coils in superconducting MRI magnets

The pulsed field of saddle-shaped x, y field gradient coils induces eddy currents in metallic structures within a superconducting MRI magnet. These eddy currents are three-dimensionally computed by a hybrid form of a FEM and an integration method formulated on an electric vector potential T. The eddy current effects are investigated while varying the resistivity and geometric parameters of cryogenic radiation shields. In this paper applications of this calculation method for slit shields and actively shielded gradient coils are presented