Modeling of coated conductor pancake coils with a large number of turns

The current distribution, the magnetic field and the AC loss are numerically studied for pancake coils with up to 200 turns, taking into account the real thickness of the conductor and the magnetic interaction between the turns. All calculations assume the critical state model with a constant critical current density. The results show a slab-like current distribution, with the absence of magnetization currents due to the radial magnetic field. Consequently, longitudinal striation, with or without twisting, cannot reduce the self-field AC loss of this system. Finally, an analytical formula has been deduced for the AC loss at current amplitude: I-m = I-c, where I-c is the critical current, for large mean coil radius and any number of turns.