ac losses and field and current density distribution during a full cycle of a stack of superconducting tapes

Starting from an existing model by Clem et al. , this paper has analyzed how the current density and magnetic field distribution of a stack of superconducting tapes with ac transport currents or applied fields will change in a full cycle. This paper assumes when the ac current or field starts to change in the other direction, a new penetrated region will begin to penetrate from the superconductor surface. If we assume Jc is constant in the critical region, this paper demonstrates that the Claassen formula ( 7 ) can be used to calculate the exact ac losses. If Jc depends on local Bz, we can use Eq. ( 9 ) to quickly predict the ac losses. This approach does not need to calculate a complete ac cycle. This saves considerably computation time while gives a result which is in close agreement with that calculated from a complete ac cycle. The calculation method can be applied for calculating a superconducting pancake coil if the coil radius is much larger than the tape width