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 J(c) is constant in the critical region, this paper demonstrates that the Claassen formula (7) can be used to calculate the exact ac losses. If J(c) depends on local B(z), 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. c 2010 American Institute of Physics. [doi:10.1063/1.3371190]