An approximate method to estimate ac loss in tape-wound superconducting coils

An approach to estimate the hysteretic loss in a coil wound with superconducting tape is presented. The loss depends on magnetic fields in the superconductor at peak coil current. For a given total current, the fields depend on how the current is distributed across the tape width. The loss is calculated as a function of a single parameter characterizing a range of plausible current distributions. The minimum should represent an upper bound to the actual loss. Results are presented for a specific pancake coil example, both isolated and incorporated as part of an assembly of stacked, identical coils.