AC loss and shielding in stacks of coated conductors: Analytic modelling and comparison to experiment

This work explores the effects of the stacking of coated conductor tapes on their AC loss and penetration fields (B_p). The penetration field B_p and AC loss of short lengths of coated conducted tape stacks are analyzed, measured, and compared to a simple analytic model. The tape widths (w) and number of tapes in the stacks (N_s) were 4 mm (N_s = 1, 3, 5, series-305) and 12 mm (N_s = 1–40, series-244). Experimentally, the losses of the series-244 and series-305 tape stacks were measured in a spinning magnet calorimeter (SMC) in which the samples are exposed to a spinning field of frequency, f, up to 110 Hz and amplitude B₀ = 566 mT and the power is measured by a calibrated boil-off calorimeter. These results were compared to calculated loss as a function of N_s for both tapes. In addition, the calculated B_p was plotted vs N_s. The basic effect observed was that stacking coated conductor tapes tended to form an effective composite with an increase B_p,comp and modified loss (For B₀ < B_p,comp, P_tot was reduced with N_s, the effect saturating for N_s > 20). This could be understood in terms of treating a stack of conductors as a composite described in terms of a Brandt equations applied to a dilute superconductor. The results show and model the significantly reduced loss that stacks of conductors can have significantly for moderate levels of applied field. Such results are directly transferrable to cables of stacked strands.