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Screening currents caused by varying magnetic fields degrade the homogeneityand stability of the magnetic fields created by $RE$BCO coated conductor coils.They are responsible for the AC loss, which is also important for other powerapplications containing windings. Since real magnets contain coils exceeding10000 turns, accurate modeling tools for this number of turns are necessary formagnet design. This article presents a fast numerical method to model coilswith no loss of accuracy. We model a 10400-turn coil for its real geometry andcoils of up to 40000 turns with the continuous approximation, which we checkedthat introduces negligible errors. The screening currents, the ScreeningCurrent Induced Field (SCIF) and the AC loss is analyzed in detail. The SCIF ismaximum at the remnant state with a considerably large value and decreasessubstantially after one day of relaxation. The instantaneous AC loss for ananisotropic magnetic-field dependent $J_c$ is qualitatively different than fora constant $J_c$, although the loss per cycle is similar. Saturation of themagnetization currents at the end pancakes causes that the maximum AC loss atthe first ramp increases with $J_c$. The presented modeling tool can accuratelycalculate the SCIF and AC loss in practical computing times for coils with anynumber of turns used in real windings, enabling parameter optimization.

Modeling of screening currents in coated conductor magnets containing up to 40000 turns