Theory of ac losses in type-II superconductors with a field-dependent surface barrier

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Abstract
The irreversible magnetic behavior of a type‐II superconductor in a periodically varying longitudinal applied magnetic field is theoretically examined. Bulk pinning is characterized by a critical current density Jc, and surface‐barrier effects are characterized by critical entry and exit fields Hen and Hex. Theoretical expressions for magnetic field and flux‐density profiles, voltage waveforms, hysteretic‐bulk and surface‐energy losses, and the ac permeability are derived for the arbitrary flux‐density (B) dependence of Jc, Hen, Hex, and the equilibrium magnetic field Heq. Numerical model calculations are performed to demonstrate the influence of the B dependence of the latter functions upon the measurable quantities.