Critical currents and AC losses in superconductor/paramagnet heterostructures
Y. A. Genenko
University of Darmstadt
Technical University of Darmstadt, Institute of Materials Science, Darmstadt, Germany
Tailoring magnetic field and current distributions in superconductor/paramagnet heterostructures represents a
prospective route to improve HTS superconductor performance in high-current and high-field applications
directed at enhancing the current-carrying capability and the critical fields of such heterostructures as well as
reducing their hysteretic alternating current (AC) loss. The talk presents a review of macroscopic
electromagnetic properties of planar or curved superconductor strips as well as cylindrical wires in various
magnetic environments of different shapes and magnetic permeabilities. Since magnetic shielding is largely a
geometrical effect, magnetic surroundings may have either detrimental or advantageous influence on
superconductor performance. Particularly, conditioning of magnetic fields permits in special cases existence of
overcritical states or drastic reduction of AC loss in thin planar superconductor strips. In the case of cylindrical
superconductor wires, magnetic coating allows substantial reduction of magnetic flux penetration into the
superconductor due to both the magnetic screening and the enhanced Bean-Livingston barrier at the
magnet/superconductor interface, which together reduce AC losses in the superconductor. For these structures,
also the magnetic cloaking effect is discussed in weak- and high-field regimes. In the case of a superconducting
tubular wire, an external magnetic coating provides a huge reduction of AC losses even for a moderate magnetic
permeability of the coating. Exact analytical results and finite-element simulations pave the way for turning the
method of conditioning of magnetic fields into applications for practical use.