Hysteresis losses and magnetic phenomena in rotating disks of type-II superconductors

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Abstract
Hysteresis losses and the evolution of the magnetic flux threading disks of V and VTi rotating slowly in various static magnetic fields H0 directed perpendicular to the axis of rotation have been investigated by continuously monitoring 〈Bz 〉 and 〈By 〉, the average components of the magnetic induction, in the plane of the disk, parallel and perpendicular to H0. A simple model is developed which satisfactorily accounts for the hysteresis losses and the magnetic behavior during the initial changes and in the subsequent quasi‐steady‐state as the rotation progresses. The analysis indicates that dψ/dx=±k′Jc (B) describes the change of orientation of the sheets of flux lines with respect to H0 with distance from the flat surfaces. Jc (B) is the critical current density and k′ (T) is the shearing inclination parameter of the flux lattice in the sample. Our results confirm the hypothesis that, regardless of the initial magnetic state of the disk, in regions where ψ (x) varies with depth, the critical slope of the B profile (i) is diamagnetic and (ii) is not shallower than for the situations where the sheets of flux lines are parallel. We stress that point (i) requires that the rotation causes flux to escape from the disk against the gradient of B near the surface when the initial magnetic configuration is uniform or paramagnetic.