On the possibility for flux penetration into a Campbell regime near the onset of irreversibility in high temperature superconductors

The onset of dissipation and of harmonic generation in response to an ac magnetic field of high temperature superconductors are used for the identification of the irreversibility line below which dissipation occurs due to flux motion in the sample. We demonstrate, however, that in the presence of a static magnetic field and for low amplitude ac fields, the penetration close to the onset may occur into the Campbell regime in which the vortex motion induced by the ac field occurs inside the pinning potential well.