FLUX JUMPING IN THIN-FILMS

The thermomagnetic flux-jump instability of the Bean critical state is considered, which may occur during flux penetration in thin films of type-II superconductors in a perpendicular magnetic field. We calculat e the applied field B-j at which this instability occurs and its depen dence on the ramp rate B-a, on the nonlinear current-voltage curve, an d on the thermal resistance between the film and the substrate. As exa mples we consider the thermomagnetic flux-jump instability at the stra ight edge of a superconducting film and of the same edge containing a small indentation of semicircular shape. The presence of a small inden tation drastically reduces the field or ramp rate at which the thermom agnetic instability occurs.