Magnetic flux penetration into finite length thin-walled niobium cylinders

The distribution of magnetic field in a finite thin-walled Nb superconducting cylinder in an axial magnetic field is analyzed. Both current density and magnetic field exhibit strong maximum in the cylinder edges. This triggers a giant flux jump in the hollow cylinder when a slowly increasing external magnetic field reaches a threshold value. Experimentally measured flux jumps were observed in a wide range of external fields, even below Hc1 of the Nb film. The field at which the jumps appear is temperature dependent. It was found that with increasing the wall thickness the singularity of the current density and magnetic field on the edges decreases, which explains the absence of giant jumps in a sample with thick walls in fields below Hc1.