text: Type-II superconductivity is characterized by two critical fields called B and B. At a magnetic field B the applied magnetic field starts to penetrate the sample, but the sample is still superconducting. Only at a field of B the sample is completely normal. For fields in between B and B magnetic flux penetrates the superconductor in well-organized patterns, the so-called Abrikosov vortex lattice similar to the pattern shown in Fig. 2. A cross section of the superconducting plate is given in Fig. 7. Far away from the plate the field is homogeneous, but in the material superconducting currents flow which squeeze the field in bundles of exactly one flux quantum. The typical field in the core is as big as 1 tesla. The currents around the vortex core flow in a layer of about 50 nm with current densities on the order of 15 A/m. That corresponds with 15 million ampère in a wire of one mm.