Strong space plasma magnetic barriers and Alfvénic collapse

We propose to interpret high-magnitude magnetic barriers in space and solar plasma as due to pile-up of magnetic field lines and their Alfvénic collapse for MHD flows. The analysis of experimental data of both Interball and Cluster spacecrafts shows that high-magnitude magnetic structures found in the Earth magnetosheath and near the magnetopause are supported by a nearly thermal transverse plasma flow, with the minimum barrier width being of the order of the ion gyroradius. The collapse termination at such scales can be explained by the balance between pile-up of magnetic field lines and backward finite-gyroradius diffusion. Intercomparison of the theory, modeling and experimental data points out that the Alfvénic collapse is in general a promising mechanism for magnetic field generation and plasma separation.