"Unfreezing" the Magnetic Field
Magnetized plasmas are threaded throughout with magnetic lines of force, which are thought of as being "frozen" in the plasma. That is, the field lines and the plasma are tied to one another, move together in the flow of the plasma, and cannot -- under normal circumstances -- merge with another parcel of magnetized plasma. However, if magnetic fields in adjacent regions have significantly different orientations, the field pattern can change, with field lines becoming "unfrozen," breaking, and the "re-connecting" with those in the adjacent region. When this happens, the energy stored in the magnetic fields is released as kinetic energy and heat.
Animation illustrating the merging of oppositely directed field lines. (Animation copyright: Center for Visual Computing, University of California at Riverside)
MMS' Holy Grail: The diffusion region