Magnetic island
= Magnetic island
A magnetic island in a planar <magnetic field> is a region of closed <magnetic field lines> surrounding an extremum of the <Cartesian magnetic flux function>. A surrounding <separatrix> can pass through a saddle of that function and separate the island from other flux regions. In ideal <incompressible flow>, the flux-function value carried by each fluid particle and the area enclosed by each material contour are conserved.