magnetic islandmedical dictionary

<physics> A magnetic topology near a rational surface where the flux surface is broken up into tubes which are not connected with each other poloidally. Islands may develop in non-ideal magnetohydrodynamic fluids, where electrical resistance becomes important and magnetic field lines are no longer frozen-in to the fluid. Then magnetic tearing and reconnection may allow field lines to link up and form islands with a local magnetic axis in a narrow region near a rational surface. (See also magnetohydrodynamic, frozen-in law). The development of islands may be caused by a small perturbation, whether internal or external, whether deliberate or accidental, and is usually associated with enhanced transport (i.e., reduced confinement). The centres of the islands are magnetic O-points, while the boundaries between islands are marked by X-points.

(09 Oct 1997)