Magnetohydrodynamics, << mag `nee` toh `hy` droh dy NAM ihks, >> often abbreviated MHD, is the study of the way in which magnetic fields interact with fluids that conduct electric current. A magnetic field is an area of magnetic force. The fluid is usually a liquid metal or a plasma, a form of matter made up of charged particles.
When a conducting fluid moves through a magnetic field, magnetic forces induce (create) an electric current in the fluid. The electric current creates a magnetic field that alters the original magnetic field. The resulting magnetic field interacts with the electric current in the fluid, creating a force that changes the fluid’s motion. Scientists and engineers studying MHD use equations (mathematical formulas) to describe all of these interactions.
The effects of MHD have many applications. Scientists and engineers use MHD effects to pump, stir, and levitate (raise) liquid metals. Engineers have attempted to develop devices that use MHD effects to generate electric power and to propel submarines, ships, and spacecraft. Scientists have experimented with using MHD effects in devices called fusion reactors that produce energy by combining the nuclei of atoms. Such experiments attempt to use artificially generated magnetic fields to keep extremely hot plasma fuel from touching the reactor’s walls.
MHD effects also occur in nature. Earth’s magnetic field, for example, is generated by the motion of liquid metal in its core. Other natural occurrences that involve MHD effects include sunspots, solar flares, and the displays of light in the sky called auroras or northern and southern lights.
