Magnetohydrodynamics

Magnetohydrodynamics (MHD), method of generating electricity by passing a high-velocity stream of plasma (gas at very high temperature) across a magnetic field. As the stream moves through the magnetic field, it has an electric current generated in it. The principle is the same as that of the electric generator, except that in magnetohydrodynamics the plasma stream rather than a coil of wire acts as the conductor. If electrodes are inserted into the plasma, a current will flow in an external circuit between them. In this way heat can be almost directly converted into electrical energy. But magnetohydrodynamics is still in the development stage, and a full-scale MHD plant has yet to be built. In practice the plasma would be heated by burning fuel or by a nuclear reactor to a temperature of 2,000°C–3,000°C (3,632°F–5,432°C). At these temperatures the gas is ionized (has electrons stripped from its atoms) and becomes conducting. Strong magnetic fields are required, and these may be provided by superconducting magnets. So far a few kilowatts of power have been generated by MHD for only a few seconds, and improvements in high-temperature technology will be needed before substantial progress can be made. MHD plants could in theory be smaller than conventional power stations and achieve a much greater efficiency because of the elimination of moving parts.

See also: Electric generator; Magnetism.