Plasma << PLAZ muh >>, in physics, is a form of matter composed of electrically charged particles. The sun and the other stars, and most of the other objects in space, consist of plasma. Lightning bolts also consist of plasma, but few other plasmas occur naturally on the earth.
Artificially created plasmas have many practical uses. For example, electricity turns the gas in the tube of a neon sign into a plasma that gives off light. A welding process called arc welding uses electricity to produce the high temperatures needed to join pieces of metal. Ion rockets use plasma fuels for trips through space. Ion rockets use electric power to expel charged particles called ions.
A plasma can be made by heating a gas or by passing an electric current through it. A gas consists of atoms or molecules. Each atom has a nucleus surrounded by one or more negatively charged particles called electrons. Great heat or a flow of electricity ionizes an atom by stripping off one or more of its electrons. These electrons then move around independently. An atom or molecule that loses electrons has a positive charge and is called an ion. As the temperature increases, more and more atoms in a plasma become ionized.
The physical and electrical qualities of a gas change greatly when it becomes a plasma because the ions and electrons in the plasma are separated. For example, most gases conduct electricity poorly and are not affected by magnetic fields. A plasma, on the other hand, conducts electricity well and is affected by magnetic fields. Gases consist of atoms that move around independently and in no definite way. The electrons and ions in a plasma may move around in groups, usually in wavelike motions. Plasmas have qualities unlike those of the three basic forms of matter—gases, liquids, and solids. For this reason, physicists consider plasma a fourth state of matter.
Scientists hope someday to generate electricity by using plasmas to control the process of nuclear fusion. Nuclear fusion gives off tremendous amounts of energy when two lightweight atomic nuclei unite to form a heavier nucleus. The energy from controlled fusion could be used as heat to make steam for electric generators. But temperatures of up to 100,000,000 °C are required to make the atomic nuclei react. Such a high temperature would melt any container. Many physicists are attempting to produce controlled fusion with hot plasmas held in place by strong magnetic fields or by some other method that does not involve use of a material container.
See also Nuclear energy (Nuclear fusion); Rocket (Ion rockets); Welding (Arc welding).
