plasma

plasma in physics, fully ionized gas of low density, containing approximately equal numbers of positive and negative ions (see electron and ion ). It is electrically conductive and is affected by magnetic fields. The study of plasma, called plasma physics, is especially important in research efforts to produce a controlled thermonuclear reaction (see nuclear energy ). Such a reaction requires extremely high temperatures; it has been computed that a temperature of about 10 million degrees Celsius would be needed to initiate the reaction between deuterium and tritium. By passing a very high electric current through plasma great heat is produced and, simultaneously, an electromagnetic field is created, causing the plasma to withdraw from the walls of its container. The contraction of the plasma, called the pinch effect, prevents the container from being destroyed, but the effect may become unstable too quickly for the fusion reaction. The properties of plasma are distinct from those of the ordinary states of matter , and for this reason many scientists consider plasma a fourth state of matter. Interstellar gases, as well as the matter inside stars, are thought to be in the form of plasma, thus making plasma a common form of matter in the universe. See also condensate .

plasma A state of matter consisting of ions and electrons moving freely. Stars consist of plasma, and plasmas exist in interstellar space; the solar wind is a plasma. Because a plasma is highly ionized, its behaviour differs from that of a normal gas. External magnetic and electric fields can affect a plasma, and the charged particles themselves can interact magnetically and electrically.

plasma In physics, an ionized gas that contains about the same amount of positive and negative ions. Plasma, often described as the fourth state of matter, occurs at extremely high temperatures, as in the interiors of the Sun and other stars and in fusion reactors.