# PlanetPhysics/Plasma

Def. Plasma is often defined as the fourth state of matter (beyond the 'usual' solid, liquid and gas phases) consisting of a mixture of ionized gas (or gases) with quasi-free electrons that, however, interact with each other and the ions in plasma, as well as the electromagnetic and gravitational fields present in the plasma.
"A gas becomes a plasma when the addition of heat or other energy causes a significant number of atoms to release some or all of their electrons. The remaining parts of those atoms are left with a positive charge, and the detached negative electrons are free to move about. Those atoms and the resulting electrically charged gas are said to be "ionized". When enough atoms are ionized to significantly affect the electrical characteristics of the gas, it is a plasma. In many cases interactions between the charged particles and the neutral particles are important in determining the behavior and usefulness of the plasma."
Ominuous examples of plasma are our sun, all the visible stars, 'neon' or mercury, fluorescent lights, plasma TV's, plasma display panels (PDPs) and computer plasma monitors, lightning and any other plasma formed during electrical discharges. Plasmas are estimated to constitute more than 99 percent of the visible Universe, but it may not be present in dark matter so called because it is invisible to our instruments except for its gravitational effects. Moreover, dark matter accounts for a very substantial part of our universe.
Plasma studies may eventually lead to controlled thermonuclear fusion as an almost inexhaustible source of energy. The international ITER experiment anticipates successful breakeven in fusion energy generation from controlled nuclear fusion in a ionized hydrogen plasma at about 200 million degrees Kelvin by the year 2030, which is supposed to happen either in France or Japan where ITER projects are centralized/located, and currently under development with an investment on the order of twelve billion US dollars (indeed: $12,000,000,000!$). This may appear as a rather high price at $60 per degree Kelvin of plasma heating, but in view of its potential to satisfy all projected mankind's energy needs for at least the next 100,000 years, this price would seem to be quite small if ITER were to be successful as claimed. A Japanese claim was published in 2008 that a high-power plasma heating device made in Japan is capable of GW delivery in plasmas, that it has already been tested, and that it will be available ahead of time to the ITER projects in France and Japan at a cost of approximately $2,000,000 USD each for 100 MW installations, with ITER expected to require at least 20 such high-power plasma heating devices.
Note that in medicine and biomedical research the term "plasma" is used with a completely different meaning as the fluid solution in which blood cells are suspended, and that contains mostly water with several dissolved salt ions, lipoproteins, enzymes, antibodies, and so on; often the term is also employed in the medical field for an artificial replacement of the entire ('biological') plasma that may contain only water and certain dissolved salt ions close to neutral pH.