Plasma

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Plasma (physics)
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Plasma

Top row: both lightning and electric sparks are everyday examples of phenomena made from plasma. Neon lights could more accurately be called "plasma lights", as the light comes from the plasma inside of them. Bottom row: A plasma globe, illustrating some of the more complex phenomena of a plasma, including filamentation. The colors are a result of relaxation of electrons in excited states to lower energy states after they have recombined with ions. These processes emit light in a spectrum characteristic of the gas being excited. The second image is of a plasma trail from Space Shuttle Atlantis during re-entry into the atmosphere, as seen from the International Space Station.

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Plasma (from Greek πλάσμα, "anything formed"[1]) is one of the four fundamental states of matter (the others being solid, liquid, and gas). Heating a gas may ionize its molecules or atoms (reducing or increasing the number of electrons in them), thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions.[2] Ionization can be induced by other means, such as strong electromagnetic field applied with a laser or microwave generator, and is accompanied by the dissociation of molecular bonds, if present.[3] The presence of a non-negligible number of charge carriers makes the plasma electrically conductive so that it responds strongly to electromagnetic fields. Plasma, therefore, has properties quite unlike those of solids, liquids, or gases and is considered a distinct state of matter. Like gas, plasma does not have a definite shape or a definite volume unless enclosed in a container; unlike gas, under the influence of a magnetic field, it may form structures such as filaments, beams and double layers. Some common plasmas are found in stars and neon signs. In the universe, plasma is the most common state of matter for ordinary matter, most of which is in the rarefied intergalactic plasma (particularly intracluster medium) and in stars. Much of the understanding of plasmas has come from the pursuit of controlled nuclear fusion and fusion power, for which plasma physics provides the scientific basis. Contents

1 Common plasmas
2 Plasma properties and parameters
o2.1 Definition of a plasma
o2.2 Ranges of plasma parameters
o2.3 Degree of ionization
o2.4 Temperatures
2.4.1 Thermal vs. non-thermal plasmas
o2.5 Potentials
o2.6 Magnetization
o2.7 Comparison of plasma and gas phases
3 Complex plasma phenomena
o3.1 Filamentation
o3.2 Shocks or double layers
o3.3 Electric fields and circuits
o3.4 Cellular structure
o3.5 Critical ionization velocity
o3.6 Ultracold plasma
o3.7 Non-neutral plasma
o3.8 Dusty plasma and grain plasma
4 Mathematical descriptions
o4.1 Fluid model
o4.2 Kinetic model
5 Artificial plasmas
o5.1 Generation of artificial plasma
5.1.1 Electric arc
o5.2 Examples of industrial/commercial plasma
5.2.1 Low-pressure discharges
5.2.2 Atmospheric pressure
6 History
7 Fields of active research
8 See also
9 Notes
10 References
11 External links

Common plasmas
Further information: Astrophysical plasma, Interstellar medium, and Intergalactic space Plasmas are by far the most common phase of ordinary matter in the universe, both by mass and by volume.[4] Our Sun, and all the stars are made of plasma, much of interstellar space is filled with a plasma, albeit a very sparse one, and intergalactic space too. In our solar system, interplanetary space is filled with the plasma of the Solar Wind that extends from the Sun out to the heliopause. Even black holes, which are not directly visible, are fuelled by accreting ionising matter (i.e. plasma),[5] and...
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