In physics and chemistry, a
plasma is typically an
ionized gas. Plasma is considered to be a distinct state of
matter, apart from gases, because of its unique properties.
Ionized refers to presence of one or more free
electrons, which are not bound to an atom or molecule. The free electric charges make the plasma electrically conductive so that it responds strongly to electromagnetic fields.
Plasma typically takes the form of neutral gas-like clouds (e.g.
stars) or charged ion beams, but may also include dust and grains (called dusty
plasmas).<1> They are typically formed by heating and ionizing a gas, stripping electrons away from atoms, thereby enabling the positive and negative charges to move more freely.
Contents
1 History
2 Common plasmas
3 Plasma properties and parameters
3.1 Definition of a plasma
3.2 Ranges of plasma parameters
3.3 Degree of ionization
3.4 Temperatures
3.5 Potentials
3.6 Magnetization
3.7 Comparison of plasma and gas phases
4 Complex plasma phenomena
4.1 Filamentation
4.2 Shocks or double layers
4.3 Electric fields and circuits
4.4 Cellular structure
4.5 Critical ionization velocity
4.6 Ultracold plasma
4.7 Non-neutral plasma
4.8 Dusty plasma and grain plasma
5 Mathematical descriptions
5.1 Fluid model
5.2 Kinetic model
6 Common artificial plasma
6.1 Examples of industrial/commercial plasma
6.1.1 Low-pressure discharges
6.1.2 Atmospheric pressure
7 Fields of active research
8 Footnotes
9 See also
10 External links
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History
Plasma arcs between the probes on a Wimshurst Machine. This device, invented in the early 1880s, has long been a popular laboratory demonstration of plasma.
This state of matter was first identified in a Crookes tube, and so described by Sir William Crookes in 1879 (he called it "radiant matter").<2> The nature of the Crookes tube "cathode ray" matter was subsequently identified by British physicist Sir J.J. Thomson in 1897,<3> and dubbed "plasma" by Irving Langmuir in 1928,<4> perhaps because it reminded him of a blood plasma.<5> Langmuir wrote:
"Except near the electrodes, where there are sheaths containing very few electrons, the ionized gas contains ions and electrons in about equal numbers so that the resultant space charge is very small. We shall use the name plasma to describe this region containing balanced charges of ions and electrons."<4>
Common plasmas
Plasmas are by far the most common phase of matter in the universe, both by mass and by volume.<6> All the stars are made of plasma, and even the space between the stars is filled with a plasma, albeit a very sparse one (See astrophysical plasma, interstellar medium and intergalactic space). In the solar system, the planet Jupiter accounts for most of the non-plasma, only about 0.1% of the mass and 10−15% of the volume within the orbit of Pluto. Notable plasma physicist Hannes Alfvén also noted that due to their electric charge, very small grains also behave as ions and form part of plasma (see dusty plasmas).
Common forms of plasma include
Artificially produced plasmas
Those found in plasma displays, including TVs
Inside fluorescent lamps (low energy lighting), neon signs
Rocket exhaust
The area in front of a spacecraft''s heat shield during reentry into the atmosphere
Fusion energy research
The electric arc in an arc lamp, an arc welder or plasma torch
Plasma ball (sometimes called a plasma sphere or plasma globe)
Plasma used to etch dielectric layers in the production of integrated circuits
More abstracts about the Plasma (Physics)