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There is debate as to whether plasma is an individual state of matter or simply a type of gas.
In physics and chemistry, plasma (also called an ionised gas) is an energetic gas-phase state of matter in which some or all of the electrons in the outer atomic orbitals have become separated from the atom or molecule. The result is a collection of ions and electrons which are no longer bound to each other. This state of matter was first identified by Sir William Crookes in 1879, and dubbed "plasma" by Irving Langmuir.
Plasma is the fourth state of matter. It is distinct from the three lower-energy phases of matter solid, liquid, and gas. Plasmas are the most common form of matter, comprising more than 99% of the known visible universeAlternate uses: See Universe (disambiguation In the first half of the 20th century, the word universe was used to mean the whole spacetime continuum in which we exist, together with all the energy and matter within it. Attempts to understand the universe. Commonly encountered forms of plasma include the SunThe Sun (also called Sol is the star in our solar system. Planet Earth orbits the Sun. Other bodies that orbit the Sun include other planets, asteroids, meteoroids, comets and dust. Not all objects passing through the solar system have been orbitally capt and other starFor alternate meanings see star (disambiguation Hubble Space Telescope of the Sagittarius Star Cloud in the Milky Way Galaxy. A star is any massive gaseous celestial body in outer space. Stars appear as shining points in the nighttime sky that twinkle becs (which are plasmas heated by nuclear fusionIn physics, nuclear fusion (a thermonuclear reaction is a process in which two nuclei join, forming a larger nucleus and releasing energy. Nuclear fusion is the energy source which causes stars to shine, and hydrogen bombs to explode. It takes considerabl), lit fluorescent lampA fluorescent lamp is a type of electric lamp that excites argon and mercury vapor to create luminescence. Fluorescent lights are more efficient than conventional incandescent lamps because less of the energy is converted to heat. Instead, most is converts, lightningFor alternate meanings, see Lightning (disambiguation). Lightning is a powerful natural electrostatic discharge produced during a thunderstorm. Lightning's abrupt electric discharge is accompanied by the emission of light. The electricity passing through, the Aurora borealis, the solar windA solar wind is a stream of particles (mostly high-energy protons ~ 500 keV) which are ejected from the upper atmosphere of a star. In the solar system, the composition of this plasma is identical to the Sun's corona, 73% hydrogen and 25% helium with the, and interstellar nebulae. A plasma is also generated in front of a spacecraft's heat shield on reentering the atmosphere.
In astrophysical plasmas, Debye screening prevents electric fields from affecting the plasma very much, but the existence of charged particles causes the plasma to generate and be affected by magnetic fields. This can and does cause extremely complex behavior. The dynamics of plasmas interacting with external and self-generated magnetic fields are studied in the academic discipline of magnetohydrodynamics.
There are two broad categories of plasma, hot plasmas and cold plasmas. The Sun is an example of a hot plasma. Full ionization takes place, and the ions and the electrons are in thermal equilibrium. This is what would commonly be known as the "fourth-state of matter". A cold plasma is one where only a small fraction of the atoms in a gas are ionized, and the electrons reach a very high temperature, whereas the ions remain at the ambient temperature. These plasmas, sometimes known as technological plasmas, can be created by using a very high electric field to accelerate electrons which ionize the atoms. The electric field is either capacitively or inductively coupled into the gas by means of a plasma source eg microwaves. Common applications of cold plasmas include Plasma-Enhanced Chemical Vapor Deposition, Plasma Ion Doping , and Reactive Ion Etching .
The term plasma is generally reserved for a system of charged particles large enough to behave collectively, excluding microscopically small collections of charged particles. The typical characteristics of a plasma are:
See plasma physics, plasma cosmology, plasma chemistry , and plasma processing for research and development topics.
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