Plasma
The word plasma has a Greek root which means to be formed or molded (the word plastic shares this root) and has a few definitions:
- in geology, a green type of chalcedony (rare - first used in 1772),
- in medicine, the fluid part of blood: see blood plasma,
- lymph[?] or milk (first used in 1845),
- an ionized gas. The remainder of this article is concerned with this meaning.
In physics and chemistry, plasma (also called an ionized gas) is an energetic state of matter in which some or all of the electrons in the outer atomic orbitals have become separated from the atom. 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.
The three lower-energy phases of matter are solid, liquid, and gas. Plasmas are the most common form of matter, comprising more than 99% of the visible universe. Commonly encountered forms of plasma include the Sun and other stars (which are plasmas heated by nuclear fusion), lit fluorescent lamps, lightning, the Aurora borealis, the solar wind, and interstellar nebulae.
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 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. 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. A microscopically small collection of charged particles isn't usually called a plasma. The typical characteristics of a plasma are:
- Debye screening lengths that are short compared to the physical size of the plasma.
- Large number of particles within a sphere with a radius of the Debye length[?].
- Mean time between collisions usually are long when compared to the period of plasma oscillations[?].
See plasma physics for active research topics.
External Links
- An educational plasma site (http://fusedweb.pppl.gov/CPEP/Chart_Pages/5.Plasma4StateMatter.html)
- Another introductory plasma site (http://www.plasmas.org/)
- http://plasma-gate.weizmann.ac.il/PlasmaI.html
- Plasma Universe (http://public.lanl.gov/alp/plasma/universe.html)
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other things of news, I do hear, that upon the reading of the House of
my Lord Chancellor, the Reasons were so bad, that my Lord Bristoll
still, advise the Lords to concur to, upon any of the Reasons of the
done on their Reasons, he would be against them; and indeed it seems the
how slightly the greatest matters are done in this world, and even in
untrue; they saying, that where any man is brought before a judge,
judge do there constantly and is obliged to commit him. Whereas the
contrary was true: and then, in the Sixth Article (I will get a copy of
diminishing of the King's power, as is said, at least things that
among the Lords, as my Lord Bristoll advised, whether, upon the whole
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very broad that there was mutiny and rebellion in the hearts of the
did do, in great fury. So that upon the Lords sending to the Commons, as
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Court, but that themselves only are a Court, and the Chief Court of
own Court with them that are none, and so will not submit so much as to
eagerness among the Lords do arise from the fear some of them have, that
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