Plasma classification (type of plasma)

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Plasmas are described by many characteristics, such as temperature, degree of ionization, and density, the magnitude of which, and approximations of the model describing them, gives rise to plasmas that may be classified in different ways.

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Cold, warm and hot plasmas

In the laboratory in the positive column of a glow discharge tube:

"..there is a plasma composed of the same number of electrons and ions. [..] In low pressure gas discharge, the collision rate between electrons and gas molecules is not frequent enough for non-thermal equilibrium to exist between the energy of the electrons and the gas molecules. So the high-energy particles are mostly composed of electrons while the energy of the gas molecules is around room temperature. We have Te >> Ti >> Tg where Te, Ti and Tg are the temperatures of the electron, ion and gas molecules, respectively. This type of plasma is called a "cold plasma".
"In a high pressure gas discharge the collision between electrons and gas molecules occurs frequently. This causes thermal equilibrium between the electrons and gas molecules. We have Te ≃ Tg. We call this type of plasma a "hot plasma".
"In cold plasma, the degree of ionization is below 10-4."[1]
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Hot plasma (thermal plasma)

A hot plasma in one which approaches a state of local thermodynamic equilibrium (LTE). A hot plasma is also called a thermal plasma, but in Russian literature, a "low temperature" plasma in order to distinguish it from a thermonuclear fusion plasma.[2] Such plasmas can be produced by atmospheric arcs, sparks and flames.[3]

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Warm plasma

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Cold plasma (non-thermal plasma)

A cold plasma is one in which the thermal motion of the ions can be ignored. Consequently there is no pressure force, the magnetic force can be ignored, and only the electric force is considered to act on the particles.[4] Examples of cold plasmas include the Earth's ionopshere (about 1000K compared to the Earth's ring current temperature of about 108K).[5], the flow discharge in a fluorescent tube, [6]

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Ultracold plasma

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Plasma ionization

The degree of ionization of a plasma is the proportion of charged particles to the total number of particles including neutrals and ions, and is defined as: α = n+/(n + n+) where n is the number of neutrals, and n+ is the number of charged particles. α is the Greek letter alpha.

In a plasma where the degree of ionization is high, charged particle collisions dominate. In plasmas with a low degree of ionization, collisions between charged particles and neutrals dominate. The degree of ionization which determines when a gas becomes a plasma will vary between different types if plasma, and may be as little as 10-6:

"Among the many types of plasma, those commonly employed for plasma processing are low temperature, low density, non-equilibrium, collision dominated-environments. By low temperature, we mean "cold" plasmas with a temperature normally ranging from 300K and 600K, by low density we mean plasmas with neutral gas number densities of approximately 1013 to 1016 molecules cm-3 (pressure between ~ 0.1 to 103 Pa) which are weakly ionized between 10-6 to 10-1"[7]

Also:

".. Coulomb collisions will dominate over collisions with neutrals in any plasma that is even just a few percent ionized. Only if the ionization level is very low (<10-3) can neutral collisions dominate."[8]

Alfvén and Arrhenius also note:

"The transition between a fully ionized plasma and a partially ionized plasma, and vice versa, is often discontinuous (Lehnert, 1970b)[9]. When the input energy to the plasma increases gradually, the degree of ionization jumps suddenly from a fraction of 1 percent to full ionization. Under certain conditions, the border between a fully ionized and a weakly ionized plasma is very sharp."[10]
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Fully ionized plasma

A fully ionized plasma has a degree of ionization approaching 1 (ie. 100%). Examples include the Solar Wind (interplanetery medium), stellar interiors (the Sun's core), fusion plasmas

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Partially ionized plasma (weakly ionized gas)

A partially ionized plasma has a degree of ionization that is less than 1. Examples include the ionosphere (2x10-3)[11], gas discharge tubes.

The aurora may exhibition properties of a weakly ionized gas and a weakly ionized plasma:

"If we observe an aurora in the night sky we get a conspicuous and spectacular demonstration of the difference between gas and plasma behavior. Faint aurorae are often diffuse and spread over large areas. They fit reasonably well into the picture of an ionized gas. The degree of ionization is so I low that the medium still has some of the physical properties of a gas that is homogeneous over large volumes. However, in certain other cases (e.g., when the auroral intensity increases), the aurora becomes highly inhomogeneous, consisting of a multitude of rays, thin arcs, and draperies a conspicuous illustration of the basic properties of most magnetized plasmas."[10]

Associate Professor of Physics, Richard Fitzpatrick, writes:

"Note that plasma-like behaviour ensues after a remarkably small fraction of the gas has undergone ionization. Thus, fractionally ionized gases exhibit most of the exotic phenomena characteristic of fully ionized gases."[12]
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Collisional plasmas

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Collisional plasma

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Non-collisional plasma

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Neutral plasmas

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Neutral plasma

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Non-neutral plasma

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Plasmas densities

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High density plasma

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Medium density plasma

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Low density plasma

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Magnetic plasmas

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Magnetic plasma

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Non-magnetic plasma

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Complex plasmas

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Dusty plasma

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Grain plasma

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Active and passive plasmas

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Passive plasma

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Active plasma

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Ideal and non-ideal plasmas

An ideal plasma is one in which Coulomb collisions are negligible, otherwise the plasma is non-ideal.


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High Energy Density Plasmas (HED plasmas)

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Footnotes

  1. ^ Kiyotaka Wasa, Shigeru Hayakawa, Handbook of Sputter Deposition Technology: Principles, Technology and Applications (Materials Science and Process Technology Series), (1992), William Andrew Inc., 304 pages, ISBN 0815512805 (page 95)
  2. ^ Maher I. Boulos, Pierre Fauchais, Emil Pfender, Thermal Plasmas: Fundamentals and Applications (1994) Springer, ISBN 0306446073 (p.6) ACADEMIC BOOK
  3. ^ Souheng Wu, Polymer Interface and Adhesion CRC Press, ISBN 0824715330, (page 299) ACADEMIC BOOK
  4. ^ Marcel Goossens, An Introduction to Plasma Astrophysics and Magnetohydrodynamics (2003) Springer, 216 pages, ISBN 1402014333, (page 25) ACADEMIC BOOK
  5. ^ The Sun to the Earth -- And Beyond: Panel Reports, National Research Council (U.S.) (2003) 246 pages, ISBN 0309089727 (p.59) FULL TEXT ACADEMIC BOOK
  6. ^ A. J. van Roosmalen, J. A. G. Baggerman, S. J. H. Brader, Dry Etching for VLSI, Springer, 254 pages, ISBN 0306438356 (page. 14)
  7. ^ Loucas G. Christophorou, James Kenneth Olthoff, Fundamental Electron Interactions With Plasma Processing Gases, (2004) in Section 3.1 Low-temperature, Low-Density, Non-Equilibrium Plasmas, 76 pages, ISBN 0306480379 (page 39)
  8. ^ Robert J. Goldston, Paul Harding Rutherford, Introduction to Plasma Physics, "Fully and Partially Ionized Plasmas" (page 164)
  9. ^ Lehnert, B., "Minimum temperature and power effect of cosmical plasmas interacting with neutral gas", Cosmic Electrodynamics (1970) 1:397.
  10. ^ a b Hannes Alfvén and Gustaf Arrhenius, Evolution of the Solar System, (1976) Part C, Plasma and Condensation, "15. Plasma Physics and Hetegony FULL TEXT
  11. ^ Francis Delobeau, The Environment of the Earth, (1971) 132 pages, ISBN 902770208X (page 13)
  12. ^ Richard Fitzpatrick, Introduction to Plasma Physics: A graduate level course,FULL TEXT "Introduction: 1.2 What is plasma?" p.6 ACADEMIC BOOK
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