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How is cold Plasma possible?

  1. Jan 13, 2005 #1
    I thought plasma was the most energetic state of matter, and that heat is proportional to energy levels? How is it possible for cold plasma then?
  2. jcsd
  3. Jan 13, 2005 #2


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    Can you put the question into some context? Where did you hear the term "cold plasma" being used? I've been following the lively doings over at the Princeton Plasma Physics Lab, where they are trying to intiate fusion by compressing (and therefore heating) plasma. To achieve ignition, they need something like 15 million degrees, so for them a plasma that is 1 million degrees is far too cold, practically freezing!
  4. Jan 13, 2005 #3
    I am not sure Iwas just reading somewhere that cold plasma exists in the sun where it is virtually not even hot enough to burn you, yet it is still excited enough that it can erradicate bacteria, and create protection from radiation(because plasma tends to have a such a strong electromagnetic field)
  5. Jan 14, 2005 #4
    A plasma is just positively ionized gas (by "positively", I mean that electrons are stripped off from the atoms, and not added to them, so the ionized atoms are positively charged). I'm quite sure there are ways to ionize a gas without heating it (shining a laser with the proper wavelength on it should do the trick I beleive), although keeping it ionized may be a problem below some treshold temperature.
  6. Jan 14, 2005 #5
    Yes, and in some contexts you can model the vacuum of space or the ionosphere as a plasma, with a quantity N electrons per m^3.
  7. Jan 17, 2005 #6
    Ultracold plasma by ionization of ultracold atoms

    See this article:

    Phys. Rev. Lett. 83, 4776–4779 (1999)
    Creation of an Ultracold Neutral Plasma
    T. C. Killian, S. Kulin, S. D. Bergeson*, L. A. Orozco§, C. Orzel, and S. L. Rolston
    National Institute of Standards and Technology, Gaithersburg, Maryland

    We report the creation of an ultracold neutral plasma by photoionization of laser-cooled xenon atoms. The charge carrier density is as high as 2 x 109 cm-3, and the temperatures of electrons and ions are as low as 100 mK and 10 µK, respectively. Plasma behavior is evident in the trapping of electrons by the positive ion cloud when the Debye screening length becomes smaller than the size of the sample. We produce plasmas with parameters such that both electrons and ions are strongly coupled.

  8. Jan 17, 2005 #7
    Yeah plasma is just gas with it's electrons stripped off. The plasma in florecent bulbs is cold by plasma standards.
  9. Jan 17, 2005 #8
    Isn't plasma matter at a highly energetic state, the next step up from gas?
  10. Jan 18, 2005 #9
    It is any gas that is electrically charged or, like solar plasmas, has had it's electron's stripped off, leaving it's nulcei bare. So techniquely it does not have to be energetic (hot) to be a plasma.
  11. Jan 18, 2005 #10
    By themselves, the free electrons inside a room-temperature metal can be said to constitute a plasma. A (-) plasma enclosed in a (+) charged crystal.
  12. Jan 18, 2005 #11


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    As I recall, any highly ionized gas can be called a plasma, and what's that stuff in plasma tvs?
  13. Jan 18, 2005 #12
    I believe that you could make ionized gas simply by sticking a needle on the top of a positively-charged Van de Graff generator. Would this be considered plasma, or is it too diluted?
  14. Jan 19, 2005 #13
    It's real plasma in the screen, real as in electrically charged gas. Plasma may seem like an exotic material, but it's really quite common.

    I just thought of something. What's blood plasma? Why do they call it a 'plasma'?
  15. Jan 19, 2005 #14
    Blood plasma is basically the mixture of liquids in the blood in which the cells are suspended. It's composed mostly of water and a bunch of organic compounds.

    According to this website, blood plasma came first, and physics plasma was named after it. It also says, though, that the connection is unclear.
  16. Jan 19, 2005 #15
    The term "Plasma" must have roots in a word that means something like "fuzzy medium". So Biologists used the term to coin the "fuzzy medium" that carries cells etc. while Physicists used the term to coin the "fuzzy medium" between highly polarized electrodes.
  17. Jan 19, 2005 #16
    It seems we have three uses of the word "Plasma" here. The biological plasma is quite different from the other two, and is simply a water-based liquid carrying various dissolved minerals and suspended organic solids used as a support and transport mechanism for living cells.

    A Plasma gas such as is found in the ionosphere is one that is highly charged due to removal of electrons from the atoms in the gas.

    The word Plasma may also be used to describe a more fundamental grouping of particles, such as the electron flux in a spark discarge, whethor from a Van de Graff generator or from any other generator, battery, etc. This type of plasma involves only electrons (or other fundamental particles) and is not made up of atoms at all.

    Plasma then in general refers to a gas or liquid which carries charged particles. Specifically, the charges may be carried on ions, disolved in a liquid such as blood plasma, or the charges on atoms, in an electron deprived ionic gas in the upper atmosphere, or in the liquid-like flux of the bare charges themselves, in a spark or other beam of energetic fundamental particles.

    In this last definition, many of the behaviors of electrons in conducters like ordinary copper wire can be thought of as if the electrons (on the surface anyway) are to some degree ionized, or free of the atoms which support them. The flux or current in the wire can be thought of as if the surface electrons were free to flow along the wire like a liquid or a gas might flow through a pipe. Even though these electrons behave in many ways like a liquid or a gas, and so fit the definition of a plasma, the wire which carries them is still quite solid to the touch and can be cool or even cold.

  18. Jan 19, 2005 #17
    As far as I know, the plasma of an electric discharge is the same that of an ionized gas. When the electrons go through, they eject electrons from the gas. You would not see anything if the electrons were alone. The glow you see from a van der Graaf is the same as aurora borealis or lightning, or a static discharge spark, all ionized gas.

    Nice reasoning, but I would need a reference to be convinced that biological plasma specifically refers to the electric charges.
  19. Jan 19, 2005 #18
    Definition of Plasma

    Loosely, and from Jackson's "Classical Electrodynamics,"

    An ionized gas should be called a plasma when the length scale which separates short range and long range behavior is short compared to the length scale of interest. Not all ionized gases are plasmas. For example, a very dilute gas of a few moving charged particles, interacting pairwise, is not a plasma. The conduction electrons in a metal are not a plasma, either. It is not always easy to tell if something is a plasma, really. Crudely, if you have to consider the inertial effects of the positive and negative charge carriers in the dynamics (say, in response to an applied electric field), then you've got a plasma.
  20. Jan 27, 2005 #19
    "Plasma" is also the name of a certain variety of green quartz. Why, you may ask? I haven't a clue. How do I know this, you might inquire? I had lots of free time in my childhood.

    Oh, by the way, I was wondering: If any substance gets heated enough, will it enter an, um, "plasmatic" state?
    Last edited: Jan 27, 2005
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