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Question- difference between plasma and ionization?

  1. Nov 1, 2004 #1
    Could someone please explain the difference between a gas that has entered its plasma state and an ionized gas?
  2. jcsd
  3. Nov 1, 2004 #2


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    It depends on the degree of ionization. Clearly, a few ions or molecules in a gas does not make it a plasma. When the degree of ionization becomes sufficient to make electrodynamic or magnetohydrodynamic effects dominate the behavior of the material then it can be classified as a plasma. One general criterion for a material to be classified as a plasma is the existence of Debye shielding and the presence of a large number of electrons/ions in a "debye sphere."
  4. Nov 1, 2004 #3
    Thanks for taking the time to answer my question. I need more detail please.

    The context of my question is related to an experiment that initiates engine combustion with plasma as opposed to a conventional spark. I am trying to understand what defines the difference between plasma ignition and the conventional spark ignition that is used in cars today. Here is a link to the experiment:


    What are the electrodynamic or magnetohydrodynamic effects that would define a plasma in this context? Am I correct that the debye length in this experiment would exist between the entire length of the distance between the + and - electrodes inside the combustion chamber? Would the area between these electrodes constitute the debye sphere?
  5. Nov 1, 2004 #4


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    That article wasn't too specific on the nature of the plasma. To determine the Debye length you need the temperature and electron density. The density gives you the plasma frequency and divide that into the thermal speed to obtain the debye length.

    Cube the debye length and multiply it by the number density to find the number of electrons in a debye sphere. If it's much greater than 1 then it "qualifies" as a plasma!
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