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Why is quasineutrality a required condition for a plasma to exist? Quasineutrality means that no density of electrons and ions should almost be equal but not exactly equal. Can anybody explain this this condition is required?

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    $\begingroup$ possible duplicate of Is a plasma a distinct phase of matter? $\endgroup$
    – Kyle Kanos
    Oct 30, 2014 at 19:01
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    $\begingroup$ See also: physics.stackexchange.com/q/12760 $\endgroup$
    – Kyle Kanos
    Oct 30, 2014 at 19:02
  • $\begingroup$ I am not asking here, the difference between plasma and gas. I was reading the conditions that plasma should follow and quasineutrality is one of them. It says that no densities of electron and ions should be of same order but not equal. I didnt understand why these quantities "should not " be equal $\endgroup$ Oct 30, 2014 at 19:13
  • $\begingroup$ The sentence "It says that no densities of electron and ions should be of same order but not equal." doesn't really make sense to me. $\endgroup$
    – ACuriousMind
    Oct 30, 2014 at 19:44
  • $\begingroup$ @seeking_infinity: I do believe that the answers to the linked question do give the necessary conditions for a plasma. $\endgroup$
    – Kyle Kanos
    Oct 30, 2014 at 19:56

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If the number of electrons and ions is exactly equal, it is still plasma. You are misunderstanding the quasineutrality requirement.

The term "plasma" was coined by Irving Langmuir with the phrase "We shall use the name plasma to describe this region containing balanced charges of ions and electrons", Oscillations in Ionized Gases Proc. Nat. Acad. Sci. U.S., vol. 14, p. 628, (1928)

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Plasma potential.

Often electrons move faster than ions and leave the plasma at a higher rate. The plasma becomes positive until the positive 'plasmas potential' slows down the rate of electron loss from the plasma until it is the same as the rate of positive ion loss. The electrons are partially held in the plasma by the attractive positive plasma potential. The positive ions are pushed out a bit more.

So plasmas are mostly a bit positive and quasineutral.

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I don't think that quasineutrality is "a required condition", but is a property of most plasmas.

Quasineutrality is the tendency for plasmas to attain electrical neutrality. It means that if a neutral plasma (with equal numbers of electrons and ions), should generate a region with a slight electrical charge, then because (a) the electric force is huge ($10^{39}$ time greater than the gravitational force), and (b) the charges are very mobile, then charges would tend to move to cancel out any charge imbalance.

The description suggests that this is a "tendency" because quasineutrality can be violated, and charged regions can be found in "double layers" and "particle beams".

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  • $\begingroup$ Dear iantresman. It is usually frown upon to directly copy-paste identical answers. (The problem is if everybody start to copy-paste identical answers en mass.) In general in such situations, please consider one of the following options: (i) Delete one of your answers. (ii) Flag for duplicate posts and delete one of your answers. (iii) If you think the two posts are not duplicates, then personalize each answer to address the two different specific questions. $\endgroup$
    – Qmechanic
    Dec 4, 2014 at 23:14
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This is just a property of matter, found in nature. It was found, that very hot matter tends to "share" electrons between all members (atoms).

If you have take, for example, a hydrogen cloud and then take all electrons out of it by magic, you will see a could of protons. But it will be unstable. Protons will repulse each other until the cloud will be completely dissolve in space.

This is why non-neutral matter is not stable and does not form a STATE.

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Plasma is a whole is neutral that is having same number of positive and negative charge but over a small length call dobye length it is not neutral so that is why it is called quasineutral... If my answer is wrong then inform me plz

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