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It is intuitive that at high temperature matter converts into plasma because of intense energy of electrons that they break away from atoms.

But how can plasma be created at low pressures?

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  • $\begingroup$ Why would pressure matter? Why not ask how can plasmas be created at high pressures? $\endgroup$ – honeste_vivere Jun 22 '18 at 14:32
  • $\begingroup$ I'm just curious as to how can Plasma be formed at low pressure $\endgroup$ – Haziq Ahmed Jun 22 '18 at 14:35
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    $\begingroup$ I know, I was asking you why the pressure part is even considered. Gas pressure really does not matter in the ionization of a gas other than at higher pressures, there may be more opportunities for recombination (i.e., neutralization). $\endgroup$ – honeste_vivere Jun 22 '18 at 14:39
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To answer your question, we should clarify what a plasma actually is: an ionized gas, i.e. a gas consisting of particles with positive and negative charges and some neutrals.

Ok, we need to ionize particles. We can do that by, for example, accelerating some free electrons (which we always have, due to background radiation, for example). These electrons need to gain enough energy such that they can ionize particles of the gas by colliding with them. If we just apply enough energy to the system, enough ionization processes will occur and we have a plasma which behaves very different from a neutral gas (due to the long-range Coulomb-interaction).

As @honeste_vivere said in the comments, it doesn't really matter what the pressure is. Plasmas do exist over quiet a large parameter space, as shown in the answer by @Kaelan Donatella.

You said that it is clear to you how plasma is created at very high pressure but not at low pressures. Lower pressure just means that the mean free path, the average distance between two collisions, is longer. When you think of my initial example, where free electrons are initially accelerated (for example by some electric fields), a lower pressure is actually helpful as it is easier to let them gain enough energy to allow them to make ionizing collisions (since they are accelerated over a longer distance).

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Is your question about temperatures or pressures? If you have a very high temperature at low pressure, you can create a plasma.

This graph resumes this well: density here is equivalent to pressure (they have the same effect)

enter image description here

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