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You have a chamber with constant amount of gas (say either helium or argon). You create the plasma with an arc and turn it off. How much of the gas used to create the plasma returns back to helium or argon as opposed to dissipating into the chamber or creating new elements?

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    $\begingroup$ That completely depends on how much energy you can pump into that gas. In most plasma experiments not much happens, except that atoms get ionized, in which case no nuclear reactions take place. All nuclei remain the same, and they simply capture all electrons when the plasma cools down. If, however, one excite this plasma strong enough, by whatever mechanism, nuclear reactions take place and some of these nuclei will change. At the end of such a process the chemical composition of the neutral gas would have changed. That's what a fusion reactor does, although not with helium or argon. $\endgroup$ – CuriousOne Aug 28 '14 at 4:15
  • $\begingroup$ Thanks for the reply! This answers my question conceptually. Can you link me to any experiments that measure the chemical composition of the gas after plasma arc? $\endgroup$ – wholesomechoice Aug 28 '14 at 14:14
  • $\begingroup$ One wouldn't measure the chemical composition, but analyze the radiation of the plasma. If it emits neutrons or gamma radiation at certain energies, nuclear reactions are taking place. $\endgroup$ – CuriousOne Aug 28 '14 at 18:21
  • $\begingroup$ Are you thinking of chemical changes (i.e. formation of molecules, as opposed to nuclear transformations), for instance as occurred in the Miller–Urey experiment? $\endgroup$ – user10851 Aug 29 '14 at 17:47
  • $\begingroup$ @Chris White no, I wasn't thinking of this but thanks for relating my question to something cool like Miller-Urey experiment. My question has been answered bellow. $\endgroup$ – wholesomechoice Aug 30 '14 at 3:45
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I think it would be a good idea if you could enlarge on your question, explaining how it arose and what experience you have with such plasmas.

The first point is that the gas is already in the chamber, so it cannot "dissipate into the chamber."

The short answer to your second question is that an arc does not create new elements. New elements can be created by radioactive decay, by irradiation with neutrons or with particles accelerated to high energy, or by thermonuclear fusion. This last can occur in a Hydrogen bomb, where there are very high temperatures and densities. It can also occur in a laboratory plasma, but only when extreme methods are used to heat and compress the plasma. Helium and argon do not undergo fusion.

If you started with helium or argon in the chamber, it will still be there after you turn the arc off, if the chamber is sealed. If the chamber is attached to a vacuum pump, it will be pumped out. That's about it. Hope this helps.

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  • $\begingroup$ Thank you for your enlightening answer. To clarify and expand on my question, by dissipate into the chamber, I had meant that the electrons knocked loose get absorbed into the metal chamber assuming the chamber is grounded. Would that create a more positive gas? After your response, I now know that this is not correct and the same gas will remain unless if dealing with higher energy plasmas (and not using Ag or He). I should have also clarified my question to say no gas flow in the chamber instead of constant amount of gas. $\endgroup$ – wholesomechoice Aug 30 '14 at 3:42

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