How does plasma act outside of a containment field?

  • #1
If you were to have some way to remove plasma out of a tokamak or stellarator, how would it act? I realize there's basically no way to actually remove plasma from those machines, but I'm curious how plasma would act in the actual atmosphere. Would it act like a plasma cutter? Would it stay somewhat together? Would it just dissipate into super heated air instantly?

Also say it was a heavier than air plasma, plasma for the sake of it and not for nuclear fusion, would it pool like a liquid? Also assume its a hot plasma, approaching nuclear fusion levels of heat?

I realize this is an odd question and I may not be explaining what I want to know correctly, however I would appreciate anyone who took the time to answer!
 
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  • #2
boneh3ad
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Plasmas are just ionized gases. An unconfined plasma will behave the same as any gas released into the atmosphere: it would flow with and diffuse into its surroundings. The only real difference would be its susceptibility to electromagnetic fields and tendency to react with it's surroundings and deionize without an energy and confinement source.
 
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  • #4
Khashishi
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If you were to have some way to remove plasma out of a tokamak or stellarator, how would it act? I realize there's basically no way to actually remove plasma from those machines, but I'm curious how plasma would act in the actual atmosphere. Would it act like a plasma cutter? Would it stay somewhat together? Would it just dissipate into super heated air instantly?
The plasma would cool down and recombine almost instantly, in a bright flash of light. In fact, there is a technique called "massive gas injection" which is being used in tokamak experiments to quickly shut down a plasma in case there is a loss of plasma control which will lead to a "disruption". Disruptions occur somewhat frequently in tokamak experiments and do some damage to the walls. With massive gas injection, a valve opens when plasma control is lost and quenches the plasma in milliseconds, reducing the damage to the walls.

Also say it was a heavier than air plasma, plasma for the sake of it and not for nuclear fusion, would it pool like a liquid? Also assume its a hot plasma, approaching nuclear fusion levels of heat?
Plasma is normally much less dense than air. In a tokamak, there is only around a microgram of plasma in the chamber. You can use PV=nRT here: if P is kept somewhat constant, then for very large T, n/V will be very small. In fact, tokamaks often have plasma pressures quite similar to the atmospheric pressure. The pressure would have to be much larger for the density to be large, which means that it would expand immediately if it was released outside (in a big explosion). Plasma is more like a gas than a liquid.

You can have pooling of heavy gases (like chlorine in trenches-- sorry for the example), but thermonuclear plasmas are too energetic to pool under Earth gravity. The thermal velocity is greater than the escape velocity.
 
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  • #5
Oh! that's exactly what I was wanting to know! Thank you so much for the help!
 
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  • #6
boneh3ad
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Keep in mind, an "explosion" of one microgram worth of plasma is pretty minor. It's not tiny, as it would have similar energy to a gram of TNT, but it's not going to knock down a building or anything.
 
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  • #7
Ohh ok, so say if it was about 100 grams of plasma that escaped, it would be similar to about a hundred kilograms of TNT? Theoretically since I doubt there are any current ways to store that much plasma.
 
  • #8
Khashishi
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If a hydrogen plasma has a temperature of (10 keV)/##k_B## = 116 MK, then that works out to about 3 GJ of kinetic energy per gram. Just use
##E = 3/2 k_B T n##
where n is the number of protons + electrons, since at this temperature hydrogen is ionized.
 
  • #9
Wait so would all of this kinetic energy be turned into an explosion? Because if that's so then 100 grams of plasma at that temperature has about as much energy as 71.7 tons of TNT. For comparison when Mythbusters made diamonds they used about 2.5 tons of a TNT equivalent. 100 grams of plasma has about 28.75 times that energy if that kinetic energy goes to an explosion. That makes me wonder about all the sci-fi weapons that if were actually attempted would end in massive explosions before it even fired.

A video of that explosion here.
 
  • #10
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I can't see how plasma could be used as a weapon. (other than thermonuclear bombs which already exist).
Once it is uncontained it's going to rapidly degenerate into normal atoms with a lot of heat emission, but an uncontained plasma can't be targetted at anything in particular.
 
  • #11
Ah I see
 

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