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What amount of energy is needed to make a field of plasma?

  1. Oct 22, 2016 #1
    How much energy would be required to generate a spherical field of plasma using an EM field? I have heard that EM fields can excite atoms in the air to create plasma- however, this may be incorrect. If correct, how much energy would be needed and would it fry anything inside because of the massive amount of heat being generated or would that heat radiate outward, creating a sort of force-field?
     
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  3. Oct 22, 2016 #2

    mfb

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    Depends on the size of the plasma, the density of the gas and how efficiently the gas absorbs the input radiation.
    There are plasma windows.
     
  4. Nov 5, 2016 #3
    When I was at michigan, our lab had a plasma source only drew a current of about 20 milliamps. I believe it was a Xenon plasma. The amount of energy needed highly depends on the density, temperature of the plasma and the ionization percentage. For a low temperature plasma, it wouldn't take much energy, just the right conditions (vacuum, thermoelectric filament or radio frequency heating, confinement)

    It may not fry anything if you were to put it inside the plasma. If it was a low temperature plasma, inserting a foreign object into it would likely just put it out. They are working on medical plasmas that are safe to touch.

    At high temperature, there wouldn't be a "force field". Plasma is all about confinement. Introducing a foreign object even into a fusion reactor would definitely obliterate said object, but it would also destroy confinement and shut the plasma down,
     
  5. Nov 5, 2016 #4

    Drakkith

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    At worst the foreign object would be scorched unless it was very, very small. The plasma density is simply too low to obliterate the object otherwise.
     
  6. Nov 5, 2016 #5
    I'm not sure. What if an edge localized mode was present? In the core region, you may be correct, but the most turbulent region is at the edge and/or divertor region. The divertor has to be designed to withstand 10MW/m^2 of power. Surely that would vaporize anything it touched.
     
  7. Nov 5, 2016 #6

    Drakkith

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    We're talking about perhaps a few grams of plasma at most within the entire reaction chamber, and only a small part of that is going to touch the object. Even though the plasma temperature is many millions of degrees, there simply isn't enough total heat stored in the plasma to vaporize an entire object.
     
  8. Nov 5, 2016 #7

    mfb

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    Existing test reactors store up to a few MJ of energy in its plasma, ITER will store hundreds of MJ (https://www.researchgate.net/figure/234922099_fig2_The-plasma-stored-energy-top-panel-the-central-temperatures-middle-panel-and-the [Broken]) and a power-plant-sized reactor will probably store a few GJ.
     
    Last edited by a moderator: May 8, 2017
  9. Nov 5, 2016 #8

    Drakkith

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    Perhaps I was mistaken then. Is that enough to vaporize an object? (I'm assuming something like a hand tool or similarly sized object)
     
    Last edited by a moderator: May 8, 2017
  10. Nov 5, 2016 #9
    The wall components are made out of tungsten, which has the highest melting point of any element. An edge localized mode can melt pieces of the wall. I think it highly depends on the location in the plasma, but at the right spot I'm sure an iron object would be pretty much obliterated
     
  11. Nov 5, 2016 #10

    mfb

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    400 MJ is sufficient to evaporate ~60 kg of copper. Energy needed to heat and melt it is taken into account.
     
  12. Nov 6, 2016 #11

    Drakkith

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    I guess in the case of a containment failure the reactor isn't destroyed because the heat gets deposited all across the interior instead of concentrated in one spot. My mistake.
     
  13. Nov 10, 2016 #12

    Ryan_m_b

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    The OP intends this to be some sort of force-field. In which case I've got two questions based on this post and the discussions around it:

    1) Is creating a suitably charged plasma bubble around an object possible? Is there any way to create arbitrary shapes of plasma (like a sphere of defined thickness) and sustain it?

    2) Regarding the energy in the plasma is it enough to divert/repel a projectile? I'm wondering if a plasma-shield (even if it were possible) would have enough time to melt, evaporate and harmlessly disperse something like a high-velocity rail gun slug.
     
  14. Nov 10, 2016 #13
    Maybe. You could set up a very large potential between a sphere and a shell surrounding said sphere to the breakdown voltage in the material between. Probably wouldn't sustain itself.
    Probably not. Ever run your finger through a candle flame quickly? That is a relatively high mass-density plasma and your finger goes right through it. Fusion plasmas have mass density less than that of air. The only way a plasma could interact with a physical projectile would be through heat transfer, but a projectile would be moving far too fast to gain any significant energy that way.

    You'd be better off setting up some kind of magnetic deflection device.
     
  15. Nov 10, 2016 #14

    Ryan_m_b

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    I was thinking along the lines of an external plasma. I.e. can you build a device that when activated creates a bubble around it, not within a chamber of any description.

    That's my intuitive thought, that even if it were possible to put a bubble of plasma around an object it would be trivial to design a weapon that could shoot through it.
     
  16. Nov 10, 2016 #15
    Even if say you had a free chunk of plasma in space, it would either

    1)Disperse rapidly onto space (remember it consists of high velocity particles)

    2) radiate all its energy away through bremmstrahlung and cool down to a normal gas
     
  17. Nov 10, 2016 #16

    mfb

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    See the plasma windows I mentioned in post 2. They are sufficient to hold the pressure difference between vacuum and the atmosphere, but they won't stop a bullet. Oh, and all existing plasma windows are millimeter- to centimeter-sized and need a lot of power.
     
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