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Would this fusion reactor work ?

  1. Oct 5, 2013 #1
    Coils produce a magnetic field which confines a big plasma ball.
    The magnetic field is rapidly increased which makes the plasma ball implode.
    In the compressed state fusion happens. The plasma ball explodes
    and compresses the surrounding magnetic field.
    This produces more induction in the surrounding coils, which is used to produce energy.
     
  2. jcsd
  3. Oct 5, 2013 #2

    mfb

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    How?
    In order to have something that could or could not work, you first need some specific design.

    It is possible to confine plasma with magnetic fields, tokamaks and stellarators do that. They cannot compress the plasma in the way you might imagine this, however.

    Why should it?
     
  4. Oct 5, 2013 #3
    Because of Faraday's law of induction.
     
  5. Oct 5, 2013 #4
    Maybe a magnetic bottle could do the job. And maybe it is possible to implode the plasma because the initial temperature of the plasma ball is much lower than the temperature of the plasma in a tokamak reactor.
     
  6. Oct 6, 2013 #5

    mfb

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    That is not much better than "because of magic", without a clear description how this should happen.

    Both tokamaks and stellarators work similar to magnetic mirrors, but they are circular so they do not lose particles at the ends. Heating can be done with the injection of fast particles or with microwaves. Where is the advantage of mirrors?
     
  7. Oct 6, 2013 #6
    There are 5 ways in which we can heat a magnetically confined plasma:
    1) Ohmic heating
    2) EM Wave heating
    3) Neutral beam heating
    4) Fusion product alpha heating
    and
    5) Compression

    Yes we can and do compressively heat plasma (just like any other fluid).

    Compressive heating isn't practical for modern large tokamaks and stellarators (except maybe during start-up). But there are alternative approached the really heavily on compressive heating. Magnetized target fusion for example.

    The second part of your proposal just wouldn't work. One reason why is that in D-T fusion most of the energy is carried away by the neutron. Since the neutrons are neutral, they would induce any currents in your coils.

    This is not really true. Yes all three are magnetic confinement devices. But beyond that the basic principles behind the tokamak and the stellarator are very very different that the basic principles behind a mirror. The Elmo Bumpy torus is the toroidal analogy of a mirror.

    What advantage are you talking about? In tokamaks and stellarators "mirror effects" give rise to neoclassical effects, enhancing radial transport (this is bad) and driving instabilities (also bad)!
     
  8. Oct 6, 2013 #7

    mfb

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    That's the similarity I meant - the confinement in two directions works very similar.

    That's why I asked, as I don't see an advantage.
     
  9. Oct 6, 2013 #8
    The advantage of a magnetic mirror machine is that it can hold a plasma ball instead of a plasma torus.
    A plasma ball has a better volume to surface ratio which would allow a more efficient explosion,
    for the same reason H-bombs aren't doughnut shaped.

    What about fusing Helium-3 with Deuterium, this would result in most products being ions instead of neutrons.

    Here's a simple description of how it could work:
    We use a huge LC-circuit, this means a huge capacitor connected to huge coils of the magnetic bottle.
    Before start the capacitor has to be sufficiently loaded with energy.
    Then the circuit is switched on, So the energy is passed from the capacitor into the magnetic field which compresses the plasma ball.
    At the time the plasma is fully compressed the capacitor should be empty and the magnetic field should be strong.
    Then the plasma explodes, compresses the surrounding magnetic field and increases the voltage in the coils (Faraday's Law of Induction).
    This loads the capacitor with the opposite charges than it had initially (this would also happen without explosion).
    After the explosion the capacitor should be loaded with more energy than it had at the beginning.
     
    Last edited: Oct 6, 2013
  10. Oct 6, 2013 #9

    Drakkith

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    Magnetic mirrors have severe problems with leaking ions out the ends. Also, the plasma in a fusion reactor does not explode.

    If you're interested in learning about fusion power, I'd recommend the following book:
    https://www.amazon.com/Principles-F...56&sr=8-1&keywords=principles+of+fusion+power
     
  11. Oct 6, 2013 #10
    Yes, but in my reactor the plasma should implode and explode, which is the reason not to use a torus here.
     
  12. Oct 6, 2013 #11

    mfb

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    That's not the way science or engineering works. You can do that in (soft) science fiction, where realism does not matter.
     
  13. Oct 6, 2013 #12
    Ok, please explain what's unrealistic about it.
    Is it impossible to unload the capacitor that fast?
    Or is the plasma ball not symmetrical enough for the implosion?
    Or would the coils have too much resistance for such strong currents?
     
    Last edited: Oct 6, 2013
  14. Oct 6, 2013 #13

    Drakkith

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    You need to understand the science behind how fusion reactors work in the first place before attempting to design one. "Exploding" and "Imploding" are not terms that mean anything in fusion power.

    The simple answer is that you don't appear to have a basic understanding of the science behind plasma physics or fusion power. And those subjects are far to broad for us to teach you. The information is out there if you want to learn however.
     
  15. Oct 6, 2013 #14
    But in this article http://en.wikipedia.org/wiki/Inertial_confinement_fusion
    "implosion", "imploding", "imploded", "implode" appear 24 times.
     
    Last edited: Oct 6, 2013
  16. Oct 6, 2013 #15
    Ok, I'm going to take a look at that.
     
  17. Oct 6, 2013 #16

    Drakkith

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    Of course, that's because of the unique nature of inertial confinement. But you're talking about magnetic confinement, which is far different.

    Edit: And more importantly, "exploding" and "imploding" aren't really useful terms in understanding how the reaction works. In inertial confinement the pellet is imploded, yes, but that in itself doesn't tell us much. We need to look at the temperature, pressure, density, and a dozen other things in order to grasp what is going on. Ask yourself, "What is it about imploding that causes fusion?" "Does it apply to my design?" Look up the differences between inertial confinement and magnetic confinement. How long does the reaction occur for during each one? Why is it different in the first place?
     
    Last edited: Oct 6, 2013
  18. Oct 7, 2013 #17
  19. Oct 7, 2013 #18
    One of the fundamental results in magnetic confinement is that you can not form topologically spherical magnetic flux surfaces. This is a direct result of the magnetic divergence constraint [itex]\nabla \cdot \vec{B}=0[/itex]. In practical terms this says that you can not magnetically confine a "plasma ball." (This result only applies to magnetically confined systems. Inertially or gravitationally confined systems can be spherically symmetric because they rely of different principles).

    This is why mirrors has end cap losses, but this is also why closed field line systems like tokamaks are toroidal.
    Mirrors do a lot of things to "plug" the end and minimize the end losses. In order to maintain magnetic confinement during the compression you would have to both increase the magnetic field everywhere self-similarly and find a way to increase the effect of the end "plugs." This is not practical.

    The other way would be to increase the magnetic field so rapidly that the plasma is inertially confined not magnetically confined. The is what the Z-machine does.

    If you instead try compressing a toroidal plasma with closed field lines then you don't have to worry about losses at the end. (Note that even though the plasma has to be toroidal, the reactor vessel doesn't have to be). The advantage of this approach is that you maintain magnetic confinement throughout the compression. As a result you don't have to ramp up you magnetic field as rapidly, nor as far. This is why there are a number of people studying FRC merging and compression (FRC=Field Reversed Configuration)

    Sorry. I didn't click on the "magnetic bottle" link and I didn't realize that it took you to a page about mirrors. I typically associate the magnetic bottle idea with all magnetic confinement concepts not just mirrors.

    Again this does not work. Even if all the energy from fusion where carried in charged particles, their monition is going to be isotropic(in all directions). In-order to capture energy from currents using a coil system you'd want the motion of these particles to be mono-directional.

    There are practical ways to directly capture the energy from charged particles.
    http://en.wikipedia.org/wiki/Direct_conversion

    I can think of about 2 dozen magnetic confinement concepts off hand. There is a conference dedicated to exploring new Innovative Confinement Concepts(ICC). They recently restructured and now call themselves the ERP(Exploratory Plasma Research).
    http://www.iccworkshops.org/

    That conference focuses on magnetic confinement. There are a number of alternative approaches to inertial confinement. And then there are the interial-electrostatic folks too.
     
  20. Oct 7, 2013 #19
    Yes that's what I wanted to do, I've never heard of the Z-machine though.

    Ok, it seems like this Stellarator-spheromak could let the plasma implode into a small ball if done right (note that the green coils form a magnetic mirror machine).

    I think you're wrong about that. The explosion increases the magnetic pressure of the surrounding field. This pushes some field lines back into the coils which produces a voltage in the coils.
    It's the same principle by which we compressed the plasma before, but now in reverse.

    Thanks for the information.
     
    Last edited: Oct 7, 2013
  21. Oct 8, 2013 #20

    russ_watters

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    This thread is hand-waving idle speculation, not engineering. Things don't happen (in an engineered device) because someone says they happen, they happen because the calculations show they happen. If you're not calculating anything, you're not doing engineering. Heck, without a diagram, you aren't even doing art! Since there is nothing useful here, this thread is closed.
     
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