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What happens to the Neutrons and Protons in a Tokamak reactor.

  1. Sep 21, 2009 #1
    As I understand it, the magnetic field confines the electrons because of the repulsion of the electrons in the plasma and the electrons traveling in the magnetic current.
    My question is what keeps the protons and neutrons released in the plasma from passing through the magnetic field in a tokamak reactor?
  2. jcsd
  3. Sep 21, 2009 #2


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    Neutrons pass right out of the plasma into the surrounding structure. The first wall must absorb the neutrons.

    The protons are charged, so like electrons they travel around/along the magnetic field lines, but their cyclotron radius is different.

    As an exercise, take the electrons and protons to have the same temperature (kinetic energy, but different velocity due to mass difference) and assuming a 10T field, calculate the cyclotron radii of the electrons and protons. And actually, if one is using D+T, then its deuterons and tritons, as well as products like p, He-3, He-4 and n.

    The plasma excludes the magnetic field, to the magnetic gradient sends the charged particles back into the plasma.

    The plasma likes to stay neutral, i.e. balance of + an - charges, so an electron leaving not only experiences the local magnetic field, but also Coulomb attraction to the plasma, which would have a net + charge if the electron were to leave.

    One problem for magnetic confinement is the leakage of neutrals, which are atoms formed from the 'recombination' of nuclei and electrons.
  4. Sep 22, 2009 #3
    Can additional fuel be added once the fusion process is started? Or can only one reaction occur at a time?
  5. Sep 22, 2009 #4


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    That's the idea. Ideally they'd be pumping in fuel as fast as it's consumed.

    But the have to get to steady-state beyond breakeven. That's hopefully what ITER will demonstrate.
  6. Sep 23, 2009 #5
    I appreciate your input, it's making this a little clearer to me. I'm actually hoping to work on the ITER project once I finish my degree. I still have a lot to learn before I'll be able to contribute. The practical problem you suggested still has me doing some research. I appreciate your comments though.
    Last edited: Sep 23, 2009
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