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Fusion with help of accelerators?

  1. Mar 13, 2012 #1
    Is it possible to use neutral beam accelerators to smash deuterium atoms at each other to acheive practical fusion?
     
  2. jcsd
  3. Mar 14, 2012 #2
    This was actually one of the first fusion experiment. The latest attempt was SIGFE at the University of Wisconsin, Madison. It was a failure; the results indicated that the neutron production was from Fe(D,2n) spallation rather than fusion. Plenty of Neutrons, though - best neutrons/Watt from any device.
     
  4. Mar 14, 2012 #3
    In this experiment they mention ion beams.If they use ions, then I do not see how could they get away from space-charge problems and similar.I meant rather to use neutral beam.
    It means just neutral atoms.Neutral beam injectors are used as plasma heaters in TOKAMAK devices.Could we make something that works like MHD generator in reverse?
    We could slightly ionize deuterium vapour just to make it conductive.And after speed it up with help of electrostatic accelerator. What speeds could we attain in this way?
     
  5. Mar 14, 2012 #4
    If you ionize your neutral atoms for acceleration then what you get is an ion beam.
    If you don't ionize them then they don't accelerate...
     
  6. Mar 14, 2012 #5
    Is it really necessary to ionize each atom?How then reilgun
    works without any ionization?Maybe small ionization is sufficient?
     
  7. Mar 14, 2012 #6

    Drakkith

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    A railgun uses the magnetic field created in the device and projectile to launch it. That requires an electromagnet which requires an electric current, which is electrons moving along the wires. You cannot accelerate individual ions using the same technique. Instead you have to use electric charge to accelerate them, which requires ionization of the atom, otherwise it is neutral and won't be accelerated.
     
  8. Mar 14, 2012 #7
    What would you say about electrohydrodynamic generator http://en.wikipedia.org/wiki/ElectrohydrodynamicsIn which electrically charged particles used to flow and generate electricity?It is not necessary to ionize all the atoms or molecules in it.Creating some small charge is quite sufficient.Do you think it wouldn`t work in reverse?Principally we could use electromagnets too.But in this case we whould need to pare deuterium with something magnetic.Maybe some Iron hydride molecules.
    There already exist some storage rings which designed for neutral atoms.
    http://accessscience.com/content/Neutral-atom-storage-ring/YB050460
    I guess if it could be stored then it could be accelerated too.
     
  9. Mar 14, 2012 #8

    Drakkith

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    None of these are effective options for fusion. Each ion still needs to be accelerated, which requires electric fields.
     
  10. Mar 14, 2012 #9
    If you add an extra electron to the hydrogen atom, you have a negatively charged atom. You can accelerate this, and if you then strip off the second electron with a very thin foil, you will have a neutral beam.

    See http://lss.fnal.gov/archive/2005/pub/fermilab-pub-05-094-ad.pdf

    Bob S
     
  11. Mar 15, 2012 #10
    Unfortunatly it will create the same space-charge problems as in case with positive ions.Problem with beam density.To get it really dense it should be constantly almost neutral.I guess.
     
  12. Mar 15, 2012 #11

    Astronuc

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    In order to magnetically confine a gas, one needs ions, either + or -. Usually this entails a fully ionized gas or plasma. In fusion plasmas, one has mixtures of ions (deuterons, tritons, 3He2+, . . . .) and electrons. Fusion reactions occur among the bare nuclei (ions), while the electrons scatter about wasting energy (brehmsstrahlung, cyclotron radiation, recombination, etc). Neutral atoms leak through magnetic fields.

    Neutral beams are used to feed and heat a plasma because neutral atoms move through magentic fields. Once in a plasma, neutrals collide with other neutrals, ions or electrons and become ionized.

    Nature favors neutrality, and plasmas are quasi-steady-state, because without energy input, they would tend to become a neutral gas.

    Ideally, a fusion plasma develops enough fusion energy to maintain the plasma AND generate surplus energy that can be extracted as thermal energy or electric current IF the charges can be separated and recombined across a load (direct conversion).
     
  13. Mar 17, 2012 #12
    What do you think the most perspective direction in fusion power research up to date?
    Something that is cheap to implement and quite simple?
     
  14. Mar 18, 2012 #13

    Drakkith

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    The most "perspective" direction? What does that mean?

    There is nothing that is cheap and simple. The closest thing in my opinion is the Polywell WB-6 device.
     
  15. Mar 18, 2012 #14
    Do you think Polywell could be treated seriously?
    And why it going to be cheap?As I know it would still require to have superconducting magnets to create strong enough magnetic field.And vacuum.So why is it going to be cheap?
     
  16. Mar 18, 2012 #15

    Drakkith

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    The Polywell is a new concept that hasn't had 30+ years of development behind it, so it might be a little to early to really say either way. The WB-6 showed very good results. Good enough that the US Navy gave them an 8 million dollar contract that they are currently under. Reports from the website aren't detailed, but say that they WB-7 and WB-8 have been working well and they are currently testing scalability factors and such. We'll have to wait and see what happens over the next few years with it.

    I didn't say it was going to be cheap. Just cheaper than other options such as Tokamaks.
     
  17. Mar 18, 2012 #16
    Why Polywell is going to be cheaper than Tokamak?
     
  18. Mar 18, 2012 #17

    Drakkith

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    As far as I know it's much less complex. The coils are simple and easy to build and you don't need to use complicated ways of helping to stabilize the plasma like you do with other designs.
     
  19. Mar 19, 2012 #18
    Bussard's explanation:
    This is why the DoD is interested in testing the scaling - this is the huge claim that Bussard put forth.

    A Tokomak's losses mount as the plasma gets more dense - and any increase in the magnetic confinement field makes the plasma more dense. A polywell can increase the well depth by multiple paths.
     
  20. Apr 3, 2012 #19
    Could somebody calculate how dense should be deuterium ion beams that directing them at each other would produce some net energy?
     
  21. Apr 4, 2012 #20
    The SIGFE, even calling every neutron a fusion, and calling their ion guns 100% efficient, was still producing on the order of Q=3*10-8, that is, for each watt out they would have had to use 26 MW.
     
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