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Nuclear fusion using miniature optical particle accelerator?

  1. Jun 25, 2015 #1
    Greetings

    I am not a physicist myself, so please forgive me, if my question/proposition will sound naif.

    I noticed some articles about accelerating electrons using laser and glass gratings:

    http://phys.org/news/2013-09-chip.html
    http://phys.org/news/2013-10-particles-compact-particle.html




    I was wondering, could the same method of acceleration be used to accelerate nuclei of Deuterium or Tritium to the D-T target at the end of such "optical accelerator", with sufficient energy for nuclear fusion to take place (which is above 100 keV, if I understand correctly)?
    If such acceleration of nuclei could be fine tuned to consume as little energy as possible, could we achieve fusion with positive net energy gain?
    I suppose such "warm" fusion would not heat the bombarded target to millions of Kelvin, but this is good so, this would prevent the device from destruction. If target could be heated enough to boil the water or to drive the thermoelectric generator, that would be enough.
    We could then mass-produce such "optical accelerators" (which can be, if I understand correctly, just ten centimeters long) and join them into arrays to produce enough heat/electricity for practical use.

    This is my idea. Do you think it is theoretically and practically feasible?

    Thank you for your answers.
     
  2. jcsd
  3. Jun 25, 2015 #2

    Drakkith

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    Staff: Mentor

    Sure, the acceleration of tritium/deuterium into a stationary target was one of the first methods used to study nuclear fusion.

    It cannot. The losses are simply too high and there is no way to reduce them. Beam-target fusion is not a viable concept.
    See here: https://en.wikipedia.org/wiki/Nuclear_fusion#Beam-beam_or_beam-target_fusion
     
  4. Jun 25, 2015 #3
    Thank you for your answer.


    I've heard of neutron generators and of fusors before, so my thinking was: if optical accelerator is orders of magnitude smaller than conventional accelerators, is then its energy consumption also orders of magnitude smaller? If it is coupled with efficient laser, could there be still some hope for gaining energy from fusion?
    Or would even a 100% efficient method of particle acceleration (all energy put into system goes 100% to accelerated particle) still not produce enough heat from fusion, as input energy would be mostly lost in ionization and bremsstrahlung at the stationary target?
    If I understood Wikipedia explanation correctly, problems with loosing energy to ionization and bremsstrahlung occur only in stationary target and could be avoided with beam-beam fusion? So put two optical accelerators facing each other - but that would probably melt delicate glass gratings and so destroy the device.

    To resume my reasoning: if optical accelerators can be made orders of magnitude smaller than conventional accelerators AND if they could also be made orders of magnitude more efficient than conventional accelerators - could there be some hope for economically viable fusion?
     
  5. Jun 25, 2015 #4
    There are existing models for fusion reactors which already are very much more efficient.
    The Tokamac design is one of the most promising and is the basis for the ITER project.
    https://en.wikipedia.org/wiki/ITER

    If things work as intended this plant ought to be able to output continuous power of 500 megawatts while needing 50 megawatts to operate.
     
  6. Jun 25, 2015 #5

    Drakkith

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    Staff: Mentor

    Nope. The cross section for the reaction is simply too low. Even with perfectly efficient accelerators you will still lose more energy from electromagnetic interactions between the nuclei than you will gain from fusion. I think that's the key here. Its not the energy loss from the accelerators that limits beam-beam fusion, it's the energy loss from the interactions of the nuclei themselves.
     
  7. Jun 25, 2015 #6

    mfb

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    2016 Award

    Staff: Mentor

    Electrostatic acceleration for energies up to 1 MeV is nearly 100% efficient, orders of magnitude better than lasers. Those can achieve ~10% efficiency in high-power applications, but if you want to focus them to really high fields the efficiency goes down significantly. To make it even worse, only a small fraction of that energy is transfered to the accelerated particles.
     
  8. Jun 25, 2015 #7

    phyzguy

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    Science Advisor

    Many people have had the idea you propose. The problem with your idea is that, in order to fuse, the two nuclei need to hit nearly head-on. Otherwise the incoming nucleus is simply deflected without achieving fusion. Since nuclei are so small in relation to atoms, most of the accelerated nuclei simply "miss", meaning that they don't strike the target nuclei head-on. The energy of the accelerated nuclei that miss targets is just wasted, and the energy generated by the small fraction of nuclei that do fuse is not enough to make up for all of the wasted energy.
     
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