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Does the fusion process cause a chain reaction?

  1. Jun 17, 2007 #1
    does the fusion process cause a chain reaction? or in a fusion reactor are lots of hydrogen atoms released to produce energy. does a fusion reactor heat water and produce steam to generate electricity? if you know anything then please let me know. thanks
  2. jcsd
  3. Jun 17, 2007 #2


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    A chain reaction in a fusion reactor is not the same as in a fission reactor. The products of fusion reaction would primarily distribute their energy into the plasma to keep the plasma sufficiently hot to continue the fusion reaction. Otherwise the energy would be extracted for generation of electricity (or heat).

    The D+T reaction produces He4 + n (fast). The n leaves the plasma, but the He4 interacts with other ions and electrons to heat them as it slows down. Somehow, it must be collected and removed from the plasma once it slows down to plasma speeds (energies). He4 does not fuse under the plasma conditions that D or T do.

    Now some fusion reaction like D+D do produce products like T or He3 which can then fuse with the D in the plasma. And the T and He3 produced by the D+D fusion have high energies with respect to the plasma, so they are more likely to occur than if they were introduced at colder temperatures.

    No fusion power plant, which produces net energy (i.e. more energy out than put in), has been built. The ITER experiment is currently being built in order to get closer to that goal.

    If the kinetic energy of the ions and electrons cannot be extracted by direct energy conversion, then the heat of the plasma will have to be collected somehow and used to heat a working fluid (e.g. steam) which would be passed through a turbine to generate electricity (via Rankine cycle).
  4. Jun 17, 2007 #3


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    So here you are referring to the energy produced by one fusion being part of the chain that contributes to or assists in another future event? Hmm, would a physicist describe chemical flammable combustion a 'chain reaction' in that sense? In fission each of the two neutrons is completely sufficient to initiate another fission event, not just a statistical piece of the pie. Also this ignition concept would apply only in the case of a magnetic confinement system (ITER), I believe, and not apply to an accelerator type of reactor (IEC) or even an implosion (laser) system?

    In any case I don't think you can say there's a chain reaction in fusion. I'm being a bit pedantic, I know, in order to disassociate any of the popular fission bad connotations from fusion.
  5. Jun 17, 2007 #4


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    Yeah - I should have limited that to magnetically confined systems, as opposed to the inertial confinement systems (IC) or inertial electrostatic confinements systems (IEC), which are pulsed systems. In the latter, the thermal energy is about the only way to get the energy out. I was going for a quick answer, since I am working today and tonight.

    No but apparently chemists, and perhaps chemical physicists would - http://nobelprize.org/nobel_prizes/chemistry/laureates/1956/press.html
    A sustained magnetically confined systems could be construed as a 'chain reaction' in the sense that the products, particular product ions, impart their energy to heat the plasma. If one can collect more energy from fusion, than is added from various heat sources, e.g. ohmic, microwave, or neutral beam injection, or lost due to recombination, cyclotron or brehmsstrahlung radiation, or diffusion of neutral atoms, then that's not too different from a chain reaction in which at least one neutron must be survive to cause another fission from those born and not parasitically captured or leaked out of the system.

    Interestingly - chain reaction has been used in conjunction with fusion, but one must remember it is not the same as the fission/neutron chain reaction.

    Fusion Chain Reaction—Chain Reaction with Charged Particles
    Michal Gryziński
    Institute of Experimental Physics, Warsaw University, Warsaw, Poland, and Institute of Nuclear Research, Warsaw, Poland
    Phys. Rev. 111, 900 - 905 (1958)

    Kinetics of compression-induced fusion chain reaction
    Gac, K.; Gacek, A.; Kaliski, S.; Sarzynski, A.
    Journal of Technical Physics, vol. 18, no. 3, 1977, p. 311-324.

    The p—p Chain Reaction
  6. Jun 17, 2007 #5


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    Ok, fair enough, a fusion chain reaction it is!
  7. Jul 17, 2007 #6
    From the Depths of Nirvana....

    17th July 2007

    RE: Cold Fusion....

    Dear All,

    I'm fairly Sure that Cold Fusion isn't as difficult as it seems??

    Does anyone else agree??

    Hope not to unlock Pandora's Box in Every Single re-incarnation!


    SBGB :surprised

    All Best Wishes
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