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Recently, I was thinking about fusion and this thought struck my mind.

  • In tokamaks, the plasma is heated to extremely high temperatures in order to supply enough energy to the ions for them to fuse. But since, the plasma follows a boltzmann maxwell distribution curve,only a few ions have have enough energy to fuse.

  • But, while this is happening, there also is a lot of energy loss due to Bremsstrahlung radiation.

Now, what I was thinking about is: If we somehow (rather mysteriously) confined a low temp plasma comprised of deuterium ions and an equal amount of electrons (quasi-neutral and approx 60000K) magnetically, and accelerate tritium ions (like a dense particle beam) and make them bombard the plasma. Could we gain net energy?

The reasons I think this would produce a Net gain of energy:

  • Well apparently, since the accelerator beam isn't in thermal equilibrium (wasn't given enough time), almost all collisions would result in fusion.

  • Previously, many people told me that the reason this can't produce net energy is because the coulomb interaction cross-section is much higher than the nuclear cross section, But I suppose that given enough density of the confined plasma, even when the nuclear cross section is smaller than the coulomb cross section to produce more energy than is lost. This is also the case in tokamaks.

  • The low plasma temperature can be helpful in producing high number densities in favor of the above point.

  • Yes, the energy of the alpha particles resulting from fusion heats the gas, but we can find ways to cool the plasma to maintain confinement.

  • I don't think that the cross section of coulomb interactions or Bremsstrahlung radiation would be considerably different from tokamaks, since we are dealing with the same energy levels (This statement is probably wrong, so it would be great if some one can help me on this)

  • Now, compared to tokamks, in which electrons have substantial amounts of energy and extremely small mass and emit a lot more Bremsstrahlung radiation than the particle beam I was talking about or ions in the plasma, radiation losses in our model might actually be smaller.

And for the to compensate for the losses, thee particle beams energy per particle must be slightly higher, for example 30 Kev instead of 25 Kev

With all this in mind, I think that the model we were talking about can produce net energy. So, where am I going wrong in my thinking? Where am I making wrong assumptions?

Any help would be appreciated

EDIT: Forgot to mention that we would actually add an equal amount electrons to the plasma as the number of ions penetrating the plasma to maintain quasi neutrality.

EDIT: This is also completely different from other questions on stack exchange. First off, I try to use confined quasi neutral plasma as a target instead of just 2 beams to increase number densities. This has NOT been asked or reviewed in the posted questions.

EDIT: I just realized that we could use a helical magnetic field to make the particles spiral. So, the particles would spiral around the field lines and along the field lines. The lower the pitch of the helix, the more the particles interact with the plasma. So this would increase collision cross sections drastically wouldn't it? Are there any disadvantages in doing this?


marked as duplicate by Jon Custer, sammy gerbil, Yashas, John Rennie, Kyle Kanos Mar 10 '17 at 11:04

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  • 1
    $\begingroup$ Duplicate of physics.stackexchange.com/q/43293/176? $\endgroup$ – endolith Mar 9 '17 at 17:12
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    $\begingroup$ "Breahtlessness radiation" !!! the spell checker must have decided it $\endgroup$ – anna v Mar 9 '17 at 17:14
  • $\begingroup$ Yeah! corrected it $\endgroup$ – Chandrahas Mar 9 '17 at 17:27
  • $\begingroup$ I am not an expert in plasma, but I can see two things wrong with an accelerator beam hitting the plasma: too few interactions because a typical beam can have maybe 10^11 or so particles ploughing through a limited area of the plasma and that a lot of the energy of the beam will be wasted as it goes through without interactions, making the energy balance unfavorable.( it takes a lot of energy to create accelerated particles). The density of electrons in ITER is 10^19 m^3 ( and the ions should follow since it is a neutral gas), so even if only the tails of energy distribution are useful, $\endgroup$ – anna v Mar 9 '17 at 17:39
  • $\begingroup$ there are orders of magnitude difference with what a beam can do, and statistical dirstribution can do $\endgroup$ – anna v Mar 9 '17 at 17:40