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Alternative methods for fusion

  1. Jul 5, 2010 #1
    Hi all, recently I've been reading up on cold fusion(although I don't know a lot about it) and how it would ideally be a good clean energy source to use. This is basically what I understand about fusion and cold fusion:

    Fusion is a nuclear reaction in which two atoms of the same element bind together to form a new element, releasing energy which can be harnessed as a power source. This kind of reaction occurs in nature, in stars specifically where hydrogen bonds together to form helium, giving off energy as heat and light.

    However, the problems with obtaining enough energy to offset the cost of production using this method are difficult to overcome. From what I understand, in order for the two atoms to be pushed together they have to first overcome their initial repelling forces before they reach a specific distance to be attracted. This is difficult to do, since it requires immense heat and a gravitational field(the heat and gravity requirements are what i read on a small article a while back, no idea if those are true or not).

    Cold fusion is still as of now a fictional method of producing a fusion reaction at or close to room temperature, making the energy output higher than the cost.

    My question is this: the problem seems to be overcoming the initial repelling forces of identical atoms, which can only be achieved through heat and a gravitational field. Is there anyway to interact with the repelling forces, or some way to cancel them out or nullify them without going using so much power?

    Supposedly a gravitational field can interact with these kinds of forces, but is there anyway to fine tune it?

    Again, I don't know a whole lot about this particular subject(or anything really) but it interests me. If anyone can answer some of these questions or point me in the right direction for good research material, I would really appreciate it.

    Thanks, -matt
     
  2. jcsd
  3. Jul 6, 2010 #2
    It does not necessarily need to be gravitational field. You need to heat the substance and keep it hot and compact long enough for enough reactions to go through to result in positive energy balance (more energy out than you put in).

    Gravitational field is one way of keeping all that hot matter in place, but it only works on stellar scales.

    The primary mechanism that scientists have been trying to perfect for the last 50 years (with limited success) is to use magnetic fields. See http://en.wikipedia.org/wiki/Tokamak.

    One other approach that became popular recently is to start with a small pellet of fusionable matter and to hit it with a short burst from a powerful laser. If you pack enough energy into the burst, the pellet will heat up to the right temperature and it will stay in one piece long enough to start fusion.

    There's a lot of useful information in Wikipedia.
     
  4. Jul 6, 2010 #3
    Well, this kills my plans to hold a hohlraum and clap really hard. All kidding aside, the issues with fusion seem to be the stability of materials bombarded by neutrons, and breeding tritium while capturing the energy. Break-even is great, but not as something you're ever going to plug into an electrical grid. Any form of fusion that produces useful energy needs to liberate its own tritium from its shielding at absurd efficiencies, and that shielding has to somehow resist becoming brittle from bombardment. This seems completely insoluble at this point, and the focus on containing plasma or initiating fusion strikes me as a red herring.
     
  5. Jul 6, 2010 #4
    Actually, what you really need to do is collide the reactants with sufficient energy to overcome the Coulomb barrier. Maxwellian heat is just one really inefficient way of imparting enough kinetic energy to the reactant particles. If you have a very high temperature then the particles will randomly collide with sufficient energy.

    Gravity makes it easy to do this with a positive energy balance but there is no reason why this can't theoretically be done with greater efficiency using other methods.

    For example, theoretically speaking, if you can fire two nucleons, say D and D at each other so that they would meet you can get fusion with much lower energy requirements. Fusion can happen with inputs as low as 10s of KeV for D-D reactions with an energy output of about 3 MeV for a 100 to 1 theoretical gain.

    Lots of amateur scientists are doing fusion in their basements and garages using this concept. IEC fusion, or Inertial Electrostatic Fusion is fusion based on electrostatically accelerating suitable ions so that they collide with sufficient energy. The University of Wisconsin and the University of Illinois Champagne/Urbana both have IEC fusion programs. See: http://www.fusor.net for more on this type of fusion.

    The problems, to date, have been achieving the efficiencies required to produce more power from the fusion than is required to create the reaction. IEC fusion is about 6 or 7 orders of magnitude away from achieving positive Q. Nonetheless, who knows, this may be the way forward. We've spent 50 plus years and countless billions trying to create mini suns using brute force Maxwellian heating. Perhaps another approach would work better if we invested the same level of resources into research.
     
  6. Jul 7, 2010 #5

    tom.stoer

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    Science Advisor

    One mechanism for cold fusion is to use myonic atoms (myonic hydrogen). If one replaces the electrons with myons the Bohr radius (scaling with 1/mass) becomes much smaller (by a factor of 200) due to the myon mass (106 MeV instead of 0.5 MeV). Therefore in myonic hydrogen the size of the molecule is much smaller which means that tunneling of the nuclei through the Coulomb barrier is less suppressed.

    Essentially you omit high temperature and/or pressure and use the quantum mechanical tunneling instead. The problem is of course that you still have to use deuterons (p,n) and tritons (p, 2n) instead of normal hydrogen (p)and that you have to prepare enough myonic hydrogen.
     
  7. Jul 7, 2010 #6
    We already have ready access to a real star, again, the issue is capturing and using that energy. A star in a bottle presents a host of new issues, of which efficiency seems to be the most soluble in the short term.
     
  8. Jul 7, 2010 #7
    Muonic catalyzed fusion can occur with protons and deuterons as well (that was the first experimental evidence of these actually). Too bad muons have such a short life span.

    As an aside, if TeV scale supersymmetry turns out to be true, with R-parity conservation shouldn't there be a long lived "lightest charged" supersymmetric particle? If so, not only would the lifetime be much longer than the muon, but its extra mass would decrease the "bohr" radius when combining in a molecule and thus reduce the coulomb barrier even more than muons.
     
  9. Jul 7, 2010 #8
    The question is whether the alpha sticking problem is going to be better solvable for SUSY particles than for muons. I can't find any explicit calculations of the sticking probability, but, assuming that it scales as m(electron)/m(catalyst), the lightest SUSY will be just as tempting, but useless, as muons.

    If it were stable enough, you could separate alpha-SUSY "atoms" and try to break them down with x-rays or high temperature, to reuse the particles.
     
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