Talk:Nuclear fusion

But where does the energy come from?

I've read the article about Nuclear fusion (shouldn't that be either "nuclear fusion" or "Nuclear Fusion") and have faied utterly to understand where the energy actually comes from.

Perhaps a few sentences that make it more explicit would be helpful for those of us who aren't physics experts.

Also, as was mentioned elsewhere in this discussion, much of this is about how to generate power from nuclear fusion when it sould be about how fusion itself works.

Thanks

Dave

Davemenc 04:01, 27 November 2005 (UTC)

Matter can be organized in different ways. Some of those ways are more stable than others. Unstable states are unstable because they have a lot of potential energy. If you take some matter and reorganize it into a more stable state, that potential energy is released. In fusion, deuterium (hydrogen-2) and tritium (hydrogen-3) are not as stable as helium and a neutron, so the reaction D + T -> He + n releases energy (the products come out of the reaction moving much faster than the reactants went in). We capture that energy as heat and use it to generate electricity. Canonymous 18:04, 15 September 2006 (UTC)

Isn't the plain English explanation just that a small part of the reactant mass ceases to exist as matter? It's converted into energy. It's a small portion, to be sure, as opposed to antimatter, where 100% of reactants are converted into some form of energy or neutrinos, with no quarks left to tell the tale. Sacxpert 10:48, 17 November 2006 (UTC)

Smart White Boy 20:16, 20 April 2007 (UTC)Might I just add, the energy release can be explained in e=mc². Energy equals lost mass times the square of the speed of light. This implies that a large amount of energy is held in a small amount of matter. That's all I wanted to add. Smart White Boy 20:16, 20 April 2007 (UTC)

I would question the stability argument. U235 is relatively stable. The fission products of U235 are both highly unstable, yet the reaction which produces them is exothermic. The paradigm of exothermic reactions leading to stable products belongs to chemistry. It does not necessarily apply to nuclear reactions, fission or fusion.

Perhaps the most lucid explanation (for the layman) is that the mass of an atom is not -quite- equal to the sum of the masses of its constituent parts. Thus, most instances of atoms being combined or split apart result in a small change of total mass. Since the sum of the system's mass and energy must be conserved, this 'mass defect' manifests iself as kinetic energy of the resultant particles. --Anteaus (talk) 22:34, 24 January 2008 (UTC)

The absorption of a neutron places some nuclei into an "invalid" quantum state; the nucleus reacts to this illegal rearrangement by "vibrating" itself into valid smaller nuclei, after throwing away various items, including x-ray photons and more neutrons. Which nuclei? Big ones, where the outer nucleons are "far" from the center of the nucleus, and at these vast distances, the outermost nucleons feel a weaker nuclear force- recall, the nuclear force works only at short distances. -Dawn McGatney 69.139.231.9 (talk) 13:04, 1 April 2008 (UTC)

Let me ask the question a different way: at the quantum level, why is fusion exothermic. It's easy to see this in fusion: you start out with a bunch of nucleons held together by strong force against electrostatic repulsion of protons. Add an extra neutron, and the nucleus is too big and splits. This releases some of the potential energy (from the repulsion). In additon, some of the gluons that were holding the nucleus together are released, that's a fair amount of mass available to convert to energy.

But to hold two or more protons together in a nucleus, you need to add gluons. That should require more energy to "generate" them. What mass is given up to make this happen? (Actually, I suspect it's more accurate to say that virtual gluons, spontaneously created and destroyed all the time, become actual when you put together a larger nucleus. Either way, you need energy to account for them. But then, my understanding of quantum chromodynamics is highly deficient. Even my knowledge of quantum electrodynamics is based on Feynman's popularization, Q.E.D.) Bgoldnyxnet (talk) 18:18, 25 November 2008 (UTC)

A large part of the "mass" of a proton already "is" energy from the beginning: The sum of the masses of the three quarks of which the proton consists only make up about 10% of the total mass of a proton, the rest is "field energy" from the strong force's field. So you have a large pool of energy to draw from in fusions. It's similar to an asteroid falling on Earth, which also produces lots of energy without destroying any particles from either the asteroid or the Earth: there the energy comes from the loss of gravitational energy of the asteroid in Earth's gravitational field. Hope this helps.--Roentgenium111 (talk) 16:25, 22 April 2009 (UTC)

BTW: I suppose you mean "fission" in your 2nd sentence? --Roentgenium111 (talk) 16:25, 22 April 2009 (UTC)

The title is a sentence (or something like one). Nuclear fusion. Midgley (talk) 16:54, 22 April 2009 (UTC)

Image

Sigh. The main image has been replaced by an animation. Though I know we are supposed to say "hooray" for anyone who takes the time to make an animation, can I state that:

1. It takes 23 seconds to watch the whole animation to figure out what happens. A diagram can be understood basically instantly. (Consider that there are even ways to do this better by means of animation. This page has a DT reaction that basically takes 4 seconds and is just as easy to understand.)
2. The animation does nothing other than showing two things coming together and a third thing coming out of it. Again, a diagram can do this much more efficiently.
3. The animation portrays the "energy" released as a circular yellow beam. This is misleading. Most of the energy out of that particular reaction is in the kinetic force of the neutron that is being released and the kinetic force of the alpha particle. This makes it look like the "energy" is some sort of separate thing from the byproducts of the reaction, which it is not. In any case it leaves out a lot of the energy. The neutron goes off with 14.1 MeV, while the alpha particle, rather than staying still in the center, flies off with a kinetic energy of 3.5 MeV.

I'm sure the image took a long time to make, but is it really the best means of expressing this particular reaction? There are some things that animations are indispensable for and much better than static diagrams (the Two-stroke engine page is a great example of this—complicated movement of materials that must be explained in many frames = great for using an animation!). I'm not sure that simple nuclear reactions are among them (seeing the two atoms tediously run into each other presents no additional information, takes a lot longer). I personally think a diagram (like this one) is a lot clearer. It gets the same information content across in a much more clear and concise manner. In this particular case, the animation is even misleading in terms of the mechanism and amount of energy released. --98.217.8.46 (talk) 02:01, 27 October 2008 (UTC)

Gamma + H2 --> p + n

n + H2 -->H3 + E1

H3 -> He3 + e-

He3 + n --> He4 + E2

---

147.236.34.10 (talk) 11:47, 17 February 2009 (UTC)vicli2@rambler.ru

break-even, boosterism

the overview claims that tokamaks have demonstrated break-even. I don't recall reading this (I didn't think any reactor designs had yet actually accomplished break-even) and a quick googling turns up lots of discussions about potential break-even designs but no break-even.

the overview also makes it sound like ITER is going to be a working model for generating energy, that generating energy from fusion is right around the corner. my understanding is that neither of these things are actually considered to be true except by those who are financially involved in ITER.

it could use a little sourcing. especially given how many contrary opinions there are about whether we should expect fusion power anytime soon. --98.217.14.211 (talk) 01:56, 5 April 2009 (UTC)

Yep. Controlled fusion for commercial power production has been "just 20 years away" for the last 50 years. I'm beginning to wonder if it won't be just 20 years away for the next 50 years, too. ;). SBHarris 01:59, 5 April 2009 (UTC)

possible fusion shortcut

It may be possible to reduce the temperature requirement for plasma formation by inducing temporary dipoles in the deuterium and tritium gas via microwave radiation. This is the same theory behind the formation of ball lightning and can be easily replicated. The modifications would be minimal, and plasma damage to the inner wall would be less extensive. —Preceding unsigned comment added by 66.66.118.233 (talk) 18:45, 8 June 2009 (UTC)

editing required

The following (Overview, end of paragraph 3) is not a sentence, but fragment lacking a verb: "However, the creation of workable designs for a reactor which will deliver ten times more fusion energy than the amount needed to heat up plasma to required temperatures (see ITER which is scheduled to be operational in 2018)." --RDK