# Tag Info

## Hot answers tagged fusion

14

To answer the question simply, $E=mc^2$. Energy is a manifestation of mass, and mass is a manifestation of energy. In a fusion or fission process, the total "energy" of the system remains constant, it just changes shape. By "energy" I mean the totality of the already present energy, and the bound energy of the mass that takes part in the reaction.

7

The binding energy curve for nucleons in nuclei shows which atoms can take part in fusion, releasing energy in the process. Fusion happens as one goes from left to right, until reaching Fe, iron. From there to the right it is fission that will release extra energy This is an example of a fusion reaction, the one that is actually being materialized in ...

7

This is a very difficult question to answer. There are (at least) two reasons. First, we have detailed, numerically exact wave functions for stable, light nuclei only up to, just recently, $A=12$ (like $^{12}C$). The Argonne-Los Alamos-Urbana collaboration uses quantum Monte Carlo (QMC) techniques to evaluate the ground and excited states of bound nucleons ...

7

You actually make reference to something which is of crucial importance to the answer to this question: "With a tokamak, I imagine that if you double the linear dimensions, the plasma volume (and hence the power production) will increase eightfold, whereas area that you have to protect against fast neutrons will only quadruple. So once you master the ...

6

There will be no attempt to utilize the energy released from fusion reactions at NIF. NIF's goal is to demonstrate that a sustained fusion reaction is possible. Such a demonstration is termed "ignition" and there is a good chance it will be achieved within the next three years. The next step is a project called LIFE which involves a prototype power plant ...

6

The Sun's energy, of course, comes from fusion. I think there's a small and totally insignificant amount of fission going on as well. The majority of the Sun's mass is hydrogen, and the vast majority of what isn't hydrogen is helium (with the ratio changing over billions of years as hydrogen is fused into helium). But since the Sun formed from the same ...

6

Fission doesn't happen in the sun. Elements are neatly divided at Iron, atoms smaller than this are energetically capable of fusion - they give off energy when fused. Atoms heavier than this can in theory be fissile, energy would be needed to fuse them but they give off energy when they split. These heavy atoms are only formed in a supernova where there is ...

5

To understand binding energy and mass defects in nuclei, it helps to understand where the mass of the proton comes from. The news about the recent Higgs discovery emphasizes that the Higgs mechanism gives mass to elementary particles. This is true for electrons and for quarks which are elementary particles (as far as we now know), but it is not true for ...

5

The big problem with controlled fusion is that the equations governing the plasma are highly non-linear. So each time the physicist increase the size of the Tokamak, new effects are discovered. So I guess that the answer is no-one really knows the correct scaling laws ! This contrasts a lot with fission reactors, where the relevant equations are ...

5

A subtle problem you seem to overlook is that the proton-proton cross section is very small, about 0.07 barns (a barn is $10^{-28}$ square meters) at the LHC energies and not dramatically different at your lower "fusion energies". It means that at the LHC, much like at your dream machine, most of the protons simply don't hit their partners. It is not really ...

5

For some recent information on the running battle between cold fusion researchers and myself over my proposed conventional (non-nuclear) explanation of the Fleishmann-Pons(-Hawkins) effect, you might want to look here: https://docs.google.com/open?id=0B3d7yWtb1doPc3otVGFUNDZKUDQ (referenced in this: ...

5

There are other interactions to consider besides the Coulomb interaction. A very nice model of the nucleus is the liquid drop model, in which one models it as a constant-density liquid with various interparticle interactions. The result is known as the semi-empirical mass formula, which I summarize here. Let $Z$ be the number of protons, $N$ the number of ...

4

ITER is aiming for 150.000.000K. Please note that this temperature of the plasma, i.e. average kinetic energy of the ions is in electron volts For example, a typical magnetic confinement fusion plasma is 15 keV, or 170 megakelvins . 15 KeV is enough to assure that the plasma does not neutralize itself and the bare nuclei have a high enough statistical ...

3

The basic idea Fuse two relatively small nuclei together; say they have masses $m_1$ and $m_2$. Get out a larger particle that has mass that's less than the sum of the original masses $M<m_1+m_2$. The missing mass $\Delta m = M-(m_1+m_2)$ is released as energy via $\Delta E=\Delta mc^2$. Why does the fused particle have less mass than the sum of the ...

3

There are actually several different "limits" one might encounter. The one everyone talks about is not fusing past iron. This comes from the fact that isotopes in the vicinity of ${}^{56}\mathrm{Fe}$ consist of the most tightly bound nuclei. See Wikipedia for a discussion and some binding energy curves. If you are interested in why there is a peak, it comes ...

2

The sun is composed mainly of Hydrogen and Helium: Chemically, about three quarters of the Sun's mass consists of hydrogen, while the rest is mostly helium. The remainder (1.69%, which nonetheless equals 5,628 times the mass of Earth) consists of heavier elements, including oxygen, carbon, neon and iron, among others. Iron is at the top of the binding ...

2

mass of a proton 1.00728 AMU, mass of C12 12 AMU, while the mass of B11 is 11.00931 AMU, so that the difference in mass p+B11-C12 is .00728+.00931 = .01659 AMU, or multiplying by 931 MeV/AMU, the energy is 15.445 MeV, and this means that the C12 is formed from B11 and a proton with 15.445 MeV more energy than the ground state. There are lots of narrow ...

2

List of fusion power technologies: http://en.wikipedia.org/wiki/List_of_fusion_power_technologies Other more well-designed fusion concepts are not fully tested yet due to lack of funding: http://www.crossfirefusion.com/nuclear-fusion-reactor/crossfire-fusion-reactor.html

2

Actually, this has been done, but it's not sustainable. Wikipedia has a brief explanation: Accelerator-based light-ion fusion is a technique using particle accelerators to achieve particle kinetic energies sufficient to induce light-ion fusion reactions. Accelerating light ions is relatively easy, and can be done in an efficient manner—all it takes is a ...

2

I have an answer to establish expectations from first principles. I have not looked up real values, nor am I hopeful of finding such values. All I'm doing here is setting a general expectation for the difference in cross sections of ion-ion fusion and ion-atom or atom-atom fusion. I should note that the one glaring piece of information missing from the ...

2

You should check out Jed Rothwell's particularly informative website for more information. As he said in his deleted answer: Cold fusion has been replicated in over 200 major laboratories, often at high signal to noise ratios. For example, tritium has been measured at millions of times background. I have a collection of 1,200 peer-reviewed journal papers ...

2

the ratio of energy to mass would arguably be lower than H-H or D-T fusion, so it would hardly be a preferred fusion reaction for space travel applications For production purposes (be them energy, manufacture, etc.) we humans usually prefer more result (i.e: more energy output) as a result of less investment (i.e: less energy expenditure) to improve the ...

2

I would not say that fusors are a waste, but so far they have turned out to not be very efficient. There are several factors working against them, compared to linear accelerator-based devices. Basically what it boils down to is the neutron production cross section. In a fusor, the ions are in a plasma, and the mean free path is huge. So the effective cross ...

2

By that logic, a battery violates the law also. "Look, all I did was put in enough energy to flip a switch, and now an LED keeps shining and shining! I got more energy out than I put in!" In nuclear fusion, we are releasing some latent energy which is present in the materials, by changing the nuclear structure into other materials that contain less energy. ...

1

You have to realize that thermodynamics emerges from the bulk properties of matter, and this is seen better when one goes to the formalism of statistical mechanics. The first law of thermodynamics is the form conservation of energy takes in the thermodynamics mathematical framework which is constrained by classical physics. As you must know from your ...

1

The nuclei of atoms are quantum systems, and as such, the nucleons have certain energy levels associated with them inside the nucleus. This is best understood with the nuclear shell model. If the repulsion due to the electromagnetic force can be overcome, the nucleons of two colliding atoms will attempt to configure themselves into the most stable low ...

1

Neutron generators use a solid target, metal lattice filled with D2 or tritium, metal hydrides. The fusion reactions D + T → n + 4He En = 14.1 MeV D + D → n + 3He En = 2.5 MeV happen within the lattice, most of the neutrons escape since they do not interact electromagnetically and generate the neutron source. There is no way a self sustaining reaction ...

1

Nobody knows the law relating the nucleus content and it's binding energy. Your peak means that at this energy some additional states are forming. The width of the peak means it's lifetime (the narrower the peak, the longer lifetime). According to this document: http://www.oecd-nea.org/janis/book/book-proton.pdf your picture occurs when He4 and 2 alpha ...

1

I'm not sure if this is what you're looking for but the most widely used reference for many nuclear reaction rates in stars in Caughlan & Fowler (1988). It's not so much a paper as an enormous reference for many reactions. I've just discovered that it isn't open access yet and I'm not sure what can be done about that... Some reaction rates have ...

1

Tidal effects are not necessarily large at the event horizon. The tidal forces decrease as the black hole gets bigger, so for a big enough black hole the tidal forces at the event horizon can be insignificant. However the tidal forces always become infinitely large as you approach the singularity. But I can answer a slight variation of your question. The ...

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