# Tag Info

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.

12

There are quite a few novel energy technologies coming through. I guess that without quantification, "breakthrough" is a subjective term. Below, I've tried to list all the energy technologies that I know of, that are not yet at commercialisation, but could be within 50 years, and that could offer at least tens of gigawatts of power. They are, in descending ...

12

The analogy is facile. Helium fuses at a temperature ($10^8\ \text{K}$) roughly ten times higher than hydrogen ($10^7\ \text{K}$), so a better analogy would be alcohol and thermite. That higher temperature is achieved only by massive gravitational contraction after hydrogen fusion [EDIT: in the core] is exhausted. EDIT: To expand, different mass stars ...

10

This'll be a very rough order of magnitude estimate, but as you'll see it's good enough. Suppose that two hydrogen atoms bump into each other. In order to fuse, the nuclei have to tunnel to within about a nuclear distance of $10^{-15}$ m of each other. The tunneling probability is something like $e^{-(2mE)^{1/2}L/\hbar}$, where $E$ is the energy gap, $m$ ...

9

As far as a catastrophic plasma disruption is concerned, it might be a problem for the first wall, and hence the ability to use the reactor. But despite the high energy per nucleon, the desity of the plasma is extremely low, the total energy is dominated by the energy in the magnetic fields, and thats not tremendous. Of course you do have the radioactivity ...

9

The next serious advance that is not an speculative/fringe idea is most likely to be fusion power. Harnessing the power of nuclear fusion has long been a goal for energy production since the first hydrogen bomb was created in the 1950s. Creating controlled fusion, rather than the chaotic variety has proven a rather challenging task here on Earth however. ...

9

The reaction rate doesn't increase that quickly with temperature, but pressure does. If you perturb a solar model, making a zone near the core marginally hotter, the increased pressure will rapidly (at roughly the soundspeed divided by a characteristic length) cause it to expand. That lowers the pressure and temperature enough to substantially quench the ...

9

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 ...

9

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 ...

8

I will give you an analogy. Molotov bombs are made by filling a plastic bottle with gasoline, attaching a wick ingeniously, lighting it and throwing it on a target, usually a car or a policeman controlling a demonstration. Now there are a number of BTUs of energy in this bottle of gasoline. I can ask paraphrasing you Could we put these Molotov s to ...

8

The WKB approximation states that in one dimension, the tunneling probability $P$ can be approximated as $\ln P=-\frac{2\sqrt{2m}}{\hbar}\int_a^b \sqrt{V-E} dx$ , where the limits of integration $a$ and $b$ are the classical turning points, $m$ is the reduced mass, the electrical potential $V$ is a function of $x$, and $E$ is the total energy. Setting ...

8

The Sun obviously produces far more energy per second than is required to fuse an iron nucleus with some other nucleus. The problem is concentrating all that energy on the iron nucleus. It's not enough to known that it takes the energy from $n$ hydrogen fusions to fuse one iron nucleus, it's getting the energetic products from those $n$ hydrogen fusion ...

7

Elements heavier than iron are only produced during supernovae; in these extreme energetic conditions atoms are bombarded by a very large number of neutrons. Rapid successive neutron capture, followed by beta decay, produces the heavier atoms. See http://en.wikipedia.org/wiki/Supernova_nucleosynthesis.

7

These are valid questions. I am a graduate student in the program so it won't surprise you that I will advocate for it, nonetheless, if you'd like to double check my claims, you're welcome to. Let's go in order: We are hoping that the next major breakthrough does come from ITER: the first burning plasma. But it is BECAUSE of the fact that a machine like ...

7

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 ...

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

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: ...

7

The problem with attempting to fuse two protons is that there is no bound state $^2$He, for the rather obvious reason that there are no neutrons present to hold the two protons together. The fusion of two protons requires one of them to undergo beta plus decay while the two protons are close, and the probability of this is vanishingly small. It happens in ...

6

During the 1970s, the Los Alamos National Laboratory carried out the PACER project, to explore the use of thermonuclear explosions as a way of generating electrical power and breeding nuclear materials. The general layout of the initially proposed fusion power plant can be seen in the following illustration: The system parameters were under exploration, ...

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 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 ...

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 ...

6

Well, if you search the internet it seems there are kids out there that make the claim of having built a fusion reactor . I watched this link. Note that in .56 minute he gives a small description, and does not claim breaking even, but that he demonstrated fusion. It is a plasma that he obviously creates and manages to fusion some deuterium that is not ...

6

The problem with proton-proton fusion is that there is no bound state of two protons. For the fusion to occur one of the protons has to turn into a neutron by beta plus decay. This is mediated by the weak force so it's a slow process and the probability of it happening while the protons are close enough to form a deuteron is very low. By contrast a deuteron ...

5

Hydrogen-1 (i.e. hydrogen with no neutrons) has a mass of 1.007825 AMU. To get energy from fusing it you have to preserve baryon number. So you look for the atom that has the lowest mass per nucleon (i.e. lowest mass average over the protons and neutrons that make it up). This lowest (most stable) atom turns out to be iron-56, which has a mass of ...

5

A heck of a lot of energy in one place always represents a local danger. The question of a more wide spread danger depends on a lot of details. Does the core reaction produce neutrons? How bad is the activation rate in the plant? Would a disaster event spread activated material over a wide area? In the absence of data I would guess "less dangerous than ...

5

I find the idea of a breakthrough technology presented by the other answers to be extremely modest. I'm almost positive that I'll get downvoted and flamed for my answer, but I have a strong desire to impress the potential for, and the implications of, a truly breakthrough energy technology. I want to begin calling attention to Jevons Paradox, as well as ...

5

Can it sustain a reaction for more than a few seconds? Yes, at JET. Lifetime of the plasma: 20–60 s At ITER: It will operate over a wide range of ITER plasma scenarios, from short plasma pulses (a few hundred seconds) with enlarged fusion power (700 MW) to long plasma pulses of 3,000 s Are these devices still huge or have they been made on a ...

5

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 ...

Only top voted, non community-wiki answers of a minimum length are eligible