This isn\’t quite nuclear physics, is it?

The company is taking a significantly different approach friom ITER and NIF, both of which aim to drive turbines from heat created by neutrons that escape in the fusion process.

Agreed that I don\’t know much about nuclear physics but that really does look rather wrong to me. Umm, aren\’t we wanting to drive turbines by capturing the heat created by the conversion of mass into energy?

So where does neutrons escaping come into it?

14 thoughts on “This isn\’t quite nuclear physics, is it?”

  1. “The problem is that it currently takes more energy to run fusion than what the process delivers. ”
    Their English isn’t too good either.

  2. The neutrons, in a typical hydrogen fusion reaction, are what carry much of the energy away from the new nucleus. In deuterium / tritium fusion, for example, the neutron carries about 4 times the kinetic energy of the helium nucleus. However, this is converted in to heat energy, transferred to a secondary heat loop and used to spin turbines.

    LPP are using hydrogen / boron fusion. This spits out 3 He nuclei, with about 1/2 the energy released of the De / Tr reaction. The fact that the energy is in the motion of He ions rather than neutrons isn’t much of a + or -. We can slow neutrons quite easily (releasing that energy). It may make the reaction instigation and maintenance easier from an engineering point of view, though (although the much higher temperatures required have their own problems.)

  3. “Heat” is just kinetic energy of moving particles, and usually most of the kinetic energy ends up in the lighter particles (simultaneous conservation of energy and momentum in generalised collisions leads to this), so in fusion much of the kinetic energy is carried by the neutrons.

    The neutrons are not confined by the magnetic field and so normally leave the plasma and smash into the chamber walls. This is in many ways a bad thing, but in several ways a good thing, one of which is that it warms the walls. You then use this low grade heat to boil water or whatever and run a conventional turbine. The remaining kinetic energy in the charged particles is trapped in the plasma and so keeps it nice and toasty.

    Wildly oversimplified description of course.

  4. So Much For Subtlety

    Well boldly going where no one without a post-graduate degree in physics should go …..

    First of all, ITER probably won’t work. If it does work, it will be marginal on the whole producing more energy than it uses thing. They aren’t close to producing useful amounts of energy yet. So the heat is waste. Because they aren’t talking about generating much of anything.

    Second, the problem is containing the plasma. If you then try to run it past a heat exchange too, God knows what would happen but given your plasma is just right for a few fractions of a second, you probably don’t want to cool it by direct contact with a cooling system. Or anything else. In fact you probably don’t want anything near by that will mess up your nice magnetic fields. So why bother with the extra complexity in building the walls of the torus?

    Third the technical complexity is vastly simpler anyway. The neutrons are captured by water. Tritium is a problem but it is not a big problem. We do this regularly. The neutrons will heat the water slightly. We have been doing that for hundreds of years. Hot plasmas – at some 1 billion-with-a-b K – are another thing altogether. Sensible to stick to the water until there is a pressing need to mess with the plasma.

    Fourth, the plasma is just right for fractions of a second. Did I mention that? It is generating heat for such a short period of time, no real energy is ever generated. But the whole thing has to be pre-heated. Which means that after you have finished, the water has to take away all the heat in the plasma you put in there when you got ready to start up. Which is likely to be a lot bigger than the energy put out. ITER promises this time it will be different, but we will see. The power involved can be large – JET, Britain’s last contribution to this once produced 16 MW I think, or do I have that M wrong? – but they had to put in 24 MW or so to get it started. Which is not going to remain in the reactor vessel. One way or another it will be transferred to the walls and hence needs to be carried away.

  5. So Much For Subtlety

    Surreptitious Evil – “LPP are using hydrogen / boron fusion.”

    Are you sure? I can only think of one reason why Iran might be involved and that would involve D-T.

  6. Tim: no, the technology LPP is working on attempts to fuse hydrogen and boron-11 (the most common isotope) to create energetic, charged helium ions. Because they’re charged, they can be used to produce electricity inductively or electrostatically, without the need for a thermal cycle.

    There are great technical difficulties in getting net energy out of this. But being able to do the conversion to electricity efficiently does make it less infeasible.

  7. Iran is interested in fusing atoms at a considerably higher rate than a power plant requires.

  8. Something hot has to get out of the plasma containment to heat up the water that drives the turbine.

    Plasma containment is magentic; it contains charged particles.

    About the only non-charged particle that will be created and will actually heat up the water is the neutrons (there are also neutrinos, but 99.99% of them will go straight through the entire planet).

    The language is a bit tortured – usually a sign that either the journalist or the editor didn’t actually understand the physics – but the meaning is pretty straightforward to pick out.

  9. There’s little wrong with the physics in the article

    The company is taking a significantly different approach friom ITER and NIF, both of which aim to drive turbines from heat created by neutrons that escape in the fusion process.
    LPP and Azad University are developing “aneutronic” fusion, which would not rely on neutrons. It would eliminate turbines by providing electricity directly through charged ions.

    Some of the wording is a bit clumsy, but there’s nothing unclear about it.

  10. Paul,

    It would eliminate turbines by providing electricity directly through charged ions.

    Some of the wording is a bit clumsy, but there’s nothing unclear about it.

    It may be clear but it is clearly bollocks. As Richard pointed out.

    The 3 He2+ ions produced have a total of 8.7MeV of thermal energy (from the fusion reaction) and a mere 79eV each of electrical energy (from the recombination of the two electrons). So if you are extracting power without using the thermal energy, you are operating at less that 0.003% efficiency. Sort of “CLASS” level, really.

    Given the temperatures this needs to operate at, I suspect you are going to need to put in more than that to get it up to the operating zone. And then you have to run the plasma containment.

  11. Having thought a little more – I’ll concede slightly. The physics may be fine but the engineering is bollocks.

    I’d also note for Richard – magnetic containment can conceivably contain protons while allowing He2+ to escape. The acceleration due to the magnetic field will be double on the proton than on the helium nucleus, therefore if you set your field strength at, say, 1.5 that necessary to retain the protons at the thermal velocity, the neutrons would escape.

  12. SE: I’m not sure what you’re conceding in #13, but your #12 is just wrong. No thermal cycle is necessary to convert the kinetic energy of the helium ions into electricity, because moving charged particles constitute an electric current already. Here‘s a technical note on the subject for you, just so you don’t have to take my word for it.

    Might I suggest that you adopt a less dogmatic tone on this subject?

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