Global warming

Discussion in 'General Discussion' started by Frank, Oct 22, 2010.

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  1. Blazkowicz

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    wrong the moon is not an energy source, it's pie in the sky (though I get that this is what you implied). it's ridiculous. it's just as you wouldn't want to pick up gold bars on the moon, but worse.

    it's like when I read "we should get out of this planet and stop putting our eggs in one basket etc." and then I stop reading.

    helium 3 fusion is like orders of magnitude more difficult than deuterium-tritium.
    and that one is not that bad. easier than what we get away with fission plants, and the fuel is readily available.

    Frank's nanoscale thermonuclear fusion : yes I would like that too, even thinked about it :) but it's high end sci-fi stuff.
    with practical fusion, even with only gigawatt sized installations and no fusion bike, I believe we can basically achieve communism.
     
  2. Grall

    Grall Invisible Member
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    Noooo...! It's awesome! Don't be such a square, Blaz. We need to get OFF this rock, if pies in the sky is what it takes to achieve that, then so be it.

    If there actually WERE gold bars on the moon you can bet your behind we'd be there in a heartbeat! :lol:
     
  3. hoho

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    Yes. You can start with telling me if and why was Mintmaster's analysis wrong or provide better proof for your claims than what Rutan had in his paper. Basically anything that hasn't been disproven already and can't be done so easily by using the knowledge we have.


    As for fusion, this looks interesting. It's not energy-positive yet but it might get there eventually. If it does it should be small enough to put in a (big?) car.
     
  4. Gubbi

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    What 1950s science magazine do you get your nuclear energy information from?

    Synchrotron induced fusion is a long way away from breakeven energy-wise.

    There are really only two avenues for fusion: inertial confinement, and *hot* fusion.

    Inertial confinement seem to be limited in our modeling capability of high pressure/temperature physics. Actual trials fall well short of the pressure/temperatures needed for ignition (and what models predict)

    Hot fusion has its own set of challenges: Turbulence in the plasma, transmutation of reactor structure, coping with photon flux, extraction of heat and of course, costs.

    And there is no such thing as clean fusion. You can have a fusion chain that produces neutrons and one that don't. But, you really need neutrons to usefully extract energy, otherwise the entire energy output is going to be in the form of photons. Good luck trying to avoid the inner wall of the reactor chamber from vapourizing with 10s of MWs per square meter. You need neutrons to be able to carry energy away from the fusion process: Neutrons penetrate quite far and thus dump their energy in a volume of matter, making energy extraction easier. The problem with neutrons is that the reactor structure itself gets transmuted.

    Cheers
     
    #1504 Gubbi, Mar 5, 2012
    Last edited by a moderator: Mar 5, 2012
  5. KimB

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    I wonder if this could be dealt with by using a plasma for the energy absorption. Though then I'm not sure how you'd be able to control the fusion reaction itself...
     
  6. Gubbi

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    A plasma is per definition fully ionized and thus mostly transparent.

    Other than lining the fusion chamber with a high-Z material and let it slowly ablate away, I don't really know how they'd go about it.

    Cheers
     
  7. Mintmaster

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    Batteries have enormous commercial impetus behind them already. Each kWh of charge/discharge can replace 1/10th of a gallon of gasoline, and for portable electronics a high density battery would be worth 10-100x that ($500 phone manufacturers would pay $10 per Wh for a superbattery even if it only lasted 300 charges).

    Unfortunately for battery makers, grid storage has to compete with natural gas, which has pretty low prices right now. A CCGT plant will need less than $0.03 of gas to produce a kWh of electricity, and the rest of the cost is just maintenance and an amortization of fixed costs. Batteries can find use in isolated applications (e.g. handling major spikes on a timescale of a few hours, as you get from solar/wind), but that's it.

    Don't hold your breath for batteries solving grid storage. However, for transportation and electronics there seems to be a big breakthrough that's near commercialization:
    http://enviasystems.com/
    400Wh/kg and $125/kWh means 50kg and $2500 is all the battery you need for a PHEV, though power density is a bit low so you'll need a supercapacitor for electric-only performance.
    That's interesting. I've never even heard of that until now. However, a quick google makes it looks horribly inefficient. Is there some short cut using the sun or bacteria or something? Electricity->hydrogen->methane->ICE/CCGT seems like it would be only 20-30% efficient.

    I just don't see it competing with EVs. There are many inherent advantages of EVs, like instant torque, low marginal cost/weight for high power, and silent ride. Due to all the energy conversions, per-mile fuel cost isn't nearly as good as for EVs, and energy cost is even worse. Unless the EV industry experiences a catastrophic collapse before economies of scale kick in, CNG doesn't have a chance.

    As for grid storage, it's not going to compete with just using natural in the first place.
     
  8. MfA

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    Well some problems have to be solved first, efficient recyclable CO2 absorbers are needed and a photocatalyst is needed which either converts CO2 to CO, or CO2 and H2O or H2 to methane.
     
  9. Mintmaster

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    Don't we achieve that kind of power extraction with current fission reactors? And don't neutrons get absorbed by the lithium banket and/or coolant?
     
  10. Grall

    Grall Invisible Member
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    Heck, why don't we create fusion power plants to deliberately CREATE lithium so we can stick it into batteries...? Considering we don't have a Dr. Manhattan in our back pocket this would be a great boon to our society! :)
     
  11. Mariner

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    Pfft. Lithium shortages aren't a problem, even if we start using Li-Ion batteries for pretty much everything.

    How about this way of doing Fusion?

    http://en.wikipedia.org/wiki/PACER_(fusion)

    :)

    Perhaps not the most economical method of generating power, as atomic warheads aren't exactly cheap!
     
  12. KimB

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    Huh? It's the other way around. Light interacts very strongly with charged particles, and a plasma is full of free charged particles. This is why the Sun emits little to no gamma rays: the photons in the Sun have a mean free path of about a millimeter. Letting the gamma rays bounce around in a plasma for a little bit before escaping dramatically lowers their temperature. So the picture is you'd have a very small fusion reaction at the center, surrounded by a much larger shell of plasma (perhaps tens of centimeters thick), and use the much more manageable temperature of the plasma to extract energy from the reaction through some sort of cooling interface.

    I'm just not sure it's remotely possible to both have a shell of plasma and a confined fusion reaction. Not without having an actual star.
     
  13. Gubbi

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    Mea culpa, I was thinking of plasma as a fully ionized gas, instead of just ionized.

    A fully ionized gas is transparent, a partly ionized gas is opaque.

    The plasma would need to be of a fairly high-Z material to avoid full ionization.

    Cheers
     
    #1513 Gubbi, Mar 6, 2012
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  14. KimB

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    Why do you think a fully-ionized gas would be transparent? The only thing that matters here, really, is the density of electrons. The denser the free electrons, the shorter the mean free path of the light, and the thinner the plasma shell can be.

    Of course, a very thin plasma is going to be rather transparent, as long as it is thinner than the mean free path of light through said plasma. As the mean free path depends on the frequency of the light, this will have to be taken into account as well.
     
  15. Gubbi

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    Well, effectively transparent.

    Once all the electrons are stripped off an ion, the only way to transfer energy to the ions is through (inverse) bremsstrahlung, where a photon interacts with an electron in the electrical field of an ion. Since the mass relationship between an electron and an ion is 1/1836A, where A is the atomic mass of the ion, and since we have conservation of momentum, the electron, on average, sees a change in velocity 1836A times larger than that of the ion, with similar change in kinetic energy. The ions are cold compared to the electrons, at least initially. It takes many interactions to transfer a non-trivial amount of the radiation field energy to the ions.

    Meanwhile the electrons quickly reaches thermal equilibrium with the radiation field, so even if the MFP is short, photons are emitted about as often as they are absorbed and with a similar spectrum.

    Btw. I looked up how they do cool tokamaks. Designers take advantage of the fact that the bulk of the energy is in the form of soft X-Rays, which penetrate up to a few millimeters in stainless steel. Energy is thus dumped in a tiny volume of the fusion chamber liner, and not just on the surface. With vigorous cooling they avoid ablating the liner away.

    Cheers
     
    #1515 Gubbi, Mar 9, 2012
    Last edited by a moderator: Mar 9, 2012
  16. KimB

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    The electrons are still there in the plasma. Most of the interaction is with the free electrons in the plasma.

    That's sort of the point. But no, the temperature is reduced dramatically by the increased surface area. This is what happens inside a star: the temperature at the surface is a fraction of the temperature at the core, where the nuclear reaction is going on. So if you have a very small reaction at the core of the chamber, the thermal equilibrium reached will be at a much lower temperature at the outer edge of the plasma shell.

    One way you can easily estimate how much the surface area changes is to just take the power output of the core, set it equal to the power output of the plasma shell, and figure out the required temperature of the plasma shell from that.

    Ahh, that's interesting. Makes good sense!
     
  17. Frank

    Frank Certified not a majority
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    Well, let's simplify it:

    If you create a huge and extremely hot plasma, where a very small amount of particles might fuse, you just threw away all the energy you pumped into the particles that didn't fuse. The vast majority.

    And you need to spend a huge amount of energy to contain that plasma as well. More wasted energy.

    Now, if we scale down to simply doing all that to a single particle, with an (almost) guaranteed hit, we just saved most of the energy, for a MUCH better return.

    So, if you can extract energy from such a vastly wasteful system as the plasma one, what do you think would be the efficiency of the controlled one?


    And we can do the targeting involved. We have machines that can etch chips on about that resolution with an electron beam, after all. And while those are pretty big, we only want a tiny fraction of their capabilities.
     
  18. hoho

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    You do realize that atomic nucleus, no to mention subatomic particles, are literally tens of thousands if not millions of times smaller than smallest features that are etched on 22nm and below chips, right? How exactly do you intend to guide them so accurately that they hit each other?
     
  19. Frank

    Frank Certified not a majority
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    Ok. I will. But not now.

    Yes, it's a kind of Fusor. It's like a plasma torus, but much smaller and everything done electrically. Much better controllability.

    Fusors are really cool. They allow you to build a functional fusion reactor in your living room. Their main problems are patents and their one-shot capability: there is no easily known way to remove the waste products and refreshing the fuel.
     
  20. Frank

    Frank Certified not a majority
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    Corrected ;)

    Ah, but there are. Multiple.

    The best known one is He3/He3 fusion. This needs a much higher energy/voltage, but that's mostly a problem for plasma ones.

    And it only generates charged particles, when done in a controlled environment.

    He3 is scarce, on Earth, but if we don't care about some radioactivity, it can be produced. And if we do care, we can extract it from air.

    There are very many plants that liquify air, and they could extract He3 from the regular helium with some more investments.

    Or, we could go to the Moon. Sounds like a plan as well. :)
     
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