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Nano Fusion? Micro Fusion? Fusion Learning Source?

  1. Jul 8, 2015 #1
    When experimenting with fusion, why do we always go so big and make extremely expensive reactors that take years to create and even construct facilities for? I've seen some failed attempts at making fusion happen in carbon nanotubes, failing in the sense that the carbon nanotubes are just completely demolished. It makes more sense to me (I'm new to this stuff) to make small reactors that could fit in your hand or smaller to have far many more experiments conducted,had the same amount of money that's put into these massive reactors been put into a large quantity of smaller projects.


    Also, what's a good way to learn about the parts related to the operating, testing, and computing inside of fusion devices? Is there any place online that has tons of data directly derived from fusion devices that I can view or is all of this stuff really not published for the public eye?

    If I were to build a fusion reactor, what could I do to make the biggest difference possible in the world's understanding of fusion?
     
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  3. Jul 8, 2015 #2

    Drakkith

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    I'm no expert, but I don't think we can't make reactors that small. Regardless of the type of reactor, the things you need, like electromagnets, fuel injectors, etc, have a limit to how small they can be before you start running into problems. In addition, for magnetic confinement reactors, the ions and electrons spiral around because of the magnetic field, so your reactor needs to be larger than the spiral diameter.

    I'm sure there are plenty of other reasons too, but those are the only ones I can think of at the moment.
     
  4. Jul 9, 2015 #3
    Yes, this is what I was assuming was the reason, I'd love to know the exact parts that are limiting size reduction in these reactors. I mean look at the new one at Lockheed Martin's Skunk Works, they're at least able to lower the reactor and its supporting system's size down to one semi truckload. Projects trying to achieve ignition might be able to be completed with even smaller fuel microcapsules and cheaper smaller lasers.
     
  5. Jul 9, 2015 #4

    Drakkith

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    Pretty much every part is contributing.
     
  6. Jul 9, 2015 #5
    I'm realizing that we probably can't scale down the amount of energy that could cause fusion with thermonuclear, because it will require a certain amount of energy to make fusion possible, and that amount of required energy requires "big" devices.
     
  7. Jul 9, 2015 #6

    Drakkith

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    Not really. The amount of energy depends on the amount of plasma. A smaller volume means less plasma and less energy needed. However, various scaling laws apply and it turns out that really, really big reactors are more efficient than small reactors. The bigger the reactor, the more output power you get per input power. That's why ITER and similar reactors are multi-ton behemoths.
     
  8. Jul 9, 2015 #7

    Drakkith

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    Note that it is very easy to perform fusion. High school students have done it using home made electrostatic fusion reactors. The hard part is getting more energy out of fusion than you put into it. That's the part that we've been chasing for 70 years or so.
     
  9. Jul 9, 2015 #8

    e.bar.goum

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    Three key parameters of a plasma reactors scale with radius: The ratio of plasma pressure to magnetic pressure ##\beta##, the product of collision frequency with thermal transit time ##\nu^*##, and the ratio of the lamor radius to the radius of the toroid ##\rho^*## in the following ways:
    β ~ nTB−2
    ν* ~ nT−2R
    ρ* ~ T 1/2B−1R−1
    So, if you want to keep those constant, and reduce ##R##,
    n ~ R−2
    T ~ R−1/2
    B ~ R−5/4
    So reducing the radius means that you've got to increase the number density, the temperature and the magnetic field a lot. The magnetic field is a bit of a killer. Anything bigger than 10T or so is a problem. So, for lots of power, and long confinement times, you need big devices.

    Also: It's not true that all fusion experiments are big and extremely expensive. Well, not on the scale of ITER. Even modest universities in countries without tonnes of research money can have fusion devices, and contribute important information to achieving fusion power. You don't have to have a power-producing fusion reactor to understand the physics processes at work! Here's a list of worldwide fusion experiments: https://en.wikipedia.org/wiki/List_of_fusion_experiments

    Further, valuable information about fusion power can be done on plasma machines (that don't do fusion at all) - for instance, you can understand what plasmas will do to the materials on the walls of ITER.
     
  10. Jul 9, 2015 #9
    I know this about fusion, being "easy" to perform, but knowing that big is more efficient than small, why can't we just come up with a goal of efficiency with these smaller reactors, that would translate to the real efficiency we want with bigger reactors, after scaling everything up?
     
  11. Jul 9, 2015 #10

    Drakkith

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    Because that's like starting out your hobby as a mountain climber by climbing Mount Everest instead of a 50 ft cliff. You try to do the easiest stuff first and then, using what you've learned, move onto the hard stuff.
     
  12. Jul 9, 2015 #11
    I could tell, without knowing much on the subject, that even producing more data on plasmas and other things involved could help fusion along its way in the end. I sometimes think that discoveries made from the LHC or really any other projects going on in Universities will end up giving us the answers that we need to achieve efficiency in fusion, rather than directly working with it.
     
  13. Jul 9, 2015 #12

    e.bar.goum

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    The LHC really won't tell you anything about conditions in plasma machines. But that is exactly what does go on at many universities (see my wiki link, for starters) - plasma physicists and materials physicists are often heavily involved in fusion research, using machines that produce plasmas or smaller fusion machines.
     
  14. Jul 9, 2015 #13
    I'm not making any sense, sorry. I meant, why can't we just work on the smaller scale and try to achieve an efficiency on that scale that "should" translate to the efficiency we dream of on the big scale, once we finally scale up to it?
     
  15. Jul 9, 2015 #14
    That's really what I want to hear, see I was starting out building a vacuum system for thin film deposition but then I realized fusion is just some deuterium and a grid away from the setup I already am finishing. I started looking into fusion and it inspired the crap outta me. I'd love to put my system to more use like what these researchers you speak of are doing.
     
  16. Jul 9, 2015 #15

    Drakkith

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    Not if they are too small. If you want to understand how plasma behaves in a magnetic field, you're going to get very, very different results from a reactor that's 3-inches across compared to a reactor that's 30 feet across. That's not to say a 3-inch reactor would be useless. On the contrary, I'm sure you could get a lot of data out of such a device. But since we HAVE to make really big reactors first, before scaling down, we need to know how plasma behaves at much larger scales in addition to the smaller scales. Plasma instability at large scales almost certainly behaves differently than at small scales.

    Also, note that we've had small-scale reactors for decades. We haven't had large-scale reactors similar to ITER until recently. Not ones that incorporate everything we've learned to date into their design and operation at least.

    I don't see any reason to believe that. The LHC is VERY different from a fusion reactor. They don't even study the same effects.

    Why would we work on something that is orders of magnitude more difficult than fusion power already is? It makes little sense to do the hard stuff before you can do the easy stuff.
     
  17. Jul 9, 2015 #16
    Okay I see what you're saying Drakkith, makes sense to me now.
     
  18. Jul 9, 2015 #17

    russ_watters

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    I'm not sure you read the answer you got. The answer is: because it is harder to make it small than big. And since they currently can't make fusion work at all, researchers are doing everything they can to make it easier!
     
  19. Jul 9, 2015 #18

    mfb

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    That is exactly what is happening, and ITER is the scaled up and improved version of previous reactors that should - based on that extrapolation - be able to get more power out than it needs for heating. Some issues are unique to larger machines, however, so you cannot test everything with smaller devices.
     
  20. Jul 9, 2015 #19
    So the ITER is expected to achieve the fusion we want to have or is it just supposed to be used for further testing and hopefully eventually the fusion we want?
     
  21. Jul 9, 2015 #20

    mfb

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    ITER won't be practical as a power plant - they don't even plan to generate electricity at all. The goal is to get about 500 MW of fusion power with 50 MW heating power. That is still too small for a power plant, but the main purpose is research.
    The next larger reactor, DEMO, is supposed to be a demonstration power plant delivering power to the grid, and giving a reliable estimate of costs of future reactors.
     
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