Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Future fusion reactor

  1. Aug 10, 2008 #1
    i was watching this show on the Science Channel and in it they talked about a new type of fusion reactor that is currently being built(construction started like 30 years ago). They said it will produce energy for entire world the same way the sun produces energy (fusing hydrogen). It's suppose to be something like 1000 times more efficient than current fusion reactors. They go on to say that water can be used to produce the energy.

    Will they just put water in the reactor, or will they split water to get hydrogen and put that hydrogen in the reactor? Can anyone explain how this reactor will work?
     
  2. jcsd
  3. Aug 10, 2008 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    I think you mean more efficent than current FISSION reactors, all the current fusion reactors are experimental machines that can only maintain fusion for a few seconds and take more energy than they generate.

    The problem with fusion is that you need incredibly high temperatures and pressures to force the positively charged hydrogen nuclei together. The centre of the sun is a good place to do this - doing it in a lab is tricky!
    Although in theory you can ultimately build a H+H fusion reactor this is the most difficult, it needs the most pressure and highest temperatures. A more likely system uses one of the heavier isotopes of hydrogen ( deuterium or tritium ) these can be obtained in very small quantities from seawater - although it takes energy to do this the plants already exist since heavy water is required for some existing fission reactors.

    The great thing about fusion, apart from the essentially unlimited fuel source (ie the ocean!) and the vastly greater energy output - there is much less waste.
     
  4. Aug 11, 2008 #3

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Was this about the ITER ?

    Actually, per unit of mass, fusion is only about 4 times more efficient than fission when compared to fast breeder reactors. But indeed, the potential advantages of fusion are the rather unlimited supply of fuel (no geopolitical concerns, you "only need water"), and the low activity of waste generated, as compared to fission. Also, the much smaller potential danger, given that the amount of fuel in a fusion reactor (a few milligrams) is very very small compared to the amount of fuel in a fission reactor (200 tons or so).

    The only problem with fusion is that "already 50 years, one says it is going to work 30 years from now". The tokamak was invented in 1954, and it would also take 30 years to make it work (1984...).
     
  5. Aug 11, 2008 #4
    the show was on the Science Channel and the title was Building the Future:the Search for Ultimate Energy. I guess it's a new series that will include maybe 4 shows with each one focusing on a different topic. They should eventually show re-runs of this episode.

    They basically said that once the reactor is made, it will be like having a small sun on earth. The fusion will be self-sustaining.
     
  6. Aug 11, 2008 #5


    I believe that the program that you are referring to is called Building the Future: The Search for the Ultimate Energy which was aired on Jun. 10, 2007 on the Discovery Channel.

    I was unable to locate a internet version of this episode, however, I noticed an interesting reference to the MIT plasma science and fusion center for a MIT electromagnetic superconducting cryostat fusion reactor featured on the Discovery Channel, video link listed in reference.

    I am somewhat puzzled however, how such a device could possibly sustain a thermonuclear fusion chain reaction, given its divergence in Tokamak engineering design.

    Reference:
    MIT cryostat fusion reactor
     
  7. Aug 11, 2008 #6
    vanesch,

    Yes. they were talking about the ITER project. Anyone who wants to find out more about it can google iter and click on wikipedia link.

    orion, the engineers building it must be confident that they will eventually be able to sustain a reaction because they are spending over 9 billion dollars on it. In fact, when they were talking about it on science channel show, they said it is the second most expensive engineering project, just behind the International Space Station.
     
  8. Aug 11, 2008 #7

    mheslep

    User Avatar
    Gold Member

    Here's one of the more noted, controversial, and long lasting attacks on ITER, Lawrence Lidsky's "The Trouble with Fusion" published in 1983. Lidsky was a noted nuclear engineering professor at MIT. Lidsky did a lot of work in the field but became increasingly skeptical of its practicality. After getting little traction for his critical questions at MIT, he wrote this.
    http://www.askmar.com/Robert Bussard/The Trouble With Fusion.pdf
    Reply years later here by an ITER - related researcher. See section III.
    http://fire.pppl.gov/fusion_critic_response_stacey.pdf
     
  9. Aug 11, 2008 #8

    Attached Files:

    Last edited: Aug 11, 2008
  10. Aug 12, 2008 #9
    Orion,

    I watched the video, which was very interesting. This reactor is definetely on a smaller scale than ITER. I was surprised when they said that the 'donut' part of the reactor levitates during fusion. I wonder if ITER will do the same thing?
     
  11. Aug 12, 2008 #10

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    No - the designs look similiar but are different.
    In a tokamak (ITER) the magnets are on the outside and the plasma forms a ring inside the chamber.
    The MIT design is almost exactly the opposite - the magnet is in a ring inside and the plasma forms a donut shape around the magnet. The levitating part is simply to avoid having any mechanical supports to the magnet which would interfere with the plasma.

    There is some controversy about ITER - some people think it is a 'snowball' project that simply scales up previous experimental reactors without considering alternative designs.
    But if you are spending $10Bn you probably want to start with a well understood conventional design.
     
  12. Aug 12, 2008 #11
    The funders and engineers building ITER must be somewhat confident it will work if their spending 10 billion on it. Lets hope so, because we could definetely use this to end the 'energy crisis' going on in the world right now.
     
  13. Aug 12, 2008 #12

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Thats the problem "funders and engineers" not the physicists!
    A project this size gets a such a momentum of administration and project management that the actual design seems almost a by-product. Once a starting point (ie scale up JET) is set, you can't consider anything different because it is a risk and the cost is so large you can't have any risk. NASA is often a good example of this problem.
     
  14. Aug 12, 2008 #13
    mgb_phys ,

    I hope it works out. I'm sure their top priority is getting the reactor to work, but how they go about doing that, like you said, is key.
     
  15. Aug 12, 2008 #14

    mheslep

    User Avatar
    Gold Member

    It seems to me that there are some serious flaws with this 'internal' magnet design, namely the the floating doughnut in any realistic reactor would quickly be destroyed by the high energy products of fusion. A great deal of work has been put towards the outer walls of tokamaks: exotics for the first wall, backed up with molten lithium to carry away the heat, etc. None of this seems possible w/ a levitated internal super conductor. Am I missing something?
     
  16. Aug 12, 2008 #15

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    I'm not an expert but I think that precisely one of the advantages of the floating design.
    In a tokakmak it's very difficult to hold large amounts of plasma with different energies in a tight ring.
    With the floating design the plasma is both held away from the ring by the field (self focussed?). The outer vacuum cryostat can be as large as you like since it isn't part of the field, so can be kept away from the plasma.

    I thought extracting the energy normally requires deliberately allowing some plasma to heat the walls which you can then use to generate steam.
     
    Last edited: Aug 12, 2008
  17. Aug 12, 2008 #16

    mheslep

    User Avatar
    Gold Member

    Yes well I grant the idea that the floating dipole might do well at plasma confinement, that is the stated purpose. But that has little to do with the high E neutrons with which a working design must be concerned. The plasma, i.e, charged nuclei and electrons, is never intended to come into contact with anything solid. In D-D or D-T fusion, the neutrons, contained by nothing other than collisions, carry almost all of the energy produced in kinetic form at MeV levels into the walls of the reactor. That is where energy is absorbed in the form of heat by the ITER design. The neutrons also a have the side effect of making the containment vessel inevitably radioactive as Lidsky pointed out (above) while slowly destroying the first wall. (I believe ITER researchers say walls can be built that would last a year in a working reactor). I'm speculating that since the MIT dipole can not be made so tough, nor can it carry away heat, that it would be destroyed no so slowly. :uhh:
     
    Last edited: Aug 12, 2008
  18. Aug 12, 2008 #17

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Good point, I didn't think of the neutrons.
    A magnet quench would be interesting in the floating design as well!
     
  19. Aug 12, 2008 #18

    mheslep

    User Avatar
    Gold Member

    Here we go, from a paper referenced on the MIT site:
    http://psfcwww2.psfc.mit.edu/ldx/pubs/presents/DPP03_kes.pdf
    and
    Ok, the authors certainly recognize this as a problem to be solved. They elsewhere state the doughnut shield will be carbon boron. Still, I had thought that allowing a wall to get that hot meant substantial heavy nuclei poisoning of the plasma. It also turns out that most of the heating comes from Bremsstrahlung radiation.
     
  20. Aug 12, 2008 #19
    If they are able to create these new fusion reactors, how would they take the energy produced by reactor and make it usable for the world? For instance, would they use the heat generated by reactor to create electricity by means of a steam turbine?
     
  21. Aug 12, 2008 #20

    Astronuc

    User Avatar

    Staff: Mentor

    The plan would be to use thermal energy to drive a power cycle like the Rankine cycle.

    Direct conversion would be ideal, but I'm not sure if it's feasible with the tokamak geometry.


    Unfortunately, none of the MIT-LDX links work. However, the temperatures (> 16000 K) would be incorrect. The highest melting points would be 3890, 3880 and 3800 K for HfC, TaC and carbon, respectively, and C's boiling point is 4300 K! I believe that the temperature should be more like 1600 K.

    Ref - http://www.ultramet.com/ceramic_protective_coatings.html
     
    Last edited: Aug 12, 2008
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Future fusion reactor
  1. Compact fusion reactor (Replies: 11)

  2. Iron Fusion Reactors (Replies: 14)

Loading...