We have ignition! ....almost

Discussion in 'Science' started by BlueRaven, Oct 14, 2013.

  1. BlueRaven

    BlueRaven Member

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    Scientists at the Lawrence Livermore National Laboratory's National Ignition Facility have achieved the highest yield of deuterium-tritium neutron energy ever recorded, by using over 1.7 megajoules of laser energy from 192 separate beams for a peak-power pulse of 350 terawatts.

    This is about thirty times as much laser energy as has ever been produced by any other group of lasers in the world, and the resulting implosion produced about three times as much neutron energy as had ever been achieved before.
    This is as close as we've ever been to achieving "ignition", the state in which a fusion reaction starts to self-sustain.

    Could we achieve a viable source of fusion power in our lifetime? This is serious science people!!

    From the NIF site: https://lasers.llnl.gov/newsroom/project_status/index.php

    From Ars (including a nice dig at the current US Gov SNAFU): http://arstechnica.com/science/2013/10/government-shutdown-slows-news-of-fusion-breakthrough/

    A couple of older articles from ExtremeTech, including some awesome photo slideshows of the target chamber and laser tubes:
    http://www.extremetech.com/extreme/101277-inside-californias-star-power-fusion-facility
    http://www.extremetech.com/extreme/123837-500mw-from-half-a-gram-of-hydrogen-the-hunt-for-fusion-power-heats-up

    Article from 2010 giving a bit of historical perspective on the 1MJ+ laser array and the joint National Ignition Campaign:
    www.yourindustrynews.com/nnsa+annou...+at+the+national+ignition+facility_45016.html
     
    Last edited: Oct 15, 2013
  2. RobRoySyd

    RobRoySyd Member

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    Very hard to see how that's going to be possible from the work being done at the NIF. Even if they achieve a self sustaining fusion reaction it's not going to last very long and there's no plan that I know of to get useable energy back out of it and it takes a lot of time to reload the targets etc.


    I would have said "very serious engineering", the science value of this effort escapes me. I'm pretty confident we already have the science of a sustainable fusion reaction done and dusted. It's now an engineering and materials science problem. Sure there's a huge amount of scientific knowledge behind the engineering but given that fusion is quite possible at home the challenge isn't the fusion bit it's things like how to feed more fuel into the chamber, how to get energy back from the extremely hot gases and how to protect the vessel for the high energy photons released by the fusion.
     
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    BlueRaven

    BlueRaven Member

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    Well pointed out, the materials science and engineering challenges are quite distinct from the theoretical physics problems that necessarily have already been dealt with to get this far.

    If we can generate usable electrical power via heat exchangers and steam turbines driven by a fission reaction, surely we can do it with fusion? The challenges and risks are obviously greater because of the higher temperatures and energy levels involved, but given recent advances in materials science such as carbon nanotubes, graphene etc., I would hope we are already well on the way to developing materials that could withstand the extreme conditions. Thermodynamic efficiency will be low at first, but the same could be said of any new method of power generation we've developed over the years.

    Fuel replenishment and radiation containment would seem to be the biggest hurdles to overcome. Perhaps an array of multiple fuel-containing hohlraums, ignited via variable beam paths focused by mirrors, contained within an electromagnetically shielded reaction chamber and replenished by some automated mechanism in a planned sequence, might be able to produce a sustained reaction that can overcome the required energy input to achieve ignition of each new source of fuel? Somewhat similar to the fuel rods in a fission reactor, but much more precisely timed and targeted.

    I'm not a nuclear physicist of course, and there's plenty of considerations that I'm probably not aware of, but it seems to me that once phenomena such as alpha heating in the early stages of ignition are fully understood and able to be manipulated and controlled, maybe we can produce a sustained and replenishable fusion reaction? Once again, I'm just chucking out ideas from a layman's perspective here, but might it not be possible to come up with some system that's analogous to the fuel rods/control rods in a fission reactor, if the process can be automated and maintained within some suitable containment system?
     
    Last edited: Oct 15, 2013
  4. RobRoySyd

    RobRoySyd Member

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    High energy particles do interesting things to most materials. That's a challenge in fission reactors and the energy is way, way lower.

    Fission reactors are run at around 300 deg C, coal fired 800 deg C. Coal has higher thermal efficiency. There's talk of going to Ultra Supercritical Steam at 850deg C to push thermal efficiency up another couple of % but then more expensive steel is required. A fusion reactor is going to run at millions deg C and most of the energy will be in X and Gamma Rays, how you convert that into thermal energy to raise steam I haven't a clue.

    No material can withstand that temperature, terrestrial fusion requires temperatures much hotter than the Sun.

    By my undertandind thermodynamic efficiency should be very high however I have no idea how thermodynamics works at those temperatures.

    The ITER tokamak machine looks way more promising.

    The problem is to get to a sustainable reaction extremely high temperatures are required and the "gas" is at extremely low pressure, the actual energy involved isn't enough to boil a cup of water because although the atoms are very hot there's so few of them.

    Fusion has been "a decade away" for the many decades I've been alive :(
    The most remarkable thing is the number of people achieving fusion in their garage today. It's way, way, way short of being self sustaining but if you're not careful major damage to your health is possible.

    I'm not a nuclear physicist either and it was only recently that I came to understand the real issues. In our sun every year less than 1 in a billion atoms undergoes fusion. That still creates a huge amount of energy because there's so many atoms and the core is very dense. The temperature inside our sun is too low to cause most atoms to undergo fusion, instead it's quantum tunnelling that allows a few to achieve fusion. We simply cannot even remotely achieve the pressure / density of the gas in the core of the Sun here on Earth. So to get a sustained reaction going we need much higher temperatures, I think around 100 times hotter.

    Now the Sun is controlled by a very elegant mechanism. One force is trying to rip it apart and another is trying to squash into something about the size of a tennis ball. it's just the right size for those two forces to keep things relatively stable for a few billion years...and then Earth is probably toast. Trying to emulate something similar, to create our own tiny Sun is no simple matter.
     
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    BlueRaven

    BlueRaven Member

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    Thanks for the excellent and detailed response. :thumbup:

    I feel a bit stupid for not seeing the obvious point that when talking about "star power", the temperatures involved are going to be orders-of-magnitude greater than anything we've ever dealt with on earth before. :rolleyes:
    Also the fact that any "small scale" fusion we can achieve will be not occurring under the kind of pressures created by a gravitational field that's much greater than anything we can achieve by artificial means.

    I think I also now get the fundamental difference between fission and fusion with regard to reclaiming the resulting energy to do useful work. If I understand it correctly, while fission produces large amounts of energy at the x/gamma-ray end of the spectrum which is basically considered as "waste" to be contained, there's still plenty of radiation being produced at microwave/infrared frequencies which can be easily harnessed to heat water (directly in a water reactor or through exchangers in a liquid sodium reactor), and the reaction occurs at temperatures that can be withstood by conventional materials. This won't be the case in a fusion reaction.

    So it seems that until we can perhaps emulate the sun's cyclical "pulsating" effect of expansion/outgassing caused by fusion being balanced against gravity (or maybe electromagnetism on a smaller scale) we won't be able to achieve the kind of pressures/densities that bring the required temperatures within a range able to be withstood by any man-made material. The sort of engineering and energy input that would be required kind of boggles the mind. :(

    I have read that "fusion is always 20 years away", as we overcome hurdles only to run into new ones. Perhaps a greater understanding of quantum tunneling etc. will bring us a bit closer.
     
  6. RobRoySyd

    RobRoySyd Member

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    Anything with "quantum" in it is very difficult to understand. It's said the more you think you understand it the less you understand it. We've been banging away at it for over a century and there's been no great breakthroughs. That's not surprising because it involves investigation of space / time so many orders of magnitude removed from the realm of subatomic particles as to boggle our minds. The difference is around the same as going from a single proton to our galaxy!

    All is not lost however, we have robust equations that lets us predict what will happen. Unlike classical physics these equations are statistical, roll of the dice stuff. They tell us that the probability of quantum effects occurring in the world you and I inhabit happening are so remote as to require us to wait for a zillion times longer than the age of the universe to observe one. We can safely assume that the reason the pen that was on your desk and is now on someone else's desk was not due to quantum tunnelling :)

    To explain quantum tunnelling consider this. Your car is on one side of a mountain and you want it on the other side. You can drive up the mountain and then recover the potential energy as it rolls down the mountain. The energy level of your car on either side of the mountain is the same. Now classical physics also says if there was a tunnel through the mountain the car could move from one side of the mountain to the other and ignoring friction no energy is required. What if the energy required to move it from one side of the mountain to the other could simply be borrowed from somewhere, there's be no need for the tunnel.

    Quantum Tunnel is exactly that, energy is borrowed from the quantum field and returned. The energy cannot be borrowed for very long, only one Plank unit of time in fact which means the car will get from one side of the mountain to the other very much faster than the speed of light. It also doesn't matter how far we want to teleport cars or people however we are a very, very long way from being able to do this. At the sub atomic level though things change, we can have a lot of dice rolling.

    Trying to fuse two nuclei is the same problem, we need to overcome the electrostatic force that stops them getting close enough to combine. When we have enough nuclei the probability of quantum tunnelling happening become sensible within our timescales, we can help the process by first separating the nuclei and electrons in a plasma, we can improve the probability by increasing the energy of collisions i.e. heating the plasma. As I've mentioned even at temperatures easily achieved at home it's possible to get fusion to happen. We can also reduce the energy levels required. Fusing two protons from a hydrogen nuclei to get a deuterium nuclei is very difficult, thankfully we have a relatively abundant supply of deuterium available so we can bypass this phase that happens in oun Sun.

    One of the most remarkable examples of fusion happening is sonoluminescence. You can buy a rig to safely demonstrate fusion, a sun in a bubble or you could simply buy a mantis shrimp. We're not the first species to use nuclear fusion as a weapon.
     
  7. Foliage

    Foliage Member

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    Only 1 in a billion undergoes fusion, as in the rest just sit idly by until their time comes along?
     
  8. RobRoySyd

    RobRoySyd Member

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    I don't know if I'd have used the word "idle" but otherwise that's my understanding. I'd be very happy to be educated as what I've posted is only my layman's understanding and if I've gotten something mixed up I'd hate for others to be misinformed.
     
  9. tornado33

    tornado33 Member

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    From what I understand though the NIF test did technically make "breakeven" thats only considering the energy fed to the fuel pellet, that comes from X rays generated when the laser beams hit the hohlraum (it contains the fuel pellet) Due to ineffeciencies of conversion, the energy of the laser beams is much larger then the energy of the resulting X rays. Thus the energy to make the laser beams is in fact still much more then what the fusion process released. So no actual breakeven.

    Considering the massive size of the NIF, its not looking great for sustainable fusion that can be implimented into feasable power stations. Perhaps Colliding beam Fusion might prove more feasable. Here is a paper on a hypothetical 100 megawatt Colliding beam Fusion reactor for space propulsion.
    http://www.boomslanger.com/images/cbfr.pdf

    Then theres electrostatic fusion and other combined approaches
    http://en.wikipedia.org/wiki/Fusion_power#Technically_viable_approaches
     
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    BlueRaven

    BlueRaven Member

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    Yeah, this seemed obvious from the numbers, but I was still wondering if I'd got it right. :lol:
    8000 joules seems a pretty meagre output from a required electrical input of 1.7 megajoules, which as you say is related to inefficiency in converting laser light to x-rays and other factors such as the limited amount of fuel and limited time scale of the reaction. Given the billions of tons of matter and mind-boggling number of atoms in the sun/stars, it's much easier to understand how a sustained reaction is possible.

    Thanks for the links, looks like I have more reading to do. :)
     
    Last edited: Oct 24, 2013
  11. Phido

    Phido Member

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    I certainly wouldn't expect anything other than experimental Fusion power plants to be built any time soon. Not for 50 to 100 years. Given the time to get approval, funding, build it, get to a level of deployable and efficient design. It might however be more useful for space propulsion or alternative purposes.

    We should consider building more modern versions of existing solutions in the intrim. Fission, coal, solar, and wind.
     
  12. RobRoySyd

    RobRoySyd Member

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    Fusion has a certain mythical appeal to it. The Sun powers almost all life on Earth so having one in a box to provide energy at our will at first glance seems very appealing. Certainly the end product is benign and easily disposed off, it's all the very high energy particles created during operation that are a considerable challenge. Here on Earth we are shielded from them by several factors and processes and still the Sun causes more deaths from radiation than anything else.

    On the other hand fission seems a safer process, the nuclei don't need much of a nudge to split and release energy that's manageable. One of the interesting avenues of research in that area is producing self sustaining fission that doesn't rely on a chain reaction. The key to success is building a very efficient particle accelerator that can produce enough neutrons that'll in turn produce enough energy when fired into say thorium that'll in turn produce more energy than is required to power the particle accelerator. Jefferson Labs recently had a breakthrough in the design of their superconducting radiofrequency cavities that's improved efficiency by a factor of four. My understanding is we're now within an order of magnitude of achieving success.

    Research in this field was also one of the justifications for building the LHC. Neither this or the work at Jefferson Labs attracts much media attention, it was only by chance that I learned of it. I guess that's understandable as it's the hard slog kind of science and engineering. Success comes from many incremental steps.
     
  13. Dark Passenger

    Dark Passenger Member

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    no offence guys but in layman's IE (hit with hammer and it works) does this whole thing mean that your creating a fusion reaction here? If so what does that mean for the average joe in his lifetime. I am very curious but i am not smart enough or just not schooled in exactly what you guys are doing. Also isn't this immensely dangerous creating a mini sun. Wouldn't that have its own gravitational pull. This probably is going to sound stupid but i have this thought of this mini sun being created then falling into the earths core and everything going sour. I know it probably won't happen that way but can't help day dreaming.
     
    Last edited: Oct 28, 2013
  14. GTR27

    GTR27 Member

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    Essentially it's about creating power positive controlled fusion. Currently, it takes more energy to start and maintain (maintain here being a very short time) a fusion reaction, than the fusion reaction can produce. I.e. it takes more energy than it makes (which is useless for anything but tests/study).

    A easier way to think of it is if you had a wood powered stove that you had to spend a tank of LPG on to light, and it only burnt for 30 secs (once lit), it wouldnt be a very effective stove (in terms of what was input (LPG, wood, time) versus what was output (30 secs of heat). In a long, roundabout way that is what has been plaguing controlled fusion since they first discovered it.

    No. Very simply, don't think of gravity as some special force that exists everywhere, gravity is related to mass (and distance). If you dont have much mass, then you wont have much gravity. So if you have a tennis ball full of grout in a vacuum (space) then that will not have much gravity on the surface of the ball at all. Likewise, a very small amount of hydrogen (in controled fusion) will have negligible gravity changes compared to the massive rock ball the facility will be built on.

    The sun has huge gravity due to the sheer amount of matter it contains, along with the massive size of it, not because it is undergoing fusion. (fusion is a by-product of the strength of the gravity of the sun).

    Im sure someone who is a proper scientist can explain things much better than myself, but that's a shortened, cut down version. Hopefully it helps :)
     
  15. Foliage

    Foliage Member

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    Lol

    A sun has gravity because it is so massive, a mini sun isn't massive hence it has no gravity (that we care about). The only things in common is the fusion reaction eg the amount of energy being released from the particles fusing together.
     
  16. Dark Passenger

    Dark Passenger Member

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    thanks for the layman explanation guys i do understand it a little better now. My next question though is how far is this going to go? I mean are these people trying to create this so when can have a never ending supply of energy? This has got my curiosity peaked now.
     
  17. Foliage

    Foliage Member

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    If we can keep it sustained then yes it would be a never ending supply of energy as the fuel is found in common sea water.

    Much the same as current fission plants (uranium) and future fission plants (thorium) are essentially never ending supplies of energy, eg we will not run out for thousands of years, hence the pro nuclear crowd arguing for more nuclear power, the fuel is only 5% of the cost of a nuclear power plant, 95% is running it with all the regulations and safety features taking up huge amounts of time and energy.

    We will never run out of fuel, when fossil fuels run out if we have not invented clean alternatives nuclear will be common place as we are energy hungry nations.
     
  18. Dark Passenger

    Dark Passenger Member

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    so is it theorised that a power plant running this tech would be much the same as a nuclear plant i.e. driven turbines? i have never even heard of a thorium plant before. Time for a look see.
     
  19. Billzilla

    Billzilla Member

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    Yep the thorium is just another way of making a heat source to generate steam. Though it's a heck of a lot safer & cleaner than a uranium plant.
     
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    BlueRaven

    BlueRaven Member

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    There's also the significant cost (and obvious physical/legislative limitations) of storing, re-processing or otherwise handling spent fissile material, with all of the associated safety standards and procedures (which aren't always adhered to).

    The elemental by-products of Fusion are much more benign, although - as has been previously pointed out - the containment of the high-energy particles from such a reaction presents major challenges.
     
    Last edited: Oct 29, 2013

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