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Continuous-self-destruction nuclear fusion

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Fusion. It's really jolly good, and when we can do it in a controlled way, it'll be even better. It'll happen sometime in the next 30 years (or, if you're reading this in the future, it'll happen sometime in the next 30 years).

Basic problem with nuclear fusion: you have to keep the fusing atoms very, very hot in a confined space. Way hotter than the vaporisation temperature of any known material. Hence the tokamak - which attempts to contain the fusing material using magnetic fields.

Howevertheless, neither tokamaks nor anything else have yet achieved useful, sustained nuclear fusion. The plasma keeps escaping from the magnetic field.

If only there were some material that could withstand fusion temperatures...

"But wait!" you hear me cry. "If all known materials are vaporised at fusion temperatures, why not just use the vaporised material as the fuel?"

So here's the plan. We take some metal which will fuse under the right conditions. Maybe beryllium (just don't inhale). From this metal, we make a bunch of rods in the form of long five-sided prisms.

We mount these rods on feeders, so that all the rods converge on the centre of an imaginary sphere. Because the rods are pentagonal, we have a dodecahedral space in the middle, entirely surrounded by the end-faces of the rods.

Now we light the blue touchpaper, and get some fusion going in this dodecahedral space. Almost immediately, the ends of the rods are vaporised. So, what we do is simply move all the rods inward, as fast as they are vaporised.

In other words, the walls of our fusion chamber are continuously replaced, and their continuous vaporisation provides the fuel for the ongoing fusion reaction.

So, there you go. Problem solved. Happy to be of service, mankind.

MaxwellBuchanan, Aug 18 2015

General Fusion https://en.m.wikipe...wiki/General_Fusion
[xaviergisz, Aug 19 2015]

Ball of Confusion... https://www.youtube...watch?v=SyMPXvpvkI8
..by The Temptations. [DrBob, Aug 25 2015]

[link]






       You may not believe this, but I proposed this exact principle many years ago, and it was denied the billions in funding I requested to develop it further.
xenzag, Aug 18 2015
  

       so beryllium doesn't melt, but simply sublimates ?
FlyingToaster, Aug 18 2015
  

       No, I'm sure beryllium will melt first, but at fusion temperatures it will go on to boil (and, indeed, to ionize).
MaxwellBuchanan, Aug 18 2015
  

       Is it a problem if the walls vaporize faster than the fuel can be spent? Can your fusion ball become too "rich?"   

       How do the material and thermal products of the reaction escape?
Cuit_au_Four, Aug 18 2015
  

       //How do the material and thermal products of the reaction escape?//   

       You could feed the rods in just a liiiiiittle bit slower, so that excess beryllium vapour had a chance to escape. In fact, with a bit of luck, the thing would be self-regulating (if the reaction gets too exciting, the rods vaporise faster than they're being fed in, leaving gaps through which plasma can escape, thereby slowing the reaction).   

       Another possible outcome is that the system would oscillate between fusion and non-fusion, venting bursts of beryllium gas between cycles. This would be very satisfying, as it would sound a bit like a gigawatt steam engine.
MaxwellBuchanan, Aug 18 2015
  

       I'm pretty sure beryllium will tend to fission, not fuse. It has just one little neutron holding two alpha particles together, and they don't really want to be together. Supply enough nuclear agitation to set the neutron loose, and the two alphas will happily zing elsewhere, separately. And you won't even get more energy out, than you put in! Think more of glass breaking, than some nitrogen-rich chemical compound decomposing explosively.
Vernon, Aug 18 2015
  

       Hmmm. Well, I could go with lithium if you prefer.
MaxwellBuchanan, Aug 18 2015
  

       To me, it still doesn't sound like you have compressed the sun's size and mass environment into a human scale machine.
wjt, Aug 19 2015
  

       Would it help if I read this out in a Stephen Hawking voice?
MaxwellBuchanan, Aug 19 2015
  

       Nope, still not imagining feasible containment.
wjt, Aug 19 2015
  

       Well, OK, imagine the initial system. The ends of the rods are pressed together hard, creating a sealed dodecahedron.   

       Then fusion gets going and, in the first few microseconds, vaporises a millimetre of the ends of the rods; but during those microseconds, the rods are all pushed inward by a millimetre.   

       Not only feasible, but feased.
MaxwellBuchanan, Aug 19 2015
  

       Where does the exhaust gas go? Your Lithium Deuteride (because that's what you should use) rods seal off the dodecahedron. The deuterium is liberated, and an energetic neutron splits the Lithium into two Tritium nucleii - fine. Now even supposing you can achieve fusion conditions inside the core, how will it be sustained? Any fusion events that occor will result in alpha particles (and lots of very energetic neutrons, but most of them will escape the core - might want some lead lined lab coats) clogging up the space. Surely, [Max], you know the difference between continuous and discrete processes? The challenge for any continuous process is cycling through reactants to prevent dilution.   

       ...Anyhow, methinks you're underestimating the pressure (and temperature, but mostly pressure) requirements for fusion, by maybe a few tens of orders of magnitude. [Do you know the secondary in a thermonuclear device is compressed not by explosives, but by the recoil forces arising from the ablation of it's surface by x-ray heating?] Your rod feed mechanisms are going to have to be able to index the rods inwards against the pressure in the core, which I understand to be in the hundreds-of-terapascals range. In fact I think your rod feed mechanism will be your real achievement here, and will make "canned fusion" look like childs' play.
Custardguts, Aug 19 2015
  

       Every time I see the word tokamak I think of the sign at Steak and Shake that glows a neon 'Takhomeasack.' Come to think of it some of their fries might be the perfect candidates for fusion trials.
RayfordSteele, Aug 20 2015
  

       I just think that mony a tokamickle maks a tokamuckle.
pertinax, Aug 20 2015
  

       //Come to think of it some of their fries might be the perfect candidates for fusion //   

       With the far superior British chip, actual fusion can be achieved with ease. Plenty of gravy and just the right amount of vinegar.
bs0u0155, Aug 20 2015
  

       I'm pretty sure it will work, [Max]. It looks like it just needs maybe 30 years of development work.
lurch, Aug 21 2015
  

       I have always imagined the plasma in the sun like the Mathmos lamp, doing twisting and turning blobby motions. Mind you at a different speed and scale.   

       I wonder if the Tokamak is missing a set of natural sun motions, inside the magnetic bottle, which would be the basis of a sustained reaction? Maybe continuous fed motion deflection plates could be the answer.
wjt, Aug 21 2015
  

       //With the far superior British chip, actual fusion can be achieved with ease.//   

       I think you're confusing this with that other energetic nuclear reaction. British fission chips are well- known.
MaxwellBuchanan, Aug 22 2015
  

       // it will eat the vessel voraciously at operating temperatures and pressures//   

       Yes, it will. On the other hand, the only consistently-over-unity* non-bomb, non-star fusion reactor as far as I know is the Z-Machine. It operates for about a microsecond at a time, after which several tons of components have to be replaced.   

       *In terms of fusion energy out divided by electrical energy in.
MaxwellBuchanan, Aug 22 2015
  

       Isn't the Tokamak totally designed around containment ? and nothing to do with macro patterns that effect nuclear species in our sol. Just getting it hot enough might not be enough. For one major thing, gravity would be a bit different.   

       Maybe a Tokamak on the end of hyper-centrifuge.
wjt, Aug 23 2015
  

       Just wondering; why a dodecahedral space with pentagonal prisms and not, say, a tetrahedral space with triangular prisms, or a cubic space with ... oblongs? I'm guessing the oblongs would be easier to machine.   

       Anyway, there's a small knot of disgruntled platonic solids out here wondering why they didn't make the grade.
pertinax, Aug 23 2015
  

       Because (a) dodecahedra look way cooler than cubes or tetrahedra and (b) I think the closer you get to a sphere, the better this will work.
MaxwellBuchanan, Aug 23 2015
  

       Not necessarily true. In a tokamak, the requisite pressure still has to be contained. It's contained by magnetic fields, but those fields still react against the machinery.
MaxwellBuchanan, Aug 23 2015
  

       [bigs], I agree completely with everything you say, except for the wrong bits, which is all of it.
MaxwellBuchanan, Aug 23 2015
  

       Many things about me are strange to the inexperienced.
MaxwellBuchanan, Aug 23 2015
  

       //the closer you get to a sphere//   

       The icosahedron is now bouncing up and down with equal parts of excitement and indignation.   

       Again, triangular prisms.
pertinax, Aug 24 2015
  

       The problem is the combination of a strong enough feed mechanism close enough to the active tips of strong enough rods.   

       Basically, if you've got a mechanical drive mechanism that can press the rods together with enough force, it's going to be massive enough that you won't be able to get close enough to the tips of the rods to prevent them from buckling.
MechE, Aug 24 2015
  

       Depends on the scale. The stiffness of the rods (that is, their resistance to buckling) goes up as way more than the square of their thickness.
MaxwellBuchanan, Aug 25 2015
  

       I just had an imaginary picture of a constant buckyball like frame and a whole lot off rods being squeezed inside as there ends vaporise. A bit like playdough through a mould press and with a kid eating the outcome.   

       I wonder if the vaporising bubbly end would supply the pressure needed. Even a strong magnetic buckyball might be the seal needed.
wjt, Aug 28 2015
  

       I just had an imaginary picture of a constant buckyball like frame and a whole lot off rods being squeezed inside as there ends vaporise. A bit like playdough through a mould press and with a kid eating the outcome.   

       I wonder if a strong seal is even necessary when the vaporising could act as a seal. A strong woven magnetic buckyball shape around the rods might be the seal needed.   

       Isn't the sun just two burns with fuel used up? Any boxed section of the sun's process would have to be a production line of fuel consumption.
wjt, Aug 28 2015
  

       I shall have words with him.   

       [Ah - the previous annotation appears to have fused and vaporised.]
MaxwellBuchanan, Aug 29 2015
  

       Ah Yes, the problem of editing thoughts outside the mind.
wjt, Aug 29 2015
  

       Meanwhile, the actual sphere is sulking like Obelix "Of course, I don't get any, because I fell in a non-euclidean surface when I was a baby".
pertinax, Aug 29 2015
  

       So the only true interface to an actual sphere, is any phagocytosis in which the sphere still still keeps the attributes that make it a sphere. Obelix does like his boars.
wjt, Sep 02 2015
  
      
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