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A physical vessel could, but not at 100 million K. The extreme temperature gradient required to sustain that temperature anywhere within a solid vessel (even if it's tens of kilometers big) will rapidly equilibrate and cause fusion processes to stop, and might also vaporize the fusion vessel (depending on the total energy content of the system, of course).
-Josh
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Also, if you're looking for isotopes to bombard with neutrons, can I recommend Ca-48?
Ah yes, *that's* the isotope I was looking for. At roughly 0.2% abundance, it's not particularly rare, either. We just need a cheap way to produce neutrons.
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
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Getting really hypothetical, if you could create some kind of region where the electrostatic interaction were weakened a bit or the strong force strengthened a bit, the diproton (Helium-2) would be stable enough to exist but would rapidly decay to deuterium (in the normal universe the energy of formation of He-2 is negative; in my hypothetical scenario it would be more than 0 but less than that of deuterium). This decay would release enough energy that you might be able to sustain some kind of fusion reaction with it.
More realistically, I suspect that if you have some neutron-heavy isotopes banging around in a plasma around fusion temperatures (maybe Be-9 mixed with H-1?) it'll throw off at least a few neutrons.
While I'm throwing crazy nuclear power ideas out there, here's one that maybe is not so crazy: Doing something to modify the distribution of energies of particles in the fusion plasma.
In a D-T fusion plasma at (say) 13 keV, there's going to be a distribution of particle speeds. Only collisions above a certain energy threshold can actually result in fusions. In general, increasing the temperature of the plasma increases the rate of fusion but also the plasma pressure, which increases the reaction rate but also makes it harder to contain.
Maybe you could widen the distribution of particle speeds and skew it somehow, so that the bulk of the system is moving around at low speeds but a smaller number of particles are moving at much higher speeds.
I don't know how this would be done but in the ideal case the bulk of the gas wouldn't even be ionized and then 1% of the nuclei would be moving around at crazy high speeds fast enough to cause fusion. A more realistic case would be a plasma with an energy distribution that shows two peaks.
-Josh
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Also, if you're looking for isotopes to bombard with neutrons, can I recommend Ca-48?
Ca-48+n->Ca-49->Sc-49->Ti-49
Ca-49 has a half-life of 9 minutes and Sc-49 of 57 minutes, so the energy will be released pretty quickly although not immediately.
Neutron absorption results in an energy of 5.14 MeV (most likely in the form of a gamma). The first decay releases 5.26 MeV (by beta emission) and the second releases 2.00 MeV (also by beta emission), for a total of 12.4 MeV per neutron.
Still probably a net loss relative to any known neutron production but it's pretty good all things considered.
Interesting idea. I think the problem is that abundant neutrons need to be generated by a fission or fusion reactor. They aren't really cheap and most of them are needed to keep the reaction going in one way or another. If you have spare neutrons, you could absorb them in Ca-48 generating 12.4MeV or into U-238 generating Pu-239, the fission of which would release 200MeV. That's 8 times the energy per neutron, since 2 are needed to breed and fission a Pu atom.
Last edited by Antius (2017-11-24 15:00:35)
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Throwing yet another wild idea out there, what if we accelerate protons at an electron cloud? Could we get some of them to undergo electron capture and become neutrons, which would carry on out of the system whilst the protons are reflected back?
Writing more practically, are there any ways we can increase the efficiency of fusors in acting as neutron sources? Ideally slow neutrons.
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
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Hmmm. Come to think of it, maybe it's worth trying that with K-40. Inject the ions and accelerate them towards a dense cloud of electrons, to try and force them to undergo decay. Think polywell fusion, except the virtual electrode itself is the target.
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A physical vessel could, but not at 100 million K. The extreme temperature gradient required to sustain that temperature anywhere within a solid vessel (even if it's tens of kilometers big) will rapidly equilibrate and cause fusion processes to stop, and might also vaporize the fusion vessel (depending on the total energy content of the system, of course).
It probably won't work for exactly this reason. This is an inertial confinement concept and is essentially an artificial star. Red dwarf stars have surface temperatures as low as 2000K despite core temperatures being several million K. This is the case because the surface area of the chronosphere is large compared to the surface area of the core, so heat spreads out as it convects through the star. However, red dwarf stars are the size of Jupiter and are as dense as platinum. So it is very likely that the minimum critical size of the reactor would be huge, even using tritium and deuterium it would probably need to be many kilometres in diameter. It would also be dangerous in a way that would make nuclear meltdowns appear tame. Who wants to be anywhere near a tank of superheated hydrogen with as much stored energy as a thermonuclear weapon? Also, if the minimum critical size is measured in kilometres, where would we find that much tritium and deuterium? Start-up costs would be excessive.
I think it could be made to work at very high pressures, because the reaction rate within the core at a pressure of 1000atm, would be huge - maybe enough to balance the rate of heat loss by conduction and convection. I don't think melting the walls would be the biggest problem, because the heat capacity of the non-plasma outer regions of the gas would be much greater than the plasma due to their greater density. The problem would be quenching the plasma due to conduction and heat loss into the colder gas. The plasma would need to generate heat at a rate that is greater than the conduction heat loss rate.
Last edited by Antius (2017-11-24 17:39:23)
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Interesting idea. I think the problem is that abundant neutrons need to be generated by a fission or fusion reactor. They aren't really cheap and most of them are needed to keep the reaction going in one way or another. If you have spare neutrons, you could absorb them in Ca-48 generating 12.4MeV or into U-238 generating Pu-239, the fission of which would release 200MeV. That's 8 times the energy per neutron, since 2 are needed to breed and fission a Pu atom.
Credit goes to Terraformer on this one, but yeah, when you're looking into alternative nuclear energy sources the low efficiency of current neutron production methods is actually a pretty big problem. I had a somewhat similar idea to use Lithium-7, in a reaction which I call NILFiR (Neutron Induced Lithium Fission Reaction):
Li-7+n->Li-8
Li-8->Be-8
Be-8->2 He-4
The first reaction releases 2.03 MeV, the second 16.01 MeV, and the third is roughly energy-neutral (this is why carbon is relatively common in the universe: In the cores of heavier, older stars there's an equilibrium between He-4 and Be-8. Be-8 is occasionally struck with another He-4; they fuse to form C-12). The total energy produced is therefore 18.03 MeV. There's some more discussion in this thread as long as you don't hold me to the accuracy or insightfulness of anything I said in 2008.
The sticking point is the same: The low efficiency of Neutron Production methods.
The big benefit to NILFiR (and various other induced-decay reactions) as I see it is that you can use a relatively common fuel and that you have way less radioactive waste afterwards and radiation during (The reaction will likely produce some tritium, which is not bad as far as radioisotopes go, as well as a good number of stray X-rays and gamma rays while the reactor is operating, plus transmutations as a result of stray neutrons. Plus, it's a lot easier to control than Uranium fission as the reaction is dependent on an outside, powered neutron source to function.
Terraformer,
I've looked into the proton/electron bombardment thing. It happens in stars sometimes (as part of what's called the Proton-electron-Proton reaction) but as far as I can tell the cross section is very low and most of the time the energy ends up getting released as bremsstrahlung, which is very disappointing.
I suppose one thing that comes to mind as far as the fusor is concerned is to use an AC+DC voltage. The voltage across the terminals will be varied according to an equation as follows:
Vo-Vi=V1+V2*cos(w*t)
Where Vo is the voltage at the outer terminal, Vi is the voltage at the inner terminal, V1 is the average voltage, V2 is the amplitude of the sine wave, and w is a parameter that determines the frequency of the sine wave.
The idea is that by tuning w to the correct value, the particles will all sync up. This increases the chance of a collision, and also means that the voltages at the grids will be tuned so that the particles are repelled from them when they are nearby.
For this to work properly, V2 needs to be greater than V1, but not too much greater.
It's also important for particles to have the same charge-to-mass ratio for the syncing to work correctly. This means that fusion reactions like D-T, D-He-3, and P-B-11 are probably no good. On the other hand, reactions between the same isotope are definitely good. These are D-D, T-T, He-3-He-3, and possibly Li-6-Li-6 or Li-7-Li-7. You might also be able to get away with D-Li-6 (Lithium 6 has exactly 3 times as much charge as Deuterium but only 2.9865 times as much mass, resulting in a difference of charge-to-mass ratio by 0.45%; Whether that will be a problem or not I don't know).
If you're after neutron production, you'd probably want to do D-D since it's the easiest. This reaction has two branches, with a 50% each probability (per the wiki article "Nuclear Fusion"):
(1) D + D -> T (1.01 MeV) + P (3.02 MeV)
(2) D + D -> He-3 (.82 MeV) + n (2.45 MeV)
In the case that Tritium is produced, you can collect it and do a T-T reaction:
T + T -> He-4 + 2 n + 11.3 MeV
If you want to use isotopes of different charge-to-weight ratios, you might be able to get away with using a voltage equation as follows:
Vo-Vi=V1+V2*cos(w1*t)+V3*cos(w2*t)
Where w1 and w2 are tuned separately for the different charge-to-weight ratios. I will be totally honest and say that I have no idea if this will work.
-Josh
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Follow-up: Varying the electrical fields as I described will generate a magnetic field. This will have some weird effects that I'm not totally comfortable speculating about.
-Josh
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Interesting paper on kinetic impact driven fusion.
https://www.jstage.jst.go.jp/article/ls … 3/_article
To achieve sufficient compression on impact, a macro projectile must be accelerated to ~200km/s into a solid target.
A typical bullet achieves acceleration between 50,000 - 100,000g. To achieve a final velocity of 200km/s with acceleration of 100,000g, an accelerator would need to be 20km long. A coil gun concept would appear to be most practical, firing two converging projectiles at individual velocities of 100km/s. This would require two opposing accelerators, each 5km long, exiting into a reaction vessel.
This would appear to be an achievable power plant, especially if the accelerators could be buried in trenches beneath the ground.
Last edited by Antius (2017-11-29 17:21:41)
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Might be unfortunate if only one accelerator fires and not the other, or if the projectiles achieve a glancing impact or miss one another. Then where does all that kinetic energy go?
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Energy leaders are convening at the White House for a summit on the commercialization of clean fusion energy
https://www.princeton.edu/news/2022/03/ … ion-energy
War in Ukraine speeds thinking on harnessing power of atoms
https://www.wdtimes.com/opinion/article … 49db6.html
Last edited by Mars_B4_Moon (2022-03-18 07:57:44)
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Why our continued use of fossil fuels is creating a financial time bomb
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