Dumb Idea

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seedload
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Dumb Idea

Post by seedload »

Please forgive me because I am really not a very bright guy. I don't understand anything about nuclear physics and I have absolutely no basis for posting an idea of any kind at all. But, if you take the time to shoot down my thought, it might bring me to a higher level of understanding - higher than none that is.

Hopefully the General forum is a good place to post bad ideas. Anyway, here it is...

Beam target fusion is basically shooting a high energy particle at a stationary target, right? I suppose that you could shoot a proton at a pile of boron and, if you could get the proton going fast enough, and you could avoid it losing energy by hitting anything else, there is a chance it will hit a boron nucleus and fuse - right?

Boron is a semi-conductor but at high temperature, it acts like a metal, right?

In a fusor, a high potential is created between an outer grid (anode) and an inner grid (cathode) that causes positively charged particles to fly into the middle at high speed and sometimes run into each other at great enough speeds to fuse. When they miss, they come around for another try - recirculating.

Fusors have a big flaw. They have a cathode. Sometimes the high energy things that are rushing in crash into the cathode and the losses from this can't be overcome.

My simpleton thought is that if you can't miss the cathode enough, make the problem the solution. Why not make the cathode out of boron11? Instead of wanting to miss the cathode, try and hit the cathode using a higher potential and achieving greater speeds. Basically, use a solid boron cathode in a fusor with a much greater potential and inject protons.

Would the protons not recirculate on misses? Would we lose too much energy to electron collisions? Is there a chemical reaction issue that I don't understand? Can boron be used as a cathode? What about boron buckyballs? Does boron have a nanotube equivalent of superconductive carbon nanotubes?

Thanks for entertaining my naiveté

MSimon
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Post by MSimon »

The scattering cross section is 60X the fusion cross section.

Say the energy loss per collision was 5%. That would give a net energy of (.95)^60 = about 1/20th.

The pB11 cross section peak is at 550 KeV multiply that by 20. 11 MeV. Output of the reaction - 8.7 MeV.

You can't get there from here.

Oh yeah. The B11 would have to be capable of absorbing 100 MW continuously without vaporizing. Energy of vaporization is under 10 eV. You are shooting 550 KeV (minimum) particles into the B11. Good luck wid dat.
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jmc
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Post by jmc »

From the point of view of just fusoring, you might be able to get a decent yield of alpha particles though, enough for an entertaining science demonstration, most reactions in a fusor are beam background gas reactions, in the case of a solid (preferably hollow) boron cathode sphere your background density would be huge! (as would the power consumption of the device)

The real killer when benchmarking this idea against a regular fusor (which hasn't got a hope of achieving breakeven at realistic power levels in anycase) would be the electrons emitted from the cathode, like MSimon said it doesn't take much to ionize an electron from boron and at solid densities the electron current would be absolutely and unbearably huge, you might get away with screening the boron sphere with a grids that provide a local electric field pointing away from the sphere, that would attract boron ions of course but at a more manageable rate, the only thing is that this cathode would then become the main cathode for attracting the hydrogen atoms so you'd be back with the same problem again. This could be overcome only through making the grid more transparent.

So essentially now your solid sphere is simply a means of increasing the background density and increasing the fusion rate that way (in exchange for higher energy losses), the question then would be: why not just shoot a beam of ions at a solid target without bothering with the sphere?

For one thing it would be easier to get higher ion densities in a spherically convergent beam then in a regular beam as they have nowhere to diverge save upscattering, this saves the amount of boron which you would have to use as a target and also the total vacuum vessel space. It also prevents the main beam ions from whacking into the vacuum vessel at full energy (although obviously fusion ions would) so I suppose the spherical geometry would give you the most fusion events per unit vacuum vessel damage.

550keV is still a very high voltage though. It migh be better to start off with a sphere made of something deuteride that conducts building the fusor from there and getting the neutron count, you could ramp up th voltage later.

Its an interesting idea for an experiment (though with no practical applications to net power production) you should mention this at:

http://www.fusor.net/

they might be interested and give you advice on how to build something like it.

MSimon
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Post by MSimon »

550 KeV is a fairly hefty drive voltage.

It is not excessive for a DC linear accelerator.
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TallDave
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Post by TallDave »

My simpleton thought is that if you can't miss the cathode enough, make the problem the solution. Why not make the cathode out of boron11?
Heh, interesting idea. It would melt/vaporize/ablate too fast to work, but still a neat twist.

drmike
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Post by drmike »

check out beam pellet fusion, it is a similar idea but without the central charge.

Impulse stuff can work once. It's getting the rep rate up for power production that is the hard part.

Helius
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Post by Helius »

TallDave wrote:
My simpleton thought is that if you can't miss the cathode enough, make the problem the solution. Why not make the cathode out of boron11?
Heh, interesting idea. It would melt/vaporize/ablate too fast to work, but still a neat twist.
Wouldn't cold Boron just ionize and slow the fuel? Forget about the high class problem of wearing down with 100MW of ash; It's the immediate "low class" problem of getting there that needs to be overcome.

MSimon
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Post by MSimon »

Helius wrote:
TallDave wrote:
My simpleton thought is that if you can't miss the cathode enough, make the problem the solution. Why not make the cathode out of boron11?
Heh, interesting idea. It would melt/vaporize/ablate too fast to work, but still a neat twist.
Wouldn't cold Boron just ionize and slow the fuel? Forget about the high class problem of wearing down with 100MW of ash; It's the immediate "low class" problem of getting there that needs to be overcome.
It makes no sense to "get there" if there is nothing useful around when we arrive.

The boron is not going to remain cold for long. Look up what it takes to vaporize 1 kg of Boron. Relative to working reactor power - it isn't much.
Engineering is the art of making what you want from what you can get at a profit.

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