Theoretical Size Limit of Fusor?

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Theo MacMillan
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Theoretical Size Limit of Fusor?

Post by Theo MacMillan »

Greetings,

I couldn't find anything on the topic in the FAQs so now I'm trying here: Is there any theoretical size limit on a fusor?

I'm not talking about making a fusor the size of my house, but rather a fusor the size of a munchkin. I'm sure there is a simple answer out there, but is there anything to the size of the reactor chamber - maybe volume of deuterium present - that makes a standard sized fusion more possible than at a small size? I know that the actual nuclear fusion occurs in an area that is extremely small relative to the rest of the chamber, but I don't know the kind of volume of deuterium needed.

Thanks,
Theo MacMillan
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Andrew Robinson
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Re: Theoretical Size Limit of Fusor?

Post by Andrew Robinson »

Is this a new standard of measure...? 2 munchkins = 1.5 Oompa-Loompas or something...... Need something less arbitrary.

FAQ: viewtopic.php?f=24&t=9981
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Steven Sesselmann
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Re: Theoretical Size Limit of Fusor?

Post by Steven Sesselmann »

Theo,

With all the fusors built in the last 15 years it has been extremely difficult to narrow down the size and shape of a fusor vs. efficiency. I started a tread called Fusion reactors by energy quotient, but to date there is not enough data to make any sense of it. Richard stands by his 6" spherical fusor design, but we frankly don't know if it is an optimal size. Then there is the issue of grid size vs shell size, even this has not been firmly optimised as fas as I have seen.

viewtopic.php?f=6&t=2826

Amateur fusor building is largely an uncoordinated individual effort, which does not produce a quick answer to simple questions like the one you have asked, yet a coordinated effort could easily answer the question, all it takes is to build 5-10 identical chambers and run them under the same conditions to see how the fusion rate scales with size, but AFAIK no one has done it.

Steven
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Richard Hull
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Re: Theoretical Size Limit of Fusor?

Post by Richard Hull »

As noted in my FAQ above and talked about in Steven's post. Definitive results are pretty much non-extant here on size, shape and grid to chamber volume ratios. I doubt there is such a thing as a theoretical limit to the size a working fusor might be constructed. I am also rather confident that monsters the size of a continent would remain forever as inefficient as a 4" fusor, but with unbelievably more fusion going on per unit time in the device. It's that efficiency issue that kills the fusor, be it made in a 4" tee or a 500 foot diameter sphere.

It all falls back to how much money you have on hand and how agressive you are in nailing down the data. With a highly concerted effort by one person who has already built at least one significant fusor and about 50,000 - 100,000 dollars spent in a thrifty manner, I think that person could reliably answer a lot of your questions in a couple of years of work and research. At the end of that effort, there would be a whole bunch of now dormant "lesser" fusors for use as planter pots. You would know for sure, about how big and in what form a fusor of significant fusion capability, compared to those preceeding it, might be constructed and have a handle on the final costs. Still, in the end you would just have a great fusor producing far less than 10e8 fusions per second costing maybe $25,000 for the thrifty would-be fusioneer.

Not one being who ever landed here was in that class, monetarily, or who also packed the gear needed to accomplish the task. Most of those of us who have been successful realize a full order of magnitude better than 10e6 fusions/sec would require a full order of magnitude more money to complete and achieve no real superiority other than braging rights, king-of-the-hillism recognition.

What we do know is that more volume means more fusion fuel available for fusion and, thereby, gas loss in the flowing gas regime... (more money...wasted deuterium).

Higher voltages within this environment definitely means more fusion...more x-rays...more danger electrically and radiation wise. (more money again...new super supply and super shielding).

The larger gas volume obtained above means much more money for a vacuum or fusion chamber regardless of shape.

Finally, this is a serious amateur effort, undertaken with obviously smallish amateur purses ( a few thousand for the most successful here). The vast majority of those seemingly so inspired to build their own fusion reactor often present themselves with knowledge and skill sets which are pretty close to zero. The number of new supposed fusioneer aspirants versus successful fusioneer ratio of late is appallingly large due to the DIY crowd stumbling in here, virtually none of whom pack the gear needed for a win.

It would wonderful to put a nice little package of precise answers to your original query, but the serious amateur's here can only supply the limited, yet hard won knowledge obtained though the doing of hands-on work. We can supply caveats and warn of blind alleys and how we have lost treasure in past follies so that you might proceed along a more well worn, but sure path.

In the end, if you think big, have really big, big money on hand to blow, as it will flow through your hands like water through a coarse sieve.


Richard Hull
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Werner Engel
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Re: Theoretical Size Limit of Fusor?

Post by Werner Engel »

There is another size limit for the chamber, which seems to be the vacuum pumps and the cost of them.
If you take a professional vacuum chamber with 1 m³ volume you will need several pumps (eg. 10-15) with a price of about 10.000 per piece.
The bigger the chamber becomes the more difficult it is to control leaks. So I think it is just a matter of price and complexity.
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Re: Theoretical Size Limit of Fusor?

Post by Jerry Biehler »

10-15 pumps to pump a 1 meter chamber? Those must be tiny pumps. One 6" diff pump can pump a chamber that size in a pretty reasonable time.
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Re: Theoretical Size Limit of Fusor?

Post by Werner Engel »

… to be precise: I’m talking about turbo pumps reaching 10e-8 mbar or better. I know that’s not normal fusor pressure regime, but for tokamaks that’s fine and a good situation to start.
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Re: Theoretical Size Limit of Fusor?

Post by Theo MacMillan »

Thanks for the advice.

Just so I understand everything, a large fusor would not gain any efficiency over a smaller one. But would a very small fusor lose any efficiency compared to a not-quite-so-small-one? Would the only real downside to a 1" fusor be that it would be impossible to measure neutron counts?

Thanks,
Theo MacMillan
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Mike Beauford
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Re: Theoretical Size Limit of Fusor?

Post by Mike Beauford »

The smaller fusors will limit how high a voltage you can use within it.
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Re: Theoretical Size Limit of Fusor?

Post by Jerry Biehler »

Werner Engel wrote:… to be precise: I’m talking about turbo pumps reaching 10e-8 mbar or better. I know that’s not normal fusor pressure regime, but for tokamaks that’s fine and a good situation to start.
I have a pretty decent sized chamber, 24" x 30" with a 2000l/s turbo that's pretty necked down and it gets down to that just fine. Within a few minutes of starting the turbo it will be down to the -6 range.
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Richard Hull
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Re: Theoretical Size Limit of Fusor?

Post by Richard Hull »

Well maintaned vacuum systems by a vacuum professional or serious enthusiast can perform rings around the neophyte's efforts in the fusor arena. We have several here that are in that lofty basement of pressures. The average person landing here knows just about zero related to vacuum as many queries still prove.

Thankfully, the fusor can work with a fine, marginal, "good enough" in the vacuumist's eyes. Big fusors?....Another matter entirely.

Good measurable results can be obtained in the 4 to 8 inch range with the ease of a win militating towards the larger 6-8 inch range. I would say a 10 to 12 inch fusor would be about the limit for a newbie on a limited budget, so shoot for a 6-8 inch chamber and hold your costs down.

Richard Hull
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Fusion is the energy of the future....and it always will be
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Re: Theoretical Size Limit of Fusor?

Post by Frank Sanns »

At one point on here I posted the specifics for a super large fusor in orbit. Only a fine outer mesh electrode would be needed around an inner grid satellite. Releasing charged ions into the freedom of space would leave them free be manipulated between inner and outer grids by the electrical potential. Large distances are ok because of the low pressure and high mean free paths.
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Re: Theoretical Size Limit of Fusor?

Post by Steven Sesselmann »

Frank,

Making a fusor in outer space certainly solves any vacuum issues one might have, but to harness any energy might be a whole other challenge, on the other hand using deuterium fusion as a space propulsion engine should be relatively simple. I imagine in it's simplest form looking like a half hemisphere fusor. One could even add some pdhpe moderator to the half hemisphere for slowing neutrons in the direction of travel.

A super thin sheet of metal foil over the exhaust side would neutralise protons and alpha particles as they pass through and provide thrust.

Steven
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Re: Theoretical Size Limit of Fusor?

Post by Frank Sanns »

Space afford many possibilities. The lack of ambient atoms and gravity allows for super large but low mass structures that could never be built on earth. It also solves building massive structures that require large amounts of energy to get into space. The payload of a single Space Shuttle could have put nearly a million square meters of Aluminum foil into space. Had it been perforated, or ultra thin, the number could have been multiples of that. Some interesting possibilities happen when you start to get to those scales.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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