Polywell size? How small can you get it?

[msutton]

Although my ultimate goal of getting a function polywell is far off in the distant future, a few questions have popped up while I was reading through the forums and net sources.

I remember it being mentioned both here on the board and in the google video that Dr. Bussard gave, that net power would take larger scaled dimensions (6 meters or something of the sort). Obviously, a vacuum chamber that could house a 6 meter polywell magnet array would be far beyond virtually anyone but someone with millions of dollars to through around. From the pictures of WB-1 through WB-6 it is clear that such a large polywell is not necessary to achieve fusion.

My question is, what would be the smallest pollywell that could create a deep enough potential well to create fusion? My knowledge of magnetic fields isn't so great, but I would think there would be some constraints based on how powerful/weak the magnets were that would dictate your chamber and magnetic grid size.

The reason I ask, is that perhaps one could create a magnetic grid in roughly the same dimensions as the grids people are using in their fusors now. If that were the case, then Dr. Bussards polywell machine could possibly be done by an armature.

[Nanos]

That is my aim, though I don't know the answer to how small, I'm trying to see how big a one I can fit in my 10" wide bell jar

At a guess going by whats been said here, one probably 1/3 to 1/2 the size of the WB1 model at most, but may easily be limited by the fact I want to use permenant magnets to a certain size.

[Richard Hester]

Nanos - you really don't want to use permanat magnets, as you would then have field lines terminating in magnet surfaces, with resulting hellacious electron bombardment. I was thinking along those lines for awhile, and subsequent comments from Bussard and Ligon made me change my mind.

[Frank Sanns]

Neodymium Iron Boron magnets are available in many shapes including doughnut shapes and hollow cylinders or flatter pieces with holes through them. If I recall, the polywell designs used around 1,000 Gauss for short contiuous runs and upto 3,000 Gauss for pulsed runs. The power required to produce these fields with conventional electromagnets is huge so doughnut shaped NIB magnets can make sense especially for a small fusor. NIB have field strengths of 10,000 Gauss and even higher with a high permeability backing material like iron. There should be no reason that a polywell core the size of a grapefruit (or smaller) could not be used to demonstrate the efficacy or non-efficacy of the polywell design.

I personally do not belive the polywell concept solves any of energy losses inherent in IEC fusion but if you believe in it then go for it.

Frank S.

[tligon]

Forget any form of "solid state" magnets if your goal is to make fusion. If your goal is to make a little machine of the general form-factor of WB1, it may make a nice little toy that will light off a glow. You can make one small and cheap that way.

I don't think WB1 was able to operate above a kilovolt. It tended to break into Paschen discharge and hold a few hundred volts. The loss lines for electrons into the faces virtually assure the thing will spew gas into the device.

Dr. Bussard had high hopes, based on the WB2 results, that WB3 might just be able to make some fusion. I could never get the voltage high enough on it while maintaining a decent potential well, but it was trying. I'd say it got halfway there. Had it had the improved form-factor of WB6, it likely would have made some fusion. It used 10 cm radius coils, and could hit something in the 1-2 kG range for 30 sec to a minute, or so. We operated it in a 3-ft diameter bell jar, and it was a little cramped when a Faraday cage was built inside that.

Don't skimp on the pumping capacity. To avoid Paschen arcs, you have to get rid of any neutrals generated. That's a key to long runs.

[Donald McKinley]

Micah,

What do you mean by the armature comment.

Don

[MarkS]

you really don't want to use permanat magnets, as you would then have field lines terminating in magnet surfaces, with resulting hellacious electron bombardment

not to mention that the subsequent heating would cause the permanent magnets to lose strength

[johnp]

What do you mean by the armature comment.


I think he meant "amateur."

[msutton]

Uh...yeah, that's what I get for a quick proof-read and trusting a spell checker. Amateur is what I meant.

[Nanos]

I've heard someone say its possible to configure permenant magnets so the field lines do not terminate in that way.

One link that hints at that is;

http://www.gatago.org/sci/physics/elect ... 89451.html

[Nanos]

Was their a specific reason the Faraday cage was inside the bell jar and not outside ?

[Nanos]

What if you had either cooling on the surface between the magnet and heatsource, or encased the magnets in something which prevented the heat from reaching them ?

Either a ceramic or maybe something coated with a Starlite material ?

Would the heating effect only be related to the amount of juice (excuse my lack of technical terms..) put into the device, and thus if you kept it low enough you could avoid generating too much heat ?

[msutton]

Tom, you've actually built these machines. Do you know if there is any specific reason why could couldn't build/buy some torus electro-magnets ala WB6 that are an inch or two in diameter to build the MaGrid? You say that WB3 was some 10cm across, was that done for a reason? I'd suspect that the strength of the magnets versus their diameter would play a role in creating the electron containment in the middle.

As for fixed magnets, I sort of ruled that out the moment I understood how WB6 worked, and how the electrons recycled back into the machine along field lines.

[msutton]

I think the problem with the fixed magnets is that the field lines run straight into the faces of the magnets. Thus, when the electrons recirculate they would be driven into the magnet. This would cause create a loss of energy as the electron as taken out of the system. Encasing the magnets in some sort of insulation wouldn't prevent the electron loss. The reason something like WB6 was so cool, was that the field lines would direct the electrons around the magnet, preventing collisions from even happening and preserving the potential well. It's better to eliminate the cause of the heat, than try to make some work around. Atleast that's what I can guess based on my very limited knowledge

[Nanos]

I look at such things as a halbach array and ponder.

[Richard Hull]

You can't fool mother nature. She has a gang of gotcha's here.

As mentioned by Tom and Richard Hester, forget permanent magnetics totally. You can't make the thing small and have it work out to Bussard's true methodology.

The only magnets potent enough are NdFeB. The termination of the lines within in the magnet will attract bomarding electrons. Plus, any neutrals will heat the magnets. These magnets will start to loose significant magnetism below 200 deg F!.... A self feeding disaster. The magnetism is then lost forever.

Those who know magnetism must realize that a 1 kilogauss field in the middle of a large area is tough to get. Tom noted that the smaller coil magnets would not run long at all.

There are a lot of issues here that I feel even Bussard did not solve or prove he solved, but they did show that bigger, in this case, is the way to go. Tom who has worked on this stuff for Bussard echo'd this.

All of the hopefuls with ideas at miniaturization, permanent magnetic heroics, etc., should try this and see all the bug-bears that will reach out and kill your dreams. Tom has been there.

Finally, you are talking a whole different gas pressure regime over a simple fusor. Cooling of any coils is a key issue.

I would love to see someone back their musings with doings.

Richard Hull

[Frank Sanns]

Since scaling up seems to be the answer to the design, lets consider the number of Hydrogen atoms in a typical chamber or cylinder. There are 6.02 x 10E23 atoms in 22.4 liters at STP and the mass of that will be only 1 gram. If we could improve the efficiency of a fusor by 100,000 to 1,000,000 times as reported then it would give the output of ~10E30 atoms. Now if we were to compress it to multiatmospheric presure then number becomes 10E35. Now we started with just one gram for fusion which is really a paultry quantity so let's scale up the mass by the amount in a typical full size welding cylinder. This put us at ~10E40. This has brought us many orders of magnitude and still in a package that somebody could carry or at least easlily dolly around. I propose that we contiue to scale this up a a bit more to around 10E54 to 10E57 number of atoms and maybe we will have some chance at doing fusion.

That number of 10E57 hydrogen atoms seems familiar to me for some reason......

Frank S.

[Richard Hull]

By golly Frank, you've hit on it! Solar proportions sounds about right to me. I am on line with that thinking since its literally seems to work "universally".

Finally, on the Halbach array comment earlier by Nanos.........

A Halbach array does not a magnetic monopole make....

It is a mere contrivance with all the usual magnetic lines returning to source all along the array. Electrons would love all those opportunities.

Richard Hull

[Nanos]

I find it interesting reading that the halbach array wasn't discovered till 1973 (Maybe earlier I wonder if there are any references anyplace to anyone doing similar work.), and wonder what other discovers might exist out there in permanent magnet land.

Another link for those interested in such related things;

http://mag-net.ee.umist.ac.uk/reports/P14/p14_2.html

[denergyguy]

Forgive my ignorance Tom, but why was the cage built "inside" the bell jar? They are used to shield from electromagnetic radiation right? Was there equipment inside the bell jar that needed to be protected?

[Chris Trent]

The more I think about it, and the more I crunch the numbers, the worse it looks for small fusors.

I cannot think of any particular reason that it cannot work for short runs, but make no mistake, it would be very short runs. The key problem I see is that the coils would heat up during use. To run enough current through through the small coils to make this work you may well be loosing hundreds of watts to resistance heating. The other half of this problem is that vacuum is a darn good insulator. With no way to get rid of the heat, the coils would be white hot in just a few moments.

You would have to find a way to cool the coils, or figure out how to keep them running at very high temperatures, or both.

I don't know of any way to do either in a 1" diameter coil.

[Richard Hull]

The limitations presented by nature and materials is what material science is all about. There always can be found clever workarounds for most issues, but some nuts are tougher to crack than others.

Intense magnetic fields in hostile environments have always been and issue. The hard love part of magnetism is that to do work with magnetic fields you need a gap. Therein, lay the rub.

In the clever 5 Tesla device noted above, the 0.3mm gap is the rub. How many experiments or processes of great import can be done in a 0.3mm gap? A look at the graph related to this device shows that sub tesla fields are the norm at about a 1" gap.....this is about the point where interesting things can be inserted.

It appears that real matter can have only so much magnetic flux strength before self de-magnetization begins. It would be cool to know the absolute limit of coercivity. They keep pushing the limit.

The current wonderment are magnets in the 60-65 MGOE range with the old 20 MGOE second generation NdFeB magnets looking pretty weak now that 50MGOE is commonly avaialble.

What does this mean? At 20 and 30MGOE it meant a lot of pinched skin and blood blisters. The new 50-60MGOE magnets will become a true danger in unqualified hands. Those pushing this envelope need to be most careful around any glass system or any vacuum setup that is easily defeated by projectiles.

Richard Hull

[Brett]

"Those pushing this envelope need to be most careful around any glass system or any vacuum setup that is easily defeated by projectiles."

LOL! Sounds like my old EE prof, "R.F. Shwartz", and his Manhattan project story about the 'second' ballistic mass separator.... Seems they had a wrench sitting on a nearby table when they fired up the first one!

[Brett]

A thought has just occured to me, I don't claim it's original: Is there any particular reason you couldn't combine the polywell concept with a charged grid, and charge the polygonal coil? The electrostatic charge would function as usual in the ordinary fusor, while the magnetic component would help prevent the circulating ions from impacting the grid.

This might be an approach to getting polywell fusion on a small scale, using the electrostatic component as a booster.

[MarkS]

I don't think the field strength would be anywhere near enough to have a polywell like effect. I would think that the field lines run directly into the gird structure, exactly opposite of the WB's. However I'm going to build a truncated cube grid mid to late November to see what happens.