torus electromagnets

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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Uthman
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torus electromagnets

Post by Uthman »

Making torus/circular/round electromagnets seems like it would be a daunting task. I did a forums search, but didn't find much that would be helpful in that regard.

Have any of you attempted to build this type of eletromagnet by hand? If so, any construction hints / tips would be greatly appreciated.

KitemanSA
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Post by KitemanSA »

I don't understand the issue. This should be remarkably easy to wind by "hand". What am I missing?

Get a toroidal shell on a wheel with an axle, like a tire. Cut a slot around the outside of the torus big enough to insert a finger or other guiding mechanism. Poke the wire thru the inner surface of the torus to hold it in place. Turn the wheel around the axle (powered, by hand, foot trundle, whatever) and guide the wire back and forth across the minor arc with your finger/ guide mechanism. Very simple.

As I asked, what am I missing?

If the torus shell is flexible you can tie off the winding and simply bend the shell out of the way while removing the winding. Otherwise you MAY have to make the torus shell in (OMG!!) two halves. :roll:

Uthman
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Post by Uthman »

That would work well for producing a spool; but for the rounded ones like in wb6 I thought there might be some other construction mechanism. Perhaps not.

GIThruster
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Post by GIThruster »

What kind of budget do you have? Before I'd settle on copper, I'd do a real appraisal of this:

http://www.superpower-inc.com/system/fi ... n_0809.pdf

SP gives out 10' lengths of their stuff as free samples and you'd need so much less than copper it seems worth considering. You can get a used cryo setup on EBay for less than $2k, IIRC.

So again, what sort of budget do you have? That's a LOT of copper. . .
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

Uthman
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Post by Uthman »

I have about 5000 dollars... total =/

I come from a software engineering background without much fab knowledge though I do have a little access.

GIThruster
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Post by GIThruster »

Why not check EBay first to see if you can get the appropriate cryo-pump and if you can find one, call the people at SP and see if they won't give you a handout?

At 240A, the 12mm tape will probably only need a few wraps. You don't have to worry about making the bundle with circular cross section (as far as I know), rectangular ought to do? Seems possible this is chump change worth of tape form SP. They make this stuff by the mile for grid cabling. They might be happy just for the free press, especially if you offered to shout loudly how nice and fun people they are.

Just be careful handling the LN. Makes fingers fall off.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

KitemanSA
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Post by KitemanSA »

Uthman wrote:That would work well for producing a spool; but for the rounded ones like in wb6 I thought there might be some other construction mechanism. Perhaps not.
That is why you start with a toroidal shell, in order to get a spool with a round minor cross-section.

KitemanSA
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Post by KitemanSA »

GIThruster wrote:What kind of budget do you have? Before I'd settle on copper, I'd do a real appraisal of this:
...
So again, what sort of budget do you have? That's a LOT of copper. . .
Come-on. Copper aint THAT expensive!

Just how big a unit do you want to make?

GIThruster
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Post by GIThruster »

Going YBCO has lots of other benefits. Eventually someone has to start wrestling with these systems for Poly. There will be lessons learned. YBCO is going to burn off much less power than copper, so technically you're much closer to Q=1. You have to cool the YBCO so there is the opportunity to build a sustainable reaction whereas copper will overheat, yes?

Lots to learn and if you can get the YBCO for free, why not pursue it? SP needs the press.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

ladajo
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Post by ladajo »

Well Famuluis said he is going to play with his YBCO again. He mucked with it a while back but had trouble with the persistance swtich if I recall.

His final intent is to build a magrid with it and test it out. That was why he had the big chamber before, but then discovered his pump would not draw the big chamber down enough to make it a player. Thus the small chamber was born.

He will have to swtich back to a larger chamber here eventually as he will dicover that paschen arcing is an issue unless he can get some space between the Magrid and the chamber. The spikey ball is unforgiving, I am firmly in the camp that it will be like a wife, robust when operating at capacity, but hard to tune. :)

kunkmiester
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Post by kunkmiester »

You don't have to worry about making the bundle with circular cross section (as far as I know), rectangular ought to do?
The first models were rectangular cross section. Problem was, the magnetic field went through the corners, and so electrons and stuff would impact the magnet casing. So you need a circular cross section that doesn't cross the magnetic field.
Evil is evil, no matter how small

D Tibbets
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Post by D Tibbets »

kunkmiester wrote:
You don't have to worry about making the bundle with circular cross section (as far as I know), rectangular ought to do?
The first models were rectangular cross section. Problem was, the magnetic field went through the corners, and so electrons and stuff would impact the magnet casing. So you need a circular cross section that doesn't cross the magnetic field.
I've wondered about how significant the coil shape is, The spherical shape is obviously the best for minimizing the metal exposure outside magnetic fields and for arcing concerns. But. I'm guessing that having the magnet casings actually touching (as in WB4) may play a larger role. With spacing and sufficiently strong magnetic fields, even square casing might be (almost ) tolerable. A near square casing with rounded corners, or an oval shape might serve. This would allow greater internal volume for windings , insulation, and cooling and possibly give a more sherical magnetic field exposure to the interior of the machine. That is, the field lines near the Wiffleball border away from the cusps might have less curvature, and this may help the qusi- sphericity of the Wiffleball, The cusp throats may also be tighter. This combination may improve performance, while easing the complexity of winding spherical crossection grids.

Dan Tibbets
To error is human... and I'm very human.

KitemanSA
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Post by KitemanSA »

Colonel_Korg wrote:I though Dr. B's and Dr. N's comments about the shapes of the coils were pretty specific.

The magnetic fields have to conform to the surface of the coil container. i.e. circular or ellipsoid cross section to that the field lines would not enter the coil casings anywhere.
So make a square coil and place a round sheath around it. It simply depends on having sufficient B strength around the coil to keep the electrons away. Once the electrons are guided around the coil, the coil cross section shouldn't matter... except in effecting how strong the B field is.

A round minor cross-section coil will provide the best mag strength for the seperation needed. And it should be quite easy to construct.

SCs need intricate plumbing that takes experts to properly design. I doubt it is something for neos to work with. Might make some mighty spectacular fireworks though!

D Tibbets
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Post by D Tibbets »

KitemanSA wrote: So make a square coil and place a round sheath around it. It simply depends on having sufficient B strength around the coil to keep the electrons away. Once the electrons are guided around the coil, the coil cross section shouldn't matter... except in effecting how strong the B field is.

A round minor cross-section coil will provide the best mag strength for the separation needed. And it should be quite easy to construct. ...
My speculations is about the curvature of the magnetic field facing the core as it is pushed out by the Wiffleball. An ornginally almost conical field will be pushed into a more gentle curve. If the magnetic field is less conical to start, the end shape may be less convex- ie- more quasi spherical. At the regions where the field dives into the cusps, there will be a curvature based on the deformed field lines. I wonder if a flatter layout of the windings facing the center would increase the steepness of the cusp throats, essentially shrinking the size of the Wiffleball holes and improving the wiffleball trapping factor. In this sense I'm thinking this would have a similar effect to increasing the number of faces. Perhaps not quite as good, but you would not be increasing the number of cusps at the same time.
One way to look at it is to keep the spherical case, then cut it and add a flat component to the inward and outward facing walls. This might have the above effects. Also, as pointed out by M. Simon, the weakest point in the magnetic fields is the central face cusps. This would be increasing the minor crossection of the magnets and so the central cusps would not be as far away and weak. The magnetic strength at the coils could therefor not need to be as strong in order to get the required strength at the center cusps. And, the increased internal casing volume would allow for more copper wire windings- more amp turns, or more coolant volume for superconductors.
If any of these speculative changes result in real advantages, it may still be not worth it if the advantages are small, but if the changes do not introduce any disadcantages (like thermal loads)...

Dan Tibbets
To error is human... and I'm very human.

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