Dodec Magnetic field?

Aero · Post by **Aero** » Sat Mar 21, 2009 6:24 pm

I've seen some very nice field maps of the Truncube. Has anyone mapped the expected magnetic field of the Dodec? I don't recall seeing any. If Dr. Bussard's estimated improvement in confinement is demonstrated before the design of a net power BFR gets to far along, and if the Dodec is much more efficient, then the net power BFR will probably be a dodec, IMO.

Perhaps if we had some dodec magnetic field maps, we could speculate on any potential improvement in confinement.

MSimon · Post by **MSimon** » Sat Mar 21, 2009 7:30 pm

Aero wrote:I've seen some very nice field maps of the Truncube. Has anyone mapped the expected magnetic field of the Dodec? I don't recall seeing any. If Dr. Bussard's estimated improvement in confinement is demonstrated before the design of a net power BFR gets to far along, and if the Dodec is much more efficient, then the net power BFR will probably be a dodec, IMO.

Perhaps if we had some dodec magnetic field maps, we could speculate on any potential improvement in confinement.

All practical engineering hinges on economics. The question will be: can a profit be made on the added costs?

Aero · Post by **Aero** » Sat Mar 21, 2009 8:09 pm

All practical engineering hinges on economics. The question will be: can a profit be made on the added costs?

True. So I guess that means that it depends on just where net power lies on the curve of power vs. radius. We think that curve looks like R^5, and Dr. Bussard thought that confinement would be improved with the dodec design. That implies to me that R - break even for a dodec should be smaller than R - break even for a truncube. So the question is, how much smaller? The dodec is more complex with twice the number, but smaller (half-sized) components. Improved confinement would mean that the components are even smaller.

That does bring up another question, though. I read somewhere (I think on this site) that there is a minimum size (radius) for superconducting coils. That is, a vendor was quoted as saying that the coils would be very hard to make if the radius of the coil was less than, IIRC, one meter. Is that still the state of the art?

KitemanSA · Post by **KitemanSA** » Sat Mar 21, 2009 9:23 pm

Aero wrote: That does bring up another question, though. I read somewhere (I think on this site) that there is a minimum size (radius) for superconducting coils. That is, a vendor was quoted as saying that the coils would be very hard to make if the radius of the coil was less than, IIRC, one meter. Is that still the state of the art?

Based of data published by American Superconductor on the allowable strain for their first and second generation HTS tapes, I posted a minimum radius of 0.8 meters. That was based on arching the tape across it's width. When arched across its thickness, the radius is more like 2.5cm. My interest was related to designing a bowed, "square" plan-form coil with rounded corners. The bow curvature would need to be greater that 0.8m radius and the corner curvature would need to be more than 2.5cm. Ultimately doable. Finicky perhaps, but doable.

Note that the AmSC HTS tape is ~0.3x4 mm dimension (IIRC). With a more square section near the smaller dimension, the coil could be smaller.

Please also note that this is based on retaining 95% of the straight capacity.

Billy Catringer · Post by **Billy Catringer** » Sat Mar 21, 2009 9:33 pm

KitemanSA wrote:
Aero wrote: That does bring up another question, though. I read somewhere (I think on this site) that there is a minimum size (radius) for superconducting coils. That is, a vendor was quoted as saying that the coils would be very hard to make if the radius of the coil was less than, IIRC, one meter. Is that still the state of the art?
Based of data published by American Superconductor on the allowable strain for their first and second generation HTS tapes, I posted a minimum radius of 0.8 meters. That was based on arching the tape across it's width. When arched across its thickness, the radius is more like 2.5cm. My interest was related to designing a bowed, "square" plan-form coil with rounded corners. The bow curvature would need to be greater that 0.8m radius and the corner curvature would need to be more than 2.5cm. Ultimately doable. Finicky perhaps, but doable.

Note that the AmSC HTS tape is ~0.3x4 mm dimension (IIRC). With a more square section near the smaller dimension, the coil could be smaller.

Please also note that this is based on retaining 95% of the straight capacity.

Just remember that you have to hold it in place without it wobbling around and that you have to pump coolant through it in the face of 3000+C. Winding the coil, whatever shape you choose, is the easy part.

KitemanSA · Post by **KitemanSA** » Sat Mar 21, 2009 9:37 pm

Billy Catringer wrote:Just remember that you have to hold it in place without it wobbling around and that you have to pump coolant through it in the face of 3000+C. Winding the coil, whatever shape you choose, is the easy part.

So true, but if you can't build it, you can't cool it.

Billy Catringer · Post by **Billy Catringer** » Sat Mar 21, 2009 9:47 pm

KitemanSA wrote:
Billy Catringer wrote:Just remember that you have to hold it in place without it wobbling around and that you have to pump coolant through it in the face of 3000+C. Winding the coil, whatever shape you choose, is the easy part.
So true, but if you can't build it, you can't cool it.

I don't doubt that a coil for a dodecahedral magrid could be wound. If no one in the states can figure it out, you can bet there is some guy in a motor shop somewhere in India that can. Like I said, winding the coil is the easy part.

KitemanSA · Post by **KitemanSA** » Sat Mar 21, 2009 10:05 pm

Billy Catringer wrote: I don't doubt that a coil for a dodecahedral magrid could be wound. If no one in the states can figure it out, you can bet there is some guy in a motor shop somewhere in India that can. Like I said, winding the coil is the easy part.

Not sure what you're getting at here, (motor shop in India?). I was just answering Aero's "other question" about the minimum size of an SC coil. Didn't mention a dodec, but the same process I would use to wind my bowed cubocto could be used to wind a bowed icosadodec. Either way, the size restrictions are the same.

TallDave · Post by **TallDave** » Sun Mar 22, 2009 1:23 am

Perhaps if we had some dodec magnetic field maps, we could speculate on any potential improvement in confinement.

In Valencia, Bussard stated his belief we could do 3-5x better on the Gmj confinement factor with a dodec, meaning 3-5x more ion density.

Aero · Post by **Aero** » Sun Mar 22, 2009 2:33 am

In Valencia, Bussard stated his belief we could do 3-5x better on the Gmj confinement factor with a dodec, meaning 3-5x more ion density.

Ok. So given that the plasma is quasi neutral, does that also mean 3-5x more electron density? And how far to the left does that shift the break-even radius of the BFR. I'm not sure what assumptions to make in order to come up with an estimate. And as I suggested above, it would be nice to see some magnetic field maps to maybe understand where the 3-5x came from.

Billy Catringer · Post by **Billy Catringer** » Sun Mar 22, 2009 4:38 am

KitemanSA wrote:
Billy Catringer wrote:Not sure what you're getting at here, (motor shop in India?). I was just answering Aero's "other question" about the minimum size of an SC coil. Didn't mention a dodec, but the same process I would use to wind my bowed cubocto could be used to wind a bowed icosadodec. Either way, the size restrictions are the same.

Sorry to confuse you, Kite. Over the past few years nearly all the wire winding on anything that needs wire wound is being done in India. i meant nothing personal about it. I just wish we would keep our skills up instead of exporting all of that kind of work.

Whatever gets wound has to be cooled and supported. The more wonderful the winding, the more difficult it becomes to wrap a workable structure around it.

KitemanSA · Post by **KitemanSA** » Sun Mar 22, 2009 2:18 pm

Billy Catringer wrote: Sorry to confuse you, Kite. Over the past few years nearly all the wire winding on anything that needs wire wound is being done in India.

Really! I did not know that. Now the comment makes more sense.

i meant nothing personal about it. I just wish we would keep our skills up instead of exporting all of that kind of work.

Me too. As an aside that I hope stops here, perhaps if we made the minimum wage law applicable to anything sold in the US rather than just what is made here, this problem would go away.

Whatever gets wound has to be cooled and supported. The more wonderful the winding, the more difficult it becomes to wrap a workable structure around it.

Not the 4xMPG-Dual (that is what I am calling the 4 stratum dual loop MPG unit). It may be a bit more difficult to wind, but it should be a HECK of a lot easier to support. The core supports itself against the magnetic loads. The TPS supports itself against the pumping / flow loads. The gravity loads are fairly simple to take care of. That is what happens when a MaGrid is locked together into one symmetric, quasi-spherical unit.

MSimon · Post by **MSimon** » Sun Mar 22, 2009 8:15 pm

Me too. As an aside that I hope stops here, perhaps if we made the minimum wage law applicable to anything sold in the US rather than just what is made here, this problem would go away.

Absolutely. However, we need a decent minimum wage law not the stuff the crooks in Washington are trying to palm off as helping. What we need is a minimum wage of $100 an hour. And even that may be too low. It would be a start though. It would keep the riff raff from getting legal jobs. Plus it would definitely keep out products made by low cost labor. Take tungsten which we import. If the miners are not getting $100 an hour we can stop all imports. Or how about oil? If the janitors at the oil companies are not getting $100 an hour we can keep the oil out. Every where along the supply chain $100 an hour or the goods get excluded.

It is such a simple plan. I wonder why it is not more popular?

KitemanSA · Post by **KitemanSA** » Mon Mar 23, 2009 1:08 am

So much for my hope that it would stop there.

Please take any responses my comment about min wage and MSimon's response to it to the topic called "Minimum Wage" in the General Forum.

KitemanSA · Post by **KitemanSA** » Mon Mar 23, 2009 1:32 am

TallDave wrote:
Perhaps if we had some dodec magnetic field maps, we could speculate on any potential improvement in confinement.
In Valencia, Bussard stated his belief we could do 3-5x better on the Gmj confinement factor with a dodec, meaning 3-5x more ion density.

The only quote I can find in the Valencia Paper regarding dodec and performance is this:

If this is built around a truncated dodecahedron, near-optimum performance is expected; about 3-5 times better than WB-6.

I am not getting how this related to confinement factors. Is the confinement factor Gmj somehow related to sphericity? That seems to be his reason to expect improved performance.

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Dodec Magnetic field?

Dodec Magnetic field?

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