Superconductors and Current capacity

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

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D Tibbets
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Superconductors and Current capacity

Postby D Tibbets » Sat Feb 26, 2011 11:18 pm

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

imaginatium
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Postby imaginatium » Mon Feb 28, 2011 10:45 am

The way I read it, it's 7.5mm=2800 A. The minor diameter is 50mm so that is a ratio of ~6.66 to 1. So according to there are ~33 windings. However, 6.5mm =1200 A. With a 50mm minor radius, the ratio is ~7.69 to 1, resulting in ~46 windings

2800 *33 =92,000 Amp-turns
1200 * 46 = 55,000 Amp-Turns

Therefore, we can see that if we made a wider cable, with fewer turns, we would get significantly greater amp-turns. So why not make it 1 turn of a 50mm cable?
Imaginatium (ih-ma-juh-ney-tee-uhm) -noun
Ubiquitous substance, frequently used as a substitute for unobtainium, when it is unavailable. Suitable for all purposes.

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am
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Postby D Tibbets » Mon Feb 28, 2011 4:56 pm

My short term memory wasn't so good. At least I was in the ball park. Your more acurate number would result in in a ~ 10% improvement., so perhaps 4 T could be obtained with a 40% packing fraction. Also, since this would be at liquid nitrogen temperatures instead of liquid helium temperatures, a layer less of insulation/cooling may serve. This would increase the packing fraction and resulting B field strength to perhaps 5 or even 6 T.

Increasing the diameter might allow for more capacity , but based on the two cables presented, the improvement is perhaps peaked at the 7.5 cm. There may be some balance between the copper core, the insulation thickness and the superconductor wrappings. Or perhaps not, no information was given.

The important point is that this design matches the performance of a older high temperature superconductor design that could carry 3,000 amps, but at a cable diameter of 7 cm. Also important is the radius of curvature of the cable. If too great, it could not be used in a Polywell. This would be especially true if you were using non round magnets- like square shapes. You could not bend the superconductor around the corners.

What I do not know is how this compares to low temperature superconductors. Using MRI machines as an example, they seem able to achieve at least 3+ T in ~ 1 meter diameters, so each cable can carry more current, and can be bent to reasonable radii of curvature.

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


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