nanotube wire coils

IntLibber · Post by **IntLibber** » Sat Apr 02, 2011 5:51 am

From my reading about carbon nanotube, one type of nanotube lattice structure is metallic and exhibits conductivity 1000 better than copper, at room temperatures, no less! How would nanotube wire coils for a polywell reduce the scale required for good power output?

KitemanSA · Post by **KitemanSA** » Sat Apr 02, 2011 2:04 pm

Several pieces of information would be required to answer your question. First, how sensitive is the nano-tube to neutron bombardment? Second, are there magnetic field effects on that conductivity? Third, how does temperature effect the conductivity?

The answers to these and other such questions, when compared to available superconductive materials, will tell you whether CNTs will have any effect; because remember, no-one expects copper windings to be useful in power reactors. The comparison should be CNT vs SC.

IntLibber · Post by **IntLibber** » Mon Apr 04, 2011 10:41 am

KitemanSA wrote:Several pieces of information would be required to answer your question. First, how sensitive is the nano-tube to neutron bombardment? Second, are there magnetic field effects on that conductivity? Third, how does temperature effect the conductivity?

The answers to these and other such questions, when compared to available superconductive materials, will tell you whether CNTs will have any effect; because remember, no-one expects copper windings to be useful in power reactors. The comparison should be CNT vs SC.

Well yes, but SC's fail rather spectacularly, I hear, when they overheat or go over-current.

Now, CNT wires are 1/20th the mass of copper, never mind SC's that tend to use heavier elements in them. This obviously makes for an advantage in polywells used in launch vehicles and spacecraft propulsion.

As for radiation resistance, I'm not sure, but I was thinking about making the torus tubing have a high beryllium content in the steel, which is a neutron reflector. Another possibility is to make the insulation for the carbon nanotube wires be made of boron nitride nanotubes, which are insulators and have excellent radiation resistance.

KitemanSA · Post by **KitemanSA** » Mon Apr 04, 2011 10:55 am

Any high power magnet will produce the same degree of spectacular end result if it "fails". The fairly low power WB6 fried itself pretty good.

My question is whether it is practical to superpose a whole bunch of low field SC magnets (parallel windings) rather than dump the entire current thru one winding. Would such a unit fail LESS spectacularly?

IntLibber · Post by **IntLibber** » Tue Apr 05, 2011 4:00 am

KitemanSA wrote:Any high power magnet will produce the same degree of spectacular end result if it "fails". The faily low power WB6 fried itself pretty good.

My question is whether it is practical to superpose a whole bunch of low field SC magnets (parallel windings) rather than dump the entire current thru one winding. Would such a unit fail LESS spectacularly?

If the magnet goes over its SC operating temperature, no. Actually SC magnets that go over temp are rather explosive, not just some sparks. Metallic coils that fail tend to short out and ground their field currents. SC coils generally don't give that option. At least, thats what I've been told.

KitemanSA · Post by **KitemanSA** » Tue Apr 05, 2011 10:05 am

A magnetic field of a certain strength has a certain amount of energy stored in it, no? And if that energy dumps instananeously, either due to short circuit or quenching, that energy will be released. Shazam, big explosion. The SCs tend to be more spectacular because they can create stronger fields, thus having more energy to release. But given the stipulation that the same field is involved...

IntLibber · Post by **IntLibber** » Tue Apr 05, 2011 10:10 am

KitemanSA wrote:A magnetic field of a certain strength has a certain amount of energy stored in it, no? And if that energy dumps instananeously, either due to short circuit or quenching, that energy will be released. Shazam, big explosion. The SCs tend to be more spectacular because they can create stronger fields, thus having more energy to release. But given the stipulation that the same field is involved...

From what I recall, the idea is that with metallic coils, the fact they remain conductive gives a path to ground, where SCs, when they go over operational temp, do not, so a lot more of the energy goes into vaporizing material in attempting to conduct to ground. I may be misremembering.

bwana · Post by **bwana** » Tue Apr 05, 2011 2:47 pm

Also, the cnt would need an insulating coating, no? Just as raw copper wire is not as good as wire that has an enamel coating. The electrons have to go round and round. A bunch of cnt formed into a doughnut will just act like a big doughnut of copper-instant short circuit.

Maybe we could genetically engineer spiders to manufacture spider silk with a cnt core? It shouldn't be hard-just give them duplex spinnerets(a relatively easy genetic anomaly to engineer) and insert a small tube feeding the central spinnerets' glands with nanotube powder. Wind that tough stuff around and would have an awesome magnet. yes silk is a good insulator-Ben Franklin used it in his kite experiment.

ladajo · Post by **ladajo** » Tue Apr 05, 2011 2:55 pm

Interesting idea.

Too note is that the failure of WB6 was due to mechanical movement of the winding at a coil penertration point. This movement occured during firings and lead to the rubbing off of the insulation at the wear point. The resulting short then corrupted the vacuum in the chamber as well as blew the power supply during the cascading failure.

Euphamistically known as an "unrecoverable fault".

IntLibber · Post by **IntLibber** » Thu Apr 14, 2011 4:51 pm

bwana wrote:Also, the cnt would need an insulating coating, no? Just as raw copper wire is not as good as wire that has an enamel coating. The electrons have to go round and round. A bunch of cnt formed into a doughnut will just act like a big doughnut of copper-instant short circuit.

Maybe we could genetically engineer spiders to manufacture spider silk with a cnt core? It shouldn't be hard-just give them duplex spinnerets(a relatively easy genetic anomaly to engineer) and insert a small tube feeding the central spinnerets' glands with nanotube powder. Wind that tough stuff around and would have an awesome magnet. yes silk is a good insulator-Ben Franklin used it in his kite experiment.

Actually, as I said, boron nitride nanotubes are highly insulative and could be used to insulate the coil wires.

ladajo · Post by **ladajo** » Thu May 12, 2011 2:21 am

As an interesting note, toady in my travels I saw up close and personal an operational 30cm(ish) diameter continuous run 3.86T superconducting magnet. I was told it cost about $350K.

I immediately had visions of polywell grandeur.

KitemanSA · Post by **KitemanSA** » Thu May 12, 2011 3:41 pm

So, IIRC, keeping the same B (~4T) while going to 2m diameter should be ABOUT $12M. ($3k * 6^2). At 6 of them... ~ $72M. X3 to cover the rest of the system. Hey, ~$200M. Sounds familiar. Where have I heard that number before?

D Tibbets · Post by **D Tibbets** » Fri May 13, 2011 1:43 am

I'm uncertain about the energy released by copper and superconducting magnets. There are two differences.First is a SC the energy is stored, in a copper wire the energy is transiting. If there is a short the power supply is what provides the energy that heats things up. I'm not sure, but I think the instantaneous energy drain may be similar, but quick acting circuit breakers may help. In a SC the only option would be a fast switch into a energy dump- thus Tom Ligon's suggestion that it might be convenient to have a mid sizsed lake near an ITER sized SC Tokamak.
The other perhaps more relevant point is that the magnetic strength is dependent on the amps * the # of windings. While not absolute, I have the impression that copper windings will be considerably greater than SC windings. This changes the amount of Amps that might short to ground if copper insulation fails or the SC quenches.

Dan Tibbets

hanelyp · Post by **hanelyp** » Fri May 13, 2011 2:04 am

I understand conductivity in high conductivity nanotubes is largely by electrons traveling ballisticly down the tube. I'd expect a strong magnetic field to divert electrons and shorten their ballistic jumps, greatly reducing conductivity.

Related, I wonder how other materials with channels of comparable dimension would conduct electrons.

93143 · Post by **93143** » Fri May 13, 2011 7:12 pm

EDIT: fixed.