Tungsten coils?

[vernes]

Hi, I'm new

I've read some of the journals and articles, and what I've understood from the last testrun in the defense owned lab is that the power needed to get fusion working (ish) is too much for the coils used.

Now the next model needs to use supercooled coils and requires the whole installation to be scaled up just to fit the supercooled coils.

What are the options of using Tungsten coils (meltingpoint 3695 K, 3422 °C, 6192 °F) and run the demonstration sized model within that limit?

Or other exotic materials based on their high melting point.

Or even weirder solutions, like vaporating the conductor inside diamond tubing, using a plasma as coil. already mentioned here.

[Tom Ligon]

Tungsten ought to work if used at liquid helium temperatures. It was one of the first supercondutors discovered.

At room temperature and above I think it would be a dreadful problem. It has high resistivity, and the resistivity skyrockets with increasing temperature.

Tungsten is the inner grid material of choice among most fusor builders, although it is a real bear to spot weld without becoming excessively brittle. The refractory properties are the reason they like it ... typical fusor operation produces a red-hot or hotter inner grid, due to ion bombardment heating.

We used it for various accelerator grids, and as an electron emitter. Thoriated tungsten is readily available and makes a robust emitter.

I think what is failing in Polywell magrids is not the copper, it is the insulation around it. The copper only melts when the insulation fails and causes arcs. White-hot tungsten won't fix that problem.

[vernes]

So if you'd make a coil out of wax, and poured ceramic clay around it, baked it until the wax was gone and just pushed a copper wire through the whole thing, you'd be all set to push the copper to it's limit?

(or fill up the cavity with gas and create an plasma)

[Tom Ligon]

I have a friend who makes copper electromagnets using copper ribbon and a ceramic compound. He claims to hold the world's record for high field intensity in copper magnets, primarily because he can run them hotter. I'd love to see him build a magrid, but he is so far busy on other projects.

I'm not sure, but I think he may use a compound called Rescor for the ceramic. Part epoxy, if it is the stuff I think it is. There might be some fiber mixed in to make sure the windings don't touch.

http://www.cotronics.com/vo/cotr/cm_castable.htm

[MSimon]

I used something as a kid called Plibrico for arc furnace experiments.

I don't know if it is till made.

[tombo]

Liquid copper coils?
The copper could be circulated to limit max temp.
hall effect pump?
I have considered a low melting NaK eutectic inside a copper tube.
My equations showed the tradeoff of thicker copper and water cooling to be better when considering resistive heating.
But someone else should check that, especially at these higher temps.
Years ago I used a room temp setting castable ceramic that was supposed to be good to ~1800C. (Aramco? I found the ad in a NASA Tech Briefs)
Also Watlow does some nice custom casting of high temp insualtion.
Molybdenum tube with liquid copper?
What does copper's resistance do after it melts?
Any trapped bubbles at high points would break the circuit.
Copper is so heavy, it woud be much worse than trapped bubbles in water systems.

[MrE]

A great idea. I was imagining how such a compound would react to a vacuum environment. People often say(in posts on this site) out gassing must be considered, though I am uncertain if it would be a particular hindrance if one were to deploy this ceramic-epoxy substance.

If a high temperature tolerance ceramic is desired, consider a fabrication device utilizing a form of Plasma assisted CVD to grow the shape of what you need and then slide in the copper. Just a random thought which is most likely impractical and will never be used.

e

[vernes]

A way to get the spacing between the wires correct while you're winding the coil before casting it in isolation-ceramics, is perhaps by making small ceramic rings/cylinders and putting all the tiny cylinders on the coper wire prior to winding the coil.

The problem however could be the copper expanding when reaching high temperatures. And with the ceramics casted so tightly around the wire, could result in breakage.

[TallDave]

Help! I need tungsten to live! TUUUUUNNNNGSTEN!

http://www.youtube.com/watch?v=oLx-e2iEyRU

Sorry, couldn't resist.

[ravingdave]

Were ceramic able to be cast around copper wire to the same degree of
thickness as the existing magnet wire insulation it would not be sufficiently
strong to withstand the slightest jostle. Were it cast with sufficient thickness to be structurally sound, the spacing between wires would be excessive. Apart from the thermal problems previously mentioned, the whole thing would constitute a horribly inefficient system (due to the high resistivity of hot conductors) if it were possible to make it operate.

I believe it has long been understood that the system is only viable with superconducting magnents. To maintain the b field with 800 amps
(or more) of continuously supplied current is a horrible waste of energy
for a production reactor. This idea is of course reasonable for a proof of concept reactor and is indeed a necessary step, but long term prospects
will require lossless superconducting magnents.


For the very brief period of time I was actually thinking about trying
to build one of these things I was leaning toward using Lead coated Copper tubing cooled by liquid helium ($0.50 / gallon ) for magnents.
Coating copper tubing with lead is relatively easy, and if a set of suitable seals could be made to accomplish high vacum sealing at very low cryogenic temperatures, I believed it might have been a viable low budget approach within the capabilities of a competent amateur.

As the only thing that was required was to convince the scientific community that the polywell fusor concept actually functioned, I wasn't concerned about blowing away my B-Field from neutron emission or heat.
If that had happened it would have proved the concept. If not, the thing could have ran for days without worrying about power consumption.
(as long as you wanted to pay for the Liquid Helium. )

In any case, wiser and more knowledgeable people are handling
this and that suits me just fine.


David

[Tom Ligon]

Where are you buying your liquid helium? I think that's cheaper than we can buy liquid helium in bulk, for our big tank!

Otherwise, a clever approach. I would not discount the possibility of doing it with other superconductors over copper, or for that matter, high temperature superconducting powder IN copper tubing, with an outer tube for the LN2. You might even get away with an MPG all-tube magrid.

I've never been any good at figuring out how to flash superconducting coils, eliminating the external path. As a practical matter, how would an amateur setup do that?

[vernes]

Were ceramic able to be cast around copper wire to the same degree of
thickness as the existing magnet wire insulation it would not be sufficiently
strong to withstand the slightest jostle. Were it cast with sufficient thickness to be structurally sound, the spacing between wires would be excessive. Apart from the thermal problems previously mentioned, the whole thing would constitute a horribly inefficient system (due to the high resistivity of hot conductors) if it were possible to make it operate.

I was actually thinking more of somethying a bit more solid.
That's why I mentioned the ceramic beads as a way to position the windings before casting the whole coil into a solid block of ceramic clay.
I'm not familair with the strength of a semisolid block of ceramic, but that's for another study entirely. The beads might create possible fracture-lines because they don't merge well with the casted clay.

I believe it has long been understood that the system is only viable with superconducting magnents. To maintain the b field with 800 amps
(or more) of continuously supplied current is a horrible waste of energy
for a production reactor. This idea is of course reasonable for a proof of concept reactor and is indeed a necessary step, but long term prospects
will require lossless superconducting magnents.

And you're absolutely right. superconductivity is a sure way to run the reactor. But this way I could at least make a coil that would not break due to the meltingpoint of plastic insulation, but due to the melting point of copper.

(SNIP SNIP)
In any case, wiser and more knowledgeable people are handling
this and that suits me just fine.

I want to build a demonstration (found out a demo reactor is somethingactually) reactor one day.

[MSimon]

Where are you buying your liquid helium? I think that's cheaper than we can buy liquid helium in bulk, for our big tank!

Otherwise, a clever approach. I would not discount the possibility of doing it with other superconductors over copper, or for that matter, high temperature superconducting powder IN copper tubing, with an outer tube for the LN2. You might even get away with an MPG all-tube magrid.

I've never been any good at figuring out how to flash superconducting coils, eliminating the external path. As a practical matter, how would an amateur setup do that?

Tom I often wondered that too. Then I found out how. You have a shorted superconducting turn (or many turns) . You wrap a heater around a small section (doesn't need to be a big heater) an then feed in current on either side of the heater. Slowly ramp up the current. When it reaches the desired level turn off the heater. And now you have a charged up coil.

[Solo]

Ok, so what's preventing the use of superconducting coils in a set-up on the scale that Dr. Nebel is working with? There are superconductors that need only LN2, not helium. In a reactor the size we are talking about, all you'd need would be a (single-turn?) superconducting coil inside a cooling jacket that would function also as the magrid's toroidal surface. No need for vacuum insulation becasue there won't be any real plasma heating on this scale. Plus, as long as it takes to cool the coils in WB-7 after a run, it seems that the coils are well-insulated thermally, so there won't be much cooling power needed. And of course, no ohmic heating from the coil! In fact, it seems to me like you'd hardly need a circulating coolant system; just do like the LDX and cool the whole thing down with a shot of LN2 and run your experiement! Heck, you could probably get several runs on power-up of the coil.

[Tom Ligon]

Solo,

I can't speak for the present team. What stopped us when I was there was a lack of experience with the materials and methods. Dr. Bussard had a lot of experience with pushing copper hard due to the Riggatron. High temperature superconductors were just getting past the "levitating pellet" stage, and there was a reluctance to delay results fiddling with a whole new technology.

That excuse is not so solid now, but that does not mean it is not still used.

Simon ... very clever! Now, who is going to build the first experimental superconducting magrid? Did I just hear Solo volunteer? All in favor?