Superconductors for Fusion

Point out news stories, on the net or in mainstream media, related to polywell fusion.

Moderators: tonybarry, MSimon

jcoady
Posts: 141
Joined: Fri Jul 15, 2011 4:36 pm

Superconductors for Fusion

Postby jcoady » Mon Sep 29, 2014 7:13 pm

There is an upcoming talk about Superconductors for Fusion this wednesday at PPPL according to their events calendar.

http://www.pppl.gov/events/calendar

You can watch these talks live using this website.

https://mediacentral.princeton.edu/id/1_rqmmkznx

They had some other fusion related talks this month but they don't seem to have been recorded or they haven't yet posted the video. They had a talk earlier this month by Tri Alpha Energy which you could have watched live but they leave it up to the presenter to decide weather or not they want the talk recorded. A lot of the fusion related talks are not recorded and you can only watch them live.

jcoady
Posts: 141
Joined: Fri Jul 15, 2011 4:36 pm

Re: Superconductors for Fusion

Postby jcoady » Mon Sep 29, 2014 7:24 pm

The videos for the two previous talks this month are now available for viewing.

http://www.pppl.gov/events/colloquium-m ... c-2-device

http://www.pppl.gov/events/colloquium-e ... uring-pppl

crowberry
Posts: 449
Joined: Sun Sep 08, 2013 6:34 am

Re: Superconductors for Fusion

Postby crowberry » Tue Sep 30, 2014 3:34 pm

Thanks jcoady! The Tri Alpha Energy talk by M. Tuszewski looks very interesting. I have not yet watched it except for the beginning. The contents of the talk is this:

C-2 device
FRC formation
FRC equilibrium
Rotational stability
Tilt stability
FRC confinement
C-2U device
Summary

The length of the talk is 1 h 11 min 40 s.

GIThruster
Posts: 4686
Joined: Tue May 25, 2010 8:17 pm

Re: Superconductors for Fusion

Postby GIThruster » Tue Sep 30, 2014 3:40 pm

IIRC, the National High Magnetic Field lab down at FL State is working with Superpower Inc for some years now, using the latter's 2nd generation high temperature superconductor tape. The stuff has a nice tight bend radius (one of the most important breakthroughs so far as use in windings) and carries fantastical amounts of current. Single turn windings with 4,000+ amps and almost 20T fields generated. The size and shape of mobile power generators like what is used aboard ships and the size of electric motors are both going to shrink fantastically. And especially when you have a motive application, this is a big deal.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Re: Superconductors for Fusion

Postby D Tibbets » Tue Sep 30, 2014 10:39 pm

GIThruster wrote:IIRC, the National High Magnetic Field lab down at FL State is working with Superpower Inc for some years now, using the latter's 2nd generation high temperature superconductor tape. The stuff has a nice tight bend radius (one of the most important breakthroughs so far as use in windings) and carries fantastical amounts of current. Single turn windings with 4,000+ amps and almost 20T fields generated. The size and shape of mobile power generators like what is used aboard ships and the size of electric motors are both going to shrink fantastically. And especially when you have a motive application, this is a big deal.


To expand on this and perhaps expose my ignorance., WB6 had ~ 100,000 amp turns for a 0.1 Tesla field, Mini B had ~ 40,000 amp turns for almost 0.3 T. My unbderstanding is that the B field at the cusp facing surface of a round electromagnet is proportional to the radius of the magnet. Thus Mini B with ~ 1/2 the radius of WB6 had 4 times the B field strength, assuming the same number of amp turns. With ~ 1/2 the number of amp turns the resultant strength was ~ twice that of WB 6, close enough for comparison, especially as the B field strength of WB6 was a moving target. Values of ~ 0.1 to 0.2 teslas was given as the capacity, depending on how much amps they pushed through it. If this superconductor with one winding gives a B field of ~ 20T with 4,000 amp turns, that suggests a radius of ~ WB6 B field *100,000 amp turns= Quoted B field *4000 amp turns / R^2 .

With ~ 1/ 20th the amp turns, the radius would have to be smaller by a factor of square root of the radius, or about 15 cm ^2 / x cm^2= 20.
This is ~ 225/ 11=20. sqr of 11 is ~ 3.3 or 3.3 cm radius of curvature for the same B field strength, but at 100 times greater B field I think the corresponding radius of curvature would be ~ 0.033 cm or 0.3 mm.

That is a pretty small radius of curvature. If true, the wire would obviously need to have a diameter much smaller than this. The current carrying capacity of supperconductors is generally given as the current carrying capacity with a cross section of one cm^2. A corresponding superconductor ribbon much smaller than 1 mm in cross section would carry ~ 10 Amps.

The numbers do not add up. Either my analysis is screwed up or something is missing. A 20 T field may be possible with many windings instead of just one, and this is not apparent in the quote. This would be consistent with ~ 20-30 T fields being generated in modest sized electromagnets with many turns. These are, I believe, cold superconductors, or even combinations of copper conductors and superconductors.
The capacity of ~ 4,000 amps/ cm^2 seems to be a common capacity for several high temperature superconductors. I have seen up to ~ 8000 Amps/ cm^2 for a cold/ liquid helium cooled super conductor.

If a superconductor can handle 4000 Amps / cm^2, and 100,000 amp turns is needed for a 15 cm radius magrid, then 25 turns or 25 cm^2 of cross section is needed. With upscaling the radius to 1-2 meters, the number of amp turns would need to go up the square of this proportion. Given that the machines are probably going to be at least several meters in diameter/ greater than 1 meter in radius, the engineering considerations are probably more concerned with the cross section of the superconductor ribbons necessary for the chosen current, and the cooling concerns to manage deep penetrating x- rays and possibly neutrons are the biggest challenges. The superconducting magnets in the LHC are possibly representative of what will be be needed for a polywell. The difference would be the additional shielding and cooling to handle the external/ penetrating thermal load. The LHC uses cold superconductors, and I suspect the tokamak plans call for this. If high temperature superconductors could be used, the cooling concerns would be improved some. The Polywell has internal magnets exposed to the plasma to a degree (through ExB diffusion) and also any x-rays or neutrons. The LHC does not have this challenge. And the tokamac has the magnets outside the first wall and cooling blanket of the reactor so it also is less challenging.

So long as the radius of curvature of the superconductor ribbon is less than a meter or so , it is probably not a concern. Considerations that can ease the situation is probably the improvement in current carrying capacity of the ribbon and the operating temperature. Liquid nitrogen temperatures are better, room temperature would be great.

What is the current carrying capacity of copper wire? And, how much cooling can you achieve with vigorous coolent flow? Ohmic heating is only a limit once you pass this cooling capacity. Also, of course, ohmic heating will consume megawatts, or even hundreds of Megawatts of power, and superconductors avoid this complication. The final question is what are the best compromises between the two approaches.

PS: Just to complicate the issue further. If you operate at liquid nitrogen temperatures the conductance of simple (high purity) copper wire is 7-8 time better than at room temperature. At 4 degrees K the conductivity is ~ 20 times better. As such, the advantages of superconductors versus the complications, become more narrow.

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

GIThruster
Posts: 4686
Joined: Tue May 25, 2010 8:17 pm

Re: Superconductors for Fusion

Postby GIThruster » Tue Sep 30, 2014 11:07 pm

Well you made me go and look it up! And you're right. The thing I was almost recalling from a couple years ago was 4100 amps carried in 20T of background field:

"The cable that carried a world record current of 4100 amperes in a background field of 19.81 tesla."

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

It's less than a page long but with pretty pictures and colors.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Re: Superconductors for Fusion

Postby D Tibbets » Fri Oct 03, 2014 12:44 am

That makes more sense. My limited understanding is that superconductors exclude the magnetic field generated by the current in the wire/ ribbon and that this buildup of magnetic field strength on the ribbon surface plays a role in the maximum current carrying capacity. Having a global background magnetic field surrounding the wire might cause similar or even magnified limitations. This seems to show that in this instance it is not a show stopper up to ~ 20 Tesla at least. I presume this has been tested repeatedly with cold superconductors as they have been used practically at such total magnetic field strengths in multiple applications. It is a valuable indication that at least one high temperature superconductor can also function in this external magnetic field strength environment.

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

jcoady
Posts: 141
Joined: Fri Jul 15, 2011 4:36 pm

Re: Superconductors for Fusion

Postby jcoady » Mon Oct 27, 2014 5:34 pm

Here is another talk with video link from MIT Professor about Superconductors for fusion.

http://www.pppl.gov/events/colloquium-l ... plications

jcoady
Posts: 141
Joined: Fri Jul 15, 2011 4:36 pm

Re: Superconductors for Fusion

Postby jcoady » Thu Nov 13, 2014 5:20 pm

The latest talk with video is now available. MIT professor talking about his students work on a fusion reactor design.

http://www.pppl.gov/events/colloquium-s ... evelopment

prestonbarrows
Posts: 78
Joined: Sat Aug 03, 2013 4:41 pm

Re: Superconductors for Fusion

Postby prestonbarrows » Fri Nov 14, 2014 4:09 am

D Tibbets wrote:What is the current carrying capacity of copper wire? And, how much cooling can you achieve with vigorous coolent flow?


It depends if you are talking pulsed or CW.

For pulsed, in terms of thermal limits, the energy in your cap bank will result in a temperature rise proportional to the mass of copper and its specific heat. Water cooling doesn't help here (except for repetition rate) since it will tend to flash boil since the energy is deposited before the water can move any distance through the piping. You are also limited by the self-inductance of the coil; more turns make it harder to change the current quickly. If you try going low-inductance, the inter-turn forces tend to make your coil explode.

For CW, inductance does not mater in steady state. Water cooling is essential though. You are power-limited by the mass flow rate of water through the system and water's specific heat. This equates to the electrical voltage*current. More turns means longer and skinnier wires meaning more resistance and lower currents for a given power. More turns also means higher fields for a given current, so it tends to wash out.

Usually, you are limited by water mass flow for CW magnets. Turbulence puts an upper limit on how much water you can cram through a tube and thus how much heat you can reject. Smaller tubing means more turns but less flow rate and lower current ratings. Fatter tubing means higher currents but less turns. Again, tending to wash out.

You are also limited in currents by a reasonable power supply (or cap bank); and in water flow buy a reasonable pump.

All in all, for CW things max out around 1T and on the order of 10-100T for non-destructive pulsed.

GIThruster
Posts: 4686
Joined: Tue May 25, 2010 8:17 pm

Re: Superconductors for Fusion

Postby GIThruster » Sat Nov 29, 2014 4:02 pm

prestonbarrows wrote:Turbulence puts an upper limit on how much water you can cram through a tube and thus how much heat you can reject.

Can you tell us is anyone looking at using supercritical CO2 for cooling instead of water? Seems to work wonderfully in the new generation of turbines and could solve both the power density and efficiency issues at once. It flows like a gas but has the density of liquid. Here are the folks to talk to:

http://www.co2turbine.com/R744/Supercri ... rbine.html
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

prestonbarrows
Posts: 78
Joined: Sat Aug 03, 2013 4:41 pm

Re: Superconductors for Fusion

Postby prestonbarrows » Sat Nov 29, 2014 8:50 pm

I know supercritical CO2 is being looked at for closed loop exchangers in the fission reactor world. I have never heard of it being used for magnets though, interesting thought.

A 5-minute look at wikipedia puts the minimum of the phase at around 1000 PSI at 90 F. This is just about the limit of standard copper tubing, so it is at least in the ballpark of feasibility. I have no idea what, if any, gains could be gotten over water in terms of heat rejection through small pipes or if it would justify the significantly added complexity. In general, you would like colder temps to reduce the wire's resistivity, but the critical point for CO2 is not all that high.

GIThruster
Posts: 4686
Joined: Tue May 25, 2010 8:17 pm

Re: Superconductors for Fusion

Postby GIThruster » Mon Dec 01, 2014 4:36 pm

I mention it just because you noted the thermal transport is limited by the water flow through the system, and that is characterized by fluid turbulence. Supercritical CO2 has a higher power density that water, and it flows like a gas rather than a liquid, but has the density of a liquid; so it is a remarkable solution in many ways. Much smaller footprint than water/steam. I'm not sure copper tubing is the way to go. It's possible this could be 3D printed and formed into a block of aluminum. That would be very strong and easy to keep cool. The trouble is you need to be able to print with 6 different materials at a time and this is what 3D printing is not good at yet.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Re: Superconductors for Fusion

Postby D Tibbets » Mon Dec 01, 2014 5:41 pm

Then there are other stratagies like Bitter magnets...

http://en.wikipedia.org/wiki/Bitter_electromagnet

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


Return to “News”

Who is online

Users browsing this forum: No registered users and 2 guests